Preparation method of anti-calcium tackifier, brine-based drilling fluid and preparation method of brine-based drilling fluid

Abstract

The invention relates to the technical field of petroleum drilling fluids, in particular to a preparation method of an anti-calcium tackifier, a brine-based drilling fluid and a preparation method. The preparation method of the anti-calcium tackifier comprises the following steps: A, uniformly mixing the white oil and the emulsifier to form an oil phase for later use; b, dissolving 2-acrylamido-2-methyl-1-propanesulfonic acid, acrylonitrile, a cationic monomer and a vinyl monomer with carboxyl in pure water, adjusting the pH value to 7.0, and uniformly stirring to form a water phase; c, dropwise adding the water phase in the step B into the oil phase in the step A, and uniformly mixing to obtain a stable inverse emulsion; and D, in a nitrogen atmosphere, adding an initiator into the stable inverse emulsion in the step C, and reacting to obtain the anti-calcium tackifier. The brine-based drilling fluid disclosed by the invention can keep good rheological property and stability in a high-temperature environment of 180 DEG C.

Description

Technical Field

[0001] The invention relates to the technical field of petroleum drilling fluid, and in particular to a preparation method of an anti-calcium viscosity enhancer, a brine-based drilling fluid and a preparation method thereof. Background Art

[0002] Drilling fluid plays a key role in the exploration and development of oil and gas, and is widely used in cooling drill bits, removing cuttings, stabilizing well walls, and controlling well pressure. According to the type of base fluid, drilling fluid is mainly divided into water-based drilling fluid and oil-based drilling fluid. Among them, water-based drilling fluid has become the most widely used type due to its low cost, good environmental friendliness and reliable rheological properties. However, as oil and gas extraction gradually extends to deep wells, ultra-deep wells and complex geological conditions, the performance of traditional water-based drilling fluids in extreme environments such as high temperature, high pressure and high salt has gradually shown limitations, mainly reflected in the dependence on bentonite and the application of barite weighting agents.

[0003] Traditional water-based drilling fluids rely on bentonite as a thickener and barite (BaSO4) as a weighting agent. The main function of bentonite is to increase the viscosity of the drilling fluid and provide good rheological properties. However, bentonite has poor salt and temperature resistance, especially in high-concentration salt water and high-temperature environments. Bentonite is prone to lose its thickening effect, resulting in a sharp drop in the viscosity and rheological properties of the drilling fluid, which in turn causes the performance of the drilling fluid to decline or even fail. On the other hand, barite is widely used as a weighting agent to increase the density of drilling fluids, especially in deep wells and high-pressure formations. However, barite is prone to particle sedimentation in high-temperature or high-salt environments, resulting in a decrease in the stability of the drilling fluid. Particle sedimentation not only affects the rheological properties of the drilling fluid, but may also cause wellbore instability, reduce drilling efficiency and increase operational risks. In addition, barite particles are insoluble in the drilling fluid. If they are not fully dispersed, they are likely to cause solid phase accumulation, thereby increasing the risk of reservoir contamination and affecting oil and gas production and formation stability. Larger barite particles may also cause additional friction loss to the drill bit, drilling tools and wellbore wall, thus affecting drilling efficiency and equipment life. The above defects make the application of traditional water-based drilling fluids in high temperature, high salt and complex environments challenging, and a new solution is urgently needed to overcome these problems.

[0004] As a new type of water-based drilling fluid system, brine-based drilling fluid has been increasingly used in deep wells, ultra-deep wells and complex oil and gas reservoir drilling operations in recent years. Compared with traditional freshwater-based drilling fluids, brine-based drilling fluids use salt solutions such as calcium chloride, sodium chloride, and sodium formate as base fluids. By increasing the salt concentration, the density of the drilling fluid is directly increased, thereby avoiding the sedimentation problem of barite particles, and making the drilling fluid have more stable rheological properties.

[0005] In addition to the inhibition mechanism of traditional calcium chloride drilling fluid, high-concentration calcium chloride soil-free water-based drilling fluid mainly enhances inhibition by reducing the activity of drilling fluid. A non-ideal semipermeable membrane is formed between the surface of the shale well wall and the water-based drilling fluid. Certain inorganic salts (such as calcium chloride) can significantly reduce the water activity of the drilling fluid and improve the efficiency of the semipermeable membrane, thereby better stabilizing the well wall. Studies have shown that compared with monovalent metal salts such as NaCl and KCl, calcium chloride solution can produce greater osmotic pressure and higher membrane efficiency, which is more conducive to maintaining the stability of the shale well wall.

[0006] However, in the preparation process of brine-based drilling fluid, how to effectively select and optimize additives, especially viscosity enhancers, fluid loss reducers and plugging agents, to improve their performance in high temperature, high pressure and high mineralization environments is still a hot topic in current research. The existing brine-based drilling fluid system still has some problems, such as the limited temperature resistance and calcium resistance of viscosity enhancers and fluid loss reducers, and the poor stability of some additives in high salt concentration or high calcium environment. These problems will lead to the instability of drilling fluid performance and even affect the safety and efficiency of underground operations. Summary of the invention

[0007] In order to solve the above technical problems, the embodiments of the present invention provide a method for preparing an anti-calcium thickener, a brine-based drilling fluid and a preparation method thereof.

[0008] To achieve the above object, the embodiments of the present invention adopt the following technical solutions:

[0009] In one aspect, the present invention provides a method for preparing an anti-calcium thickener, comprising the following steps:

[0010] A. Mix the white oil and emulsifier to form an oil phase and set aside;

[0011] B. dissolving 2-acrylamide-2-methyl-1-propanesulfonic acid, acrylonitrile, cationic monomer and vinyl monomer with carboxyl group in pure water, adjusting the pH value to 7.0, and stirring to form an aqueous phase;

[0012] C. Add the aqueous phase in step B dropwise into the oil phase in step A, and mix well to obtain a stable inverse emulsion;

[0013] D. In a nitrogen atmosphere, an initiator is added to the stable inverse emulsion in step C to obtain an anti-calcium thickener after reaction.

[0014] In some embodiments, in step A, the mass ratio of the volume of the white oil to the emulsifier is 75 mL:2 g.

[0015] In some embodiments, the emulsifier consists of sorbitan oleate and polysorbate 80 in a mass ratio of 1:1.

[0016] In some embodiments, in step B, the mass ratio of the 2-acrylamido-2-methyl-1-propanesulfonic acid, acrylonitrile, cationic monomer and carboxyl-containing vinyl monomer is (40-50): (10-20): (20-30): (15-25).

[0017] In some embodiments, the cationic monomer includes at least one of dimethyldiallylammonium chloride, methacryloyloxyethyltrimethylammonium chloride, and (3-acrylamidopropyl)trimethylammonium chloride.

[0018] In some embodiments, the carboxyl-containing vinyl monomer includes acrylic acid and / or methacrylic acid.

[0019] In some embodiments, in step D, the initiator comprises potassium persulfate and / or sodium bisulfite.

[0020] In some embodiments, in step D, the mass of the initiator is 0.1%-0.3% of the total mass of 2-acrylamide-2-methyl-1-propanesulfonic acid, acrylonitrile, cationic monomer and carboxyl-containing vinyl monomer, and the reaction temperature is 40-55°C.

[0021] On the other hand, the present invention also provides a brine-based drilling fluid, which comprises the following raw materials, in parts by weight: 400 parts of brine, 8-12 parts of anti-calcium fluid loss reducer, 4-10 parts of anti-calcium viscosity enhancer, 12-16 parts of plugging agent and 16-20 parts of bridging agent, wherein the anti-calcium viscosity enhancer is the anti-calcium viscosity enhancer prepared by the above-mentioned preparation method;

[0022] The brine includes calcium chloride and / or calcium bromide; the plugging agent is asphalt powder; and the bridging agent is ultrafine calcium carbonate.

[0023] On the other hand, the present invention also provides a method for preparing a brine-based drilling fluid, comprising the following steps:

[0024] Add anti-calcium filtrate reducer, anti-calcium viscosity enhancer, plugging agent and bridging agent into brine and mix well to obtain brine-based drilling fluid.

[0025] Compared with the prior art, the present invention has at least the following beneficial effects:

[0026] 1. The tackifier of the present invention combines the synergistic effect of multiple monomers and has excellent calcium and salt resistance, tackifying effect and high temperature stability. The quaternary ammonium salt group in the cationic monomer forms a zwitterionic polymer with the anionic group in AMPS and MAA, and utilizes the anti-polyelectrolyte effect to significantly improve the calcium and salt resistance, while reducing the interference of calcium ions to the polymer through electrostatic shielding and complexation. The rigid structure of acrylonitrile enhances the cohesion and high temperature stability of the molecular chain, and the carboxyl group provided by methacrylic acid further strengthens the complexation with calcium ions. In addition, the hydrophobic group in the quaternary ammonium salt monomer optimizes the tackifying performance through hydrophobic association, so that the tackifier shows significant viscosity enhancement effect, rheological stability and persistence in deep wells, ultra-deep wells and complex salt layer environments. Therefore, the tackifier of the present invention has excellent temperature and calcium resistance, and is added to the drilling fluid system, which can effectively improve the viscosity of the drilling fluid under high concentration calcium ion conditions compared to other tackifiers.

[0027] 2. The brine-based drilling fluid of the present invention can maintain good rheological properties and stability under high temperature environment of 180°C. The density of the drilling fluid is directly increased by dissolving salts such as calcium chloride and calcium bromide, thereby avoiding the particle sedimentation problem caused by the traditional barite weighting method. This weighting method not only makes the drilling fluid more fluid and stable, but also reduces the risk of reservoir pollution caused by solid phase particles, further improving the environmental protection characteristics of the system. By optimizing the brine concentration and introducing anti-calcium filtration reducers and anti-calcium thickeners, the system exhibits excellent salt resistance and can remain stable in an environment with high concentrations of calcium ions and high salt content.

[0028] In summary, the present invention provides a brine-based drilling fluid system and a preparation method thereof, which has significant technological advancement and broad application prospects, and provides an efficient, environmentally friendly and high-performance drilling fluid solution for deep well and complex downhole operations. DETAILED DESCRIPTION

[0029] The technical solutions in some embodiments of the present disclosure are described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present disclosure, not all of the embodiments. Based on the embodiments provided by the present disclosure, all other embodiments obtained by ordinary technicians in this field belong to the scope of protection of the present disclosure.

[0030] 1. Preparation Example of Anti-calcium Thickener

[0031] Example 1

[0032] A method for preparing an anti-calcium thickener, comprising the following steps:

[0033] (1) Add 150 mL of 3# white oil and 4 g of emulsifier (Span80:Tween80=1:1, i.e., the mass ratio of sorbitan oleate to polysorbate 80 is 1:1) into a beaker, stir and disperse at 4000 r / min for 10 minutes to form an oil phase;

[0034] (2) Dissolve 45 g of 2-acrylamido-2-methyl-1-propanesulfonic acid, 12 g of acrylonitrile, 25 g of methacryloyloxyethyl trimethylammonium chloride and 18 g of methacrylic acid in 100 mL of pure water, adjust the pH value to 7.0 with a 40% by mass sodium hydroxide aqueous solution, and stir to form an aqueous phase;

[0035] (3) slowly dripping the aqueous phase of step (2) into the oil phase of step (1) under stirring, stirring at 6000 r / min for 40 minutes to form a stable inverse emulsion;

[0036] (4) Add the emulsion obtained in step (3) into a three-necked flask and continue to introduce nitrogen;

[0037] (5) heating the reaction system obtained in step (4) to 40° C., adding 0.1 g of ammonium persulfate and 0.1 g of sodium bisulfite as initiator, and reacting;

[0038] (6) After step (5) is reacted for 4 hours and the reaction is complete, the mixture is naturally cooled to room temperature to obtain a white viscous emulsion-like liquid.

[0039] Example 2

[0040] A method for preparing an anti-calcium thickener, comprising the following steps:

[0041] (1) Add 150 mL of 3# white oil and 4 g of emulsifier (Span80:Tween80=1:1) into a beaker, stir and disperse at 4000 r / min for 10 minutes to form an oil phase;

[0042] (2) Dissolve 45 g of 2-acrylamido-2-methyl-1-propanesulfonic acid, 15 g of acrylonitrile, 22 g of methacryloyloxyethyl trimethylammonium chloride and 18 g of acrylic acid in 100 mL of pure water, adjust the pH value to 7.0 with a 40% by mass sodium hydroxide aqueous solution, and stir to form an aqueous phase;

[0043] (3) slowly dripping the aqueous phase of step (2) into the oil phase of step (1) under stirring, stirring at 6000 r / min for 40 minutes to form a stable inverse emulsion;

[0044] (4) Add the emulsion obtained in step (3) into a three-necked flask and continue to introduce nitrogen;

[0045] (5) heating the reaction system obtained in step (4) to 40° C., adding 0.05 g of ammonium persulfate and 0.05 g of sodium bisulfite as initiator, and reacting;

[0046] (6) After step (5) is reacted for 4 hours and the reaction is complete, the mixture is naturally cooled to room temperature to obtain a white viscous emulsion-like liquid.

[0047] Example 3

[0048] A method for preparing an anti-calcium thickener, comprising the following steps:

[0049] (1) Add 150 mL of 3# white oil and 4 g of emulsifier (Span80:Tween80=1:1) into a beaker, stir and disperse at 4000 r / min for 10 minutes to form an oil phase;

[0050] (2) Dissolve 50 g of 2-acrylamido-2-methyl-1-propanesulfonic acid, 15 g of acrylonitrile, 25 g of (3-acrylamidopropyl)trimethylammonium chloride and 20 g of acrylic acid in 110 mL of pure water, adjust the pH value to 7.0 with a 40% sodium hydroxide aqueous solution, and stir evenly to form an aqueous phase;

[0051] (3) slowly dripping the aqueous phase of step (2) into the oil phase of step (1) under stirring, stirring at 6000 r / min for 40 minutes to form a stable inverse emulsion;

[0052] (4) Add the emulsion obtained in step (3) into a three-necked flask and continue to introduce nitrogen;

[0053] (5) heating the reaction system obtained in step (4) to 40° C., adding 0.15 g of ammonium persulfate and 0.15 g of sodium bisulfite as initiator, and reacting;

[0054] (6) After step (5) is reacted for 4 hours and the reaction is complete, the mixture is naturally cooled to room temperature to obtain a white viscous emulsion-like liquid.

[0055] Example 4

[0056] A method for preparing an anti-calcium thickener, comprising the following steps:

[0057] (1) Add 150 mL of 3# white oil and 4 g of emulsifier (Span80:Tween80=1:1) into a beaker, stir and disperse at 4000 r / min for 10 minutes to form an oil phase;

[0058] (2) Dissolve 40 g of 2-acrylamido-2-methyl-1-propanesulfonic acid, 12 g of acrylonitrile, 30 g of (3-acrylamidopropyl)trimethylammonium chloride and 18 g of methacrylic acid in 100 mL of pure water, adjust the pH value to 7.0 with a 40% sodium hydroxide aqueous solution, and stir evenly to form an aqueous phase;

[0059] (3) slowly dripping the aqueous phase of step (2) into the oil phase of step (1) under stirring, stirring at 6000 r / min for 40 minutes to form a stable inverse emulsion;

[0060] (4) Add the emulsion obtained in step (3) into a three-necked flask and continue to introduce nitrogen;

[0061] (5) heating the reaction system obtained in step (4) to 40° C., adding 0.1 g of ammonium persulfate and 0.1 g of sodium bisulfite as initiator, and reacting;

[0062] (6) After step (5) is reacted for 4 hours and the reaction is complete, the mixture is naturally cooled to room temperature to obtain a white viscous emulsion-like liquid.

[0063] Comparative Example 1

[0064] A method for preparing an anti-calcium thickener is as described in Example 1, except that methacryloyloxyethyl trimethylammonium chloride is not added.

[0065] Comparative Example 2

[0066] A method for preparing an anti-calcium thickener is as described in Example 1, except that the methacryloyloxyethyl trimethylammonium chloride in the reaction is replaced with dimethyl diallyl ammonium chloride.

[0067] Comparative Example 3

[0068] A method for preparing an anti-calcium thickener is as described in Example 1, except that no acrylonitrile is added.

[0069] Comparative Example 4

[0070] A method for preparing an anti-calcium thickener is as described in Example 1, except that methacrylic acid in the reaction is replaced by acrylic acid.

[0071] 2. Performance test:

[0072] The anti-calcium thickeners prepared in Examples 1-4 and Comparative Examples 1-4 were subjected to performance tests, and the specific methods are as follows:

[0073] Preparation of brine-based slurry: Add 160g CaCl2 to 400mL distilled water, stir at 5000r / min for 20min, and obtain 40% CaCl2 brine-based slurry after full dissolution.

[0074] 2% of the anti-calcium thickener prepared in Examples 1-4 and Comparative Examples 1-4 was added to 400 mL of brine-based slurry (i.e., 8 g of anti-calcium thickener was added to 400 mL of brine-based slurry), stirred at 10000 r / min for 20 min, and the rheological performance parameters such as apparent viscosity, plastic viscosity, and dynamic shear force of the prepared drilling fluid were evaluated according to GB / T16783.1-2014 Field Test of Drilling Fluids in the Petroleum and Natural Gas Industry Part 1 Water-based Drilling Fluids. The prepared drilling fluid was added to an aging tank, placed in a roller furnace for high-temperature aging at 180°C for 16 hours, and the rheological performance parameters such as apparent viscosity, plastic viscosity, and dynamic shear force of the drilling fluid were measured again. The experimental results are shown in Table 1.

[0075] Table 1 Evaluation results of tackifier performance

[0076]

[0077] It can be seen from Table 1 that both the embodiment and comparative example samples can significantly increase the viscosity of the brine-based slurry before aging. Moreover, the embodiment samples have a better viscosity-increasing effect. After aging at 180°C, due to the influence of high-temperature aging, the viscosity of the embodiment and comparative example drilling fluid samples both decreased. However, the viscosity of the embodiment samples decreased less than before aging, and still had a good viscosity-increasing effect.

[0078] In the comparative samples, the performances vary greatly due to different monomer designs. Comparative Example 1 lacks a cationic monomer, resulting in the molecular chain not having an anti-polyelectrolyte effect, which leads to poor viscosity-enhancing performance of the drilling fluid, and a large decrease in the viscosity of the drilling fluid after high-temperature aging.

[0079] In Comparative Example 2, methacryloyloxyethyl trimethyl ammonium chloride is replaced with dimethyl diallyl ammonium chloride. It can be seen that the thickener with anti-polyelectrolyte effect can still maintain a relatively high viscosity in the brine-based slurry, indicating that the anti-polyelectrolyte effect of the molecular chain plays a dominant role in improving the temperature and salt resistance of the thickener, and the hydrophobic association structure is secondary.

[0080] Comparative Example 3 does not contain acrylonitrile. Acrylonitrile has a good rigid structure and can effectively improve the temperature resistance of the polymer. The lack of acrylonitrile makes the molecular chain of the thickener lack a rigid structure, resulting in easy degradation at high temperatures, poor temperature resistance, and significant performance degradation after aging.

[0081] In Comparative Example 4, methacrylic acid is replaced by acrylic acid. Compared with methacrylic acid, acrylic acid increases the flexibility of the polymer to a certain extent and reduces its stability in a high temperature environment.

[0082] In summary, it can be seen that the anti-calcium thickener prepared in the embodiments of the present invention has excellent anti-calcium thickening performance. It is used to prepare a brine-based drilling fluid system. The performance of the obtained drilling fluid system is significantly better than that of the thickener prepared in the comparative example. In the present invention, the anti-calcium thickener prepared in Example 1 is selected to prepare a drilling fluid system for illustration.

[0083] The anti-calcium thickener used in the following examples and comparative examples is the anti-calcium thickener prepared in Example 1.

[0084] The following anti-calcium fluid loss agent is a hyperbranched polymer fluid loss agent, which is prepared according to Example 1 in Chinese patent document CN113527575B, and its specific preparation process is as follows:

[0085] 1) Preparation of pentaerythritol polyene monomer: Weigh 10 g of pentaerythritol, 66.8 g of allyl bromide, 50 g of sodium hydroxide and 6.68 g of tetrabutylammonium bromide, add them into a 500 mL three-necked flask in sequence, stir for 5 h at room temperature and for 24 h at 60° C. After the reaction is completed, filter out the white solid, wash the solid with 80 mL of ether, repeat the washing 3 times, dry the filtrate with anhydrous sodium sulfate, remove the ether by rotary evaporation at room temperature, and obtain a light yellow oily liquid, which is pentaerythritol polyene monomer.

[0086] 2) Preparation of hyperbranched polymer fluid loss reducer: Weigh component A, component B, component C, pentaerythritol polyene monomer and water according to the weight percentage of the above components.

[0087] Component A: 4 g of N,N,N-trimethyl-3 (2-methylallylamino)-1-ammonium chloride, 4 g of dimethyldiallylammonium chloride, 4 g of N,N,N-trimethylphenylmethylammonium chloride, and 4 g of methacryloyloxyethyltrimethylammonium chloride. Component A accounts for 3.2% of the total weight of the reaction mixture.

[0088] Component B: 8 g of sodium 2-acrylamide-2-methylpropanesulfonate, 8 g of sodium methacryloyloxyethylsulfonate, 8 g of N-vinyl pyrrolidone, and 8 g of sodium styrenesulfonate. Component B accounts for 6.4% of the total weight of the reaction mixture.

[0089] Component C: 16 g acrylamide, 16 g sodium acrylate, 16 g vinyl acetate, component C accounts for 9.6% of the total weight of all reaction mixtures.

[0090] Pentaerythritol polyene monomer: 20 g, accounting for 4% of the total weight of all reaction mixtures.

[0091] Water: 384g.

[0092] A total of 116 g of the above-mentioned component A, component B, component C, and pentaerythritol polyene monomer are put into 384 g of water and stirred, nitrogen is continuously introduced, and the temperature is raised to 50° C., 0.05 g of ammonium persulfate and sodium bisulfite are added, and after reacting for 5 hours, the reactants are cooled to room temperature to obtain a transparent viscous product, which is purified with anhydrous ethanol to obtain a white solid, which is dried at 100° C. for 24 hours and then crushed to obtain a white powdery hyperbranched polymer filtrate reducer.

[0093] 3. Drilling fluid preparation example

[0094] Example 1

[0095] The preparation method of brine-based drilling fluid comprises the following steps: firstly, adding 160 g of calcium chloride into 400 mL of distilled water, stirring at a speed of 5000 r / min for 20 min, and obtaining brine-based slurry after sufficient dissolution.

[0096] Take 400mL brine-based slurry, add 10g of anti-calcium filtrate reducer, 8g of anti-calcium viscosity enhancer, 12g of plugging agent and 16g of bridging agent in sequence, and stir at high speed for 20min after adding each raw material; the speed of high-speed stirring is 10000r / min, and the density is 1.25g / cm 3 Brine-based drilling fluid.

[0097] Example 2

[0098] The preparation method of brine-based drilling fluid comprises the following steps: firstly, adding 320 g of calcium chloride into 400 mL of distilled water, stirring at a speed of 5000 r / min for 20 min, and obtaining brine-based slurry after sufficient dissolution.

[0099] Take 400mL of brine-based slurry, add 10g of anti-calcium fluid loss reducer, 8g of anti-calcium viscosity enhancer, 12g of plugging agent and 16g of bridging agent in sequence, and stir at high speed for 20min after adding each raw material; the speed of high-speed stirring is 10000r / min, and the density is 1.4g / cm 3 Brine-based drilling fluid.

[0100] Example 3

[0101] The preparation method of brine-based drilling fluid comprises the following steps: firstly, adding 300 g of calcium chloride and 230 g of calcium bromide into 400 mL of distilled water, stirring at a speed of 5000 r / min for 20 min, and obtaining brine-based slurry after sufficient dissolution.

[0102] Take 400mL brine-based slurry, add 10g of anti-calcium fluid loss reducer, 8g of anti-calcium viscosity enhancer, 12g of plugging agent and 16g of bridging agent in sequence, and stir at high speed for 20min after adding each raw material; the speed of high-speed stirring is 10000r / min, and the density is 1.6g / cm 3 Brine-based drilling fluid.

[0103] Comparative Example 1

[0104] A brine-based drilling fluid is different from Example 1 in that no anti-calcium fluid loss reducer is added.

[0105] Comparative Example 2

[0106] A brine-based drilling fluid differs from Example 1 in that no anti-calcium thickener is added.

[0107] Comparative Example 3

[0108] A brine-based drilling fluid is different from Example 1 in that: on the basis of Example 1, barite barium sulfate is used to increase the weight of the solution to 1.4 g / cm 3 .

[0109] 4. Performance test:

[0110] The drilling fluids prepared in Examples 1-3 and Comparative Examples 1-3 were subjected to performance tests, and the specific methods are as follows:

[0111] (1) Rheological filtration performance evaluation

[0112] According to GB / T16783.1-2014 Field Test of Drilling Fluids in Petroleum and Natural Gas Industry Part 1 Water-based Drilling Fluids, the rheological performance parameters of the prepared drilling fluid system, such as apparent viscosity, plastic viscosity, dynamic shear force, and API filtration loss of the drilling fluid, were evaluated. The drilling fluid system was transferred to a stainless steel high-temperature aging tank and aged at 180°C for 16 hours. The above rheological parameters of the drilling fluid system, the API filtration loss of the drilling fluid system, and the high-temperature and high-pressure filtration loss at 180°C were measured again. The experimental results are shown in Table 2.

[0113] (2) Evaluation of inhibition performance

[0114] The shale in the reservoir section was washed, dried, crushed, and passed through a 6-10 mesh sieve. 50 g of each was weighed and added to different aging tanks. Different concentrations of shale inhibitor aqueous solutions were added to the aging tanks. The aging tanks were rolled at 180°C for 16 hours. The drill cuttings after aging were passed through a 40 mesh sieve, washed, dried, and weighed as m. The rolling recovery rate was calculated according to the following formula. The experimental results are shown in Table 3

[0115] S=m / 50*100%

[0116] Where:

[0117] S——shale rolling recovery rate, %;

[0118] m——residue weight, g.

[0119] Measurement results

[0120] Table 2 Evaluation of rheological filtration performance of brine-based drilling fluid

[0121]

[0122] It can be seen from Table 2 that the drilling fluids of the examples and the comparative examples before aging have good filtration reduction effects. After aging, the viscosity of Examples 1, 2, and 3 is slightly reduced, the medium pressure filtration loss is very small, and the high temperature and high pressure filtration loss is less than 15 mL, indicating that the drilling fluid system of the examples has good temperature and calcium resistance and filtration reduction performance.

[0123] In Example 3 and Example 2, since the calcium ion content is higher than that in Example 1, the viscosity and shear force are also slightly higher, and the filtration loss is slightly smaller, indicating that the introduction of calcium ions enhances the ionic strength and stability of the solution, further improves the ion shielding effect, and makes the molecular chain more stable. At the same time, the multiple synergistic effects of anti-calcium filtration reducer, anti-calcium thickener and plugging agent enhance the temperature and salt resistance of the drilling fluid system, and form a denser filter cake in a high-concentration salt environment. Since Comparative Example 1 does not contain an anti-calcium filtration reducer, the medium-pressure filtration loss and high-temperature and high-pressure filtration loss are significantly higher than those in Example 1, which shows that the anti-calcium filtration reducer plays a key role in controlling filtration loss and enhancing the stability of the filter cake. The lack of filtration reducer causes a sharp decrease in the filtration loss performance of the system. Comparative Example 2 lacks an anti-calcium thickener, so the apparent viscosity and plastic viscosity of Comparative Example 2 are significantly lower than those of Example 1, which are 16.5 mPa·s and 13.0 mPa·s before aging, and further reduced to 12.0 mPa·s and 10.0 mPa·s after aging. This shows that the anti-calcium thickener is indispensable for maintaining the viscosity and stability of the system. The lack of thickener greatly reduces the rheological properties of the system. Comparative Example 3 uses barite for weighting, and the high-temperature and high-pressure filtration loss after aging increases significantly to 28.4 mL. This is because the barite particles are easy to settle, resulting in poor filter cake stability, and the insufficient dispersibility of barite makes the high-temperature performance of the system inferior to that of the brine-weighted system.

[0124] Table 3 Evaluation of rolling recovery rate of drilling fluid inhibition performance

[0125]

[0126] The hydration inhibition performance of drilling fluid is crucial for inhibiting the hydration expansion of clay minerals and stabilizing the wellbore formation. Clean water has a poor inhibitory effect on mud shale, which makes it easy for mud shale to hydrate, swell and produce mud, so the recovery rate is low. Clean water cannot effectively prevent the rupture of mud shale, which easily leads to the expansion of pores and cracks. After adding calcium chloride, calcium ions enhance the chemical stability of mud shale through Na+ / Ca²⁺ exchange, reduce the hydration capacity of mud shale, and improve the stability of rock interface. Calcium salts effectively reduce the expansion and rupture of mud shale through chemical inhibition, so the recovery rate is improved. The embodiment contains key additives such as anti-calcium filtration reducer, anti-calcium thickener, and plugging agent, and the synergistic effect of these additives significantly enhances the inhibition performance of drilling fluid. Anti-calcium filtration reducer controls the filtration loss of drilling fluid, anti-calcium thickener increases viscosity, and plugging agent enhances the plugging effect on rock formation, effectively improves the stability of mud shale, thereby significantly improving the rolling recovery rate. In Comparative Example 1, due to the lack of anti-calcium filtration reducer, its effect in inhibiting hydration and expansion of shale is insufficient, resulting in a low recovery rate. Due to the lack of anti-calcium thickener in Comparative Example 2, the viscosity of the drilling fluid is relatively low, which affects the stability of the drilling fluid under high temperature and high pressure conditions, reduces the adhesion and plugging properties of the drilling fluid, and causes a decrease in recovery rate. The recovery rate of Comparative Example 3 is the lowest among all comparative samples. The sample is weighted with barite, and the barite particles are large, easy to settle, and the particle size is uneven, resulting in poor rheological properties and poor filtration of the drilling fluid. Although barite can provide a higher density, it cannot effectively improve inhibition like brine-based drilling fluid, so the recovery rate is significantly lower than that of the embodiment.

[0127] In the description of this specification, specific features, structures, materials or characteristics may be combined in an appropriate manner in any one or more embodiments or examples.

[0128] The above is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art can easily think of changes or substitutions within the technical scope disclosed by the present invention, which should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention should be based on the protection scope of the claims.

Claims

1. A method for preparing an anti-calcium thickener, characterized in that: The following steps are involved: A. Mix the white oil and emulsifier to form an oil phase and set aside; B. dissolving 2-acrylamide-2-methyl-1-propanesulfonic acid, acrylonitrile, cationic monomer and vinyl monomer with carboxyl group in pure water, adjusting the pH value to 7.0, and stirring to form an aqueous phase; C. Add the aqueous phase in step B dropwise into the oil phase in step A, and mix well to obtain a stable inverse emulsion; D. In a nitrogen atmosphere, an initiator is added to the stable inverse emulsion in step C to obtain an anti-calcium thickener after reaction.

2. The preparation method according to claim 1, characterized in that: In step A, the volume ratio of the white oil to the emulsifier is 75 mL: 2 g.

3. The preparation method according to claim 2, characterized in that: The emulsifier is composed of sorbitan oleate and polysorbate 80 in a mass ratio of 1:

1.

4. The preparation method according to claim 1, characterized in that: In step B, the mass ratio of the 2-acrylamide-2-methyl-1-propanesulfonic acid, acrylonitrile, cationic monomer and carboxyl-containing vinyl monomer is (40-50): (10-20): (20-30): (15-25).

5. The preparation method according to claim 4, characterized in that: The cationic monomer includes at least one of dimethyldiallylammonium chloride, methacryloyloxyethyltrimethylammonium chloride and (3-acrylamidopropyl)trimethylammonium chloride.

6. The preparation method according to claim 4, characterized in that: The vinyl monomer having a carboxyl group includes acrylic acid and / or methacrylic acid.

7. The preparation method according to claim 1, characterized in that: In step D, the initiator includes potassium persulfate and / or sodium bisulfite.

8. The preparation method according to claim 1, characterized in that: In step D, the mass of the initiator is 0.1%-0.3% of the total mass of 2-acrylamide-2-methyl-1-propanesulfonic acid, acrylonitrile, cationic monomer and vinyl monomer with carboxyl group, and the reaction temperature is 40-55°C.

9. A brine-based drilling fluid, characterized in that: The raw materials include, by weight: 400 parts of brine, 8-12 parts of anti-calcium fluid loss reducer, 4-10 parts of anti-calcium thickener, 12-16 parts of plugging agent and 16-20 parts of bridging agent, wherein the anti-calcium thickener is the anti-calcium thickener prepared by the preparation method according to any one of claims 1 to 8; The brine includes calcium chloride and / or calcium bromide; The plugging agent is asphalt powder; The bridging agent is ultrafine calcium carbonate.

10. A method for preparing a brine-based drilling fluid as claimed in claim 9, characterized in that: The following steps are involved: Add anti-calcium filtrate reducer, anti-calcium viscosity enhancer, plugging agent and bridging agent into brine and mix well to obtain brine-based drilling fluid.

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