Plugging agent, application thereof and water-based drilling fluid system

Abstract

The invention relates to the field of drilling fluid, and discloses a plugging agent, application thereof and a water-based drilling fluid system. The plugging agent comprises a flexible material, a rigid inorganic mineral material and a high-molecular polymer, wherein the flexible material is selected from asphalt and / or white oil. The plugging agent provided by the invention has a good plugging effect and plays a role in plugging micro-cracks in real time. A water-based drilling fluid system containing the plugging agent has a certain corrosion effect on reservoir microcracks in a well completion stage, the permeability of the reservoir is increased, the flowback resistance of coal bed gas is reduced, the requirements of reservoir protection and drilling within 120 DEG C are met, subsequent acid fracturing operation and reservoir transformation are avoided, and the productivity of the coal bed gas is improved.

Description

Technical Field

[0001] The present invention relates to the field of drilling fluid, in particular to a plugging agent and application thereof and a water-based drilling fluid system. Background Art

[0002] During the coalbed methane drilling process, due to the characteristics of low mechanical strength, strong stress sensitivity, and widespread distribution of micro-fractures in coal reservoirs, the drilling process is susceptible to damage from the invasion of insoluble solid particles in the drilling fluid and damage from drilling pressure, which affects the effectiveness of coalbed methane development. At present, my country's coalbed methane drilling basically follows the oil and gas drilling technology. The shielding temporary plugging technology can effectively avoid leakage and effectively protect the reservoir, and has been widely used in recent years. In order to enhance the plugging ability of drilling fluids on fractured formations, the most commonly used method is physical bridge plugging. The temporary plugging material used in physical bridge plugging utilizes the decrease in the permeability of the plugging layer caused by the solid-phase particle plugging agents already in the drilling fluid system entering the formation, forming an effective shielding ring in front of the reservoir to prevent further damage to the reservoir. The blockage is removed by acidification, and the reservoir permeability is restored, thereby achieving the purpose of increasing production. Commonly used plugging materials include high-water-loss plugging materials (such as permeable materials, fibrous materials, diatomaceous earth, porous inert materials, filter aids and coagulants, etc.), soft and hard plugging materials, inorganic gelling plugging agents, temporary plugging materials, chemical plugging materials, high-temperature plugging materials, composite plugging materials and bridge plugging materials. Currently, the commonly used plugging materials have achieved good application results in actual use, but they also face some problems. For example, non-deformable materials (such as mica, etc.) use high-concentration solid particles with a specific particle size distribution to produce a bridging plugging effect at the cracks, but the high concentration of solid phase particles has a significant effect on the rheological properties of the drilling fluid. Asphalt temporary plugging materials usually have fluorescence, which interferes with subsequent logging and affects the accurate judgment of the reservoir. Most bridging materials are not acid-soluble and can easily cause permanent damage to fracture-vuggy reservoirs. Acid-soluble materials are mainly limestone and ultrafine calcium carbonate. Physical sealing is achieved through the particle size grading of acid-soluble limestone or ultrafine calcium carbonate and the use of particle shape and elastic materials. However, subsequent acidification and unblocking are required to restore the permeability of the fractures and vuggy reservoirs, which increases the cost of subsequent operations.

[0003] Therefore, there is an urgent need for a drilling fluid system that can effectively protect coalbed methane reservoirs, reduce the penetration depth and filtration loss of drilling fluid in fractures, and at the same time, acid dissolve the reservoir with the degradation products of the plugging agent, thereby increasing the permeability of the reservoir without acidizing operations. Summary of the Invention

[0004] The purpose of the present invention is to overcome the problem in the prior art that solid particles in the drilling fluid during coal seam drilling are prone to clogging reservoir fractures and contaminating the coalbed methane reservoir, resulting in the need for acid declogging before completion testing operations. The present invention provides a plugging agent and its application and a water-based drilling fluid system suitable for coalbed methane reservoir protection. The plugging agent has a good plugging effect and plays the role of real-time plugging of microcracks.

[0005] In order to achieve the above-mentioned object, the present invention provides a plugging agent in a first aspect, wherein the plugging agent comprises: a flexible material, a rigid inorganic mineral material and a high molecular polymer; wherein,

[0006] The flexible material is selected from asphalt and / or white oil.

[0007] A second aspect of the present invention provides a water-based drilling fluid system, wherein the water-based drilling fluid system comprises: a water-based drilling fluid base slurry and the plugging agent provided by the present invention.

[0008] A third aspect of the present invention provides a use of the plugging agent provided by the present invention in reducing the penetration depth and filtration loss of drilling fluid in cracks in coalbed methane reservoirs.

[0009] Through the above technical solution, the beneficial effects of the present invention include at least:

[0010] The plugging agent provided by the present invention is compounded with flexible materials, rigid inorganic mineral materials and high molecular polymers, which can reduce the penetration depth and filtration loss of drilling fluid in fractures. At the same time, the degradation products of the plugging agent acid dissolve the reservoir, thereby achieving the purpose of increasing reservoir permeability, reducing coalbed methane return resistance and increasing coalbed methane production capacity without acidizing operations.

[0011] The water-based drilling fluid system for coalbed methane reservoir protection provided by the present invention can effectively improve the reservoir protection effect. There are few acid-resistant solid phases in the system. After the degradation of the high molecular polymer, the pH value of the well slurry can be significantly reduced (in the preferred case, the pH value is as low as below 1), which can cause certain dissolution of the reservoir, increase the permeability, reduce the coalbed methane return resistance, help to restore the reservoir permeability before subsequent return, and improve the coalbed methane production capacity.

[0012] The water-based drilling fluid system provided by the present invention can effectively protect coalbed methane reservoirs. This system can form a temporary plugging layer on the surface of fracture-cavity reservoirs during drilling, reducing the amount and depth of drilling fluid intrusion. It requires a small number of treatment agents and self-degrades over time to achieve self-blocking. Furthermore, by utilizing the low pH value of degradation products in water-based drilling fluid, it can cause some dissolution of the reservoir, increase permeability, reduce coalbed methane flowback resistance, and improve coalbed methane production capacity.

[0013] In a preferred embodiment of the present invention, in a water-based drilling fluid system, a fluid loss reducer combined with a plugging agent can improve the quality of the mud cake; a plugging agent formed by compounding plugging agents of different particle sizes and strengths, including flexible materials (asphalt and / or industrial white oil), rigid inorganic mineral materials, and high molecular polymers, can effectively plug microcracks or pores with a fracture width or pore throat size of ≤100 μm, thereby reducing harmful solid phase intrusion into the formation and achieving the purpose of reservoir protection; the rigid plugging agent (inorganic mineral material), weighting agent, and inorganic salt have a composite weighting effect, and the inorganic salt has the function of maintaining a stable slurry flow pattern. DETAILED DESCRIPTION

[0014] The endpoints of the ranges and any values ​​disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoints of each range, the endpoints of each range and individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered to be specifically disclosed herein.

[0015] The first aspect of the present invention provides a plugging agent, wherein the plugging agent comprises: a flexible material, a rigid inorganic mineral material and a high molecular polymer; wherein,

[0016] The flexible material is selected from asphalt and / or white oil.

[0017] In order to further improve the synergistic effect of the flexible material, the rigid inorganic mineral material and the high molecular polymer, preferably, in the plugging agent, the weight ratio of the flexible material, the rigid inorganic mineral material and the high molecular polymer is 10:(5-20):(5-10).

[0018] According to the present invention, preferably, the flexible material is a mixture of asphalt and white oil. When the asphalt and white oil are compounded as the flexible material, the emulsified droplets of the white oil after high-speed stirring can better play a plugging role.

[0019] In order to better seal irregular cracks through self-deformation, preferably, in the flexible material, the weight ratio of the asphalt to the white oil is (0.3-3):1, preferably (0.5-1.5):1.

[0020] In order to better seal irregular cracks through self-deformation, preferably, the softening point of the asphalt is 60-150°C, preferably 60-120°C.

[0021] According to the present invention, preferably, the asphalt is selected from at least one of natural asphalt, emulsified asphalt and sulfonated asphalt, preferably natural asphalt and / or emulsified asphalt.

[0022] In a preferred embodiment of the present invention, the flexible material is a mixture of natural asphalt and / or emulsified asphalt and white oil. Preferably, the weight ratio of the natural asphalt and / or emulsified asphalt to the white oil is (0.3-3):1, more preferably (0.5-1.5):1.

[0023] The present invention has no particular limitation on the type of white oil, and conventional industrial white oil in the art can be used.

[0024] In a specific embodiment of the present invention, the industrial white oil is selected from one or more of 5# industrial white oil, 7# industrial white oil, 10# industrial white oil and 15# industrial white oil.

[0025] In order to better cooperate the rigid inorganic mineral material with the flexible material and the high molecular polymer to improve the effect of blocking micro cracks, preferably, the average particle size of the rigid inorganic mineral material is 3-50 μm.

[0026] According to the present invention, the rigid inorganic mineral material is preferably selected from at least one of limestone, calcium carbonate, magnesium carbonate, and magnesite powder, and is preferably selected from limestone and / or calcium carbonate. Limestone and / or calcium carbonate having an average particle size of 3-50 μm can better cooperate with the flexible material and polymer to seal microcracks.

[0027] According to the present invention, preferably, the weight average molecular weight of the polymer is 10,000-95,000 g / mol. Selecting a polymer with a weight average molecular weight within this range can not only better perform the plugging while drilling function, but also achieve self-degradation after a certain period of time.

[0028] According to the present invention, preferably, the average particle size of the high molecular polymer is 7-50 μm.

[0029] According to the present invention, the high molecular weight polymer is preferably selected from at least one of polyvinyl alcohol, polyglycolic acid, and polybutylene succinate, and is preferably selected from polyvinyl alcohol and / or polyglycolic acid. Polyvinyl alcohol and / or polyglycolic acid having an average particle size of 7-50 μm can more effectively and effectively seal microcracks in real time.

[0030] In a preferred embodiment of the present invention, by compounding a rigid inorganic mineral material of a specific type and particle size, a polymer, and a flexible material of a specific type, the synergistic effect of the inorganic mineral material, the polymer, and the rigid and flexible material as a plugging agent is further enhanced. The addition of this compounded plugging agent enhances the water-based drilling fluid system's plugging effectiveness.

[0031] A second aspect of the present invention provides a water-based drilling fluid system, wherein the water-based drilling fluid system comprises: a water-based drilling fluid base slurry and the plugging agent provided by the present invention.

[0032] The water-based drilling fluid system provided by the present invention can effectively protect coalbed methane reservoirs. This system can form a temporary plugging layer on the surface of fracture-cavity reservoirs during drilling, reducing the amount and depth of drilling fluid intrusion. It requires a small number of treatment agents and self-degrades over time to achieve self-blocking. Furthermore, by utilizing the low pH value of degradation products in water-based drilling fluid, it can cause some dissolution of the reservoir, increase permeability, reduce coalbed methane flowback resistance, and improve coalbed methane production capacity.

[0033] According to the present invention, preferably, in the water-based drilling fluid system, the weight ratio of the water-based drilling fluid base slurry to the plugging agent is (2.8-11):1.

[0034] According to the present invention, preferably, the water-based drilling fluid base slurry comprises a fluid loss reducer, an inorganic salt and / or a metal oxide, and water.

[0035] In the present invention, in the coalbed methane low-solid phase water-based drilling fluid system, the fluid loss reducer is combined with the plugging agent to improve the mud cake quality; by adopting the plugging agent containing flexible materials, rigid inorganic mineral materials and high molecular polymers, it is possible to effectively plug micro cracks or pores with a fracture width or pore throat size of ≤100 μm, thereby reducing the invasion of harmful solid phases into the formation and achieving the purpose of reservoir protection; the rigid inorganic mineral materials and inorganic salts and / or metal oxides have a composite weighting effect, and the inorganic salts and / or metal oxides have the function of maintaining the stability of the well slurry flow pattern.

[0036] According to the present invention, preferably, the water-based drilling fluid base slurry comprises 0.5-2.5 parts by weight of the fluid loss control agent, and 10-25 parts by weight of the inorganic salt and / or metal oxide, respectively, based on 100 parts by weight of water. The fluid loss control agent, inorganic salt and / or metal oxide content in the water-based drilling fluid base slurry falling within these ranges can better meet the requirements for regulating slurry flow patterns and controlling fluid loss during coalbed methane drilling.

[0037] According to the present invention, preferably, the fluid loss reducer is selected from copolymer fluid loss reducers.

[0038] According to the present invention, the copolymer-based fluid loss additive preferably contains structural units derived from N-isopropylacrylamide, sodium styrene sulfonate, N-vinylpyrrolidone, and acryloyloxybutyltrimethylammonium chloride. This copolymer-based fluid loss additive can better meet the fluid loss control requirements for medium-pressure, high-temperature, and high-pressure applications.

[0039] According to the present invention, preferably, in the copolymer-based fluid loss additive, the molar ratio of the structural unit derived from N-isopropylacrylamide, the structural unit derived from sodium styrene sulfonate, the structural unit derived from N-vinylpyrrolidone and the structural unit derived from acryloyloxybutyltrimethylammonium chloride is 4:(6-15):(4-10):(0.5-2), preferably 4:(6-14):(4-8):(0.5-1.6).

[0040] In the present invention, the content of each structural unit in the polymer can be tested by conventional methods in the prior art, such as infrared spectroscopy, nuclear magnetic resonance, and the amount of monomers fed during the polymerization process. Preferably, the amount of monomers fed is used to determine the content of each structural unit in the polymer. Specifically, the feed ratio of each monomer actually participating in the polymerization is determined by testing the content of unreacted monomers, thereby determining the content of each structural unit in the polymer. Furthermore, in the present invention, the content of each unreacted monomer in the tested polymer is less than 0.02% by weight, indicating that substantially all monomers participate in the polymerization reaction. Specifically, the content of the residual monomers is measured using liquid chromatography.

[0041] According to the present invention, preferably, the weight average molecular weight of the copolymer-based fluid loss additive is 300,000-500,000 g / mol.

[0042] In the present invention, the copolymer-based fluid loss additive can be prepared in the laboratory. For example, the preparation method of the copolymer-based fluid loss additive can include the following steps:

[0043] In the presence of a solvent, a first initiator and a second initiator, N-isopropylacrylamide, sodium styrene sulfonate, N-vinylpyrrolidone and acryloyloxybutyltrimethylammonium chloride are mixed in a molar ratio of 4:(6-15):(4-10):(0.5-2) to carry out a copolymerization reaction; the copolymerization product is sheared, dried and crushed to obtain a copolymer-type fluid loss additive.

[0044] Furthermore, during the copolymerization reaction, N-isopropylacrylamide, sodium styrenesulfonate, N-vinylpyrrolidone and acryloyloxybutyltrimethylammonium chloride are mixed in a molar ratio of 4:(6-14):(4-8):(0.5-1.6).

[0045] In a preferred embodiment, the first initiator and the second initiator are used in amounts such that the weight ratio of the first initiator, the second initiator and N-isopropylacrylamide is (0.05-0.4):(0.025-0.2):1.

[0046] Furthermore, during the copolymerization reaction, the amounts of the first initiator and the second initiator are such that the weight ratio of the first initiator, the second initiator and N-isopropylacrylamide is (0.06-0.35):(0.025-0.18):1.

[0047] In a preferred embodiment, the first initiator is selected from at least one of azobisisobutyronitrile, ammonium persulfate and hydrogen peroxide; and / or the second initiator is selected from at least one of ferrous sulfate, sodium bisulfite and sodium sulfite.

[0048] In a preferred embodiment, when the copolymerization reaction is carried out, the amount of the solvent used is such that the weight ratio of the total weight of N-isopropylacrylamide, sodium styrene sulfonate, N-vinylpyrrolidone and acryloyloxybutyltrimethylammonium chloride to the solvent is (17-71):100, preferably (15-20):1.

[0049] In a preferred embodiment, the solvent is water.

[0050] In a preferred embodiment, the copolymerization reaction temperature is 30-50° C. and the reaction time is 1-5 hours.

[0051] In a preferred embodiment of the present invention, the preparation method of the copolymer fluid loss additive comprises the following steps:

[0052] Sodium styrene sulfonate and N-vinyl pyrrolidone are added to water at room temperature, stirred until completely dissolved, and then the pH of the solution is adjusted to 6-9 with a pH regulator (for example, one or more of sodium hydroxide, potassium hydroxide and lithium hydroxide). N-isopropylacrylamide and acryloyloxybutyltrimethylammonium chloride are added to the solution. After the solution temperature is lowered to 35-45° C., nitrogen is injected into the solution for 15-30 minutes. Initiator 1 and initiator 2 are added dropwise to the mixed solution under stirring. After stirring, the mixture is sealed and the solution temperature is maintained at 30-50° C. After isothermal reaction for 1-5 hours, the gel product is sheared, dried at 100-105° C. for 4-8 hours, and crushed to obtain a copolymer fluid loss additive. The crushing can be performed using a crusher. Preferably, the crushing is performed at a crusher speed of 10,000-18,000 rpm for 0.5-3 minutes, preferably 1.2-1.8 minutes.

[0053] According to the present invention, preferably, the inorganic salt and / or metal oxide is selected from at least one of sodium chloride, potassium chloride, sodium formate, potassium formate, cesium formate, calcium chloride and calcium oxide, preferably at least one of sodium chloride, potassium chloride, sodium formate, potassium formate, calcium chloride and calcium oxide, more preferably a mixture of sodium chloride and / or potassium chloride, calcium chloride and calcium oxide.

[0054] Preferably, in the inorganic salt and / or metal oxide, the weight ratio of sodium chloride and / or potassium chloride, calcium chloride and calcium oxide is 20:(0.01-0.15):(0.01-0.1).

[0055] In order to further improve the weighting effect, preferably, the water-based drilling fluid slurry further includes a weighting agent. The inorganic mineral material and the weighting agent, inorganic salt and / or metal oxide have a composite weighting effect.

[0056] According to the present invention, preferably, in the water-based drilling fluid slurry, based on 100 parts by weight of water, the content of the weighting agent is 10-25 parts.

[0057] According to the present invention, the weighting agent is preferably selected from at least one of barite, micromanganese ore powder, and hematite powder, and is preferably selected from barite and / or micromanganese ore powder. Using barite and / or micromanganese ore powder as a weighting agent can more effectively increase well slurry density, more effectively reduce the solids content in the well slurry, and stabilize the flow pattern.

[0058] In a preferred embodiment of the present invention, the plugging agent provided by the first aspect of the present invention is compounded with a fluid loss control agent, an inorganic salt and / or a metal oxide, and a weighting agent, and has a good synergistic effect with the fluid loss control agent, the inorganic salt and / or the metal oxide, and the weighting agent, thereby further improving the plugging effect of the water-based drilling fluid system.

[0059] The present invention has no particular restrictions on the preparation method of the water-based drilling fluid system and the order of mixing the components, as long as the components can be fully dispersed in the water-based drilling fluid system. In order to make the components of the water-based drilling fluid system more fully dispersed in water, according to a preferred embodiment of the present invention, the preparation method of the water-based drilling fluid system includes the following steps:

[0060] Step 1: Slowly add the fluid loss reducer into the water to completely dissolve it;

[0061] Step 2: adding the flexible material, inorganic salt and / or metal oxide, and high molecular polymer to the base slurry obtained in step 1, and stirring evenly;

[0062] Step 3: Add rigid inorganic mineral materials and weighting agents to the mixed base slurry obtained in step 2, and stir to obtain a low-solid water-based drilling fluid system for coalbed methane reservoir protection.

[0063] A third aspect of the present invention provides a use of the plugging agent provided by the present invention in reducing the penetration depth and filtration loss of drilling fluid in cracks in coalbed methane reservoirs.

[0064] The present invention adopts a plugging agent compounded with plugging agents of different particle sizes and strengths, such as flexible materials, rigid inorganic mineral materials and high molecular polymers, which can effectively reduce the penetration depth and filtration loss of drilling fluid in cracks. At the same time, the degradation products of the plugging agent acid dissolve the reservoir, which helps to reduce the coalbed methane backflow resistance and increase the coalbed methane production capacity.

[0065] After the water-based drilling fluid system provided by the present invention is used to plug coalbed methane micro-cracks, it will self-degrade over a period of time, reducing the density of the plugging agent entering the coalbed cracks. At the same time, the self-degradation products are water and carbon dioxide, which lower the pH around the plugging layer, dissolve the matrix, and facilitate backflow.

[0066] The present invention will be described in detail below through examples and comparative examples. In the following examples, unless otherwise specified, conventional methods are used; and the reagents and materials used, unless otherwise specified, can be obtained from commercial sources.

[0067] Example 1

[0068] The copolymer fluid loss additive is prepared according to the following method:

[0069] Add sodium styrene sulfonate and N-vinyl pyrrolidone to water at room temperature, stir until completely dissolved, and then adjust the pH of the solution to 7 with a pH regulator (sodium hydroxide). Add N-isopropylacrylamide and acryloyloxybutyltrimethylammonium chloride to the solution, reduce the solution temperature to 40°C, and fill the solution with nitrogen for 25 minutes. Add the first initiator and the second initiator dropwise to the mixed solution under stirring, stir evenly, seal, and maintain the solution temperature at 35°C. After constant temperature reaction for 4.5 hours, the gel product is sheared, dried at 105°C for 7 hours, and crushed (crusher speed 18000 rpm, crushing for 1.5 minutes) to obtain a copolymer fluid loss reducer. Among them,

[0070] The molar ratio of N-isopropylacrylamide, sodium styrene sulfonate, N-vinyl pyrrolidone and acryloyloxybutyltrimethylammonium chloride is 4:14:8:1; the weight ratio of the first initiator (ammonium persulfate), the second initiator (sodium bisulfite) and N-isopropylacrylamide is 0.28:0.1:1; and the weight ratio of the total weight of N-isopropylacrylamide, sodium styrene sulfonate, N-vinyl pyrrolidone and acryloyloxybutyltrimethylammonium chloride to water is 18:100.

[0071] This embodiment provides a water-based drilling fluid system suitable for coalbed methane reservoir protection. The water-based drilling fluid includes the following components:

[0072] 0.5 parts by weight of copolymer fluid loss reducer, 4 parts by weight of natural asphalt (softening point 90°C), 5 parts by weight of 5# industrial white oil, 20 parts by weight of sodium chloride, 0.1 parts by weight of calcium chloride, 0.1 parts by weight of calcium oxide, 5 parts by weight of polyglycolic acid (average particle size of 15 μm, weight-average molecular weight of 15,000 g / mol), 15 parts by weight of limestone (average particle size of 4 μm), 10 parts by weight of barite, and 100 parts by weight of water.

[0073] In this embodiment, the water-based drilling fluid is prepared by the following method:

[0074] Add copolymer filtrate reducer to water, stir and dissolve it completely, then add natural asphalt and 5# industrial white oil and stir for 5 minutes, then add sodium chloride, calcium chloride, calcium oxide and polyglycolic acid respectively, stir evenly, then add limestone and barite, and stir for 30 minutes to obtain storage-protection water-based drilling fluid.

[0075] Example 2

[0076] This embodiment provides a water-based drilling fluid system suitable for coalbed methane reservoir protection. The water-based drilling fluid includes the following components:

[0077] Copolymer fluid loss reducer (a copolymer fluid loss reducer was prepared according to the method in Example 1, except that the molar ratio of N-isopropylacrylamide, sodium styrene sulfonate, N-vinyl pyrrolidone and acryloyloxybutyltrimethylammonium chloride was 4:8.5:6:0.9), 1 part by weight of latex asphalt (softening point 100°C), 5 parts by weight of 7# industrial white oil, 4 parts by weight of potassium chloride, 18 parts by weight of calcium chloride, 0.12 parts by weight of calcium oxide, 0.05 parts by weight of polyvinyl alcohol (average particle size of 30 μm, weight average molecular weight of 40,000 g / mol), 17 parts by weight of limestone (average particle size of 10 μm), 20 parts by weight of barite, and 100 parts by weight of water.

[0078] In this embodiment, the water-based drilling fluid is prepared by the following method:

[0079] Add copolymer filtrate reducer to water, stir and dissolve it completely, then add latex asphalt and 7# industrial white oil and stir for 5 minutes, then add potassium chloride, calcium chloride, calcium oxide and polyvinyl alcohol respectively, stir evenly, then add limestone and barite, and stir for 30 minutes to obtain storage-protection water-based drilling fluid.

[0080] Example 3

[0081] This embodiment provides a water-based drilling fluid system suitable for coalbed methane reservoir protection. The water-based drilling fluid includes the following components:

[0082] Copolymer fluid loss reducer (a copolymer fluid loss reducer was prepared according to the method in Example 1, except that the molar ratio of N-isopropylacrylamide, sodium styrene sulfonate, N-vinylpyrrolidone and acryloyloxybutyltrimethylammonium chloride was 4:11:7:0.9), 2 parts by weight of latex asphalt (softening point 110°C), 4.5 parts by weight of 10# industrial white oil, 20 parts by weight of potassium chloride, 0.15 parts by weight of calcium chloride, 0.06 parts by weight of calcium oxide, 6 parts by weight of polyvinyl alcohol (average particle size of 45 μm, weight average molecular weight of 80,000 g / mol), 17 parts by weight of limestone (average particle size of 30 μm), 20 parts by weight of barite, and 100 parts by weight of water.

[0083] In this embodiment, the water-based drilling fluid is prepared by the following method:

[0084] Add copolymer filtrate reducer to water, stir and dissolve it completely, then add latex asphalt and 10# industrial white oil and stir for 5 minutes, then add potassium chloride, calcium chloride, calcium oxide and polyvinyl alcohol respectively, stir evenly, then add limestone and barite, and stir for 30 minutes to obtain storage-protection water-based drilling fluid.

[0085] Example 4

[0086] A water-based drilling fluid system was prepared according to the formulation and method of Example 3, except that the weight ratios of the structural units in the copolymer-based fluid loss additive were different. Specifically, the molar ratio of N-isopropylacrylamide, sodium styrenesulfonate, N-vinylpyrrolidone, and acryloyloxybutyltrimethylammonium chloride was replaced by a molar ratio of N-isopropylacrylamide, sodium styrenesulfonate, N-vinylpyrrolidone, and acryloyloxybutyltrimethylammonium chloride of 4:11:7:0.9, with a molar ratio of N-isopropylacrylamide, sodium styrenesulfonate, N-vinylpyrrolidone, and acryloyloxybutyltrimethylammonium chloride of 4:11:7:2.5. This produced a water-based drilling fluid.

[0087] Example 5

[0088] A water-based drilling fluid system was prepared according to the formula and method of Example 3, except that 10# industrial white oil was used instead of an equal weight of latex asphalt to obtain a water-based drilling fluid.

[0089] Example 6

[0090] A water-based drilling fluid system was prepared according to the formula and method of Example 3, except that latex asphalt with a different softening point was used. Specifically, "latex asphalt (softening point 40°C)" was used instead of "latex asphalt (softening point 110°C)" to prepare a water-based drilling fluid.

[0091] Example 7

[0092] A water-based drilling fluid system was prepared according to the formulation and method of Example 3, except that the weight ratio of latex asphalt to 10# industrial white oil was different. Specifically, 6 parts by weight of latex asphalt (softening point 110°C) and 4.5 parts by weight of 10# industrial white oil were replaced with 7 parts by weight of latex asphalt (softening point 110°C) and 3.5 parts by weight of 10# industrial white oil. A water-based drilling fluid was obtained.

[0093] Example 8

[0094] A water-based drilling fluid system was prepared according to the formula and method of Example 3, except that sepiolite (average particle size 33 μm) was used instead of an equal weight of limestone (average particle size 30 μm).

[0095] Example 9

[0096] A water-based drilling fluid system was prepared according to the formulation and method of Example 3, except that limestone with a different average particle size was used. Specifically, limestone with an average particle size of 1 μm was substituted for limestone with an average particle size of 30 μm. A water-based drilling fluid was obtained.

[0097] Example 10

[0098] A water-based drilling fluid system was prepared according to the formulation and method of Example 3, except that a different type of polymer was used. Specifically, polyvinyl alcohol (average particle size 45 μm, weight-average molecular weight 80,000 g / mol) was replaced with polystyrene (average particle size 45 μm, weight-average molecular weight 85,000 g / mol). This produced a water-based drilling fluid.

[0099] Example 11

[0100] A water-based drilling fluid system was prepared according to the formulation and method of Example 3, except that polyvinyl alcohols with different weight-average molecular weights were used. Specifically, polyvinyl alcohol (average particle size of 45 μm, weight-average molecular weight of 120,000 g / mol) was substituted for polyvinyl alcohol (average particle size of 45 μm, weight-average molecular weight of 80,000 g / mol). A water-based drilling fluid was obtained.

[0101] Example 12

[0102] A water-based drilling fluid system was prepared according to the formulation and method of Example 3, except that the average particle size of the polyvinyl alcohol was different. Specifically, polyvinyl alcohol (average particle size of 5 μm, weight-average molecular weight of 80,000 g / mol) was substituted for polyvinyl alcohol (average particle size of 45 μm, weight-average molecular weight of 80,000 g / mol). A water-based drilling fluid was obtained.

[0103] Example 13

[0104] A water-based drilling fluid system was prepared according to the formulation and method of Example 3, except that the molar ratios of the monomers in the copolymer-based fluid loss control agent were different. Specifically, when preparing the copolymer-based fluid loss control agent, the molar ratio of N-isopropylacrylamide, sodium styrenesulfonate, N-vinylpyrrolidone, and acryloyloxybutyltrimethylammonium chloride was replaced with a molar ratio of N-isopropylacrylamide, sodium styrenesulfonate, N-vinylpyrrolidone, and acryloyloxybutyltrimethylammonium chloride of 4:11:7:0.9. This produced a water-based drilling fluid.

[0105] Example 14

[0106] A water-based drilling fluid system was prepared according to the formulation and method of Example 3, except that the inorganic salts and / or metal oxides were used in different combinations. Specifically, 20 parts by weight of potassium chloride, 0.15 parts by weight of calcium chloride, and 0.06 parts by weight of calcium oxide were replaced with 20 parts by weight of calcium chloride and 0.21 parts by weight of calcium oxide. This resulted in a water-based drilling fluid.

[0107] Example 15

[0108] A water-based drilling fluid system was prepared according to the formulation and method of Example 3, except that the proportions of the components in the inorganic salts and / or metal oxides were different. Specifically, "20 parts by weight of potassium chloride, 0.06 parts by weight of calcium chloride, and 0.15 parts by weight of calcium oxide" were replaced with "20 parts by weight of potassium chloride, 0.15 parts by weight of calcium chloride, and 0.06 parts by weight of calcium oxide." This produced a water-based drilling fluid.

[0109] Example 16

[0110] A water-based drilling fluid system was prepared according to the formula and method of Example 3, except that the weight ratio of the plugging agent to the water-based drilling fluid base slurry was different. The specific formula is as follows:

[0111] A water-based drilling fluid was prepared by mixing 2 parts by weight of a copolymer fluid loss control agent (prepared according to the method in Example 3), 2 parts by weight of latex asphalt (110° C.), 1.5 parts by weight of 10# industrial white oil, 20 parts by weight of potassium chloride, 0.15 parts by weight of calcium chloride, 0.06 parts by weight of calcium oxide, 2 parts by weight of polyvinyl alcohol (average particle size of 45 μm, weight-average molecular weight of 80,000 g / mol), 5.7 parts by weight of limestone (average particle size of 30 μm), 20 parts by weight of barite, and 100 parts by weight of water.

[0112] Example 17

[0113] A water-based drilling fluid system was prepared according to the formulation and method of Example 3, except that a different polymer was used. Specifically, polyvinyl chloride (average particle size 45 μm, weight-average molecular weight 80,000 g / mol) was substituted for polyvinyl alcohol (average particle size 45 μm, weight-average molecular weight 80,000 g / mol). This produced a water-based drilling fluid.

[0114] Comparative Example 1

[0115] A water-based drilling fluid system was prepared according to the formula and method of Example 3, except that latex asphalt and 10# industrial white oil were replaced with equal parts by weight of limestone (average particle size of 30 μm) to prepare a water-based drilling fluid.

[0116] Comparative Example 2

[0117] A water-based drilling fluid system was prepared according to the formula and method of Example 3, except that latex asphalt and 10# industrial white oil were replaced with equal parts by weight of rubber material (average particle size of 30 μm) to prepare a water-based drilling fluid.

[0118] Test Case

[0119] The rheological properties and sand bed invasion depth of the drilling fluid were evaluated according to the rheological properties test procedures and plugging test methods specified in "SY / T 5621 Drilling Fluid Test Procedure" and "SY / T 5840 Indoor Test Methods for Bridging and Plugging Materials for Drilling Fluids". The results are shown in Table 1.

[0120] Table 1

[0121]

[0122] The results in Table 1 show that the density of the drilling fluids obtained in Examples 1-3 of the present invention is 1.2-1.45 g / cm 3 , dynamic shear force is 5-9.5Pa, initial / final shear force is 2-3Pa / 7-9Pa, and dynamic plastic ratio is 0.36-0.41; the system is suitable for drilling in coalbed methane reservoirs with a width of ≤100μm, has a good plugging effect, and plays a role in real-time plugging of micro-cracks; the system meets the requirements of coalbed methane reservoir protection and drilling within 120°C. In addition, in Comparative Example 1, latex asphalt and industrial white oil are replaced by limestone in equal parts by weight. Compared with Example 1-17, the plugging effect is significantly reduced. In Comparative Example 2, latex asphalt and industrial white oil are replaced by rubber materials in equal parts by weight. Compared with Example 1-17, the plugging effect is significantly reduced, and the depth of entry into the sand bed is significantly increased.

[0123] Furthermore, the weight ratio of the structural units in the copolymer-based fluid loss additive in Example 4 was outside the optimal range. Compared with Example 3, the fluid loss reduction effect was weakened, the sand bed penetration depth increased, and the system's plugging while drilling performance deteriorated. In Example 5, the flexible material used only white oil and did not contain asphalt. Compared with Example 3, the sand bed penetration depth increased, and the plugging effect weakened. In Example 6, the softening point of the latex asphalt in the flexible material was outside the optimal range. Compared with Example 3, the medium-pressure fluid loss and sand bed plugging effect at room temperature did not change significantly, but the plugging effect was significantly reduced under high-temperature and high-pressure conditions. In Example 7, the weight ratio of emulsified asphalt to white oil was outside the optimal range. Compared with Example 3, the medium-pressure and high-temperature and high-pressure fluid loss increased, and the sand bed penetration depth increased. In Example 8, the inorganic mineral material was sepiolite, a non-preferred material. Compared with Example 3, the wellbore thickening and plugging effect decreased. In Example 9, the limestone particle size was outside the optimal range. Compared with Example 3, the plugging effect decreased, and the fluid loss and sand bed penetration depth both increased. The high molecular weight polymer selected in Example 10 is a non-preferred material. Compared with Example 3, the pH value increased after degradation, and the degradation effect became worse. The weight-average molecular weight of polyvinyl alcohol in Example 11 is not within the most preferred range. Compared with Example 3, the pH value increased after degradation. The average particle size of polyvinyl alcohol in Example 12 is not within the most preferred range. Compared with Example 3, the depth of entry into the sand bed increased. The molar ratio of each monomer of the copolymer-type fluid loss reducer in Example 13 is not within the most preferred range. Compared with Example 3, the fluid loss increased and the sand bed plugging effect decreased. The combination of inorganic salts and / or metal oxides in Example 14 does not meet the most preferred requirements. Compared with Example 3, the flow pattern deteriorated, the fluid loss increased, the depth of entry into the sand bed increased, and the pH value increased after degradation. The proportions of each component in the inorganic salts and / or metal oxides in Example 15 are not within the most preferred range. Compared with Example 3, the flow pattern deteriorated, the depth of entry into the sand bed increased, and the fluid loss increased significantly. In Example 16, the weight ratio of the plugging agent to the water-based drilling fluid base slurry was not within the optimal range. Compared with Example 3, the fluid loss increased, and the sand bed plugging effect decreased. The type of polymer used in Example 17 did not meet the optimal range. Compared with Example 3, the fluid loss increased, the sand bed plugging effect decreased, and the pH value increased after degradation. This shows that when the weight ratio of the structural units in the copolymer-based fluid loss reducer, the combination of the flexible material, the type and particle size of the inorganic mineral material, the type, weight-average molecular weight, and average particle size of the polymer, the combination of the inorganic salt and / or metal oxide, and the weight ratio of the plugging agent to the water-based drilling fluid base slurry meet the optimal conditions, the plugging and degradation effects can be further improved.

[0124] The preferred embodiments of the present invention have been described in detail above, but the present invention is not limited thereto. Within the technical concept of the present invention, various simple variations of the technical solution of the present invention may be made, including combining the various technical features in any other appropriate manner. These simple variations and combinations should also be regarded as disclosed in the present invention and fall within the scope of protection of the present invention.

Claims

1. A plugging agent, characterized in that: The plugging agent includes: flexible materials, rigid inorganic mineral materials and high molecular polymers; wherein, The flexible material is selected from asphalt and / or white oil.

2. The plugging agent according to claim 1, characterized in that In the plugging agent, the weight ratio of the flexible material, the rigid inorganic mineral material and the high molecular polymer is 10:(5-20):(5-10).

3. The plugging agent according to claim 1 or 2, characterized in that: The flexible material is a mixture of asphalt and white oil; Preferably, in the flexible material, the weight ratio of the asphalt to the white oil is (0.3-3):1, preferably (0.5-1.5):1; Preferably, the softening point of the asphalt is 60-150°C, preferably 60-120°C; Preferably, the asphalt is selected from at least one of natural asphalt, emulsified asphalt and sulfonated asphalt, preferably natural asphalt and / or emulsified asphalt; Preferably, the flexible material is a mixture of natural asphalt and / or emulsified asphalt and white oil.

4. The plugging agent according to any one of claims 1 to 3, characterized in that: The average particle size of the rigid inorganic mineral material is 3-50 μm; Preferably, the rigid inorganic mineral material is selected from at least one of limestone, calcium carbonate, magnesium carbonate and magnesite powder, preferably selected from limestone and / or calcium carbonate; Preferably, the high molecular polymer is selected from at least one of polyvinyl alcohol, polyglycolic acid and polybutylene succinate, preferably selected from polyvinyl alcohol and / or polyglycolic acid; Preferably, the weight average molecular weight of the high molecular weight polymer is 10,000-95,000 g / mol; Preferably, the average particle size of the high molecular polymer is 7-50 μm.

5. A water-based drilling fluid system, characterized in that: The water-based drilling fluid system comprises: a water-based drilling fluid base slurry and the plugging agent according to any one of claims 1 to 4; Preferably, in the water-based drilling fluid system, the weight ratio of the water-based drilling fluid base slurry to the plugging agent is (2.8-11):

1.

6. The water-based drilling fluid system according to claim 5, characterized in that: The water-based drilling fluid base slurry includes a fluid loss reducer, an inorganic salt and / or a metal oxide, and water; Preferably, in the water-based drilling fluid slurry, based on 100 parts by weight of water, the weight portions of the fluid loss reducer, inorganic salt and / or metal oxide are 0.5-2.5 parts and 10-25 parts respectively.

7. The water-based drilling fluid system according to claim 6, characterized in that: The fluid loss reducer is selected from copolymer fluid loss reducers; Preferably, the copolymer fluid loss additive contains a structural unit derived from N-isopropylacrylamide, a structural unit derived from sodium styrene sulfonate, a structural unit derived from N-vinylpyrrolidone, and a structural unit derived from acryloyloxybutyltrimethylammonium chloride; Preferably, in the copolymer-based fluid loss additive, the molar ratio of the structural unit derived from N-isopropylacrylamide, the structural unit derived from sodium styrene sulfonate, the structural unit derived from N-vinylpyrrolidone, and the structural unit derived from acryloyloxybutyltrimethylammonium chloride is 4:(6-15):(4-10):(0.5-2), preferably 4:(6-14):(4-8):(0.5-1.6); Preferably, the weight average molecular weight of the copolymer-based fluid loss additive is 300,000-500,000 g / mol.

8. The water-based drilling fluid system according to claim 6 or 7, characterized in that: The inorganic salt and / or metal oxide is selected from at least one of sodium chloride, potassium chloride, sodium formate, potassium formate, cesium formate, calcium chloride and calcium oxide, preferably at least one of sodium chloride, potassium chloride, sodium formate, potassium formate, calcium chloride and calcium oxide.

9. The water-based drilling fluid system according to any one of claims 6 to 8, characterized in that: The water-based drilling fluid slurry further includes a weighting agent; Preferably, in the water-based drilling fluid slurry, the weighting agent is contained in an amount of 10-25 parts by weight based on 100 parts by weight of water; Preferably, the weighting agent is selected from at least one of barite, micromanganese ore powder and hematite powder, preferably selected from barite and / or micromanganese ore powder.

10. Use of the plugging agent according to any one of claims 1 to 4 in reducing the penetration depth and fluid loss of drilling fluid in cracks of coalbed methane reservoirs.

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