Salt hydrotropy drilling and grinding fluid system as well as preparation method and application thereof

Abstract

The invention relates to the technical field of oilfield chemistry, in particular to a salt-assisted drilling and grinding fluid system as well as a preparation method and application thereof, the salt-assisted drilling and grinding fluid system comprises the following raw materials in percentage by mass: 1.8-3.2% of a salt inhibitor, 1.5-2% of a tackifier, 0.5-2% of a lubricant and the balance of water; the salt inhibitor is one or more of metal complexing agents, and the lubricant is modified silicone grease. According to the salt hydrotropy drilling and grinding fluid system, solubilization and crystallization inhibition effects on salt scale of a high-salt-content oil and gas reservoir can be achieved, and the phenomena that a production channel is blocked and a pipe column is blocked by salt due to underground salt crystallization of the high-salt-content oil and gas reservoir can be effectively avoided; and during mechanical drilling and grinding dredging operation, drilling and grinding liquid is dissolved and scales are formed, the drilling and grinding time efficiency is improved, and the risks of damage, wellhead stabbing leakage and the like caused by sudden release of high pressure to eject an oil pipe are reduced. In addition, the hydrotropy drilling and grinding fluid system further has good temperature resistance and salt resistance, good resistance reduction performance and good chip carrying capacity.

Description

Technical Field

[0001] This invention relates to the field of oilfield chemical technology, specifically to a salt-assisted dissolving drilling fluid system, its preparation method, and its application. Background Technology

[0002] With the continuous development of oil and gas exploration and development, high-salinity oil and gas reservoirs are one of the important areas for increasing oilfield reserves and production. During the development of high-salinity oil and gas reservoirs, as the temperature and pressure decrease during the flowback of formation fluids, when the ion concentration reaches the salt dissolution limit, salt will precipitate from the flowback fluid, resulting in salt crystallization and scaling, clogging the wellbore, affecting normal drainage and production, and restricting the progress of oil and gas reservoir exploration and evaluation. Currently, inhibitors have been developed mainly for scaling such as sodium chloride and calcium carbonate, including mixed cyanides, synthetic fatty acids, amine compounds, and maleic anhydride. However, the main salt crystallization in the alkaline lake-type shale oil of the Permian Fengcheng Formation in the Mahu Depression of the Junggar Basin is sodium bicarbonate. Laboratory evaluations have shown that these products are not very effective in solubilizing and inhibiting sodium bicarbonate crystallization. Furthermore, a literature search revealed no research or products on sodium bicarbonate-related salt-assisted dissolution drilling fluids. Therefore, there is an urgent need to develop a drilling fluid system with salt-assisted dissolution and crystallization inhibition properties to solve the problem of wellbore scaling treatment in high-sodium bicarbonate oil and gas reservoirs. Summary of the Invention

[0003] This invention provides a salt-assisted dissolving drilling fluid system that overcomes the shortcomings of the prior art and can effectively solve the problems of blocked production channels and stuck tubing caused by salt crystallization in existing salt oil and gas reservoirs.

[0004] One of the technical solutions of the present invention is achieved through the following measures: a salt-assisted drilling fluid system, wherein the raw materials are composed of 1.8% to 3.2% salt inhibitor, 1.5% to 2% thickener, 0.5% to 2% lubricant by mass percentage, and the remainder is water; the salt inhibitor is one or more of metal complexing agents, and the lubricant is modified silicone grease.

[0005] The following are further optimizations and / or improvements to one of the above-mentioned inventive technical solutions: The salt inhibitors mentioned above are one or two of the following: disodium ethylenediaminetetraacetate, diethylenetriaminepentaacetic acid, and aziridine triacetic acid.

[0006] The salt suppressant mentioned above is a mixture of disodium ethylenediaminetetraacetate and diethylenetriaminepentaacetic acid, with a mass ratio of disodium ethylenediaminetetraacetate to diethylenetriaminepentaacetic acid of 0.8 to 1.2:1 to 2.

[0007] The aforementioned tackifier is a mixture of tackifier PF-VIS and sodium sulfite, with a mass ratio of PF-VIS to sodium sulfite of 2 to 3:1.

[0008] The above-mentioned lubricant is a fluorine-modified silicone grease.

[0009] The above-mentioned salt-assisted drilling fluid system is obtained by the following method: First, add the required amount of salt inhibitor to water, stir and dissolve to obtain a first mixture; Second, add the required amount of thickener to the first mixture, stir and dissolve thoroughly to obtain a second mixture; Third, add the required amount of lubricant to the second mixture, stir thoroughly to obtain the salt-assisted drilling fluid system.

[0010] In the first step above, the required amount of salt inhibitor is added to the water, stirred and dissolved, and the pH value is adjusted to 7.0 to 7.5 to obtain the first mixture.

[0011] The second technical solution of the present invention is achieved through the following measures: a method for preparing a salt-assisted dissolving drilling fluid system, comprising the following steps: The first step is to add the required amount of salt inhibitor to water, stir and dissolve to obtain the first mixture; the second step is to add the required amount of thickener to the first mixture, stir and dissolve thoroughly to obtain the second mixture; the third step is to add the required amount of lubricant to the second mixture, stir thoroughly to obtain the salt-assisted drilling fluid system.

[0012] The following are further optimizations and / or improvements to the second technical solution of the above invention: In the first step above, the required amount of salt inhibitor is added to the water, stirred and dissolved, and the pH value is adjusted to 7.0 to 7.5 to obtain the first mixture.

[0013] The third technical solution of the present invention is achieved through the following measures: the application of a salt-assisted dissolving drilling fluid system in the exploitation of high-salt oil and gas reservoirs.

[0014] This invention provides a salt-assisted drilling fluid system that offers excellent auxiliary effects for oil and gas extraction and exploration in high-salinity oil and gas reservoirs through single-agent optimization and formulation system optimization. It can solubilize and inhibit crystallization of salt scale in high-salinity oil and gas reservoirs, effectively preventing blockage of production channels and salt-stuck tubing caused by downhole salt crystallization. Furthermore, during mechanical drilling and unblocking operations, the drilling fluid dissolves scale, improving drilling efficiency and reducing the risk of damage to the top tubing and wellhead leakage caused by sudden release of high pressure. In addition, this salt-assisted drilling fluid system also exhibits good temperature and salt resistance, good drag reduction, and good cuttings carrying capacity. Attached Figure Description

[0015] Appendix Figure 1 The figure shows the changes in solubility after adding three salt-suppressing agents of different concentrations in Experiment 1 of this invention.

[0016] Appendix Figure 2 The changes in salt inhibition rate after adding three salt inhibitors at different concentrations in Experiment 2 of this invention.

[0017] Appendix Figure 3This is the microstructure of sodium bicarbonate scale formed in sample 1 of the present invention (Experiment 4) without the addition of a salt inhibitor.

[0018] Appendix Figure 4 The microstructure of sodium bicarbonate scale formed after adding salt inhibitor to scale sample 1 in Experiment 4 of this invention.

[0019] Appendix Figure 5 This is the microstructure of sodium bicarbonate scale formed in scale sample 2 without the addition of a salt inhibitor in Experiment 4 of this invention.

[0020] Appendix Figure 6 The microstructure of sodium bicarbonate scale formed after adding salt inhibitor to scale sample 2 in Experiment 4 of this invention.

[0021] Appendix Figure 7 This is the microstructure of sodium bicarbonate scale formed in scale sample 3 without the addition of a salt inhibitor in Experiment 4 of this invention.

[0022] Appendix Figure 8 The microstructure of sodium bicarbonate scale formed after adding salt inhibitor to scale sample 3 in Experiment 4 of this invention. Detailed Implementation

[0023] This invention is not limited to the following embodiments, and specific implementation methods can be determined according to the technical solutions and actual conditions of this invention. Unless otherwise specified, all chemical reagents and chemicals mentioned in this invention are well-known and commonly used chemical reagents and chemicals in the prior art; unless otherwise specified, all percentages in this invention are mass percentages; unless otherwise specified, all solutions in this invention are aqueous solutions with water as the solvent, for example, hydrochloric acid solution is an aqueous solution of hydrochloric acid; room temperature in this invention generally refers to a temperature between 15°C and 25°C, generally defined as 25°C.

[0024] The present invention will be further described below with reference to embodiments: Example 1: The salt-assisted drilling fluid system is composed of the following raw materials by mass percentage: 1.8% to 3.2% salt inhibitor, 1.5% to 2% thickener, 0.5% to 2% lubricant, and the remainder is water; the salt inhibitor is one or more metal complexing agents, and the lubricant is modified silicone grease.

[0025] Example 2: As an optimization of the above example, the salt suppressant is one or two of ethylenediaminetetraacetic acid disodium salt, diethylenetriaminepentaacetic acid, and aziridine triacetic acid.

[0026] Example 3: As an optimization of the above example, the salt suppressant is a mixture of disodium ethylenediaminetetraacetate and diethylenetriaminepentaacetic acid, with a mass ratio of disodium ethylenediaminetetraacetate to diethylenetriaminepentaacetic acid of 0.8 to 1.2:1 to 2.

[0027] Example 4: As an optimization of the above example, the tackifier is a mixture of tackifier PF-VIS and sodium sulfite, with a mass ratio of PF-VIS to sodium sulfite of 2 to 3:1. The PF-VIS tackifier can be the PF-VIS product of Dongying Shida Science and Technology Innovation Co., Ltd.

[0028] Example 5: As an optimization of the above examples, the lubricant is a fluorinated silicone grease. The fluorinated silicone grease can be the SFR-I product of Dongying Shida Science and Technology Innovation Co., Ltd.

[0029] This invention addresses the shortcomings of currently widely used slippery water-jet drilling fluid systems by optimizing the treatment agents. The optimized PF-VIS thickener solution exhibits excellent thickening ability, temperature resistance, and shear dilution resistance; the fluorine-modified silicone grease SFR-I possesses excellent lubrication and drag reduction properties.

[0030] Example 6: The salt-assisted drilling fluid system was prepared according to the following steps: First, add the required amount of salt inhibitor to water, stir and dissolve to obtain a first mixture; Second, add the required amount of thickener to the first mixture, stir and dissolve thoroughly to obtain a second mixture; Third, add the required amount of lubricant to the second mixture, stir thoroughly to obtain the salt-assisted drilling fluid system.

[0031] Example 7: As an optimization of Example 6 above, in the first step, the required amount of salt inhibitor is added to the water, and after stirring and dissolving, the pH value is adjusted to 7.0 to 7.5 (i.e., adjusted to weak alkalinity) to obtain the first mixture.

[0032] Example 8: Application of this salt-assisted drilling fluid system in the exploitation of high-salt oil and gas reservoirs.

[0033] Example 9: The salt-coated drilling fluid system comprises, by mass percentage, 1% disodium ethylenediaminetetraacetate, 1% diethylenetriaminepentaacetic acid, 1% PF-VIS thickener, 0.5% sodium sulfite, 1% fluorine-modified silicone grease, and the remainder being water.

[0034] The preparation process is as follows: First, add the required amount of disodium ethylenediaminetetraacetate and diethylenetriaminepentaacetic acid to the required amount of water, stir to dissolve, and then adjust the pH to 7.2 with a 10% sodium hydroxide aqueous solution to obtain the first mixture; Second, add the thickener PF-VIS and sodium sulfite to the first mixture in sequence, stir to dissolve thoroughly to obtain the second mixture; Third, add fluorine-modified silicone grease to the second mixture, stir thoroughly to obtain the salt-assisted solution drilling fluid system.

[0035] Example 10: This salt-coated drilling fluid system comprises, by mass percentage, 1.5% diethylenetriaminepentaacetic acid, 1.5% PF-VIS thickener, 0.5% sodium sulfite, 1% fluorinated silicone grease, and the remainder being water. Its preparation process is the same as in Example 9.

[0036] Example 11: This salt-coated drilling fluid system comprises, by mass, 100 parts water, 1.5% disodium ethylenediaminetetraacetate, 1% diethylenetriaminepentaacetic acid, 1% PF-VIS thickener, 0.5% sodium sulfite, 1% fluorinated silicone grease, and the remainder being water. Its preparation process is the same as in Example 9.

[0037] Comparative example: Unlike Example 9, no salt inhibitor was added.

[0038] Experimental section: Experiment 1: Evaluation of Solubility Test protocol: The drilling fluid systems prepared using three salt suppressants—EDTA-2Na (disodium ethylenediaminetetraacetate), NTA (nitroglycerin triacetic acid), and DTPA (diethyltriaminepentaacetic acid)—with different concentration gradients (all other components being identical) were compared and optimized using the "SYT 5523-2016 Oilfield Water Analysis Methods" protocol. The experimental results are shown below. Figure 1 .from Figure 1 As can be seen from the data, with the increase of the salt suppressant dosage, the HCO3 in the solution... - The concentration and solubility of HCO3 increased sharply. When the amount of salt inhibitor increased from 1% to 2%, the concentration and solubility of HCO3... - The rate of increase in HCO3 concentration gradually leveled off. Among the three salt suppressants, EDTA-2Na showed the best salt suppressant effect, reducing the concentration of HCO3 in the solution. - The concentration and solubility of the highest are of the two, which can exceed 30%. DTPA and NTA have similar salt inhibition effects, with solubility rates of less than 15%.

[0039] Experiment 2: Evaluation of Salt Inhibition Rate Test protocol: Drilling fluid systems formulated with different concentration gradients of EDTA-2Na, NTA, and DTPA (all other components were identical) were compared and optimized. Concentration gradients were used for comparison and optimization. Experimental results are shown below. Figure 2 .from Figure 2 As can be seen, with the increase of the salt-inhibiting agent dosage, the salt-inhibiting effect of EDTA-2Na first increases and then decreases, with the best salt-inhibiting effect when the salt-inhibiting agent dosage is between 0.8% and 1.2%. The salt-inhibiting rate of DTPA increases with the increase of the salt-inhibiting agent dosage, and when the salt-inhibiting agent dosage is 0.5%, the salt-inhibiting rate continues to increase.

[0040] The data shows that when the amount of EDTA-2Na is 1%, the solubility is 22.48% and the salt inhibition rate is 92.92%, while the salt inhibition rate of 2% DTPA is over 91.79%. Therefore, the combination of EDTA-2Na and DTPA can achieve better salt inhibition effect.

[0041] Experiment 3: Optimization of Salt Inhibitor Compound Formulation Three scale samples (scale 1: carbonate scale 1, scale 2: carbonate scale 2, and scale 3: carbonate scale 3) were weighed out at 16g each and dissolved in 100mL of deionized water. Different ratios of EDTA-2Na and DTPA were added to evaluate the solubilization rate and salt inhibition rate of the salt inhibitor. The experimental results are shown in Table 1. The data in Table 1 show that the compound salt inhibitor of 1% EDTA-2Na + 1% DTPA has a good salt-solubilizing effect, with solubilization rates of 58%, 55.97%, and 30.978% for scale samples 1, 2, and 3, respectively, and salt inhibition rates of 85.70%, 80.11%, and 80.56%, respectively.

[0042] Based on experiments one through three, it can be seen that using a mixture of EDTA-2Na and DTPA as a salt inhibitor has significant solubilizing and salt-inhibiting effects, with a solubilization rate of up to 58% and a salt inhibition rate of over 80%.

[0043] Experiment 4: Study on the mechanism of action of salt inhibitors 16.4 g of each of the three types of scale (scale sample 1, scale sample 2, and scale sample 3) were added to 100 mL of deionized water, sealed, and heated to 60 °C, then cooled to room temperature to obtain a saturated scale solution. Two equal portions of the 60 °C saturated scale solution were taken; one portion was added to the drilling fluid of Comparative Example 1, and the other portion was added to the salt-coated drilling fluid system of Example 8. The microstructure of the sodium bicarbonate scale in the solution was observed using a Dutch Apreo S cryo-scanning electron microscope and compared with the morphology of sodium bicarbonate scale formed in the scale solution after the addition of the salt inhibitor. Combining the aforementioned salt inhibition performance evaluation experimental results and basic theories, the mechanism of action of the salt inhibitor was explored. The results are shown in […]. Figures 3 to 8 ( Figures 3 to 8 Both images on the left and right are microscopic images at different magnifications.

[0044] Figures 3 to 8 The results show that the scale formed after adding Comparative Example 1 is distributed irregularly at multiple angles, with relatively large particles. These large salt particles settle and accumulate in the reservoir, forming salt clumps that adhere to the walls of pores and throats, easily causing salt blockage. The scale formed after adding Example 9 is needle-shaped (…). Figure 4 and Figure 8 ) or columnar ( Figure 6 The particles are significantly smaller and have a looser structure, and they move with the fluid under the influence of the water flow.

[0045] The formation process of sodium bicarbonate scale mainly includes the formation of crystal nuclei, the aggregation of crystal nuclei, and crystal growth. Salt inhibitors generally achieve their salt-inhibiting effect by affecting these three processes.

[0046] Salt inhibitors exert their salt-suppressing effect through three mechanisms. One is the chelation mechanism: after aminopolycarboxylate salts EDTA-2Na and DTPA dissociate in water, the negatively charged carboxylate ions react with the scale-forming cations Na+. + By chelating to form a stable water-soluble cyclic structure, the number of scale-forming cations is reduced, thus preventing Na+ from forming. + With HCO3 - The combination generates NaHCO3, thereby reducing the formation of crystal nuclei. Figure 4 The results showed that the addition of salt inhibitors EDTA-2Na and DTPA significantly reduced the number of crystal nuclei, significantly improved the surface smoothness of the precipitated crystals, and resulted in uniform particle size, regular crystal shape, and clear edges. This indicates that EDTA-2Na and DTPA can react with Na... + The first mechanism involves the formation of complexes, which stabilize the active state of chemical substances in the water, reduce the lattice energy that resists their dissolution, and make it easier for water molecules to penetrate into the crystal, thereby increasing their solubility. The second mechanism involves lattice distortion. Salt inhibitors adsorb onto the surface of newly precipitated salt crystals, interfering with (distorting) the normal scaling state of the salt scale surface. This prevents other crystal nuclei or ions from binding to growth sites, inhibiting or partially inhibiting the continued growth of salt crystals, resulting in loose salt scale. Figure 6 and Figure 8 The results show that numerous tiny cracks, depressions, and pores appear on the surface of the salt crystals, creating a loose structure that is easily carried away by water flow, thus controlling salt precipitation. Thirdly, there is the electrostatic repulsion mechanism. This is because the salt inhibitor EDTA-2Na adsorbs on the salt crystal surface, forming a diffused electric double layer that charges the surface and inhibits the aggregation of salt crystals. The salt inhibitor can also adsorb on the scale surface, forming the same diffused electric double layer, thus charging the scale surface as well. This prevents salt crystals that cannot aggregate from depositing on the scale surface, achieving the purpose of salt suppression.

[0047] Comparison of the microscopic morphology of the scale crystal surface before and after the addition of the salt inhibitor shows that the compound salt inhibitor suppressed the formation and aggregation of salt crystals, resulting in significantly smaller and looser-structured particles. The salt inhibitors DTPA and EDTA-2Na mainly play an inhibitory role in the formation of sodium bicarbonate scale through chelation solubilization, lattice distortion, and electrostatic repulsion mechanisms.

[0048] Experiment 5: Effect of pH on the salt-suppressing effect of compound salt-suppressing agents Saturated solutions of three scale samples (scale sample 1, scale sample 2, and scale sample 3) were prepared and dissolved in the salt-assisted drilling fluid system of Example 9. After heating to dissolve and cooling, hydrochloric acid and sodium bicarbonate solutions were added to adjust the pH value. The effect of pH value change on scale sample dissolution was observed. Under different pH values, all three scale samples could be completely dissolved in water without salt crystallization, indicating that pH value has no effect on the salt suppression effect of the salt-assisted drilling fluid system, and also indicating that the salt-assisted drilling fluid system of the present invention has wide applicability in use.

[0049] Experiment 6: Comparison of Tougheners Based on the required viscosity of the drilling fluid, a drilling fluid is prepared using guar gum, PAC-HV (the thickener PAC-HV is a product of Dongying Shida Science and Technology Innovation Co., Ltd.), HE300 (the thickener HE300 is a product of Shandong Lianmeng Chemical Co., Ltd.), and PF-VIS as thickeners.

[0050] The rheological properties of various drilling fluids were tested before and after hot rolling at 130℃ for 16h. Using the viscosity after aging as an indicator, the thickener with better rheological properties and temperature resistance was selected. The 0.2% guar gum solution exhibited poor temperature resistance; after aging, its apparent viscosity decreased from 77 mPa·s to 6 mPa·s. The apparent viscosities of the 1% PAC-HV solution before and after aging were 87.5 mPa·s and 62.5 mPa·s, respectively, demonstrating good rock-carrying capacity but poor fluidity. The viscosities of the 1% HE300 and 1% PF-VIS solutions before and after aging ranged from 18.85 mPa·s to 46.5 mPa·s, exhibiting both certain rock-carrying capacity and good fluidity. Since salt jamming frequently occurs in high-salt oil and gas reservoirs, the salt resistance of drilling fluids is crucial. HE300 exhibited poor salt resistance; therefore, PF-VIS was selected as the optimal thickener. Compared with guar gum solution, PF-VIS solution has good temperature resistance, moderate apparent viscosity and plastic viscosity before and after aging, good fluidity, and low friction between solid and liquid phases; it has a high dynamic-to-plastic ratio before and after aging, indicating that the solution has enhanced resistance to shear dilution and can effectively carry rock cuttings at low shear rates.

[0051] Furthermore, the effect of the amount of thickener added on the rheological properties of each formulation was investigated. With the increase of thickener addition, the apparent viscosity of each formulation before and after aging increased significantly. PF-VIS with a mass concentration of 1% to 1.5% is more likely to meet the requirements of high drag reduction performance of drilling fluid in the early stage of drilling plug and high viscosity of drilling fluid to carry cuttings in the later stage of drilling, which can effectively reduce the risk of stuck drill and improve drilling efficiency.

[0052] Experiment 7: Selection of Lubricant Drilling fluids require good lubrication properties to further reduce fluid friction and improve drill plug efficiency. To improve the lubrication performance of the drilling fluid system, lubricant optimization was conducted. The lubrication coefficients of different formulations were tested using an extreme pressure lubrication tester. Experimental results showed that the lubrication coefficient and friction coefficient of the system significantly decreased after adding lubricant. Compared with the lubricant from Dongying Shida Science and Technology Innovation Co., Ltd., the fluorinated modified silicone grease SFR-I exhibited superior lubrication and drag reduction performance, with a friction coefficient less than 0.17 before and after aging. Therefore, a mass concentration of 0.5% to 2% SFR-I was selected as the optimal lubricant.

[0053] Experiment 8: Construction of Salt-Suppressing Drilling Fluid System Different mass fractions of carbonate scale were added to the salt-assisted drilling fluid system of Example 9, and the rheological properties and lubrication properties of different formulations were tested. The experimental results are shown in Tables 2 and 3.

[0054] Formula 1: Example 9; Formula 2: Formula 1 + 10% salt scale; Formula 3: Formula 1 + 15% salt scale; Formula 4: Formula 1 + saturated salt scale.

[0055] As shown in Table 2, the higher the amount of salt scale added, the higher the apparent viscosity of the drilling fluid system before and after aging, and the better its rock-carrying capacity. After adding salt scale, the dynamic-plastic ratio of the system after aging also increased significantly, from 0.36 to over 1.22, improving the system's resistance to shear dilution. The apparent viscosity of the salt scale-saturated drilling fluid system before aging was 53.85 mPa·s, and the plastic viscosity was 29.4 mPa·s. After aging, the apparent viscosity was 42.55 mPa·s, and the plastic viscosity was 19.24 mPa·s. The rheological properties before and after aging both meet the requirements of the drilling fluid, indicating that the constructed salt-assisted dissolving drilling fluid has good temperature resistance. Table 3 shows that with the increase of salt scale addition, the lubrication coefficient and friction coefficient slightly increase, while the drag reduction rate decreases. The friction coefficient of the salt-saturated drilling fluid system after aging is 0.1429, and the drag reduction rate is 57.97%, which is not much different from that without salt, indicating that the salt-co-dissolving drilling fluid system of the present invention is applicable to various salt concentrations.

[0056] Experiment 9: Performance Evaluation of Drilling Fluid System Rheological properties and temperature resistance: The viscosity of the drilling fluid was tested using a six-speed rheometer. The salt-assisted drilling fluid system of Example 9 was stored in a standard container, and the drilling fluid was tested at different rotation speeds. The apparent viscosity of the drilling fluid was calculated based on the values ​​at different rotation speeds, and the rheological properties of the drilling fluid are shown in Table 4. From the data in Table 4, it can be seen that the apparent viscosity of the drilling fluid system before aging is 50 mPa·s. Although the fluidity is relatively weakened, the friction, gel strength, and shear dilution properties are greatly improved, resulting in enhanced overall rock-carrying performance. After aging at 130℃ for 16h, the apparent viscosity of the drilling fluid system is 21.55 mPa·s, exhibiting good fluidity and good rock-carrying capacity. Therefore, it can be seen that the viscosity of the salt-assisted drilling fluid system of the present invention decreases significantly after aging at 130℃ for 16h, with an apparent viscosity of 21.55 mPa·s and a plastic viscosity of 15.9 mPa·s. The rheological properties still meet the requirements of the drilling fluid, indicating that the drilling fluid system can withstand a high temperature of 130℃.

[0057] Lubrication and drag reduction performance: The performance of drilling fluid has a significant impact on drilling. Ideally, drilling fluid requires low friction and a drag reduction rate ≥ 50%. The lubrication performance of the salt-coated drilling fluid system in Example 9 was tested using an EP-B extreme pressure lubrication tester. The rheological properties of the drilling fluid were obtained by calculating the friction coefficient based on the lubrication coefficient, as shown in Table 5. The data in Table 5 show that the friction coefficient of the drilling fluid system before aging was 0.1681, with a drag reduction rate of 50.57%. After aging, the friction coefficient was 0.1659, with a drag reduction rate of 51.20%. A good drilling fluid has a drag reduction rate of 50-65%, and the salt-coated drilling fluid system of this invention meets the drag reduction requirements for drilling fluids.

[0058] Salt and calcium resistance: The salt-coated drilling fluid system of Example 9 was supplemented with 10wt% NaCl and 1.0wt% CaCl2, and the rheological properties before and after hot rolling at 130℃ for 16h were tested to evaluate the system's resistance to salt and calcium contamination. The experimental results are shown in Table 6.

[0059] Formula 1: Example 9; Formula 2: Formula 1 + 10% NaCl; Formula 3: Formula 1 + 1% CaCl2.

[0060] The data in Table 6 show that the addition of 10% NaCl and 1% CaCl2 has little effect on the apparent viscosity of the drilling fluid system, but increases the dynamic plasticity ratio, indicating that the salt-coated drilling fluid system has good salt and calcium resistance. The data in Table 6 also show that the apparent viscosity of the drilling fluid system after aging decreases from 50 mPa·s to approximately 24 mPa·s. Although the rock-carrying capacity of the system decreases, it still remains within a suitable range.

[0061] The effects of 10% NaCl and 1% CaCl2 on the lubrication performance of the salt-assisted drilling fluid system were further investigated. The experimental results are shown in Table 7. Table 7 shows that the lubrication coefficient and friction coefficient of the salt-assisted drilling fluid systems with the addition of 10% NaCl and 1% CaCl2 increased slightly before aging, but remained at a low level. After aging, the friction coefficient decreased, indicating good lubrication capability.

[0062] In summary, the flux system of the present invention has good salt solubilization and salt crystallization inhibition effects, and its temperature resistance, rheological properties, lubrication performance, salt and calcium resistance performance evaluation results are excellent. It can withstand high temperature of 130℃, has good fluidity and good rock carrying capacity, and has good salt and calcium resistance.

[0063] The above technical features constitute the embodiments of the present invention, which have strong adaptability and implementation effect. Unnecessary technical features can be added or removed according to actual needs to meet the needs of different situations.

Claims

1. A salt-assisted dissolution drilling and grinding fluid system, characterized in that The raw materials are composed of 1.8% to 3.2% of salt inhibitor, 1.5% to 2% of viscosity enhancer, 0.5% to 2% of lubricant, and the rest is water in terms of mass percentage; the salt inhibitor is one or more of metal complexing agents, and the lubricant is modified silicone grease.

2. The salt-assisted dissolution drilling and grinding fluid system according to claim 1, characterized in that The salt inhibitor is one or two of disodium ethylenediaminetetraacetic acid, diethylenetriaminepentaacetic acid and nitrilotriacetic acid.

3. The salt-assisted dissolution drilling and grinding fluid system according to claim 2 is characterized in that The salt inhibitor is a mixture of disodium ethylenediaminetetraacetate and diethylenetriaminepentaacetic acid, and the mass ratio of disodium ethylenediaminetetraacetate to diethylenetriaminepentaacetic acid is 0.8 to 1.2:1 to 2.

4. The salt-assisted dissolution drilling and grinding fluid system according to any one of claims 1 to 3, characterized in that The thickener is a mixture of thickener PF-VIS and sodium sulfite, and the mass ratio of the thickener PF-VIS to the sodium sulfite is 2 to 3:

1.

5. The salt-assisted dissolution drilling and grinding fluid system according to any one of claims 1 to 4, characterized in that The lubricant is fluorine-modified silicone grease.

6. The salt-assisted dissolution drilling and grinding fluid system according to any one of claims 1 to 5, characterized in that It is obtained by the following method: the first step is to add the required amount of salt inhibitor into water, and stir to dissolve to obtain a first mixed solution; the second step is to add the required amount of viscosity enhancer into the first mixed solution, and stir to dissolve to obtain a second mixed solution; the third step is to add the required amount of lubricant into the second mixed solution, and stir to obtain a salt-assisted dissolution drilling and grinding fluid system.

7. The salt-assisted dissolution drilling and grinding fluid system according to claim 6, characterized in that In the first step, a required amount of salt inhibitor is added to water, and after stirring to dissolve, the pH value is adjusted to 7.0 to 7.5 to obtain a first mixed solution.

8. A method for preparing the salt-assisted dissolution drilling and grinding fluid system according to claims 1 to 7, characterized in that Follow these steps: The first step is to add the required amount of salt inhibitor to water, stir and dissolve to obtain a first mixed solution; the second step is to add the required amount of viscosity enhancer to the first mixed solution, stir and dissolve to obtain a second mixed solution; the third step is to add the required amount of lubricant to the second mixed solution, stir and dissolve to obtain a salt-assisted dissolution drilling and grinding fluid system.

9. The method for preparing the salt-assisted dissolution drilling and grinding fluid system according to claim 8, characterized in that In the first step, a required amount of salt inhibitor is added to water, and after stirring to dissolve, the pH value is adjusted to 7.0 to 7.5 to obtain a first mixed solution.

10. Use of the salt-assisted dissolution drilling and grinding fluid system according to claims 1 to 7 in the exploitation of high-salinity oil and gas reservoirs.

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