Soil-phase-free low-damage fractured reservoir protection drilling fluid and preparation method thereof

Abstract

The invention discloses a soil-phase-free low-damage fractured reservoir protection drilling fluid and a preparation method thereof, the rheological property of the soil-phase-free low-damage fractured reservoir protection drilling fluid can well meet the drilling requirements, and the API (American Petroleum Institute) filter loss and high-temperature and high-pressure filter loss of the drilling fluid can be obviously reduced. The problems of high solid phase content and high solid phase dissolvability in the prior art are solved.

Description

Technical Field

[0001] The invention belongs to the field of drilling, and in particular relates to a soil-free low-damage fractured reservoir protection drilling fluid, and also relates to a preparation method of the drilling fluid. Background Art

[0002] Drilling and completion fluid reservoir protection technology is a key technology to achieve drilling geological goals, improve single well productivity and reservoir utilization. Conventional reservoir protection technology usually adds oil-soluble resins or acid-soluble extremely matched calcium carbonate to the drilling and completion fluid to shield and temporarily plug the reservoir pores, and uses oil dissolution or acid dissolution during production transformation to restore reservoir permeability. However, for gas reservoirs, especially fractured gas reservoirs, the shielding and temporary plugging ability of conventional reservoir protection drilling fluids cannot meet the reservoir protection requirements. This is because in gas reservoirs, the solubility rate of oil-soluble resins is greatly reduced, while granular acid-soluble temporary plugging agents such as calcium carbonate have low shielding ability for fractures. In addition, acid-soluble plugging agents must rely on acidification transformation after completion to achieve reservoir protection effects, and not all wells carry out acidification transformation measures, which also limits their scope of application.

[0003] In order to improve the reservoir protection effect of reservoir protection drilling fluid on oil and gas reservoirs, especially fractured oil and gas reservoirs, and improve the applicability of reservoir protection drilling fluid in the drilling and completion processes of gas reservoirs and oil and gas reservoirs that have not been acidified, it is necessary to develop a reservoir protection drilling fluid system with low solid content, high solid solubility rate, the ability to efficiently plug fractured gas reservoirs, and the ability to degrade under in situ conditions such as reservoir temperature and pressure. Summary of the invention

[0004] The purpose of the present invention is to provide a soil-free, low-damage fractured reservoir protection drilling fluid, which solves the problems of high solid content and high solid solubility in the prior art.

[0005] Another object of the present invention is to provide a method for preparing the above-mentioned drilling fluid.

[0006] The technical scheme adopted by the present invention is that the soil-free low-damage fractured reservoir protection drilling fluid is composed of the following raw materials in parts by weight: 10,000 parts of water, 50-300 parts of polymer flow pattern regulator, 20-30 parts of sodium bicarbonate, 10-20 parts of sodium hydroxide, 300-500 parts of friction reducer, 30-50 parts of metal ion shear enhancer, 300-500 parts of degradable fluid loss reducer, 500-800 parts of composite inhibitor, 50-150 parts of waterproof locking agent, 100-300 parts of composite temporary plugging agent and 0-12,000 parts of acid-soluble weighting agent.

[0007] The present invention is also characterized in that:

[0008] The polymer flow pattern regulator is one or more of hydrophobic associating polymers, dendritic polymers, and hyperbranched resins, and the friction reducing agent is one or more of polymer alcohols, fatty acid esters, graphite, and mineral oils.

[0009] The metal ion cutting agent can be Zn 2+ 、Al 3+ Cr 3+ , Ca 2+ Mg 2+ The degradable plugging agent may be a mixture of one or more of starch, modified starch, polylactic acid powder, and polyester polymer materials in any proportion.

[0010] The composite inhibitor can be a mixture of one or more of polyacrylamide potassium salt, potassium chloride, sodium formate and potassium formate in any proportion, and the waterproof lock agent can be a mixture of one or more of anionic surfactants, cationic surfactants, nonionic surfactants, silicon-containing surfactants and fluorine-containing surfactants in any proportion.

[0011] The oil-soluble temporary plugging agent can be one or a combination of C5 petroleum resin, C9 petroleum resin, a copolymer of C5 and C9 petroleum resin, and the acid-soluble weighting agent can be limestone or manganese tetraoxide.

[0012] Another technical solution adopted by the present invention is a method for preparing a soil-free low-damage fractured reservoir protection drilling fluid, which is specifically implemented according to the following steps:

[0013] Step 1: First, add a polymer flow regulator into water, then add sodium bicarbonate into the water, stir until completely uniform at room temperature, and stand for 24-48 hours to obtain a drilling fluid base slurry;

[0014] Step 2: Stir the drilling fluid base slurry, and add sodium hydroxide, friction reducer, metal ion shear enhancer, degradable filtration reducer, composite inhibitor, waterproof lock agent, composite temporary plugging agent, acid-soluble weighting agent into it in sequence to obtain a soil-free, low-damage fracture reservoir protection drilling fluid.

[0015] Another technical solution of the present invention is also characterized in that:

[0016] The polymeric flow pattern regulator is one or more of a hydrophobic associating polymer, a dendritic polymer, and a hyperbranched resin.

[0017] The acid-soluble weighting agent is limestone or manganese tetraoxide.

[0018] The particle size of manganese tetraoxide is less than 10 μm, and the density is ≥ 4.7 g / cm 3

[0019] The beneficial effects of the present invention are:

[0020] The present invention provides a soil-free low-damage fractured reservoir protective drilling fluid and a preparation method thereof. The rheological properties of the soil-free low-damage fractured reservoir protective drilling fluid can well meet drilling requirements, and can significantly reduce the API filtration loss and high-temperature and high-pressure filtration loss of the drilling fluid. In addition, the solid-phase oil-solubility and acid-solubility of the soil-free low-damage fractured reservoir protective drilling fluid is 96.52%, and the solid-phase particle damage can be eliminated through subsequent production and transformation processes, thereby increasing the permeability recovery value of the reservoir and reducing the skin coefficient. Permeability recovery value determination experiments have shown that the permeability recovery value of the soil-free low-damage fractured reservoir protective drilling fluid after oil dissolution is 13.85% higher than that of general drilling fluid, and the permeability recovery value of the soil-free low-damage fractured reservoir protective drilling fluid after biodegradation is further increased to 95.88%. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 It is a pressure curve trend diagram of general drilling fluid;

[0022] Figure 2 It is a pressure curve change trend diagram of the drilling fluid for protecting the soil-free low-damage fractured reservoir. DETAILED DESCRIPTION

[0023] The present invention is described in detail below with reference to the accompanying drawings and specific embodiments.

[0024] The invention is used for preparing a soil-free low-damage fracture reservoir protection drilling fluid, which contains a polymer flow pattern regulator, sodium bicarbonate, sodium hydroxide, a friction and drag reducing agent, a metal ion shearing agent, a degradable fluid loss reducer, a composite inhibitor, a waterproof locking agent, a composite temporary plugging agent and an acid-soluble weighting agent. Based on 10,000 parts by weight of water, the polymer flow pattern regulator is 50-300 parts, the sodium bicarbonate is 20-30 parts, the sodium hydroxide is 10-20 parts, the friction and drag reducing agent is 300-500 parts, the metal ion shearing agent is 30-50 parts, the degradable fluid loss reducer is 300-500 parts, the composite inhibitor is 500-800 parts, the waterproof locking agent is 50-150 parts, the composite temporary plugging agent is 100-300 parts, and the acid-soluble weighting agent is 0-12,000 parts. The polymer flow pattern regulator can be one or a combination of hydrophobic associating polymers, dendritic polymers, and hyperbranched resins.

[0025] Preferably, the hydrophobically associating polymer may be one or more of acrylamide (AM)-acrylic acid (AA)-methylpropanesulfonic acid (AMPS) copolymer, dodecyl methacrylamide (PEDMAM)-acrylic acid (AA)-methylpropanesulfonic acid (AMPS) copolymer, acrylamide (AM)-methacryloyloxyethyltrimethylammonium chloride (DMC)-dimethyldiallylammonium chloride (DMDAAC) copolymer, and each of the hydrophobically associating polymers has a molecular weight of ≥30,000 and a critical associating concentration of ≤800 mg / L;

[0026] Preferably, the dendrimer is an ethylenediamine core dendrimer, and the molecular weight of the preferred ethylenediamine core dendrimer is ≥6000, the terminal groups include -COOCH3, -COONa, -NH2, and the number of terminal groups is ≥30;

[0027] Preferably, the hyperbranched resin includes one or more of hyperbranched acrylic resin, hyperbranched polyamide, and hyperbranched polyhydroxy organic acid polyester, and each hyperbranched resin has a molecular weight of ≥350 g / mol and a viscosity of ≥500 cP;

[0028] The friction reducing agent can be one or more of polyol, fatty acid ester, graphite, and mineral oil. The preferred friction reducing agent is a mixture of polyol and graphite in any proportion.

[0029] Preferably, the effective content of the polyol is ≥99% and the hydroxyl value is ≥25;

[0030] Preferably, the lubricity coefficient reduction rate of the graphite is ≥40%, and the water content is ≤10%.

[0031] The metal ion cutting agent can be Zn 2+ 、Al 3+ Cr 3+ , Ca 2+ Mg 2+ One or both of the following.

[0032] The degradable plugging agent can be one or a mixture of several of starch, modified starch, polylactic acid powder, and polyester polymer materials in any proportion.

[0033] Preferably, the effective content of starch and modified starch is ≥90%, and the API fluid loss reduction rate is ≥20%;

[0034] Preferably, the molecular weight of the polylactic acid powder and the polyester polymer material is ≥ 8 million, and the API filtration loss reduction rate is ≥ 20%.

[0035] The composite inhibitor can be a mixture of one or more of polyacrylamide potassium salt, potassium chloride, sodium formate and potassium formate in any proportion.

[0036] The waterproof lock agent can be a mixture of one or more of anionic surfactants, cationic surfactants, nonionic surfactants, silicon-containing surfactants and fluorine-containing surfactants in any proportion.

[0037] Preferably, the surface tension of anionic surfactants, cationic surfactants and nonionic surfactants is ≤30mN / N, and the foaming rate is ≤5%;

[0038] Preferably, the surface tension of the silicon-containing surfactant and the fluorine-containing surfactant is ≤25mN / N, and the foaming rate is ≤5%;

[0039] The oil-soluble temporary plugging agent may be one or a combination of C5 petroleum resin, C9 petroleum resin, a copolymer of C5 and C9 petroleum resin.

[0040] The acid-soluble weighting agent may be limestone or manganese tetraoxide;

[0041] Preferably, the limestone has different particle size distributions and a consistency of ≥95% with the formation pore diameter distribution;

[0042] Preferably, the particle size of manganese tetraoxide is less than 10 μm and the density is ≥ 4.7 g / cm 3 .

[0043] Preferably, the acid-soluble weighting agent is added when the density of the drilling fluid is less than 1.68 g / cm 3 When the density of drilling fluid is greater than 1.68g / cm 3 Manganese tetraoxide is used as an acid-soluble weighting agent.

[0044] When the density of drilling fluid is greater than 1.68g / cm 3 When using manganese tetraoxide as an acid-soluble weighting agent, the density of manganese tetraoxide is 4.8g / cm 3 The density of conventional barite weighting agent is 4.2g / cm 3 When the drilling fluid of the same density is prepared, the use of manganese tetraoxide can reduce the solid content in the drilling fluid. In addition, the use of polymer instead of bentonite in the drilling fluid can also reduce the solid content of the drilling fluid. At the same time, the acid solubility of the weighting agent manganese tetraoxide and limestone powder is more than 90%, and the filtration reducer and composite temporary plugging agent used can be acid-soluble or degraded, which can greatly increase the solubility rate of the solid phase.

[0045] The method for preparing a soil-free low-damage fractured reservoir protection drilling fluid comprises the following steps:

[0046] Step 1: first add a polymer flow regulator into water, then add sodium bicarbonate thereto, and stir at room temperature until completely uniform to obtain a drilling fluid base slurry;

[0047] Preferably, the drilling fluid base slurry is measured. If the density of the drilling fluid is less than 1.07 g / cm 3 , then there is no need to add acid-soluble weighting agent. When the drilling fluid density is not less than 1.07g / cm 3 Acid soluble weighting agents are only needed when

[0048] Preferably, when the density of the drilling fluid is less than 1.68 g / cm 3 When the density of drilling fluid is greater than 1.68g / cm 3 Manganese tetraoxide is used as an acid-soluble weighting agent.

[0049] Step 2: While stirring the drilling fluid base slurry, sodium hydroxide, friction reducer, metal ion shear enhancer, degradable fluid loss reducer, composite inhibitor, waterproof lock agent, composite temporary plugging agent, acid-soluble weighting agent are added thereto in sequence to obtain a soil-free, low-damage fracture reservoir protection drilling fluid.

[0050] Preferably, the density of the drilling fluid is measured and the type of the weighting agent is selected before adding the weighting agent in step 2.

[0051] Preferably, the curing time in step 1 is 24-48 hours, the stirring speed in step 2 is 9000-11000 r / min, and the stirring time is 20-40 min.

[0052] Example 1

[0053] This embodiment provides a method for preparing a soil-free, low-damage fractured reservoir protection drilling fluid, and the specific steps are as follows:

[0054] Step 1: Add 30 parts by weight of sodium carbonate into 10,000 parts by weight of water while stirring until the sodium carbonate is completely dissolved;

[0055] Step 2: The aqueous solution is placed in a high stirring cup, stirred at a speed of 8000 r / min, and 50 parts by weight of dodecyl methacrylamide (PEDMAM)-acrylic acid (AA)-methylpropane sulfonic acid (AMPS) copolymer, 20 parts by weight of ethylenediamine core dendritic polymer, and 30 parts by weight of hyperbranched acrylic resin are added in sequence, and then stirred at room temperature for 120 minutes to obtain a drilling fluid base slurry.

[0056] Among them: the molecular weight of the copolymer of dodecyl methacrylamide (PEDMAM)-acrylic acid (AA)-methylpropane sulfonic acid (AMPS) is 45,000, and the critical association concentration is 365 mg / L; the molecular weight of the ethylenediamine core dendrimer is 7,700, the terminal groups are -COONa and -NH2, and the number of terminal groups is 67; the molecular weight of the hyperbranched acrylic resin is 408 g / mol, and the viscosity is 572 cP;

[0057] Step 3: placing the drilling fluid base slurry in a high stirring cup, stirring at a speed of 11000 r / min, and adding 3 parts by weight of aluminum citrate shearing agent under stirring;

[0058] Step 4: placing the drilling fluid base slurry in a high stirring cup, stirring at a speed of 11000 r / min, and adding 15 parts by mass of caustic soda according to the alkali-sensitive critical pH value determined in the sensitivity experiment of the reservoir under stirring conditions, so that the pH value of the drilling fluid is less than the critical pH value;

[0059] Step 5: Continue to add 300 parts by weight of polyol and 100 parts by weight of graphite to the drilling fluid at a stirring speed of 11000 r / min.

[0060] Wherein: the effective content of the polyol is 99%, and the hydroxyl value is 28; the lubricity coefficient reduction rate of the graphite is ≥40%, and the water content is ≤10%;

[0061] Step 6: Continue to add 200 parts by mass of sodium carboxymethyl starch ([C6H7O2(OH)2OCH2COONa]n) and 200 parts of polylactic acid powder to the above drilling fluid at a stirring speed of 11000 r / min, and control the medium-pressure filtration loss of the drilling fluid to below 4, wherein: the effective content of the sodium carboxymethyl starch is 92%, and the API filtration loss reduction rate is 35%; the molecular weight of the polylactic acid powder is 11 million, and the API filtration loss reduction rate is 37%;

[0062] Step 7: Continue to add 100 parts by weight of potassium polyacrylamide and 600 parts by weight of sodium formate to the drilling fluid at a stirring speed of 11000 r / min.

[0063] Step 8: Continue to add 50 parts by weight of a waterproofing agent sodium dodecylbenzene sulfonate and 50 parts by weight of an organic silicon waterproofing agent to the drilling fluid at a stirring speed of 11000 r / min.

[0064] Wherein: the surface tension of the sodium dodecylbenzene sulfonate is 30mN / N, and the foaming rate is 5%; the surface tension of the silicone is 23mN / N, and the foaming rate is 0;

[0065] Step 9: Continue to add 100 parts by weight of a modified product of C5 petroleum resin to the drilling fluid at a stirring speed of 11000 r / min, wherein the oil solubility of the petroleum resin is 94%;

[0066] Step 10: Continue to add limestone to the above drilling fluid at a stirring speed of 11000r / min to make the density of the drilling fluid reach 1.20g / cm3. The limestone is compounded by limestones of different particle sizes, and the compounding mass ratio is 1000 mesh: 500 mesh: 100 mesh = 15%: 35%: 50%, to obtain a soil-free, low-damage fractured reservoir protection drilling fluid.

[0067] The condition for adding acid-soluble weighting agent is that when the density of drilling fluid is less than 1.68g / cm 3 When the density of drilling fluid is greater than 1.68g / cm 3 Manganese tetraoxide is used as an acid-soluble weighting agent.

[0068] Example 2

[0069] The present embodiment provides a soil-free, low-damage fractured reservoir protection drilling fluid, which is composed of the following raw materials in parts by weight: 10,000 parts of water, 50-300 parts of a polymer flow pattern regulator, 20-30 parts of sodium bicarbonate, 10-20 parts of sodium hydroxide, 300-500 parts of a friction reducer, 30-50 parts of a metal ion shear enhancer, 300-500 parts of a degradable fluid loss reducer, 500-800 parts of a composite inhibitor, 50-150 parts of a waterproof locking agent, 100-300 parts of a composite temporary plugging agent, and 0-12,000 parts of an acid-soluble weighting agent.

[0070] The acid-soluble weighting agent is limestone or manganese tetraoxide.

[0071] When the required drilling fluid density is lower than 1.07 g / cm3, the acid-soluble weighting agent is added in an amount of 0. When the required drilling fluid density is not less than 1.07 g / cm3, the acid-soluble weighting agent needs to be added.

[0072] Example 3

[0073] This embodiment provides a method for preparing a soil-free, low-damage fractured reservoir protection drilling fluid, and the specific steps are as follows:

[0074] Step 1: Add 30 parts by weight of sodium carbonate into 10,000 parts by weight of water while stirring until the sodium carbonate is completely dissolved;

[0075] Step 2: Place the above aqueous solution in a high stirring cup, stir at a speed of 8000 r / min, and add 50 parts by weight of dodecyl methacrylamide (PEDMAM)-acrylic acid (AA)-methylpropane sulfonic acid (AMPS) copolymer, 20 parts by weight of ethylenediamine core dendritic polymer, and 30 parts by weight of hyperbranched acrylic resin in sequence, and then continue stirring at room temperature for 120 minutes to obtain a drilling fluid base slurry.

[0076] Among them: the molecular weight of the copolymer of dodecyl methacrylamide (PEDMAM)-acrylic acid (AA)-methylpropane sulfonic acid (AMPS) is 45,000, and the critical association concentration is 365 mg / L; the molecular weight of the ethylenediamine core dendrimer is 7,700, the terminal groups are -COONa and -NH2, and the number of terminal groups is 67; the molecular weight of the hyperbranched acrylic resin is 408 g / mol, and the viscosity is 572 cP;

[0077] Step 3: placing the drilling fluid base slurry in a high stirring cup, stirring at a speed of 11000 r / min, and adding 3 parts by weight of aluminum citrate shearing agent under stirring;

[0078] Step 4: placing the drilling fluid base slurry in a high stirring cup, stirring at a speed of 11000 r / min, and adding 15 parts by mass of caustic soda according to the alkali-sensitive critical pH value determined in the sensitivity experiment of the reservoir under stirring conditions, so that the pH value of the drilling fluid is less than the critical pH value;

[0079] Step 5: Continue to add 300 parts by weight of polyol and 100 parts by weight of graphite to the drilling fluid at a stirring speed of 11000 r / min.

[0080] Wherein: the effective content of the polyol is 99%, and the hydroxyl value is 28; the lubricity coefficient reduction rate of the graphite is ≥40%, and the water content is ≤10%;

[0081] Step 6: Continue to add 200 parts by mass of sodium carboxymethyl starch ([C6H7O2(OH)2OCH2COONa]n) and 200 parts of polylactic acid powder to the above drilling fluid at a stirring speed of 11000 r / min, and control the medium-pressure filtration loss of the drilling fluid to below 4, wherein: the effective content of the sodium carboxymethyl starch is 92%, and the API filtration loss reduction rate is 35%; the molecular weight of the polylactic acid powder is 11 million, and the API filtration loss reduction rate is 37%;

[0082] Step 7: Continue to add 100 parts by weight of potassium polyacrylamide and 600 parts by weight of sodium formate to the drilling fluid at a stirring speed of 11000 r / min.

[0083] Step 8: Continue to add 50 parts by weight of secondary amine salt of waterproof lock agent and 50 parts by weight of organic silicon waterproof lock agent to the above drilling fluid at a stirring speed of 11000 r / min.

[0084] Wherein: the secondary amine salt is 30mN / N, and the foaming rate is 5%; the surface tension of the organic silicon is 23mN / N, and the foaming rate is 0;

[0085] Step 9: Continue to add 100 parts by weight of a modified product of C5 petroleum resin to the drilling fluid at a stirring speed of 11000 r / min, wherein the oil solubility of the petroleum resin is 94%;

[0086] Step 10: Continue to add limestone to the above drilling fluid at a stirring speed of 11000r / min to make the density of the drilling fluid reach 1.20g / cm3. The limestone is compounded by limestones of different particle sizes, and the compounding mass ratio is 1000 mesh: 500 mesh: 100 mesh = 15%: 35%: 50%, to obtain a soil-free, low-damage fractured reservoir protection drilling fluid.

[0087] The condition for adding acid-soluble weighting agent is that when the density of drilling fluid is less than 1.68g / cm 3 When the density of drilling fluid is greater than 1.68g / cm 3 Manganese tetraoxide is used as an acid-soluble weighting agent.

[0088] Example 4

[0089] This embodiment provides a method for preparing a soil-free, low-damage fractured reservoir protection drilling fluid, and the specific steps are as follows:

[0090] Step 1: Add 30 parts by weight of sodium carbonate into 10,000 parts by weight of water while stirring until the sodium carbonate is completely dissolved;

[0091] Step 2: Place the above aqueous solution in a high stirring cup, stir at a speed of 8000 r / min, and add 50 parts by weight of dodecyl methacrylamide (PEDMAM)-acrylic acid (AA)-methylpropane sulfonic acid (AMPS) copolymer, 20 parts by weight of ethylenediamine core dendritic polymer, and 30 parts by weight of hyperbranched acrylic resin in sequence, and then continue stirring at room temperature for 120 minutes to obtain a drilling fluid base slurry.

[0092] Among them: the molecular weight of the copolymer of dodecyl methacrylamide (PEDMAM)-acrylic acid (AA)-methylpropane sulfonic acid (AMPS) is 45,000, and the critical association concentration is 365 mg / L; the molecular weight of the ethylenediamine core dendrimer is 7,700, the terminal groups are -COONa and -NH2, and the number of terminal groups is 67; the molecular weight of the hyperbranched acrylic resin is 408 g / mol, and the viscosity is 572 cP;

[0093] Step 3: placing the drilling fluid base slurry in a high stirring cup, stirring at a speed of 11000 r / min, and adding 3 parts by weight of aluminum citrate shearing agent under stirring;

[0094] Step 4: placing the drilling fluid base slurry in a high stirring cup, stirring at a speed of 11000 r / min, and adding 15 parts by mass of caustic soda according to the alkali-sensitive critical pH value determined in the sensitivity experiment of the reservoir under stirring conditions, so that the pH value of the drilling fluid is less than the critical pH value;

[0095] Step 5: Continue to add 300 parts by weight of polyol and 100 parts by weight of graphite to the drilling fluid at a stirring speed of 11000 r / min.

[0096] Wherein: the effective content of the polyol is 99%, and the hydroxyl value is 28; the lubricity coefficient reduction rate of the graphite is ≥40%, and the water content is ≤10%;

[0097] Step 6: Continue to add 200 parts by mass of sodium carboxymethyl starch ([C6H7O2(OH)2OCH2COONa]n) and 200 parts of polylactic acid powder to the above drilling fluid at a stirring speed of 11000 r / min, and control the medium-pressure filtration loss of the drilling fluid to below 4, wherein: the effective content of the sodium carboxymethyl starch is 92%, and the API filtration loss reduction rate is 35%; the molecular weight of the polylactic acid powder is 11 million, and the API filtration loss reduction rate is 37%;

[0098] Step 7: Continue to add 100 parts by weight of potassium polyacrylamide and 600 parts by weight of sodium formate to the drilling fluid at a stirring speed of 11000 r / min.

[0099] Step 8: Continue to add 50 parts by weight of a waterproof locking agent fatty alcohol polyoxyethylene ether and 50 parts by weight of an organosilicon waterproof locking agent to the above drilling fluid at a stirring speed of 11000 r / min.

[0100] Wherein: the fatty alcohol polyoxyethylene ether salt is 30mN / N, and the foaming rate is 5%; the surface tension of the organic silicon is 23mN / N, and the foaming rate is 0;

[0101] Step 9: Continue to add 100 parts by weight of a modified product of C5 petroleum resin to the drilling fluid at a stirring speed of 11000 r / min, wherein the oil solubility of the petroleum resin is 94%;

[0102] Step 10: Continue to add limestone to the above drilling fluid at a stirring speed of 11000r / min to make the density of the drilling fluid reach 1.20g / cm3. The limestone is compounded by limestones of different particle sizes, and the compounding mass ratio is 1000 mesh: 500 mesh: 100 mesh = 15%: 35%: 50%, to obtain a soil-free, low-damage fractured reservoir protection drilling fluid.

[0103] The condition for adding acid-soluble weighting agent is that when the density of drilling fluid is less than 1.68g / cm 3 When the density of drilling fluid is greater than 1.68g / cm 3 Manganese tetraoxide is used as an acid-soluble weighting agent.

[0104] The drilling fluid prepared in the examples was characterized and evaluated for performance as follows:

[0105] Test 1. General performance test

[0106] The soil-free low-damage fractured reservoir protection drilling fluid was stirred at a speed of 11000r / min for 5min using a high-speed stirrer. The viscosity and shear performance, density and other related properties of the drilling fluid were measured using a drilling fluid densitometer, a six-speed viscometer and other equipment in accordance with GBT 16783.1-2006 Field test of drilling fluids in the petroleum and natural gas industry, Part 1: Water-based drilling fluids. The test results are shown in Tables 1 and 2:

[0107] Table 1 General properties of drilling fluid

[0108]

[0109] Table 2 Drilling fluid anti-pollution performance

[0110]

[0111]

[0112] The on-site filtration loss is qualified when it is less than 10mL. It can be seen from Tables 1 and 2 that the filtration loss of the drilling fluid is very low, and other conventional properties meet the needs of drilling. The drilling fluid has good temperature resistance. After aging for 20 days at 100°C, the viscosity, filtration loss, and pH value have not changed significantly; the ability to resist rock chip pollution is good, the system has a high capacity limit for inferior solid phases, and the filtration loss and pH value have not changed significantly after pollution; the ability to resist salt and calcium pollution is strong, and salt pollution and calcium pollution do not thicken the system, and the pH value remains stable.

[0113] Test 2. Test of acid solubility and oil solubility of mud cake

[0114] Test method: After testing the medium-pressure filtration loss of the above drilling fluid, scrape the mud cake and dry it in a thermostat at 60°C to constant weight. Take 10.04g of the dried mud cake, soak it in 200mL of 15% hydrochloric acid solution, react in a thermostat at 60°C for 2h, filter it, and wash the mud cake residue with deionized water until the pH value of the filtered solution is about 7. The filtered residue is placed in a thermostat at 60°C and dried to constant weight, and the mass of the residue and filter paper is recorded as m1. Then soak the residue in 200mL of kerosene, react in a thermostat at 60°C for 2h, filter it, and dry it in a thermostat at 60°C to constant weight, and the mass of the residue and filter paper is recorded as m2. Perform a blank test, and measure the mass of the filter paper after filtering with water and filtering with kerosene, and drying it to constant weight in a thermostat at 60°C, respectively, and record it as m3 and m4. The calculation formulas for acid solubility rate Ra, oil solubility rate Ro and total solubility rate Rt are:

[0115]

[0116]

[0117] R t =R a +R o

[0118] The test results are shown in Table 3:

[0119] Table 3 Acid solubility and oil solubility of mud cake

[0120]

[0121] It can be seen from Table 3 that the solid phase oil solubility and acid solubility of the soil-free low-damage fractured reservoir protection drilling fluid is 96.52%. The solid phase particle damage can be eliminated through subsequent production and transformation processes, thereby increasing the permeability recovery value of the reservoir and reducing the skin coefficient.

[0122] Test 3. Reservoir damage assessment test

[0123] Experimental method: The reservoir damage experimental method is carried out in accordance with the "Dynamic simulation evaluation experiment of conventional sandstone reservoir drilling fluid damage" in the industry standard SY / T 6540-2021 "Indoor evaluation method for drilling fluid and completion fluid damage to reservoirs", and further simulates the determination of permeability recovery value after pickling and degradation. Every 1 minute, a set of pressure data is recorded, and the pressure curve is drawn and compared with the general reservoir drilling fluid (such as Figure 1 , Figure 2 shown).

[0124] Determination of permeability recovery value after pickling: Use 15% hydrochloric acid (on-site pickling concentration) to displace 0.5 times the pore volume, then soak 1 cm from the contaminated end with hydrochloric acid of the same concentration for 2 hours, and finally test the permeability recovery value of the core. Record a set of pressure data every 1 minute and draw a pressure curve.

[0125] Determination of permeability recovery value after degradation: put the contaminated end of the core upward into a 400mL wide-mouth bottle with a sealing stopper, add kerosene to the wide-mouth bottle, the depth of kerosene is just level with the contaminated section of the core, put it in a biological incubator for degradation, the degradation time is 60 days, and finally measure the permeability and recovery value of the core. Record a set of pressure data every 1 minute and draw a pressure curve. The test results are shown in Table 4.

[0126] Table 4 Reservoir damage experimental test results

[0127]

[0128]

[0129] Note: General reservoir section drilling fluid formula: 3% bentonite + 0.3% caustic soda + 3% SMC + 3% PNH + 3% + 3% RH-3 + 7% KCl + 2% FT-1 + oil-soluble resin + barite.

[0130] It can be seen from Table 4 that both drilling fluid systems use oil-soluble reservoir protection agents, but the permeability recovery value of the soil-free low-damage fractured reservoir protection drilling fluid after oil dissolution is 13.85% higher than that of general drilling fluid. This is because the soil-free low-damage fractured reservoir protection drilling fluid does not contain bentonite, and the particle size distribution of limestone has been optimized, which increases the temporary plugging rate of the temporary plugging agent and reduces the damage of the filtrate and solid phase of the drilling fluid to the reservoir. In addition, most of the materials used in the soil-free low-damage fractured reservoir protection drilling fluid can be acid-soluble or biodegraded, and the permeability recovery value after acid dissolution and biodegradation is much higher than that of general reservoir section drilling fluid. Figure 1 From the pressure curve change trend in the drilling fluid formula, it can be found that the equilibrium pressure changes little during the oil dissolution, acid dissolution and biodegradation process, indicating that the acid dissolution and biodegradation measures have little effect on the recovery of reservoir permeability. Figure 2 From the pressure curve change trend, it can be found that the equilibrium pressure of the low-damage drilling fluid formula during acid dissolution and biodegradation is continuously lower than that after oil dissolution, indicating that acid dissolution and biodegradation further relieve the reservoir damage and improve the permeability recovery value of the core. Through the analysis of the basic properties and reservoir protection performance of the soil-free low-damage fractured reservoir protection drilling fluid, the following conclusions can be drawn:

[0131] 1. The conventional performance and anti-pollution performance of the soil-free low-damage fractured reservoir protection drilling fluid are excellent, which can meet the basic requirements of on-site drilling for drilling fluid;

[0132] 2. The acid and oil dissolution experiments on the drilling fluid mud cake prove that the solid phase oil and acid dissolution rates of the soil-free low-damage fractured reservoir protection drilling fluid are high, which can improve the recovery rate of reservoir damage;

[0133] 3. Judging from the permeability recovery value of the core, the reservoir protection effect of the soil-free low-damage fractured reservoir protection drilling fluid is better than the drilling fluid system used in general reservoir sections.

Claims

1. A soil-free, low-damage fractured reservoir protection drilling fluid, characterized in that: The invention is composed of the following raw materials in parts by weight: 10,000 parts of water, 50-300 parts of polymer flow pattern regulator, 20-30 parts of decalcifier, 10-20 parts of pH regulator, 300-500 parts of friction reducer, 30-50 parts of metal ion shear enhancer, 300-500 parts of degradable filtration reducer, 500-800 parts of composite inhibitor, 50-150 parts of waterproof locking agent, 100-300 parts of composite temporary plugging agent and 0-12,000 parts of acid-soluble weighting agent.

2. The soil-free low-damage fractured reservoir protection drilling fluid according to claim 1, characterized in that: The polymer flow pattern regulator is one or more of hydrophobic associating polymers, dendritic polymers, and hyperbranched resins, and the friction reducing agent is one or more of polymer alcohols, fatty acid esters, graphite, and mineral oils.

3. The soil-free low-damage fractured reservoir protection drilling fluid according to claim 1, characterized in that: The metal ion cutting agent can be Zn 2+ 、Al 3+ Cr 3+ , Ca 2+ Mg 2+ The degradable plugging agent may be a mixture of one or more of starch, modified starch, polylactic acid powder, and polyester polymer materials in any proportion.

4. The soil-free low-damage fractured reservoir protection drilling fluid according to claim 1, characterized in that: The composite inhibitor can be a mixture of one or more of polyacrylamide potassium salt, potassium chloride, sodium formate and potassium formate in any proportion, and the waterproof lock agent can be a mixture of one or more of anionic surfactants, cationic surfactants, nonionic surfactants, silicon-containing surfactants and fluorine-containing surfactants in any proportion.

5. The soil-free low-damage fractured reservoir protection drilling fluid according to claim 1, characterized in that: The oil-soluble temporary plugging agent may be one or a combination of C5 petroleum resin, C9 petroleum resin, a copolymer of C5 and C9 petroleum resin, and the acid-soluble weighting agent may be limestone or manganese tetraoxide.

6. A method for preparing a soil-free, low-damage fractured reservoir protection drilling fluid, characterized in that: Follow the steps below to implement it: Step 1: First, add a polymer flow regulator into water, then add sodium bicarbonate into the water, stir until completely uniform at room temperature, and stand for 24-48 hours to obtain a drilling fluid base slurry; Step 2: Stir the drilling fluid base slurry, and add sodium hydroxide, friction reducer, metal ion shear enhancer, degradable filtration reducer, composite inhibitor, waterproof lock agent, composite temporary plugging agent, acid-soluble weighting agent into it in sequence to obtain a soil-free, low-damage fracture reservoir protection drilling fluid.

7. The method for preparing the soil-free low-damage fractured reservoir protection drilling fluid according to claim 6, characterized in that: The polymer flow pattern regulator is one or more of a hydrophobic associating polymer, a dendritic polymer, and a hyperbranched resin.

8. The method for preparing the soil-free low-damage fractured reservoir protection drilling fluid according to claim 6, characterized in that: The acid-soluble weighting agent is limestone or manganese tetraoxide.

9. The method for preparing the soil-free low-damage fractured reservoir protection drilling fluid according to claim 8, characterized in that: The particle size of the manganese tetraoxide is less than 10 μm, and the density is ≥ 4.7 g / cm 3 .

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