Environment-friendly high-temperature resistant high-density composite salt drilling fluid, preparation method and application thereof

Abstract

The application provides an environment-friendly high-temperature-resistant high-density composite salt drilling fluid and a preparation method and application thereof, and comprises the following components in parts by weight: 100 parts of base fluid, 1.5-2 parts of inorganic suspending agent, 0.3-1 part of alkaline pH regulator, 1.5-2 parts of high-temperature-resistant polymer fluid loss additive, 1-1.2 parts of high-temperature-resistant resin fluid loss additive, 2-3 parts of salt-resistant high-temperature-resistant cut increasing and viscosity increasing agent, 25-30 parts of stabilizing inhibitor, 6-8 parts of high-temperature-resistant plugging agent and 110-120 parts of weighting agent. The environment-friendly high-temperature-resistant high-density composite salt drilling fluid has good high-temperature rheological stability and sedimentation stability, and the temperature resistance can reach above 200 DEG C through testing, the high-temperature high-pressure fluid loss is low, the treatment agent used is non-biologically toxic and easy to biodegrade, and meets the technical requirements of the current oil and gas field drilling operation on environment-friendly working fluid.

Description

Technical Field

[0001] This invention relates to the field of oil drilling fluid technology, and more specifically, to an environmentally friendly, high-temperature resistant, high-density composite salt drilling fluid, its preparation method, and its application. Background Technology

[0002] With the continued growth of global energy demand, the focus of oil and gas exploration and development, both domestically and internationally, is rapidly shifting towards deeper and ultra-deep formations. Currently, there are two main technical routes in this field, but both have significant drawbacks: polysulfonated drilling fluid systems are technically mature and have good high-temperature resistance, but the sulfonated treatment agents used in them are highly biotoxic (EC50 values ​​are often below 1000 mg / L), resulting in high drilling waste treatment costs, significant environmental risks, and non-compliance with increasingly stringent environmental regulations. While existing conventional environmentally friendly water-based drilling fluid systems have solved the toxicity problem, there is an irreconcilable contradiction between their temperature resistance and high-density stability. When the density increases, the addition of large amounts of weighting agents can easily trigger sedimentation and stratification at high temperatures, leading to downhole accidents. Simultaneously, conventional environmentally friendly treatment agents are prone to degradation and failure in high-temperature and high-salt environments, leading to uncontrolled filtration loss and rheological deterioration, increasing the risk of bottomhole sand settling and wellbore collapse, affecting safe drilling progress, and failing to meet the needs of efficient development of deep resources.

[0003] Chinese patent application number CN201710389023.X discloses a non-sulfonated high-temperature resistant filtration loss-reducing drilling fluid. The drilling fluid formula provided is as follows: by weight, 1% 4% bentonite, 0.25% 3% CCM, 2% 4% NMPS, 0.5% 2% MMC, 3% 5% Na2CO3, 0.25% 1% DM and balance water. Summary of the Invention

[0004] In view of this, the present invention proposes an environmentally friendly, high-temperature resistant, high-density composite salt drilling fluid, its preparation method, and its application, aiming to solve the problem that existing drilling fluids are difficult to simultaneously meet the requirements of high temperature above 200℃ and 1.9 g / cm³ under the premise of being non-toxic, easily biodegradable, and environmentally friendly. 3 The above-mentioned high-density working conditions have long-term issues related to maintaining excellent rheological properties, filtration runoff control, and sedimentation stability.

[0005] Specifically, the first aspect of this invention proposes an environmentally friendly high-temperature resistant, high-density composite salt drilling fluid, comprising the following components in parts by weight: 100 parts base fluid, 0.5-2.5 parts inorganic suspending agent, 0.1-1.5 parts alkaline pH adjuster, 1-2 parts high-temperature resistant polymer filtration reducer, 0.6-1.2 parts high-temperature resistant resin filtration reducer, 1.6-3.2 parts salt-resistant, high-temperature resistant shearing and viscosity-enhancing agent, 15-30 parts stabilizing inhibitor, 4-10 parts high-temperature resistant plugging agent, and 100-130 parts weighting agent.

[0006] Furthermore, the aforementioned environmentally friendly high-temperature resistant high-density composite salt drilling fluid comprises the following components in parts by weight: 100 parts base fluid, 1.5-2 parts inorganic suspending agent, 0.3-1 parts alkaline pH adjuster, 1.5-2 parts high-temperature resistant polymer filtration reducer, 1-1.2 parts high-temperature resistant resin filtration reducer, 2-3.2 parts salt-resistant and high-temperature shearing thickener, 25-30 parts stabilizing inhibitor, 6-8 parts high-temperature resistant plugging agent, and 110-125 parts weighting agent.

[0007] Furthermore, in the aforementioned environmentally friendly high-temperature resistant high-density composite salt drilling fluid, the inorganic suspending agent is selected from one or two of bentonite and attapulgite.

[0008] Furthermore, in the aforementioned environmentally friendly high-temperature resistant high-density composite salt drilling fluid, the high-temperature resistant polymer filtration loss reducer is prepared by the following method: 2-Acrylamido-2-methylpropanesulfonic acid, acrylamide, N-vinylpyrrolidone and acrylic acid were dissolved in deionized water in a mass ratio of (1~5):(8~15):(1~5):(0.5~1.5), the pH was adjusted to 6~7, and an initiator was added under nitrogen protection at 40~100℃ to carry out free radical polymerization. After the free radical polymerization reaction is completed, the reaction product is quickly poured into a precipitant, filtered to obtain a precipitate, and the precipitate is washed and dried to obtain a white solid, which is the high-temperature polymer filtration loss reducer.

[0009] Furthermore, in the aforementioned environmentally friendly, high-temperature resistant, high-density composite salt drilling fluid, the mass ratio of 2-acrylamido-2-methylpropanesulfonic acid, acrylamide, N-vinylpyrrolidone, and acrylic acid is 3:11:3:1.

[0010] Furthermore, in the aforementioned environmentally friendly high-temperature resistant high-density composite salt drilling fluid, the stabilizing inhibitor is at least one of potassium chloride and sodium chloride.

[0011] Furthermore, in the aforementioned environmentally friendly high-temperature resistant high-density composite salt drilling fluid, the high-temperature resistant plugging agent is at least one of methacrylate copolymer and ultrafine calcium carbonate.

[0012] The second aspect of this invention provides a method for preparing an environmentally friendly high-temperature resistant, high-density composite salt drilling fluid, comprising the following steps: adding a suspending agent to a base fluid, and hydrating it under stirring conditions for a first preset time to obtain a pre-hydrated base slurry; An alkaline pH adjuster is added to the prehydrated slurry, and the mixture is stirred at a preset speed for a second preset time. High-temperature resistant polymer filtration loss reducer, high-temperature resistant resin filtration loss reducer, salt and high-temperature resistant shearing thickener, stabilizing inhibitor, high-temperature resistant plugging agent and weighting agent are added in sequence. After each treatment agent is added, the mixture is stirred for a third preset time to obtain an environmentally friendly high-temperature resistant high-density composite salt drilling fluid.

[0013] Furthermore, in the above-mentioned method for preparing the environmentally friendly high-temperature resistant high-density composite salt drilling fluid, the first preset time can be 12-36 hours; and / or the stirring speed can be 8000-12000 rpm, preferably 11000 rpm. The second preset time is 60-120 minutes; and / or the third preset time is 20-45 minutes.

[0014] This invention also provides a high-temperature resistant, high-density composite salt drilling fluid suitable for use in mountain and lake environments, with a bottom-hole circulation temperature of 200-220℃ and a drilling fluid density of 1.9 g / cm³. 3 Applications in deep or ultra-deep wells.

[0015] The present invention has the following beneficial effects: 1. The various drilling fluid treatment agents in this invention have good compatibility, the system is easy to prepare, simple to use, inexpensive, non-toxic, easily biodegradable, and have excellent environmental performance, meeting the specific requirements of on-site construction in deep and ultra-deep high-temperature and high-pressure formations in Xinjiang.

[0016] 2. Based on the key technical challenges of deep and ultra-deep oil and gas drilling and production, this invention optimizes the combination of filtration loss reducers, plugging agents, and cutting agents, and determines the various treatment agents required for the drilling fluid system configuration, thus forming a drilling fluid system with excellent rheological filtration performance, high-temperature stability, plugging performance, and environmental performance for deep and ultra-deep oil and gas drilling in Xinjiang.

[0017] 3. The drilling fluid system of this invention for deep and ultra-deep oil and gas drilling was evaluated in laboratory experiments for its rheological properties, filtration loss reduction performance, plugging performance, high-temperature stability, and environmental performance. Experiments showed that this environmentally friendly, high-temperature resistant, high-density composite salt drilling fluid system exhibits excellent performance: after aging at 200℃, the system's AV remains around 37 mPa·s, API filtration loss is controlled within 3.8 mL, HTHP filtration loss is controlled within 17.8 mL, and it has good settling stability; moreover, it is non-toxic, readily biodegradable, and has excellent environmental performance, fully meeting the stringent requirements for deep and ultra-deep oil and gas drilling in Xinjiang. Attached Figure Description

[0018] Figure 1 The graphs show the API filtration loss of the drilling fluid systems in Examples 1-4 and Comparative Examples 1-2 of this invention as a function of temperature. Figure 2The graphs show the HTHP filtration loss of the drilling fluid systems in Examples 1-4 and Comparative Examples 1-2 of this invention as a function of temperature. Detailed Implementation

[0019] The following describes preferred embodiments of the present invention. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of the present invention, and these improvements and modifications are also considered to be within the scope of protection of the present invention.

[0020] This invention provides an environmentally friendly high-temperature resistant, high-density composite salt drilling fluid, comprising the following components in parts by weight: 100 parts base fluid, 0.5-2.5 parts inorganic suspending agent, 0.1-1.5 parts alkaline pH adjuster, 1-2 parts high-temperature resistant polymer filtration reducer, 0.6-1.2 parts high-temperature resistant resin filtration reducer, 1.6-3.2 parts salt and high-temperature resistant shearing and thickening agent, 15-30 parts stabilizing inhibitor, 4-10 parts high-temperature resistant plugging agent, and 100-130 parts weighting agent.

[0021] Preferably, the environmentally friendly high-temperature resistant high-density composite salt drilling fluid comprises the following components in parts by weight: 100 parts base fluid, 1.5-2 parts inorganic suspending agent, 0.3-1 parts alkaline pH adjuster, 1.5-2 parts high-temperature resistant polymer filtration reducer, 1-1.2 parts high-temperature resistant resin filtration reducer, 2-3.2 parts salt-resistant and high-temperature shearing thickener, 25-30 parts stabilizing inhibitor, 6-8 parts high-temperature resistant plugging agent, and 110-125 parts weighting agent.

[0022] More preferably, the environmentally friendly high-temperature resistant high-density composite salt drilling fluid comprises the following components in parts by weight: 100 parts base fluid, 0.5 parts inorganic suspending agent bentonite, 1.2 parts inorganic suspending agent attapulgite, 1 part alkaline pH adjuster, 1.8 parts high-temperature resistant polymer filtration reducer, 1.2 parts high-temperature resistant resin filtration reducer, 3.2 parts salt and high-temperature resistant shearing and thickening agent, 0.5 parts high-temperature resistant plugging agent GBJ, 5.6 parts high-temperature resistant plugging agent Carb, and 124 parts weighting agent.

[0023] Specifically, the base liquid is fresh water.

[0024] The inorganic suspending agent is selected from one or both of bentonite and attapulgite. Preferably, the inorganic suspending agent is composed of bentonite and attapulgite, with a mass ratio of bentonite to attapulgite of 1:2.4 (e.g., 0.5 parts bentonite and 1.2 parts attapulgite). The alkaline pH adjuster is sodium hydroxide (NaOH) or potassium hydroxide, which provides the basic alkaline conditions.

[0025] The high-temperature resistant polymer filtration loss reducer is prepared by the following method: 2-Acrylamido-2-methylpropanesulfonic acid (AMPS), acrylamide (AM), N-vinylpyrrolidone (NVP) and acrylic acid (AA) were dissolved in deionized water, and the pH was adjusted to 6-7. Under nitrogen protection, an initiator was added at 40-100°C to carry out a free radical polymerization reaction. The amount of initiator added accounted for 0.5% of the total mass of the reaction system.

[0026] After the free radical polymerization reaction is completed, the reaction product is quickly poured into a precipitant, filtered to obtain a precipitate, and the precipitate is washed and dried to obtain a white solid, which is the high-temperature polymer filtration loss reducer.

[0027] The mass ratio of 2-acrylamido-2-methylpropanesulfonic acid, acrylamide, N-vinylpyrrolidone, and acrylic acid is (1~5):(8~15):(1~5):(0.5~1.5), preferably 3:11:3:1. This polymer contains structural units such as amide groups, sulfonic acid groups, lactam rings, and carboxyl groups, which can improve the hydration stability of the polymer chain and its adsorption film-forming ability under high temperature and high salt conditions.

[0028] The initiator is ammonium persulfate or potassium persulfate. The precipitant is anhydrous ethanol.

[0029] The temperature for free radical polymerization is 60–80℃, and the reaction time is 6–12 h.

[0030] The high-temperature resistant resin filtration reducer is BDF-300S, a multi-component copolymer complex for drilling fluid filtration reduction produced by Bohang Branch of China Petroleum Offshore Engineering Co., Ltd. It is suitable for high-temperature drilling scenarios such as deep and ultra-deep wells, effectively controlling drilling fluid filtration loss and ensuring drilling operation safety. In this embodiment, the resin filtration reducer is responsible for reinforcing the high-temperature, high-pressure filter cake and sealing micropores; the combination of the two reduces drilling fluid filtration loss. The salt-resistant, high-temperature, and shear-lifting viscosity enhancer is DVS-100, a high-temperature shear-lifting agent for drilling fluid produced by Bohang Branch of China Petroleum Offshore Engineering Co., Ltd. DVS-100 is a multi-component copolymer based on AMPS, providing excellent viscosity enhancement and shear-lifting capabilities for the drilling fluid system. The polymer filtration reducer is responsible for high-temperature salt-resistant adsorption film formation and ensuring filter cake density.

[0031] The stabilizing inhibitor is at least one of potassium chloride (KCl) and sodium chloride (NaCl), which inhibits the hydration swelling and dispersion of clay minerals in the formation, thereby maintaining wellbore stability. Preferably, the stabilizer is composed of KCl and NaCl in a mass ratio of 1:1.8 (e.g., 10 parts KCl and 18 parts NaCl). The high-temperature resistant plugging agent is at least one of GBJ and Carb. GBJ is a biomimetic wall-stabilizing agent that can significantly improve the cohesive strength and cementation of the wellbore rock. This material can effectively solve the problem of wellbore instability in complex formations through a "mechanical-chemical" coupling. Preferably, the high-temperature resistant plugging agent is composed of GBJ and Carb in a mass ratio of 1:11.2 (e.g., 0.5 parts GBJ and 5.6 parts Carb). GBJ can be XZ-GBJ, a drilling fluid plugging and anti-collapse agent methacrylate copolymer produced by Tianjin Tiancheng Tuoyuan Technology Development Co., Ltd.

[0032] Carb is 3000-mesh ultrafine calcium carbonate, which serves to bridge and add weight.

[0033] The weighting agent is barite BaSO4.

[0034] The environmentally friendly, high-temperature resistant, high-density composite salt drilling fluid of this invention employs a salt-resistant and high-temperature resistant polymer filtration reducer, which is combined with a high-temperature resistant resin filtration reducer and high-concentration composite salts (KCl and NaCl). This allows the polymer and salt ions to work synergistically, forming a more stable and dense spatial network structure, enabling the drilling fluid system to maintain excellent suspension capacity and rheological stability even under high-density conditions. Furthermore, the biomimetic wall-stabilizing agent GBJ is introduced into the high-density environmentally friendly drilling fluid system. GBJ not only performs conventional plugging functions, but its unique "mechanical-chemical" coupling properties allow it to tightly bond with the "polymer-salt" framework structure, forming a hydrogel film "biomimetic shell" with strong cohesion and adhesion. This film can tightly coat the surface of the wellbore rock, effectively sealing micropores and cracks, significantly enhancing the cohesion of the wellbore rock, increasing rock strength, and thus greatly reducing the risk of wellbore spalling, collapse, and other instability. The components of this invention have good compatibility and can be fully adapted to the complex drilling environment of deep formations in Xinjiang. All its performance indicators meet the safety drilling requirements of deep and ultra-deep wells in the Tarim Oilfield of Xinjiang, and can effectively provide technical support for deep and ultra-deep well operations.

[0035] This invention also provides a method for preparing an environmentally friendly, high-temperature resistant, high-density composite salt drilling fluid, comprising the following steps: (1) Add a suspending agent to the base liquid and hydrate it under stirring conditions for a first preset time to obtain a pre-hydrated base slurry; the first preset time can be 12 to 36 hours.

[0036] (2) Add an alkaline pH adjuster to the prehydrated slurry and stir at a preset speed for a second preset time; the stirring speed can be 8000~12000 rpm, preferably 11000 rpm. The second preset time is 60 minutes to 120 minutes.

[0037] (3) Add the following agents in sequence: high-temperature resistant polymer filtration reducer, high-temperature resistant resin filtration reducer, salt and high-temperature resistant shearing thickener, stabilizing inhibitor, high-temperature resistant plugging agent, and weighting agent. Stir for a third preset time after each addition to obtain an environmentally friendly high-temperature resistant high-density composite salt drilling fluid. The third preset time is 20-45 minutes, preferably 30 minutes.

[0038] In practice, bentonite and attapulgite are added to fresh water according to the specified ratio while stirring. NaOH is then added and stirred at 11,000 rpm for 120 minutes. Then, high-temperature resistant polymer filtration reducer, high-temperature resistant resin filtration reducer, salt-resistant and high-temperature shearing thickener, stabilizing inhibitor, high-temperature resistant plugging agent, and weighting agent are added sequentially. Each time a treatment agent is added, the mixture is stirred for 30 minutes to obtain an environmentally friendly high-temperature resistant high-density composite salt drilling fluid system.

[0039] This invention also provides an environmentally friendly, high-temperature resistant, high-density composite salt drilling fluid as described in any of the above claims, with a bottom-hole circulation temperature of 200-220°C and a drilling fluid density of 1.9 g / cm³. 3 Applications in deep or ultra-deep wells.

[0040] The environmentally friendly, high-temperature resistant, high-density composite salt drilling fluid provided by this invention exhibits excellent high-temperature rheological stability and sedimentation stability. Testing shows its temperature resistance can reach over 200℃, with low filtration loss under high temperature and pressure. Furthermore, the treatment agents used are non-biotoxic and readily biodegradable, meeting the current technical requirements for environmentally friendly working fluids in oil and gas field drilling operations. Therefore, this drilling fluid system is suitable for deep and ultra-deep well drilling operations under high-temperature and high-density conditions, and is particularly suitable for drilling in typical high-temperature and high-pressure formations such as the Tarim Basin.

[0041] The present invention has the following beneficial effects: 1. The various drilling fluid treatment agents in this invention have good compatibility, the system is easy to prepare, simple to use, inexpensive, non-toxic, easily biodegradable, and have excellent environmental performance, meeting the specific requirements of on-site construction in deep and ultra-deep high-temperature and high-pressure formations in Xinjiang.

[0042] 2. Based on the key technical challenges of deep and ultra-deep oil and gas drilling and production, this invention optimizes the combination of filtration loss reducers, plugging agents, and cutting agents, and determines the various treatment agents required for the drilling fluid system configuration, thus forming a drilling fluid system with excellent rheological filtration performance, high-temperature stability, plugging performance, and environmental performance for deep and ultra-deep oil and gas drilling in Xinjiang.

[0043] 3. The drilling fluid system of this invention for deep and ultra-deep oil and gas drilling was evaluated in laboratory experiments for its rheological properties, filtration loss reduction performance, plugging performance, high-temperature stability, and environmental performance. Experiments showed that this environmentally friendly, high-temperature resistant, high-density composite salt drilling fluid system exhibits excellent performance: after aging at 200℃, the system's AV remains around 37 mPa·s, API filtration loss is controlled within 3.8 mL, HTHP filtration loss is controlled within 17.8 mL, and it has good settling stability; moreover, it is non-toxic, readily biodegradable, and has excellent environmental performance, fully meeting the stringent requirements for deep and ultra-deep oil and gas drilling in Xinjiang.

[0044] The present invention will be further illustrated below with reference to the embodiments, the purpose of which is to better understand the content of the present invention and to demonstrate the essential features of the present invention. Therefore, the embodiments should not be regarded as a limitation on the scope of protection of the present invention.

[0045] The following detailed description is provided with reference to specific embodiments: Example 1 (1) Add 0.5g bentonite and 1.2g attapulgite to 100g base liquid, and hydrate for 24 hours under stirring conditions to obtain prehydrated base slurry; (2) Add 1g of alkaline pH adjuster to the prehydrated base slurry and stir at 11000rpm for 120 minutes; (3) 1.8g of high temperature resistant polymer filtration reducer, 1.2g of high temperature resistant resin filtration reducer, 3.2g of salt and high temperature resistant cutting and thickening agent, 10g of stabilizing inhibitor KCl, 18g of stabilizing inhibitor NaCl, 0.5g of high temperature resistant plugging agent GBJ, 5.6g of high temperature resistant plugging agent Carb and 124g of weighting agent were added in sequence. After each addition of a treatment agent, the mixture was stirred for 30 minutes to obtain an environmentally friendly high temperature resistant high density composite salt drilling fluid.

[0046] Example 2 (1) Add 0.5g bentonite and 1.2g attapulgite to 100g base liquid, and hydrate for 24 hours under stirring conditions to obtain prehydrated base slurry; (2) Add 1g of alkaline pH adjuster to the prehydrated base slurry and stir at 11000rpm for 120 minutes; (3) Add 1g of high temperature resistant polymer filtration reducer, 0.6g of high temperature resistant resin filtration reducer, 3.2g of salt and high temperature resistant cutting and thickening agent, 10g of stabilizing inhibitor KCl, 18g of stabilizing inhibitor NaCl, 0.5g of high temperature resistant plugging agent GBJ, 5.6g of high temperature resistant plugging agent Carb and 124g of weighting agent in sequence. Stir for 30 minutes after each addition of a treatment agent to obtain an environmentally friendly high temperature resistant high density composite salt drilling fluid.

[0047] Example 3 (1) Add 0.5g bentonite and 1.2g attapulgite to 100g base liquid, and hydrate for 24 hours under stirring conditions to obtain prehydrated base slurry; (2) Add 1g of alkaline pH adjuster to the prehydrated base slurry and stir at 11000rpm for 120 minutes; (3) Add 1g of high temperature resistant polymer filtration reducer, 0.6g of high temperature resistant resin filtration reducer, 1.6g of salt and high temperature resistant cutting and thickening agent, 10g of stabilizing inhibitor KCl, 18g of stabilizing inhibitor NaCl, 0.5g of high temperature resistant plugging agent GBJ, 5.6g of high temperature resistant plugging agent Carb and 124g of weighting agent in sequence. Stir for 30 minutes after each addition of a treatment agent to obtain an environmentally friendly high temperature resistant high density composite salt drilling fluid.

[0048] Example 4 (1) Add 0.5g bentonite and 1.2g attapulgite to 100g base liquid, and hydrate for 24 hours under stirring conditions to obtain prehydrated base slurry; (2) Add 1g of alkaline pH adjuster to the prehydrated base slurry and stir at 11000rpm for 120 minutes; (3) Add 1.8g of high temperature resistant polymer filtration reducer, 1.2g of high temperature resistant resin filtration reducer, 1.6g of salt and high temperature resistant shearing thickener, 10g of stabilizing inhibitor KCl, 18g of stabilizing inhibitor NaCl, 0.5g of high temperature resistant plugging agent GBJ, 5.6g of high temperature resistant plugging agent Carb and 124g of weighting agent in sequence. Stir for 30 minutes after each addition of a treatment agent to obtain an environmentally friendly high temperature resistant high density composite salt drilling fluid.

[0049] Comparative Example 1 Add 2g of bentonite to fresh water while stirring. After hydration for 24 hours, stir at 11,000 rpm for 20 minutes. Then, add 0.2g of caustic soda, 6g of sulfomethylphenol resin type III (SMP-3), 1g of modified lignite resin (TSH-2), 5g of natural bitumen powder, 3g of modified lignin sulfonate filtration reducer (LYM), 1g of modified lignite resin (JNJS-220), 3g of ultrafine calcium carbonate, 7g of KCl, 1g of graphite, 0.5g of low-viscosity polyanionic cellulose (PAC-LV), and 1.9g of barite. Stir for 30 minutes after each addition to obtain the polysulfonate drilling fluid system.

[0050] Comparative Example 2 Add 2g of bentonite to fresh water while stirring. After hydration for 24 hours, stir at 11,000 rpm for 20 minutes. Then, add 0.2g of caustic soda, 4g of SMP-3, 4g of TSH-2, 3g of natural bitumen powder, 2g of LYM, 1g of JNJS-220, 3g of ultrafine calcium carbonate, 7g of KCl, 1g of graphite, 0.5g of PAC-LV, and 1.9g of barite in sequence. Stir for 30 minutes after each addition of a treatment agent to obtain the polysulfonate drilling fluid system.

[0051] Experimental Example 1 To verify the technical effect of the present invention, the rheological parameters, filtration loss at normal temperature and pressure, high temperature and high pressure, and settling stability of the drilling fluid systems of Examples 1-4 and Comparative Examples 1-2 were tested according to the national standard GB / T29170-2012 "Laboratory Testing of Drilling Fluids for Petroleum and Natural Gas Industry". The experimental results are shown in Table 1. Table 1. Rheological filtration and sedimentation stability tests of drilling fluid systems in Examples 1-4 and Comparative Examples 1-2.

[0052] Combined with Table 1, Figure 1 and Figure 2 It is understood that the technical effect of the system of the present invention does not come from the independent action of a single treatment agent, but is the result of the synergistic combination of the high-temperature polymer filtration loss reducer, the high-temperature resin filtration loss reducer, the salt and high-temperature shearing and thickening agent, the composite salt stabilizing inhibitor, and the high-temperature blocking agent.

[0053] Figure 1 The results show that the API filtration loss in each embodiment remained at a low level within the temperature range of 25–220°C. Although some temperature points were not the absolute lowest compared to the comparative examples, Examples 1–4 were still able to stably control the API filtration loss within the range of approximately 2.2–4.2 mL after high-temperature aging. This indicates that the system of the present invention can maintain a relatively dense, low-permeability filter cake under high-salt, high-density conditions. This further demonstrates the applicability of the system to high-temperature deep well conditions. Figure 2The results show that at 200°C, the HTHP filtration losses of Examples 1-4 were 16.8 mL, 18.8 mL, 17.8 mL, and 15.8 mL, respectively, while those of Comparative Examples 1 and 2 were as high as 40.8 mL and 48.0 mL, respectively. At 220°C, the HTHP filtration losses of Examples 1-4 were still controlled between 16.6 and 22.0 mL, while those of Comparative Examples 1 and 2 increased to 42.6 mL and 51.6 mL, respectively. This demonstrates that the system of the present invention has significant advantages over polysulfonate systems in controlling filtration loss under high temperature and high pressure, maintaining excellent filtration loss reduction even under the combined effects of high temperature, high pressure, high density, and high salt.

[0054] Meanwhile, the rheological and sedimentation stability data in Table 1 further demonstrate the aforementioned synergistic effect. In Example 1, after aging at 200℃, AV was 36.0 mPa·s, PV was 24.0 mPa·s, YP was 11.0 Pa, and the HTHP filtration loss was 16.8 mL. Furthermore, the glass rod could still fall freely, there was no significant resistance to stirring, and no water separation on the surface. In contrast, in Comparative Examples 1 and 2, although the API filtration loss remained relatively low at 200℃, the HTHP filtration loss increased to 40.8 mL and 48.0 mL respectively, and significant soft settling, water separation, or increased stirring resistance were observed. This indicates that conventional polysulfonate systems struggle to simultaneously achieve filtration loss control, rheological stability, and sedimentation stability under high temperature, high pressure, and high density conditions.

[0055] The results indicate that the high-temperature resistant polymer filtration loss reducer and the high-temperature resistant resin filtration loss reducer together construct a temperature- and salt-resistant framework. The polymer component improves the hydration and dispersibility of the system and its continuous film-forming ability at high temperatures, while the resin component further enhances the density and high-temperature structural strength of the filter cake. The salt- and high-temperature resistant shearing and thickening agent maintains suitable dynamic shear force and suspension capacity in a complex salt environment, allowing a large amount of weighting agent to remain at 1.9 g / cm³. 3 It does not easily settle in high-density systems; the KCl / NaCl composite salt stabilizing inhibitor, while inhibiting clay hydration and dispersion, is compatible with the salt-resistant polymer system, preventing system instability caused by high salt content; GBJ and ultrafine calcium carbonate plugging agents synergistically form a tight-fitting plugging layer by enhancing wellbore cementation / cohesion and micro / nano particle bridging and filling effects, respectively. The combined effects of these components, through a specific high-temperature resistant polymer / resin filtration loss reduction combination, a composite salt environment, a shearing viscosifier, and the compatibility of the GBJ / Carb plugging system, allow the drilling fluid to maintain a stable operating temperature of 200–220℃ and 1.9 g / cm³. 3 Under high-density conditions, it simultaneously achieves low HTHP filtration loss, suitable rheological properties, and excellent settling stability, resulting in a synergistic improvement in overall performance. This comprehensive performance is significantly superior to that of comparative polysulfonated drilling fluid systems, and it better meets the requirements for safe drilling under high-temperature and high-density conditions in deep and ultra-deep wells.

[0056] Experimental Example 2 Referring to the national standard GB / T29170-2012 "Laboratory Testing of Drilling Fluids for Petroleum and Natural Gas Industry", the anti-contamination ability of the drilling fluid system in Example 1 was tested, and the experimental results are shown in Table 2.

[0057] Table 2. Anti-fouling ability of the drilling fluid in Example 1 of the present invention.

[0058] As can be seen from Table 2, Example 1 has good anti-fouling performance. After being contaminated with 7% potassium chloride and 15% sodium chloride powder, and after aging at 150, 180, 200 and 220℃ for 24 hours, its rheological properties and filtration performance showed little change and were basically stable.

[0059] Experimental Example 3 The environmental performance of the two drilling fluid systems was evaluated in accordance with SY / T6788-2020 "Environmental Protection Technical Evaluation Requirements for Water-Soluble Oilfield Chemical Agents", and the results are shown in Table 3.

[0060] Table 3 Comparison of biotoxicity and biodegradability of drilling fluids from Example 1 and Comparative Example 1

[0061] As can be seen from Table 3, the environmentally friendly high-temperature resistant high-density composite salt drilling fluid system of the present invention is non-biotoxic and easily biodegradable, and its environmental performance is significantly improved compared with polysulfonate drilling fluid.

[0062] In summary, the drilling fluid of this invention eliminates the need for polysulfonate treatment agents, exhibits better high-temperature filtration loss reduction performance, and uses readily available and inexpensive synthetic materials, making it suitable for large-scale industrial production and possessing promising prospects for oilfield application. It performs well at high temperatures (200℃) and high densities (1.9 g / cm³). 3 Under harsh working conditions, it achieves a synergistic balance of excellent settling stability, controllable rheological properties, and efficient filtration loss reduction in the drilling fluid system, while also meeting environmental protection requirements. This effectively solves the technical challenge of achieving both safe drilling and green construction in ultra-deep oil and gas drilling.

[0063] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the scope of protection of the present invention. Therefore, the scope of protection of this patent should be determined by the appended claims.

Claims

1. An environmentally friendly, high-temperature resistant, high-density composite salt drilling fluid, characterized in that, It comprises the following components in parts by weight: 100 parts base liquid, 0.5-2.5 parts inorganic suspending agent, 0.1-1.5 parts alkaline pH adjuster, 1-2 parts high-temperature resistant polymer filtration loss reducer, 0.6-1.2 parts high-temperature resistant resin filtration loss reducer, 1.6-3.2 parts salt and high-temperature resistant shearing and thickening agent, 15-30 parts stabilizing inhibitor, 4-10 parts high-temperature resistant sealing agent, and 100-130 parts weighting agent.

2. The environmentally friendly, high-temperature resistant, high-density composite salt drilling fluid according to claim 1, characterized in that, The environmentally friendly high-temperature resistant high-density composite salt drilling fluid comprises the following components in parts by weight: 100 parts base fluid, 1.5-2 parts inorganic suspending agent, 0.3-1 parts alkaline pH adjuster, 1.5-2 parts high-temperature resistant polymer filtration reducer, 1-1.2 parts high-temperature resistant resin filtration reducer, 2-3.2 parts salt and high-temperature resistant shearing and thickening agent, 25-30 parts stabilizing inhibitor, 6-8 parts high-temperature resistant plugging agent, and 110-125 parts weighting agent.

3. The environmentally friendly, high-temperature resistant, high-density composite salt drilling fluid according to claim 1, characterized in that, The inorganic suspending agent is selected from one or both of bentonite and attapulgite.

4. The environmentally friendly high-temperature resistant, high-density composite salt drilling fluid according to claim 1, characterized in that, The high-temperature resistant polymer filtration loss reducer is prepared by the following method: 2-Acrylamido-2-methylpropanesulfonic acid, acrylamide, N-vinylpyrrolidone and acrylic acid were dissolved in deionized water in a mass ratio of (1~5):(8~15):(1~5):(0.5~1.5), the pH was adjusted to 6~7, and an initiator was added under nitrogen protection at 40~100℃ to carry out free radical polymerization. After the free radical polymerization reaction is completed, the reaction product is quickly poured into a precipitant, filtered to obtain a precipitate, and the precipitate is washed and dried to obtain a white solid, which is the high-temperature polymer filtration loss reducer.

5. The environmentally friendly, high-temperature resistant, high-density composite salt drilling fluid according to claim 4, characterized in that, The mass ratio of 2-acrylamido-2-methylpropanesulfonic acid, acrylamide, N-vinylpyrrolidone and acrylic acid is 3:11:3:

1.

6. The environmentally friendly high-temperature resistant, high-density composite salt drilling fluid according to claim 1, characterized in that, The stabilizing inhibitor is at least one of potassium chloride and sodium chloride.

7. The environmentally friendly, high-temperature resistant, high-density composite salt drilling fluid according to claim 1, characterized in that, The high-temperature sealing agent is at least one of methacrylate copolymer and ultrafine calcium carbonate.

8. A method for preparing an environmentally friendly, high-temperature resistant, high-density composite salt drilling fluid, characterized in that, Includes the following steps: A suspending agent is added to the base liquid, and after hydration for a first preset time under stirring conditions, a pre-hydrated base slurry is obtained. An alkaline pH adjuster is added to the prehydrated slurry, and the mixture is stirred at a preset speed for a second preset time. High-temperature resistant polymer filtration loss reducer, high-temperature resistant resin filtration loss reducer, salt and high-temperature resistant shearing thickener, stabilizing inhibitor, high-temperature resistant plugging agent and weighting agent are added in sequence. After each treatment agent is added, the mixture is stirred for a third preset time to obtain an environmentally friendly high-temperature resistant high-density composite salt drilling fluid.

9. The preparation method of the environmentally friendly high-temperature resistant high-density composite salt drilling fluid according to claim 8, characterized in that, The first preset duration can be 12 to 36 hours; and / or the stirring speed can be 8000 to 12000 rpm, preferably 11000 rpm. The second preset duration is 60 to 120 minutes; and / or the third preset duration is 20 to 45 minutes.

10. The environmentally friendly, high-temperature resistant, high-density composite salt drilling fluid as described in any one of claims 1-7 has a bottom-hole circulation temperature of 200-220°C and a drilling fluid density of 1.9 g / cm³. 3 Applications in deep or ultra-deep wells.

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