Drilling fluid for sandstone heat storage geothermal well and use method of drilling fluid
By using a drilling fluid system and equipment with specific components in sandstone geothermal wells, the problems of low drilling efficiency, high waste discharge, and high cost in existing technologies have been solved, achieving efficient drilling and low-cost drilling fluid application.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-12-29
- Publication Date
- 2026-03-27
AI Technical Summary
Existing sandstone geothermal drilling fluid systems have shortcomings in improving drilling efficiency, reducing waste slurry discharge, and controlling drilling fluid costs, which affect the development and utilization of sandstone geothermal resources.
A drilling fluid system comprising base slurry, calcium chloride, polyacrylamide, carboxymethyl cellulose, hydrolyzed polyacrylonitrile ammonium salt, anti-collapse fluid loss agent, and extreme pressure lubricant is adopted. By adding these components in different well sections and combining them with equipment such as vibrating screens and centrifugal desanders, the viscosity, density, and pH of the drilling fluid are controlled to reduce fluid loss. Plastic ball lubricant is used for well sealing.
It improved drilling efficiency by 20%, reduced waste slurry discharge by 30%, lowered drilling fluid costs by 30%, and ensured wellbore stability and the success rate of electric logging.
Abstract
Description
Technical Field
[0001] This invention relates to the field of drilling fluid technology, and in particular to a drilling fluid for geothermal wells in sandstone geothermal reservoirs and its application method. Background Technology
[0002] my country's sandstone geothermal reservoirs are widely distributed and have large recoverable reserves, occupying an important position among geothermal resources. In 2023, the recoverable reserves in Shandong Province alone reached 5.757 billion cubic meters. 3 This is equivalent to 0.95 billion tons of standard coal. Currently, sandstone geothermal resources play a crucial role in clean heating in northern China, and the development and utilization of sandstone geothermal resources are of great significance to my country's energy structure adjustment and energy security.
[0003] Currently, sandstone geothermal well drilling primarily utilizes fine-dispersion drilling fluid systems (used for raw water well drilling) and polymer drilling fluid systems (used for oil drilling). However, both fine-dispersion and polymer drilling fluid systems have limitations in improving drilling efficiency, reducing waste fluid emissions, and controlling drilling fluid costs during sandstone geothermal well drilling, hindering the further development and utilization of sandstone geothermal resources.
[0004] Therefore, researching drilling fluid systems specifically designed for geothermal wells in sandstone geothermal reservoirs is of great significance for the development and utilization of geothermal resources in sandstone geothermal reservoirs, as it can effectively improve drilling and completion efficiency, reduce waste slurry discharge, and lower drilling fluid costs. Summary of the Invention
[0005] The purpose of this invention is to address the shortcomings of existing technologies by providing a drilling fluid for geothermal wells in sandstone geothermal reservoirs and its application method.
[0006] To achieve the above-mentioned objectives, the present invention provides the following technical solution: This invention provides a drilling fluid for geothermal wells in sandstone geothermal reservoirs, the drilling fluid comprising base slurry, calcium chloride, polyacrylamide, carboxymethyl cellulose, hydrolyzed polyacrylonitrile ammonium salt, anti-collapse and fluid loss agent, and extreme pressure lubricant; During drilling, base slurry, calcium chloride, and polyacrylamide are added. Calcium chloride and polyacrylamide are added during the drilling process to 200m from the top of the thermal reservoir. From 200m from the top of the thermal reservoir to the completion of drilling, polyacrylamide, carboxymethyl cellulose, hydrolyzed polyacrylonitrile ammonium salt, anti-collapse and dehydration agent, and extreme pressure lubricant are added.
[0007] Preferably, in the addition of base slurry, calcium chloride and polyacrylamide during drilling, the mass of calcium chloride is 1.5-2% of the volume of base slurry, and the mass of polyacrylamide is 0.3-0.5% of the volume of base slurry.
[0008] Preferably, during the drilling process to 200m from the top of the thermal reservoir, calcium chloride and polyacrylamide are added. Specifically, depending on the condition of the drilling fluid on site, the mass of calcium chloride is added to 1.5-2% of the base slurry volume, and the mass of polyacrylamide is added to 0.3-0.5% of the base slurry volume.
[0009] Preferably, during the drilling process from 200m from the top of the thermal reservoir to completion, polyacrylamide, carboxymethyl cellulose, hydrolyzed polyacrylonitrile ammonium salt, anti-collapse fluid loss agent, and extreme pressure lubricant are added. Specifically, depending on the condition of the drilling fluid on site, the following amounts are added: polyacrylamide at 0.2-0.3% of the base slurry volume, carboxymethyl cellulose at 0.25-0.6% of the base slurry volume, hydrolyzed polyacrylonitrile ammonium salt at 1-1.5% of the base slurry volume, anti-collapse fluid loss agent at 0.3-0.5% of the base slurry volume, and extreme pressure lubricant at 1-2% of the base slurry volume.
[0010] Preferably, the drilling fluid for geothermal wells in sandstone reservoirs also contains plastic ball lubricant.
[0011] Preferably, the base slurry is a water-based base slurry, which contains water and bentonite, with the mass of bentonite being 3-4% of the water.
[0012] The present invention also provides a method for using the drilling fluid for geothermal wells in sandstone geothermal reservoirs, comprising the following steps: 1) Add base slurry, calcium chloride and polyacrylamide to prepare drilling fluid, and control the Marvifell funnel viscosity and density of the base slurry; 2) Start drilling. Every 100m of drilling, add calcium chloride and polyacrylamide according to the condition of the drilling fluid on site to control the Marvife funnel viscosity and density of the drilling fluid, and continue drilling to 200m from the top of the thermal reservoir. 3) Add polyacrylamide, carboxymethyl cellulose, hydrolyzed polyacrylonitrile ammonium salt, anti-collapse fluid loss agent and extreme pressure lubricant according to the condition of the drilling fluid on site, control the Marvife funnel viscosity, density and pH value of the drilling fluid, and continue drilling until completion; 4) Add plastic balls as lubricant and seal the well.
[0013] Preferably, in step 1), the Marviate of the base slurry is controlled to be ≤30s and the density of the base slurry is controlled to be ≤1.08g / mL. Step 2) The Marviate of the drilling fluid is controlled to be 30~32s, and the density of the drilling fluid is controlled to be <1.12g / mL; Step 3) The Marshall funnel viscosity of the drilling fluid is controlled to be 32~40s, the density of the drilling fluid is controlled to be 1.10~1.16g / mL, and the pH value of the drilling fluid is controlled to be 8~9; during the process from 200m away from the top of the thermal reservoir to the thermal reservoir, the water loss of the drilling fluid is controlled to be ≤30mL, and after entering the thermal reservoir, the water loss of the drilling fluid is controlled to be ≤10mL. After adding the plastic ball lubricant as described in step 4), the lubrication coefficient of the drilling fluid is <0.14.
[0014] The beneficial effects of this invention are: 1) The drilling fluid of this invention comprises a dual-inhibition system of inorganic compound inhibitor (calcium chloride) and organic polymer wall-protecting inhibitor (polyacrylamide), exhibiting low viscosity and density, thus laying the foundation for efficient drilling. In the upper and middle sections of sandstone geothermal wells, this dual-inhibition system, combined with commonly used equipment such as vibrating screens, centrifugal desanders, and centrifuges, effectively removes the solid phase from the drilling fluid. This not only effectively controls formation mud production and reduces waste mud discharge, but also ensures borehole wall stability in the upper and middle sections through organic polymer wall protection. At a distance of 200 meters from the top of the geothermal reservoir... The use of inorganic compound inhibitors is discontinued at point m, and natural consumption effectively saves on subsequent drilling fluid usage, reducing drilling fluid costs. Simultaneously, extreme pressure lubricants are added to alleviate the gradually increasing adsorption resistance, fully utilizing the lubricant's action time to lay the foundation for improved lubrication performance of the drilling fluid before electrical logging. Appropriately releasing water loss in the well section above the hot reservoir can effectively improve drilling efficiency in the middle and upper sections. Adding small plastic ball lubricants before final electrical logging in highly deviated directional wells ensures successful logging on the first attempt, improves drilling efficiency, and avoids adding lubricant throughout the well, thus controlling drilling fluid composition.
[0015] 2) In sandstone geothermal drilling projects in Shandong, Hebei, Henan, Shanxi, and Shaanxi, the drilling fluid and usage method of this invention are used, which increases drilling efficiency by 20%, reduces waste slurry discharge by 30%, and reduces drilling fluid cost by 30%. Detailed Implementation
[0016] This invention provides a drilling fluid for geothermal wells in sandstone geothermal reservoirs, the drilling fluid comprising base slurry, calcium chloride, polyacrylamide, carboxymethyl cellulose, hydrolyzed polyacrylonitrile ammonium salt, anti-collapse and fluid loss agent, and extreme pressure lubricant; During drilling, base slurry, calcium chloride, and polyacrylamide are added. Calcium chloride and polyacrylamide are added during the drilling process to 200m from the top of the thermal reservoir. From 200m from the top of the thermal reservoir to the completion of drilling, polyacrylamide, carboxymethyl cellulose, hydrolyzed polyacrylonitrile ammonium salt, anti-collapse and dehydration agent, and extreme pressure lubricant are added.
[0017] In this invention, the mass of calcium chloride added during drilling, including the base slurry, calcium chloride, and polyacrylamide, is preferably 1.5-2% of the base slurry volume, more preferably 1.6-1.9%, and even more preferably 1.7-1.8%; the mass of polyacrylamide is preferably 0.3-0.5% of the base slurry volume, more preferably 0.35-0.45%, and even more preferably 0.4%.
[0018] In this invention, during the drilling process to a point 200m from the top of the thermal reservoir, calcium chloride and polyacrylamide are added. Specifically, the amount of calcium chloride added is preferably 1.5-2% of the base slurry volume, more preferably 1.6-1.9%, and even more preferably 1.7-1.8%, depending on the condition of the drilling fluid on site. The amount of polyacrylamide added is preferably 0.3-0.5% of the base slurry volume, more preferably 0.35-0.45%, and even more preferably 0.4%.
[0019] In this invention, for the middle and upper well sections, where the proportion of mudstone is relatively large and the formation naturally produces mud, it is preferable to use the upper limit of the addition amount of both calcium chloride and polyacrylamide, and vice versa.
[0020] In this invention, during the drilling process from 200m from the top of the thermal reservoir to completion, polyacrylamide, carboxymethyl cellulose, hydrolyzed polyacrylonitrile ammonium salt, anti-collapse fluid loss agent, and extreme pressure lubricant are added. Specifically, the mass of polyacrylamide added is preferably 0.2-0.3% of the base slurry volume, more preferably 0.22-0.28%, and even more preferably 0.25%; the mass of carboxymethyl cellulose is preferably 0.25-0.6% of the base slurry volume, more preferably 0.3-0.5%, and even more preferably 0.35-0.45%; the mass of hydrolyzed polyacrylonitrile ammonium salt is preferably 1-1.5% of the base slurry volume, more preferably 1.1-1.4%, and even more preferably 1.2-1.3%; the mass of the anti-collapse fluid loss agent is preferably 0.3-0.5% of the base slurry volume, more preferably 0.35-0.45%, and even more preferably 0.4%; and the mass of the extreme pressure lubricant is preferably 1-2% of the base slurry volume, more preferably 1.2-1.8%, and even more preferably 1.5%. For formations with good stability, the lower limit of the anti-collapse and fluid loss agent should be used, and vice versa. During drilling, when the frictional resistance of the drill string is low, the lower limit of the extreme pressure lubricant should be preferred, and vice versa.
[0021] In this invention, the drilling fluid for geothermal wells in sandstone geothermal reservoirs preferably further includes plastic ball lubricant.
[0022] In this invention, the base slurry is preferably a water-based base slurry, which preferably contains water and bentonite. The mass of bentonite is preferably 3-4% of the water, more preferably 3.2-3.8%, and even more preferably 3.5%. For strata with a large clay layer, the lower limit of the bentonite content is preferred, and vice versa.
[0023] The present invention also provides a method for using the drilling fluid for geothermal wells in sandstone geothermal reservoirs, comprising the following steps: 1) Add base slurry, calcium chloride and polyacrylamide to prepare drilling fluid, and control the Marvifell funnel viscosity and density of the base slurry; 2) Start drilling. Every 100m of drilling, add calcium chloride and polyacrylamide according to the condition of the drilling fluid on site to control the Marvife funnel viscosity and density of the drilling fluid, and continue drilling to 200m from the top of the thermal reservoir. 3) Add polyacrylamide, carboxymethyl cellulose, hydrolyzed polyacrylonitrile ammonium salt, anti-collapse fluid loss agent and extreme pressure lubricant according to the condition of the drilling fluid on site, control the Marvife funnel viscosity, density and pH value of the drilling fluid, and continue drilling until completion; 4) Add plastic balls as lubricant and seal the well.
[0024] In this invention, the polyacrylamide in step 2) is preferably added after being prepared into a polyacrylamide solution, and the concentration of the polyacrylamide solution is preferably 1.5~2.5%, more preferably 2%.
[0025] In this invention, during the process of continuing drilling until completion in step 3), polyacrylamide, carboxymethyl cellulose, hydrolyzed polyacrylonitrile ammonium salt, anti-collapse and fluid loss agent, and extreme pressure lubricant are preferably added every 100m of drilling fluid, according to the condition of the drilling fluid on site, to control the Marvifeld funnel viscosity, density and pH value of the drilling fluid.
[0026] In this invention, the polyacrylamide in step 3) is preferably added after being prepared into a polyacrylamide solution, and the concentration of the polyacrylamide solution is preferably 1.5~2.5%, more preferably 2%; Step 3) The hydrolyzed polyacrylonitrile ammonium salt is preferably added after being prepared into a hydrolyzed polyacrylonitrile ammonium salt solution. The concentration of the hydrolyzed polyacrylonitrile ammonium salt solution is preferably 1.5~2.5%, more preferably 2%. Step 3) The anti-collapse and water loss agent is preferably prepared into an anti-collapse and water loss agent solution and then added. The concentration of the anti-collapse and water loss agent solution is preferably 1.5~2.5%, and more preferably 2%.
[0027] In this invention, the carboxymethyl cellulose is preferably a carboxymethyl cellulose solution, and the concentration of the carboxymethyl cellulose solution is preferably 1.5-2.5%, more preferably 2%.
[0028] In this invention, the Marviate of the base slurry controlled in step 1) is preferably ≤30s, more preferably ≤29s, and even more preferably ≤28s; the density of the base slurry is preferably ≤1.08g / mL, more preferably ≤1.07g / mL, and even more preferably ≤1.06g / mL. Step 2) The Marvimetric viscosity of the drilling fluid is preferably controlled to be 30~32s, more preferably 31s; the density of the drilling fluid is preferably <1.12g / mL, more preferably <1.11g / mL, and even more preferably <1.10g / mL. Step 3) The Marshall funnel viscosity of the drilling fluid is preferably controlled to be 32-40 s, more preferably 34-38 s, and even more preferably 35-36 s; the density of the drilling fluid is preferably controlled to be 1.10-1.16 g / mL, more preferably 1.12-1.14 g / mL, and even more preferably 1.13 g / mL; the pH value of the drilling fluid is preferably controlled to be 8-9, and even more preferably 8.5; during the process from 200 m from the top of the thermal reservoir to the thermal reservoir, the water loss of the drilling fluid is preferably controlled to be ≤30 mL, more preferably ≤28 mL, and even more preferably ≤25 mL; after entering the thermal reservoir, the water loss of the drilling fluid is preferably controlled to be ≤10 mL, more preferably ≤9 mL, and even more preferably ≤8 mL. After adding the plastic ball lubricant in step 4), the lubrication coefficient of the drilling fluid is preferably <0.14, more preferably <0.12, and even more preferably <0.08.
[0029] In this invention, during the drilling process described in step 3) until completion, it is preferable to first control the Marvifell funnel viscosity of the drilling fluid to 32-35 s, the drilling fluid density to 1.10-1.12 g / mL, the drilling fluid pH value to 8, and the drilling fluid water loss to ≤30 mL, drilling to a point 100 m from the top of the thermal reservoir; then, depending on the condition of the drilling fluid on site, add polyacrylamide, carboxymethyl cellulose, hydrolyzed polyacrylonitrile ammonium salt, anti-collapse water loss agent, and extreme pressure lubricant to control the Marvifell funnel viscosity of the drilling fluid to 32-38 s. The drilling fluid density is 1.10~1.13 g / mL, the pH value is 8~9, and the fluid loss is ≤15 mL, until drilling reaches the thermal reservoir. Finally, based on the drilling fluid conditions on site, polyacrylamide, carboxymethyl cellulose, hydrolyzed polyacrylonitrile ammonium salt, anti-collapse fluid loss agent, and extreme pressure lubricant are added to control the Marvifeld funnel viscosity of the drilling fluid at 32~40 s, the drilling fluid density at 1.12~1.16 g / mL, the pH value at 8~9, and the fluid loss ≤10 mL, until drilling is complete. During this step of adding polyacrylamide, carboxymethyl cellulose, hydrolyzed polyacrylonitrile ammonium salt, anti-collapse fluid loss agent, and extreme pressure lubricant, the concentration of the adhesive and the use of solids control equipment are used to control the Marvifeld funnel viscosity and density of the drilling fluid at each stage.
[0030] In this invention, the molecular weight of the polyacrylamide is preferably 8 million to 12 million, more preferably 9 million to 11 million, and even more preferably 10 million.
[0031] In this invention, the pH value of the drilling fluid is preferably controlled by adding sodium hydroxide.
[0032] In this invention, the process of controlling the Marshall funnel viscosity, density and pH value of drilling fluid is preferably carried out simultaneously with commonly used solids control equipment such as vibrating screen, centrifugal desander, and centrifuge.
[0033] The technical solutions provided by the present invention will be described in detail below with reference to the embodiments, but they should not be construed as limiting the scope of protection of the present invention.
[0034] In the embodiments and comparative examples of the present invention, the molecular weight of polyacrylamide is 10 million, the anti-collapse and dehydration agent is KFT, a high-temperature and salt-resistant dehydration agent for drilling fluid, the extreme pressure lubricant is SLUB, and the small ball lubricant is a plastic ball with a diameter of 1-2 mm.
[0035] Example 1
[0036] Drilling fluids for geothermal wells in sandstone reservoirs contain base fluid, calcium chloride, polyacrylamide, carboxymethyl cellulose, hydrolyzed polyacrylonitrile ammonium salt, anti-collapse and fluid loss agent, and extreme pressure lubricant.
[0037] Drilling fluids for sandstone geothermal reservoirs were applied to well ZK03 in the Dezhou Finance and Economics Smart Agriculture Energy Transformation Project, as detailed below: Drilling fluid was prepared by adding base slurry, calcium chloride, and polyacrylamide. The mass of calcium chloride was 1.5% of the volume of base slurry, and the mass of polyacrylamide was 0.3% of the volume of base slurry. The base slurry consisted of water and bentonite, with the mass of bentonite being 3% of the water. The Marshall funnel viscosity of the base slurry was 28 s. Drilling commenced, and every 100 m of drilling, calcium chloride and polyacrylamide were added according to the condition of the drilling fluid on site, until the mass of calcium chloride was 1.5% of the volume of base slurry and the mass of polyacrylamide was 0.3% of the volume of base slurry. The polyacrylamide was added in gel form. By adjusting the gel concentration and using solids control equipment such as vibrating screens, centrifugal desanders, and centrifuges, the Marshall funnel viscosity of the drilling fluid was controlled to be 30 s, and the drilling fluid density was controlled to be 1.06 g / mL. Drilling continued until 200 m from the top of the thermal reservoir. The cuttings recovery rate during this process was >92%.
[0038] Stop adding calcium chloride. Based on the drilling fluid conditions, add polyacrylamide, carboxymethyl cellulose, hydrolyzed polyacrylonitrile ammonium salt, anti-collapse fluid loss agent, and extreme pressure lubricant until the mass of polyacrylamide is 0.2% of the base slurry volume, carboxymethyl cellulose is 0.3% of the base slurry volume, hydrolyzed polyacrylonitrile ammonium salt is 1% of the base slurry volume, anti-collapse fluid loss agent is 0.3% of the base slurry volume, and extreme pressure lubricant is 1% of the base slurry volume. Polyacrylamide, carboxymethyl cellulose, hydrolyzed polyacrylonitrile ammonium salt, anti-collapse fluid loss agent, and extreme pressure lubricant are added in gel form. By adjusting the gel concentration and using solids control equipment such as a vibrating screen, centrifugal desander, and centrifuge, control the drilling fluid's Marshall funnel viscosity to 33s, drilling fluid density to 1.12 g / mL, and drilling fluid fluid loss to 25 mL. Use sodium hydroxide to adjust the drilling fluid pH to 8. Drill to 100m from the top of the thermal reservoir. Then, based on the drilling fluid conditions at the site, polyacrylamide, carboxymethyl cellulose, hydrolyzed polyacrylonitrile ammonium salt, anti-collapse fluid loss agent, and extreme pressure lubricant were added until the mass of polyacrylamide was 0.2% of the base slurry volume, the mass of carboxymethyl cellulose was 0.3% of the base slurry volume, the mass of hydrolyzed polyacrylonitrile ammonium salt was 1% of the base slurry volume, the mass of anti-collapse fluid loss agent was 0.3% of the base slurry volume, and the mass of extreme pressure lubricant was 1% of the base slurry volume. Polyacrylamide, carboxymethyl cellulose, hydrolyzed polyacrylonitrile ammonium salt, anti-collapse fluid loss agent, and extreme pressure lubricant were added in gel form. By adjusting the gel concentration and using solids control equipment such as vibrating screens, centrifugal desanders, and centrifuges, the Marsh funnel viscosity of the drilling fluid was controlled to be 35s, the drilling fluid density to be 1.14 g / mL, and the drilling fluid fluid loss to be 15 mL. The pH of the drilling fluid was adjusted to 8.5 using sodium hydroxide, and drilling proceeded until the hot reservoir was reached. Finally, based on the drilling fluid conditions at the site, polyacrylamide, low-viscosity carboxymethyl cellulose, hydrolyzed polyacrylonitrile ammonium salt, anti-collapse fluid loss agent, and extreme pressure lubricant were added until the mass of polyacrylamide was 0.2% of the base slurry volume, the mass of low-viscosity carboxymethyl cellulose was 0.3% of the base slurry volume, the mass of hydrolyzed polyacrylonitrile ammonium salt was 1% of the base slurry volume, the mass of anti-collapse fluid loss agent was 0.3% of the base slurry volume, and the mass of extreme pressure lubricant was 1% of the base slurry volume. Polyacrylamide, carboxymethyl cellulose, hydrolyzed polyacrylonitrile ammonium salt, anti-collapse fluid loss agent, and extreme pressure lubricant were added in gel form. By adjusting the gel concentration and using solids control equipment such as vibrating screens, centrifugal desanders, and centrifuges, the Marsh funnel viscosity of the drilling fluid was controlled to be 38s, the drilling fluid density to be 1.16 g / mL, and the drilling fluid fluid loss to be 9 mL. The pH of the drilling fluid was adjusted to 8.5 using sodium hydroxide until drilling was completed. Based on the condition of the drilling fluid on site, add plastic ball lubricant at a mass of 0.3% of the drilling fluid volume. The lubrication coefficient of the drilling fluid is 0.14. Perform electrical logging and well sealing.
[0039] Example 2
[0040] Drilling fluids for geothermal wells in sandstone reservoirs contain base fluid, calcium chloride, polyacrylamide, carboxymethyl cellulose, hydrolyzed polyacrylonitrile ammonium salt, anti-collapse and fluid loss agent, and extreme pressure lubricant.
[0041] Drilling fluids for sandstone geothermal reservoirs were applied to well ZK04 in the Dezhou Finance and Economics Smart Agriculture Energy Transformation Project, as detailed below: Drilling fluid was prepared by adding base slurry, calcium chloride, and polyacrylamide. The mass of calcium chloride was 2% of the volume of base slurry, and the mass of polyacrylamide was 0.5% of the volume of base slurry. The base slurry consisted of water and bentonite, with the mass of bentonite being 4% of the water. The Marshall funnel viscosity of the base slurry was 28 s. Drilling commenced, and every 100 m of drilling, calcium chloride and polyacrylamide were added according to the condition of the drilling fluid on site, until the mass of calcium chloride was 2% of the volume of base slurry and the mass of polyacrylamide was 0.5% of the volume of base slurry. The polyacrylamide was added in gel form. By adjusting the gel concentration and using solids control equipment such as vibrating screens, centrifugal desanders, and centrifuges, the Marshall funnel viscosity of the drilling fluid was controlled to be 29 s, and the drilling fluid density was 1.06 g / mL. Drilling continued until 200 m from the top of the thermal reservoir. The cuttings recovery rate during this process was >95%.
[0042] Stop adding calcium chloride. Based on the drilling fluid conditions, add polyacrylamide, carboxymethyl cellulose, hydrolyzed polyacrylonitrile ammonium salt, anti-collapse fluid loss agent, and extreme pressure lubricant until the mass of polyacrylamide is 0.3% of the base slurry volume, carboxymethyl cellulose is 0.3% of the base slurry volume, hydrolyzed polyacrylonitrile ammonium salt is 1.5% of the base slurry volume, anti-collapse fluid loss agent is 0.5% of the base slurry volume, and extreme pressure lubricant is 1.2% of the base slurry volume. Polyacrylamide, carboxymethyl cellulose, hydrolyzed polyacrylonitrile ammonium salt, anti-collapse fluid loss agent, and extreme pressure lubricant are added in gel form. By adjusting the gel concentration and using solids control equipment such as a vibrating screen, centrifugal desander, and centrifuge, control the drilling fluid's Marshall funnel viscosity to 33s, drilling fluid density to 1.12 g / mL, and drilling fluid fluid loss to 15 mL. Use sodium hydroxide to adjust the drilling fluid pH to 9. Drill to 100 m from the top of the thermal reservoir. Then, based on the drilling fluid conditions at the site, polyacrylamide, hydrolyzed polyacrylonitrile ammonium salt, anti-collapse fluid loss agent, low-viscosity carboxymethyl cellulose, and extreme pressure lubricant were added until the mass of polyacrylamide was 0.3% of the base slurry volume, the mass of hydrolyzed polyacrylonitrile ammonium salt was 1.5% of the base slurry volume, the mass of low-viscosity carboxymethyl cellulose was 0.3% of the base slurry volume, the mass of anti-collapse fluid loss agent was 0.5% of the base slurry volume, and the mass of extreme pressure lubricant was 1.2% of the base slurry volume. Polyacrylamide, carboxymethyl cellulose, hydrolyzed polyacrylonitrile ammonium salt, anti-collapse fluid loss agent, and extreme pressure lubricant were added in gel form. By adjusting the gel concentration and using solids control equipment such as vibrating screens, centrifugal desanders, and centrifuges, the Marsh funnel viscosity of the drilling fluid was controlled to be 35s, the drilling fluid density to be 1.13 g / mL, and the drilling fluid fluid loss to be 10 mL. The pH of the drilling fluid was adjusted to 8 using sodium hydroxide, and drilling proceeded until the hot reservoir was reached. Finally, based on the drilling fluid conditions at the site, polyacrylamide, hydrolyzed polyacrylonitrile ammonium salt, anti-collapse fluid loss agent, low-viscosity carboxymethyl cellulose, and extreme pressure lubricant were added until the mass of polyacrylamide was 0.3% of the base slurry volume, the mass of hydrolyzed polyacrylonitrile ammonium salt was 1.5% of the base slurry volume, the mass of anti-collapse fluid loss agent was 0.5% of the base slurry volume, the mass of low-viscosity carboxymethyl cellulose was 0.4% of the base slurry volume, and the mass of extreme pressure lubricant was 1.2% of the base slurry volume. Polyacrylamide, carboxymethyl cellulose, hydrolyzed polyacrylonitrile ammonium salt, anti-collapse fluid loss agent, and extreme pressure lubricant were added in the form of a gel. By adjusting the gel concentration and using solids control equipment such as a vibrating screen, centrifugal desander, and centrifuge, while adding high-viscosity carboxymethyl cellulose, the Marshall funnel viscosity of the drilling fluid was controlled to be 38s, the drilling fluid density to be 1.15 g / mL, and the drilling fluid fluid loss to be 6 mL. The pH of the drilling fluid was adjusted to 9 using sodium hydroxide until drilling was completed. Based on the condition of the drilling fluid on site, add plastic ball lubricant at a mass of 0.4% of the drilling fluid volume. The lubrication coefficient of the drilling fluid is 0.08. Perform electrical logging and well sealing.
[0043] For a single well, the drilling cycle of Examples 1 and 2 is 4 to 5 days, the waste slurry discharge is 200 to 300 cubic meters, and the drilling fluid cost is 40,000 to 50,000 yuan.
[0044] Example 3
[0045] Drilling fluids for geothermal wells in sandstone reservoirs contain base fluid, calcium chloride, polyacrylamide, hydrolyzed polyacrylonitrile ammonium salt, anti-collapse and fluid loss agent, carboxymethyl cellulose, and extreme pressure lubricant.
[0046] The drilling fluid used in sandstone geothermal reservoirs was applied to well DC3 at the No. 1 energy station of the Dongying Economic and Technological Development Zone Geothermal Clean Heating Project, as detailed below. Drilling fluid was prepared by adding base slurry, calcium chloride, and polyacrylamide. The mass of calcium chloride was 1.5% of the volume of base slurry, and the mass of polyacrylamide was 0.3% of the volume of base slurry. The base slurry consisted of water and bentonite, with the mass of bentonite being 4% of the water. The Marshall funnel viscosity of the base slurry was 28 s. Drilling commenced, and every 100 m of drilling, calcium chloride and polyacrylamide were added according to the condition of the drilling fluid on site, until the mass of calcium chloride was 1.5% of the volume of base slurry and the mass of polyacrylamide was 0.3% of the volume of base slurry. The polyacrylamide was added in gel form. By adjusting the gel concentration and using solids control equipment such as vibrating screens, centrifugal desanders, and centrifuges, the Marshall funnel viscosity of the drilling fluid was controlled to be 30 s, and the drilling fluid density was controlled to be 1.07 g / mL. Drilling continued until 200 m from the top of the thermal reservoir. The cuttings recovery rate during this process was >92%.
[0047] Stop adding calcium chloride. Based on the drilling fluid conditions, add polyacrylamide, carboxymethyl cellulose, hydrolyzed polyacrylonitrile ammonium salt, anti-collapse fluid loss agent, and extreme pressure lubricant until the mass of polyacrylamide is 0.25% of the base slurry volume, carboxymethyl cellulose is 0.3% of the base slurry volume, hydrolyzed polyacrylonitrile ammonium salt is 1.2% of the base slurry volume, anti-collapse fluid loss agent is 0.5% of the base slurry volume, and extreme pressure lubricant is 1.5% of the base slurry volume. Polyacrylamide, carboxymethyl cellulose, hydrolyzed polyacrylonitrile ammonium salt, anti-collapse fluid loss agent, and extreme pressure lubricant are added in gel form. By adjusting the gel concentration and using solids control equipment such as a vibrating screen, centrifugal desander, and centrifuge, control the drilling fluid's Marshall funnel viscosity to 35s, drilling fluid density to 1.14 g / mL, and drilling fluid fluid loss to 15 mL. Use sodium hydroxide to adjust the drilling fluid pH to 8. Drill to 100m from the top of the thermal reservoir. Then, based on the drilling fluid conditions at the site, polyacrylamide, carboxymethyl cellulose, hydrolyzed polyacrylonitrile ammonium salt, anti-collapse fluid loss agent, and extreme pressure lubricant were added until the mass of polyacrylamide was 0.25% of the base slurry volume, carboxymethyl cellulose was 0.3% of the base slurry volume, hydrolyzed polyacrylonitrile ammonium salt was 1.2% of the base slurry volume, anti-collapse fluid loss agent was 0.5% of the base slurry volume, and extreme pressure lubricant was 1.5% of the base slurry volume. Polyacrylamide, carboxymethyl cellulose, hydrolyzed polyacrylonitrile ammonium salt, anti-collapse fluid loss agent, and extreme pressure lubricant were added in gel form. By adjusting the gel concentration and using solids control equipment such as vibrating screens, centrifugal desanders, and centrifuges, the Marsh funnel viscosity of the drilling fluid was controlled to be 36s, the drilling fluid density to be 1.15 g / mL, and the drilling fluid fluid loss to be 10 mL. The pH of the drilling fluid was adjusted to 8 using sodium hydroxide, and drilling proceeded until the hot reservoir was reached. Finally, based on the drilling fluid conditions at the site, polyacrylamide, hydrolyzed polyacrylonitrile ammonium salt, anti-collapse fluid loss agent, low-viscosity carboxymethyl cellulose, and extreme pressure lubricant were added until the mass of polyacrylamide was 0.25% of the base slurry volume, the mass of hydrolyzed polyacrylonitrile ammonium salt was 1.2% of the base slurry volume, the mass of anti-collapse fluid loss agent was 0.5% of the base slurry volume, the mass of low-viscosity carboxymethyl cellulose was 0.3% of the base slurry volume, and the mass of extreme pressure lubricant was 1.5% of the base slurry volume. Polyacrylamide, carboxymethyl cellulose, hydrolyzed polyacrylonitrile ammonium salt, anti-collapse fluid loss agent, and extreme pressure lubricant were added in gel form. The gel concentration was adjusted, and solids control equipment such as vibrating screens, centrifugal desanders, and centrifuges were used. High-viscosity carboxymethyl cellulose was added to control the Marshall funnel viscosity of the drilling fluid to 40s, the drilling fluid density to 1.16g / mL, and the drilling fluid fluid loss to 7mL. Sodium hydroxide was used to adjust the pH of the drilling fluid to 9 until drilling was completed. Based on the condition of the drilling fluid on site, add plastic ball lubricant at a mass of 0.5% of the drilling fluid volume. The lubrication coefficient of the drilling fluid is 0.1. Perform electrical logging and well sealing.
[0048] Example 4
[0049] Drilling fluids for geothermal wells in sandstone reservoirs contain base fluid, calcium chloride, polyacrylamide, hydrolyzed polyacrylonitrile ammonium salt, anti-collapse and fluid loss agent, carboxymethyl cellulose, and extreme pressure lubricant.
[0050] The drilling fluid used in sandstone geothermal reservoirs was applied to well XSC1 at the No. 1 energy station of the Dongying Economic and Technological Development Zone Geothermal Clean Heating Project, as detailed below: Drilling fluid was prepared by adding base slurry, calcium chloride, and polyacrylamide. The mass of calcium chloride was 2% of the volume of base slurry, and the mass of polyacrylamide was 0.5% of the volume of base slurry. The base slurry consisted of water and bentonite, with the mass of bentonite being 3% of the water. The Marshall funnel viscosity of the base slurry was 28 s. Drilling commenced, and every 100 m of drilling, calcium chloride and polyacrylamide were added according to the condition of the drilling fluid on site, until the mass of calcium chloride was 2% of the volume of base slurry and the mass of polyacrylamide was 0.5% of the volume of base slurry. The polyacrylamide was added in gel form. By adjusting the gel concentration and using solids control equipment such as vibrating screens, centrifugal desanders, and centrifuges, the Marshall funnel viscosity of the drilling fluid was controlled to be 30 s, and the drilling fluid density was controlled to be 1.06 g / mL. Drilling continued until 200 m from the top of the thermal reservoir. The cuttings recovery rate during this process was >95%.
[0051] Stop adding calcium chloride. Based on the drilling fluid conditions, add polyacrylamide, carboxymethyl cellulose, hydrolyzed polyacrylonitrile ammonium salt, anti-collapse fluid loss agent, and extreme pressure lubricant until the mass of polyacrylamide is 0.3% of the base slurry volume, carboxymethyl cellulose is 0.3% of the base slurry volume, hydrolyzed polyacrylonitrile ammonium salt is 1.5% of the base slurry volume, anti-collapse fluid loss agent is 0.5% of the base slurry volume, and extreme pressure lubricant is 2% of the base slurry volume. Polyacrylamide, carboxymethyl cellulose, hydrolyzed polyacrylonitrile ammonium salt, anti-collapse fluid loss agent, and extreme pressure lubricant are added in gel form. By adjusting the gel concentration and using solids control equipment such as a vibrating screen, centrifugal desander, and centrifuge, control the drilling fluid's Marshall funnel viscosity to 33s, drilling fluid density to 1.12 g / mL, and drilling fluid fluid loss to 15 mL. Use sodium hydroxide to adjust the drilling fluid pH to 8. Drill to 100 m from the top of the thermal reservoir. Then, based on the drilling fluid conditions at the site, polyacrylamide, carboxymethyl cellulose, hydrolyzed polyacrylonitrile ammonium salt, anti-collapse fluid loss agent, and extreme pressure lubricant were added until the mass of polyacrylamide was 0.3% of the base slurry volume, the mass of carboxymethyl cellulose was 0.3% of the base slurry volume, the mass of hydrolyzed polyacrylonitrile ammonium salt was 1.5% of the base slurry volume, the mass of anti-collapse fluid loss agent was 0.5% of the base slurry volume, and the mass of extreme pressure lubricant was 2% of the base slurry volume. Polyacrylamide, carboxymethyl cellulose, hydrolyzed polyacrylonitrile ammonium salt, anti-collapse fluid loss agent, and extreme pressure lubricant were added in gel form. By adjusting the gel concentration and using solids control equipment such as a vibrating screen, centrifugal desander, and centrifuge, the Marsh funnel viscosity of the drilling fluid was controlled to be 37s, the drilling fluid density to be 1.13g / mL, and the drilling fluid fluid loss to be 10mL. The pH of the drilling fluid was adjusted to 8 using sodium hydroxide, and drilling proceeded until the hot reservoir was reached. Finally, based on the drilling fluid conditions at the site, polyacrylamide, hydrolyzed polyacrylonitrile ammonium salt, anti-collapse fluid loss agent, low-viscosity carboxymethyl cellulose, and extreme pressure lubricant were added until the mass of polyacrylamide was 0.3% of the base slurry volume, the mass of hydrolyzed polyacrylonitrile ammonium salt was 1.5% of the base slurry volume, the mass of anti-collapse fluid loss agent was 0.5% of the base slurry volume, the mass of low-viscosity carboxymethyl cellulose was 0.3% of the base slurry volume, and the mass of extreme pressure lubricant was 2% of the base slurry volume. Polyacrylamide, carboxymethyl cellulose, hydrolyzed polyacrylonitrile ammonium salt, anti-collapse fluid loss agent, and extreme pressure lubricant were added in gel form. The gel concentration was adjusted, and solids control equipment such as vibrating screens, centrifugal desanders, and centrifuges were used. High-viscosity carboxymethyl cellulose was added to control the Marshall funnel viscosity of the drilling fluid to 40s, the drilling fluid density to 1.16g / mL, and the drilling fluid fluid loss to 6mL. Sodium hydroxide was used to adjust the pH of the drilling fluid to 9 until drilling was completed. Based on the condition of the drilling fluid on site, add plastic ball lubricant at a mass of 0.7% of the drilling fluid volume. The lubrication coefficient of the drilling fluid is 0.08. Perform electrical logging and well sealing.
[0052] For a single well, the drilling cycle of Examples 3 and 4 is 7 to 8 days, the waste slurry discharge is 250 to 350 cubic meters, and the drilling fluid cost is 50,000 to 60,000 yuan.
[0053] Example 5
[0054] Drilling fluids for geothermal wells in sandstone reservoirs contain base fluid, calcium chloride, polyacrylamide, carboxymethyl cellulose, hydrolyzed polyacrylonitrile ammonium salt, anti-collapse and fluid loss agent, and extreme pressure lubricant.
[0055] Drilling fluids for sandstone geothermal reservoirs were applied to geothermal wells in the Binzhou City Zhanhua District Clean Energy Comprehensive Utilization Project, as detailed below: Drilling fluid was prepared by adding base slurry, calcium chloride, and polyacrylamide. The mass of calcium chloride was 1% of the volume of base slurry, and the mass of polyacrylamide was 0.4% of the volume of base slurry. The base slurry consisted of water and bentonite, with the mass of bentonite being 4% of the water. The Marshall funnel viscosity of the base slurry was 28 s. Drilling commenced, and every 100 m of drilling, calcium chloride and polyacrylamide were added according to the condition of the drilling fluid on site, until the mass of calcium chloride was 1% of the volume of base slurry and the mass of polyacrylamide was 0.4% of the volume of base slurry. The polyacrylamide was added in gel form. By adjusting the gel concentration and using solids control equipment such as vibrating screens, centrifugal desanders, and centrifuges, the Marshall funnel viscosity of the drilling fluid was controlled to be 30 s, and the drilling fluid density was 1.10 g / mL. Drilling continued until 200 m from the top of the thermal reservoir. The cuttings recovery rate during this process was >92%.
[0056] Stop adding calcium chloride. Based on the drilling fluid conditions, add polyacrylamide, carboxymethyl cellulose, hydrolyzed polyacrylonitrile ammonium salt, anti-collapse fluid loss agent, and extreme pressure lubricant until the mass of polyacrylamide is 0.2% of the base slurry volume, carboxymethyl cellulose is 0.4% of the base slurry volume, hydrolyzed polyacrylonitrile ammonium salt is 1% of the base slurry volume, anti-collapse fluid loss agent is 0.4% of the base slurry volume, and extreme pressure lubricant is 1% of the base slurry volume. Polyacrylamide, carboxymethyl cellulose, hydrolyzed polyacrylonitrile ammonium salt, anti-collapse fluid loss agent, and extreme pressure lubricant are added in gel form. By adjusting the gel concentration and using solids control equipment such as a vibrating screen, centrifugal desander, and centrifuge, control the drilling fluid's Marshall funnel viscosity to 32s, drilling fluid density to 1.11 g / mL, and drilling fluid fluid loss to 14 mL. Use sodium hydroxide to adjust the drilling fluid pH to 8. Drill to 100m from the top of the thermal reservoir. Then, based on the drilling fluid conditions at the site, polyacrylamide, carboxymethyl cellulose, hydrolyzed polyacrylonitrile ammonium salt, anti-collapse fluid loss agent, and extreme pressure lubricant were added until the mass of polyacrylamide was 0.2% of the base slurry volume, the mass of carboxymethyl cellulose was 0.4% of the base slurry volume, the mass of hydrolyzed polyacrylonitrile ammonium salt was 1% of the base slurry volume, the mass of anti-collapse fluid loss agent was 0.4% of the base slurry volume, and the mass of extreme pressure lubricant was 1% of the base slurry volume. Polyacrylamide, carboxymethyl cellulose, hydrolyzed polyacrylonitrile ammonium salt, anti-collapse fluid loss agent, and extreme pressure lubricant were added in gel form. By adjusting the gel concentration and using solids control equipment such as vibrating screens, centrifugal desanders, and centrifuges, the Marsh funnel viscosity of the drilling fluid was controlled to be 34 s, the drilling fluid density to be 1.12 g / mL, and the drilling fluid fluid loss to be 10 mL. The pH of the drilling fluid was adjusted to 8 using sodium hydroxide, and drilling proceeded until the hot reservoir was reached. Finally, based on the drilling fluid conditions at the site, polyacrylamide, low-viscosity carboxymethyl cellulose, hydrolyzed polyacrylonitrile ammonium salt, anti-collapse fluid loss agent, and extreme pressure lubricant were added until the mass of polyacrylamide was 0.2% of the base slurry volume, the mass of low-viscosity carboxymethyl cellulose was 0.3% of the base slurry volume, the mass of hydrolyzed polyacrylonitrile ammonium salt was 1% of the base slurry volume, the mass of anti-collapse fluid loss agent was 0.4% of the base slurry volume, and the mass of extreme pressure lubricant was 1% of the base slurry volume. Polyacrylamide, carboxymethyl cellulose, hydrolyzed polyacrylonitrile ammonium salt, anti-collapse fluid loss agent, and extreme pressure lubricant were added in gel form. The gel concentration was adjusted, and solids control equipment such as vibrating screens, centrifugal desanders, and centrifuges were used. High-viscosity carboxymethyl cellulose was added to adjust the Marsh funnel viscosity of the drilling fluid to 38s, the drilling fluid density to 1.15 g / mL, and the drilling fluid fluid loss to 9 mL. Sodium hydroxide was used to adjust the pH of the drilling fluid to 9 until drilling was completed. Based on the condition of the drilling fluid on site, 0.3% of the drilling fluid mass of plastic ball lubricant was added, resulting in a lubrication coefficient of 0.14 for the drilling fluid, and then electrical logging was performed to seal the well.
[0057] Based on a single well, the drilling cycle of Example 5 is 3 to 4 days, the waste slurry discharge is 150 to 200 cubic meters, and the drilling fluid cost is 30,000 to 40,000 yuan.
[0058] Comparative Example 1
[0059] The PAM potassium salt system drilling fluid suppresses salt loss and fluid loss during drilling. It consists of a base fluid, PAM, potassium chloride, salt-resistant copolymer, polyanionic cellulose, hydrolyzed polyacrylonitrile ammonium salt, salt-resistant fluid loss reducer, anti-collapse fluid loss reducer, and extreme pressure lubricant. The mass percentages are as follows: PAM 1% of the base fluid volume, potassium chloride 4%, salt-resistant copolymer 0.5%, polyanionic cellulose 1%, hydrolyzed polyacrylonitrile ammonium salt 2%, salt-resistant fluid loss reducer 1%, anti-collapse fluid loss reducer 1%, and extreme pressure lubricant 2%. This drilling fluid composition is maintained throughout the drilling process.
[0060] The method was applied to wells ZK01 and ZK02 in the Dezhou Finance and Economics Smart Agriculture Energy Transformation Project, adjusting the Marsh funnel viscosity of the drilling fluid to 35-50s, the drilling fluid density to 1.10-1.18g / mL, the drilling fluid pH value to 8-9, and the water loss to 10-15mL.
[0061] Based on a single well, the drilling cycle in this comparative example is 6 to 7 days, the waste slurry discharge is 300 to 400 cubic meters, and the drilling fluid cost is 70,000 to 80,000 yuan.
[0062] Comparative Example 2
[0063] The methyl-inhibiting drilling fluid consists of a base fluid, potassium polyacrylate, potassium chloride, sulfonylmethylphenol resin, anti-collapse fluid loss agent, salt-resistant fluid loss agent, sodium carbonate, and an extreme pressure lubricant. Specifically, the mass percentages of potassium polyacrylate, potassium chloride, sulfonylmethylphenol resin, anti-collapse fluid loss agent, salt-resistant fluid loss agent, sodium carbonate, and extreme pressure lubricant are 1%, 2%, 1%, 1%, 1%, 0.3%, and 2%, respectively. This drilling fluid composition is maintained throughout the drilling process.
[0064] It was applied to the Dongying Thermal Power Station No. 2 in 2023 to regulate the Marshall funnel viscosity of the drilling fluid to 30~55s, the density of the drilling fluid to 1.10~1.20g / mL, the pH value of the drilling fluid to 7~9, and the water loss to 10~15mL.
[0065] Based on a single well, the drilling cycle in this comparative example is 9 to 12 days, the waste slurry discharge is 400 to 500 cubic meters, and the drilling fluid cost is 80,000 to 100,000 yuan.
[0066] Comparative Example 3
[0067] The low-solids polymer-inhibited drilling fluid consists of a base slurry, polyacrylamide, hydrolyzed polyacrylonitrile ammonium salt, carboxymethyl cellulose, an anti-collapse fluid loss agent, and an extreme pressure lubricant. The mass percentages of polyacrylamide, hydrolyzed polyacrylonitrile ammonium salt, carboxymethyl cellulose, anti-collapse fluid loss agent, and extreme pressure lubricant are all 1% and 2% of the base slurry, respectively. This drilling fluid composition is maintained throughout the drilling process.
[0068] The method was applied to the drilling of the Luyuan Geothermal Project in Zhanhua District, Binzhou City, and the Marshall funnel viscosity of the drilling fluid was adjusted to 35~50s, the density of the drilling fluid was 1.10~1.20g / mL, the pH value of the drilling fluid was 7~9, and the water loss was 10~15mL.
[0069] Based on a single well, the drilling cycle in this comparative example is 5 to 7 days, the waste slurry discharge is 300 to 400 cubic meters, and the drilling fluid cost is 50,000 to 70,000 yuan.
[0070] As can be seen from the above embodiments, the present invention provides drilling fluid for sandstone geothermal wells and its application method. The drilling fluid for sandstone geothermal wells includes base slurry, calcium chloride, polyacrylamide, hydrolyzed polyacrylonitrile ammonium salt, anti-collapse and fluid loss agent, carboxymethyl cellulose, and extreme pressure lubricant. It adopts a dual inhibition system of inorganic compound calcium chloride and organic polymer polyacrylamide. In the middle and upper sections of the sandstone geothermal well, the dual inhibition system of inorganic compound inhibitor and organic polymer wall protection inhibitor is used. In the middle and lower sections, the addition of inorganic compound calcium chloride is stopped, and the addition of organic polymer polyacrylamide inhibitor, as well as the matching extreme pressure lubricant, hydrolyzed polyacrylonitrile ammonium salt, carboxymethyl cellulose, and anti-collapse and fluid loss agent is carried out. By controlling the composition and performance of drilling fluid in different sections, the drilling cycle is significantly shortened, the drilling efficiency is improved, and the drilling fluid cost and waste slurry discharge are reduced. Compared to traditional drilling methods that use drilling fluids with the same composition throughout the entire drilling process, the drilling fluid of this invention, combined with its application method, increases drilling efficiency by 20%, reduces waste slurry discharge by 30%, and lowers drilling fluid costs by 30%. It is suitable for sandstone geothermal wells and provides a strong foundation for efficient drilling of sandstone geothermal wells.
[0071] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.
Claims
1. A drilling fluid for geothermal wells in sandstone reservoirs, characterized in that, The drilling fluid for geothermal wells in sandstone geothermal reservoirs includes base slurry, calcium chloride, polyacrylamide, carboxymethyl cellulose, hydrolyzed polyacrylonitrile ammonium salt, anti-collapse and fluid loss agent, and extreme pressure lubricant. During drilling, base slurry, calcium chloride, and polyacrylamide are added. Calcium chloride and polyacrylamide are added during the drilling process to 200m from the top of the thermal reservoir. From 200m from the top of the thermal reservoir to the completion of drilling, polyacrylamide, carboxymethyl cellulose, hydrolyzed polyacrylonitrile ammonium salt, anti-collapse and dehydration agent, and extreme pressure lubricant are added.
2. The drilling fluid for geothermal wells in sandstone geothermal reservoirs according to claim 1, characterized in that, In the addition of base slurry, calcium chloride, and polyacrylamide during drilling, the mass of calcium chloride is 1.5-2% of the volume of base slurry, and the mass of polyacrylamide is 0.3-0.5% of the volume of base slurry.
3. The drilling fluid for geothermal wells in sandstone geothermal reservoirs according to claim 1 or 2, characterized in that, During the drilling process to a point 200m from the top of the thermal reservoir, calcium chloride and polyacrylamide are added. Specifically, depending on the condition of the drilling fluid on site, the amount of calcium chloride added is 1.5-2% of the base slurry volume, and the amount of polyacrylamide added is 0.3-0.5% of the base slurry volume.
4. The drilling fluid for geothermal wells in sandstone geothermal reservoirs according to claim 3, characterized in that, During the drilling process from 200m from the top of the thermal reservoir to completion, polyacrylamide, carboxymethyl cellulose, hydrolyzed polyacrylonitrile ammonium salt, anti-collapse fluid loss agent, and extreme pressure lubricant are added. Specifically, depending on the condition of the drilling fluid on site, the following amounts are added: polyacrylamide at 0.2-0.3% of the base mud volume, carboxymethyl cellulose at 0.25-0.6% of the base mud volume, hydrolyzed polyacrylonitrile ammonium salt at 1-1.5% of the base mud volume, anti-collapse fluid loss agent at 0.3-0.5% of the base mud volume, and extreme pressure lubricant at 1-2% of the base mud volume.
5. The drilling fluid for geothermal wells in sandstone geothermal reservoirs according to claim 1 or 4, characterized in that, The drilling fluid for geothermal wells in sandstone geothermal reservoirs also contains plastic ball lubricant.
6. The drilling fluid for geothermal wells in sandstone reservoirs according to claim 5, characterized in that, The base slurry is a water-based base slurry, which contains water and bentonite, with the bentonite comprising 3-4% of the water content.
7. The method of using the drilling fluid for sandstone geothermal wells according to any one of claims 1 to 6, characterized in that, It includes the following steps: 1) Add base slurry, calcium chloride and polyacrylamide to prepare drilling fluid, and control the Marvifell funnel viscosity and density of the base slurry; 2) Start drilling. Every 100m of drilling, add calcium chloride and polyacrylamide according to the condition of the drilling fluid on site to control the Marvife funnel viscosity and density of the drilling fluid, and continue drilling to 200m from the top of the thermal reservoir. 3) Add polyacrylamide, carboxymethyl cellulose, hydrolyzed polyacrylonitrile ammonium salt, anti-collapse fluid loss agent and extreme pressure lubricant according to the condition of the drilling fluid on site, control the Marvife funnel viscosity, density and pH value of the drilling fluid, and continue drilling until completion; 4) Add plastic balls as lubricant and seal the well.
8. The method of using drilling fluid for sandstone geothermal wells according to claim 7, characterized in that, Step 1) The Marviate of the base slurry is controlled to be ≤30s and the density of the base slurry is controlled to be ≤1.08g / mL; Step 2) The Marviate of the drilling fluid is controlled to be 30~32s, and the density of the drilling fluid is controlled to be <1.12g / mL; Step 3) The Marshall funnel viscosity of the drilling fluid is controlled to be 32~40s, the density of the drilling fluid is controlled to be 1.10~1.16g / mL, and the pH value of the drilling fluid is controlled to be 8~9; during the process from 200m away from the top of the thermal reservoir to the thermal reservoir, the water loss of the drilling fluid is controlled to be ≤30mL, and after entering the thermal reservoir, the water loss of the drilling fluid is controlled to be ≤10mL. After adding the plastic ball lubricant as described in step 4), the lubrication coefficient of the drilling fluid is <0.14.