A soil-free temporary plugging reservoir protection drilling fluid and its preparation method and application

Abstract

The present invention relates to a soil-free temporary plugging reservoir protection drilling fluid and a preparation method and application thereof, and belongs to the field of marine oil and gas drilling and production technology. The temporary plugging reservoir protection drilling fluid comprises the following components: natural seawater, sodium hydroxide, sodium chloride, potassium chloride, ethylene glycol, fluid loss reducer, viscosity enhancing coating agent, polyamine, drilling fluid starch, anti-mud packing lubricant, modified resin, self-unplugging plugging agent, hydrate inhibitor and glass microbeads. The soil-free temporary plugging reservoir protection drilling fluid of the present invention has a plugging rate of up to 96.6% in the core plugging experiment, which significantly improves the plugging performance of the drilling fluid. It can be seen from the unplugging experiment that the reservoir permeability recovery rate can reach up to 85.6%, which ensures the production capacity and fluid fluidity of the reservoir, and has significant advantages in effectively protecting the formation and improving the stability of the wellbore. In the linear expansion experiment conducted on the drilling fluid, it was shown that the expansion inhibition effect on the formation rock was significant.

Description

Technical Field

[0001] The invention relates to a soil-free temporary plugging reservoir protection drilling fluid and a preparation method and application thereof, belonging to the technical field of offshore oil and gas drilling and production. Background Art

[0002] Compared with conventional onshore and offshore oil exploration and development, the exploration and development of deepwater areas face unique challenges. Deepwater areas are far from the coast, and the sediments carried by wind, rivers and oceans are relatively fine. The rocks in the formations usually show characteristics such as easy expansion, high dispersion, and easy leakage. These factors lead to excessive solid particles in the drilling process, which in turn affects the efficiency of drilling operations. In addition, as the water depth increases, the density safety window of deepwater drilling fluid gradually narrows. In addition, the low temperature of the seabed mud line and the limitations of offshore operating conditions all put higher requirements on the performance of drilling fluids. Deepwater drilling fluids not only need to adapt to complex geological conditions, but also need to remain stable in low temperature and high pressure environments to ensure the smooth progress of drilling operations.

[0003] Therefore, deepwater drilling projects require more sophisticated planning and advanced technical support to cope with complex geological and environmental challenges and ensure that the exploration and development of oil and gas resources can be carried out efficiently and safely. If overbalanced drilling is used, the drilling fluid will invade the formation under a positive pressure difference, causing the rock in the formation to be soaked by the fluid, reducing the mechanical properties of the well wall and causing well wall instability. In the case of severe well wall instability, when selecting a drilling fluid system, it is necessary to enhance the plugging ability and hydration inhibition performance of the drilling fluid. At the same time, the rheology and filtration properties of the drilling fluid must be adjusted to adapt to the complex drilling environment. These measures can not only effectively prevent well wall instability, but also improve the efficiency and safety of the overall drilling operation.

[0004] At present, there are few studies on deepwater reservoir protection drilling fluids, mainly focusing on synthetic-based drilling fluids, such as: Patent document CN109971440A discloses an environmentally friendly and easily degradable synthetic-based drilling fluid, which selects natural products or their modified substances as the emulsifier and fluid loss reducer of the system to prepare an environmentally friendly and easily degradable synthetic-based drilling fluid. In addition to the advantages of oil-based / synthetic-based systems such as strong inhibition and good lubricity, the system has low biological toxicity and is easy to degrade, which can meet the environmental protection requirements during the construction process. Patent document CN108276974A discloses a deepwater constant rheology synthetic-based drilling fluid, which improves the constant rheological properties of the deepwater constant rheology synthetic-based drilling fluid through the synergistic effect of emulsifiers, synthetic organic fluid loss reducers and natural organic fluid loss reducers, and has a real "constant rheology". In summary, current research on deepwater reservoir protection drilling fluids is mainly focused on synthetic-based drilling fluids. However, synthetic-based drilling fluids are relatively expensive, and the rheological properties of synthetic-based drilling fluid systems vary greatly with temperature. When the temperature changes greatly, the viscosity and shear force are difficult to control. In particular, when synthetic-based drilling fluids are stationary for a long time, the viscosity and shear force change more greatly, which is more likely to cause well leakage.

[0005] Therefore, developing a low-cost water-based drilling fluid system for deepwater oil and gas reservoirs that can meet the needs of deepwater offshore oil and gas drilling is currently one of the key research directions in the field of offshore oil and gas drilling and production technology. Summary of the invention

[0006] In view of the shortcomings of the existing technology, especially the problems that drilling fluid easily invades the reservoir during deepwater oil and gas reservoir drilling and the cost of synthetic-based drilling fluid is high, the present invention provides a soil-free temporary plugging reservoir protection drilling fluid and a preparation method and application thereof.

[0007] The soil-free temporary plugging reservoir protection drilling fluid of the present invention can maintain excellent rheological properties under low temperature and high pressure conditions on the seabed, significantly reduce filtration loss and have a good plugging effect, and can automatically unblock according to changes in reservoir temperature, thereby restoring the reservoir permeability during shallow gas production, significantly improving the reservoir protection effect, and having low cost.

[0008] The technical solution of the present invention is as follows:

[0009] A soil-free temporary plugging reservoir protection drilling fluid, the temporary plugging reservoir protection drilling fluid comprising the following components:

[0010] Natural seawater, sodium hydroxide, sodium chloride, potassium chloride, ethylene glycol, fluid loss reducer, viscosity enhancing coating agent, polyamine, starch for drilling fluid, anti-mud packing lubricant, modified resin, self-unblocking plugging agent, hydrate inhibitor and glass microspheres;

[0011] Wherein, relative to 100 parts by weight of natural seawater, the content of sodium hydroxide is 0.05-0.5 parts by weight, the content of sodium chloride is 10-15 parts by weight, the content of potassium chloride is 4-8 parts by weight, the content of ethylene glycol is 15-25 parts by weight, the content of fluid loss reducer is 1-5 parts by weight, the content of viscosity increasing coating agent is 0.05-0.5 parts by weight, the content of polyamine is 1-5 parts by weight, the content of starch for drilling fluid is 1-5 parts by weight, the content of anti-mud balling lubricant is 1-6 parts by weight, the modified resin is 1-5 parts by weight, the self-unblocking plugging agent is 2-8 parts by weight, the content of hydrate inhibitor is 1-5 parts by weight, and the content of glass microspheres is 1-5 parts by weight;

[0012] The self-unblocking plugging agent is obtained by free radical polymerization reaction with isopropyl acrylamide, ethyl acrylate and 2-acrylamide-2-methylpropane sulfonic acid as polymerization monomers, and the molar ratio of isopropyl acrylamide, ethyl acrylate and 2-acrylamide-2-methylpropane sulfonic acid is 1: (0.05-0.1): (0.001-0.002).

[0013] Preferably according to the present invention, in the temporary plugging reservoir protection drilling fluid, relative to 100 parts by weight of natural seawater, the content of sodium hydroxide is 0.1 parts by weight, the content of sodium chloride is 12 parts by weight, the content of potassium chloride is 5 parts by weight, the content of ethylene glycol is 20 parts by weight, the content of filtrate reducer is 2 parts by weight, the content of viscosity increasing coating agent is 0.1 parts by weight, the content of polyamine is 2 parts by weight, the content of starch for drilling fluid is 2 parts by weight, the content of anti-mud balling lubricant is 3 parts by weight, the modified resin is 2 parts by weight, the self-unblocking plugging agent is 3 parts by weight, the content of hydrate inhibitor is 2 parts by weight, and the content of glass beads is 2 parts by weight.

[0014] Preferably according to the present invention, the fluid loss reducer is one of modified starch PF-FLOTROL and polyanionic cellulose PAC-LV or a mixture of both.

[0015] Further preferably, the fluid loss reducer is a mixture of modified starch PF-FLOTROL and polyanionic cellulose PAC-LV, and the weight ratio of modified starch PF-FLOTROL to polyanionic cellulose PAC-LV is 1:2.

[0016] Preferably according to the present invention, the viscosity enhancing coating agent is xanthan gum XC.

[0017] Preferably according to the present invention, the polyamine is a polyamine inhibitor PF-UHIB.

[0018] Preferably according to the present invention, the starch for drilling fluid is carboxymethyl starch CMS for drilling fluid.

[0019] Preferably according to the present invention, the anti-mud balling lubricant is PF-HLUB.

[0020] Preferably according to the present invention, the modified resin is PF-LSF.

[0021] Preferably, according to the present invention, the self-blocking plugging agent is prepared according to the following method:

[0022] (1) adding polymer monomers isopropyl acrylamide, ethyl acrylate and 2-acrylamido-2-methylpropanesulfonic acid into DMF solvent in a molar ratio of 1: (0.05-0.1): (0.001-0.002), stirring thoroughly until dissolved to obtain a polymer solution, and adjusting the pH value of the polymer solution to neutral; introducing nitrogen to remove oxygen, and then placing in a 50-60° C. water bath, and continuously introducing nitrogen for 40 minutes to complete deoxygenation;

[0023] (2) Add initiator a and react at a constant temperature for 5-6 hours under nitrogen protection. Initiator a is azobisisobutyronitrile;

[0024] (3) After the reaction is completed, the product obtained by the reaction is washed with anhydrous ethanol, dried, and crushed to obtain a self-unblocking plugging agent.

[0025] Preferably, in step (1), the total mass concentration of the polymerizable monomers in the polymer solution is 0.2-0.5 g / mL; and the stirring speed is 150-200 r / min.

[0026] Preferably, according to the present invention, in step (2), the amount of initiator a added is 0.1% of the total mass of the polymerization monomers.

[0027] Preferably, in step (3), the washing is performed by washing with ethanol for 3-5 times, and the drying is performed at 60° C. for 24 hours.

[0028] Preferably according to the present invention, the hydrate inhibitor is PVPK90.

[0029] The method for preparing the soil-free temporary plugging reservoir protection drilling fluid comprises the following steps:

[0030] Ethylene glycol is added to natural seawater, and the mixture is stirred at 3000-5000rpm and 25℃ for 8-12 minutes. Then, a self-unblocking plugging agent, a modified resin, an anti-mud bag lubricant, starch for drilling fluid, a polyamine, a fluid loss reducer and a hydrate inhibitor are added in sequence, and the mixture is stirred at 6000r / min-8000r / min for 15-25min. Subsequently, the rotation speed is increased to 10000r / min-12000r / min, and a viscosity increasing coating agent is added, and the mixture is fully stirred for 25-35min. Sodium chloride and potassium chloride are added in sequence according to the proportion, and the mixture is stirred for 15-25min. Sodium hydroxide is added to adjust the pH value of the drilling fluid system to between 8 and 9. Finally, glass microbeads are added in the proportion, and the mixture is stirred for 15-25min to obtain a soil-free low-density temporary plugging reservoir protection drilling fluid.

[0031] The density of the soil-free temporary plugging reservoir protection drilling fluid of the present invention is 1.05-1.07 g / cm 3 .

[0032] The application of the soil-free temporary plugging reservoir protection drilling fluid as a drilling fluid system is applied to deepwater oil and gas reservoir drilling to inhibit the expansion of formation rocks, thereby protecting the formation and improving the stability of the wellbore.

[0033] Through the above technical solution, the beneficial effects of the present invention are:

[0034] 1. The components of the soil-free temporary plugging reservoir protection drilling fluid of the present invention have good compatibility, the system is convenient to prepare, simple to use, cheap, environmentally friendly and non-toxic, and meets the specific requirements of deepwater formation on-site construction.

[0035] 2. In view of the problem that drilling fluid easily invades the reservoir during the drilling process of deep-water oil and gas reservoirs and the high cost of synthetic-based drilling fluids, the present invention adopts an unconventional, laboratory-made self-blocking plugging agent. When the temperature is higher than its phase transition temperature, it precipitates in the drilling fluid with a wide particle size distribution, thereby effectively blocking pores or cracks of different sizes; when the reservoir temperature is below the temperature sensitive point, it dissolves in the drilling fluid again to achieve self-blocking, restore the reservoir permeability, and reduce damage to the reservoir. The drilling fluid has good rheological properties and filtration properties under low-temperature conditions on the seabed, thereby effectively solving the problem of low-temperature viscosity increase of the drilling fluid.

[0036] 3. The soil-free temporary plugging reservoir protection drilling fluid of the present invention adds ethylene glycol, which can not only effectively adjust the density of the drilling fluid, but also inhibit the formation of hydrates during the drilling process. At the same time, adding the hydrate inhibitor PVPK90 into the system and using it in combination with ethylene glycol can better enhance the inhibition effect and effectively reduce the hydrate formation rate.

[0037] 4. The soil-free temporary plugging reservoir protection drilling fluid of the present invention has a plugging rate of up to 96.6% in the core plugging experiment, which significantly improves the plugging performance of the drilling fluid. The unblocking experiment shows that the reservoir permeability recovery rate can reach up to 85.6%, which ensures the production capacity and fluid fluidity of the reservoir, and has significant advantages in effectively protecting the formation and improving the stability of the wellbore. In the linear expansion experiment conducted on the drilling fluid, it was shown that the expansion inhibition effect on the formation rock was significant. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 The linear expansion rate diagram of drilling fluid F1 and DF4-DF6. DETAILED DESCRIPTION

[0039] The present invention is further described below with reference to specific examples, but is not limited thereto. The raw materials used in the examples are all conventional raw materials and can be obtained commercially; the methods described are all prior art unless otherwise specified.

[0040] Fluid loss reducers PF-FLOTROL and PAC-LV were purchased from Tianjin PetroChina Boxing Engineering Technology Co., Ltd.;

[0041] Xanthan gum was purchased from Shandong Juxin New Materials Co., Ltd.;

[0042] The anti-balling lubricant was PF-HLUB, purchased from China Oilfield Services Limited;

[0043] Polyamine inhibitor PF-UHIB was purchased from Beijing Konjie Energy and Environmental Protection Technology Co., Ltd.;

[0044] Glass microspheres were purchased from Zhengzhou Shenglait Hollow Microsphere New Material Co., Ltd.

[0045] The “parts” involved in the following preparation examples and embodiments are by weight unless otherwise specified.

[0046] Example 1

[0047] The preparation method of the self-blocking plugging agent comprises the following steps:

[0048] (1) Add polymer monomers isopropyl acrylamide, ethyl acrylate and 2-acrylamido-2-methylpropanesulfonic acid in a molar ratio of 1:0.05:0.001 into a three-necked flask filled with DMF solvent, stir thoroughly at 200 r / min until dissolved to obtain a polymer solution, and adjust the pH value of the polymer solution to neutral; introduce nitrogen into the flask to remove oxygen, and then place the mixed solution in a 60°C water bath, and continue to introduce nitrogen for 40 minutes to complete deoxygenation;

[0049] (2) Add 0.1% initiator AIBN and react at a constant temperature for 5 hours under nitrogen protection;

[0050] (3) After the reaction is completed, the product obtained by the reaction is washed three times with anhydrous ethanol, dried at 60°C for 24 hours, and crushed to obtain a self-unblocking plugging agent C1 with a phase change temperature of 16.5°C.

[0051] Example 2

[0052] The preparation method of the self-unblocking plugging agent is carried out according to Example 1, except that the molar ratio of isopropyl acrylamide, ethyl acrylate and 2-acrylamido-2-methylpropane sulfonic acid is 1:0.07:0.001, and a self-unblocking plugging agent C2 with a phase transition temperature of 14.9°C is obtained.

[0053] Example 3

[0054] The preparation method of the self-unblocking plugging agent is carried out according to Example 1, except that the molar ratio of isopropyl acrylamide, ethyl acrylate and 2-acrylamido-2-methylpropane sulfonic acid is 1:0.1:0.001, and a self-unblocking plugging agent C3 with a phase transition temperature of 13.5°C is obtained.

[0055] Example 4

[0056] The preparation method of the self-unblocking plugging agent is carried out according to Example 1, except that the molar ratio of isopropyl acrylamide, ethyl acrylate and 2-acrylamido-2-methylpropane sulfonic acid is 1:0.1:0.002, and a self-unblocking plugging agent C4 with a phase transition temperature of 14.0°C is obtained.

[0057] Example 5

[0058] A soil-free temporary plugging reservoir protection drilling fluid. In the temporary plugging reservoir protection drilling fluid, relative to 100 parts by weight of natural seawater, the content of sodium hydroxide is 0.1 parts by weight, the content of sodium chloride is 12 parts by weight, the content of potassium chloride is 5 parts by weight, the content of ethylene glycol is 20 parts by weight, the content of fluid loss reducer is 2 parts by weight, the content of xanthan gum XC is 0.1 parts by weight, the content of polyamine inhibitor PF-UHIB is 2 parts by weight, the content of carboxymethyl starch CMS for drilling fluid is 2 parts by weight, the content of anti-mud balling lubricant PF-HLUB is 3 parts by weight, the content of modified resin PF-LSF is 2 parts by weight, the self-unplugging plugging agent prepared in Example 1 is 3 parts by weight, the content of hydrate inhibitor PVPK90 is 2 parts by weight, and the content of glass microspheres is 2 parts by weight. The fluid loss reducer is a mixture of modified starch PF-FLOTROL and polyanionic cellulose PAC-LV, and the weight ratio of the modified starch PF-FLOTROL to the polyanionic cellulose PAC-LV is 1:2.

[0059] The preparation method of the soil-free temporary plugging reservoir protection drilling fluid comprises the following steps:

[0060] Ethylene glycol was added to natural seawater, and stirred at 4000 rpm and 25°C for 10 minutes. Then, self-unplugging plugging agent, modified resin PF-LSF, anti-mud balling lubricant PF-HLUB, carboxymethyl starch CMS for drilling fluid, polyamine, fluid loss reducer and hydrate inhibitor PVPK90 were added in sequence, and stirred at 7000 r / min for 20 minutes. Then, the speed was increased to 10000 r / min, and xanthan gum XC was added, and stirred for 30 minutes. Sodium chloride and potassium chloride were added in sequence according to the proportion and stirred for 20 minutes. Sodium hydroxide was added to adjust the pH value of the drilling fluid system to between 8 and 9. Finally, glass beads were added according to the proportion and stirred for 20 minutes to obtain a soil-free low-density temporary plugging reservoir protection drilling fluid. The prepared water-based drilling fluid was recorded as F1.

[0061] Example 6

[0062] The drilling fluid for temporary plugging of reservoirs without soil phase described in Example 5 is different from the drilling fluid for temporary plugging of reservoirs without soil phase described in Example 5 in that:

[0063] The self-removing plugging agent is the self-removing plugging agent C2 obtained in Example 2, and the prepared water-based drilling fluid is recorded as F2.

[0064] Example 7

[0065] The drilling fluid for temporary plugging of reservoirs without soil phase described in Example 5 is different from the drilling fluid for temporary plugging of reservoirs without soil phase described in Example 5 in that:

[0066] The self-removing plugging agent is the self-removing plugging agent C3 obtained in Example 3, and the prepared water-based drilling fluid is recorded as F3.

[0067] Example 8

[0068] The drilling fluid for temporary plugging of reservoirs without soil phase described in Example 5 is different from the drilling fluid for temporary plugging of reservoirs without soil phase described in Example 5 in that:

[0069] The self-removing plugging agent is the self-removing plugging agent C4 obtained in Example 4, and the prepared water-based drilling fluid is recorded as F4.

[0070] Example 9

[0071] A soil-free temporary plugging reservoir protection drilling fluid. In the temporary plugging reservoir protection drilling fluid, relative to 100 parts by weight of natural seawater, the content of sodium hydroxide is 0.05 parts by weight, the content of sodium chloride is 10 parts by weight, the content of potassium chloride is 4 parts by weight, the content of ethylene glycol is 15 parts by weight, the content of filtrate reducer is 1 part by weight, the content of xanthan gum XC is 0.05 parts by weight, the content of polyamine inhibitor PF-UHIB is 1 part by weight, the content of carboxymethyl starch CMS for drilling fluid is 1 part by weight, the content of anti-mud balling lubricant PF-HLUB is 1 part by weight, the content of modified resin PF-LSF is 1 part by weight, the self-unblocking plugging agent prepared in Example 1 is 2 parts by weight, the content of hydrate inhibitor PVPK90 is 1 part by weight, and the content of glass microspheres is 1 part by weight. The fluid loss reducer is a mixture of modified starch PF-FLOTROL and polyanionic cellulose PAC-LV, and the weight ratio of the modified starch PF-FLOTROL to the polyanionic cellulose PAC-LV is 1:2.

[0072] The preparation method is carried out according to Example 1.

[0073] Example 10

[0074] A soil-free temporary plugging reservoir protection drilling fluid. In the temporary plugging reservoir protection drilling fluid, relative to 100 parts by weight of natural seawater, the content of sodium hydroxide is 0.5 parts by weight, the content of sodium chloride is 15 parts by weight, the content of potassium chloride is 8 parts by weight, the content of ethylene glycol is 25 parts by weight, the content of filtrate reducer is 5 parts by weight, the content of xanthan gum XC is 0.5 parts by weight, the content of polyamine inhibitor PF-UHIB is 5 parts by weight, the content of carboxymethyl starch CMS for drilling fluid is 5 parts by weight, the content of anti-mud balling lubricant PF-HLUB is 6 parts by weight, the content of modified resin PF-LSF is 5 parts by weight, the self-unblocking plugging agent prepared in Example 1 is 8 parts by weight, the content of hydrate inhibitor PVPK90 is 5 parts by weight, and the content of glass microspheres is 5 parts by weight. The fluid loss reducer is a mixture of modified starch PF-FLOTROL and polyanionic cellulose PAC-LV, and the weight ratio of the modified starch PF-FLOTROL to the polyanionic cellulose PAC-LV is 1:2.

[0075] The preparation method is carried out according to Example 1.

[0076] Embodiment 11

[0077] A soil-free temporary plugging reservoir protection drilling fluid. In the temporary plugging reservoir protection drilling fluid, relative to 100 parts by weight of natural seawater, the content of sodium hydroxide is 0.2 parts by weight, the content of sodium chloride is 11 parts by weight, the content of potassium chloride is 6 parts by weight, the content of ethylene glycol is 18 parts by weight, the content of filtrate reducer is 3 parts by weight, the content of xanthan gum XC is 0.2 parts by weight, the content of polyamine inhibitor PF-UHIB is 3 parts by weight, the content of carboxymethyl starch CMS for drilling fluid is 3 parts by weight, the content of anti-mud balling lubricant PF-HLUB is 4 parts by weight, the content of modified resin PF-LSF is 3 parts by weight, the self-unplugging plugging agent prepared in Example 1 is 6 parts by weight, the content of hydrate inhibitor PVPK90 is 3 parts by weight, and the content of glass microspheres is 3 parts by weight. The fluid loss reducer is a mixture of modified starch PF-FLOTROL and polyanionic cellulose PAC-LV, and the weight ratio of the modified starch PF-FLOTROL to the polyanionic cellulose PAC-LV is 1:2.

[0078] The preparation method is carried out according to Example 1.

[0079] Comparative Example 1

[0080] A soil-free low-density temporary plugging reservoir protection drilling fluid, relative to 100 parts by weight of natural seawater, comprises 0.1 parts by weight of sodium hydroxide, 12 parts by weight of sodium chloride, 5 parts by weight of potassium chloride, 20 parts by weight of ethylene glycol, 2 parts by weight of a fluid loss reducer, 0.1 parts by weight of xanthan gum XC, 2 parts by weight of a polyamine inhibitor PF-UHIB, 2 parts by weight of carboxymethyl starch CMS for drilling fluid, 3 parts by weight of an anti-mud balling lubricant PF-HLUB, 2 parts by weight of a modified resin PF-LSF, 0.1 parts by weight of a self-unplugging plugging agent prepared in Example 1, 2 parts by weight of a hydrate inhibitor PVPK90, and 2 parts by weight of glass microspheres. The fluid loss reducer is a mixture of modified starch PF-FLOTROL and polyanionic cellulose PAC-LV, the weight ratio of modified starch PF-FLOTROL to polyanionic cellulose PAC-LV is 1:2, and water-based drilling fluid DF1 is prepared.

[0081] Comparative Example 2

[0082] A soil-free low-density temporary plugging reservoir protection drilling fluid, relative to 100 parts by weight of natural seawater, comprises 0.1 parts by weight of sodium hydroxide, 12 parts by weight of sodium chloride, 5 parts by weight of potassium chloride, 20 parts by weight of ethylene glycol, 2 parts by weight of a fluid loss reducer, 0.1 parts by weight of xanthan gum XC, 2 parts by weight of a polyamine inhibitor PF-UHIB, 2 parts by weight of carboxymethyl starch CMS for drilling fluid, 3 parts by weight of an anti-mud balling lubricant PF-HLUB, 2 parts by weight of a modified resin PF-LSF, 8 parts by weight of a self-unplugging plugging agent prepared in Example 1, 2 parts by weight of a hydrate inhibitor PVPK90, and 2 parts by weight of glass microspheres. The fluid loss reducer is a mixture of modified starch PF-FLOTROL and polyanionic cellulose PAC-LV, the weight ratio of modified starch PF-FLOTROL to polyanionic cellulose PAC-LV is 1:2, and the prepared water-based drilling fluid is recorded as DF2.

[0083] Comparative Example 3

[0084] A soil-free low-density temporary plugging reservoir protection drilling fluid, relative to 100 parts by weight of natural seawater, comprises 0.1 parts by weight of sodium hydroxide, 12 parts by weight of sodium chloride, 5 parts by weight of potassium chloride, 20 parts by weight of ethylene glycol, 2 parts by weight of a fluid loss reducer, 0.1 parts by weight of xanthan gum XC, 2 parts by weight of a polyamine inhibitor PF-UHIB, 2 parts by weight of carboxymethyl starch CMS for drilling fluid, 3 parts by weight of an anti-mud balling lubricant PF-HLUB, 2 parts by weight of a modified resin PF-LSF, 10 parts by weight of a self-unplugging plugging agent prepared in Example 1, 2 parts by weight of a hydrate inhibitor PVPK90, and 2 parts by weight of glass microspheres. The fluid loss reducer is a mixture of modified starch PF-FLOTROL and polyanionic cellulose PAC-LV, the weight ratio of modified starch PF-FLOTROL to polyanionic cellulose PAC-LV is 1:2, and the prepared water-based drilling fluid is recorded as DF3.

[0085] Comparative Example 4

[0086] A soil-free low-density temporary plugging reservoir protection drilling fluid, which is the same as that described in Example 1, except that:

[0087] The self-unblocking plugging agent is 2500 mesh ultrafine calcium carbonate, and its preparation method is as described in Example 1. The prepared water-based drilling fluid is recorded as DF4.

[0088] Comparative Example 5

[0089] A soil-free low-density temporary plugging reservoir protection drilling fluid, which is the same as that described in Example 1, except that:

[0090] The self-unblocking plugging agent sulfonated asphalt is prepared as described in Example 1, and the prepared water-based drilling fluid is recorded as DF5.

[0091] Comparative Example 6

[0092] A soil-free low-density temporary plugging reservoir protection drilling fluid, which is the same as that described in Example 1, except that:

[0093] Without adding the self-removing plugging agent, the preparation method is as described in Example 1, and the water-based drilling fluid is obtained and is recorded as DF6.

[0094] Test Example 1

[0095] The density of the drilling fluids F1-F4 and DF1-DF6 is 1.05 g / cm 3 , 1.06g / cm 3 , 1.06g / cm 3 , 1.07g / cm 3 , 1.05g / cm 3 , 1.06g / cm 3 , 1.06g / cm 3 , 1.07g / cm 3 , 1.07g / cm 3 , 1.05g / cm 3 The rheology and filtration of the drilling fluid system were tested at room temperature (25°C) and low temperature (2°C), and the performance indicators are shown in the table below.

[0096] Table 1 Rheological and filtration properties of drilling fluid

[0097]

[0098] It can be seen from Table 1 that the soil-free low-density temporary plugging reservoir protection drilling fluid of Examples 5-8 exhibits a good rheological filtration effect. At the same time, compared with Comparative Examples 4 and 5, the addition of the self-unplugging plugging agent in Examples 5-8 effectively reduces the filtration loss of the drilling fluid system; wherein the change in the monomer ratio during the synthesis of the self-unplugging plugging agent only affects its phase change temperature, and has little effect on its drilling fluid rheology and filtration loss.

[0099] Test Example 2

[0100] The above-mentioned drilling fluids F1-F4 and DF1-DF6 were subjected to core plugging and deplugging experimental tests.

[0101] The specific method of the core plugging experiment is as follows: Take 500mL of drilling fluid F1-F4 and DF1-DF6 respectively, stir at 6000rpm / min for 20min, and use the change of water drive pressure before and after the core plugging experiment to characterize the plugging rate of the drilling fluid. The specific operation steps are as follows:

[0102] (1) The dried core (φ=2.5cm×5cm) was vacuumed for 4h, saturated with simulated formation water, and water was displaced into the core to measure the permeability before plugging. 1 ;

[0103] (2) Set the confining pressure to 5 MPa and the back pressure to 2 MPa. Use drilling fluids F1-F4 and DF1-DF6 to displace the core. Adjust the drilling fluid flow rate to 2 mL / min for continuous displacement. Measure the permeability of the core after plugging.

[0104] The specific method of core plugging removal experiment is as follows:

[0105] 4°C cold water was injected in reverse at 1 mL / min to simulate the decrease in reservoir temperature. The injection was continued for 8 h and the core permeability was measured.

[0106] The core plugging rate calculation formula is:

[0107]

[0108] The results are shown in Table 2.

[0109] Table 2

[0110]

[0111] According to the data in Table 2, the soil-free low-density temporary plugging reservoir protection drilling fluid prepared in the embodiment of the present invention has a plugging rate of up to 96.6% in the core plugging experiment, which significantly improves the plugging performance of the drilling fluid. From the results of the unplugging experiment, it can be seen that the reservoir permeability recovery rate can reach up to 85.6%, ensuring the production capacity and fluid fluidity of the reservoir. The above results show that the drilling fluid has significant advantages in effectively protecting the formation and improving the stability of the wellbore.

[0112] Test Example 3

[0113] The hydration inhibition of the drilling fluids F1 and DF4-DF6 was evaluated. The specific operation method is as follows: 500 mL of drilling fluids F1 and DF4-DF6 were poured into beakers, and artificial simulated cores were immersed in the drilling fluids to observe their linear expansion rates. The results are shown in Figure 1 .

[0114] In the linear expansion experiment of the drilling fluid, Figure 1The results show that the drilling fluid F1 with the addition of self-unblocking plugging agent has a significant effect on inhibiting the expansion of formation rocks. The drilling fluid effectively limits the expansion of rocks, further verifying its superior performance under complex geological conditions. This experimental result shows that the drilling fluid not only has excellent plugging and unblocking performance, but also can provide rock expansion inhibition in actual drilling operations, thereby enhancing the stability of the wellbore. In summary, the drilling fluid has shown broad prospects and important practical value in drilling applications in deepwater and other complex environments.

Claims

1. A soil-free temporary plugging reservoir protection drilling fluid, characterized in that: The temporary plugging reservoir protection drilling fluid comprises the following components: Natural seawater, sodium hydroxide, sodium chloride, potassium chloride, ethylene glycol, fluid loss reducer, viscosity enhancing coating agent, polyamine, starch for drilling fluid, anti-mud packing lubricant, modified resin, self-unblocking plugging agent, hydrate inhibitor and glass microspheres; Wherein, relative to 100 parts by weight of natural seawater, the content of sodium hydroxide is 0.05-0.5 parts by weight, the content of sodium chloride is 10-15 parts by weight, the content of potassium chloride is 4-8 parts by weight, the content of ethylene glycol is 15-25 parts by weight, the content of fluid loss reducer is 1-5 parts by weight, the content of viscosity increasing coating agent is 0.05-0.5 parts by weight, the content of polyamine is 1-5 parts by weight, the content of starch for drilling fluid is 1-5 parts by weight, the content of anti-mud balling lubricant is 1-6 parts by weight, the modified resin is 1-5 parts by weight, the self-unblocking plugging agent is 2-8 parts by weight, the content of hydrate inhibitor is 1-5 parts by weight, and the content of glass microspheres is 1-5 parts by weight; The self-unblocking plugging agent is obtained by free radical polymerization reaction with isopropyl acrylamide, ethyl acrylate and 2-acrylamide-2-methylpropane sulfonic acid as polymerization monomers, and the molar ratio of isopropyl acrylamide, ethyl acrylate and 2-acrylamide-2-methylpropane sulfonic acid is 1: (0.05-0.1): (0.001-0.002); The fluid loss reducer is a mixture of modified starch PF-FLOTROL and polyanionic cellulose PAC-LV, and the weight ratio of modified starch PF-FLOTROL to polyanionic cellulose PAC-LV is 1:2; The viscosity-enhancing coating agent is xanthan gum XC, and the polyamine is a polyamine inhibitor PF-UHIB; The starch for drilling fluid is carboxymethyl starch CMS for drilling fluid, the anti-mud balling lubricant is PF-HLUB, and the modified resin is PF-LSF; The self-blocking plugging agent is prepared according to the following method: (1) adding polymer monomers isopropyl acrylamide, ethyl acrylate and 2-acrylamido-2-methylpropanesulfonic acid into DMF solvent in a molar ratio of 1: (0.05-0.1): (0.001-0.002), stirring thoroughly until dissolved to obtain a polymer solution, and adjusting the pH value of the polymer solution to neutral; introducing nitrogen to remove oxygen, and then placing in a 50-60° C. water bath, and continuously introducing nitrogen for 40 minutes to complete deoxygenation; (2) Add initiator a and react at a constant temperature for 5-6 hours under nitrogen protection. Initiator a is azobisisobutyronitrile; (3) After the reaction is completed, the product obtained by the reaction is washed with anhydrous ethanol, dried, and crushed to obtain a self-unblocking plugging agent; The hydrate inhibitor is PVPK90.

2. The soil-free temporary plugging reservoir protection drilling fluid according to claim 1, characterized in that: In the temporary plugging reservoir protection drilling fluid, relative to 100 parts by weight of natural seawater, the content of sodium hydroxide is 0.1 parts by weight, the content of sodium chloride is 12 parts by weight, the content of potassium chloride is 5 parts by weight, the content of ethylene glycol is 20 parts by weight, the content of filtrate reducer is 2 parts by weight, the content of viscosity increasing coating agent is 0.1 parts by weight, the content of polyamine is 2 parts by weight, the content of starch for drilling fluid is 2 parts by weight, the content of anti-mud balling lubricant is 3 parts by weight, the modified resin is 2 parts by weight, the self-unblocking plugging agent is 3 parts by weight, the content of hydrate inhibitor is 2 parts by weight, and the content of glass microspheres is 2 parts by weight.

3. The soil-free temporary plugging reservoir protection drilling fluid according to claim 1, characterized in that: In step (1), the total mass concentration of the polymerizable monomers in the polymer solution is 0.2-0.5 g / mL; the stirring speed is 150-200 r / min; in step (2), the amount of initiator a added is 0.1% of the total mass of the polymerizable monomers; in step (3), the washing is performed by washing with ethanol for 3-5 times, and the drying is performed at 60° C. for 24 h.

4. The method for preparing the soil-free temporary plugging reservoir protection drilling fluid according to any one of claims 1 to 3, characterized in that: The steps include: Ethylene glycol is added to natural seawater, and the mixture is stirred at 3000-5000rpm and 25℃ for 8-12 minutes. Then, a self-unblocking plugging agent, a modified resin, an anti-mud bag lubricant, starch for drilling fluid, a polyamine, a fluid loss reducer and a hydrate inhibitor are added in sequence, and the mixture is stirred at 6000r / min-8000r / min for 15-25min. Subsequently, the rotation speed is increased to 10000r / min-12000r / min, and a viscosity increasing coating agent is added, and the mixture is fully stirred for 25-35min. Sodium chloride and potassium chloride are added in sequence according to the proportion, and the mixture is stirred for 15-25min. Sodium hydroxide is added to adjust the pH value of the drilling fluid system to between 8 and 9. Finally, glass microbeads are added in the proportion, and the mixture is stirred for 15-25min to obtain a soil-free low-density temporary plugging reservoir protection drilling fluid.

5. The use of the soil-free temporary plugging reservoir protection drilling fluid according to claim 1, characterized in that: As a drilling fluid system, it is used in deepwater oil and gas reservoir drilling to inhibit the expansion of formation rocks, thereby protecting the formation and improving the stability of the wellbore.

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