Film-forming plugging type drilling fluid suitable for drilling complex strata on plateau, preparation method and application

Abstract

This invention discloses a film-forming and plugging drilling fluid suitable for drilling in complex formations at high altitudes, its preparation method, and its application. The film-forming and plugging drilling fluid comprises the following components by mass percentage: pH adjuster 0.1%-0.2%, shearing agent 0.2%-0.6%, film-forming system A agent 5%, film-forming system B agent 1%-3%, drilling fluid viscosity inhibitor 0.05%-0.1%, single-seal anti-collapse plugging agent 1%, ultrafine calcium carbonate 2%, bentonite 4%, chemical inhibitor 4%, and modified asphalt anti-collapse agent 1%. The film-forming system of this invention exhibits excellent core protection performance, significantly improving core recovery quality, outstanding wall protection performance, and significantly increasing drilling efficiency.

Description

Technical Field

[0001] This invention relates to the fields of oil and gas drilling engineering and geological exploration technology, and in particular to a film-forming and plugging drilling fluid suitable for drilling in complex formations on plateaus, its preparation method and application. Background Technology

[0002] In geological surveys, mineral resource exploration, and engineering geological drilling in complex tectonic regions such as the Qinghai-Tibet Plateau, strata commonly encounter permafrost, carbonaceous mudstone, and shale. These strata exhibit extremely high water sensitivity, easily undergoing hydration expansion and spalling upon contact with water, leading to wellbore instability, collapse, and even severe borehole accidents such as stuck drill bits or buried drill bits, potentially resulting in borehole abandonment. Currently, high-solids polymer drilling fluids or potassium-based drilling fluid systems are commonly used for these strata. However, existing technologies primarily rely on increasing clay content or raising inhibitor concentrations to maintain wellbore stability, which has significant drawbacks. 1. Insufficient filtration control: Traditional systems have difficulty forming an effective low-permeability barrier on the pore wall quickly, and the filtrate can easily penetrate deep into the formation, causing hydration stress, which is one of the fundamental causes of pore wall instability.

[0003] 2. Poor core protection: The intrusion of filtrate will dissolve and damage the core, especially carbonaceous mudstone core, resulting in low core recovery rate and poor quality. The core surface is honeycomb-like and the internal structure is destroyed, which seriously affects the accuracy of geological analysis.

[0004] 3. Limited inhibition efficiency: It is difficult to completely inhibit the hydration of highly water-sensitive minerals by relying solely on chemical inhibitors (such as K⁺), and the high solid content easily leads to difficulties in rheological control, high pump pressure, and low mechanical drilling speed.

[0005] 4. Low construction efficiency: Frequent handling of complex borehole wall conditions consumes a lot of time, resulting in low monthly efficiency and high project costs.

[0006] Therefore, developing a new drilling fluid system that can actively form an efficient isolation layer on the surface of the wellbore rock to fundamentally block water phase intrusion, while also possessing strong inhibition and excellent rheological properties, is an urgent need to solve the drilling challenges in complex formations on plateaus. Summary of the Invention

[0007] This invention aims to solve the problems of insufficient control of drilling fluid loss, poor core protection, limited inhibition efficiency, and low construction efficiency, and provides a film-forming and plugging drilling fluid suitable for drilling in complex formations on plateaus, its preparation method, and its application.

[0008] To achieve the above-mentioned technical objectives, the technical solution provided by this invention is as follows: A film-forming and plugging drilling fluid suitable for drilling in complex formations at high altitudes comprises the following components by mass percentage: pH adjuster 0.1%-0.2%, shearing agent 0.2%-0.6%, film-forming system A agent 5%, film-forming system B agent 1%~3%, drilling fluid viscosity inhibitor 0.05%~0.1%, single-seal anti-collapse plugging agent 1%, ultrafine calcium carbonate 2%, bentonite 4%, chemical inhibitor 4%, and modified asphalt anti-collapse agent 1%.

[0009] Furthermore, the pH adjuster is caustic soda, the bentonite includes either sodium-based or calcium-based bentonite, and the chemical inhibitor is potassium chloride.

[0010] pH adjusters are used to establish and maintain a strongly alkaline environment (pH). 12-14) Stabilizes the system and enhances the efficacy of the inhibitor; the cutting agent is used to establish and adjust the dynamic-plastic ratio of the drilling fluid, ensuring effective suspension and carrying of cuttings; Film-forming system A and film-forming system B are two wall-protecting materials with strong film-forming and cementing properties. They are yellow and white free-flowing powders, respectively, and have good anti-collapse and wall-protecting effects on highly water-sensitive dispersed stripped formations, and can significantly improve the quality of core samples. They are common wall-protecting materials used in drilling operations; the drilling fluid viscosity-enhancing inhibitor has the functions of increasing viscosity and inhibiting clay hydration; 1% single-seal anti-collapse plugging agent and 2% ultrafine calcium carbonate (particle size ≤10μm) form a "bridging-filling" synergistic sealing, effectively sealing formation microfractures of different sizes; bentonite provides basic viscosity and wall-building capacity; 4% potassium chloride (KCl) provides K⁺, effectively inhibiting shale hydration through ion exchange; 1% modified asphalt anti-collapse agent forms a hydrophobic layer by adhering to the well wall, further consolidating the well wall stability.

[0011] Furthermore, the particle size of ultrafine calcium carbonate is ≤10μm.

[0012] Furthermore, the film-forming plugging drilling fluid funnel has a viscosity of 20~30 s, a density of 1.05~1.10 g / cm³, an API filtration loss of ≤15 ml, and a high-temperature and high-pressure filtration loss that can be further reduced depending on the operating conditions. The mud cake thickness is ≤1 mm and is tough and dense, with a pH value of 12~14.

[0013] This invention also provides a method for preparing a film-forming and plugging drilling fluid suitable for drilling in complex formations at high altitudes, comprising the following steps: Step 1: Pre-hydration and alkalization; Step 2: Construct the manifold structure; Step 3: Core film formation and sealing; Step 4: Replenish solid phase and suppress; Step 5: Performance fine-tuning; Step 6: Maturation and testing.

[0014] Furthermore, in step 1, prehydration and alkalization: add caustic soda to clean water and stir for a certain period of time until the pH value of the system rises uniformly to above 10.

[0015] Among them, pH pre-control: establishing an alkaline environment in the early stage is the basis for the effectiveness of subsequent treatment agents.

[0016] Furthermore, in step 2, a flow structure is constructed: the formulation amount of the shearing agent is added, and stirring is maintained to ensure that it is fully dissolved and swollen, forming a preliminary gel structure.

[0017] Furthermore, in step 3, the core film formation and sealing: the film-forming system A agent, film-forming system B agent and single-seal anti-collapse plugging agent are added in sequence, and the stirring time is extended to 20-30 minutes to ensure that the film-forming polymer is fully expanded and uniformly mixed with the plugging agent. The thorough stirring in this step (20-30 minutes) is the key process control point for forming an effective isolation membrane, which directly affects the wall protection and core protection effect of the system.

[0018] Furthermore, in step 4, solid phase replenishment and inhibition are carried out: Bentonite, potassium chloride, ultrafine calcium carbonate and modified asphalt anti-collapse agent are added in sequence under continuous stirring. Each material is stirred for 5-10 minutes after being added to ensure uniform dispersion.

[0019] Further, step 5: performance fine-tuning: Finally, add the prescribed amount of drilling fluid viscosity inhibitor, stir for 10-15 minutes, and make final adjustments to the viscosity and inhibitory properties of the system.

[0020] Further, step 6: maturation and testing: Stop stirring, circulate or let the drilling fluid stand for maturation for 2-4 hours, and use a standard API instrument to test its key performance indicators such as funnel viscosity, density, API filtration loss and mud cake quality. Once qualified, it can be pumped into the wellbore for use.

[0021] After maturation, the system must pass API standard testing to ensure that its performance (viscosity 20-30s, filtration loss ≤15ml, etc.) meets the standards before it can be put into the well, thus ensuring construction safety and effectiveness.

[0022] This invention also provides an application of a film-forming and plugging drilling fluid suitable for drilling in complex formations on plateaus. This film-forming and plugging drilling fluid is suitable for drilling operations in permafrost, carbonaceous mudstone, highly water-sensitive mudstone and shale, and fractured and unstable formations in plateau areas.

[0023] When applying this system, it is recommended to use a high-efficiency solid phase control system, including a sand separator (100% utilization) and a centrifuge (no less than 50% utilization), to maintain the system's low solid content and long-term stable performance.

[0024] The present invention has the following beneficial effects: 1. The film-forming and plugging drilling fluid formulation of this invention has a synergistic effect, and the pH adjuster is used to establish and maintain a strongly alkaline environment (pH). 12-14) Stabilizes the system and enhances the efficacy of the inhibitor; the cutting agent is used to establish and adjust the dynamic-plastic ratio of the drilling fluid, ensuring effective suspension and carrying of cuttings; Film-forming system A and film-forming system B are two wall-protecting materials with strong film-forming and cementing properties. They are yellow and white free-flowing powders, respectively, and have good anti-collapse and wall-protecting effects on highly water-sensitive dispersed stripped formations, and can significantly improve the quality of core samples. They are common wall-protecting materials used in drilling operations; the drilling fluid viscosity-enhancing inhibitor has the functions of increasing viscosity and inhibiting clay hydration; 1% single-seal anti-collapse plugging agent and 2% ultrafine calcium carbonate (particle size ≤10μm) form a "bridging-filling" synergistic sealing, effectively sealing formation microfractures of different sizes; bentonite provides basic viscosity and wall-building capacity; 4% potassium chloride (KCl) provides K⁺, effectively inhibiting shale hydration through ion exchange; 1% modified asphalt anti-collapse agent forms a hydrophobic layer by adhering to the well wall, further consolidating the well wall stability.

[0025] 2. The preparation method of this invention strictly follows the sequence of "alkalization → cutting → film formation and sealing → replenishing solid phase → final fine-tuning". The stirring time of each step is based on scientific evidence to ensure that the functions of each component are fully utilized. Attached Figure Description

[0026] Figure 1 For comparison of core samples showing the effects, A represents the core sample with traditional drilling fluid, and B represents the core sample with film-forming plugging drilling fluid. Detailed Implementation

[0027] The technical solution of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0028] Furthermore, the technical features involved in the different embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0029] Example 1 The film-forming and plugging drilling fluid in this embodiment is prepared through the following steps: (1) Preparation of base slurry S11: According to the base slurry ratio, accurately weigh 1000mL of clean water and 40.0g of sodium bentonite.

[0030] S12: Add water to a high-speed mixing cup and stir at 3500 rpm. Slowly and evenly add sodium-based bentonite. After adding, increase the speed to 11000 rpm and continue stirring at high speed for 20 minutes. During stirring, pause 1-2 times to scrape off the bentonite particles adhering to the cup wall and stirring rod.

[0031] S13: Seal the mixing cup and cure it at room temperature for no less than 24 hours to allow the sodium bentonite to fully hydrate and pre-disperse, resulting in a uniform base slurry.

[0032] (2) Drilling fluid preparation S21: According to the above specific formula, accurately weigh all the treatment agents except bentonite and water.

[0033] S22: Pour the cured base slurry into the mixing cup and start high-speed mixing at 11,000 rpm for 5 minutes to ensure the base slurry is uniform.

[0034] S23: Adjust the stirring speed to 3500 rpm, slowly add 1.5g of sodium hydroxide (NaOH), and stir until completely dissolved (about 2-3 minutes). Then adjust the speed to 11000 rpm and stir at high speed for 3 minutes to allow the pH of the system to initially rise and stabilize.

[0035] S24: Adjust the speed to 3500 rpm and slowly add 4.0 g of shearing agent (XC). After adding, adjust the speed to 11000 rpm and stir at high speed for 20 minutes, scraping the wall 1-2 times during the process to ensure that XC is fully swollen and that the initial shearing force and dynamic shearing force of the system are established.

[0036] S25: While stirring at 11000 rpm, add the following treatment agents sequentially and slowly, stirring continuously for at least 2 minutes after each addition before adding the next: Film-forming system A agent (CMJ-1) 50.0g, modified asphalt anti-collapse agent (FT-1) 10.0g, single-seal anti-collapse and plugging agent (QS-2) 10.0g, ultrafine calcium carbonate 20.0g.

[0037] S26: Maintain high-speed stirring at 11000 rpm, and add the following treatment agents in sequence, stirring for 1 minute after each addition: Film-forming system agent B (CMJ-2) 20.0g, drilling fluid viscosity inhibitor (PAC-LV) 0.8g.

[0038] S27: Adjust the speed to 3500 rpm and slowly add 40.0g of potassium chloride (KCl). After adding, adjust the speed back to 11000 rpm and stir at high speed for 20 minutes to completely dissolve the KCl and allow all the treatment agents to work fully in an inhibitory environment.

[0039] S28: Stop stirring, remove the drilling fluid, and let it stand for at least 4 hours (or overnight) to mature.

[0040] S29: Before use, stir at high speed at 11000 rpm for 5-10 minutes, and then conduct a full set of performance tests (density, rheology, filtration loss, pH, etc.) to ensure that it meets the design specifications.

[0041] Example 2 The film-forming plugging drilling fluid prepared above was applied to the drilling project of Tuodi 1 well in the Tonam area of ​​Tibet. The well was started on July 29, 2025, and completed on September 8, 2025, with a total construction period of 42 days and a drilling depth of 800.3 meters. The use of this film-forming plugging drilling fluid has the following significant advantages and positive effects: 1. Excellent core protection performance, significantly improving the quality of core extraction. Problems with traditional systems: see Figure 1 As shown in (A), when drilling encounters carbonaceous mudstone formations, high-solids flushing fluids can easily cause core dissolution, resulting in an uneven, honeycomb-like surface. Some cores are scattered and lost, and obvious traces of water infiltration can be seen after splitting them open. The integrity and representativeness of the cores are poor.

[0042] The effects of this film-forming system are as follows: See Figure 1 As shown in (B), the extracted carbonaceous mudstone core is intact and smooth, without any dissolution or dispersion, and the core recovery rate meets the design requirements. After splitting the core, the interior is dry with no trace of water infiltration, effectively preserving the original lithological characteristics of the strata and providing a reliable basis for geological analysis.

[0043] 2. Excellent borehole wall performance, reducing the in-hole accident rate to 0%. This system, with its low filtration loss, strong inhibition, and high plugging properties, creates a stable borehole wall environment in carbonaceous mudstone formations. The borehole diameter is regular, with no reduction or expansion, and the drilling process is smooth with no risk of stuck drill bit or obstruction. There were no borehole wall collapses during the entire construction process, with only very few sporadic falling pieces, which could be quickly removed through mud circulation; It successfully solved the problem that traditional flushing fluids could not cope with the hydration and collapse of carbonaceous mudstone, achieving stable working conditions throughout the borehole and reducing the accident rate to 0%.

[0044] 3. Drilling efficiency has been significantly improved, and the monthly drilling efficiency has met the target. After adopting the film-forming system, the average monthly efficiency of Tuodi 1 well reached 571.64 meters, and all wells were successfully completed. Compared with previous construction in the same area (where traditional flushing fluids caused frequent borehole accidents, resulting in multiple borehole failures and low monthly efficiency), the construction efficiency has been significantly improved, effectively shortening the construction period for a single well.

[0045] 4. Solid-phase control assists in ensuring system performance stability. The machine is equipped with solids control equipment such as desanders and centrifuges to strictly control the solids content of the drilling fluid. During the drilling process, the desander was used 100% of the time, effectively removing coarse solid particles (particle size ≥ 44 μm) from the system. The centrifuge utilization rate should not be less than 50% to separate fine solid particles (particle size 2~44μm), avoid excessive solid content leading to abnormal viscosity and increased filtration loss, and ensure long-term stable performance of film-forming drilling fluid.

[0046] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

[0047] The above detailed embodiments are a description of the present invention. It should not be considered that the specific embodiments of the present invention are limited to these descriptions. For those skilled in the art, several simple deductions and substitutions can be made without departing from the concept of the present invention, and all of these should be considered to fall within the protection scope of the present invention.

Claims

1. A film-forming and plugging drilling fluid suitable for drilling in complex formations at high altitudes, characterized in that, This film-forming and plugging drilling fluid comprises the following components by weight percentage: pH adjuster 0.1%-0.2%, shearing agent 0.2%-0.6%, film-forming system A agent 5%, film-forming system B agent 1%~3%, drilling fluid viscosity inhibitor 0.05%~0.1%, single-seal anti-collapse plugging agent 1%, ultrafine calcium carbonate 2%, bentonite 4%, chemical inhibitor 4%, and modified bitumen anti-collapse agent 1%.

2. The film-forming and plugging drilling fluid suitable for drilling in complex formations on plateaus, as described in claim 1, is characterized in that... The pH adjuster is caustic soda, the bentonite includes either sodium-based or calcium-based bentonite, the chemical inhibitor is potassium chloride, and the ultrafine calcium carbonate particle size is ≤10μm.

3. The film-forming and plugging drilling fluid suitable for drilling in complex formations on plateaus, as described in claim 1, is characterized in that... The film-forming plugging drilling fluid funnel has a viscosity of 20~30 s, a density of 1.05~1.10 g / cm³, an API filtration loss of ≤15 ml, and a filtration loss under high temperature and high pressure that can be further reduced depending on the operating conditions. The mud cake thickness is ≤1 mm and is tough and dense, with a pH value of 12~14.

4. A method for preparing a film-forming and plugging drilling fluid suitable for drilling in complex formations on plateaus, as described in any one of claims 1-3, characterized in that, Includes the following steps: Step 1: Pre-hydration and alkalization; Step 2: Construct the manifold structure; Step 3: Core film formation and sealing; Step 4: Replenish solid phase and suppress; Step 5: Performance fine-tuning; Step 6: Maturation and testing.

5. The method for preparing a film-forming and plugging drilling fluid suitable for drilling in complex formations on plateaus, as described in claim 4, is characterized in that... In step 1, prehydration and alkalization: add caustic soda to clean water and stir for a certain period of time until the pH value of the system rises uniformly to above 10.

6. The method for preparing a film-forming and plugging drilling fluid suitable for drilling in complex formations on plateaus, as described in claim 4, is characterized in that... In step 2, the flow structure is constructed: the formulation amount of the shearing agent is added, and stirring is maintained to allow it to fully dissolve and swell, forming a preliminary gel structure.

7. The method for preparing a film-forming and plugging drilling fluid suitable for drilling in complex formations on plateaus, as described in claim 4, is characterized in that... In step 3, core film formation and sealing: add the film-forming system A agent, film-forming system B agent and single-seal anti-collapse plugging agent in the formula amount in sequence, and extend the stirring time to 20-30 minutes.

8. The method for preparing a film-forming and plugging drilling fluid suitable for drilling in complex formations on plateaus, as described in claim 4, is characterized in that... In step 4, replenish the solid phase and inhibit: under continuous stirring, add bentonite, potassium chloride, ultrafine calcium carbonate and modified asphalt anti-collapse agent in sequence, stirring for 5-10 minutes after each material is added.

9. The method for preparing a film-forming and plugging drilling fluid suitable for drilling in complex formations on plateaus, as described in claim 4, is characterized in that... Step 5: Performance fine-tuning: Finally, add the prescribed amount of drilling fluid viscosity inhibitor and stir for 10-15 minutes; Step 6: Maturation and testing: Stop stirring and circulate or let the drilling fluid stand for 2-4 hours to mature.

10. An application of a film-forming and plugging drilling fluid suitable for drilling in complex formations at high altitudes, characterized in that, This film-forming and plugging drilling fluid is suitable for drilling operations in permafrost layers, carbonaceous mudstone layers, highly water-sensitive mudstone and shale layers, and fractured and unstable formations in plateau areas.

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