A drilling fluid suitable for ultra-deep coal seam gas wells

Abstract

The present application belongs to the field of drilling technology, and particularly relates to a drilling fluid suitable for super-deep coal seam gas well, which comprises the following components in parts by weight: water 100 parts, caustic soda 0.1-0.2 parts, asphalt material 4-6 parts, resin material 3-4 parts, lignite material 1-2 parts, salt-resistant soil 1-2 parts, superfine calcium 2-3 parts, filtration reducer 0.8-1.5 parts, film-forming solid wall agent 1-2 parts, ammonium salt inhibitor 1-1.5 parts, potassium chloride 5-7 parts, and organic salt 10-15 parts. The drilling fluid system is used in the drilling process, and has good rheological property, strong lubricity, strong inhibition and plugging capacity, and high temperature resistance up to 180 DEG C. In a high-temperature environment, the failure of the water-based drilling fluid leads to stable rheological property and filtration property, and meets the requirements of well wall anti-sloughing in the drilling of formations with developed fractures and low strength, and the requirements of drilling anti-sloughing in the super-deep coal seam gas well with alternating coal and mudstone formations.

Description

Technical Field

[0001] This invention belongs to the field of drilling technology, and in particular relates to a drilling fluid suitable for ultra-deep coalbed methane wells. Background Technology

[0002] As conventional oil and gas resources gradually deplete, unconventional oil and gas resources such as heavy oil, oil sands, shale oil, shale gas, and coalbed methane are increasingly becoming development hotspots. They play a crucial role in drilling engineering for oil and gas. A circulating fluid used in the drilling process is mainly composed of a mixture of water, clay, chemical additives, and other components. It can carry and suspend rock cuttings, cool and lubricate the drill bit, stabilize the wellbore, and transmit hydraulic energy.

[0003] Currently, with the growth in energy demand and the depletion of conventional oil and gas resources, coalbed methane development is receiving attention. However, ultra-deep coalbed methane wells face numerous challenges, including high well temperatures, the easy degradation of traditional drilling fluid systems at high temperatures, the failure of filtration control agents leading to uncontrolled rheological and filtration performance, difficulties in carrying sand in steep and horizontal sections, easy deposition of cuttings causing stuck pipe, poor coal seam stability, easy collapse, resulting in operation interruption and stuck pipe, complex formation pressure, difficulty in designing drilling fluid density, and the potential for well kicks and blowouts if improper. Therefore, solving the problems of drilling fluid resistance to high temperatures, collapse prevention, and ensuring safe drilling in coal seams is urgent. Summary of the Invention

[0004] The purpose of this invention is to address the above-mentioned problems by providing a drilling fluid suitable for ultra-deep coalbed methane wells.

[0005] To achieve the above objectives, the present invention adopts the following technical solution: a drilling fluid suitable for ultra-deep coalbed methane wells, the drilling fluid comprising the following components in parts by weight: 100 parts water, 0.1-0.2 parts caustic soda, 4-6 parts asphalt material, 3-4 parts resin material, 1-2 parts lignite material, 1-2 parts salt-resistant soil, 2-3 parts ultrafine calcium, 0.8-1.5 parts filtration loss reducer, 1-2 parts film-forming and wall-fixing agent, 1-1.5 parts ammonium salt inhibitor, 5-7 parts potassium chloride, and 10-15 parts organic salt.

[0006] In the aforementioned drilling fluid suitable for ultra-deep coalbed methane wells, the drilling fluid has a pH value of 9-10, a density of 1.10-2.00 g / cm3, a temperature resistance of 180℃, and an HTHP filtration loss of less than 8 mL.

[0007] In the aforementioned drilling fluid suitable for ultra-deep coalbed methane wells, the asphalt material is sulfonated asphalt.

[0008] In the aforementioned drilling fluid suitable for ultra-deep coalbed methane wells, the resin material is sulfonated phenolic resin.

[0009] In the aforementioned drilling fluid suitable for ultra-deep coalbed methane wells, the lignite material is potassium humate.

[0010] In the aforementioned drilling fluid suitable for ultra-deep coalbed methane wells, the lignite material is potassium humate.

[0011] In the aforementioned drilling fluid suitable for ultra-deep coalbed methane wells, the filtration loss reducer is produced by solution polymerization using a molecular structure design concept, through the selection of temperature- and salt-resistant monomers. The introduced monomer repeating units have a large spatial volume to improve the rigidity, temperature resistance, salt resistance, shear resistance, and HTHP filtration loss reduction performance of the copolymer molecules. Furthermore, a shielding technology is used to protect the amide groups to prevent hydrolysis under sodium hydroxide conditions.

[0012] In the aforementioned drilling fluid suitable for ultra-deep coalbed methane wells, the film-forming and wall-stabilizing agent is a high-molecular polymer film-forming and wall-stabilizing agent.

[0013] In the aforementioned drilling fluid suitable for ultra-deep coalbed methane wells, the ammonium salt inhibitor is a polyquaternary ammonium salt inhibitor.

[0014] In the aforementioned drilling fluid suitable for ultra-deep coalbed methane wells, the organic salt is a formate-type organic salt.

[0015] Compared with existing technologies, the advantages of a drilling fluid suitable for ultra-deep coalbed methane wells are: 1. This drilling fluid can withstand temperatures up to 180℃, solving the problem of rheological and filtration performance deterioration caused by the failure of traditional water-based drilling fluid filtration reducers at high temperatures. The temperature- and salt-resistant filtration reducer, through special design and polymerization, improves molecular rigidity, temperature and salt resistance, shear resistance, and filtration performance, and can maintain the stability of drilling fluid performance at high temperatures, ensuring safe and efficient drilling operations and reducing the risk of accidents caused by high temperatures.

[0016] 2. This drilling fluid utilizes the synergistic effect of "dual-stage" plugging materials of micron and nano materials to form a dense mud cake and form a film to block water. Multiple filtration loss reducers are combined to reduce water loss, ammonium salt inhibitors and potassium chloride inhibit mudstone hydration and expansion, and organic salts reduce water activity, effectively preventing wellbore instability and collapse. It has a significant plugging effect on coal, rock, and interbedded rock, ensuring safe drilling in coal seams.

[0017] 3. This drilling fluid has good viscoelasticity and shear dilution properties, which can effectively suspend and carry rock cuttings, ensure wellbore cleanliness, and maintain wellbore stability. In field applications of ultra-deep coalbed methane wells, it has strong rheological properties, lubricity, and anti-plugging capabilities, meeting the drilling needs of complex formations, achieving successful well completion with good results, and providing reliable technical support for drilling ultra-deep coalbed methane wells. Attached Figure Description

[0018] Figure 1This is a diagram illustrating the high-temperature resistance mechanism of a high-temperature resistant and salt-resistant filtration loss reducing agent for drilling fluids suitable for ultra-deep coalbed methane wells, provided by this invention. Figure 2 This is a diagram of the hydrophobic micro-crosslinked structure of a temperature-resistant, salt-resistant, and filtration-reducing agent for drilling fluids suitable for ultra-deep coalbed methane wells, provided by this invention. Figure 3 This invention provides a thermogravimetric curve of a temperature- and salt-resistant filtration loss reducing agent for drilling fluids suitable for ultra-deep coalbed methane wells; Figure 4 This invention provides a thermogravimetric performance evaluation table for a drilling fluid anti-temperature and anti-salt filtration loss reducing agent suitable for ultra-deep coalbed methane wells. Detailed Implementation

[0019] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0020] Example 1: A drilling fluid suitable for ultra-deep coalbed methane wells, comprising the following components in parts by weight: 100 parts water, 0.1-0.2 parts caustic soda, 4-6 parts asphalt material, 3-4 parts resin material, 1-2 parts lignite material, 1-2 parts salt-resistant soil, 2-3 parts ultrafine calcium, 0.8-1.5 parts filtration loss reducer, 1-2 parts film-forming and wall-fixing agent, 1-1.5 parts ammonium salt inhibitor, 5-7 parts potassium chloride, and 10-15 parts organic salt.

[0021] The drilling fluid has a pH of 9–10, a density of 1.10–2.00 g / cm³, a temperature resistance of 180℃, and an HTHP filtration loss of less than 8 mL.

[0022] The asphalt material is sulfonated asphalt, the resin material is sulfonated phenolic resin, the lignite material is potassium humate, and the filtration loss reducer is a solution polymerized using a molecular structure design concept, through the selection of temperature- and salt-resistant monomers. The introduced monomer repeating units have a large spatial volume to improve the rigidity, temperature resistance, salt resistance, shear resistance, and HTHP filtration loss reduction performance of the copolymer molecules. The filtration loss reducer also uses shielding technology to protect the amide groups and prevent hydrolysis under sodium hydroxide conditions. The film-forming and wall-fixing agent is a high molecular weight polymer film-forming and wall-fixing agent, the ammonium salt inhibitor is a polyquaternary ammonium salt inhibitor, and the organic salt is a formate organic salt.

[0023] Example 2: A drilling fluid suitable for ultra-deep coalbed methane wells, comprising the following components in parts by weight: 100 parts water, 0.12-0.18 parts caustic soda, 4.5-5.5 parts asphalt material, 3.2-3.8 parts resin material, 1.2-1.8 parts lignite material, 1.2-1.8 parts saline-resistant soil, 2.2-2.8 parts ultrafine calcium, 1.0-1.3 parts filtration loss reducer, 1.2-1.8 parts film-forming and wall-fixing agent, 1.2-1.3 parts ammonium salt inhibitor, 5.5-6.5 parts potassium chloride, and 11-14 parts organic salts.

[0024] The drilling fluid has a pH of 9–10, a density of 1.30–1.80 g / cm³, a temperature resistance of 180℃, and an HTHP filtration loss of less than 7 mL.

[0025] Example 3: A drilling fluid suitable for ultra-deep coalbed methane wells, comprising the following components in parts by weight: 100 parts water, 0.15 parts caustic soda, 5 parts asphalt material, 3.5 parts resin material, 1.5 parts lignite material, 1.5 parts salt-resistant soil, 2.5 parts ultrafine calcium, 1.1 parts filtration loss reducer, 1.5 parts film-forming and wall-fixing agent, 1.25 parts ammonium salt inhibitor, 6 parts potassium chloride, and 12.5 parts organic salt.

[0026] The drilling fluid has a pH of 9–10, a density of 1.35–1.6 g / cm³, a temperature resistance of 180℃, and an HTHP filtration loss of less than 6.5 mL.

[0027] The present invention is described as follows: The temperature- and salt-resistant filtration reducer in the drilling fluid system of the present invention adopts a molecular structure design concept. Through the optimal selection of temperature- and salt-resistant monomers, it is polymerized using a solution method. The introduced monomer repeating units have a large spatial volume, which effectively increases steric hindrance, thereby improving the rigidity of the copolymer molecules and enhancing their resistance to temperature, salt, and shear, as well as their HTHP filtration reduction performance. A shielding technology is employed to protect the amide groups (-CONH-) to prevent hydrolysis under sodium hydroxide conditions, allowing them to function as a protective agent and reduce filtration loss under high-temperature conditions. With the increase of the filtration reducer dosage, the drilling fluid filtration loss significantly decreases. This is because, under the same conditions, the number of adsorption groups and hydration groups both increase, with an increase in hydration groups, thus reducing filtration loss. The volume decreased significantly, but the pH value remained unchanged. In core CT scans before and after coal and rock plugging, the plugging rate of this drilling fluid system increased from 75% to 94%, and the plugging rate in interbedded rock increased from 78% to 92%. It was field-applied in an ultra-deep coalbed methane well (vertical depth 4381 meters) in the Longdong area of ​​the Ordos Basin with a depth of over 4000 meters. During the drilling process, this drilling fluid system was used. It has good rheological properties, lubricity, strong plugging inhibition ability, and temperature resistance up to 180℃. Failure in high-temperature environment resulted in stable rheological and filtration properties of the water-based drilling fluid. It meets the wellbore anti-collapse requirements in formations with fracture development and low strength, and meets the drilling anti-collapse requirements of coal and mudstone interbedded formations in ultra-deep coalbed methane wells. The well has been successfully completed, and the field application effect is good.

[0028] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A drilling fluid suitable for ultra-deep coalbed methane wells, characterized in that, The drilling fluid comprises the following components in parts by weight: 100 parts water, 0.1-0.2 parts caustic soda, 4-6 parts asphalt material, 3-4 parts resin material, 1-2 parts lignite material, 1-2 parts salt-resistant soil, 2-3 parts ultrafine calcium, 0.8-1.5 parts filtration loss reducer, 1-2 parts film-forming and wall-fixing agent, 1-1.5 parts ammonium salt inhibitor, 5-7 parts potassium chloride, and 10-15 parts organic salt.

2. The drilling fluid suitable for ultra-deep coalbed methane wells according to claim 1, characterized in that, The drilling fluid has a pH of 9-10, a density of 1.10-2.00 g / cm3, a temperature resistance of 180℃, and an HTHP filtration loss of less than 8 mL.

3. The drilling fluid suitable for ultra-deep coalbed methane wells according to claim 1, characterized in that, The asphalt material is sulfonated asphalt.

4. The drilling fluid suitable for ultra-deep coalbed methane wells according to claim 1, characterized in that, The resin material is sulfonated phenolic resin.

5. The drilling fluid suitable for ultra-deep coalbed methane wells according to claim 1, characterized in that, The lignite material is potassium humate.

6. The drilling fluid suitable for ultra-deep coalbed methane wells according to claim 1, characterized in that, The lignite material is potassium humate.

7. The drilling fluid suitable for ultra-deep coalbed methane wells according to claim 1, characterized in that, The filtration loss reducer is formulated using a molecular structure design concept, through solution polymerization of optimized temperature- and salt-resistant monomers. The introduced monomer repeating units have a large spatial volume to improve the rigidity, temperature resistance, salt resistance, shear resistance, and HTHP filtration loss reduction performance of the copolymer molecules. Furthermore, a shielding technology is used to protect the amide groups and prevent hydrolysis under sodium hydroxide conditions.

8. The drilling fluid suitable for ultra-deep coalbed methane wells according to claim 1, characterized in that, The film-forming and wall-stabilizing agent is a high molecular polymer film-forming and wall-stabilizing agent.

9. The drilling fluid suitable for ultra-deep coalbed methane wells according to claim 1, characterized in that, The ammonium salt inhibitor is a polyquaternary ammonium salt inhibitor.

10. The drilling fluid suitable for ultra-deep coalbed methane wells according to claim 1, characterized in that, The organic salt is a formate organic salt.

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