An additive for water-based drilling fluid base mud, water-based drilling fluid

Abstract

The present invention relates to an additive for water-based drilling fluid base slurry and a water-based drilling fluid, belonging to the technical field of drilling fluids. The additive for water-based drilling fluid base slurry mainly consists of a vinyl monomer multi-polymer, an amphoteric ion polymer coating agent, a filtration reducer, a shale inhibitor, a liquid lubricant, and an oil and gas reservoir protection agent; the mass ratio of the vinyl monomer multi-polymer, the amphoteric ion polymer coating agent, the filtration reducer, the shale inhibitor, the liquid lubricant, and the oil and gas reservoir protection agent is 0.2 - 0.4:0.3 - 0.5:0.5 - 1:1 - 2:4 - 8:2 - 3; the oil and gas reservoir protection agent is nano-crosslinked starch microspheres and fibers with a nano-scale diameter, and the mass ratio of the nano-crosslinked starch microspheres to the fibers is 2 - 4:1. The water-based drilling fluid using this slurry additive has good compatibility and rheology, obvious filtration reduction effect, strong pressure-bearing plugging and filtration reduction ability, and low damage to the reservoir.

Description

Technical Field

[0001] The present invention relates to an additive for water-based drilling fluid base slurry and a water-based drilling fluid, belonging to the technical field of drilling fluids. Background Art

[0002] Drilling fluid is the liquid used throughout the process from drilling the oil layer to the production of the oil well. It has functions such as stabilizing the wellbore, preventing fluid intrusion into the well to cause well kick, and cleaning the bottom of the well to carry drill cuttings and suspended solids. It is an important part of oilfield chemicals. As drilling gradually develops towards deeper and more complex areas, the requirements for the performance of drilling fluid are getting higher and higher, and more attention is paid to the protection of oil and gas reservoirs. In order to achieve sustainable development, a drilling fluid system that can effectively protect oil and gas reservoirs and has good comprehensive performance needs to be applied. For example, in the prior art, the Chinese invention application with the publication number CN102352224A discloses a salt-resistant, strongly inhibitory, reservoir-protecting drilling fluid. The drilling fluid system includes the following components in parts by weight: 2 to 4 parts of bentonite, 1 to 3 parts of salt-resistant clay, 0.1 to 0.2 parts of soda ash, 100 parts of water, 0.4 to 0.8 parts of viscosity increasing agent ST-MH, 2 to 3 parts of filtration reducer KNT, 0.2 to 0.6 parts of shale inhibitor SET-H, 2 to 6 parts of organic composite potassium salt BPC, 2 to 3 parts of bridging plugging agent MF-II, and 2 to 3 parts of biological enzyme reservoir protection agent CVS. This drilling fluid prevents wellbore collapse by improving the inhibition and plugging properties of the system and controls downhole complex situations during drilling. However, there are still certain deficiencies in the damage of the drilling fluid to the drilled reservoir during use. There is serious leakage in the long open-hole horizontal section, causing serious reservoir damage, and it cannot be restored through post-treatment, resulting in low gas production and poor development effect. Summary of the Invention

[0003] The object of the present invention is to provide an additive for water-based drilling fluid base slurry, which can reduce the damage of water-based drilling fluid to the reservoir.

[0004] The object of the present invention also lies in providing a water-based drilling fluid.

[0005] In order to achieve the above object, the technical solution adopted for the additive for water-based drilling fluid base slurry of the present invention is:

[0006] A water-based drilling fluid base slurry additive mainly consists of a vinyl monomer multi-polymer, an amphoteric ion polymer coating agent, a filtration reducer, a shale inhibitor, a liquid lubricant, and a reservoir protection agent; the mass ratio of the vinyl monomer multi-polymer, the amphoteric ion polymer coating agent, the filtration reducer, the shale inhibitor, the liquid lubricant, and the reservoir protection agent is 0.2 - 0.4:0.3 - 0.5:0.5 - 1:1 - 2:4 - 8:2 - 3; the reservoir protection agent is nano-crosslinked starch microspheres and fibers with a nanoscale diameter, and the mass ratio of the nano-crosslinked starch microspheres to the fibers is 2 - 4:1.

[0007] When the water-based drilling fluid base slurry additive of the present invention is used in a water-based drilling fluid, the water-based drilling fluid has good compatibility and rheology, obvious filtration reduction effect, strong pressure-bearing plugging and filtration reduction ability, and low damage to the reservoir.

[0008] The reservoir protection agent in the water-based additive can play an important role in pressure-bearing, temporary plugging, and filtration reduction during the drilling process, protecting the reservoir from the invasion of the drilling fluid, and enabling the reservoir to have a relatively high permeability recovery value after being unblocked. The surface morphology of the fibers in the reservoir protection agent is in a bundle-rod structure, with a nanoscale particle size, forming a complement with the starch microspheres in terms of morphology and particle size. The compounding of nano-scale starch microspheres and fibers with a nanoscale diameter can fill and plug the micro-pores between the microspheres and the formation, as well as between the microspheres after the starch microspheres are bridged and plugged, achieving a better filtration reduction effect.

[0009] Furthermore, the mass ratio of the nano-crosslinked starch microspheres to the fibers is 3:1.

[0010] Furthermore, the length of the fibers is 3 - 5 μm, and the diameter is 80 - 100 nm. The fibers are plant fibers, such as wheat straw fibers. Furthermore, the nano-crosslinked starch microspheres have the following particle size distribution characteristics: 200 ≥ D10 ≥ 60 nm, 400 nm ≥ D50 ≥ 200 nm, 600 nm ≥ D90 ≥ 400.

[0011] The nano-crosslinked starch microspheres can be prepared by existing technologies. For example, the nano-crosslinked starch microspheres can be prepared by a method including the following steps: heating the solution obtained by mixing esterified nano-starch crystals and water to boiling and maintaining for a period of time; then adding an amphoteric ion surfactant and a stabilizer and mixing evenly, then adding an inorganic salt solution and a crosslinking agent, and performing solid-liquid separation, washing and drying after the reaction. The time for maintaining the solution obtained by mixing esterified nano-starch crystals and water at boiling is 10 to 20 min, for example, 15 min. The mass ratio of the esterified nano-starch crystals, the stabilizer, the amphoteric ion surfactant, the crosslinking agent and the inorganic salt is 2 to 4:25 to 35:1:0.4 to 0.6:0.6 to 0.9, for example, 2:30:1:0.5:0.75. The mass ratio of the esterified nano-starch crystals to water is 1 to 2:50, for example, 1:50. Before adding the amphoteric ion surfactant and the stabilizer, the temperature of the material is reduced to 10 to 30 °C, for example, 20 °C. The stabilizer is polyethylene glycol, preferably a combination of polyethylene glycol 600 and polyethylene glycol 20000, and the mass ratio of polyethylene glycol 600 to polyethylene glycol 20000 is 4 to 6:1, for example, 5:1. The crosslinking agent is preferably glutaraldehyde. The amphoteric ion surfactant is dimethyldodecylsulfopropylammonium salt. The inorganic salt is a potassium chloride solution with a concentration of 4 to 6%, for example, 5%.

[0012] The esterified nano-starch crystals are obtained by adding nano-starch crystals to a sodium trimetaphosphate solution, mixing evenly, standing for treatment, then heating for curing treatment, and performing solid-liquid separation, washing and drying. The mass ratio of the nano-starch crystals to the sodium trimetaphosphate is 2.2:2.4 to 2.6, for example, 2.2:2.5. The concentration of the sodium trimetaphosphate solution is 4 to 6%, for example, 5%. The time for standing treatment after mixing evenly is 0.5 to 1.5 h, for example, 1 h. The temperature of the curing treatment is 20 to 30 °C, for example, 25 °C, and the time is 0.5 to 1.5 h, for example, 1 h.

[0013] The nano-starch crystals are obtained by heating the starch and water mixed solution to boiling, maintaining for a period of time and then cooling, then adding a poor solvent, standing, performing solid-liquid separation, and washing and drying the obtained solid. The starch is preferably wheat starch. The mass ratio of the starch to water is 4 to 6:100, for example, 5:100. The time for maintaining the starch and water mixed solution at boiling is 15 to 25 min, for example, 20 min. Cooling after maintaining for a period of time is to reduce the temperature to 10 to 50 °C, for example, to 20 °C. The poor solvent is preferably ethanol. The addition amount of the poor solvent to the mass of the starch is 200:4 to 6, for example, 200:5.

[0014] Liquid lubricants can effectively reduce the frictional resistance between the drill string and the open hole wall, as well as between the drill string and the metal casing, with the aims of increasing the drilling speed, preventing pipe sticking, and reducing drill string wear. Further, the liquid lubricant is white oil.

[0015] Further, the vinyl monomer multi - copolymer is vinyl monomer multi - copolymer PAC141.

[0016] Further, the zwitterionic polymer coating agent is the strong zwitterionic polymer coating agent FA367. The strong zwitterionic polymer coating agent FA367 can inhibit the viscosity of the drilling fluid, coat the drill cuttings, stabilize the wellbore, reduce the filtration loss, and play an anti - collapse role; at the same time, through stirring, the strong zwitterionic polymer coating agent can be evenly mixed into the water - based drilling fluid to ensure the uniformity of the water - based drilling fluid from top to bottom and its stable chemical properties.

[0017] Further, the filtration reducer is a high - temperature resistant filtration reducer. Even further, the filtration reducer is the high - temperature resistant filtration reducer MG - 1. The high - temperature resistant filtration reducer MG - 1 can prevent clay dehydration under high - temperature conditions, enhance the ability to protect the colloid, and maintain the stability of the drilling fluid colloid by maintaining and enhancing the ability of the clay surface to bind water.

[0018] Further, the anti - collapse agent is the non - fluorescent anti - collapse agent WFT - 666 and / or the anti - collapse agent FT - 3000.

[0019] Further, the mass ratio of the vinyl monomer multi - copolymer, the zwitterionic polymer coating agent, the filtration reducer, the anti - collapse agent, the liquid lubricant, and the reservoir protection agent is 0.2 - 0.4:0.4:0.6 - 1:1 - 2:4 - 7:2 - 3.

[0020] The technical solution adopted for the water - based drilling fluid of the present invention is as follows:

[0021] A water - based drilling fluid mainly consists of a water - based base slurry and additives for the water - based drilling fluid base slurry; the additives mainly consist of a vinyl monomer multi - copolymer, a zwitterionic polymer coating agent, a filtration reducer, an anti - collapse agent, a liquid lubricant, and a reservoir protection agent; the mass ratio of the vinyl monomer multi - copolymer, the zwitterionic polymer coating agent, the filtration reducer, the anti - collapse agent, the liquid lubricant, and the reservoir protection agent is 0.2 - 0.4:0.3 - 0.5:0.5 - 1:1 - 2:4 - 8:2 - 3; the reservoir protection agent is nano - crosslinked starch microspheres and fibers with a nanoscale diameter, and the mass ratio of the nano - crosslinked starch microspheres to the fibers is 2 - 4:1.

[0022] The water-based drilling fluid of the present invention is a low-cost and environmentally friendly water-based drilling fluid, which has good compatibility and rheology, obvious filtration loss reduction effect, strong pressure-bearing plugging and filtration loss reduction ability, and low damage to the reservoir. For the low-cost and environmentally friendly water-based drilling fluid of the present invention, the on-site application results show that the core permeability recovery rate > 80%, the pressure-bearing capacity after film formation > 10 MPa, and the water loss reduction effect is obvious.

[0023] Furthermore, the mass ratio of the micron-sized cross-linked starch microspheres to the fibers is 3:1. The raw material cost of this reservoir protection agent is low, it is environmentally friendly and easily degradable. It not only reduces reservoir pollution, but also reduces the application cost per cubic meter of the drilling fluid after addition by more than 30% compared with the drilling fluid added with the current non-permeable agent.

[0024] The diameter of the fiber is nanoscale. Furthermore, the length of the fiber is 3 - 5 μm, and the diameter is 80 - 100 nm. The fiber is a plant fiber, such as wheat straw fiber. The nanoscale cross-linked starch microspheres have the following particle size distribution characteristics: 200 ≥ D10 ≥ 60 nm, 400 nm ≥ D50 ≥ 200 nm, 600 nm ≥ D90 ≥ 400.

[0025] The water-based base slurry can be prepared with reference to the existing technology of existing water-based drilling fluids. Furthermore, the water-based base slurry is composed of bentonite, sodium carbonate and water; the mass ratio of bentonite, sodium carbonate and water is 3 - 5:0.5 - 1:100, for example 3 - 4:0.6 - 1:100. Among them, bentonite is preferably calcium-based bentonite. Sodium carbonate can increase the slurry-making rate of the drilling fluid and adjust the pH of the water-based base slurry. To optimize the slurry-making effect of the water-based base slurry, further, the water-based base slurry is prepared by a method including the following steps: mixing water, bentonite and sodium carbonate evenly, and sealing for hydration for 16 - 24 h.

[0026] Furthermore, for every 100 mL of the water-based base slurry, the mass of the vinyl monomer multi-copolymer in the corresponding additives is 0.175 - 0.4 g, for example 0.175 - 0.35 g. The dosage of the vinyl monomer multi-copolymer in this drilling fluid is small, and various properties of the drilling fluid are taken into account on the basis of ensuring operation economy.

[0027] According to different formation conditions, further, the water-based drilling fluid also includes barite. Furthermore, the density of the water-based drilling fluid is 1.25 - 1.29 g / cm 3 . When the water-based drilling fluid includes barite, further, the preparation method of the water-based drilling fluid includes the following steps: adding additives for the water-based drilling fluid base slurry to the water-based base slurry, stirring evenly, and sealing for curing. This method has a simple process, can be carried out on existing production equipment, and has good adaptability to on-site applications.

[0028] Further, the liquid lubricant is white oil.

[0029] Further, the vinyl monomer multi - copolymer is vinyl monomer multi - copolymer PAC141; the zwitterionic polymer coating agent is zwitterionic polymer strong coating agent FA367; the filtration reducer is high - temperature resistant filtration reducer MG - 1; the shale inhibitor is non - fluorescent shale inhibitor WFT - 666 and / or shale inhibitor FT - 3000.

[0030] Further, the mass ratio of the vinyl monomer multi - copolymer, the zwitterionic polymer coating agent, the filtration reducer, the shale inhibitor, the liquid lubricant and the reservoir protection agent is 0.2 - 0.4:0.4:0.6 - 1:1 - 2:4 - 7:2 - 3.

[0031] To optimize the homogeneity of the water - based drilling fluid, further, the time for sealed curing is 16 - 24 h. Specific Embodiments

[0032] The technical solution of the present invention will be further described below in conjunction with specific embodiments.

[0033] In the following examples, the zwitterionic polymer strong coating agent FA367, high-temperature resistant filtration reducer MG-1, and non-fluorescent anti-collapse agent WFT-666 were purchased from Henan Jinma Petroleum Technology Co., Ltd.; the vinyl monomer multi-copolymer PAC141 was purchased from Puyang Meijing Chemical Materials Co., Ltd.; the liquid lubricant white oil was purchased from Zhengzhou Feiteng Chemical Co., Ltd.; the industrial sodium carbonate was purchased from Henan Yuheng Environmental Protection Technology Co., Ltd.; the barite was purchased from Nanyang Yanan Industry Co., Ltd. The bentonite used in the water-based mud was first-class bentonite (calcium-based bentonite). The oil and gas reservoir protection agent is a mixture obtained by mixing nano-crosslinked starch microspheres and wheat straw fibers in a mass ratio of 3:1. The length of the wheat straw fibers is 3-5 μm, and the diameter is 80-100 nm. The nano-crosslinked starch microspheres were prepared according to the method disclosed in the Chinese invention patent with the authorized announcement number CN 113122211B. The specific preparation method includes the following steps: Add 5 parts of cereal starch to 100 parts of deionized water, boil for 20 min, then let the liquid cool to 20 °C. Gradually add 200 parts of ethanol dropwise to the liquid. After the addition, let it stand to obtain the bottom insoluble matter. After centrifugation, stirring and washing, and drying at 25 °C for 2.5 h, nano-starch crystals are obtained; Weigh 2.5 parts of sodium trimetaphosphate to prepare 50 parts of sodium trimetaphosphate solution, then add 2.2 parts of nano-starch crystals, mix well and let it stand for impregnation for 1 h. Then let the solution cure at 25 °C for 1 h. After centrifugation, stirring and washing, and drying at 25 °C for 2 h, esterified nano-starch crystals are obtained; Mix 2 parts of esterified nano-starch crystals with 100 parts of deionized water, heat the resulting solution to boiling, keep it for 15 min, then let the liquid cool to 20 °C. Add 30 parts of stabilizer (polyethylene glycol 600: polyethylene glycol 20000 = 5:1) and 1 part of dimethyldodecylsulfopropyl ammonium salt to the liquid, and mix well; Weigh 0.75 part of potassium chloride at 30 °C to prepare 15 parts of inorganic salt solution, and simultaneously add it dropwise to the liquid with 0.5 part of glutaraldehyde at the same temperature. After the addition, continue the reaction for 3 h. After centrifugation, washing and drying, white powdery nano-crosslinked starch microspheres are obtained; The prepared nano-crosslinked starch microspheres have the following typical particle size distribution characteristics: 200 ≥ D10 ≥ 60 nm, 400 nm ≥ D50 ≥ 200 nm, 600 nm ≥ D90 ≥ 400.

[0034] Example 1

[0035] The water-based drilling fluid base slurry additive of this embodiment is composed of vinyl monomer multi-component copolymer PAC141, zwitterionic polymer strong coating agent FA367, high-temperature resistant fluid loss reducer MG-1, non-fluorescent anti-collapse agent WFT666, liquid lubricant white oil, and oil and gas reservoir protection agent; the mass ratio of vinyl monomer multi-component copolymer PAC141, zwitterionic polymer strong coating agent FA367, high-temperature resistant fluid loss reducer MG-1, anti-collapse agent WFT666, liquid lubricant white oil, and oil and gas reservoir protection agent is 0.7:1.4:3.5:3.5:14:7.

[0036] Example 2

[0037] The water-based drilling fluid base slurry additive of this embodiment is composed of vinyl monomer multi-component copolymer PAC141, zwitterionic polymer strong coating agent FA367, high-temperature resistant fluid loss reducer MG-1, non-fluorescent anti-collapse agent WFT666, liquid lubricant white oil, and oil and gas reservoir protection agent; the mass ratio of vinyl monomer multi-component copolymer PAC141, zwitterionic polymer strong coating agent FA367, high-temperature resistant fluid loss reducer MG-1, non-fluorescent anti-collapse agent WFT666, liquid lubricant white oil, and oil and gas reservoir protection agent is 1.4:1.4:2.1:7:24:7.

[0038] Example 3

[0039] The water-based drilling fluid base slurry additive of this embodiment is composed of vinyl monomer multi-component copolymer PAC141, zwitterionic polymer strong coating agent FA367, high-temperature resistant fluid loss reducer MG-1, non-fluorescent anti-collapse agent WFT666, liquid lubricant white oil, and oil and gas reservoir protection agent; the mass ratio of vinyl monomer multi-component copolymer PAC141, zwitterionic polymer strong coating agent FA367, high-temperature resistant fluid loss reducer MG-1, anti-collapse agent WFT666, liquid lubricant white oil, and oil and gas reservoir protection agent is 1.4:1.4:2.8:3.5:21:10.5.

[0040] Example 4

[0041] The water-based drilling fluid of this embodiment is a low-cost and green environmental protection type water-based drilling fluid, which is composed of a water-based base slurry, barite and additives; among them, the water-based base slurry is obtained by mixing water, bentonite and industrial sodium carbonate, and the mass ratio of water, bentonite and industrial sodium carbonate is 350:14:2.1; the additives are composed of vinyl monomer multi-component copolymer PAC141, zwitterionic polymer strong coating agent FA367, high temperature resistant filtration reducer MG-1, non-fluorescent anti-collapse agent WFT666, liquid lubricant white oil and oil and gas reservoir protection agent, and the mass ratio of vinyl monomer multi-component copolymer PAC141, zwitterionic polymer strong coating agent FA367, high temperature resistant filtration reducer MG-1, non-fluorescent anti-collapse agent WFT666, liquid lubricant white oil and oil and gas reservoir protection agent is 0.7:1.4:3.5:3.5:14:7.

[0042] The preparation method of the water-based drilling fluid of this embodiment includes the following steps:

[0043] 1) Preparation of the water-based base slurry: Add bentonite and industrial sodium carbonate to distilled water, stir at high speed for 20 minutes, put it into a sealed wide-mouth bottle, and hydrate at room temperature for 24h to obtain the water-based base slurry.

[0044] 2) Add additives to the water-based base slurry under stirring conditions, stir at high speed for 30 min, and seal and cure for 24 h; the dosage of each component in the additives corresponding to every 400 mL of the water-based base slurry is: vinyl monomer multi-component copolymer PAC141 0.7 g, zwitterionic polymer strong coating agent FA367 1.4 g, high temperature resistant filtration reducer MG-1 3.5 g, non-fluorescent anti-collapse agent WFT666 3.5 g, liquid lubricant white oil 14 g, oil and gas reservoir protection agent 7 g; after the sealed curing is completed, add barite according to the drilling fluid specific gravity of 1.25 - 1.29 g / cm 3 and stir at high speed for 10 min to obtain the water-based drilling fluid.

[0045] Example 5

[0046] The water-based drilling fluid of this embodiment is a low-cost and green environmental protection type water-based drilling fluid, which is composed of a water-based base slurry, barite and additives; among them, the water-based base slurry is obtained by mixing water, bentonite and industrial sodium carbonate, and the mass ratio of water, bentonite and industrial sodium carbonate is 350:10.5:3.5; the additives are composed of vinyl monomer multi-component copolymer PAC141, zwitterionic polymer strong coating agent FA367, high temperature resistant filtration reducer MG-1, non-fluorescent anti-collapse agent WFT666, liquid lubricant white oil and oil and gas reservoir protection agent, and the mass ratio of vinyl monomer multi-component copolymer PAC141, zwitterionic polymer strong coating agent FA367, high temperature resistant filtration reducer MG-1, non-fluorescent anti-collapse agent WFT666, liquid lubricant white oil and oil and gas reservoir protection agent is 1.4:1.4:2.1:7:24:7.

[0047] The preparation method of the water-based drilling fluid in this embodiment includes the following steps:

[0048] 1) Preparation of the water-based base slurry: Add bentonite and industrial sodium carbonate to distilled water, stir at high speed for 20 minutes, put it into a sealed wide-mouth bottle, and hydrate at room temperature for 24 hours to obtain the water-based base slurry.

[0049] 2) Add additives to the water-based base slurry under stirring conditions, stir at high speed for 30 minutes, and seal and cure for 24 hours; the dosage of each component in the additive corresponding to every 400 mL of the water-based base slurry is: vinyl monomer multi-component copolymer PAC141 1.4 g, zwitterionic polymer strong coating agent FA367 1.4 g, high-temperature resistant filtration reducer MG-1 2.1 g, non-fluorescent anti-collapse agent WFT666 7 g, liquid lubricant white oil 24 g, oil and gas reservoir protection agent 7 g; after the sealing and curing is completed, add barite according to the drilling fluid specific gravity of 1.26 g / cm 3 Stir at high speed for 10 minutes to obtain the water-based drilling fluid.

[0050] Example 6

[0051] The water-based drilling fluid in this embodiment is a low-cost and green environmental protection type water-based drilling fluid, which is composed of a water-based base slurry, barite and additives; among them, the water-based base slurry is obtained by mixing water, bentonite and industrial sodium carbonate, and the mass ratio of water, bentonite and industrial sodium carbonate is 350:14:2.8; the additive is composed of vinyl monomer multi-component copolymer PAC141, zwitterionic polymer strong coating agent FA367, high-temperature resistant filtration reducer MG-1, non-fluorescent anti-collapse agent WFT666, liquid lubricant white oil and oil and gas reservoir protection agent; the mass ratio of vinyl monomer multi-component copolymer PAC141, zwitterionic polymer strong coating agent FA367, high-temperature resistant filtration reducer MG-1, non-fluorescent anti-collapse agent WFT666, liquid lubricant white oil and oil and gas reservoir protection agent is 1.4:1.4:2.8:3.5:21:10.5.

[0052] The preparation method of the water-based drilling fluid in this embodiment includes the following steps:

[0053] 1) Preparation of the water-based base slurry: Add bentonite and industrial sodium carbonate to distilled water, stir at high speed for 20 minutes, put it into a sealed wide-mouth bottle, and hydrate at room temperature for 24 hours to obtain the water-based base slurry.

[0054] 2) Add additives to the water-based base mud under stirring conditions, stir at high speed for 30 min, and cure hermetically for 24 h; the dosage of each component in the additive corresponding to every 400 mL of water-based base mud is as follows: vinyl monomer multi-copolymer PAC141 1.4 g, zwitterionic polymer strong coating agent FA367 1.4 g, high-temperature resistant filtration reducer MG-1 2.8 g, non-fluorescent anti-collapse agent WFT666 3.5 g, liquid lubricant white oil 21 g, oil and gas reservoir protection agent 10.5 g; after the end of hermetic curing, add barite according to the drilling fluid density of 1.26 g / cm 3 Add barite and stir at high speed for 10 min to obtain the water-based drilling fluid.

[0055] Comparative Example 1

[0056] The difference between the drilling fluid of this comparative example and the water-based drilling fluid of Example 4 is only that: this comparative example does not add the oil and gas reservoir protection agent. In this comparative example, barite is added during the preparation of the water-based drilling fluid to make the density of the water-based drilling fluid 1.26 g / cm 3 .

[0057] Comparative Example 2

[0058] The difference between the drilling fluid of this comparative example and the water-based drilling fluid of Example 4 is only that: this comparative example replaces the oil and gas reservoir protection agent in the water-based drilling fluid of Example 4 with starch microspheres. In this comparative example, barite is added during the preparation of the water-based drilling fluid to make the density of the water-based drilling fluid 1.26 g / cm 3 .

[0059] Experimental Example 1

[0060] Take the drilling fluids of Examples 4 to 6 and Comparative Example 1 for performance tests. (In Table 1, the green environmental protection type drilling fluids 1 to 4 are the drilling fluids obtained by adding different amounts of barite in Example 4. The blank group is Comparative Example 1.) The experimental effects of the drilling fluids of other examples are equivalent to those of Example 4. Use unconventional reservoir evaluation equipment to evaluate the pressure-bearing temporary plugging performance of this drilling fluid. The specific steps are as follows: (1) Comparative Example 1 (without the oil and gas reservoir protection agent) is used as the blank control group. The drilling fluids of Examples 4 to 6 are used as the test groups; (2) Test the blank group. The pump speed is 1.0 mL / min. Use a permeameter to displace the drilling fluid of Comparative Example 2. When the liquid comes out at the end of the core holder, stop the displacement. Record the inlet and outlet pressure difference P1 at this time, relieve the pressure, and empty the pipeline; (3) Test the test groups. The pump speed is 1.0 mL / min. Displace the core with different example drilling fluids. When the pressure reaches stability, record the highest value P2 at this time, stop pumping, relieve the pressure, and empty the pipeline; (4) Calculate the membrane pressure-bearing capacity of the drilling fluid. The pressure value of the test group minus the pressure value of the blank group is equal to the pressure-bearing strength of the membrane. That is, the pressure-bearing strength P = P2 - P1. The results are shown in Table 1.

[0061] Table 1 Film Bearing Strength of Water-Based Drilling Fluids (Core Permeability 120×10 -3 μm 2 )

[0062] Experimental formula <![CDATA[Drilling fluid density / (g / cm 3 )]]> Maximum bearing pressure value / MPa Bearing strength / MPa Green environmental protection water-based drilling fluid 1 1.25 12.07 8.52 Green environmental protection water-based drilling fluid 2 1.26 13.96 10.41 Green environmental protection water-based drilling fluid 3 1.27 14.89 11.34 Green environmental protection water-based drilling fluid 4 1.28 15.30 11.75 Example 5 1.26 11.86 8.31 Example 6 1.26 11.74 8.19 Blank group 1.26 3.55 -

[0063] As can be seen from Table 1, for the artificial core with a liquid-measured permeability of 120×10 -3 μm 2 , when the drilling fluid of the comparative example discharged liquid at the end of the core holder, the pressure difference between the inlet and outlet was small, indicating that the drilling fluid used did not form an effective plugging film in the core and only had a weak pressure-bearing capacity. In contrast, after adding this green and environment-friendly water-based drilling fluid, as the pumped volume increased, the inlet pressure continued to rise and then reached a stable state, and there was no liquid discharge at the end of the core, indicating that the drilling fluid had formed a plugging film on the core section, indicating that this water-based drilling fluid had a strong temporary plugging and pressure-bearing ability.

[0064] Experimental Example 2

[0065] Application Effect of the Green and Environment-Friendly Drilling Fluid 1 in Well Zhang 1319 in Experimental Example 1

[0066] Well Zhang 1319 is an oil production well located in the Zhangdian Nose Structural Belt of the Nanyang Sag, belonging to the N38 fault block of the Zhangdian Oilfield in the Nanyang Sag of the Nanxiang Basin. The well type is a directional well, with a designed well depth of 3550 m and a completed well depth of 3550 m. This low-cost green and environment-friendly water-based drilling fluid was used in this well, and the on-site drilling fluid performance during actual drilling is shown in Table 2 below.

[0067] Table 2 Actual Drilling Performance of Low-Cost Green and Environment-Friendly Water-Based Drilling Fluid

[0068] Well depth / m <![CDATA[D / (g / cm 3 )]]> FV / s FL / mL AV / mPa.s PV / mPa·s YP / Pa GEL / Pa pH 2115 1.25 57 4.2 32 22 10 3 / 6 8.5 2344 1.29 62 3.5 33 24 9 3 / 7 8

[0069] As can be seen from Table 2, as the drilling depth increased, the fluid loss of the well slurry in Well Zhang 1319 decreased from 4.2 mL to 3.5 mL. The test results of the apparent viscosity and plastic viscosity of the well slurry showed that the well slurry using this low-cost green and environment-friendly water-based drilling fluid did not show a significant increase in viscosity with the increase of the drilling depth, indicating that the performance of this water-based drilling fluid was good.

[0070] To further evaluate the reservoir protection effect of this water-based drilling fluid, a core contamination experiment was carried out on the on-site well slurry and cores of Well Zhang 1319, and the results are shown in Table 3. The test method of the core contamination experiment was based on SY / T6540-2002 "Indoor Evaluation Method for Drilling and Completion Fluids Damaging Oil Reservoirs", and a high-temperature and high-pressure dynamic damage evaluation instrument was used to simulate the reservoir invasion and damage determination under the actual formation drilling and completion fluid circulation state.

[0071] Table 3 Comparison of Core Dynamic Contamination Experiments

[0072]

[0073] As can be seen from Table 3, when the water-based drilling fluid of the present invention is used to plug the core, the permeability recovery value of the core after plug removal is above 82.07%; in contrast, after the core is polluted by the drilling fluid of the comparative example, the permeability recovery value of the plugged core is generally low, indicating that this green and environmentally friendly water-based drilling fluid can effectively reduce the damage to the reservoir during the drilling process.

Claims

1. An additive for the base slurry of a water-based drilling fluid, characterized in that: It is mainly composed of a vinyl monomer multi - copolymer, an amphoteric ion polymer coating agent, a filtration loss reducer, a shale inhibitor, a liquid lubricant, and a reservoir protection agent; the mass ratio of the vinyl monomer multi - copolymer, the amphoteric ion polymer coating agent, the filtration loss reducer, the shale inhibitor, the liquid lubricant, and the reservoir protection agent is 0.2~0.4: 0.3~0.5: 0.5~1: 1~2: 4~8: 2~3; the reservoir protection agent is nano - crosslinked starch microspheres and fibers with a nanoscale diameter, and the mass ratio of the nano - crosslinked starch microspheres to the fibers is 2~4:

1. The vinyl monomer multi - copolymer is the vinyl monomer multi - copolymer PAC141; the amphoteric ion polymer coating agent is the amphoteric ion polymer strong coating agent FA367; the filtration loss reducer is the high - temperature resistant filtration loss reducer MG - 1; the shale inhibitor is the non - fluorescent shale inhibitor WFT - 666 and / or the shale inhibitor FT - 3000; the length of the fibers is 3~5μm, and the diameter is 80~100nm; the nano - crosslinked starch microspheres have the following particle size distribution characteristics: 200≥D10≥60nm, 400nm≥D50≥200nm, 600nm≥D90≥400.

2. A water-based drilling fluid, characterized in that: It is mainly composed of an aqueous base mud and an additive for the aqueous drilling fluid base mud; the additive is mainly composed of a vinyl monomer multi - copolymer, an amphoteric ion polymer coating agent, a filtration loss reducer, a shale inhibitor, a liquid lubricant, and a reservoir protection agent; the mass ratio of the vinyl monomer multi - copolymer, the amphoteric ion polymer coating agent, the filtration loss reducer, the shale inhibitor, the liquid lubricant, and the reservoir protection agent is 0.2~0.4: 0.3~0.5: 0.5~1: 1~2: 4~8: 2~3; the reservoir protection agent is nano - crosslinked starch microspheres and fibers with a nanoscale diameter, and the mass ratio of the nano - crosslinked starch microspheres to the fibers is 2~4:

1. The vinyl monomer multi - copolymer is the vinyl monomer multi - copolymer PAC141; the amphoteric ion polymer coating agent is the amphoteric ion polymer strong coating agent FA367; the filtration loss reducer is the high - temperature resistant filtration loss reducer MG - 1; the shale inhibitor is the non - fluorescent shale inhibitor WFT - 666 and / or the shale inhibitor FT - 3000; the length of the fibers is 3~5μm, and the diameter is 80~100nm; the nano - crosslinked starch microspheres have the following particle size distribution characteristics: 200≥D10≥60nm, 400nm≥D50≥200nm, 600nm≥D90≥400.

3. The water-based drilling fluid according to claim 2, characterized in that: The aqueous base mud is composed of bentonite, sodium carbonate, and water; the mass ratio of bentonite, sodium carbonate, and water is 3~5: 0.5~1:

100.

4. The water-based drilling fluid according to claim 3, characterized in that: For every 100mL of the aqueous base mud, the mass of the vinyl monomer multi - copolymer PAC141 in the corresponding additive is 0.175~0.4g.

5. The water-based drilling fluid according to claim 4, wherein: The aqueous drilling fluid also includes barite, and the density of the aqueous drilling fluid is 1.25~1.29g / cm3.

6. The water-based drilling fluid according to claim 2, wherein: The liquid lubricant is white oil.

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