BRIEF DESCRIPTION OF THE INVENTION

The instant invention is directed to shear-thickening fluids, which may be used for plugging flow channels in or near wellbores. The fluid composites comprise a water-swellable granular material phase (clay for short) having a particle size of 10-60 mesh (Tyler) present in sufficient quantity so as to be capable of rapidly forming a paste having a shear strength of at least 1000 Pascals upon interaction with the aqueous phase employed which can preferably constitute any of the known hydratable clays such as bentonite; a nonaqueous hydrophobic phase (oil for short) which comprises a hydrocarbonaceous component and a surfactant- strengthening agent component, and an aqueous phase which comprises water and a water soluble polymer which, when permitted to interact with the clay, results in a semi-rigid high-strength paste.

The granular clay is suspended in the oil phase and the aqueous phase is also suspended as discrete droplets in the oil phase so that the oil phase is the continuous phase, the system being identified as a granular clay oil external system.

The granular clay and the aqueous phase are kept sepa¬ rate from each other by an intervening oil phase until such time as their interaction is desired. Such interaction is effected by rupturing the oil phase envelope by the application of a shear force sufficient to rip apart the oil phase envelope and thereby mix the clay and aqueous components resulting in the formation of a paste having the strength of at least 1000 Pascals.

Such a sufficient shear force can be encountered by the fluid composite upon passage through the orifices of a drill bit or nozzle or by the application of a sufficiently high pumping velocity during ordinary pipe flow.

In drilling or production operations, this fluid is pumped down the drill pipe only when necessary for the specific purpose of controlling a blowout or sealing off a zone

of lost circulation or blocking some other unwanted flow path. This material is not to be confused with typical well circulation-drilling fluids containing clay and water- polymer components.

The material of the instant invention is stable to the forces exerted upon it during pumping down the well pipe. However, passing through the nozzles of the drill bit at a high differential pressure applies a sufficient force to rupture the oil envelope and mix the clay and water-polymer components into a semi-rigid, high-strength paste capable of plugging the wellbore or sealing a circu¬ lation thief zone or other unwanted flow channel.

The stiff past formed by this invention will have a shear strength in the range from 2000 to 30,000 lb./100 ft-*. The ability of this paste to resist flow in some particular flow channel will depend on well-lmown physical principles. In channels with circular cross-section, the pressure re¬ quired to move a plug will be L P - UOTJ where P is the differential pressure across the plug, in psi

-if is the shear strength.of the paste in lb/100 ft . L is the length of the plug, in ft. D is the diameter of the channel, in inches.

The instant stiff paste can also stop pre-existing unwanted flows provided that the paste is injected into the unwanted flow at an appropriately high rate and provided that the unwanted flow is existing through a flow channel long enough for a paste plug to be formed.

The exact placement of a paste plug in or near a wellbore will depend on the problem to be treated. For example, if unwanted fluid was entering the wellbore at the bottom and flowing uphole, the past plug would be formed as close to the bottom of the hole as possible. On the other hand, if fluid was flowing downhole from and depart¬ ing the wellbore undesireably into a thief formation', the

composite would be pumped into the wellbore just above the thief zone so that the past would be formed at the flow channels in that zone and plug them. Other possible uses of the present invention can also be envisioned, such as blocking channels in cement behind casing, repairing leaks in casing or tubing, placing temporary plug in various places, etc. BACKGROUND OF THE INVENTION

During drilling or production of an oil or gas well, there are occasionally unwanted fluid flows in or near the wellbore, and there are also occasionally unwanted channels open downhole where unwanted flow could take place. On these occasions, it may be necessary to introduce fluids into the well to kill the well, or at the very least, terminate the unwanted flow or seal the unwanted channels. Examples of these problems are:

• unwanted influx of formation fluid into the well bore (blowout),

• loss of drilling fluid into the fractures or vugs in the formation (lost circulation),

• channels in cement behind casing,

• holes in casing,

• improperly sealing liner hangers.

A typical scenerio involves formation fluid influx into the wellbore which cannot be contained by closing the blow¬ out preventers or by circulating the high density drilling mud. For example, when an unusually high pressure forma¬ tion is encountered, it may be necessary to employ drilling mud at such a high weight that a formation above the high pressure zone is fractured. This fractured zone then be¬ comes a "lost zone" (thief zone) into which mud flows at such a high rate that circulation is lost. The lost circu¬ lation may be so severe that it ultimately becomes im¬ possible to maintain a column of mud above the high pressure zone sufficient to impart the necessary hydrostatic head to offset the high pressures in the high pressure zone.

As this occurs, the well becomes increasingly susceptible to blowout into the lost zone or to the surface.

There are a number of techniques which are em¬ ployed when one or another of these problems are encountered A common solution is to force a cement slurry into the un¬ wanted flow channel. This procedure is often successful, although sometimes multiple treatments are necessary, as long as there is no significant flow present in the un¬ wanted channel. Cement is useless against a pre-established flow because cement has almost no flow resistance until it is set. Thus it is always necessary to stop the flow be¬ fore using cement to plug the flow channel.

The hydrostatic head of various fluids is often employed to prevent or stop unwanted movement of fluids up the wellbore. In particular, most blowouts involve the un¬ controlled flow of formation fluids into the wellbore and then upwards in the wellbore. This type of blowout can be controlled by injecting fluid at the proper density and rate into the wellbore at or near the point of influx. In practice the required density and rate may be difficult to obtain.

One technique involves placing a high density barite (barium sulfate) slurry in the annulus just above the high pressure zone to provide the extra hydrostatic head needed to stop or prevent formation fluid influx. If the barite slurry remains deflocculated after placement at the bottom of the well and relatively undisturbed, the barite settles uniformly to form a hard plug. One problem with using barite to form a plug, however, is that barite's ability to form a plug varies greatly depending upon the formation temperature, the operating conditions, and the quality of barite used. For example, it is sometimes dif¬ ficult to plug a well in the presence of a significant flow movement in the wellbore. If the fluid influx is not killed immediately by the hydrostatic head of the barite slurry,

the settling barite will usually not stop the unwanted flow.

The unwanted loss of fluids from the wellbore is often treated by injecting a slurry of fiberous, lu py, or flakey material tato the wellbore at the region of the loss. These "lost circulation materials ^' ' are intended to plug or bridge over, i.e., form a mat over, the channels through which the fluid is entering the rock.

A pasty material known as "gunk" is sometimes used as a lost circulation material and occasionally to form temporary plugs in the wellbore. Gunk is a slurry of dry powdered bentonite in diesel oil. A typical gunk recipe is 350 lb of bentonite in of bbl of diesel oil. This slurry is quite fluid when mixed and remains fluid as long as it is kept dry. Mixing gunk slurry with an approximately equal volume of water causes the clay to hydrate giving a stiff paste. If formed at the right time and at the right place, this gunk paste is an effective lost circulation and plugging material. However, since the gunk slurry will hydrate and thicken immediately upon contacting water, it must be kept dry until it has been pumped downhole to the place where a plug is desired. The mixing of the gunk slurry with water takes place downhole as the two fluids are commingled. In some cases, there is some control over the ratio of gunk slurry to water, .in other cases, this con¬ trol cannot be achieved. Since gunk only achieves adequate flow resistance to form a plug within a certain range of gunk/water ratios, the performance of gunk as a plugging agent has beenerratic. In particular, gunk is seldom useful for blowout control because the requirement of having the proper gunk/water ratio is difficult to satisfy.

DISCLOSURE

The composites of the instant invention solve a multitude of well-control problems, in particular the problems of thief zone control and blowout control and pre¬ vention. A low viscosity material, stable to pumping, is pumped down a well pipe and forced through the orifices of

the drill bit ozzl or other means of effectuating a pres¬ sure drop at a point where it is desired to plug the well¬ bore or thief zone. Upon being subjected to shear forces of sufficient intensity to rupture the oil membrane separati the clay and the water-polymer phases, the material sets up into an extremely high viscosity, semi-rigid, high- strength paste which itself can have a shear strength in ex¬ cess of 2,000 pounds per 100 square feet.

The shear thickening fluids of the instant inven¬ tion are a multicomponent composite, comprising a water swellable granular material (for the purposes of this specification, the term ".day" shall be employed) which can broadly be described as any clay which, in the presence of water or of certain water-polymer materials employed here swells into a high viscosity solid mass; a hydrophobic phase comprising a hydrocarbon component and a surfactant componen and an aqueous phase component made up of water and a water soluble polymer. Enough water swellable granular material is employed to result in the formation of a paste possessing a strength of at least 2000 lbs/100 ft. ² .

Preferred clays useful in the instant invention would include any members of the montmorrillonite (smectite) "group or the attapulgite group. Clays which swell strongly and absorb large quantities of water will perform better in this invention than those which do not. Clays which have been chemically treated, as with soda ash or sodium poly- acrylate, to increase their ability to absorb water and form a stiff past will show improved performance in the instant invention.

In general, the hydrocarbon phase comprises a liquid oil, preferably any low aromatic content oil, typical mineral oil, paraffinic oils of from 6 to 1000 carbons (pro¬ vided they are liquid at the temperature at which they are employed--that is, during composite preparation and utili¬ zation) motor oils such as diesel fuel or kerosene, substitu paraffinic oils wherein the substituents are selected from •

the group consisting of halogens, amines, sulfates, nitrates, carboxylates, hydroxyls, etc. Preferred oils are the Cg- liquid paraffins.

These hydrophobic nonaqueous materials are prefer¬ ably mixed with oil soluble surfactants so as to enhance their surface activity. A wide variety of surfactants can be used in the instant invention. These surfactants in¬ clude anionic, cationic, nonionic and ampholytic surfactants. These surfactants are described in the book Surface Active Agents and Detergents by Schwartz, Perry and Beich, I er- ^' science Publishers, Inc., New York, New York.

The only requirement which must be met by the sur- ^' factant is that it be able to stabilize the aqueous phase droplets and clay particles in the oil phase sufficie tly to protect the mixture from premature gelling under low shear mixing or pumping conditions.

Anionic surfactants include carboxylic acids, i.e., fatty acids, resin acids, tall oil acids and acids from paraffin oxidation products. Also included among the anionic surfactants are alkyl sulfonates, alkylaryl sulfonates, mohogany and petroleum sulfonates, phosphates and lignin derivatives.

Cationic surfactants include quaternary ammonium compounds, e.g., salts of long chain primary, secondary and tertiary amines as well as quaternary amine salts with 7 to

40 carbon atoms. Styrene copolymers containing pendant quaternary ammonium groups including derivatives of tri- methyla ine or dimethylethanolamine are also useful cationic surfactants.

Unprotonated amines fall into the class of non- ionic surfactants. A preferred group of amines have the general formula:

R N R ₂ wherein R, R-^, and ₂ may be independently selected from the group consisting of hydrogen, C^ to C20 alkyl, Cg to C20 aryl and C to C2 alkylaryl radicals.

Various polyamine derivatives are useful within the scope of the instant invention. The preferred poly¬ amine derivatives are those having the general formula:

wherein R3 ^{» R} 4 ^» e, Rg, R7, Rg, Ro and y are chosen from the group consisting of hydrogen, C to C20 alkyl, Cg to C20 a*cyl _> 7 to C2 alkaryl radicals and substituted deriva¬ tives thereof, and x is an integer of from 1 to 100. The substituted derivatives are preferably selected from the group consisting of oxygen, nitrogen, sulfur, phosphorus and halogen containing derivative. The most preferred material is:

H2N(CH ₂ CH ₂ NH)3-CH ₂ H ₂ NH ₂ In general, the preferred surfactants are the products ob¬ tained by the reaction of the polyamine described above with various polyalkenyl succinic anhydrides, such as polyisobutylene succinic anhydride, polypropenyl succinic anhydride and polybutenyl succinic anhydride.

A preferred polyamine derivative formed by re¬ acting together an alkyl succinic radical and the polyamine has the general formula:

/ ^*

(A) wherein n varies from 10 to 60, preferably 10 to 30, most preferably 15-17; x varies from 1 to 100, preferably 3 to 10; R5, Rg, Ry, Rg, Rg are hydrogen C^ to C ₂ o alkyl, Cg to ^c 20 ^ar y**- _» Cy to C20 alkaryl radical and substituted deriva-. tive thereof, preferably hydrogen; and y is selected from the group consisting of hydrogen and oxygen containing hydrocarbyl radicals having up to 10 carbons, e.g., acetyl. Typically, the surfactants have a molecular weight on the order of about 1000. As previously stated, a most pre¬ ferred characteristic of the surfactants is oil solubility.

Nonionic systems also include the polyethenoxy surfactants, i.e., polyethoxy ethers of alkyl phenols, polyethoxy ethers of alcohols, etc. The polyethenoxy ethers are especially useful in the invention as their solubility may be varied according to the weight of ethylene oxide added to the alkyl phenol starting material. Another nonionic surfactant which is particularly useful is sorbi- tan monooleate which is known in the trade by the name of Span-80 and manufactured by the Atlas Chemical Company. Ampholytic surfactants contain both an acidic and a basic function in their structure and therefore will be cat¬ ionic or anionic according to the pH of the solution in which they are dissolved.

The final component of the shear sensitive well control fluids of the instant invention is an aqueous phase comprising water and a water soluble and/or a water swellable polymer. Typical .nlymers include p lyacrylamides including homo* polymers, acr lamide lightly cross-linked by between about

500 and 5000 pa ts per million by weight of the monomers present with such agents as tnethylene-bisacrylamide or di- vinyl benzene, and a major portion of acrylamide copoly- merized with a minor portion of other ethylinically un- saturated monomers copolymerizable therewith; or polystyrene sulfonate and polyvinlytoluene sulfonate and water soluble salts thereof; or polyethyleneoxide and polyvinyl alcohol. Th preferred water-swellable polymer is polyacrylamide. These water soluble-water swellable polymers are hydrolyzed to a degree ranging from 0-50%, preferably 0-157 _o , most preferably 1-77- or less.

The polyacrylamides and related polymers which can be used in the practice of the present invention include polymers selected from the group consisting of polyacryl¬ amides and polymethacrylamides wherein up to about 75 per¬ cent of the carboxamide groups can be hydrolyzed to carboxyl groups; polyacrylic acid and polymethacrylic acid; poly- acrylates; polymers of N-substituted acrylamides wherein the nitrogen atoms in the carboxamide groups can have from 1 to 2 alkyl substituents which contain from 1 to 4 carbon atoms, copolymers of acrylamide with another ethlenically unsaturated monomer copolymerizable therewith, sufficient acrylamide being present in the monomer mixture to impart said water-dispersible properties to the resulting copolymer when it is mixed with water, and wherein up to about 50 per¬ cent of the carboxamide groups can be hydrolyzed to car¬ boxyl groups; and admixtures of such polymers. Presently preferred polyacrylamide type polymers include the various substantially linear homopolymers and copolymers of acryl¬ amide and me hacrylamide. By substantially linear it is meant that the polymers are substantially free of cross- linking between the polymer chains.

All the polymers useful in the practice of the in¬ vention are characterized by having high molecular weight. The molecular weight is not critical so long as the polymer

- Il ¬

ls water swellable and/or water soluble; however, it is preferred that the weight range between about 2-8 million, preferably 1 million. It is preferred that the polymer have a molecular weight of at least 100,000. The upper limit of molecular weight is unimportant so long as the polymer is at least water soluble or water swellable or higher, and meeting said conditions, can be used.

The granular clay will be suspended in the oil phase while discrete droplets of the water-polymer phase will also be suspended in the oil phase (the discrete granular clay particles and encapsulated water-polymer droplets existing as separate entities, separated by the suspending oil phase) which oil phase in this embodi¬ ment is thus the continuous phase.

The granular clay and the water polymer are kept separate by the oil continuous phase until such time as their mixing is deliberately desired, and this is accom¬ plished by subjecting the composite to a shear force as, for example, by passage through the nozzle of a drill bit, of sufficient intensity to rupture the oil-phase envelope.

It has been discovered that the use of granular clay will result in an oil continuous system. Clay is termed granular if it has a mea particle size of approxi¬ mately 10-60mash(Tyler), more preferably 10-40 mesh, most preferably20-40 mesh. The clay should preferably have re¬ moved from it fines of 2100 mesh. This results in a compo¬ site exhibiting greater low shear stability. The presence of excessive fine clay particles will cause premature thickening of the final composite.

Because of the resistance to hydration exhibited by granular clay, one can employ a greater loading of granu¬ lar clay in the composite as compared to powdered clay. For those systems utilizing granular clay (particularly granular bentonite), the components are present in the composite in the following ranges:

Part by Weight

Composites possessing Granular Clay 100 5 min. low shear stability Surfactant 5.5 - 29 2000 lb/100 ft/ paste Hydrocarbon oil 25 - 130 strength after high shear Polymer .1 - 6.7 Water 25 - 400

Part by Weight

Compositions possessing Granular Clay 100 5 min. low shear stability Surfactant 5.5 - 25 and 5000 lb/100 ft. paste Hydrocarbon oil 25 - 110 strength after high shear Polymer .1 - 6.7 Water 50 - 350

Part by Weight

Preferred composition Granular Clay 100 possessing 5 min. low Surfactant 5.5 - 20 shear stability and Hydrocarbon oil 25 - 75 10,000 lb/100 ft paste Polymer .1 - 6.7 strength after high shear Water 100 - 300

In the preferred embodiment, the clay is a granular bentonite clay, the polymer is polyacrylamide, the hydrocarbon oil is S100N, a C _Λ paraffinic hydrocarbon, and the surfactant is chosen from the group of materials having formula corresponding to compound A, previously defined. Most preferably, polyamines of the formula A-. or A ₀ (below) are employed.

0

(A _χ )

Poly-amine k- is available as Paranox 100 from Exxon Chemi¬ cal Company..

(A ₂ )

Polyamine A ₂ is available as Paranox 106 from Exxon Chemi¬ cal Company.

In addition, the composition may have included in it either in the oil phase or in the water-polymer phase, preferably the oil phase, a fiberous material such as fiber¬ glass, asbestos wood fiber, cellulose, shreaded paper, cotton seed hulls, sugar can bagasse, pencil shavings, peanut shells, etc., which is substantially impervious to the action of the water-polymer phase and to the oil phase. These added materials serve the purpose of imparting in¬ creased mechanical strength and rigidity to the paste which forms upon rupture of the oil envelope when the clay and water-polymer phases interact.

The shear thickening fluid may also have added to it ma¬ terials such as barite, hemalite, galena, ilmenite, etc., which are commonly used for increasing the density of drill¬ ing fluids. These weighting agents are not water-swellable and will not participate in the shea -thic ening effect of the instant invention but would be added if higher density formulations were particularly desired. If used, the weighting agents will absorb some of the surfactant, es¬ pecially if the agent is finely powdered. Consequently, an additional volume of surfactant would have to be added to make up for this absorbed portion, so as to maintain the stability of the composition.

For the purposes of the specification, a paste is defined as being capable of sealing a lost circulation

zone or a blowout if it develops a shear strength of at least 2000 pounds per 100 square feet.

The mixtures of the instant invention have been found to function quite well at temperatures of 300 ^β F or higher as would be actually encountered in well con¬ trol situations.

With the proviso that the clay and the aqueous phase are never mixed together before their introduction into the oil phase, the components of the instant in¬ vention may be mixed in any order. In general, the oil-surfactant and clay are mixed together employing any convenient mixing apparatus. Alternatively, the oil- surfactant phase may have the aqueous polymer phase suspended in it first. This emulsion can be kept "on hand" in its premixed form. To this then is added the clay, when needed, to control a blowout or seal a thief zone. Clearly, then it can be seen that the clay can be added to a pre¬ mixed oil and surfactant or the clay can be added to the oil and then have the surfactant added, or vise-versa, or the oil, or surfactant or oil-surfactant can be added to the clay, this clay, oil-surfactant -emulsion then being added to or having added to it the premixed water polymer system. The oil surfactant can have the premixed'water-polymer added to it and then the clay added.

Preferably, the oil and surfactant are mixed to¬ gether first and then the clay is added. These results in the formation of a granular clay in oil/surfactant emulsion. Next this encapsulated clay has added to it the water/ polymer solution. The resulting material will be oil- surfactant phase continuous.

It has been determined that the use of the water soluble polymer, such as polyacrylamide serves two beneficial functions. First, it improves the stability of the initial shear-thickening mixture by re¬ ducing the tendency of the mixture to thicken prematurely. Second, it gives a higher strength paste after high shear mixing. It has been determined that the hydrolysis

of the polyacrylamide has a direct effect on the behavior of the material mixtures, ϋnhydrolyzed polyacrylamide re¬ sults in a material which has a greater paste strength after high shear but has shorter low shear thickening time. Hydrolyzed polymer, on the other hand, gives the material a greater degree of stability but reduces the ul imate strength of the paste. Degree of hydrolysis may range, therefore, from 0% to 50%, preferably 0 to 15%, more prefer¬ ably 1 to 7% or less. It has been determined that, within the above constraints, low shear thickening time (i.e., stability) is roughly independent of polymer concentration within the concentration ranges previously recited, while paste strength tends to increase with increased polymer concentrations.

In the practice of this invention, it is necessary to choose a specific formulation, from the ranges given above, that will perform well in the particular situation at hand. Examples of uncontrolled variables which will in¬ fluence the selection of a formulation are:

1. The depth in a wellbore at which the treat¬ ment is to be applied.

2. The temperature downhole where the treatment will be applied.

3. The type of mixing and pumping equipment which will be used to preparedthe material and inject it into the wellbore.

4. The type of unwanted flow or flow channel to be blocked.

Example 1 below contains a number of different specific formulations for shear-thickening fluid and shows the re¬ lationship between composition and performance. Example 1

The following example illustrates the practice of the instant invention on a laboratory scale. The many dif¬ ferent formulations tested in this example will clarify the relationship between composition and performance.

The components used in the formulations of this example are specifically identified as follows:

Oil - S-100N paraffinic oil available from Exxon Co., USA Surfactant - Surfactant A ₂ - available as

Paranox 106 surfactant available from Exxon Chemical Co., USA

Clay - KWK granular bentorite, available from American Colloid Co. (Mesh Size 20-70) Polymer - P-250 polyacrylamide available from American Cyanamide Co. (Degree of Hydrolyses 1% ) All samples of shear-thickening fluid in this ex¬ ample were prepared according to the following general procedure.

(1) A known weight of surfactant was dissolved in a known weight of oil.

(2) A known weight of granular bentonite was mixed with the oil/surfactant solution re¬ sulting in a slurry of clay in oil/surfactant.

(3) Polyacrylamide was dissolved in water to give a solution of the desired strength.

(4) The aqueous solution of polyacrylamide was added to the clay slurry with mixing result¬ ing in the suspension of discrete droplets of polymer solution in the oil/surfactant to give an oil continuous phase system.

In order to more accurately identify comnosites which will be useful under typical field conditions, a set of laboratory criteria was established to simulate the per¬ formance needed in the field. To this end, it was determined that for a composite to be useful, it must be pumpable, i.e., resistant to low shear forces for at least 5 minutes. It is also necessary that once mixed, sheared, and thickened, the composite must have a shear strength of at least 2000 pounds per 100 ft. The limits used to describe the operable

CV

ranges of the various components used in the composite were chosen so as to result in a composite satisfying these criteria.

Shear strength of the fluid was measured by noting the distance a hollow, open-ended cylinder (3.5 inches long, 1.4 inches in diameter, and 0.01 inches wall thickness) would sink into the fluid under the force of various weight. Shear strength was then calculated from the following equation:

_c . „ Total Weight in

Shear Strength _m Grams x 3.6 in lb/100 Ft. Penetration

Distance in Inches

Standard formulations of granular bentonite L.M. well control fluid were prepared and mixed in a jacketed, low-shear mixing cell with an inside diameter of 2.9 inches and an inside height of 4.3 inches and a single egg beater impeller with an overall blade width of 1.8 inches and blade height of 2.7 inches. The jacket temperature of the cell was maintained at 95°C f203 ^o F) with circulating hot water and the impeller was maintained at 500 RPM with a constant speed motor. The cell was tightly covered during mixing in order to prevent loss of water by evaporation from the fluid. The formulations were mixed for varying periods of time and then forced through a 1/4" nozzle with a differential pres¬ sure of 1500 psi. Shear strengths of the fluid before and after passage through the high-shear nozzle were measured and plotted as a function of low-shear mixing time. The effect of oil phase surfactant concentration on the results was determined by carrying out duplicate sets of experiments at high and low oil phase surfactant concentrations.

Plots of shear s rength before and after high shear as a function of low-shear mixing time at high and low levels of oil phase surfactant concentration are given in Figures 1 and 2. In general, shear strength prior to high shear in¬ creases slowly with low-shear mixing until a point at which shear strength rises quite rapidly with additional low-shear mixing. This point is called the low-shear thickening time.

Following high shear, shear strengths of granular bentonite L_M_ well control fluid jump to intermediate values after short periods of low shear mixing well before the low- shear thickening point. Oil phase surfactant concentration has a pronounced effect on this data. The lower level of surfactant, 21.7% Paranox 106 in S100N, gives higher shear strengths after shorter periods of low-shear mixing.

These experiments were chosen to resemble field conditions for use of L.M. well control fluid as closely as possible. The period of time during which the fluid can be mixed under low shear before the thickening point reflects the "low shear stability" of the fluid. The ability of the fluid to form a high-strength paste following one pass through the high shear nozzle after various time periods of low shear mixing reflects the "high shear sensitivity" of the fluid. The optimum well control fluid formulation will possess both maximum low shear stability and maximum high shear sensitivity simultaneously. On this basis the lower oil phase sur¬ factant concentration used in these experiments is the preferred concentration because it yields substantially greater high shear sensitivity with little reduction low shear stability.

The low-shear thickening time of granular bentonite L.M. well con-trol fluid was relatively insensitive to H ₂ 0/ Clay weight ratio while the paste strength after high shear exhibited a pronounced optimum in the range of 1-3 H2θ-Clay (Figure 3). See also Table I. In contrast to this, low- shear thickening time increased linearly with (Oil + Surfactant Clay weight ratio, and paste strength after high shear de¬ creased at nearly the same rate (Figures 4, 5, and 6). See also Tables II, III and IV. Aqueous phase weight percent of P-250 had relatively little effect on the low-shear thickening time of granular bentonite well control fluid as long as it was higher than a minimum value of about 0.5% (Figure 7). See also Table V. Paste strength of granular bentonite L.M. well control fluid after ϋgh shear increased linearly with aqueous phase weight percent P-250. Table VI presents a

compilation of the data presented in the foregoing figures and tables.

Example 2

The following example illustrates the practice of the instant invention to create a plug in an actual wellbore. In this example the wellbore is plugged in the absence of any pre-existing fluid flow.

The wellbore used in this example had been drilled with a 7 7/8" diameter rock bit to a_total depth of 2600 ft. The formations drilled were interbedded sands and shales; there were no significant drilling problems. The well had 8 5/8" surface casing set at 1718 ft. The wellbore was filled with 10.5 ppg water-base drilling mud.

The shear-thickening fluid used in this example contained:

945 lb S-100N Oil (Exxon USA) 105 lb Paranox 106 (Surfactant. A ₂ Exxon Chemical Co) 1800 lb KW Granular Bentonite (American Colloid Co) 30 lb P-250 Polyacrylamide (American Cyanomide) 8.6 lb Fresh Water

These ingredients were mixed in a Halliburton ribbon blender which had two 50 bbl compartments. The mix¬ ing steps were:

(1) Dissolve the polyacrylamide in the water in one compartment of the blender.

(2) Mix the oil and surfactant in the other compartment.

(3) Add the clay to the oil/surfactant and con¬ tinue mixing.

(4) Transfer the polymer solution into the com¬ partment with the clay slurry and mix gently to form the shear-thickening emulsion.

The drill string used in this example was 2 7/8" EUE tubing with a 7 7/8" rock bit on bottom. The bit was placed at 2568 ft. depth. The bit contained three 9/32" nozzles.

The shear- hickening material was pumped into the well with a Halliburton cementing truck. Steps in the pumping operation were:

(1) Rig up and circulate well with Halliburton

(2) Pump 2 bbl water spacer

(3) Pump 11 bbl shear-thickening fluid at one bbl/min.

(4) Pump 2 bbl water spacer

(5) Pump 13 bbl mud at 6 bbl/min.

(6) Stop pumps

At this point the last of the shear-thickening material had just exited the bottom of the drill string through the bit. Passage through the bit nozzles had thickened the material into a stiff paste which had been forced up around the bottom of the drill string. Based on the volume pumped, 200 ft. of annulus was filled with paste. The pump pressure during displacement of the shear-thickening material (step 6, above) started at 2000 psi and reached 2900 psi even though the rate was reduced to 5 bbl/min. at the end of the displacement.

The fact that a plug had been placed in the annulus was shown by measuring the drag on the pipe and by trying to move the plug by pumping under it at a low rate. The pipe drag was 30,000 lbs. The plug could not be moved by pumping down the drill string, at 900 psi surface pressure the formation broke down. Example 3

The following example illustrates the practice of the instant invention to stop a pre-existing gas flow. This test was not performed in an actual well but rather in a simulated wellbore.

The simulated wellbore in this example consisted of 172 ft. of 4" ID pipe. This pipe was open at one end and had multiple connectionsat the other end for intro¬ duction of gas and shear-thickening paste and for measuring the simulated bottom-hole pressure. The gas used in this example was air. This air was supplied from a 105 psig

c :?ι

reservoir and passed through a low meter and a throttling valve before entering the 4" pipe.

The shear- hickening material used in this example was prepared with the same formulation used in Example 2 above, The mixing steps were similar except that a truck-mounted concrete mixer was used instead of a Halliburton ribbon blender to prepare the final emulsion. About 1000 gal. of shear-thickening emulsion were prepared. This emulsion was pumped into the 4" pipe by a high-pressure constant-rate pump. Before entering the 4" pipe, the emulsion was sheared through a valve which was adjusted to have a 1200-1500 psi pressure drop at the flow rate being used.

In this example, the air throttling valve was first opened and adjusted to give an air flow rate of 197 Mscf/d. After this flow was established in the 4" pipe, the shear- hickening-emulsion pump was started and the shear valve adjusted to give 1200-1500 psi pressure drop at the valve. The emulsion pump ratewis 100 gpm. In less than a minute, the shear-thickened paste had plugged the 4" pipe and stopped the air flow. The pressure in the in¬ jection end of the 4" pipe reached several hundred psi. The air flow did not resume even though the injection of paste was stopped. Subsequent testing showed that the paste plug in the 4" pipe would withstand pressure gradients of 10 psi/ft. without moving.

-3Z-

-

TABLE II

LOW SHEAR THICKENING TIMES AND PASTE STRENGTHS AFTER HIGH SHEAR FOR GRANULAR BENTONITE

L.M. . SHEAR THICKENING FLUID AS A FUNCTION OF (OIL + SURF)/CLAY WEIGHT RATIO*

Surfactant Oil . Clay Polymer Water

Low Shear Paste Strength

Paranox Granular Cyanamer "011+Surf ^, 7 Thickening after

Sample 106 SlOON Bentonite P-250 Distilled Clay Time High Shear # Grams Grams Grams Grams Grams WelRht Ratio Minutes lb/100 ft ²

446 3.75 33.8 75 1.25 124 0.50 3.1 17,700

447 4.35 39.4 75 1.25 124 • 0.58 5.2 17, 700

448 5.03 45.2 75 1.25 124 0.67 9.3 15,700

449 5.48 49.3 75 1.25 124 0.73 9.3 14,700

450 6.00 54.0 75 1.25 124 0.80 12.2 11,900

451 6.98 62.8 75 1.25 124 0.93 16.7 9,100

452 7.58 68.2 75 1.25 124 1.01 18.7 5,400

453 9.00 81.0 75 ,1.25 124 1.20 24.0 4,500

454 11.98 103.3 75 1.25 124 1.53 33.3 1,100

■*(Oil + Surr) » J.U7. rαi ^β uuA ιuu m SIUUN; rixeα H«I ratios; Data plotted In Figure *».

TABLE III

LOW SHEAR THICKENING TIMES AND PASTE STRENGTHS AFTER HIGH SHEAR OF GRANULAR BENTONITE L.M. SHEAR THICKENING FLUID AS A FUNCTION OF (OIL + SURF)/CLAY WEIGHT RATIO*

Surfactant Oil Clay Polymer Water

Low Shear Paste Strength

Paranox Granular Cyanamer "Oil+Surf"/ Thickening after

Sample 106 SlOON Bentonite P-250 Distilled Clay Time High Shear

Grams Grams Grams Grams Grams ! _• -.____.-. n_.-._-. Minutes -lIb-./-1110-Λ0 «ft<-.

272 4.9 12.6 75 1.25 124 0.30 1.1 13,300

406 6.5 23.5 75 1.25 124 0.40 6.5 20, 100

186 8.1 29.4 75 1.25 124 0.50 15.8 14,500 219 8.1 29.4 75 1.25 124 0.50 15.0 19,000 285 8.1 29.4 75 1.25 124 0.50 15.2 16,500

254 9.5 34.3 75 1.25 124 0.58 16.7

407 9.8 35.2 75 1.25 124 0.60 22.0 19,500

270 11.4 41.1 75 1.25 124 0.70 ^' 26.5 7,200

271 14.6 52.9 75 1.25 124 0.90 40.0 5,200

90 19.5 70.5 75 1.25 124 1.20 >97.5 2,200

TABLE IV

LOW SHEAR THICKENING TIMES AND PASTE STRENGTHS AFTER HIGH SHEAR OF GRANULAR BENTONITE

L.M. SHEAR THICKENING FLUID AS A FUNCTION OF (OIL + SURF)/CLAY WEIGHT RATIO*

Surfactant Oil Clay Polymer Water

Low Shear Paste Strengtl

Granular Cyanamen - ^■ OiHSurf"/ Thickening after

Sample ECA-5025 SlOON Bentonite P-250 Fresh Clay Time High Shear

# Grams Grams Grams Grams Grams Weight Ratio Minutes lb/100 ft ²

346 9.4 21.9 75 1.25 124 0.42 10 12, 100

344 13.1 30.6 75 1.25 124 0.58 20.9 12,900

345 15.8 36.7 75 1.25 124 0.70 33 9,600

408 20.3 47.2 75 1.25 124 0.90 long 2,600 (Distilled)

*(0il + Surf) - 30.07.. Paranox 106 in SlOON; fixed H ₂ 0 Clay (1.65) and polymer/clay (0.0167) weight ratios; data plotted in Figure 6.

^• ^Untreated well water, also used in the large scale test of Example 2.

TABLE V LOW SHEAR THICKENING TIMES AND PASTE STRENGTHS AFTER HIGH SHEAR OF GRANULAR BENTONITE

L.M. SHEAR THICKENING FLUID AS A FUNCTION OF AQUEOUS PHASE WEIGHT 7. P- 250* Surfactant Oil Clay Polymer Water

Paste

Aqueous Low Shear Strength

Paranox Granular Cyanamer Phase Thickening after

Sample 106 SlOON Bentonite P-250 Distilled Weight Time High Shear „ # Grams Grams Grams Grams Grams 7. P-250 Minutes LB/100 Ft. ²

276 8.1 29.4 75 0 125 0 1 15,000

395 8.1 29.4 75 0.125 125 0.10 10.2 16, 700

394 8.1 29.4 75 0.312 125 0.25 11.3 14,700

393 8.1 29.4 75 0.625 124 0.50 13 15,500 277 8.1 29.4 75 0.625 124 0.50 12.9 18,300

186 8.1 29.4 75 1.25 124 1.0 15.8 14,500 219 8.1 29.4 75 1.25 124 1.0 15.0 19,000 285 8.1 29.4 75 1.25 124 1.0 15.2 16,500

142 8.1 29.4 75 1.25 123 2.0 14.3 21,300 142 8.1 29.4 75 2.50 123 2.0 16.7 18,900

275 8.1 29.4 75 3.75 121 3.0 16.7 26,800 282 8.1 29.4 75 3.75 121 3.0 17.3

TABLE VI COMPOSITION RANGES OF GRANULAR BENTONITE L.M. SHEAR THICKENING FLUID

Source of Data Figure 3 Figure 4 Figure 5 Figure 6 Figure 7

Composition Expressed in Parts by Weight

Granular Clay 100 100 100 100 100

Paranox 106 10.9 5.5-1 8.0-26 10.5-28 10.β

SlOON 38.5 45-130 29-94 2-67 39.2

P-250 1.66 1.6 1.67 1.67 0.1-6.7

H ₂ 0 25-400 165 165 165 166.7-160

Overall Composition Ranges Based on Combined Date of Figures 3 through 7

Parts by Weight

Granular Clay 100

Paranox 106 5.5-29

SlOON 25-130

'

P-250 0.1-6.7

H ₂ 0 25-400

TA3LE VII

COMPARISON OF GRANULAR BENTONITE TO POWDERED

BENTONITE IN SHEAR SENSITIVE

L.M. WELL CONTROL FLUID ^I

Total Powdered Granular 3entonite Bentonite Bentonite

200 Mesh 20-40 Mesh grams gel gel gel gel ₃ time^/ strength- ³ time*/ strength _ (min) (lb/100 ft* (min) (lb/100 ft ² )

30 24 / 11,400 780 / 2,100

45 10 / 16,500 22 / 10,800

60 0 / 15 / 26,000

^• • ^■ Basic Formula: 30.5 g oil (32.5% Surfactant A ₂ in SlOON)

30-60 g Bentonite Clay 125 g 17o P-250 in Water

Gel time measured in jacketed low shear mixing cell, 500 RPM, 91°C.

-"- ^■ Gel strength measured after hand kneading at room temperature.

This set of data.show that it is possible to stabilize a greater weight of granular bentonite than powdere bentonite with a fixed amount of water, oil, surfactant, and polymer in L.M. well control fluid. At the highest clay load ing, the granular bentonite fluid is able to withstand 15 minutes of low shear mixing at 500 P_FM and 91°C, whereas the powdered bentonite fluid gels immediately. As a consequence of the higher clay loadings attainable with the granular bentonite fluid, it exhibits higher gel strengths than the powdered bentonite fluid.

Apart from higher gel strength, the initial phase continuity of granular bentonite well control fluid is un¬ expectedly different from that of powdered bentonite fluid. Following mixture of all the components in the standard manner, granular bentonite fluid is oil external whereas powdered bentonite fluid is water external.

- ^" .- .-

The difference in phase continuity between the two fluids affects their response to changes in temperature and shear. Over the temperature range of 47° to 95°C, the gel time of powdered bentonite fluid decreases from 120 to 25 minutes, very nearly as the inverse square of the change in temperature. In contrast to this, the gel time of granular bentonite fluid over the same temperature range decreases as the inverse first power of the change in temperature. See Figure 8. The fluids compared in that figure have the following compositions:

Powdered bentonite 30.5 g Oil (32.5% Surf. A ₂ in SlOON) formulation 30.5 g Powdered bentonite

125. g 1% P-250 in water

Granular bentonite 37.5 g Oil (21.7% Surf. A, in SlOON) formulation 75. g KWK Volclay (20-40 mesh bentonite)

125. g 1% P-250 in water

Similarly, the gel time of powdered bentonite fluid decreases as the inverse square of mixer RPM, whereas the gel time of granular bentonite fluid varies as the inverse first power of mixer RPM. See Figure 9. The fluids compared in that figure have the following compositions:

Powdered bentonite 30.5 g Oil (32.5% Surf. A _£ in SlOON) formulation 30.5 g Powdered bentonite

125. g 1% P-250 in water

Granular bentonite 43.7 g Oil (21.7% Surf. A _? in SlOON) formulation 75. g KWK Volclay (20-40 mesh bentonite)

125. g 1% P-250 in water

In addition to its effect on response to temperature and shear, the initial phase continuity of well control fluid affects the relationship between composition and gel time. The most striking effect is seen in the relationship between water/clay ratio and gel time, presented in Figure 10. The fluids compared in that figure have the following compositions:

Powdered bentonite 22.3 g Oil (32% Surf. A ₂ in SlOON) formulation 30.5 g Powdered bentonite 1.0 g P-250 73.2 - 229. g Water

Granular bentonite 37.5 g Oil (22% Surf. A _? in SlOON) formulation 75. g KWK Volclay (20-50 mesh bentonite) 1.25 g P-250 30. - 337. g Water

The gelled granular bentonite fluid also retains a significantly higher fraction of its gel strength when mixed with additional water than does the powdered bentonite fluid.

TABLE VIII

GEL STRENGTH RETENTION IN THE PRESENCE OF

ADDITIONAL WATER ¹ POWDERED AND GRANULAR BENTONITE WELL CONTROL FLUIDS

Additional ^• Gel Strength Gel Strength Water Wt.% Lb/100 Sq.Ft. Retained

Powdered 0 8,900 100% Bentonite 20 4,000 45%

40 1,800 20%

100 50 6%

Granular 0 25,400 100% Bentonite 20 21,000 * 80%

40 14,200 56%

100 4,800 22%

Fluids mixed to 80% of gwl time in jacketed cell at 500 RPM and 95°C, passed through high shear piston cell, mixed with additional water, and kneaded by hand until maximum strength attained.

Powdered bentonite 30.5 g Oil (32.5% Surf. A in SlOON) formula 30.5 g Powdered bentonite 125. g 1% P-250 in water

Granular bentonite 37.5 g Oil (21.7 Surf. A in SlOON) formula: 75. g ^" KWK Volclay (20-40 mesh bentonite) 125. g 1% P-250 in water

The influence of Clay Mesh range on the low shear gel time of granular bentonite liquid membrane well control fluid was determined. The well control fluids listed were formu- layed in the standard manner previously recited employing the following components in the concentrations indicated: 125. g VS. P-250 in water 37.5 g oil (21. TL Surf. A ₂ in SlOON) 75. g KWK-Volclay ground and sieved to the mesh ranges indicated. The components were mixed in the jacketed sample cell at 500 RPM and 95°C and ex¬ hibited a strong dependence on clay mesh size, as presented in Table IX:

TABLE IX

Low Shear

Mesh Range Gel Time (Min.)

>100 mesh 1.7

80/100 3.7

60/80 4.6

40/60 7.0

20/40 13.0

<20 14.3

Liquid Membrane well control fluids containing granular bentonite, powdered bentonite and mixtures of granular and powdered bentonite were prepared and examined for low shear gel time/high shear gel strength. The results are presented in Table X.

TABLE X

Total 1- Granular Bentonite in Formula ³

S Grams ! Bentonite 1007. 677. 507. 337. 07.

| 30 780/2,100* 17/7,100 24/11,400 45 22/10,800 8/15,900 5/20,300 10/16,500 60 15/26,000 4/26,000

*Gel time* minutes/gel _itrenβth ² . 11j/100 ft. ²

- ϊel time measured In jacketed low shear mixing cell, 500 rpm, 91°C Gel strength measured after hand kneading at room temperature

³ Basic formula: 30.5g oil (32.57. Surf. A ₂ In SlOON) xg Bentonite Clay 125g 17. P-250

As can be seen, systems employing mixtures of granular bentonite and powdered bentonite are inferior to systems employing either alone, with respect to either low shear gel times of high shear gel strength. Ftxrther, Table X shows that equivalent clay loadings (30g) 100% granular yields an inoperable system while powdered functions quite well. Similarly, at a 60g loading, 100% granular systems functions in a remarkably superior manner while powdered systems cannot even be formulated (the systems set up almost instantly, see also Table VII).