Self-degradable acidifiable plugging agent, drilling fluid and application of self-degradable acidifiable plugging agent

Abstract

The invention relates to a self-degradable acidifiable plugging agent, a drilling fluid and application of the self-degradable acidifiable plugging agent and the drilling fluid. The plugging agent is prepared from a high-strength acid-soluble supporting material, a water-swelling flexible polymer and acid-soluble fibers, the mass ratio of the high-strength acid-soluble support material to the water-swelling flexible polymer to the acid-soluble fiber is (3-5): (1.5-3.5): (0.5-1.5); the water-swelling flexible polymer is mainly formed by polymerizing 2-acrylamido-2-methylbenzene sulfonic acid, acrylamide, a cross-linking agent and a calcium carbonate filler; the high-strength acid-soluble supporting material is dolomite particles. Compared with the conventional water-based drilling fluid, the self-degradable acidifiable drilling fluid disclosed by the invention has the advantages of higher plugging capacity, stable well wall, small friction resistance, good reservoir protection effect, high salt resistance and capability of self degradation. Meanwhile, raw materials are easy to obtain, the production cost is low, the environment is not polluted, and the drilling fluid has wide application prospects in drilling engineering of fractured hydrocarbon reservoirs.

Description

Technical Field

[0001] The present invention relates to a self-degradable acidifiable plugging agent, a drilling fluid and their applications, belonging to the technical field of well plugging in oil well operations. Background Art

[0002] Well leakage is one of the downhole complex accidents that seriously affect the normal operation of drilling engineering. For fractured reservoirs, it will also cause irreversible damage to the reservoir. Bridging (plugging) plugging materials, high water loss plugging materials, temporary plugging materials, chemical plugging materials, composite plugging materials and other plugging technologies have been developed at home and abroad. In recent years, a new type of plugging material, intelligent composite plugging material, has been developed. It uses shape memory alloy to sense the temperature change at the leakage point. Based on the memory effect and superelastic effect of the alloy, the lap joint and winding between alloy wires are used to achieve an ideal plugging effect. However, these plugging technologies mainly have the following problems: First, the deformability of the plugging agent itself during the plugging process is poor, and particles slightly larger than the pores and cracks of the leakage layer or not matching the shape of the pores and cracks of the leakage layer are not easy to enter, forming a pile on the surface of the leakage layer and not penetrating deep into the leakage layer; Second, the plugging material does not have expansibility or only has a small expansion amount, and it is not easy to stay stably in the leakage layer under the action of external stress; Third, the plugging material lacks rigid bridging particles, resulting in a small plugging strength and insufficient pressure-bearing capacity; Fourth, after plugging operations in the oil and gas layer area, due to the inability of the plugging material to degrade or dissolve in acid by itself, it damages the oil and gas layer. For the above reasons, when using these plugging materials, it is easy to cause poor plugging effect in fractured reservoirs, repeated leakage after plugging, and damage to the oil and gas layer.

[0003] The Chinese invention patent document with the application publication number CN114525118A discloses "Drilling Plugging Agent Composition, Drilling Plugging Agent and Its Preparation Method and Application". Among them, the drilling plugging agent composition contains the following components stored independently or in combination of two or more: basic drilling fluid, component A, component B, fiber component, filling component, component C; Component A is a combination of aluminum alloy particles GYD and marble particles with a weight ratio of 0.1-6:1; Component B is selected from at least one of Retter flaky materials, mica flakes and shredded plastics; The average length of component B is 0.2-5mm, the average width is 0.2-5mm, and the average thickness is 0.2-0.5mm; The average length of the fiber component is 3-20mm, and the average diameter is 5-30μm; Component C is elastic graphite with a resilience rate of not less than 30%. This composition can prepare a drilling plugging agent with strong pressure-bearing capacity, high acid dissolution rate and good temperature resistance. However, this plugging composition has complex components, some components are expensive, and the acid dissolution rate of the prepared plugging agent ranges from 80% to 93% in 15wt% hydrochloric acid. Summary of the Invention

[0004] The first object of the present invention is to provide a self-degrading acidifiable plugging agent to solve the problems of complex composition, high production cost, low acid dissolution rate, and poor reservoir protection effect of the self-degrading acidifiable plugging agent in the prior art.

[0005] The second object of the present invention is to provide a self-degrading acidifiable drilling fluid. Compared with conventional water-based drilling fluids, this self-degrading acidifiable drilling fluid has the advantages of strong plugging ability, stable wellbore, low frictional resistance, good reservoir protection effect, and strong salt resistance. Moreover, the raw materials of the drilling fluid are easily available, the production cost is low, and the environmental pollution is small.

[0006] The third object of the present invention is to provide the application of the self-degrading acidifiable plugging agent or the self-degrading acidifiable drilling fluid in drilling in fractured oil and gas reservoirs to solve the above problems.

[0007] To achieve the above objects, the technical solution of the self-degrading acidifiable plugging agent in the present invention is as follows:

[0008] A self-degrading acidifiable plugging agent, which is composed of a high-strength acid-soluble support material, a water-absorbing and swelling flexible polymer, and an acid-soluble fiber; the mass ratio of the high-strength acid-soluble support material, the water-absorbing and swelling flexible polymer, and the acid-soluble fiber is 3-5: 1.5-3.5: 0.5-1.5; the water-absorbing and swelling flexible polymer is mainly formed by polymerizing 2-acrylamido-2-methylbenzenesulfonic acid, acrylamide, a cross-linking agent, and a calcium carbonate filler; the high-strength acid-soluble support material is dolomite particles.

[0009] The beneficial effects of the above technical solution are as follows: The self-degrading acidifiable plugging agent of the present invention contains a biodegradable polymer, an acidifiable high-strength support material, and an acidifiable fiber, and can be self-degraded and acid-soluble. Under 3 wt% hydrochloric acid, the acid dissolution rate is above 95%. Moreover, the composition of the plugging agent is simple, without a complex preparation process, and is easy to be widely promoted and used.

[0010] Preferably, the acid-soluble fiber is a polyacrylonitrile fiber; more preferably, the acid-soluble fiber is SRXW-10 (length 6 ± 1 mm, diameter 10 ± 1.5 μm), purchased from Shandong Tai'an Haosong Fiber Co., Ltd.

[0011] As a further improvement, the particle size of the high-strength acid-soluble support material is 0.005-5 mm.

[0012] The beneficial effects of the above technical solution are as follows: The particle size range of the high-strength acid-soluble support material of the present invention is widely distributed, which can meet the needs of different fractures to the greatest extent, and the application range is relatively wide.

[0013] As a further improvement, the mass ratio of 2-acrylamido-2-methylbenzenesulfonic acid: acrylamide: crosslinking agent: calcium carbonate filler is 80-100: 120-150: 1-2: 50-80.

[0014] In order to achieve the above object, the technical solution of the self-degradable acidifiable drilling fluid in the present invention is:

[0015] A self-degradable acidifiable drilling fluid, comprising water and a self-degradable acidifiable plugging agent, and 5-10 g of the self-degradable acidifiable plugging agent is added to every 100 mL of water.

[0016] The beneficial effects of the above technical solution are as follows: The amount of the plugging agent used in the self-degradable acidifiable drilling fluid of the present invention is small, and the plugging agent does not affect the basic performance of the drilling fluid, and can achieve a good plugging effect, and can be self-degraded and acidified at the reservoir part, with less damage to the reservoir.

[0017] As a further improvement, based on 100 mL of water, the water-based drilling fluid comprises the following components: 3-4 g of bentonite, 0.1-0.2 g of sodium carbonate, 1-2 g of hydrolyzed polyacrylonitrile sodium salt, 0.1-0.2 g of potassium polyacrylate, 0.3-0.5 g of low-viscosity polyanionic cellulose, 1-2 g of sulfonated asphalt, 1-3 g of sulfonated lignite resin, 1-2 g of polyaluminum chloride, and 1-2 g of nano-polyester.

[0018] In order to achieve the above object, the technical solution of the application of the self-degradable acidifiable plugging agent or the self-degradable acidifiable drilling fluid in drilling in fractured hydrocarbon reservoirs in the present invention is:

[0019] An application of a self-degradable acidifiable plugging agent or a self-degradable acidifiable drilling fluid in drilling in fractured hydrocarbon reservoirs.

[0020] The beneficial effects of the above technical solution are as follows: The self-degradable acidifiable drilling fluid of the present invention has good rheology, lubricity, and filtration loss reduction properties, has a good plugging effect, can be self-degraded and acidified at the reservoir part, and has less damage to the reservoir. Specific embodiments

[0021] The following combines specific embodiments to further describe the present invention. It should be noted that, on the premise of no conflict, any combination of the following-described embodiments or technical features can form a new embodiment. The equipment and raw materials used can be purchased from the market or are commonly used in the art. The methods in the following embodiments are conventional methods in the art unless otherwise specified.

[0022] The high-strength acid-soluble proppant material of the present invention (the main chemical component is CaCO 3 85-90%, MgCO 3(10-15%), using dolomite as raw material, a high-strength acid-soluble support material is obtained through grinding, where the proportion of mm-level support material is 80-90% and the proportion of μm-level support material is 10-20%.

[0023] The present invention adopts the aqueous solution polymerization method. Using 2-acrylamido-2-methylbenzenesulfonic acid and acrylamide as monomers, sodium bisulfite and ammonium persulfate as initiators, and N,N-methylenebisacrylamide as a crosslinking agent, a polymer is polymerized, and then a filler is added. After adjusting the pH, a water-absorbing and swelling flexible polymer is obtained. The specific preparation process is as follows:

[0024] (1) Components and dosages prepared

[0025] 80-100 kg of 2-acrylamido-2-methylbenzenesulfonic acid, 120-150 kg of acrylamide, 80-85 kg of 40% sodium hydroxide solution, 8-10 kg of sodium bisulfite, 8-10 kg of ammonium persulfate, 1-2 kg of N,N-methylenebisacrylamide, 50-80 kg of calcium carbonate-based filler (particle size 0.005-5 mm) (crab shell powder and / or shrimp shell powder), 1000-1200 kg of water.

[0026] (2) Reaction process

[0027] a. Respectively prepare a mixed solution of monomers by mixing 2-acrylamido-2-methylbenzenesulfonic acid, acrylamide and water, prepare an initiator aqueous solution by dissolving sodium bisulfite and ammonium persulfate in water, and prepare a crosslinking agent solution by dissolving N,N-methylenebisacrylamide in water for standby.

[0028] b. Dispose of the mixed solution of monomers prepared by mixing 2-acrylamido-2-methylbenzenesulfonic acid, acrylamide and water in a reaction kettle at one time, gradually heat up to 50 °C, and sequentially add the initiator and the crosslinking agent, stir well, and control the reaction time within 1 hour.

[0029] c. When the reaction time is reached, maintain the temperature at 50 °C, add the filler, neutralize with sodium hydroxide solution, cool down to form a gel-like substance, dry and cut into pellets with a particle size of 1-2 mm, and obtain the product after packaging.

[0030] The water-based drilling fluid of the present invention specifically includes the following components:

[0031] Based on 100 mL of water, 3-4 g of bentonite, 0.1-0.2 g of sodium carbonate, 1-2 g of hydrolyzed polyacrylonitrile sodium salt, 0.1-0.2 g of potassium polyacrylate, 0.3-0.5 g of low-viscosity polyanionic cellulose, 1-2 g of sulfonated asphalt, 1-3 g of sulfonated lignite resin, 1-2 g of polyaluminum chloride, 1-2 g of nano-polyester.

[0032] Among them, the acid-soluble fiber is SRXW-10 (length 6±1 mm, diameter 10±1.5 μm), with the trade name: polyacrylonitrile fiber (RY-Fiber), purchased from Shandong Tai'an Haosong Fiber Co., Ltd. The hydrolyzed sodium polyacrylonitrile is Na-HPAN, the potassium salt of polyacrylamide is KPAM, the low-viscosity polyanionic cellulose is PAC-LV, the sulfonated asphalt is FT-1, the lignite resin for drilling fluid is SPNH, the polyaluminum chloride is PAC, and the nano polyester is NP-1.

[0033] I. The specific embodiments of the self-degrading acidifiable plugging agent of the present invention are as follows:

[0034] Example 1

[0035] The self-degrading acidifiable plugging agent of this example is composed of a high-strength acid-soluble support material, a water-absorbing and swelling flexible polymer (particle size 1-2 mm), and an acid-soluble fiber; the mass ratio of the high-strength acid-soluble support material, the water-absorbing and swelling flexible polymer, and the acid-soluble fiber is 3:1.5:0.5.

[0036] The high-strength acid-soluble support material is composed of dolomite particles with particle sizes of 5 mm, 1 mm, 0.5 mm, and 5-10 μm, in a ratio of 4:2:1:1; the acid-soluble fiber is SRXW-10 fiber (length 6±1 mm, diameter 10±1.5 μm).

[0037] The water-absorbing and swelling flexible polymer is formed by polymerizing 2-acrylamido-2-methylbenzenesulfonic acid, acrylamide, a cross-linking agent, and a calcium carbonate filler. The amounts of each substance are 80 kg of 2-acrylamido-2-methylbenzenesulfonic acid, 120 kg of acrylamide, 80 kg of 40% sodium hydroxide solution, 8 kg of sodium bisulfite, 8 kg of ammonium persulfate, 1 kg of N,N'-methylenebisacrylamide, 50 kg of filler (particle size 0.005-0.5 mm), and 1000 kg of water.

[0038] Example 2

[0039] The self-degrading acidifiable plugging agent of this example is composed of a high-strength acid-soluble support material, a water-absorbing and swelling flexible polymer (particle size 1-2 mm), and an acid-soluble fiber; the mass ratio of the high-strength acid-soluble support material, the water-absorbing and swelling flexible polymer, and the acid-soluble fiber is 4:2.5:1.

[0040] The high-strength acid-soluble support material is composed of dolomite particles with particle sizes of 5 mm, 1 mm, 0.5 mm, and 5-10 μm, in a ratio of 4:2:1:1; the acid-soluble fiber is SRXW-10 fiber (length 6±1 mm, diameter 10±1.5 μm).

[0041] The water-swellable flexible polymer is formed by polymerizing 2-acrylamido-2-methylbenzenesulfonic acid, acrylamide, a crosslinking agent, and a calcium carbonate filler. The amounts of each substance are 85 kg of 2-acrylamido-2-methylbenzenesulfonic acid, 125 kg of acrylamide, 81 kg of 40% sodium hydroxide solution, 8.5 kg of sodium bisulfite, 8.5 kg of ammonium persulfate, 1.2 kg of N,N'-methylenebisacrylamide, 55 kg of filler (particle size 0.5 - 1 mm), and 1050 kg of water.

[0042] Example 3

[0043] The self-degrading acidifiable plugging agent of this example is composed of a high-strength acid-soluble support material, a water-swellable flexible polymer (particle size 1 - 2 mm), and acid-soluble fibers; the mass ratio of the high-strength acid-soluble support material, the water-swellable flexible polymer, and the acid-soluble fibers is 5:3.5:1.5.

[0044] The high-strength acid-soluble support material is composed of dolomite particles with particle sizes of 5 mm, 1 mm, 0.5 mm, and 5 - 10 μm in a ratio of 4:2:1:1; the acid-soluble fibers are SRXW-10 fibers (length 6 ± 1 mm, diameter 10 ± 1.5 μm).

[0045] The water-swellable flexible polymer is formed by polymerizing 2-acrylamido-2-methylbenzenesulfonic acid, acrylamide, a crosslinking agent, and a calcium carbonate filler. The amounts of each substance are 90 kg of 2-acrylamido-2-methylbenzenesulfonic acid, 130 kg of acrylamide, 82 kg of 40% sodium hydroxide solution, 9.0 kg of sodium bisulfite, 9.0 kg of ammonium persulfate, 1.4 kg of N,N'-methylenebisacrylamide, 60 kg of filler (particle size 1 - 2 mm), and 1100 kg of water.

[0046] Example 4

[0047] The self-degrading acidifiable plugging agent of this example is composed of a high-strength acid-soluble support material, a water-swellable flexible polymer (particle size 1 - 2 mm), and acid-soluble fibers; the mass ratio of the high-strength acid-soluble support material, the water-swellable flexible polymer, and the acid-soluble fibers is 3:1.5:0.5.

[0048] The high-strength acid-soluble support material is composed of dolomite particles with particle sizes of 3 mm, 0.1 mm, 0.05 mm, and 5 - 10 μm in a ratio of 3:2:1:1; the acid-soluble fibers are SRXW-10 fibers (length 6 ± 1 mm, diameter 10 ± 1.5 μm).

[0049] The water-swellable flexible polymer is formed by polymerizing 2-acrylamido-2-methylbenzenesulfonic acid, acrylamide, a cross-linking agent, and a calcium carbonate filler. The amounts of each substance are as follows: 92 kg of 2-acrylamido-2-methylbenzenesulfonic acid, 135 kg of acrylamide, 83 kg of 40% sodium hydroxide solution, 9.2 kg of sodium bisulfite, 9.2 kg of ammonium persulfate, 1.6 kg of N,N'-methylenebisacrylamide, 65 kg of filler (particle size 2 - 3 mm), and 1130 kg of water.

[0050] Example 5

[0051] The self-degradable acidifiable plugging agent of this example is composed of a high-strength acid-soluble support material, a water-swellable flexible polymer (particle size 1 - 2 mm), and acid-soluble fibers; the mass ratio of the high-strength acid-soluble support material, the water-swellable flexible polymer, and the acid-soluble fibers is 4:2.5:1.

[0052] The high-strength acid-soluble support material is composed of dolomite particles with particle sizes of 3 mm, 0.1 mm, 0.05 mm, and 5 - 10 μm in a ratio of 3:2:1:1; the acid-soluble fiber is SRXW-10 fiber (length 6 ± 1 mm, diameter 10 ± 1.5 μm).

[0053] The water-swellable flexible polymer is formed by polymerizing 2-acrylamido-2-methylbenzenesulfonic acid, acrylamide, a cross-linking agent, and a calcium carbonate filler. The amounts of each substance are as follows: 95 kg of 2-acrylamido-2-methylbenzenesulfonic acid, 140 kg of acrylamide, 84 kg of 40% sodium hydroxide solution, 9.6 kg of sodium bisulfite, 9.6 kg of ammonium persulfate, 1.8 kg of N,N'-methylenebisacrylamide, 70 kg of filler (particle size 3 - 4 mm), and 1150 kg of water.

[0054] Example 6

[0055] The self-degradable acidifiable plugging agent of this example is composed of a high-strength acid-soluble support material, a water-swellable flexible polymer (particle size 1 - 2 mm), and acid-soluble fibers; the mass ratio of the high-strength acid-soluble support material, the water-swellable flexible polymer, and the acid-soluble fibers is 5:3.5:1.5.

[0056] The high-strength acid-soluble support material is composed of dolomite particles with particle sizes of 3 mm, 0.1 mm, 0.05 mm, and 5 - 10 μm in a ratio of 3:2:1:1; the acid-soluble fiber is SRXW-10 fiber (length 6 ± 1 mm, diameter 10 ± 1.5 μm).

[0057] The water-swellable flexible polymer is formed by polymerizing 2-acrylamido-2-methylbenzenesulfonic acid, acrylamide, a cross-linking agent, and a calcium carbonate filler. The amounts of each substance are 100 kg of 2-acrylamido-2-methylbenzenesulfonic acid, 150 kg of acrylamide, 85 kg of 40% sodium hydroxide solution, 10 kg of sodium bisulfite, 10 kg of ammonium persulfate, 2.0 kg of N,N'-methylenebisacrylamide, 80 kg of filler (particle size 4 - 5 mm), and 1200 kg of water.

[0058] II. Specific examples of the self-degrading acidifiable drilling fluid of the present invention are as follows:

[0059] Example 7

[0060] The self-degrading acidifiable drilling fluid of this example includes the self-degrading acidifiable plugging agent of Example 1, and 5 g of the self-degrading acidifiable plugging agent is added to every 100 mL of water.

[0061] The specific components are as follows:

[0062] Based on 100 mL of water, 3 g of bentonite, 0.1 g of sodium carbonate, 1 g of Na-HPAN, 0.1 g of KPAM, 0.3 g of PAC-LV, 1 g of sulfonated asphalt, 1 g of SPNH, 1 g of polyaluminum chloride, 1 g of NP-1, and 5 g of the self-degrading acidifiable plugging agent. A density regulator is added to adjust the density of the drilling fluid to be between 1.20 - 1.25 g / cm 3 between.

[0063] Example 8

[0064] The self-degrading acidifiable drilling fluid of this example includes the self-degrading acidifiable plugging agent of Example 2, and 7.5 g of the self-degrading acidifiable plugging agent is added to every 100 mL of water.

[0065] The specific components are as follows:

[0066] Based on 100 mL of water, 3.5 g of bentonite, 0.15 g of sodium carbonate, 1.5 g of Na-HPAN, 0.15 g of KPAM, 0.4 g of PAC-LV, 1.5 g of sulfonated asphalt, 3 g of SPNH, 1.5 g of polyaluminum chloride, 1.5 g of NP-1, and 7.5 g of the self-degrading acidifiable plugging agent. A density regulator is added to adjust the density of the drilling fluid to be between 1.20 - 1.25 g / cm 3 between.

[0067] Example 9

[0068] The self-degrading acidifiable drilling fluid of this example includes the self-degrading acidifiable plugging agent of Example 3, and 10 g of the self-degrading acidifiable plugging agent is added to every 100 mL of water.

[0069] The specific components are as follows:

[0070] Based on 100 mL of water, 4 g of bentonite, 0.2 g of sodium carbonate, 2 g of Na-HPAN, 0.2 g of KPAM, 0.5 g of PAC-LV, 2 g of sulfonated asphalt, 3 g of SPNH, 2 g of polyaluminum chloride, 2 g of NP-1 and 10 g of self-degradable acidifiable lost circulation material. Add a density regulator to adjust the density of the drilling fluid to be between 1.20 - 1.25 g / cm 3 Between.

[0071] Example 10

[0072] The self-degradable acidifiable drilling fluid of this example includes the self-degradable acidifiable lost circulation material of Example 4, and 5 g of self-degradable acidifiable lost circulation material is added per 100 mL of water.

[0073] The specific components are as follows:

[0074] Based on 100 mL of water, 3 g of bentonite, 0.1 g of sodium carbonate, 1 g of Na-HPAN, 0.1 g of KPAM, 0.3 g of PAC-LV, 1 g of sulfonated asphalt, 1 g of SPNH, 1 g of polyaluminum chloride, 1 g of NP-1 and 5 g of self-degradable acidifiable lost circulation material. Add a density regulator to adjust the density of the drilling fluid to be between 1.20 - 1.25 g / cm 3 Between.

[0075] Example 11

[0076] The self-degradable acidifiable drilling fluid of this example includes the self-degradable acidifiable lost circulation material of Example 5, and 7.5 g of self-degradable acidifiable lost circulation material is added per 100 mL of water.

[0077] The specific components are as follows:

[0078] Based on 100 mL of water, 3.5 g of bentonite, 0.15 g of sodium carbonate, 1.5 g of Na-HPAN, 0.15 g of KPAM, 0.4 g of PAC-LV, 1.5 g of sulfonated asphalt, 3 g of SPNH, 1.5 g of polyaluminum chloride, 1.5 g of NP-1 and 7.5 g of self-degradable acidifiable lost circulation material. Add a density regulator to adjust the density of the drilling fluid to be between 1.20 - 1.25 g / cm 3 Between.

[0079] Example 12

[0080] The self-degradable acidifiable drilling fluid of this example includes the self-degradable acidifiable lost circulation material of Example 6, and 10 g of self-degradable acidifiable lost circulation material is added per 100 mL of water.

[0081] The specific components are as follows:

[0082] Based on 100 mL of water, there are 4 g of bentonite, 0.2 g of sodium carbonate, 2 g of Na-HPAN, 0.2 g of KPAM, 0.5 g of PAC-LV, 2 g of sulfonated asphalt, 3 g of SPNH, 2 g of polyaluminum chloride, 2 g of NP-1, and 10 g of self-degradable acidifiable plugging agent. Add a density regulator to adjust the density of the drilling fluid to be between 1.20 - 1.25 g / cm 3 3.

[0083] III. Experimental Examples Application of Self-degradable Acidifiable Plugging Agent or Self-degradable Acidifiable Drilling Fluid in Drilling of Fractured Oil and Gas Reservoirs

[0084] Experimental Example 1 Basic Performance Evaluation of Self-degradable Acidifiable Drilling Fluid

[0085] Perform performance tests on the self-degradable acidifiable drilling fluid of Example 7 (adjusted to a density between 1.20 - 1.25 g / cm 3 3 with the addition of barite). The experimental effects of the self-degradable acidifiable drilling fluids of other examples are equivalent to those of Example 7. The specific results are shown in Table 1.

[0086] Table 1 Basic Performance Evaluation of the Self-degradable Acidifiable Drilling Fluid of Example 7

[0087]

[0088]

[0089] Experimental Example 2 Evaluation of Resistance to NaCl and CaCl 2 Pollution Performance

[0090] Add different concentrations of NaCl and 0.2% CaCl 2 (fixed concentration) to the self-degradable acidifiable drilling fluid of Example 7, and measure its rheological properties and API FL . The experimental effects of the self-degradable acidifiable drilling fluids of other examples are equivalent to those of Example 7. The specific results are shown in Table 2. It can be seen from Table 2 that adding different concentrations of NaCl and 0.2% CaCl 2 has little effect on the rheological properties and filtration loss of the self-degradable acidifiable drilling fluid.

[0091] Table 2 Evaluation of the Ability of the Self-degradable Acidifiable Drilling Fluid of Example 7 to Resist NaCl and 0.2% CaCl 2

[0092]

[0093] Note: Thermal rolling conditions: 100 °C × 16 h.

[0094] Experimental Example 3 Evaluation of Resistance to Drill Cuttings Invasion Pollution

[0095] ​The drill cuttings from the Wushenqi oilfield shale formation are dried and crushed indoors, screened through a 100-mesh sieve, and then added to the self-degradable acidifiable drilling fluid of Example 7. The experimental effects of the self-degradable acidifiable drilling fluids of other examples are comparable to those of Example 7. The specific results are shown in Table 3.

[0096] Table 3 Evaluation of the Resistance of Self-degradable Acidifiable Drilling Fluid for Fractured Reservoirs to the Invasion of Drill Cuttings from Shale Formations

[0097]

[0098]

[0099] Note: Thermal rolling conditions: 100 °C × 16 h.

[0100] Experimental Example 4 Lubricating Performance Detection

[0101] In this experimental example, a high-temperature and high-pressure friction resistance evaluation device is selected. Using the formula of the self-degradable acidifiable drilling fluid of Example 7, barite is added to adjust the density of the drilling fluid according to Table 4, and then its friction coefficient is detected. The specific results are shown in Table 4. It can be seen from Table 4 that the mud cake friction coefficients of the self-degradable drilling fluids with different densities are all lower than 0.06, indicating good lubricating performance.

[0102] Table 4 Friction Coefficients of Self-degradable Acidifiable Drilling Fluid for Fractured Reservoirs

[0103]

[0104] Note: Experimental temperature: 120 °C.

[0105] Experimental Example 5 Thermal Rolling Recovery Rate

[0106] The self-degradable acidifiable drilling fluid of Example 7 and the conventional polymer sulfonated drilling fluid are selected. Core samples from the Wushenqi oilfield shale formation are used for the shale rolling recovery rate test. The test standard is GB / T 29170-2012. The experimental results are shown in Table 5. It can be seen from Table 5 that the recovery rate of the self-degradable acidifiable drilling fluid of the present invention is significantly higher than that of the conventional polymer sulfonated drilling fluid.

[0107] Table 5 Comparison of Thermal Rolling Recovery Rates

[0108]

[0109] Among them, the formula of the conventional polymer sulfonated drilling fluid is: based on 100 mL of water, 4 g of bentonite, 3 g of sulfonated phenolic resin, 3 g of sulfonated lignite, 0.1 g of FA367, 0.5 g of xy-27, 2 g of highly acid-soluble sulfonated asphalt, 3 g of hydrolyzed polyacrylonitrile ammonium salt, 3 g of ultrafine calcium carbonate, and barite is used to adjust the density to between 1.20 - 1.25 g / cm 3 Between.

[0110] Degree of damage to fractured reservoirs in Experimental Example 6

[0111] Using a high-temperature and high-pressure JHDS-2 dynamic fluid loss instrument and a JHST permeability gradient tester, evaluate the degree of damage of self-degradable acidifiable drilling fluid for fractured reservoirs to reservoir cores. The operation method is as follows: 1) Accurately measure data such as the length, diameter, dry weight, and gas-measured permeability of the columnar core; 2) Saturate the core sample and calculate the core porosity; 3) Select a suitable core to prepare an artificial fracture and fill a rectangular stainless steel gasket in the fracture; 4) Install the fractured core into the core dynamic fluid loss instrument and the permeability gradient tester, apply a certain confining pressure of 1.5 MPa, and measure the forward original permeability Ko; 5) Conduct a reverse damage test on the core sample for 2 h, with a damage pressure difference of 3.5 MPa, and measure the forward permeability Kd after damage; 6) Release the pressure and take out the core, accurately measure the fracture aperture, and calculate the core permeability recovery value Kd / Ko. The results are shown in Table 6.

[0112] Table 6 Protection effect of self-degradable acidifiable drilling fluid on the reservoir (fracture width 3 - 5 mm)

[0113]

[0114] Note: Test temperature: 100 °C, confining pressure: 1.5 MPa. The specific formula of the conventional polymer sulfonated drilling fluid can be seen in Example 5.

[0115] Experimental Example 7 Verification of acid solubility rate of self-degradable acidifiable drilling fluid

[0116] Prepare 1 - 5 wt% HCl and acidify for 72 hours (experimental temperature is 20 ± 5 °C) to evaluate the dissolution rate of the self-degradable acidifiable plugging agent in hydrochloric acid. The results are shown in Table 7.

[0117] Table 7 Acid solubility rate of self-degradable acidifiable drilling fluid

[0118]

[0119]

[0120] The results show that within the same time, the acid solubility rates of 3% and 5% concentration of HCl are relatively high, reaching 95%, and the residual amounts are less.

[0121] Experimental Example 8 Verification of plugging effect on fractured formations

[0122] Place the artificial core (with a fracture width of about 3 - 5 mm) into the core holder, and use a positive displacement pump to displace and apply the self-degrading acidifiable drilling fluid of Example 7, allowing it to pass through the artificial fractured core. At the beginning, the displacement pressure continuously rises and then suddenly drops. The pressure at this time is the bearing pressure. The experiment is carried out with a displacement flow rate of 5 - 10 mL / min. To ensure that the plugging fluid does not overflow from the periphery of the core, the confining pressure of the core needs to be 1.5 - 2 MPa greater than the displacement pressure. As the pump pressure of the positive displacement pump continuously increases, the reading of the pressure gauge also continuously rises. After stabilizing the pressure for 10 minutes, record the reading of the pressure gauge and the volume of the liquid at the outlet end of the core. Taking the leakage volume being less than 20 mL after stabilizing the pressure for 15 days as the evaluation criterion for a "good" plugging effect. The specific results of two parallel experiments are shown in Table 8.

[0123] Table 8 Plugging Performance of Self-degrading Acidifiable Drilling Fluid (Fracture 3 - 5 mm)

[0124] Displacement pressure (MPa) Example 7 Example 7 5.0 5.5 ml (15 days) 6 ml (15 days) 7.5 6 ml (15 days) 7 ml (15 days) 10.0 7 ml (15 days) 7 ml (15 days) 12.5 7 ml (15 days) 8 ml (15 days) 15.0 13 ml (15 days) 12.5 ml (15 days) 17.5 15 ml (15 days) 14.5 ml (15 days) 20 19 ml (15 days) 18.5 m (15 days) 22.5 142 mL (Leakage volume in 15 min) 130 mL (Leakage volume in 15 min)

[0125] As can be seen from the above table, when using the self-degrading acidifiable drilling fluid in fractured reservoirs, during the process of the displacement pressure increasing from 5 MPa to 20 MPa, there is no significant leakage within 15 days, and the plugging is successful. Thus, it can be seen that the self-degrading acidifiable plugging system of the present invention can achieve a good plugging effect on the formation.

[0126] The above is only a preferred embodiment of the present invention and is not intended to limit the present invention. The scope of patent protection of the present invention is subject to the claims. All equivalent structural changes made by using the content of the specification of the present invention should, by the same token, be included within the protection scope of the present invention.

Claims

1. A self-degradable acidifiable plugging agent, characterized in that: The plugging agent is composed of a high-strength acid-soluble supporting material, a water-swellable flexible polymer and an acid-soluble fiber; the mass ratio of the high-strength acid-soluble supporting material, the water-swellable flexible polymer and the acid-soluble fiber is 3-5:1.5-3.5:0.5-1.5; the water-swellable flexible polymer is mainly formed by polymerization of 2-acrylamide-2-methylbenzenesulfonic acid, acrylamide, a cross-linking agent and a calcium carbonate filler; the high-strength acid-soluble supporting material is dolomite particles.

2. The self-degradable acidifiable plugging agent according to claim 1, characterized in that: The particle size of the high-strength acid-soluble supporting material is 0.005-5 mm.

3. The self-degradable acidifiable plugging agent according to claim 1, characterized in that: The mass ratio of the 2-acrylamide-2-methylbenzenesulfonic acid: acrylamide: cross-linking agent: calcium carbonate filler is 80-100: 120-150: 1-2: 50-80.

4. A self-degradable acidifiable drilling fluid, characterized in that: The invention comprises water and the self-degradable acidifiable plugging agent according to any one of claims 1 to 3, wherein 5 to 10 g of the self-degradable acidifiable plugging agent is added to every 100 mL of water.

5. The self-degradable acidifiable drilling fluid according to claim 4, characterized in that: Based on 100 mL of water, the self-degradable acidifiable drilling fluid includes the following components: 3-4 g of bentonite, 0.1-0.2 g of sodium carbonate, 1-2 g of hydrolyzed sodium polyacrylonitrile, 0.1-0.2 g of potassium polyacrylate, 0.3-0.5 g of low-viscosity polyanionic cellulose, 1-2 g of sulfonated asphalt, 1-3 g of sulfonated lignite resin, 1-2 g of polyaluminium chloride and 1-2 g of nano-polyester.

6. Use of the self-degradable acidifiable plugging agent according to any one of claims 1 to 3 or the self-degradable acidifiable drilling fluid according to claim 4 or 5 in drilling in fractured oil and gas layers.

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