Title of Invention:

ACID MATRIX APPLICATIONS: WELL STIMULATION AND COMPLETION FLUIDS USING VISCOELASTIC SURFACTANTS AND MODIFIED ADDITIVES

Technical field [0001]

The present invention relates to a composition for an oil or gas well formation and a producing method of the composition, and a forming method of the oi i or gas we i !,

Background Art [0002]

Viscoelastic surfactants (VES) as part of fracturing fluids and proppant transport fluids compositions during a fracture treatment is a departure from the use of polymer Vi scosi tiers: namely geis based on polymers like natural guar and synthetic polyacrylamides. Viscosity of a VES fluid is created by self-assembl of surfactant small molecules in solution to create spherical, rod shaped and bi continuous structures of lyotropic liquid crystalline order micelles. Entanglement of these flexible and higher order micelles imparts increased viscosity to the solution. Hydraulic fracturing (HF) has been used for many years for completion phase in drilling and a variety of stimulation fluids have been developed over the years that can withstand high pump rates, shear stresses, and high temperatures and pressures in the bore hole. In a completion stage in drilling (exploration and production), retained permeability and leak-off (fluid loss) control are two of the most important requirements. The main goal eventually is to achieve high conductivity pathways, which do not damage or lower the productivity of completed wells.

[0003]

Gross-linked polymer gels are the most predominant viscosifying media in a number of oilfield fluid compositions providing good leak-off control. However, they are disadvantageous in retained permeability if all the polymers introduced are not degraded and can have poor fluid loss performance. VES as HF fluids have been reported in a number of patents (Patents 1-10, end of document). Since they are polymer free compositions and viscosity is mainly achieved by control of concentrations towards higher order micelle structures, they can be easily recovered and do not require a gel breaker for control· in addition, they can minimize fracture height growth and increase effective fracture length -in achieving effective productivity from we 11 completion operations. With VES fluids, elasticity and micellar structure rather than the viscosity of fluid are the main property drivers. An important advantage is that VES fluids can efficiently do stimulation at lower viscosities with reduced friction pressure end thus reduce the energy for pumping fluids downhole towards greater fracture lengths (horizontal), enable better fracture geometry control, and with deeper formations. Other possible uses of VES technology includes filter cake removal, selective matrix diversion, permeability preservation, and coiled tubing clean out. Yet, VES has some disadvantages: 1) Poor stability at high concentrations and temperatures, 2) poor stability with complex brine conditions or highly salt saturated environments, 3) lack of viscosity-elastic control once deployed with other chemical components and additives, and 4) cost. A typical preferable vol me for stim lation and completion operation using i sees i tying polymer such as guar, xanthan gum, pol acr la ide is about 2-3% of the volume of water. The preferable volume for VES is about 3-10% of the volume of water in general, the cost of a VES viscosifier can be up to 3X that of a polymer viscosifier. It is important to justify any price differential with advantages in thermal stability, brine stability, pressure control, pumping rate control, non-use of breakers, easy clean-up, stimuli -responsive behavior, and controlled release of actives, etc.

[0004]

A number of surfactant types and architectures can be used for formulating VES fluids, including anionic, cationic, and zwitter ionic surfactants (Literature 1-11, see end of document). It is preferable to create stable mice! i es with high-temperature and brine chemistry stability. A surfactant composition that creates useful rheology within concentrations ranging from 31 to 8% can be deemed cost-effecti e for demanding applications. The exact surfactant concentration often depends on the bottom hole temperature and desired fluid viscosity. In addition, a VES fluid can break to water- like Newtonian viscosity by exposure to liquid hydrocarbons or dilution with reservoir brines. Fine control of viscosity can further be achieved with a “breaker" introduced rationally for control at certain stages of a we i I -comp I et i on operation. The effectivity of the VES and a breaker control can be measured via conductivity tests and monitoring the retained permeability. This can be extended towards monitoring the effect on fracture propagation length, well connectivity, formation preservation, and can also be augmented in the field with tracer analysis. Another important property monitored with VES and we I i —comp i et I on operation is the fluid loss property. By pressurizing the fluid flow to a control led permeability formation

(simulated in the lab with a core flooding experiment), the cumulative fluid volume flowing into the core can be measured as a function of time and obtain the total fluid I oss coeff i c i ent vs. permeab i I i t i es.

[0005]

Other than HF applications, VES for well stimulation and completion applications are also important. The availability of various VES fluid systems is an advantage for working with different formation characteristics, base lithology, mineral compositions, formation fluids (brine chemistry) and operations (e. g. different pumping configurations). Tight gas we Ms. unconventional wells, shale, coal beds, and wells which have adverse capillary effects including sub-irreduoible water saturation and hydrocarbon saturation necessitates oilfield chemicals that are optimized for a specific well condition. The low productivity of both old and new wells can be boosted by stimulation and completion procedures, e. g. acid stimulation and the use of diverters. Herein, VES stimulation fluids can have advantages: 1) employment of complementing surfactant systems, 2) benign to formation (no polymer residue or formation damage), 3) lower surface tension, 4) does not require biocides or clay control agents, 5) insensitive to salinity, and 6) the flowback fluid can be reused. [0006]

Acid stimulation is preferable for carbonate reservoirs (caicite and dolomite) to optimize productivity. When the productivity decreases as a result of formation damage or low natural permeability, acid well stimulation can increase productivity by creating more conductive flow paths between the reservoir and the borehole. Stimulation methods in carbonate sequences are classified into two main groups: matrix treatments arid acid fracturing treatments. Matrix stimulation using VES fluids involves pumping acids, solvents, or other treatment chemicals into the formation at less than the reservoir fracture pressure. When acids are introduced into a carbonate formation, some of the minerals in the rock dissolve, which creates intricate, high- permeability channels or wormholes. Matrix treatments are often applied in zones with good natural permeability to counteract damage in the near-wellbore area. Acid fracturing stimulat ons, in contrast, are performed above the fracture pressure of the formation. A viscous pad (a fracturing fluid that does not contain proppant) is pumped into the formation at pressures above the fracture-initiation pressure, which fractures the rock. Then an acid stage is pumped to etch the fracture surfaces. The acid also creates conductive wormholes at or near the fracture surfaces. After stimulation, the fracture closes, but the increased conductivity between the formation and the well remains because of the etching and the creation of wormholes. In carbonate reservoirs, hydrochloric acid (HCI) is the most commonly applied stimulation fluid. Organic acids such as formic or acetic acid are used, mainly in retarded-acid systems or in high-temperature applications, to acidize either sandstones or carbonates.

[0007]

Diversion is a technique used in injection treatments, such as matrix stimulation, to ensure uniform distribution of the treatment fluid across the treatment interval. Injected fluids tend to follow the path of least resistance, and this may lead to inadequate treatment of the least permeable areas within the stimulation interval. [0008]

Using diversion methods it is possible to focus treatment on the areas that require more stimulation. To be effective, the diversion effect should be temporary to enable the full productivity of the well to be restored when the treatment is completed. There are two main categories of diversion: mechanical and chemical· Focusing on the use of chemical diversion; while polymer based fluids have been used, there is a high interest on VES based diversion fluids due to its advantages In f iction reduction and prevention of formation damage. In extended-reach wells, coiled tubing (CT) can be used to deliver the treatment to the reservoir. The treatment can be made up of the VES fluid composition (3—10%) and in 20-281 HGi with a corrosion inhibitor.

[0009]

There have been previously reported prior art and patents for VES in general and they include:

1. Principles of VES fluids formation: worm I ike micelles at higher concentrations.

2. Investigative methods for VES fluids.

3. St i mu I i -responsive properties of VES fluids.

4. Stability of VES Fl ids. 5. Different materials classes of VES fluids.

[0010]

Patents Related to oilfield chemical applications:

1. Hydraulic Fracturing Fluids

2. Completion Fluids

3. St ! mu I at ion Fluids

4. I OR

5. enhanced oil recovery (EOR)

[0011]

The patents by Sch I umberger, Ha!liburton, Baker Hughes, BJ Services are predominant. [0012]

Reports on highly stable VES Fluids with acid matrix or media DOES NOT contain much by way of particle, nanopart ic!e additives, nanocellulose ingredients.

[0013]

There are no reports on the use of modified nanopart icies and nanomaterials for VES fluids in oilfield stimulation and matrix acid treatments

[0014]

There is potential for reporting enhanced properties including stimuli -responsive properties of VES f luids and other actions of Self-diverting, control led pH change, controlled dissolution, and higher temperature performance.

[0015]

These Patents, Applications, and Publications that may be studied include the fol lowing:

US Patent No. : US 7, 992, 640 B2 August 2011

By Tianping Huang (Baker Hughes Inc.)

ORGA IC AGIO TREATI G FLUIDS WITHVISCOELASTICSURFACTANTS AND INTERNAL BREAKERS

US Patent No. : US 7,303,019 B2 December 2007

By Thomas We I ton (Halliburton Energy Services)

VISCOELASTIC SURFACTANT FLUIDS AND ASSOCATED DIVERTING METHODS US Patent No. : US 7, 159, 659 B2 January 2007

By Thomas We! ton (Ha! ! i burton Energy Services)

VISCOELASTIC SURFACTANT FLUIDS AND ASSOCATED ACD!ZI G METHODS

US Patent No. : US 7, 159, 659 B2

October 2006

By QI Qu (BJ Services)

ACID DIVERTI G SYSTEM CONTAINI G QUATERNARY A I E

US Patent App I i cat ion No. : US 2005/0126786AΊ June 2005

By Diankui Fu (Sch lumberger Technology Corporation)

VISCOELASTIC ACID

US Patent App I i cat ion No. : US 2010/0331223 A1 December 2010

By Lei ing Li (Sch lumberger Technology Corporation)

ACID VISCOSITY ENHANCER FOR VISCOELASTIC SURFACTANTS

US Patent App I . : US US 2014/024619SA1 September 2014

By Nisha Pandya (Ha I i i burton Energy Services)

BRANCHED VISCOELASTIC SURFACTANT FOR HIGH TEMPERATURE ACIDIZING

US Patent App I . : US 2011/0152135 A1 June 2011

By Yiyan Chen (Sch lumberger)

VISCOELASTIC SURFACTANT ACID TREATMENT

US Patent App I . : US 2006/0118302 A1 June 2006 By Michael Fuller (Schlumberger)

SELF DIVERTING MATRIX ACID

US Patent Appl : US 2013/0274.148 A1 October 2013

By Valerie Lafitte (Schlumberger)

FLUIDS AND METHODS I CLUDI G NANOCELLULOSE

Accompanying Patents and Applications US Patent No. : US 2015/0072902 A1 March 2015

By Thomas Wei ton (Schlumberger Technology Corporation) FLUIDS AND METHODS INCLUDING NANOCELLULOSE

1, New Formulations:

To develop a new Viscoelastic Surfactant (VES) formulation with nanostructured complexes as viscosifying additives for completion and stimulation fluid applications and investigate their effectiveness. This includes modification of the VES formulation with any of the following : a) nanomaterial complexes, b) polymeric surfactant complexes, c) viscosifying polymer, and d) modified polymer and nanomaterial additives. This action will result in: a) st i i i -respons ve properties or control, b) better stability at higher T and brine concentrations, and c) cost- effectiveness and performance.

[0017]

2, Optimization of Formulation:

To determine the best properties of these new V'ES compositions (nanomaterials and polymer complexes) in terms of structure-compos it ion-property relationships-· physicochemical character Ization and standardized testing methods should be performed. This involves the characterization of the formulation stability, viscosity measurements, rheology, high T rheology, as against various concentrations - to result in demonstrating cost-effective or low cost/high performance ratio advantages. D fferentiation from existing VES formulations should be observed in superior properties and added functional ity. Other additives resulting in enhanced and additional function may include: scale inhibitors, biocides, corrosion inhibitors, traces, fluid loss agents, formation stabilizers, stimui i—response properties. The use of cellulose nanocrystals (CNC) also called nanocellulose as an additive is of high interest, particularly because of its renewabi!ity and sustainability. The ability of nanocel lu!ose materials to complex with VES fluids will be of high interest in augmenting the stability of the worm-like micelles and differentiation between other nanofiber interactions. For example, CNC and nanofibers can influence shear rate properties and stability with VES at higher temperature.

[0018]

3, Acid Stimulation Formulation:

To develop a new VES and nanostructured complexes as viscosifying media for acid stimulation, acid fracturing, and diversion applications. This differentiation from existing and reported VES formulations under highly acidic condition is done by incorporating: a) polyelectrolyte complexes, b) polymeric surfactant complexes, and c) nanomater iai additives that wi 11 result in: a) sti ui i-responsive properties (such as self-diverting properties), b) higher stability at high Ϊ and brine concentrations, and c) cost-effec iveness and performance. While common surfactants are used, the importance of investigating cationic, anionic, and zwitter ionic group against va ious counterions are important. The addition of nanomaterial s and polymers can further improve these formulation performance. The application of surface modification by various silanes (sulfonate, carbonate, epoxy, amine, etc.) and polymer grafting by surface initiated polymerization (SiP) will be new. The demonstration includes determining the use of various organic counterions to the surfactants suitable for acid conditions and testing on analogous caicite/doicmite mineral type dissolution is included. Specifications on viscosity, viscoelastic behavior, T and P stability, pH stab i I ity, brine stab i ! ity will be determined.

[0019]

4. Further Optimization of Form lation with synergistic additives:

To investigate the optimized properties of these new VES complexes (polymer and nanopart icies) further in terms of structure-composition-property relationships for acid stimulation, fracturing, and diversion, additives against corrosion, scaling, fluid loss prevention, etc. can be added. This will involve physico-che ical characterization and standardized testing methods - with other additives resulting in enhanced and additional function which include: scale inhibitors, biocides, corrosion inhibitors, traces, fluid loss agents, formation stabilizers, stimul i-response properties.

The present inventors have diligently studied to soive the above problems, and as a result, have found that the above problems can be solved by combini g a viscoelastic- surfactant with a modified nanomater iai, and thereby completed the present invention. [0021]

More specifically, the present invention is as follows.

1 A composition for an oil or gas well formation, comprising: a viscoelastic surfactant: and a modified nanomaterial.

2, The composition according to item 1, wherein the modified nanomaterial comprises a nanocellulose.

3 The composition according to item 1 or 2, wherein the modified nanomater ia I has, on its surface, at least one selected from the group consisting of a sulfate group, a sulfite group, a carboxy group, an ethylene oxide chain, an amino group, an ester group, a silane group and a tertiary ammonium group.

4 The composition according to item 3, wherein the modified nanomater ia! has the sulfate group on its surface

5, The composition according to any one of items 1 to 4, wherein the modified nanomater ia! has a grafted polymer on its surface. 6. The composition according to any one of items 1 to 5, further comprising: a counterion compound which has a counterion portion against to an ionic group of the viscoelastic surfactant.

7. The composition according to item 6, wherein the counterion compound comp ises an organic acid salt.

8. The composition according to item 6 or 7, wherein the counte ion compound comprises at least a carboxylic acid salt or a sulfonic acid salt.

9. The composition accordi g to any one of items 6 to 8, wherein the viscoelastic surfactant comprises at least one selected from the group consisting of a cationic surfactant, an anionic surfactant, a zwitter ionic surfactant and amphoteric surfactant.

10. The composition according to any one of items 6 to 9, wherein the viscoelastic surfactant comprises a compound represented by formula

(1) :

R-N(R ^; V X (1) wherein, R ^! is an aliphatic group having 10 to 20 carbon atoms, R ² is an aliphatic group having 1 to 6 carbon atoms and X is a negative ion.

11. The composition according to any one of items 1 to 10, further comprising a polymer and/or an additive.

12. The composition according to item 11, wherein the polymer comprises at least one selected from the group consisting of polyacrylamide, po I y (a i !ylamine hydrochloride), poiy (ethylene glycol) polyethylene inline polyvinyl alcohol, poly (4-sty renesu I tonic ac i d-co-ma i e i c acid), polyvinyl pyrrol idone, polya! I y I amine, and po I y (d i a 11 y I dimethyl ammonium), po!yanl!ine, poiy (4-vinylpyid ne), poiyani i ine emerald ine. 13. The composition according to item 1 further comprising a solvent.

14. A method of producing a composition, comprising: a step of mixing a modified nanomater la! and a viscoelastic surfactant.

15. A method of forming an oil or gas we! I, comprising: a step of preparing a fluid comprising: a solvent; a viscoelastic surfactant: a modified nanomater la ! ; and an acid material, and a step of introducing the fiuid Into the well.

Advantageous Effaeta of Invention [0022]

According to the present invention, a composition, for an oil or gas well formation, excellent in stability and seif-diverting acid property, and a producing method of the composition, and a forming method of the oil or gas well can be provided.

[002.3]

Figure 1 shows acid sensitivity of viscoelastic surfactant in comparing between

Example 1 and Comparative Example 1.

Figure 2 shows HCi spending test in comparing between Example 1 and Comparative

Example 1.

Figure 3 shows HGI spending test in comparing between Examples 4 to 5 and Comparative Example 1, and appearance of samples.

Figure 4 shows HCI spending test in comparing between Example 4 and Comparative

Examples 1.

Figure 5 shows viscoelastic surfactant candidates.

Figure 6 shows HCI spending test in comparing between Examples 6 to 8 and Comparative Example 2. Figure 7 shows HGi spending test in comparing between Examples 9 to 11 and Comparative Example 3.

Figure 8 shows HGi spending test in comparing between Examples 9, 11, 12 and Comparative Example 3.

Figure 9 shows modifying agent candidates.

Figure 10 shows IGA result of CNO-APTES and CNC-AEAPTMS.

Figure 11 shows a scheme of medication of CNG, and FUR and IGA result of cationic-ONO,

Figure 12 shows FT!R and IGA result of PDMEAMA grafted CMC.

Figure 13 shows FTIR of polymer grafted PPEGME A grafted CNC.

Figure 14 shows viscosity differences between temperatures in comparing between Examples 13 to 16.

Figure 15 shows additive candidates.

Figure 16 shows HGi spending test in comparing in comparing between Examples 17 to 22.

Figure 17 shows HGI spending test in comparing in comparing between Examples 19 and 22.

Figure 18 shows HGI spending test in comparing in comparing between Examples 23 to 25and 31, and Comparative Examples 4 to 6 and 12.

Figure 19 shows HGi spending test in comparing in comparing between Examples 26 to 2Sand 31, and Comparative Examples 7 to 9 and 12.

Figure 20 shows HGI spending test in comparing in comparing between Examples 29 to 31 and Comparative Examples 10 to 12.

Hereinafter, embodiments of the present nvention (hereinafter, a iso referred to as the ^" this embodiment ^" ) wii! be described in detail. The embodiments described below are given merely for illustrating the present invention. The present invention is not limited only by these embodiments.

[0025]

1. Composition for sn oil or gas wall formation

A composition for an oil or gas well formation, in this embodiment., comprises a viscoelastic surfactant and a modified nanomater al, The composition is excellent in self-diverting acid property and stability.

[0026] As described n Example section, a viscosity of the composition is change based on acid concentration or pH. The viscosity of the composition may be control ied by supplying acid or consuming acid. The term “self-d vert ng acid property” in this disclosure means the property changing the viscosity based on acid (see also figs. 5 and 6 etc...). Especially, for an oil or gas well formation, the change rate of the viscosity is preferably large.

[0027]

As described in Example section, it Is preferable that the self-diverting acid property is keep in various pH or temperature. Especially, for an oil or gas well formation, the composition is exposed to various pH or temperature. The term “stability” in this disclosure means that the self-diverting acid property is keep in va ious pH or temperature.

[0028]

1.1. Vi scse I st i o surfactant

Examples of the viscoelastic surfactant include, but not particularly limited to, at least one selected from the group consisting of a cationic surfactant, an anionic surfactant, a zwitter ionic surfactant, and an amphoteric surfactant. The viscoelastic surfactant comprises an ionic group. The viscoelastic surfactant may be used singly, or may be used in combination of two or more thereof

[0029]

Examples of such ionic group include, but not particularly limited to, a positive charge group such as ammonium group, and a negative charge group such as carboxylic acid, sulfonic acid, sulfate, phosphonate. Among them, ammonium group, carboxylic acid, and sulfonic acid are preferred, at least one selected from the group consisting of carboxylic acid and sulfonic acid is more preferred. By using such viscoelastic surfactant, the self-diverting acid property and the stability tends to improve.

[0030]

1.1.1. Gat i an ic Surfactant,

A cationic surfactant has a positively charged group. Examples of such cationic surfactant, but not particularly li ited to, a!kylamine, alky!diamine, alkyl etheram i ne, a Iky I quaternary ammonium, dialkyl quaternary ammonium, and alkyl ester quaternary am on i urn.

[0031] Some of such cationic surfactant may be represented, but not particularly limited to, by fol lowing formula (1) :

R ^; -N'(R ² ) ₃ X- (1) wherein, R ¹ represents alkyl, alkenyl, eye I oa iky I, aryl alky I, a Iky I ary I, aikylarylaikyl, alky! ethera I ky I , s I ky I am i nos I ky I , alky!amidoa!ky!, or alkyl esters I ky I , R ² each independently represents alkyl, alkenyl, cycloalkyl, X is a negative ion.

[0032]

The number of carbon atoms in the group represented by R ¹ is preferably 8 to 30, 10 to 20. R ¹ may be linear, branched, or cyclic structure. Among them, R ¹ preferably represents aliphatic group, such as alkyl, alkenyl, eycioa!kyi, ary!alky!, aikylary!, and aikylarylaikyl.

[0033]

The number of carbon atoms in the group represented by R ² is preferably 1 to 20, 1 to 6. R ² may be linear, branched, or cyclic structure. Among them, R ² preferably represents aliphatic group, such as alkyl.

[0034]

The negative ion represented by X ¹ is as describe above. Among them, the organic anion and the haiogen ion is preferred, the halogen ion is more preferred.

[0035]

Among them, cetyl trimethyl ammonium bromide (GTAB) represented following formula is preferred.

B r

[0036]

1.1.2. Anionic Surfactant,

An anionic surfactant has a negatively charged group. Examples of such anionic surfactant, but not particularly limited to, alkyl carboxylat.es, alky! ether carboxyl ates, alkyl sulphates, alkyl ether sulphates, alkyl sulfonate, alkyl ether sulfonate, alkyl sulfate, alkyl ether sulfate, alkyl phosphates and alkyl ether phosphates.

[0037]

Some of such anionic surfactant may be represented, but not particularly limited to, by foi lowing formula (2.) : R-Z (2) wherein, R represents alkyl, alkenyl, cycloalkyl, ary la Iky I, a iky I ary I, alkyl ary I a I ky I , alkyl ethera I ky I . a Iky I am I noalky I, a I ky I ami doa I ky I . or alkyl estera i ky I,

Z represents negatively charged group

[0038]

The number of carbon atoms in the group represented by R is preferably 8 to 30, 10 to 20. R ^! may be linear, branched, or cyclic structure. Among them, R preferably represents aliphatic group, such as alkyl, alkenyl, cyoioalkyi, ary!alky!, aikylary!, and alkyl ary I a I ky I .

[0039]

Z represents the negatively charged hydrophilic head of the surfactant. Examples of the negatively charged group represented by Z include, but not particularly limited to, carboxyl ate COO, sulfonate S0 ₃ , sulfate SO4 ^" , phosphonate, phosphate, and combinations thereof.

[0040]

1.1.3. Z ittoriorsie Surfactant

Zwitter ionic surfactant is associated with both negative and positive portions. Examples of such zwitter ionic surfactant include, but not particularly limited to, alkyl betaine, a I ky I am i dobeta 1 ne, alkyl amino oxide and a Iky I quaternary ammonium carboxy late.

[0041]

Some of such zw i tter ionic surfactant may be represented, but not particularly limited to, by fol lowing formula (3).

R'-N ⁺ (R ² ) R ³ Z (3) wherein, R represents a iky I, alkenyl, cyoioalkyi, ary la Iky I, alkylary!, a I ky I ary I a I ky I, a iky I ethera iky I, a Iky I am I noalky I, a Iky I ami doa Iky I, or a Iky I estera Iky I, R ² each independentl represents alkyl, alkenyl, cyoioalkyi, R ³ represents alkenyl, Z represents negatively charged group.

[0042]

R, R ^? , and Z are the same as describe above. The number of carbon atoms in the group represented by R ³ is preferably 1 to 20, 1 to 6. R ³ may be linear, branched, or cyclic structure.

[0043] Among them, the foliowing zwitterionic surfactants are preferred.

Lauryl Sutfobetaine (5B3-12) from Alfa Chemistry

[0044]

1.1.4. Anphoter i c surf actant

Amphoteric surfactant is both a positively charged moiety and a negatively charged moiety over a certain pH range. The amphoteric surfactant a iso has only a negatively charged moiety over a certain pH range (e, g, typically slightly alkaline) and only a positively charged moiety at a different pH (e. g. typically moderately acidic). Examples of such zwitterionic surfactant Include, but not particularly limited to, a compound represented by following formula (4).

R ^! -NH ^÷ (R ² ) R ³ GQQ ^~ (4) wherein, W is an aliphatic group having 10 to 20 carbon atoms, R ² and R ³ i$ an a! iphatic group having I to 6 carbon atoms.

[0045]

1.1.5. Content of V i sees I ast i c Su rf actant

The content of the viscoelastic surfactant is preferably 0.1 weight % or more, 0.5 weight % or more, 1.0 weight ¾ or more, 1.5 weight % or more, 2.0 weight % or more. When the content of the viscoelastic surfactant is 0.1 weight % or more, the seif- diverting acid property tends to improve,

[0046]

The content of the viscoelastic surfactant is preferably 30 weight % or less, 20 weight % or less, 10 weight % or less, 75 weight % or less, 5.0 weight % or less, based on the total amount of the composition. When the content of the viscoelastic surfactant is 90 weight % or iess, the stability tends to improve.

[0047] if viscoeiastic surfactant is used in combination of two or more, the above content of the viscoeiastic surfactant is totai amount of them.

[0048]

1,2. Counterion compound

The composition may further comprise a counterion compound which has a counterion portion against to an ionic group of the viscoeiast c surfactant. When the viscoeiastic surfactant is the cationic surfactant, the counterion compound means an anionic compound. In addition, when the v scoeiastic surfactant is the anionic surfactant, the counterion compound means a cationic compound. Furthermore, when the viscoeiastic surfactant is the 2witter ionic surfactant or the amphoteric surfactant, the counte ion compound means the cat ionic compound and/or the anionic compound.

[0049]

Exampies of such counterion compound include, but not particularly limited to, an inorganic counterion compound and an organic counterion compound. Among them, the organic counterion compound is preferred. By using such counterion compound, the self-diverting acid property and the stability tends to improve.

[0050]

The inorganic counterion compound includes, but not particularly limited to, alkali metal inorganic salt such as sodium chloride, and potassium bromide; and alkaline earth metal inorganic salt such as calcium chloride,

[0051]

The organic counterion compound includes, but not particularly limited to, aliphatic carboxylic acid; alicyclic carboxylic acid; aromatic carboxylic acid such as benzoates, salicylate, naphthalene carboxyl ate, naphthalene d i carboxyl ate; aliphatic sulfonic acid alicyclic sulfonic acid, aromatic sulfonic acid such as benzene sulfonate, a !kyi benzene sulfonate naphthalene sulfonate; aliphatic alcohol; alicyclic alcohol; aromatic alcohol such as, phenol, naphtha I; a I iphatic amine; ai i eye i ic amine; aromatic amine.

[0052]

Among them, an organic acid, such as aromatic carboxylic acid and aromatic sulfonic acid, is preferred, sodium salicylate and sodium dodecyl benzene sulfonate is more preferred. By using such counterion compound, the self-diverting acid property and the stability tends to improve. [0053]

1.3. Isdified nanometer i a!

The term ^" nanomaterials ^" as used in this disclosure, is intended to include any suitable known nanoscale materia! having a nano-scaie size in at least one dimension. Examples of such the modified nanomater i a I include, but not particularly limited to, nanocel I u lose, carbon nanotube, graphene, nanofiber, nanoclay such as silicate, particles such as silica nanoparticle, modified silica nanoparticles, titanium oxide nanoparticle. The modified nanomater I a I may be used singly, or may be used in combination of two or more thereof. A shape of nanomater iais may be spherical, whisker, or fiber

[0054]

Among them, nanoce 11 u I ose and nanoolay are preferred, nanocel lulose is more preferred. NanoceMu!ose is also called cellulose nanofibers (CNF), micro† ibrl I lated cellulose (MFC) or cellulose nanocrystal (CNC). By using nanocel lulose, the self-diverting acid property and the stability tends to improve

[0055]

The term ^" modified ^" or “functionalized” as used in this disclosure, means that the nanomater iais has an introduced functional group and/or a grafted polymer on its surface.

[0056]

Examples of such the functional group include, but not particularly limited to, at least one selected from the group consistin of a sulfate group, a sulfite group, a oarboxy group, an ethylene oxide chain, an amino group, an ester group, a silane group and a tertiary ammonium group

[0057]

Among them, Ionic group is preferred, sulfate group, carboxy group, an amino group, and silane group are more preferred, sulfate group, carboxy group are further preferred, and su!fate group are more further preferred. By using nanocei lulose having such group on its surface, the self-diverting acid property and the stability tends to improve.

[0058]

Examples of such the grafted polymer include, but not particularly limited to, poly (meth) aery! ic acid, poly ( eth) aery i ate methyl, poly (meth) aery late ethyl, poly (meth) aery i ate propyl, po!y(meth) acrylate butyl, poly (meth) acrylate benzyl, poly (meth) aery late cyc!ohexyi, poly (meth) aery I ate 2-hydroxyethy !, poly (meth) aery late 2-hydroxypropy I , poly (po I ya I ky I enegi yco I (meth) aery I ate) , poly (a I koxypo I ya i ky I eneg I yco I (meth) aery late), po i y (di ethyl am inoethyi (meth) acrylate), poly (dimethyl ami noethyl (meth) acrylate), polyacrylamide, N, N- d i ethy I ( etha) aery I am i de, po I yea I ky I eneg I yco I .

[0059]

Among them, poly (poly (ethylene glycol) methyl ether methacrylate), poly (2- (di methy I ami no) ethyl methacrylate) are preferred. By using nanocell u lose having such grafted polymer on its surface, the self-diverting acid property and the stability tends to improve

[0060]

The content of the modified nanomater iai is preferably 0.01 weight I or more, 0.05 weight I or more, 0.1 weight ¾ or more, 0.2 weight % or more, 0.3 weight I or more. When the content of the modified nano aterial is 0.05 weight. % or more, the self- diverting acid property tends to improve.

[0061]

The content of the modified nanomaterial is preferably 2.0 weight % or less, 10 weight % or less, 5.0 weight % or less, 3.0 weight % or less, 2.0 weight. I or less, based on the total amount of the composition. When the content of the modified nanomaterial is 20 weight % or less, the stability tends to improve.

[0062]

The weight ratio of the viscoelastic surfactant to the modified nanomaterial is preferably 1.0 times or more, 2.0 times or more, 3.0 times or more, 4.0 times or more. When the weight ratio of the viscoelastic surfactant to the modified nanomaterial is

1 0 times or more, the self-diverting acid property tends to improve.

[0063]

The weight ratio of the viscoelastic surfactant to the modified nanomaterial is preferably 2.0 times or less, 15 times or less, 10 times or less. When the weight ratio of the viscoelastic surfactant to the modified nanomater iai is 20 times or less, the stability tends to decrease.

[0064] 1.4. Polymer

The composition may further comprise a polymer when needed. Examples of the polymer include, but not particularly limited to, at least one selected from the group consisting of polyacrylamide, po I y (a ! !y!amine hydrochloride), poly (ethylene glycol) po!yethyleneimine, polyvinyl alcohol, po I y (4— sty renesu I f on i c ac i d~co~ma I e i c acid), polyvinylpyrrolidone, po!yal lyla ine, po I y (d i a 11 y I dimethyl ammonium), polyaniline, poly (4-viny!pyidine), and po I yanii ine emerald ine, in addition, the polymer includes polyelectrolyte,

[0065]

Among them, a polymer contain nitrogen atom is preferred. As such additive polymer, polyacrylamide, po I y (a i lylamine hydrochlo ide), polyvinyl alcohol, poly (4- styrenesu I f on i c ac i d-co-ma I e i c acid), polyvinylpyrrolidone, poiyaily I am ine, po I y (d i a 11 y I dimethyl ammonium), polyaniline, poly (4-vinyipyidine), and poivani!!ne emerald ine are more preferred. By using such polymer, the self-diverting acid property and the stability tends to improve

[0066]

The content of the polymer is preferably 0.1 weight % or more, 0.2 weight % or more, 0.3 weight I or more. When the content of the polymer is 0.5 weight % or more, the self-diverting acid property tends to improve.

[0067]

The content of the polymer is preferably 10 weight % or less, 7.5 weight % or less, 5 weight % or less, based on the total amount of the composition. When the content of the polymer is 10 weight % or less, the stability tends to improve.

[0068]

1.5. Additives

The composition may further comprise additives when needed. Examples of the additive include, but not particularly limited to, at least one selected from the group consisting of scale inhibitors, biocides, corrosion inhibitors, traces, fluid loss agents, formation stabilizers, st i u I i -response agents. The additives may be used s ngly, or may be used in combination of two or more thereof.

[0069] 1.6. Solvent

The composition may further comprise solvent when need. Examples of the solvent include, but not particularly limited to, water. The composition may include water as a brine.

[0070]

The content of the solvent is preferably 30 weight I or more, 40 weight % or more, 50 weight % or more, 60 weight ¾ or more, 70 weight. ¾ or more, 80 weight % or more, 90 weight % or more. The content of the solvent is preferably 97 weight % or less, 95 weight % or less, 90 weight % or less, 80 weight I or less, 70 weight % or less, 60 weight % or less, based on the total amount of the composition. When the content of the solvent is within the above range, the self-diverting acid property and the stabi 11 ty tends to improve.

[0071]

1.7. Other Components

The composition may further comprise other components when need. Examples of such other component include, but not particularly limited to, acid material such as HCI,

HP.

[0072]

As the describe above, the viscosity of the composition is change based on acid concentration or pH. The viscosity of the composition may be controlled by supplying acid or consuming acid. Therefore, if the composition contain acid, the concentration of acid is not limited. In view of the seif-diverting acid property and the stability, the concentration range of acid is preferable 0. i to 40 weight %.

[0073]

1.8. Viscoelastic Property

1.8.1 Acid Sensitivity of the composition

The viscosity of the composition at specified temperature decrease with an increasing in acid concentration. A rate of a viscosity at 25 °C of the composition including 4 weight % acid to a viscosity at 25 °C of the composition including 20 wei ht ¾ acid is preferably 25 to 50, 30 to 45, 30 to 40.

[0074]

Preferable viscosity range at 25 °c, 58S ¹ , for each acid concentration, of the composition is following A viscosity at 25 ^a C of the composition including 4 wei ht % acid is preferably 500 to 1000 cP, 525 to 900 cP, 550 to 800 cP.

A viscosity at 2.5 °C of the composition including 8 wei ht % acid is preferably 450 to 1000 cP. 475 to 900 cP, 500 to 800 cP.

A viscosity at 25 °C of the composition including 12 weight I acid is preferably 200 to 400 cP, 225 to 375 cP, 250 to 350 cP.

A viscosity at 25 °C of the composition including 16 weight. % acid is preferably 50 to 250 cP, 75 to 225 cP, 100 to 200 cP.

A viscosity at 25 °C of the composition including 20 weight % acid is preferably 1 to 100 cP, 1 to 75 cP. 1 to 50 cP.

[0075]

A rate of a viscosity at 40 °C of the composition including 4 weight % acid to a v scosity at 25 °C of the composition including 20 weight % acid is preferably 25 to 50. 30 to 45. 30 to 40.

[0076]

Preferable viscosity range at 40 °C, 58S , for each acid concentration, of the composition is foil owing

A viscosity at 40 °C of the composition Including 4 weight I acid is preferably 500 to 1000 cP, 525 to 900 cP. 550 to 800 cP.

A viscosity at 40 °C of the composition including 8 weight % acid is preferably 450 to 1000 cP, 475 to 900 cP, 500 to 800 cP.

A viscosity at 40 °C of the composition including 12 weight % acid is preferably 200 to 400 cP, 225 to 375 cP, 250 to 350 cP.

A viscosity at 40 °C of the composition including 16 weight % acid is preferably 30 to 200 cP, 40 to 175 cP, 50 to 150 cP.

A viscosity at 40 °C of the composition including 20 weight I acid is preferably 1 to 100 cP, 1 to 75 cP, 1 to 50 cP.

[0077]

A rate of a viscosity at 50 °C of the composition including 4 weight ¾ acid to a viscosity at 25 °C of the composition including 20 weight I acid is preferably 25 to 50, 30 to 45, 30 to 40.

[0078] Preferable viscosity range at 50 °C. 58S ^~ ', for each acid concentration, of the composition is fol lowing

A viscosity at 50 °C of the composition including 4 weight % acid is preferably 250 to 700 oP, 275 to 550 cP. 300 to 400 cP.

A viscosi y at 50 °C of the composition including 8 wei ht % acid is preferably 250 to 700 cP, 275 to 550 cP, 300 to 500 cP

A viscosity at 50 °C of the composition including 12 weight % acid is preferably 60 to 250 cP, 80 to 225 cP, 100 to 200 cP.

A viscosity at 50 °C of the composition including 16 weight ¾ acid is preferably 30 to 200 cP, 40 to 175 cP, 50 to 150 cP.

A viscosity at 50 °C of the composition including 20 weight I acid is preferably 1 to 100 cP, I to 75 cP, 1 to 50 cP.

[0079]

The composition has the self-diverting acid property. The se I f-di verting acid property can be described acid spending test. When the acid is being spent by reaction with calcium carbonate or other reactive minerals, the viscosity of the composition increase.

[0080]

A rate of a viscosity at 25 ^c' C of the composition spent 12 weight I acid to a viscosity at 25 °C of the composition spent 4 weight % is preferably 20 to 60, 25 to 55. 30 to 50.

[0081]

A rate of a viscosity at 25 °C of the composition spent 18 weight ¾ acid to a viscosity at 25 °C of the composition spent 12 weight % is preferably 0.016 toO.05, 0018 to 0.04, 0.02 to 0.03.

[0082]

Preferable viscosity range at 25 °C, 58S ^~! , for each acid spent, of the composition is f o ! I ow ! ng

A viscosity at 25 °C of the composition spent 4 weight I acid is preferably 1 to 100 cP, 1 to 75 cP, 1 to 50 cP.

A viscosity at 25 °C of the composition spent 8 weight % acid is preferably 250 to 700 cP, 275 to 550 cP, 300 to 500 cP. A viscosity at 25 °C of the composition spent 12 weight % acid is preferably 500 to 1000 cP, 525 to 900 cP, 550 to 800 cP.

A viscosity at 25 °C of the composition spent 16 weight % acid is preferably 300 to 800 oP, 350 to 700 cP. 400 to 600 cP.

A viscosity at 25 °C of the composition spent 18 weight % acid is preferably 1 to 100 cP, 1 to 75 cP, 1 to 50 cP.

[0083]

2. Method of Producing the Opposition

A method of producing a composition comprises a step of mixing a modified nanomater I a i and a viscoelastic surfactant in the mixing step, other component may be mixed when need

[0084]

The mixing step may include the following steps in following order: a step of mixing the modified nanomater ia! with solution to obtain solution A: a step of adding the polymer the additive, the acid and/or the solution into the solution A to obtain solution B; a step of adding the viscoelastic surfactant into the solution B to obtain solution G. In addition, the mixing step may include a step addition the counterion compound such as sodium salicylate into solution C

[0085]

A mixing method in the mixing step is not particularly limited, and hitherto known processes can be applied. Examples of such method include mechanical mixing method such as vertex and the like, and son i cat ion.

[0086]

3, iethod of For ing an Oil or Oas We I i

A method of forming an oil or gas well comprises a step of preparing a fluid comprising a solvent., a viscoelastic surfactant, a modified nanometer iai, and an acid material, and a step of introducing the fluid into the well.

[0087] in addition, the method of forming an oil or gas well may further Include a step of supplying acid in the fluid introduced into the well. The fluid which include the composition waste or consume acid for reacting with minerals such as cal cite or dolomite. The fluid can keep forming the well by the acid supplying step

[0088] 4. §«ary

The disclosure involves the development of high performance and functional viscosified oilfield chemicals based on viscoelastic surfactants (VES) for well-stimulation and completion applications. This includes acid well stimulation, formation control and diversion to create higher permeability and conductivity pathways in wells. By focusing on acid or acid treatment formulations, the stability of the VES was tested against various concentrations and composition in the presence of brine, controlled pressure and temperatures and its effect on viscosity or rheology. The formulation included the addition of nanocel !uiose, polymer, nanoparticles, and other additives to enhance performance and functionality towards cost-effectiveness. This involve the modification of the particles and additives with salinization and grafting of polymers. Comp!exation with polymers on the additives were also done. Tests included physico-chemical determination of properties against various control colloidal formulations. The improvement and control in the property was evident with the resulting formulation showing the combination of cationic VES and nanocellulose (CNC) have superior performance. Also modification with grafted or compiexed colloidal polymer solutions enabled st i u i I -responsiveness. The higher stability of the cat i on i c— VES— CNC composition was demonstrated against a host of brine, temperature, and pH conditions which showed better acid stimulation properties as against VES without the modified additives. The results also confirmed uses for acid stimulation against concentration with acid spending tests ind cating self-divert ng acid (SDA) behavior. Lastly, higher temperature performance was observed with the stability of the VES-GNC vs. control samples.

[0089]

4.1. We have developed viscosify!ng media for completion and stimulation of oi i/gas wells with low and high permeability and depth. This involves the preparation of acidified viscoelastic surfactant (VES) media based on cationic, anionic, zwitter ionic, and amphoteric surfactants with a compatible counterion compound resulting in a concentration dependent viscous behavior stable at ambient to high temperature. This is exemplified with the CTAB-NaSal or cetytri methyl ammonium bromide- sodium salicylate system and other combination of surfactants and counterion compounds thereof. The phenomena is based on the formation of higher order worm-like micelles and thei networking-gel properties. [0090]

4.2. Additives can be formulated and combined at a specific order with the VES— Complex resulting in a stabilized colloidal solution and vi seas if led networked gel resulting in a higher stability and higher temperature property. The additives can be based on particle, chemically and surface modified particle, or small molecule resulting in a nanostructured complex.

[0091]

4.3. Molecule and large molecule additives can be formulated and combined at a specific order with the VES-Comp ! ex resulting in a stabilized colloidal solution and viscosified networked gei resulting in a higher stability and higher temperature property. The additives can be based on chemicals exhibiting: corrosion inhibition, scaling inhibition, biocide, fluid loss agent, formation stabilizer, etc. resulting in a complex fluid.

[0092]

4.4. Specifically, nanopart icie materials can be added at. a specific order based on: si I ica nanoparti cie, modified si ! ica nanoparticles, nanoclay, cellulose in combination with cationic, anionic and zwitter ionic composition. Physico-che ical characterization and standardized testing methods based on these optimized formulations results in higher stability and stimuli -responsive properties.

[0093]

4.5. Specifically, polymer materials can be added at a specific order based on: po ! ye I ectro I yte, water-soluble polymers, and other polymers, in combination with cationic, anionic and zwitter ionic composition. Physico-chemical character ization and standardized testing methods based on these optimized formulations results in higher stability and st i mu I i -responsive properties.

[0094]

4.6. Specifically, nanoparticle materials can be added at a specific order based on: nanccel!ulose (CNG) derived from celiulosic sources (wood pulp, cotton, agricultural waste, etc.) in combination with cationic, anionic and zwitter ionic composition. Physico-chemical characterization and standardized testing methods based on these optimized formulations results in higher stability and st i u I i -responsive properties. [0095] 4.7. Specifically, chemically and surface modified nanoparticle materials can be added at a specific order based on: nanoceMu!ose (CNC) in combination with cationic, anionic and zwitter ionic composition. Physico-chemical characterization and standardized testing methods based on these optimized formulations results in higher stability and sti uli -responsive properties.

[0096]

4.8. Specifically, nanoparticle materials can be added at. a specific order based on: nanoce! I u lose (CNC) in combination with cationic, anionic and zw!tter!onic composition demonstrated a good enhancement in diverting and self-diverting acid (8DA) properties and good break down of micelle when depleting most of HGi with stimuli responsive properties.

[0097]

4.9. Specifically, nanoparticle materials based on: nanocellulose (CNC) in combination with cationic, anionic and zwitter ionic composition demonstrated a good enhancement in stability and viscosity at higher temperatures with rheometry done for example at1GGs ¹ of shear rate, 400 psi and ramping temperature from 77F (25°G) to 350F (176°C) with a ramping rate lOF/min.

[0098]

4.10. Specif ica! !y, polymer materials based on commercial ly derived polymers complexed with CNC in combination with cationic, anionic and zwitter ionic composition demonstrated a good viscosity enhancement in stability at higher temperatures and 8DA properties with stimuli responsiveness,

[0099]

4.11. Specif ica i I y, surface modified nanoparti ole, polymer materials based on grafting the polymers on the surfaces and complexed with CNC in combination with cationic, anionic and zwitter ionic compositions. They have demonstrated a good viscosity enhancement in stability at higher temperatures and SDA properties with stimuli responsiveness.

[0100]

4.12. Specif ical !y, surface modified nanopart ic!e, polymer materials based on grafting the polymers on the surfaces and complexed with CNC in combination with cationic, anionic and zwitter ionic compositions. Grafting involves: 1) surface initiated polymerization (SIP) or “grafting from” , 2) “grafting to or grafting onto" , and 3) “grafting through” . The method can also involve ohemical adsorption or physical adsorption. They have demonstrated a good viscosity enhancement in stability at higher temperatures and SDA properties with stimuli responsiveness.

The present invention will be described below in more detail with reference to examples, but it should be construed that the scope of the present invention Is in no way limited to these examples,

[01023

1, Control Experiments,

Specify a current formulation of a VES and acid stimulation fluid composition and designated as a control or a published patent composition. This can be d fferentiated by the type of surfactants and other additives in the current formulations it is important to identify the ratio or percentage of the surfactant, the counterion compound, and determination of a minimum percolation threshold of a desired property. It should be possible to identify the different type of surfactants used including any co-surfactants and solvents and the presence of soluble salts.

[0103]

2, Stab i I ity comparison.

The first step is to determine the stability of the fluids under acid conditions of various pH. Acid spending tests will simulate the ability of the VES formulation to react with calcite and dolomite formations. it is important then to monitor the changes of the VES in stability over time with various pH and temperature conditions [0104]

3, le Compos i t i ons.

Modifications in the compositions with counterion compounds, polymer complexes, and chemical structure of the surfactants. This will involve determining the advantages of cationic, anionic, and zw i t ter ionic surfactants. Fluids, which can contain two or more different surfactants: preferably anionic or non ionic, thereby leaving reservoir rocks water-wet for better fluid mobility through the formation. Specific organic counterion compounds will be used that are more suitable for acid stimulation conditions. Various surface modification protocols of the add i t i veby silanes (sulfonate, carbonate, epoxy, amine, etc) or with polymer grafting will lead to acid stability and st i mu I i -responsive properties. By oarefui design, these fluids have been specifically tailored to give characteristics of viscosity, solubility and temperature stability suited to specific sti ulation applications.

[0105]

4, Testing and Characterization.

Physico-Chemical Characterization and Experiments include:

1) viscosity measurements of various concentrations (1-10%) of VES vs T, salt conditions.

2) Viscosity measurements against various pH and salt conditions.

3) Viscosity decrease monitoring vs increasing shear rate in cp or Pas.

4) Rheology and viscoelastic properties. Tests will be done against controlled additives with known or reported compositions: a) rheology, b) stability with T and P, c) stability with pH and salt, d) flow conditions in controlled permeabilities, e) ability to be a carrier for other additives (non-water soluble).

[0106]

Desirable properties to be monitored include: higher viscosity across a wide range of temperatures, particularly at the high end and at the low surfactant loading which reduces cost. They should also be effective in a number of salt bri es, including seawater needed to effect formation stability. The maintenance of high viscosity at low pH and various salt conditions is important for acid stimulation and acid fracturing applications. St i u I i— responsive properties should also be observed - shift in peak dissolution rates, shift in viscosity with concentration range, and shift In viscosity with time.

[0107]

5. Fo lym@r Composition and lanost metis ring.

Polymer-surfactant complexes are generally more stable than small molecule surfactants. Addition of polymers, nanopart icies and nanostructuring of complexes will necessitate the following:

1) investigate improved stability of po i ye i ectro I yte-surf actant complexes and higher order micelles at particular concentrations.

2) investigate the formation of stable complexes to show st i mu I i -responsive properties and gradient properties (concentration dependence). [0108]

In particular, the addition of clay and silica nanomater la I s, graphene nanoparticles, nanocellulose nanopartic!es and nanofibers can lead to micellar stability and better colloidal properties with minimum percolation threshold. The additives can lead to stimuli -responsiveness, improved fluid loss prevention, increased corrosion resistance, and fluid stability at high T and P conditions. in-si tu polymerized polymer-polyelectrolyte complexes or polymer-grafted nanoparticle complexes (surface modification) as new additives to YES fluids is possible.

[0109]

6, Acid Stimulation and Fracturing Properties.

After determining the stability of the formulated VES and nanomater ia I formulated VES under low pH (high acid content) and various salt concentrations their ability to react with the simulated formation minerals will be investigated. Stimulation of carbonate rocks usually involves a reaction between an acid and the minerals cal cite (GaGCy or dolomite GaMg(G0 ₃ ) ₂ like composition. Reaction rate with these minerals will be observed by titration type analysis both at ambient and pressurized conditions. Various acid concentrations involving HCI with 1 - 30 wt% addition w ll be used. The change in viscosity will also be monitored as a function of time using viscosity and rheology measurements with temperature control.

[0110]

7, The Ha in Protocol and formulation:

Preparation of VES compositions of a specific surfactant (or with co-surfactant) and counterion compounds range from 1-10% by weight concentrations. This is simply done by the addition of the surfactant to water and brine or salt to result in a translucent clear solution and increase in viscosity (shear thining). The mixing can be done by manual and mechanical mixers or the use of son i cat ion. Once the VES solution is prepared it can be tested for physico-chemical properties including viscosity or rheology. In addition, various compositions containing polymers, nanomaterial s, and actives (additives) and repeat the measurements as in previous benchmarking with control experiments. This has the potential to stabilize these micelles through complexes that result In stable networks and anchoring of micelles through orthogonal assembly.

[0111] EMIPLE TOTAL CONCENTRATION PROTOCOLS:

Assuming from a total of 100% in which the rest of the composition is Water using Cetyl trimethyl ammonium bromide (CTAB) as an example surfactant:

CTAB-VES1 : CTAB (6 wt. %) + CaC 1 ₂ (30wt %) + Water (64 wt%)

CTAB-VES 2: CTAB (6 wt I) + Na Sal icy I ate (0.5 wt%) + Water (93.5 wt%)

COMM-VES 3: Commercial Surfactant (6 wt %) + Na Salicylate (1 wt%) + Water (93 wt!), Commercial Surfactant (6 wt %) + CaC 1 ₂ (30wt I) + Water (64 wt%) assume dilution from a stated wi% of a commercial sample.

CTAB-VES - NANO with CTAB: (Y wt I) + Na Salicylate (0.5 wt%) + Nanoadditive (X wt%) + Water (93.5 wt%) .

CTAB-VES - POLY with CTAB: (Y wt %) + Na Salicylate (0.5 wt%) + Poly (X %) + Water (93.5 wt%)

CTAB-VES - ACTIVE with CTAB: (Y wt %) + Na Sa! icy late (0.5 wt%) + ACTIVE (X wt%) + Water (93.5 wt%)

AC1BF I CATION : Add varying concentrations of HC! in order to Adjust pH CONTROL: Commercial surfactant or polymer sample [0112]

9, PROPERTIES DESIRED:

Some of the properties to be monitored include the following:

1. Stability at various temperatures to maintain viscosity value and retain transparency or cloud point. Viscosity in cp (10 x) 500-10 sec! range, which decreases from 50 - 100 °C or with increasing shear rate.

- higher concentrations, addition of salts, and addition of alcohol co-surfactants is acceptable for stabilization.

2. Stability in fresh water or brine conditions up to seawater (100,000-300,000 ppm)

3. Stability at low pH conditions with 1-20 wt % of added acid content.

4. Stability of VES under various acidic conditions with specified higher pressures and temperatures.

[0113]

10. VISCOSITY AID RHE0LO0Y:

Initial formulation: * Viscosity at various temperatures - Though most of the temperatures in acid stimulationareambienttemperatures.

* ViscosityvsTimeataconstanttemperature

* Different concentrations:3-10% of VES, 5-15% of HCL and HF, 5-15% with NaC!, MgorGaCU,orBufferSait

* pHfrom0-7,Viscositymeasurements,varioustemperatures-25to60° C.

* Change inViscosityvs increasingamountsofHCisequence (spentacid)

* Increasingconcentrationovertime.

* Seif-DivertingAcid (SDA)Properties

* StagesofdifferentViscoscifyingPropertieswithchanges inpermeability

* Permeabilitytosimulatecaiciteandsandstoneformations [OH4]

11. DATA ORESULTS

The resultsofthestudypertainingtothemethodologiesusedandthecompo sitionsand conditionsareoutlinedfromA-G.

[0115]

The best results are:Use of GTAB surfactants with added cationic- CNC and polymer grafted CNC demonstrating the best improvement of viscosity at both room temperature and 60°G. TheCNC-PoiyvinyialcoholorCNC-PVA premixed solid (P1) also resulted in improved viscosity at higher temperature. The self-diverting acid properties show stimui!-responsive behavior on all the studies resulting in the ability to shift dissolution properties with pH. The summary of the procedures and results in each sectionfromA-Garethususedtosupporttheclaims inthispatentfiling.

[0116]

A) StudiedHCIspeningofCTABVESwithCelIloseHanoerystal(GIG):

Typicalpreparingprocedurefor12%HCIspentsolution (20%max,8% remaining) Compositions was produced by mixing components shown in table 1. First, master soluionAof GNGwaspreparedbydissolingGNC inwaterandsonicationforover1h. And then,hydrochloricacid,water,CTABwasadded inthisordertothesolutionAand vertex mixed untilthe CTAB totally dissolved to obtain solution B. Finally, NaSa! solutionaddedto the solutionB andvertexmixed. Gelled-1ike solutionwillform in seconds. Theobtained solutionwasallowedtosettledownforovernightto removethe bubbles. TheamountofHC!wasadjustedbasedonHCIconcentration. [0117]

The acid sensitivities of the compositions are shown in Figure 1. in Figure 1, the vertical axis shows vi cosity, and the horizontal axi shows HO I concentration added in the composition. Figure 1 (a) to (c) show the acid sensitivities at 25 to 60 °C.

[0118] Table 1

* : CTAB: etyl trimethyl ammonium bromide *2 : NaSa I : sod i urn sa II cy i ate

*3: GNC: GOOH functionalized GNC obtained from Aioter a

[0119]

The HCI spending test with CTAB VES - G C is important for proving the seif- diverting acid properties (SDA) for acid well stimulation as well as formation control.

The addition of CMC (obtained from Aioterra which is -GOOH functionalized) has the effect of increasing the viscosity in general especially at higher concentration - although the effect is almost incremental at low concentration (Figure 1).

The CTAB behaved well mostly at higher concentration (more viscous) but did not remain as stable when the temperature increased.

The Acid spending test showed a higher viscosity at the peak of the spending (Figure 2). In general, the CNC demonstrated an enhancement in viscosity in the middle of spending curve-better diverting. However, the CNC demonstrated no influence on the point, of breaking-same good break down The CMC size (whiskers or nanorods and nanofibers) can still be parametrized to achieve better performance such as modification of the -OH group of the polysaccharide with salinization, polymerization, or comp iexat ion.

[0120]

The composition for HGI spending test was obtained by the same operations as above, except that GaC 12 was added to the gelled- 1 ike solution. The amount of CaG 12 was adjusted based on spent HCI amount. [0121]

The self-diverting acid property of the compos i t i on by HCI spending test are shown in Figure 2. in Figure 2, the vertical axis shows viscosity, and the horizontal axis shows HCI spent amount in the composition. The acid spending test simulated the ability of the composition to react with calcite and dolomite formations. Figure 2 (a) and (b) show viscosity behaviors of Example 1 depending on share rate at 25°C. Figure 2 (c) shows a difference of the self- iverting acid property between Example 1 and Comparative Example 1.

[0122]

B) Studied HCf spen ing of CTAB ¥ES ith Nara a

Compositions was produced by mixing components shown in table 2. The compositions including nanociay was obtained by the same operations as above, except that instead of the G G, nanoc!ay was used.

[0123] Table 2

*1 : CTAB: cetyl tri methyl ammonium bromide *2 : NaSa I : sod I urn sal I oy I ate *3: Laponite-ER: anoC!ay obtained from BYK [0124]

The HC! spending test with CTAB VE3 - Nanoclay is important for proving the self-diverting acid properties (SDA) for acid well stimulation as well as formation control

The addition of Nanociay has the effect of increasing the viscosity in general especially at higher concentration - although the effect is almost incremental.

The CTAB behaved well mostly at higher concentration (more viscous) but did not remain as stable when the temperature increased.

Nanoclays charges and hydrophobic ity can still be modified to surface modification with silane or cationic surfactants. - HC! Spending Test w th NanoClay

With loading of 0.25% and 0.5% of nanociay, the viscosity increased. However, increase of viscosity from 025% to 0.5% does not as obvious as CNC. The possible reason could be the aggregation of nanociay in acid.

[0125]

C) ¥ES Surfactant studies with su I f ated-CNC obtained from Celluforce

Compositions was produced by mixing components shown in table 3. The compositions including sulfated-CNC were obtained by the same operations as above, except that instead of the CNC, sulfated-CNC was used. [0126]

Table 3

*1: GTAB: cetyl tri methyl ammonium bromide

*2: NaSa I : sodium sal icy late

*3: su ! fated— CNC: obtained from Celluforce

[0127]

The self-diverting acid property of the composition by HCI spending test are shown in Figure 3. In Figure 3, the vertical axis shows viscosity, and the horizontal axis shows HCI spent amount in the composition. Figure 3 shows viscosity behaviors of Examples 4 and 5, and Comparative Example 1

[0128]

Summary Discussion of CNC additives

• The previous carboxyl ated CNC (Aioterra) demonstrated good performance, which increased the ighest viscosity but does not. influence the break viscosity, However, the use of the s I fated CNC (Ce i I uForce) demonstrated the highest viscosity stability at higher temperature -but also increased in the break v i scos i ty.

• Adding sulfonated CNC would make the CTAB-VES less transparent but still iscous.

• With increasing concentration of CNC, the highest viscosity in HCI spending tests are increased. • The viscosity at 01 and 18% are also increased.

[0129]

HG! spend ng test at high temperature

With the increase of temperature from 25°0 to 60°G, the viscosity decreased from around 500cPs to around 200cPs. Compared to the GTAB system without any additive, the VES with 05% su I fated CNC demonstrated an increase in viscosity in aii temperatures. This indicated the CNC helps the VES maintain high viscosity at higher temperature (Figures 3 and 4),

[0130]

The zwitter ionic surfactant and the counterion compound with su I fated CNC demonstrated a good stability with temperature. With less than 3% surfactant in total, the viscosity remains over lOOcPs even at 50°C. (Figure 6) Examples of zwitterionic surfactants and the counterion compound are shown in Figure 5.

[0131]

Compared a!! the different VES, the GTAB with 0.5% CNC demonstrated the highest viscosity at both 50°G and 60°C. While the zwitter ionic/an ionic VES demonstrated a good viscosity stability from 50°C to 60°C but a shift in the break behavior. AM the VES systems demonstrated higher than lOOcPs viscosity at 6Q ⁿ C.

[0132]

The self-diverting acid property at high temperature by HG! spending test are shown in Figure 4. in Figure 4, the vertical axis shows viscosity, and the horizontal axis shows HC! spent amount in the composition. Figure 4 (a) and (b) show viscosity behaviors of Examples 4 and Comparative Example 1 at high temperature.

[0133]

Compositions was produced by mixing components shown in table 4. The compositions including were obtained by the same operations as above, except that instead of some components, following components were used.

[0134] Table 4 *3: SB3-18: Stearyi Sur Ifobetaine obtained form Sigma- Aidrich

*2: SOBS: Sodium Dodecy I Benzene Sulfonate obtained form Sigma- Aldrich

*3: su!fated-GNC: obtained from Ceiluforce

*4: Laponite ER: nanoc!ay obtained from BYK

*5: Laponite RDS: nanoclay obtained from BYK

[0135]

The se!f-di verting acid property of the composition by HOI spen ing test are shown in Figure 6. Figure 6 (a) to (b) show the viscosities of Examples 6 to 8 and Comparative Example 2 at 25 to 60 °C.

[0136]

D) Study of CTAB VES in Acid Spen ing and the addition of small molecular and polymers (Figure 7 and 8),

Compositions was produced by mixing components shown in table 5. The compositions were obtained by the same operations as above, except that additive was added into the compos i t i on.

[0137]

Table 5

*1 : GTAB: cetyl tri methyl ammonium bromide

*2: NaSal: sodium sal icy I ate

*3: su!fated-CNC: obtained from Celiuforce

*4 PEG 550: polyethylene glycol having 550 of a weight average molecular weight *5 PEG 2000: polyethylene g!ycol having 2000 of a weight average molecular wei ht [0138]

The self-diverting acid property of the composition by HC! spending test are shown in Figures 7 and 8. Figure 7 (a) to (b) show the viscosities of Examples 9 to 12 and Comparative Example 3 at 25 to 60 °C. Figure 8 shows the viscosities based on additives at 70°C in 8 wt! HCi spent solution (max 2.0wtl). 1. 0.5% CNC demonstrated good enhancements in viscosity compared with no additive and can also increase the performance at 60-G, which is consistent with our previous result.

2. Add i rig 0.5% ethy I ene g i yco I may not s i gn i f i cant i y i nf i uence the v i scos i ty at high temperature.

3. Adding 0.5% polyethylene glycol (PEG) slightly increases the viscosity at both room temperature and 60°C

4. The influence of PEG is dependent on Molecular weight, the higher molecular weight the higher the stability.

[0140]

At 7Q°C, the evaporation of GTAB is severe. By controlling the same operation time, the viscosities can be compared relatively. The result demonstrated CNC will increase the viscosity of CTAB VES, and adding a higher MW PEG to CTAB VES and CNC will also improve the viscosity.

[0141]

E) Study of silane functional izad GG:

Procedure and Synthesis of silans functionalized GNG of various silane structures (Figure 9):

Silana modification by direct mixing silane agent end su I feted C G powders:

1. 2. ml silane was added to a vial contains 500 mg su I fated CNC powders

2. Vigorously stirring was applied to make sure the powders dispersed uniformed.

3. The reaction was heated to 40°C and the mixture was allowed to react 36 h

4. The suspension was purified by vacuum fi I t rat i on and wash with 50 ml of ethanol [0142]

For APTMS:

• After functionalization, the initial thermal degradation temperature and temperature at the maximum degradation rate are both increased, which could be due to the interaction between the silane and CNC (Si-O-C).

• The Increase in the residue mass is attributed to the siloxyl group, which is also supported by the literature.

[0143] ForAEAPTS:

• The initial thermal degradation temperature and temperature at the maximum degradationrateareboth increased.

• No residue mass difference, which could be attributed the less functionalization (smallerN-Hpeak)

[0144]

SummaryofResultsforSilaneSurfaceFunctionalizedGNCandvisco sitymeasurements:

The formulation 3%CTAB+0.5¾NaSai+0.5%(CNC) after 12IHCI spent (20%max) was tested.

According to the viscosity study results, ailthe silane modified CNG demonstrated negligible viscosity change over non-modified CNC, which could be due to allthe silane agentmake the GNC more hydrophobic.(Figure 10) Therefore the silanemodified

CNGtendtoformbigaggregationsandwillnotdispersewe11inVES:

1. FourSManemodifiedCNGhasbeenprepared. However,FTIRandGG—MS implythe functionalization is not successful. The TGA of CNG-APTES and GNC-AEAP ^' flS demonstrated the significant difference with the unmodified GNC, while GNC— GPTESdemonstrated nodifference. PreparedwithCTABand aSa!,theCNC-GPTES demonstrated no influence with viscosty, while CNG-APTES and CNC—AEAPTMS demonstrated negative fluence on the viscosity. A highertemperature trial willbeconductedtooptimizethefunctionalization.

2. Graphene Oxide was added to the Zwitterionic/Anionic system as the second additive,however,the inflenceoftheGOontheviscosity isnotsignificant.

3. Theviscosity result inzwltterionicVESdemonstratedthesame results,allthe silane modified CNG demonstrated lowerviscosity than non—modified CNC,which couldbeduetoailthesilaneagentmaketheCNCmorehydrophobic.

[0145]

ProceduresForCationic odifseatsonofCNG:

PreparationofCationicCNG

1. Sulfated GNC aqueous suspension (2 wt ¾) was treated with diluted alkaline solution (NaOH,2wt%)for30minat roomtemperature.

2. 2,3-Epoxypropyl trimethyl ammonium chloride (EPTMAC) was dropping into the suspensionwiththeNaOHasthecatalyst,andthereaction lastedfor6hat65 °G, 3. Afterthe reaction, the suspension (~2wt %)was precipitated in ethanol,and theproductwascollectedbycentrifugation.

4. The EPTAG—oationic cellulose nanocrystals (Cationic-GNC) were redispersed by dialysisagainstthedistilledwater (-2wt.¾)for5days

[0146]

IR and DSC date confirmed the successful grafting of the cationic silane on CNG (Figure 11)

[0147]

Step 1 : synthesis of OlC-initiator

1. Sulfated CNG (1g) were dispersed into dry N,N-dimethylformamide (DIF) (60 mL) by stirring and sonicated for 1 h at room temperature. After triethylamine (TEA) (2,50 g) and N.N-dimethyi-4-aminopyridine(DMAP) (180 g)were added into the suspension, the solution of 2—bromoisobutyryibromide (BiBB) (7.80 g) in DF wasaddeddropwise intothemixturefor2h.

2. The mixture was stirred at room temperature for another 12 h before 10 ml methanolwas introduced. After centrifugation (4,4k rp), the crude product waswashedwithMethanolforthreetimes.

[0148]

Step 2: synthesis of polymer grafted CNC

1. A mixture of CNGs-Br suspension (30g), Monomer(Poly(ethylene glycol) methyl ether methacrylate (PEGMEMA), 2-(Dimethylamino)ethyl Methacrylate (DMAEMA), 2g), Methanoi (around 2.0 ml) and Gu(I)Br (28mg)were placed into the Schienk tubewithamagneticstirringbar.

2. After being purged with for 30 nun, degassed 1,1,4,7,10,10- Hexamethy!triethyienetetramine (HMTETA) (20mI in 1ml Methanoi) were injected intothemixture. T

3. he polymerizationwas carried out at room temperature forovernight, and then theSchienktubewasopenedtoairtoquenchthe reaction.

4. Afterdilutingwithethanol,thesuspensionwascentrifuged (4,4k rpm),andthe supernatantwascollectedandwashwithMethanoifor3times.

[0149] Compositions was produced by mixing components shown in table 6. The compositions were obtained by the same operations as above, except that grafted CNC were used.

[0150]

Table 6

*1: GTAB: cetyl trimethyl ammonium bromide

*2: aSa!: sodium salicylate

*3: su I fated— CNC : obtained from Ce!luforce

*4 Cat i on i c~CNC: mod i f i ed-CNC obtained by the above.

*5 PD AEMA-CNC : grafted-CNC obtained by the above.

*6 CNC-PVA-p remixed: a mix of sulfated-CNG (0.5 wt!) and polyvinyl alcohol (0.5 wt!) [0151]

The self-diverting acid property of the composition by HCI spending test are shown in Figure 13. Figure 13 show the viscosities of Examples 13 to 16 at. 25 to 60 °C in 12 wt! HGI spent solution (max 20 wtl).

[0152]

Results for the Synthesis and Surface Initiated polymerization (SIP) on GIG FTIR spectra demonstrated the successful functionalization of ATRP-initiator and polyme ization of PDMAE A by detecting G~0 stretching (Figure 12). With only ATRP- initiator, the CMC is less thermally stab i e (161 °C) . After S!P polymeriza ion, the degradation temperature is increased to 231 °G. Besides, CNC— PDMAEMA has less residue mass, which also supported the successful polymerization or grafting of PDMAEMA on CNC. Likewise the successful grafting of CNC—PPEGMEMA was shown in Figure 13.

[0153]

Results with Viscosity measurements

Synthesis of cationic- CMC and polymer grafted CNC was performed. The result demonstrated the successful functionalization, which was proved by FTIR and IGA (Figures 12-13). Gat on I c-GNC and po!ymer-grafted-CNG demonstrated the best improvement of viscosity at both room temperature and 60°G. The GNG-Po I yv i rty i alcohol or CNG-PVA premixed solid (1:1) was also tested as the additive. 1wt% is added to the VES. This viscosity demonstrated the same improved viscosity as directly adding 0.5% of each in the VES. The results are summarized in Figure 14.

[0154]

6) Study of Additive pol mer

G-1. Exam le A

Compositions was produced by mixing components shown in table 6 based on following method.

[0155]

Typical preparing procedure for 12%HG ! spent solution (20% max, 8% remaining)

1. Master solution of 2wt% GNC was prepared by dissolving GNG in water and son i cat ion for over 1h.

2. 2.5g of 2wt%GNG so I ut i on was added to a 20 L via!

3. 50mg-300mg polymer was added to the vial

4. 2.3g of Hydrochloric acid was added to the vial

5. 42g of water was wadded to the vial

6. The solution was vertex mixed and sonicated until the polymer totally dissolved

7. 0.3g of GTAB was added to the solution and vertex mixed until the GTAB totally d i sso I ved.

8. Master solution of 5wt% aSa I was prepared by dissolving !SfaSa I in water.

9. Ig of 5wt% NaSa! solution was added to the GTAB solution and vertex mixed. Gelied-like solution will form in seconds

10. 1 8g of CaC 1 ₂ was added to the gelled-! ike solution and vertex mixed. Calculated from HCI spent 1g MG i to 1.5g GaG .

11. The solution was allowed to settle down for overnight to remove the bubbles.

[0156] Table 7

*1: CTAB: cetyl tri methyl ammonium bromide

*2: NaSal: sodium sai icy late

*3: su I fated— CNC: obtained from Ce i I uforce

*4 PSS : poly (4-styrenesu!fonic ac i d-co-ma I e i c acid) sodium salt obtained by Sigma Aldrich.

*5 PAM: poiyacryi amide obtained by Sigma -Aldrich.

*6 PVR: polyvinylpyrrolidone obtained by Sigma -Aldrich

*7 PAH: po I y (a i I y ! am I ne hydroch lor i de) obtai ned by Sigma Aldrich

*8 PDADMAC: pol y (d i a 11 y I dimethyl ammonium chloride) obtai ned by Sigma -Aldrich

[0157]

The self-diverting acid property of the composition by HCi spending test are shown in Figure 16. Figure 16 shows the viscosities based on difference of additives and a content of additives in 12% HGI spent solution (20% max, 8% remaining).

[0158]

PVR:

Adding 0.51 of PVP, the result demonstrated an increase in viscosity. Adding 1 % of PVR the result demonstrated a higher increase in viscosity but do not have much difference with adding 3170°C was tried, showing later.

[0159]

PAM: Adding 0.5% of PAM demonstrate no difference in viscosity at 60°C, while adding i% or 3% will make the solution too viscos to be measured at 58S ^~1 (! imitation of the viscometer).

[0160]

PAH, PDADMAC and PSS

Adding PAH and PDADMAC does not influence to the viscosity, while PSS will decrease the viscosity.

[0161]

Acid spending studies also showed consistent behavior for PYP. HC I spent test is to prepare different HC! and CaG i ₂ concentration to simulate the HC! spent condition 05% CNC VES solution demonstrated a seif-diverting property under the condition of total 20% HCI spent test and total 28% HCi test. Adding 0.5% PYP demonstrated the same seif-diver ing property but higher viscosity.

[0162]

The se!f-di verting acid property of the composition by HCI spending test are shown in Figure 17. Figure 17 shows the viscosities based PVP.

[0163]

05 % CNC VES solution demonstrates a self-diverting property under the condition of total 20% HCI spent test and total 28% HC! test.

Adding 0.5% PVP demonstrates the same seif- diverting property but higher viscosity. [0164]

Further studies were made on these polymers (Figures 18 to 20) based on viscosity at a higher Temperature:

[0165]

6-2. Examp I Q B

Compositions was produced by mixing components shown in tables 8 and 9. The compositions were obtained by the same operations as above.

[0166] Table 8

[0167]

[0168]

*1 : GTAB: cetyl tri methyl ammonium bromide

*2: NaSal: sodium salicylate

*3: su!fated-CNG: obtained from Geiluforce

*4: PV'P (Mw =10000) : polyvinylpyrrolidone (Mw =40000) obtained by Sigma -Aldrich *5: PV'P (Mw =40000) : polyvinylpyrrolidone (Mw =10000) obtained by Sigma -Aldrich *6: P4VP: poly (4-vinylpyidine) (Mw =60000) obtained by Sigma -Aldrich *7: PAG A (Mw 84000) : poly (ethyiene glycol) -co-poly (propylene glycol) -co-poly (ethylene glycol) having Mw 84000 obtained by Sigma -Aldrich

*8: PAG B (Mw 44000) : poly (ethyiene glycol) -co-poly (prop lene lycol) -co-poly (ethylene glycol) having Mw 44000 obtained by Sigma -Aldrich

*9: PAG C (Mw 11000): po!y (ethylene glycol) -co-poly (propylene glycol) -co-poly (eth iene glycol) having Mw 11000 obtained by Sigma -Aldrich

*10: PEI : polyethylene i m i ne having Mw 10000 obtained by Sigma -Aldrich

*11: PA : polyaniline having Mw 65000 obtained by Sigma -Aldrich

[0169]

The seif-diverting acid property of the composition by HC! spending test are shown in Figure 18. Figure 18 (a) shows the viscosities of the composition containing PVP having Mw 10000. Figure 18 (b) shows the viscosities of the composit on contain ng PVP having Mw 10000. Figure 18 (c) shows the viscosities of the composition containing P4VP.

[0170]

PVP (MwIGOOO) demonstrated no big difference in viscosity, while PVP (Mw4Q000) demonstrated the increase in viscosity. This indicated the molecular weight of PVP will influence the viscosity of the VES solution. Comparing Polymer -only solution and No-additive solution, increase can be detected.

P4VP demonstrating no effective difference in viscosity. 1 % demonstrating slightly increase, however, the difference is very slight,

[0171]

The seif-diverting acid property of the composition by HGI spending test are shown in Figure 19. F gure 19 (a) shows the viscosities of the composition containing PAG A

(Mw 84000). Figure 22 (b) shows the viscosities of the composition containing PAG B

(Mw 44000). Figure 19 (c) shows the viscosities of the composition containing PAG G

(Mw 11000).

[0172]

The triblock copolymer of po!y (ethylene glycol) -co-poly (propylene glycol) -co- poly (ethylene glycol) demonstrating a negative influence on the viscosity. By adding 0.5 % of the polymer, the viscosity will drop to less than 2G0cPs. With all 8.4k, 4.4k and 1.1k, the viscosity does not have much difference, th s indicates the result might be due to the amphiphilic block of the polymer, which will influence the mice! I e condition.

[0173]

The self-diverting acid property of the composition by HCi spending test are shown in Figure 20. Figure 20 (a) shows the viscosities of the composition containing PAG A (Mw 84000). Figure 20 (b) shows the viscosities of the composition containing PAG B (Mw 44000) ,

[0174]

The polyethylene imine (PEI, Mw 10000, Branched) demonstrating a positive influence on the viscosity at 0.5%. with more than 0.5%, the viscosity might decrease. However, the influence on the viscosity is not very effective.

Po!yanl!ine (PA, Mw 65000, e eraldine base) demonstrating a large increase in 1%, but no big difference at 0.5 wtl and 3%. This could be due to the acidic condition will transfer emeraldine base to quaternary salt and interact with the CNC [0175] in summary, eight different polymers in 3 different concentration were studied as co- additive. The results demonstrated PVP (40K) demonstrated an obvious increase in viscosity at 0.5%, 1%, which is consist with previous result. PVP (1 OK) and P4VP (65K) demonstrated no big difference with the viscosity. PE ! (1 OK, branched) demonstrated a slight increase in viscosity. However, the triblock copolymer of poly (eth lene gi yco I )-co-po I y (propylene I yco I )-co-poiy (ethylene glycol) degraded the viscosity of the V ^' ES solution,

[0176]

Other embodiments of the present invention are as follows.

1.A composition for an oil or gas well formation, comprising: a viscoelastic surfactant: and a modified nanomater iai.

2. The composition of cl aim 1, wherein the nanomaterial comprises a nanocellulose.

3, The composition of claim 1 or 2, wherein the nanomateria! comprises at least a sulfate group, a sulfite group, a carboxy group, an ethylene oxide chain, an amino group, an ester group, a silane group or a tertiary ammonium group on its surface.

4. The composition of claim 3, wherein the nanoparticle comprises sulfate group on Its surface

5. The composition of any one of claims I to 4, wherein the modified nanomater ia! has a grafted polymer on its surface.

6. The composition of any one of claims 1 to 5, wherein the viscoelastic surfactant comprises a surfactant and a counterion.

7. The composition of claim 6, wherein the counterion comprises an organic acid salt.

8. The composition of claim 6 or 7, wherein the counterion comprises at !east a carboxylic acid salt or a sulfonic acid salt.

9. The composition of any one of claims 6 to 8, wherein the surfactant comprises at least one selected from the group consisting of cationic surfactants, anionic surfactants, zwitter ionic surfactants and amphoteric surfactants.

10. The composition of any one of claims 6 to 9, wherein the surfactant comprises a compound of formula (1):

R -NiR-; _.: · X (1) wherein, R ^! Is an aliphatic group having 10 to 20 carbon atoms, R ² is an aliphatic group having 1 to 6 carbon atoms and X is a negative ion.

11. The composition of any one of claims 1 to 10, further comprising: an additive which is at least one selected from the group consisting of: particles other than the nanopart i c I e ; polymers; and molecules resulting in a nanostructured complex.

12. The composition of claim 11, wherein the polymer comprises at least polyacrylamide, poly (a I !yla inehydrooh!oride), poly (ethy !enegolycol) polyethylene! mine or po I yv I ny I a I coho I .

13. A method of producing a composition, comprising: adding a modified nanomater i a! ; and adding a viscoelastic surfactant.

14. A method of forming an oil or gas well, comprising: preparing a fluid comprising: a solvent: a viscoelastic surfactant; a modified nanomater la ! ; and an acid material, and introducing the fluid into the well.

[0177]

PATENTS:

1. Whalen R T. Viscoelastic surfactant fracturing fluids and a method for fracturing subterranean formations: U. S. Patent. 6, 035, 936 [P] 2000 -3-14.

2. Hughes T L. Jones T 6 J. Tustin G J. Viscoelastic surfactant based gelling composition for wellbore service fluids: U. S. Patent 6, 232, 274 [P] . 2001-5-15.

3. Dahayanake S, Yang J, iu J H Y, et al. Viscoelastic surfactant fluids and related methods of use: U. S. Patent 6, 258, 858 [P] 2001-7-10.

4. Nelson E B, Lungwitz B, Di smuke K, et al. Viscosity reduction of viscoelastic surfactant based fluids: U. S. Patent 6, 881, 709 [P], 2005-4-19. 5. Crews J B, Huang T. Use of nano-sized phyi !osi i icate minerals in viscoelastic surfactant fluids: U. S. Patent 9, 145, 510 [P] 2015-9-29.

6. Pandya N K, Wadekar S D, Pathre G S Branched viscoelastic surfactant for high-temperature acidizing: U. S. Patent 9, 359, 545 [P] 2016-6-7

7. Li L, Lin L, Abad C, et ai. Acidic internal breaker for viscoelastic surfactant fluids in brine: U. S. Patent 9, 284, 482[P] . 2016-3-15.

8. Huang T, Mutual solvent-soluble and/or alcohol b!ends-solubie particles for viscoelastic surfactant fluids: U. S. Patent 8, 653, 012 [P], 2014-2-18.

9. Svoboda C, Moore L T, Evans F E. Viscoelastic surfactant based wellbore fluids and methods of use: U S. Patent 9, 353, 306 [P] 2016-5-31.

10. Gurmen M N, Fredd C N. Viscoelastic surfactant rheology modification: U. S

Patent 9, 034, 806 [P] 2015-5-19.

[0178]

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