Temperature-sensitive plugging type water-based drilling fluid for oil and gas drilling as well as preparation method and application of temperature-sensitive plugging type water-based drilling fluid

Abstract

The invention relates to a temperature-sensitive plugging type water-based drilling fluid for oil and gas drilling as well as a preparation method and application thereof, and belongs to the technical field of deepwater shallow oil and gas reservoir drilling and production. The water-based drilling fluid comprises the following components: natural seawater, a filtrate reducer, polyamine, ethylene glycol, sodium hydroxide, potassium chloride, xanthan gum, an anti-balling lubricant, a hydrate double-effect inhibitor, a temperature-sensitive blocking agent and glass beads. The water-based drilling fluid provided by the invention is used for deep water shallow oil and gas reservoir drilling, and can maintain good rheological property and reduce filtration loss and plugging performance under seabed low-temperature and high-pressure conditions. And the temperature-sensitive plugging agent can effectively enhance the plugging capability of the drilling fluid, especially in a low-temperature deepwater environment, a stable plugging layer can be rapidly formed, and the phenomena of collapse and hole shrinkage of a well wall are remarkably reduced.

Description

Technical Field

[0001] The present invention relates to a temperature-sensitive plugging water-based drilling fluid for oil and gas drilling, a preparation method and application thereof, and belongs to the technical field of drilling and production of deep-water shallow oil and gas reservoirs. Background Art

[0002] Natural gas hydrates are solid, ice-like substances formed by small gas molecules, such as hydrocarbons, and water molecules under low temperature and high pressure. They are widely found in marine sediments and terrestrial permafrost, with total resources approximately twice that of traditional fossil fuels. Due to the limited resources and environmental pollution of traditional fossil fuels, the search for clean, new alternative energy sources has become a key development direction. As a new, efficient, and clean fossil fuel, natural gas hydrates are considered an ideal alternative energy source for the 21st century and have attracted widespread attention from scholars worldwide.

[0003] Generally speaking, the temperature and pressure conditions of the formations near the upper and lower boundaries of a natural gas hydrate reservoir are near the equilibrium curve for natural gas hydrates. Natural gas hydrates may be associated with shallow gas. Due to the narrow drilling fluid density window during deepwater drilling, the presence of shallow gas will seriously affect the safety of deepwater drilling. In deepwater drilling, in addition to the hazards of gas invasion and gas blowout caused by drilling into shallow gas, drilling directly into the hydrate layer during drilling can cause the drilling fluid to invade the reservoir, resulting in an increase in the hydrate layer's temperature or a decrease in pressure, which can cause the hydrate to decompose, leading to wellbore instability, lost circulation, blowouts, and other problems. Generally, when drilling into shallow oil and gas reservoirs in deepwater, due to the poor compaction of the formation, maintaining a drilling fluid pressure greater than the formation fluid pressure (but not exceeding the fracture pressure) is considered a safer practice.

[0004] When the wellbore pressure exceeds the formation pressure, the drilling fluid will seep into the formation due to the pressure differential. Practice has shown that this intrusion can alter the properties of the surrounding rock, such as rock strength and pore pressure. Furthermore, when the drilling fluid invades the hydrate formation, frictional heat generated by the drill tool and the temperature of the drilling fluid can cause hydrate decomposition, exacerbating wellbore instability. Currently, the addition of plugging materials such as nano-silica and nano-calcium carbonate to hydrate drilling fluids can effectively reduce drilling fluid intrusion during drilling of hydrate reservoirs. However, these materials have the following issues: 1) They tend to agglomerate, affecting the effectiveness of plugging microfractures; and 2) they are difficult to decompose, which can reduce reservoir permeability, damage the hydrate reservoir, and hinder subsequent recovery.

[0005] Therefore, developing a high-performance water-based drilling fluid for drilling deep-water shallow oil and gas reservoirs with strong sealing performance and less damage to the reservoir is one of the important research directions in the current field of deep-water shallow oil and gas reservoir drilling technology. Summary of the Invention

[0006] In order to solve the deficiencies of the existing technology, especially the problem of drilling fluid intrusion into the reservoir during drilling of deep-water shallow oil and gas reservoirs, the present invention provides a temperature-sensitive plugging water-based drilling fluid for oil and gas drilling, and its preparation method and application.

[0007] The water-based drilling fluid of the present invention is used for drilling deepwater shallow oil and gas reservoirs. It can maintain good rheological properties, reduce filtration and achieve plugging performance under low-temperature and high-pressure conditions on the seabed. Furthermore, the temperature-sensitive plugging agent of the present invention can effectively enhance the plugging ability of the drilling fluid, particularly in low-temperature deepwater environments, and can quickly form a stable plugging layer, significantly reducing wellbore collapse and shrinkage. It has good adaptability to the complex geological conditions commonly found in deepwater shallow gas drilling, can effectively control the hydration expansion and dispersion behavior of clay, slow the formation of formation cracks, and thus maintain wellbore stability during the drilling process.

[0008] The technical solutions of the present invention are as follows: A temperature-sensitive plugging water-based drilling fluid for oil and gas drilling, the water-based drilling fluid comprising the following components: Natural seawater, fluid loss additive, polyamine, ethylene glycol, sodium hydroxide, potassium chloride, xanthan gum, anti-balling lubricant, dual-effect hydrate inhibitor, temperature-sensitive plugging agent and glass beads; wherein, relative to 100 parts by weight of natural seawater, the content of the fluid loss agent is 1-5 parts by weight, the content of the polyamine is 1-3 parts by weight, the content of the ethylene glycol is 15-25 parts by weight, the content of the sodium hydroxide is 0.05-0.5 parts by weight, the content of the potassium chloride is 3-8 parts by weight, the content of the xanthan gum is 0.1-0.5 parts by weight, the content of the anti-balling lubricant is 3-8 parts by weight, the content of the dual-effect hydrate inhibitor is 0.5-5 parts by weight, the content of the temperature-sensitive plugging agent is 1-3 parts by weight, and the content of the glass microspheres is 1-5 parts by weight; The temperature-sensitive plugging agent is obtained by free radical polymerization using isopropyl acrylamide, butyl methacrylate and acrylic acid as polymerization monomers, and the molar ratio of isopropyl acrylamide, butyl methacrylate and acrylic acid is (91-97): (8-2):1.

[0009] Preferably, according to the present invention, the fluid loss additive is one of modified starch PF-FLOTROL and modified cellulose PF-PAC-LV, or a mixture of the two.

[0010] Further preferably, the fluid loss additive is modified cellulose PF-PAC-LV.

[0011] According to the present invention, preferably, the polyamine is the polyamine inhibitor PF-UHIB.

[0012] According to the preferred embodiment of the present invention, the anti-balling lubricant is PF-HLUB.

[0013] According to the present invention, preferably, the dual-action hydrate inhibitor is polyvinylpyrrolidone (PVP).

[0014] Preferably, according to the present invention, in the water-based drilling fluid, relative to 100 parts by weight of natural seawater, the content of the fluid loss reducer is 1-3 parts by weight, the content of the polyamine is 1-1.5 parts by weight, the content of ethylene glycol is 20 parts by weight, the content of sodium hydroxide is 0.1 parts by weight, the content of potassium chloride is 4-6 parts by weight, the content of xanthan gum is 0.1-0.15 parts by weight, the content of the anti-mud balling lubricant is 5 parts by weight, the content of the dual-effect hydrate inhibitor is 1 part by weight, the content of the temperature-sensitive plugging agent is 1-2.5 parts by weight, and the content of the glass microspheres is 1-2 parts by weight.

[0015] According to the present invention, the temperature-sensitive plugging agent is prepared according to the following method: (1) Add the polymer monomers isopropyl acrylamide, butyl methacrylate and acrylic acid to N,N-dimethylformamide (DMF), then heat the mixed solution in a water bath and mechanically stir to fully dissolve the monomers, and continuously introduce nitrogen for deoxygenation; (2) Slowly add the initiator to the reaction system through a constant pressure dropping funnel and maintain the reaction under a nitrogen atmosphere; (3) After the reaction is completed, the product is washed, dried, and crushed to obtain a temperature-sensitive plugging agent.

[0016] Preferably, according to the present invention, in step (1), the molar ratio of isopropylacrylamide, butyl methacrylate and acrylic acid is (91-97): (8-2): 1.

[0017] Preferably, according to the present invention, in step (1), the volume ratio of the total mass of the polymer monomers isopropylacrylamide, butyl methacrylate and acrylic acid to N,N-dimethylformamide DMF is (20-40):30, unit, g / mL.

[0018] Preferably, according to the present invention, in step (1), the water bath heating temperature is 35-45° C., the mechanical stirring speed is 200-300 rpm, and the stirring time is 10-15 minutes.

[0019] Preferably, according to the present invention, in step (1), the time for introducing nitrogen is 20-60 minutes, and the introduction of nitrogen can exhaust the air in the reaction system.

[0020] According to the preferred embodiment of the present invention, in step (2), the initiator is azobisisobutyronitrile, and the added mass of the initiator is 0.05-0.2% of the total mass of the polymerization monomers; the initiator is added to the system in the form of an N,N-dimethylformamide solution of the initiator.

[0021] Most preferably, in step (2), the mass of the added initiator is 0.1% of the total mass of the polymerization monomers.

[0022] According to the preferred embodiment of the present invention, in step (2), the reaction time is maintained at 6 to 7 hours, and the stirring rate during the reaction is 200 to 400 rpm.

[0023] According to the preferred embodiment of the present invention, in step (3), the washing step is to pour the reaction product into an excess of 30°C deionized water and stir for 10 minutes to allow the material to fully precipitate, transfer the suspension to a Buchner funnel for suction filtration, and wash the obtained white solid with anhydrous ethanol to remove impurities.

[0024] According to the preferred embodiment of the present invention, in step (3), the drying step is to place the solid sample in a vacuum drying oven at 50° C. and dry it for 12 hours.

[0025] The method for preparing the temperature-sensitive plugging water-based drilling fluid for oil and gas drilling comprises the following steps: According to the ratio, ethylene glycol is added to natural seawater, and the mixture is stirred at 7000-9000 rpm and 25°C for 8-12 minutes. Then, an anti-mud balling lubricant, xanthan gum, polyamine, a filtrate reducer, and a temperature-sensitive plugging agent are added in sequence, and the mixture is stirred at 9000 r / min-10000 r / min for 15-25 minutes. Subsequently, the rotation speed is increased to 11000 r / min-12000 r / min, and a dual-effect hydrate inhibitor is added, and the mixture is fully stirred for 25-35 minutes. Sodium hydroxide is added to adjust the pH value of the drilling fluid system to between 9 and 10. Finally, glass microbeads and potassium chloride are added according to the ratio, and the mixture is stirred for 15-25 minutes to obtain a temperature-sensitive plugging water-based drilling fluid for oil and gas drilling.

[0026] The above-mentioned temperature-sensitive plugging water-based drilling fluid is used as a drilling fluid system in drilling deep-water shallow oil and gas reservoirs. During the drilling process of deep-water shallow oil and gas reservoirs, the drilling fluid is prevented from invading the pores of the sediment, maintaining the stability of the well wall, preventing collapse, and ensuring drilling continuity.

[0027] The technical features and beneficial effects of the present invention are as follows: 1. The water-based drilling fluid of this invention exhibits excellent rheological properties at both room and low temperature conditions for deepwater shallow oil and gas reservoirs. It also has a low API filtration loss, effectively reducing filtrate intrusion into the formation during drilling and helping to maintain wellbore stability.

[0028] 2. The water-based drilling fluid of the present invention achieved a plugging rate of up to 97.6% in the core plugging experiment, significantly improving the plugging performance of the drilling fluid. The high plugging rate effectively prevented the drilling fluid from invading the hydrate reservoir, thereby maintaining the stability of the well wall and ensuring safe drilling.

[0029] 3. The water-based drilling fluid of the present invention is added with a temperature-sensitive plugging agent, which shows a good plugging effect during the intrusion of the hydrate reservoir and prevents further invasion of the drilling fluid; compared with ultrafine calcium carbonate and nano-silicon dioxide, the pressure difference fluctuation of the temperature-sensitive plugging agent of the present invention is smaller, showing better plugging performance.

[0030] 4. The filtrate reducer in the water-based drilling fluid of the present invention can form a dense mud cake, effectively reducing the penetration of water in the drilling fluid into the formation. The temperature-sensitive plugging agent can prevent the filtrate from further percolating, and can dissolve in water again when the reservoir temperature is lower than its phase transition temperature, thereby realizing intelligent unblocking. The polyamine inhibitor PF-UHIB is adsorbed on the clay surface through positively charged ammonium ions, and strengthens the bondage to the clay flakes through hydrogen bonding, preventing the entry of water molecules and inhibiting the hydration and expansion of the clay. The dual-effect hydrate inhibitor can effectively limit the formation and decomposition of hydrates, while playing a role in safe drilling and protecting the reservoir; the joint interaction enables the drilling fluid to effectively plug micro-cracks in the formation, prevent the drilling fluid from invading the sediment pores during the drilling process of deep-water shallow oil and gas reservoirs, maintain the stability of the well wall, prevent collapse, and ensure drilling continuity. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 The curves of the pressure difference between the inlet and outlet during the intrusion of drilling fluids F1-F4, DF1-DF3 and pure water into the hydrate sediment layer; Figure 2 This is the result of nuclear magnetic resonance imaging of the drilling fluid invading the hydrate reservoir; Figure 3 This is the pressure difference curve between the inlet and outlet after the drilling fluid is injected and cold water is injected into the sand filling pipe in reverse direction; Figure 4 Magnetic resonance imaging results of the reverse injection process of cold water hydrate reservoir. DETAILED DESCRIPTION

[0032] The present invention will be further described below with reference to specific embodiments, but is not limited thereto.

[0033] Meanwhile, the experimental methods described in the following examples, unless otherwise specified, are conventional methods; the reagents, materials and equipment, unless otherwise specified, can be obtained from commercial channels.

[0034] The modified cellulose PF-PAC-LV in the examples was purchased from Shanghai Kanglang Biotechnology Co., Ltd. Polyamine inhibitor PF-UHIB was purchased from Beijing Kenojie Energy and Environmental Protection Technology Co., Ltd.; Ethylene glycol was purchased from Shanghai Titan Technology Co., Ltd.; Sodium hydroxide and potassium chloride were purchased from Sinopharm Chemical Reagent Co., Ltd. Xanthan gum was purchased from Shandong Juxin New Materials Co., Ltd.; The anti-balling lubricant was PF-HLUB purchased from China Oilfield Services Limited; The hydrate dual-action inhibitor PVP was purchased from Shanghai Aladdin Biochemical Technology Co., Ltd.; Glass microspheres were purchased from Zhengzhou Shenglait Hollow Microsphere New Materials Co., Ltd.

[0035] Unless otherwise specified, the "parts" mentioned in the following preparation examples and embodiments are by weight.

[0036] Example 1 The preparation method of the temperature-sensitive plugging agent comprises the following steps: (1) Add 30 g of a mixture of isopropyl acrylamide, butyl methacrylate, and acrylic acid in a molar ratio of 91:8:1 to 200 mL of N,N-dimethylformamide (DMF). Place the mixed solution in a 40°C water bath and stir at a stirring speed of 200 r / min until fully dissolved. Continue to introduce nitrogen for 40 minutes to complete deoxygenation. (2) Weigh 0.03 g of azobisisobutyronitrile initiator, dissolve it in N,N-dimethylformamide, and slowly add the initiator to the reaction system through a constant pressure dropping funnel. Continue the reaction for 6 hours under a nitrogen atmosphere. (3) After the reaction is completed, the reaction product is poured into an excess of 30°C deionized water and stirred for 10 minutes to allow the polymer to fully precipitate. The suspension is transferred to a Buchner funnel for filtration, and the resulting white solid is washed with anhydrous ethanol to remove impurities. Finally, the solid sample is placed in a 50°C vacuum drying oven and dried for 12 hours to obtain a temperature-sensitive plugging agent with a phase transition temperature of 13.8°C, which is recorded as A1.

[0037] Example 2 The preparation method of the temperature-sensitive plugging agent is the same as that described in Example 1, except that the molar ratio of isopropyl acrylamide, butyl methacrylate and acrylic acid is 93:6:1, and the obtained temperature-sensitive plugging agent has a phase transition temperature of 14.6°C, which is recorded as A2; Example 3 The preparation method of the temperature-sensitive plugging agent is the same as that described in Example 1, except that the molar ratio of isopropyl acrylamide, butyl methacrylate and acrylic acid is 95:4:1, and the obtained temperature-sensitive plugging agent has a phase transition temperature of 15.7°C, which is recorded as A3; Example 4 The preparation method of the temperature-sensitive plugging agent is the same as that described in Example 1, except that the molar ratio of isopropyl acrylamide, butyl methacrylate, and acrylic acid is 97:2:1, and a temperature-sensitive plugging agent with a phase transition temperature of 17.3° C. is obtained, which is recorded as A4; Example 5 A temperature-sensitive plugging water-based drilling fluid for oil and gas drilling, the water-based drilling fluid comprising the following components: Natural seawater, modified cellulose PF-PAC-LV, polyamine PF-UHIB, ethylene glycol, sodium hydroxide, potassium chloride, xanthan gum, anti-mud balling lubricant PF-HLUB, polyvinylpyrrolidone PVP, the temperature-sensitive plugging agent A1 prepared in Example 1, and glass microspheres; Wherein, relative to 100 parts by weight of natural seawater, the content of modified cellulose PF-PAC-LV is 2 parts by weight, the content of polyamine PF-UHIB is 1 part by weight, the content of ethylene glycol is 20 parts by weight, the content of sodium hydroxide is 0.1 parts by weight, the content of potassium chloride is 5 parts by weight, the content of xanthan gum is 0.1 parts by weight, the content of anti-mud balling lubricant PF-HLUB is 5 parts by weight, the content of polyvinylpyrrolidone PVP is 1 part by weight, the content of temperature-sensitive plugging agent A1 prepared in Example 1 is 2 parts by weight, and the content of glass microspheres is 2 parts by weight; The preparation method of the temperature-sensitive plugging water-based drilling fluid for oil and gas drilling comprises the following steps: Ethylene glycol was added to natural seawater according to the proportion, and the mixture was stirred at 8000 rpm and 25°C for 10 minutes. Then, an anti-balling lubricant PF-HLUB, xanthan gum, polyamine PF-UHIB, modified cellulose PF-PAC-LV, and the temperature-sensitive plugging agent A1 prepared in Example 1 were added in sequence, and the mixture was stirred at 10000 r / min for 20 minutes. Subsequently, the speed was increased to 11000 r / min, and polyvinylpyrrolidone (PVP) was added, and the mixture was fully stirred for 20 minutes. Sodium hydroxide was added to adjust the pH value of the drilling fluid to 10. Finally, glass microspheres and potassium chloride were added according to the proportion, and the mixture was stirred for 20 minutes to obtain a temperature-sensitive plugging water-based drilling fluid for oil and gas drilling. The obtained water-based drilling fluid was recorded as F1.

[0038] Example 6 The temperature-sensitive plugging water-based drilling fluid for oil and gas drilling described in Example 5 differs in that: The temperature-sensitive plugging agent is the self-removing plugging agent A2 obtained in Example 2, and the prepared water-based drilling fluid is recorded as F2.

[0039] Example 7 The temperature-sensitive plugging water-based drilling fluid for oil and gas drilling described in Example 5 differs in that: The temperature-sensitive plugging agent is the self-removing plugging agent A3 obtained in Example 3, and the prepared water-based drilling fluid is recorded as F3.

[0040] Example 8 The temperature-sensitive plugging water-based drilling fluid for oil and gas drilling described in Example 5 differs in that: The temperature-sensitive plugging agent is the self-removing plugging agent A4 obtained in Example 4, and the prepared water-based drilling fluid is recorded as F4.

[0041] Example 9 The temperature-sensitive plugging water-based drilling fluid for oil and gas drilling described in Example 5 differs in that: Relative to 100 parts by weight of natural seawater, the content of modified cellulose PF-PAC-LV is 2 parts by weight, the content of polyamine PF-UHIB is 1 part by weight, the content of ethylene glycol is 20 parts by weight, the content of sodium hydroxide is 0.1 parts by weight, the content of potassium chloride is 5 parts by weight, the content of xanthan gum is 0.1 parts by weight, the content of anti-mud balling lubricant PF-HLUB is 5 parts by weight, the content of polyvinylpyrrolidone PVP is 1 part by weight, the content of temperature-sensitive plugging agent A1 prepared in Example 1 is 1 part by weight, and the content of glass microspheres is 2 parts by weight. The obtained water-based drilling fluid is recorded as F5.

[0042] Example 10 The temperature-sensitive plugging water-based drilling fluid for oil and gas drilling described in Example 5 differs in that: Relative to 100 parts by weight of natural seawater, the content of modified cellulose PF-PAC-LV is 2 parts by weight, the content of polyamine PF-UHIB is 1 part by weight, the content of ethylene glycol is 20 parts by weight, the content of sodium hydroxide is 0.1 parts by weight, the content of potassium chloride is 5 parts by weight, the content of xanthan gum is 0.1 parts by weight, the content of anti-mud balling lubricant PF-HLUB is 5 parts by weight, the content of polyvinylpyrrolidone PVP is 1 part by weight, the content of temperature-sensitive plugging agent A1 prepared in Example 1 is 1.5 parts by weight, and the content of glass microspheres is 2 parts by weight. The obtained water-based drilling fluid is recorded as F6.

[0043] Example 11 The temperature-sensitive plugging water-based drilling fluid for oil and gas drilling described in Example 5 differs in that: Relative to 100 parts by weight of natural seawater, the content of modified cellulose PF-PAC-LV is 2 parts by weight, the content of polyamine PF-UHIB is 1 part by weight, the content of ethylene glycol is 20 parts by weight, the content of sodium hydroxide is 0.1 parts by weight, the content of potassium chloride is 5 parts by weight, the content of xanthan gum is 0.1 parts by weight, the content of anti-mud balling lubricant PF-HLUB is 5 parts by weight, the content of polyvinylpyrrolidone PVP is 1 part by weight, the content of temperature-sensitive plugging agent A1 prepared in Example 1 is 2.5 parts by weight, and the content of glass microbeads is 2 parts by weight. The obtained water-based drilling fluid is recorded as F7.

[0044] Example 12 The temperature-sensitive plugging water-based drilling fluid for oil and gas drilling described in Example 5 differs in that: Relative to 100 parts by weight of natural seawater, the content of modified cellulose PF-PAC-LV is 1 part by weight, the content of polyamine PF-UHIB is 1 part by weight, the content of ethylene glycol is 15 parts by weight, the content of sodium hydroxide is 0.05 parts by weight, the content of potassium chloride is 3 parts by weight, the content of xanthan gum is 0.1 parts by weight, the content of anti-mud bag lubricant PF-HLUB is 3 parts by weight, the content of polyvinylpyrrolidone PVP is 0.5 parts by weight, the content of temperature-sensitive plugging agent A1 prepared in Example 1 is 1 part by weight, and the content of glass microbeads is 1 part by weight.

[0045] Example 13 The temperature-sensitive plugging water-based drilling fluid for oil and gas drilling described in Example 5 differs in that: Relative to 100 parts by weight of natural seawater, the content of modified cellulose PF-PAC-LV is 5 parts by weight, the content of polyamine PF-UHIB is 3 parts by weight, the content of ethylene glycol is 25 parts by weight, the content of sodium hydroxide is 0.5 parts by weight, the content of potassium chloride is 8 parts by weight, the content of xanthan gum is 0.5 parts by weight, the content of anti-mud ball lubricant PF-HLUB is 8 parts by weight, the content of polyvinylpyrrolidone PVP is 5 parts by weight, the content of temperature-sensitive plugging agent A1 prepared in Example 1 is 3 parts by weight, and the content of glass microbeads is 5 parts by weight.

[0046] Example 14 The temperature-sensitive plugging water-based drilling fluid for oil and gas drilling described in Example 5 differs in that: Relative to 100 parts by weight of natural seawater, the content of modified cellulose PF-PAC-LV is 2 parts by weight, the content of polyamine PF-UHIB is 1 part by weight, the content of ethylene glycol is 22 parts by weight, the content of sodium hydroxide is 0.1 parts by weight, the content of potassium chloride is 6 parts by weight, the content of xanthan gum is 0.15 parts by weight, the content of anti-mud bag lubricant PF-HLUB is 8 parts by weight, the content of polyvinylpyrrolidone PVP is 2 parts by weight, the content of temperature-sensitive plugging agent A1 prepared in Example 1 is 2 parts by weight, and the content of glass microbeads is 1 part by weight.

[0047] Comparative Example 1 A strong-sealing, temperature-sensitive water-based drilling fluid for drilling deepwater shallow oil and gas reservoirs. The fluid comprises, relative to 100 parts by weight of natural seawater, 2 parts by weight of modified cellulose PF-PAC-LV, 1 part by weight of polyamine PF-UHIB, 20 parts by weight of ethylene glycol, 0.1 parts by weight of sodium hydroxide, 5 parts by weight of potassium chloride, 0.1 parts by weight of xanthan gum, 5 parts by weight of an anti-balling lubricant PF-HLUB, 1 part by weight of polyvinylpyrrolidone (PVP), 2 parts by weight of 1000-mesh ultrafine calcium carbonate, and 2 parts by weight of glass microspheres. The preparation method was carried out according to Example 5 to obtain a water-based drilling fluid, which was designated as DF1.

[0048] Comparative Example 2 A strong-sealing, temperature-sensitive water-based drilling fluid for drilling deepwater shallow oil and gas reservoirs. The fluid comprises, relative to 100 parts by weight of natural seawater, 2 parts by weight of modified cellulose PF-PAC-LV, 1 part by weight of polyamine PF-UHIB, 20 parts by weight of ethylene glycol, 0.1 parts by weight of sodium hydroxide, 5 parts by weight of potassium chloride, 0.1 parts by weight of xanthan gum, 5 parts by weight of an anti-balling lubricant PF-HLUB, 1 part by weight of polyvinylpyrrolidone (PVP), 2 parts by weight of 800-mesh nano-silica, and 2 parts by weight of glass microspheres. The preparation method was carried out according to Example 5 to obtain a water-based drilling fluid, which was designated as DF2.

[0049] Comparative Example 3 A strong-sealing temperature-sensitive water-based drilling fluid for drilling deepwater shallow oil and gas reservoirs. The water-based drilling fluid does not contain a plugging agent. Relative to 100 parts by weight of natural seawater, the content of modified cellulose PF-PAC-LV is 2 parts by weight, the content of polyamine PF-UHIB is 1 part by weight, the content of ethylene glycol is 20 parts by weight, the content of sodium hydroxide is 0.1 parts by weight, the content of potassium chloride is 5 parts by weight, the content of xanthan gum is 0.1 parts by weight, the content of anti-mud balling lubricant PF-HLUB is 5 parts by weight, the content of polyvinyl pyrrolidone (PVP) is 1 part by weight, and the content of glass microspheres is 2 parts by weight. The preparation method was carried out according to Example 5 to obtain a water-based drilling fluid, which was designated as DF3.

[0050] Test Example 1 The rheological properties and filtration properties of drilling fluids F1-F7 and DF1-DF3 were tested as follows: Take 500mL of drilling fluids F1-F7 and DF1-DF3 respectively and stir them at 6000rpm / min for 20 minutes. Then, according to the national standard "GB / T29170-2012 Laboratory Test of Drilling Fluids in Petroleum and Natural Gas Industry", the API water loss (FL API , mL) and rheological parameters at room temperature and 4°C, including apparent viscosity (AV, mPa·s), plastic viscosity (PV, mPa·s), and dynamic shear force (YP, Pa). The results are shown in Table 1.

[0051] Table 1 Rheological and filtration properties of drilling fluid As can be seen from the data in Table 1, the temperature-sensitive strong plugging water-based drilling fluids F1-F7 of the present invention for deep-water shallow oil and gas reservoirs exhibit good rheological properties at room temperature and low temperature conditions. At the same time, the API filtration loss of the water-based drilling fluids F1-F7 is low, which effectively reduces the invasion of the filtrate into the formation during the drilling process and helps to maintain the stability of the well wall. The comparative results show that the water-based drilling fluid of the present invention is superior to ultrafine calcium carbonate and nano-silicon dioxide in terms of filtration loss reduction performance. Compared with the water-based drilling fluids F1-F4, the change in the monomer ratio can affect the phase transition temperature of the thermosensitive polymer, but has little effect on its filtration loss reduction performance, ensuring that it can effectively reduce filtration loss in reservoirs at different temperatures.

[0052] Test Example 2 Drilling fluids F1-F7 and DF1-DF3 were tested for core plugging performance. The specific method is as follows: Take 500mL of drilling fluids F1-F7 and DF1-DF3 respectively, stir at 6000rpm / min for 20min, and use the change in water drive pressure before and after the core plugging experiment to characterize the plugging efficiency of the drilling fluid. The specific operation steps are as follows: (1) The dried core (φ = 2.5 cm × 5 cm) was vacuumed for 4 h, saturated with simulated formation water, and water was displaced into the core. The permeability before plugging was measured as K1; (2) The confining pressure was set to 5 MPa and the back pressure was set to 2 MPa. The cores were displaced with drilling fluids F1-F4 and DF1-DF6. The flow rate of the drilling fluid was adjusted to 2 ml / min for continuous displacement. The permeability of the cores after plugging was measured. The test results are shown in Table 2.

[0053] The core plugging rate calculation formula is:

[0054] Table 2

[0055] The data in Table 2 show that the water-based drilling fluids F1-F7 prepared in the examples of the present invention achieved a plugging rate of up to 97.6% in core plugging experiments, significantly improving the plugging performance of the drilling fluid. This high plugging rate effectively prevented the drilling fluid from invading the hydrate reservoir, thereby maintaining wellbore stability and ensuring safe drilling.

[0056] Test Example 3 Based on the device and method disclosed in Chinese patent document CN114893175A, damage to natural gas hydrate reservoirs caused by drilling fluid intrusion was assessed. Using this device, the plugging performance of drilling fluids F1-F4 and DF1-DF3 in hydrate deposits was tested.

[0057] 300 mL of drilling fluids F1-F4 and DF1-DF3 were stirred at 6000 rpm for 20 minutes. A low-field nuclear magnetic resonance system was used to simulate the invasion of the drilling fluid into the hydrate reservoir during drilling. The plugging performance of the drilling fluid was evaluated by recording the pressure differential between the inlet and outlet of the sand packing pipe.

[0058] The quartz sand used in the experiment has a particle size of 80-100 mesh. The specific steps are as follows: Mixed quartz sand and water were placed in a sand-filled tube and the confining pressure was set to 6 MPa. Methane gas was then slowly introduced while the temperature of the holder was lowered to 2°C to generate hydrates under constant volume conditions.

[0059] After hydrate formation, the back pressure was adjusted to a pressure close to the phase equilibrium pressure of hydrates in the sediments, and the outlet pressure in the sand filling pipe was kept constant. Then, pure water, drilling fluids F1-F4, and DF1-DF3 were injected into the hydrate sediment layer at a rate of 1 mL / min, respectively, to simulate the process of drilling fluid invading the hydrate formation under the action of pressure difference, and the changes in the inlet and outlet pressures of the sand filling pipe were recorded. The test results are shown in Figure 1 .

[0060] pass Figure 1 It can be seen that the drilling fluids F1-F4 with temperature-sensitive plugging agents showed good plugging effects during the intrusion of hydrate reservoirs. The inlet and outlet pressure difference gradually increased and stabilized at about 4.3 MPa. Figure 2 Magnetic resonance imaging (NMR) images of drilling fluid F1 invading the hydrate reservoir indicate that the thermosensitive polymer particles effectively blocked sediment pores, preventing further intrusion of the drilling fluid. Compared to ultrafine calcium carbonate and nanosilica, drilling fluids F1-F4 containing thermosensitive plugging agents exhibited less differential pressure fluctuation, demonstrating superior plugging performance.

[0061] Test Example 4 The plugging removal effects of drilling fluids F1-F4 and DF1-DF3 were tested. The specific operations are as follows: After the drilling fluid is injected, cold water is injected into the sand filling pipe in reverse to make it flow through the blocked area. During the injection process, a low flow rate of 0.5 mL / min is used to record the pressure changes at the inlet and outlet of the sand filling pipe. The results are shown in Figure 3 .

[0062] according to Figure 3 When cooling water was initially injected, the inlet and outlet pressure difference of drilling fluids F1-F4 changed little, indicating that the temperature-sensitive polymer particles were still blocking the flow path of the sediment. As time increased to about 10 minutes, the inlet and outlet pressure difference dropped sharply from about 4 MPa to about 1.9 MPa within 5 minutes. Figure 4Magnetic resonance imaging results from the reverse injection process into the cold-water hydrate reservoir indicate that the thermosensitive polymer particles that blocked the pores of the hydrate sediments gradually dissolved in the cooling water, restoring the reservoir's permeability. In contrast to the thermosensitive polymer, nanosilica and ultrafine calcium carbonate showed no significant decrease in pressure drop during reverse injection, and their particles continued to clog the pores, complicating subsequent hydrate recovery.

Claims

1. A temperature-sensitive plugging water-based drilling fluid for oil and gas drilling, characterized in that: The water-based drilling fluid comprises the following components: Natural seawater, fluid loss additive, polyamine, ethylene glycol, sodium hydroxide, potassium chloride, xanthan gum, anti-balling lubricant, dual-effect hydrate inhibitor, temperature-sensitive plugging agent and glass beads; wherein, relative to 100 parts by weight of natural seawater, the content of the fluid loss agent is 1-5 parts by weight, the content of the polyamine is 1-3 parts by weight, the content of the ethylene glycol is 15-25 parts by weight, the content of the sodium hydroxide is 0.05-0.5 parts by weight, the content of the potassium chloride is 3-8 parts by weight, the content of the xanthan gum is 0.1-0.5 parts by weight, the content of the anti-balling lubricant is 3-8 parts by weight, the content of the dual-effect hydrate inhibitor is 0.5-5 parts by weight, the content of the temperature-sensitive plugging agent is 1-3 parts by weight, and the content of the glass microspheres is 1-5 parts by weight; The temperature-sensitive plugging agent is prepared by free radical polymerization using isopropyl acrylamide, butyl methacrylate and acrylic acid as polymerization monomers, wherein the molar ratio of isopropyl acrylamide, butyl methacrylate and acrylic acid is (91-97): (8-2): 1; The fluid loss additive is one or a mixture of modified starch PF-FLOTROL and modified cellulose PF-PAC-LV; The polyamine is a polyamine inhibitor PF-UHIB; The anti-mud balling lubricant is PF-HLUB; The dual-action hydrate inhibitor is polyvinylpyrrolidone (PVP).

2. The temperature-sensitive plugging water-based drilling fluid for oil and gas drilling according to claim 1, characterized in that: The fluid loss additive is modified cellulose PF-PAC-LV.

3. The temperature-sensitive plugging water-based drilling fluid for oil and gas drilling according to claim 1, characterized in that: In the water-based drilling fluid, relative to 100 parts by weight of natural seawater, the content of the fluid loss reducer is 1-3 parts by weight, the content of the polyamine is 1-1.5 parts by weight, the content of ethylene glycol is 20 parts by weight, the content of sodium hydroxide is 0.1 parts by weight, the content of potassium chloride is 4-6 parts by weight, the content of xanthan gum is 0.1-0.15 parts by weight, the content of the anti-mud balling lubricant is 5 parts by weight, the content of the dual-effect hydrate inhibitor is 1 part by weight, the content of the temperature-sensitive plugging agent is 1-2.5 parts by weight, and the content of the glass microspheres is 1-2 parts by weight.

4. The temperature-sensitive plugging water-based drilling fluid for oil and gas drilling according to claim 1, characterized in that: The temperature-sensitive plugging agent is prepared as follows: (1) Add the polymer monomers isopropyl acrylamide, butyl methacrylate and acrylic acid to N,N-dimethylformamide (DMF), then heat the mixed solution in a water bath and mechanically stir to fully dissolve the monomers, and continuously introduce nitrogen for deoxygenation; (2) Slowly add the initiator to the reaction system through a constant pressure dropping funnel and maintain the reaction under a nitrogen atmosphere; (3) After the reaction is completed, the product is washed, dried, and crushed to obtain a temperature-sensitive plugging agent.

5. The temperature-sensitive plugging water-based drilling fluid for oil and gas drilling according to claim 4, characterized in that: In step (1), the molar ratio of isopropylacrylamide, butyl methacrylate and acrylic acid is (91-97): (8-2): 1, the volume ratio of the total mass of the polymer monomers isopropylacrylamide, butyl methacrylate and acrylic acid to N,N-dimethylformamide (DMF) is (20-40): 30, unit, g / mL, the water bath heating temperature is 35-45°C, the mechanical stirring speed is 200-300 rpm, the stirring time is 10-15 minutes, and the time for introducing nitrogen is 20-60 minutes. The introduction of nitrogen can exhaust the air in the reaction system.

6. The temperature-sensitive plugging water-based drilling fluid for oil and gas drilling according to claim 4, characterized in that: In step (2), the initiator is azobisisobutyronitrile, and the added mass of the initiator is 0.05-0.2% of the total mass of the polymerization monomer; the initiator is added to the system in the form of an N,N-dimethylformamide solution of the initiator, the reaction time is maintained at 6-7 hours, and the stirring rate during the reaction is 200-400 rpm.

7. The temperature-sensitive plugging water-based drilling fluid for oil and gas drilling according to claim 4, characterized in that: In step (3), washing is performed by pouring the reaction product into an excess of 30°C deionized water and stirring for 10 minutes to allow the material to fully precipitate, transferring the suspension to a Buchner funnel for suction filtration, and washing the obtained white solid with anhydrous ethanol to remove impurities. Drying is performed by placing the solid sample in a vacuum drying oven at 50°C for 12 hours.

8. A method for preparing the temperature-sensitive plugging water-based drilling fluid for oil and gas drilling according to any one of claims 1 to 7, comprising the following steps: According to the ratio, ethylene glycol is added to natural seawater, and the mixture is stirred at 7000-9000 rpm and 25°C for 8-12 minutes. Then, an anti-mud balling lubricant, xanthan gum, polyamine, a filtrate reducer, and a temperature-sensitive plugging agent are added in sequence, and the mixture is stirred at 9000 r / min-10000 r / min for 15-25 minutes. Subsequently, the rotation speed is increased to 11000 r / min-12000 r / min, and a dual-effect hydrate inhibitor is added, and the mixture is fully stirred for 25-35 minutes. Sodium hydroxide is added to adjust the pH value of the drilling fluid system to between 9 and 10. Finally, glass microbeads and potassium chloride are added according to the ratio, and the mixture is stirred for 15-25 minutes to obtain a temperature-sensitive plugging water-based drilling fluid for oil and gas drilling.

9. The use of the temperature-sensitive plugging water-based drilling fluid according to any one of claims 1 to 7 as a drilling fluid system in drilling deep-water shallow oil and gas reservoirs, which prevents the drilling fluid from invading the pores of the sediment during the drilling process of deep-water shallow oil and gas reservoirs, maintains the stability of the well wall, prevents collapse, and ensures drilling continuity.

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