NL2014039B1 - Microemulsion completion fluid and use thereof. - Google Patents

Abstract

The present disclosure discloses a microemulsion completion fluid, comprising an oil phase, an aqueous phase, a surfactant, a cosurfactant, a salt, and a cleaning agent, wherein the cleaning agent is selected from a group consisting of oxidants and bio-enzymes. The microemulsion completion fluid according to the present disclosure has excellent comprehensive performance, and is advantageous in relieving formation damage caused by a drilling fluid, especially by a water-based drilling fluid, so as to improve yield of crude oil in production. The completion fluid according to the present disclosure has broad application prospects.

Description

Titel: MICROEMULSION COMPLETION FLUID AND USE

THEREOF

Cross-Reference to Related Application

This application claims benefit of CN 201310718405.4, filed on December 23, 2013, the entirety of which is incorporated herein for reference.

Field of the Invention

The present disclosure relates to the field of drilling additives, in particular to a completion fluid used in oil fields.

Background of the Invention “Drilling fluids” is a general term for a variety of circulating fluids that can satisfy various requirements in the work of well drilling during an oil and gas drilling process due to multiple functions thereof. A drilling fluid, as the “blood” in well drilling, plays an important role in drilling operations. The main functions of the drilling fluid include 1) carrying and suspending cuttings, 2) stabilizing borehole walls and balancing formation pressure, 3) cooling and lubricating a drill bit and a drill string, and 4) transferring hydrodynamic forces. In the drilling process, dense inner and outer filter cakes need to be formed by the drilling fluid in order to effectively prevent solid and liquid phases from invading the reservoirs. The filter cakes formed may be removed by perforation. In non-perforation completion, however, filter cakes cannot be pierced by perforation, and would therefore largely reduce the permeability in the near-wellbore area. Hence, the lockage effect of filter cakes must be eliminated to the largest extent before developing an oil and gas well.

At present, filter cakes can be removed substantially through methods of two aspects: physical methods and chemical methods. The physical methods are mainly accomplished by mechanical means, with a scraper and a cyclone tractor hoist as two special removing tools in the clearance work of the outer filter cake. However, through the physical methods, only the outer cake can be removed, while the inner cake which would severely damage the reservoirs cannot be effectively cleared up. In the chemical methods, filter cakes are destructed essentially through chemical reactions with an acid. Conventional chemical methods for removal of filter cakes mainly include acidification treatment, complex clearance by acidification plus oxidation, enzymatic treatment, and the like. Removing the filter cakes through the chemical methods would often lead to secondary damages. Even the mildest enzymatic treatment cannot effectively eliminate the damage of water lock. Currently, the drilling fluid system widely used includes water-based drilling fluids, which generally cause large formation damage. Therefore, it is necessary to achieve a high yield by removing filter cakes and reducing the damage of water lock.

Summary of the Invention

To eliminate the defects that exist in the prior art for removing filter cakes, the present disclosure aims to provide a microemulsion completion fluid which is stable, can be manufactured through a simple process, and is efficient in relieving formation damage caused by a drilling fluid, especially in relieving formation damage caused by a water-based drilling fluid.

According to one aspect of the present disclosure, a microemulsion completion fluid is provided, comprising an oil phase, an aqueous phase, a surfactant, a cosurfactant, a salt, and a cleaning agent, wherein the cleaning agent is selected from a group consisting of oxidants and bioenzymes.

The microemulsion completion fluid according to the present disclosure can only be formed with addition of a certain amount of the surfactant, oil phase, aqueous phase and the cosurfactant which are beneficial for improvement of the emulsifying effect. The salt is also advantageous for stability of the microemulsion. The microemulsion completion fluid obtained possesses extremely low interfacial tension (lower than 10 3mN/m) and can effectively relieve damage of water lock in the near-wellbore area. The microemulsion completion fluid obtained according to the present disclosure has homogeneous particle sizes and stable performance, and would not aggregate, settle, or the like after being placed for a long time. The droplets of microemulsion have particle sizes of 10 to lOOnm. In one specific embodiment, the D90 value of the particle size of the microemulsion droplets formed ranges from 50 to lOOnm. The particle size in the present disclosure can be tested using laser nanometer particle size analyzer LB-550.

In the microemulsion completion fluid according to the present disclosure, the cleaning agent can degrade ingredients of polymers and the like of the filter cakes contained in the drilling fluid, so as to perform a function of destructing the filter cakes. The cleaning agent can be selected from commonly used oxidants and bio-enzymes. In one preferred embodiment, the cleaning agent can be at least one selected from a group consisting of magnesium peroxide, potassium permanganate, potassium persulfate, sodium persulfate, cellulase, amylase, glucoamylase, modified cellulase, and modified amylase.

In one specific embodiment of the microemulsion completion fluid according to the present disclosure, based on 100 parts by weight of the microemulsion completion fluid, the contents of the oil phase, the aqueous phase, the surfactant, the cosurfactant, the salt, and the cleaning agent respectively account for 20-50 parts, 30-60 parts, 2-10 parts, 2-20 parts, 2-10 parts, and 1-8 parts, preferably 35-50 parts, 30-45 parts, 4-8 parts, 10-20 parts, 2-5 parts, and 4-8 parts. Within the ranges as described above, stable completion fluid can be obtained, while outside the ranges as described above, emulsion cannot be formed due to easy layering or merely coarse emulsion can be formed. The microemulsion presents high efficient in removing filter cakes and in removing water lock.

In one specific embodiment according to the present disclosure, the microemulsion completion fluid consists of the oil phase, the aqueous phase, the surfactant, the cosurfactant, the salt, and the cleaning agent as described above.

In one specific embodiment of the microemulsion completion fluid, the oil phase can be at least one selected from a group consisting of white oil, kerosene, diesel oil, and vegetable oil.

In another specific embodiment of the microemulsion completion fluid, the surfactant can be at least one selected from a group consisting of alkyl sulfonates (e.g. Cio-C is alkyl sulfonates), alkylbenzene sulfonates (e.g. Cio-Cis alkylbenzene sulfonates), alkyl sulfates (e.g. Cio-Cis alkyl sulfates), rhamnolipid, octyl phenol polyoxyethylene ether-10 (OP-10), polyoxyethylene sorbitan monostearate (Tween60), sorbitan monooleate polyoxyethylene ether (Tween80), and sorbitan fatty acid ester 80 (Span80).

In another specific embodiment of the microemulsion completion fluid according to the present disclosure, the surfactant can be an alcohol, preferably at least one selected from a group consisting of monohydric alcohols, polyhydric alcohols, polyethylene glycol, and polyglycerol.

In one specific embodiment, the salt can be an inorganic salt or an organic salt, preferably at least one selected from a group consisting of sodium chloride, potassium chloride, calcium chloride, magnesium chloride, sodium formate, potassium formate, sodium acetate, and potassium acetate.

According to the present disclosure, the completion fluid can be a microemulsion completion fluid, and a thermodynamically stable and isotropic disperse system that is spontaneously generated after being compounded. The completion fluid is characterized by ultralow interfacial tension, rather small emulsion particle sizes, prodigious solublizing power for both oil and water, etc. Compared with a completion fluid in the prior art, the microemulsion completion fluid according to the present disclosure not only can degrade polymers contained in the filter cakes, so as to eliminate damages caused by filter cake blockage, but also can improve the interfacial property of the pore throat and the emulsion blockage in areas near borehole walls, reduce flow resistance of the oil phase, and reduce or remove damages caused by water lock. The oil layer can thus be protected and the yield per well can be increased.

According to another aspect of the present disclosure, use of the microemulsion completion fluid as described above in relieving formation damage caused by a water-based drilling fluid is further provided.

The microemulsion completion fluid according to the present disclosure can destroy the polymers contained in the filter cakes by means of oxidation, enzymolysis, and the like. As a result, cracks can occur on the filter cakes, which then will become loose, thus benefiting flowback of oil and gas. Meanwhile, the microemulsion completion fluid according to the present disclosure also can play a role of degradation against polymers that have invaded into formation pore. Damages to the stratum can thus be effectively relieved. The microemulsion completion fluid according to the present disclosure possesses ultralow interfacial tension and can easily intrude into a pore throat in the formation rocks so as to improve the interfacial properties of the pore throat. At the same time, the microemulsion completion fluid according to the present disclosure has sufficiently strong solubhzing power, so that it can be dissolved into water or oil, thus improving the conditions of emulsion blockage in the pore throat near the borehole walls, eliminating the Jamin effect, and reducing flow resistance of the oil phase. The completion fluid of the present disclosure can clear up filter cakes of water-based drilling fluid, reduce damage of water lock in the reservoirs, and thus improve permeability of the oil phase and the yield per well.

According to still another aspect of the present disclosure, use of the microemulsion completion fluid in oil exploration is further provided. The completion fluid is favorable for use in eliminating formation damage by a drilling fluid, especially by a water-based drilling fluid. The microemulsion completion fluid according to the present disclosure has excellent comprehensive performance, and can be advantageous in improving the interfacial property of a pore throat, reducing resistance in driving water by oil when the oil is put into operation, and decreasing displacement flowback pressure. Meanwhile, the microemulsion completion fluid according to the present disclosure can effectively improve the conditions of emulsion blockage in the pore throat near borehole walls, eliminate the Jamin effect, and reduce the flow resistance of the oil phase. This would increase the yield of the crude oil. In one specific embodiment, after compounding is performed in a well-drilling site, during the last circulation of the drilling fluid, the microemulsion completion fluid that has been formulated can be added into the wellbore, followed by open hole completion or completion by putting down a screen pipe after pulling out of the hole.

The microemulsion completion fluid according to the present disclosure has excellent comprehensive performance, and is advantageous in relieving formation damage by a drilling fluid, especially a water-based drilling fluid, so as to improve yield of crude oil in production. The completion fluid according to the present disclosure has broad application prospects.

Detailed Description of the Emhodiments

The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used herein, the singular forms “a,” “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises” and/or “comprising,” when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, group of elements, components, and/or groups thereof.

Language such as “including,” “comprising,” “having,” “containing,” or “involving,” and variations thereof, is intended to be broad and encompass the subject matter fisted thereafter, as well as equivalents, and additional subject matter not recited. Further, whenever a composition, a group of elements, process or method steps, or any other expression is preceded by the transitional phrase “comprising,” “including” or “containing,” it is understood that it is also contemplated herein the same composition, group of elements, process or method steps or any other expression with transitional phrases “consisting essentially of,” “consisting of,” or “selected from the group of consisting of,” preceding the recitation of the composition, the group of elements, process or method steps or any other expression.

The present disclosure will be explained in further details with reference to examples, which, however, will not limit the present disclosure.

The capacity of the microemulsion completion fluid in removing a filter cake and damage of water lock will be studied in the following methods, respectively.

Filter-cake removal efficiency: A filter cake was obtained after performing a medium-pressure filtration experiment using a water-based drilling fluid. Clear water was added in a medium-pressure filtration cup, and a piece of filter paper with the filter cake thereon was placed on the rim of the filter cup. The amount of the clear water through the filter cake in 7.5 min was measured as Ql according to the API standard, which preceded soak of the filter cake in a completion fluid for 16 h at 90 °C. The amount of clear water through the soaked filter in 7.5 min was then measured as Q2 by the aforementioned method. The ratio of Q2 to Ql was calculated to obtain the filter-cake removal efficiency. A larger ratio would indicate higher removal efficiency.

Water-lock removal efficiency: A low permeability core was soaked saturatedly in standard brine and an oil-phase displacement pressure P1 thereof at a certain displacement flow was measured. Reverse displacement was then performed to the core using a microemulsion completion fluid, followed by measurement of an oil-phase displacement pressure P2 at the same flow as mentioned above. The ratio of P2 to PI was calculated to obtain the water-lock removal efficiency. A smaller ratio would indicate higher removal efficiency.

Example 1

Based on a total weight of 100 parts, 40 parts of water, 2 parts of sodium chloride (which was dissolved in the 40 parts of water), 40 parts of white oil, 3 parts of sodium dodecylbenzene sulfonate, 10 parts of n-butyl alcohol, 5 parts of magnesium peroxide were weighed, put into a beaker, homogeneously mixed, and stirred at a low speed for 5 min to form a microemulsion. The D90 value, filter-cake removal efficiency, and water-lock removal efficiency of the microemulsion were tested to be 55.3 nm, 6.82, and 0.35, respectively.

Example 2

Based on a total weight of 100 parts, 30 parts of water, 2 parts of sodium chloride (which was dissolved in the 30 parts of water), 36 parts of white oil, 8 parts of sodium dodecyl sulfate, 20 parts of n-butyl alcohol, 4 parts of magnesium peroxide were weighed, put into a beaker, homogeneously mixed, and stirred at a low speed for 5 min to form a microemulsion. The D90 value, filter-cake removal efficiency, and water-lock removal efficiency of the microemulsion were tested to be 64.2 nm, 6.35, and 0.26, respectively.

Example 3

Based on a total weight of 100 parts, 32 parts of water, 2 parts of sodium formate (which was dissolved in the 32 parts of water), 44 parts of white oil, 3 parts of sodium dodecylbenzene sulfonate, 3 parts of Tween60, 12 parts of polyethylene glycol (PEG600), 4 parts of magnesium peroxide were weighed, put into a beaker, homogeneously mixed, and stirred at a low speed for 5 min to form a microemulsion. The D90 value, filter-cake removal efficiency, and water-lock removal efficiency of the microemulsion were tested to be 85.3 nm, 7.53, and 0.28, respectively.

Example 4

Based on a total weight of 100 parts, 30 parts of water, 2 parts of potassium chloride (which was dissolved in the 30 parts of water), 50 parts of kerosene, 4 parts of sodium dodecyl sulfonate, 10 parts of n-amyl alcohol, 4 parts of cellulase were weighed, put into a beaker, homogeneously mixed, and stirred at a low speed for 5 min to form a microemulsion. The D90 value, filter-cake removal efficiency, and water-lock removal efficiency of the microemulsion were tested to be 52.9 nm, 9.44, and 0.21, respectively.

Example 5

Based on a total weight of 100 parts, 33 parts of water, 5 parts of sodium acetate (which was dissolved in the 33 parts of water), 40 parts of white oil, 4 parts of Tween80, 13 parts of n-butyl alcohol, 5 parts of glucoamylase were weighed, put into a beaker, homogeneously mixed, and stirred at a low speed for 5 min to form a microemulsion. The D90 value, filter-cake removal efficiency, and water-lock removal efficiency of the microemulsion were tested to be 74.3 nm, 10.67, and 0.24, respectively.

Example 6

Based on a total weight of 100 parts, 32 parts of water, 2 parts of magnesium chloride (which was dissolved in the 32 parts of water), 42 parts of white oil, 4 parts of sodium dodecyl sulfate, 12 parts of n-butyl alcohol, 3 parts of magnesium persulfate, and 5 parts of cellulase were weighed, put into a beaker, homogeneously mixed, and stirred at a low speed for 5 min to form a microemulsion. The D90 value, filter-cake removal efficiency, and water-lock removal efficiency of the microemulsion were tested to be 95.1 nm, 10.99, and 0.26, respectively.

Example 7 (for comparison) A bio-completion fluid (comprising 8 parts of cellulase, 2 parts of flow regulator CX-802, 3 parts of surfactant (sodium dodecylbenzene sulfonate), and water as a balance) was used for test. The filter-cake removal efficiency and water-lock removal efficiency of the bio-completion fluid were tested to be 7.49 and 0.47, respectively.

Example 8 (for comparison)

An oxidant-containing completion fluid (comprising 5 parts of magnesium peroxide, 3 parts of viscosifier SD-2, and a balance of water) was used for test. The filter-cake removal efficiency and water-lock removal efficiency of the oxidant-containing completion fluid were tested to be 6.87 and 0.54, respectively.

Comparative Example 1

Niobium hydroxide (a commonly used acid treatment solution in the art, which is a mixed acid composed of hydrofluoric acid and hydrochloric acid) was used for test. The filter-cake removal efficiency and water-lock removal efficiency thereof were tested to be 5.69 and 0.78, respectively.

Comparative Example 2

Based on a total weight of 100 parts, 25 parts of water, 3 parts of sodium chloride (which was dissolved in the 25 parts of water), 52 parts of white oil, 12 parts of sodium dodecylbenzene sulfonate, 3 parts of n-butyl alcohol, 5 parts of magnesium peroxide were weighed, put into a beaker, homogeneously mixed, and stirred at a low speed for 5 min. Coarse emulsion having large particle sizes, instead of microemulsion, was formed. The D90 value, filter-cake removal efficiency, and water-lock removal efficiency of the coarse emulsion were tested to be 129.6 pm, 1.32, and 1.47, respectively.

The above data indicate that the microemulsion completion fluid according to the present disclosure has not only higher filter-cake removal efficiency, but also higher water-lock removal efficiency than the completion fluids in the prior art. The microemulsion completion fluid according to the present disclosure has excellent comprehensive performance, and can be advantageous in improving the interfacial property of a pore throat, reducing resistance in driving water by oil when the oil is put into operation, and decreasing displacement flowback pressure. Meanwhile, the microemulsion completion fluid according to the present disclosure can effectively improve the conditions of emulsion blockage in the pore throat near borehole walls, eliminate the Jamin effect, and reduce the flow resistance of the oil phase. This would increase the yield of the crude oil.

It should be noted that the above examples are only used to explain, rather than to limit the present disclosure in any manner. Although the present disclosure has been discussed with reference to preferable examples, it should be understood that the terms and expressions adopted are for describing and explaining instead of limiting the present disclosure. The present disclosure can be modified within the scope of the claims, or can be amended without departing from the scope or spirits of the present disclosure. Although the present disclosure is described with specific methods, materials, and examples, the scope of the present disclosure herein disclosed should not be limited by the particularly disclosed examples as described above, but can be extended to other methods and uses having the same functions.

Claims (10)

A microemulsion production liquid comprising an oil phase, an aqueous phase, a surfactant, a co-surfactant, a salt and a cleaning agent, wherein the cleaning agent is selected from the group consisting of oxidants and bio-enzymes and wherein, based on 100 parts by weight of the microemulsion production liquid, the content of the surfactant is 2-10 parts, preferably 4-8 parts. The microemulsion production liquid according to claim 1, wherein the cleaning agent is at least one selected from the group consisting of magnesium peroxide, potassium permanganate, potassium persulfate, sodium persulfate, cellulose, amylase, glucoamylase, modified cellulose and modified amylase. 3. The microemulsion production liquid according to claim 1 or 2, wherein the content of the oil phase, the aqueous phase, the co-surfactant, the salt and the cleaning agent is based on 100 parts by weight of the microemulsion production liquid, 20-50 parts, respectively. Are -60 parts, 2-20 parts, 2-10 parts and 1-8 parts, preferably 35-50 parts, 30-45 parts, 10-20 parts, 2-5 parts, and 4-8 parts. The microemulsion production fluid according to any of claims 1-3, wherein the oil phase is at least one selected from the group consisting of white oil, kerosene, diesel oil and vegetable oil. The microemulsion production fluid according to any of claims 1-4, wherein the surfactant is at least one selected from the group consisting of alkyl sulfonates, alkyl benzene sulfonates, alkyl sulfatee, rhamnolipid, octylphenol polyoxyethylene ether-10, polyoxyethylene sorbitan monostearate, sorbitan monooleate polyoxyethylene ether polyoxyethylene ether and sorbitan fatty acid ester 80. The microemulsion production fluid according to any one of claims 1-5, wherein the cosurfactant is at least one selected from the group consisting of monohydric alcohols, polyhydric alcohols, polyethylene glycol, and polyglycerol. The microemulsion production liquid according to any of claims 1-6, wherein the salt is an inorganic salt or an organic salt, preferably at least one selected from the group consisting of sodium chloride, potassium chloride, calcium chloride, magnesium chloride, sodium format, potassium format and potassium acetate. The microemulsion production liquid according to any of claims 1-7, wherein the microemulsion production liquid consists of the oil phase, the aqueous phase, the surfactant, the co-surfactant, the salt and the cleaning agent. Use of the microemulsion production fluid according to any of claims 1-8 in reducing deposition damage caused by water-based drilling fluid. Use of the microemulsion production liquid according to any of claims 1-8 in the extraction of oil.