FIELD OF INVENTION

The present invention relates generally to oil and gas field, more particularly to a method for treating oil well using an emulsion composition, such as a microemulsion or a nanoemulsion.

BACKGROUND OF THE INVENTION

In the art of enhanced oil recovery from an oil well, chemicals such as alkaline- surfactant-polymer (ASP) or surfactant-polymer (SP) are commonly used. However, the aforementioned chemicals are generally not compatible with calcium and magnesium ions. Hence, continued use of such chemicals may result in formation of undesired scale deposits along well pipeline or pumping unit. Further, the chemicals are not entirely effective in seawater. High amount of salt in the seawater may affect performance of ASP or SP rendering them difficult to achieve an effective interfacial tension between oil reservoir and oil well. In view of the above, nanoemulsion is now used to avoid the abovementioned drawbacks.

There are certain patented technologies disclosing the use of emulsions in enhanced oil recovery. For example, United States Patent Publication No. US 8357639 B2 disclosed a nanoemulsion suitable for use in the oil field. Nevertheless, application steps for using nanoemulsion are not disclosed. The present invention provides a method for using an emulsion in oil well remediation, also known to enhance oil recovery.

SUMMARY OF INVENTION One aim of the present invention is to provide a method suitable for use in most kind of oil wells. More particularly, the method comprises steps of flushing the oil well with an emulsion composition, in which the emulsion used is compatible with seawater, hardwater, or the like. Hence, scale formation in the oil well can be avoided. Furthermore, the emulsion composition used is chemically stable, hence having low dependency on environmental changes, such as pH, ionic strength, type of rocks, and temperature.

Another aim of the present invention is to provide an environmental friendly method for enhancing oil recovery from oil wells. More particularly, the emulsion composition used is biodegradable.

Another aim of the present invention is to provide a flexible method for enhancing oil recovery from oil wells. In certain embodiments, the emulsion composition can work in association with water flooding method and/or polymer flooding method to achieve better well remediation.

Another aim of the present invention is to provide an effective method for enhancing oil recovery from oil wells. More particularly, the method increases flowability of the oil reservoir in the oil wells.

At least one of the preceding aspect is met, in whole or in part, by the present invention, in which one of the embodiments of the present invention is an enhanced oil recovery method from an oil well comprising a step of: introducing an emulsion composition having dispersed oil-in-water or water-in-oil droplet size of equal or less than 1 p (1 x 10 ⁶ meter) in an amount of 0.01 % to 100 % to pore volume of oil reservoir into the oil well, such that interfacial tension (IFT) between the oil well and the reservoir reduces to 10 ⁴ mM/m or lower thereby enable removal of oil therefrom. In one preferred embodiment, the method further comprises a step of pre-flushing the oil well with treated seawater in an amount of 0.01 % to 10 % to pore volume of the oil reservoir.

In certain embodiment, the method further comprises a step of introducing a polymeric solution into the oil well, in which the polymeric solution is in an amount of 0.15 % to 100 % to pore volume of oil reservoir into the oil well.

Preferably, the polymeric solution comprises water and polymer selected from any one or a combination of polyacylamine or derivatives thereof, xanthan gum, hydroxyethyl cellulose, carboxymethyl cellulose, and guar gum.

Advantageously, the polymer solution used has a polymer concentration of 0.05 w/w % to 2 w/w % in water.

In certain embodiment, the method further comprises a step of introducing the oil well with an aqueous solution in an amount of 0.15 % to 200 % to pore volume of the oil reservoir.

Preferably, the aqueous solution is any one or a combination of water, treated seawater, and brine.

In certain embodiment, the method further comprises a step of diluting the emulsion composition to a concentration of 0.1 w/w% to 20 w/w% in water, treated seawater or brines.

Advantageously, the emulsion composition comprises an aqueous phase in 0.5 to 60% by weight of total composition; an non-aqueous phase in 15 to 90% by weight of total composition; a surfactant in 2 to 60% by weight of total composition; and a compound having Chemical structure I in 1 to 30% by weight of total composition,

(Chemical structure I) RI-CONH-[R ₂ -NH-R3] I-HNOC-R4 in which Ri, R?, R3 and R4 are linear, branched or aromatic carbon-containing substituents having 2 to 26 carbon atoms and n is an integer ranges from 1 to 100, wherein each of the substituents comprises an alkyl group, carbonyl group, a carboxylic group, an amine group, or an amide group.

Preferably, the emulsion composition further comprises a co-surfactant in 1% to 30% by weight of the total composition, in which co-surfactant comprises a short-chain surfactant, a short-chain non-ionic surfactant, an alcohol, an amide, and/or a mixture thereof.

Preferably, the aforementioned brine is selected from ammonium chloride, potassium chloride, sodium chloride, sodium formate, potassium chloride, potassium formate, sodium bromide, calcium chloride, calcium bromide and mixtures thereof.

DETAILED DESCRIPTION OF THE INVENTION

Exemplary, non-limiting embodiments of the invention will be disclosed. However, it is to be understood that limiting the description to the preferred embodiments of the invention is merely to facilitate discussion of the present invention and it is envisioned that those skilled in the art may devise various modifications without departing from the scope of the appended claim.

The term “emulsion” herein refers to microemulsion or nanoemulsion having dispersed oil-in-water or water-in-oil. The present invention is an enhanced oil recovery method from an oil well comprising a step of: introducing an emulsion composition in an amount of 0.01 % to 100 % to pore volume of oil reservoir into the oil well, such that interfacial tension (IFT) between the oil well and the reservoir reduces to 10 ⁴ mM/m or below thereby enable removal of oil therefrom. In one embodiment, the IFT can be reduced to 10 ⁶ mN/m.

The step of introducing the emulsion composition can be conducted by injecting it into an oil well and flooding thereof, such that there is sufficient contact between the emulsion, the oil reservoir, and undesired deposits along the oil well. Advantageously, the composition to seep through rocks or cracks in the oil well as well. Upon sufficient contact, the emulsion adsorbs onto the reservoir surfaces and oil surfaces. It reduces the contact angle and facilitate the reduction in interfacial tension. It shall be noted that further introduction of water therein helps remove excess oils within the pores.

If necessary, the method comprises a step of pre-flushing the oil well with treated seawater. The seawater used is preferably treated to remove bacteria, fungus, and oxygen. Generally, the step of pre-flushing is conducted before the step of introducing the emulsion composition thereinto. More particularly, the oil well is pre-flushed with treated seawater in an amount of 0.01 % to 10 % to pore volume of the oil reservoir.

In accordance to preceding description, the step of introducing the emulsion composition into the oil well may work in association with aqueous solution and/or polymer flooding in different sequences. Aqueous solution flooding herein is also generally known as“water flooding” in the art. Particularly, aqueous solution flooding herein uses water, treated seawater, or brine. The brine used is selected from ammonium chloride, potassium chloride, sodium chloride, sodium formate, potassium chloride, potassium formate, sodium bromide, calcium chloride, calcium bromide and mixtures thereof. On the other hand, polymer flooding herein preferably uses biosynthesized and/or water-soluble polymer. More particularly, the polymeric solution comprises polymer selected from any one or a combination of polyacylamine or derivatives thereof, xanthan gum, hydroxyethyl cellulose, carboxymethyl cellulose, and guar gum.

In one embodiment, the method comprised of sequential steps: (1) pre-flusing the oil well with treated seawater in an amount of 0.01 % to 10 % to pore volume of the oil reservoir; (2) introducing a nanoemulsion composition in an amount of 0.01 % to 50 % to pore volume of oil reservoir into the oil well, such that interfacial tension (IFT) between the oil well and the reservoir reduces to 10 ⁴ mM/m or below thereby enable removal of oil therefrom; and then (3) introducing the oil well with an aqueous solution in an amount of 0.15 % to 100 % to pore volume of the oil reservoir.

In another embodiment, the method comprised of sequential steps: (1) pre-flusing the oil well with treated seawater in an amount of 0.01 % to 10 % to pore volume of the oil reservoir; (2) introducing a nanoemulsion composition in an amount of 0.01 % to 100 % to pore volume of oil reservoir into the oil well, such that interfacial tension (IFT) between the oil well and the reservoir reduces to 10 ⁴ mM/m or below thereby enable removal of oil therefrom; (3) introducing a polymeric solution into the oil well, in which the polymeric solution is in an amount of 0.15 % to 100 % to pore volume of oil reservoir into the oil well; and then (4) introducing the oil well with an aqueous solution in an amount of 0.15 % to 100 % to pore volume of the oil reservoir.

Alternatively, the method comprises an embodiment where the nanoemulsion and the polymer solution are mixed prior to introducing into the oil well. In this embodiment, the method comprised of sequential steps: (1) pre-flusing the oil well with treated seawater in an amount of 0.01 % to 10 % to pore volume of the oil reservoir; (2) introducing a mixture of nanoemulsion composition and polymer solution in an amount of 0.01 % to 100 % to pore volume of oil reservoir into the oil well, such that interfacial tension (IFT) between the oil well and the reservoir reduces to 10 ⁴ mM/m or below thereby enable removal of oil therefrom; (3) introducing an extra dose of polymeric solution into the oil well, in which the polymeric solution is in an amount of 0.15 % to 100 % to pore volume of oil reservoir into the oil well; and then (4) introducing the oil well with an aqueous solution in an amount of 0.15 % to 200 % to pore volume of the oil reservoir.

More particularly, the emulsion composition used is preferably diluted with water, treated seawater, or brine to a predetermined concentration prior to use. The brine used is selected from ammonium chloride, potassium chloride, sodium chloride, sodium formate, potassium chloride, potassium formate, sodium bromide, calcium chloride, calcium bromide and mixtures thereof. The seawater used is preferably treated to remove bacteria, fungus, and oxygen. In the preferred embodiment, the method comprises a step of introducing a nanoemulsion composition having concentration of 0.1-20 w/w% in water into the oil well.

The emulsion composition used preferably comprises an aqueous phase in 0.5 to 60% by weight of total composition; an non-aqueous phase in 15 to 90% by weight of total composition; a surfactant in 2 to 60% by weight of total composition; and a compound having Chemical structure I in 1 to 30% by weight of total composition,

(Chemical structure I) RI-CONH-[R ₂ -NH-R3] I-HNOC-R4 in which Ri, R?, R3 and R4 are linear, branched or aromatic carbon-containing substituents having 2 to 26 carbon atoms and n is an integer ranges from 1 to 100, wherein each of the substituents comprises an alkyl group, carbonyl group, a carboxylic group, an amine group, or an amide group.

Optionally, the emulsion used may further comprised of 1-5 w/w% of biocides selected from glutaraldehyde, terakis-hydroxymethylphosphonium sulfate, n- alkyldimethyl-benzylammonium chloride and mixtures thereof.

Optionally, the emulsion used may also further comprised of 1-5 w/w% of chelating agents selected from amino trimethylene phosphonic acids, polyhydric alcohol phosphate esters, hexamethylenediaminetetra (methylenephosphonic acid) and mixtures thereof.

Optionally, the emulsion used may also further comprised of 1-5 w/w% of corrosion inhibitors selected from phosphate esters, amine salts of polycarboxylic acids, quaternary ammonium ammonium salts, quaternary iminium salts, amidoamines, imidazolines, ethoxylated fatty amines, ethoxylated fatty diamines and mixtures thereof. Optionally, the emulsion used may also further comprised of 1-5 w/w% of pH buffers, if necessary.

The present invention may be embodied in other specific forms without departing from its essential characteristics. The described embodiments are to be considered in all aspects only as illustrative and not restrictive. The scope of the invention is, therefore indicated by the appended claims rather than by the foregoing description. All changes, which come within the meaning and range of equivalency of the claims, are to be embraced within their scope.