Drilling fluid, construction method of drilling fluid and method for drilling along coal seam

Abstract

The invention discloses a drilling fluid, a construction method of the drilling fluid and a method for drilling along a coal seam, and relates to the field of coal mine ground drilling. The drilling fluid comprises the following components in percentage by mass: 0.1%-0.2% of caustic soda, 0.1%-0.2% of sodium carbonate, 3%-5% of bentonite, 0.5%-1% of salt-resistant and high-temperature-resistant fluid loss agent, 0.5%-1% of modified starch, 0.5%-1% of polyanionic cellulose, 0.5%-1% of salt-resistant copolymer, 2%-3% of cationic emulsified asphalt, 0.5%-1% of sulfonated asphalt, 11.5%-12.5% of potassium chloride, 11.5%-12.5% of sodium chloride, 0.3%-0.5% of shale inhibitor and 1% of shale inhibitor. 1.5% of a complex aluminum inhibitor, 0.1%-0.5% of a film-forming agent, barite powder and the balance of saturated salt water. The drilling fluid has the advantages that a drilling fluid system suitable for drilling of a soft and easily collapsed coal seam is formed, and the safety in a drilling well of a long-distance coal seam section is guaranteed.

Description

Technical Field

[0001] The invention relates to the field of coal mine surface drilling, and in particular to a drilling fluid, a method for constructing the drilling fluid, and a method for drilling along a coal seam. Background Art

[0002] In coal mining, the development of coalbed methane and gas control in soft and low-permeability coal seams need to be solved urgently. Horizontal wells are the key technology to achieve coalbed methane development and gas control. For example, the patent document with publication number CN115749923A discloses a method for pre-extraction of gas by staged fracturing of horizontal wells through tunnels in a joint well-ground excavation strip. During the drilling process of long-distance coal seam sections, problems such as drilling holes, rock powder carrying, and hole wall lubrication affect the later development of coalbed methane and gas control, and drilling fluid plays a vital role in these problems. At present, when conventional drilling fluids are applied to soft and low-permeability coal seams, due to the poor stability of the formation, coal seam collapse and block falling are prone to occur; the sand return of the vibrating screen is poor, and there is a phenomenon of sedimentation or rock debris accumulation bed when drilling; the friction resistance of the well wall is large, and it is difficult to smoothly lower the casing. Summary of the invention

[0003] The technical problem to be solved by the present invention is to form a drilling fluid system suitable for drilling in soft and easily collapsed coal seams, so as to ensure the safety of drilling in long-distance coal seam sections.

[0004] The present invention solves the above technical problems through the following technical means: a drilling fluid, comprising the following components by mass fraction: 0.1% to 0.2% caustic soda + 0.1% to 0.2% soda ash + 3% to 5% bentonite + 0.5% to 1% salt-resistant and high-temperature-resistant fluid loss reducer + 0.5% to 1% modified starch + 0.5% to 1% polyanionic cellulose + 0.5% to 1% salt-resistant copolymer + 2% to 3% cationic emulsified asphalt + 0.5% to 1% sulfonated asphalt + 11.5% to 12.5% ​​potassium chloride + 11.5% to 12.5% ​​sodium chloride + 0.3% to 0.5% shale inhibitor + 1% to 1.5% complex aluminum inhibitor + 0.1% to 0.5% film-forming agent + barite powder, and the balance is saturated brine.

[0005] A method for constructing a drilling fluid, for constructing the drilling fluid, comprises the following steps:

[0006] Step 1: measuring the performance of a single drilling fluid material in different proportions in fresh water, unsaturated salt water and saturated salt water, selecting the drilling fluid material and determining the addition ratio range of the drilling fluid material according to the measurement data;

[0007] Step 2: Using a solution of saturated brine + 0.1% to 0.2% caustic soda + 0.1% to 0.2% soda ash + 3% to 5% bentonite as the base slurry, measure the drilling fluid performance of different dosage ratio combinations of various drilling fluid materials, determine the optimal dosage ratio of the drilling fluid based on the measurement data, and determine the amount of barite powder to be added based on the optimal dosage ratio of the drilling fluid and the specific gravity required on site.

[0008] As an optimized technical solution, in step one, the properties measured include apparent viscosity, plastic viscosity, dynamic shear force, dynamic plastic ratio, initial shear ratio, final shear ratio, filtration loss and pH value.

[0009] As an optimized technical solution, in step 2, the properties measured include density, apparent viscosity, plastic viscosity, dynamic shear force, dynamic plastic ratio, initial shear ratio, final shear ratio, filtration loss and pH value.

[0010] As an optimized technical solution, in step one and step two, the measuring instruments used include a mixer, a densitometer, a six-speed rotational viscometer, a medium-pressure filter loss meter and a mud cake viscosity coefficient tester.

[0011] A method for drilling along a coal seam, using the drilling fluid, comprises sequentially performing first-opening vertical well section drilling, second-opening connecting well section drilling and third-opening horizontal well section drilling; before the third-opening drilling, the drilling fluid is prepared as the third-opening drilling fluid and hydrated, and the second-opening drilling fluid is first used to penetrate the casing and cementing cement; before the third-opening is about to enter the coal seam, the hydrated third-opening drilling fluid is used for circulation until the borehole is filled with the third-opening drilling fluid.

[0012] The advantages of the present invention are: drilling fluid materials are selected, material ratios are determined through indoor experiments, and the amount of related materials is optimized according to the actual performance on site to form a drilling fluid system suitable for drilling in soft and easily collapsed coal seams, thereby ensuring the safety of drilling in long-distance coal seam sections. The drilling fluid system: 1) has a strong anti-collapse ability and can effectively prevent coal seam collapse and block falling. The film-forming agent can form a film around the well wall to prevent free water from entering the formation; the asphalt material can form a seal and bond to the cracks in the formation, further improving the stability of the formation. 2) It has good carrying capacity, the vibrating screen returns sand well, and there is no precipitation or rock debris accumulation bed when drilling. 3) It has good lubrication properties and effectively reduces friction resistance. The system does not add special lubricants, and the emulsified asphalt in the system has certain lubrication properties. During directional drilling, the torque is stable, the friction resistance is small, and the casing is smoothly lowered in the later stage. DETAILED DESCRIPTION

[0013] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described in combination with the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the protection scope of the present invention.

[0014] The embodiment of the present invention discloses a drilling fluid, comprising the following components by mass fraction: 0.1% to 0.2% caustic soda + 0.1% to 0.2% soda ash + 3% to 5% bentonite + 0.5% to 1% salt-resistant and high-temperature-resistant fluid loss reducer + 0.5% to 1% modified starch + 0.5% to 1% polyanionic cellulose + 0.5% to 1% salt-resistant copolymer + 2% to 3% cationic emulsified asphalt + 0.5% to 1% sulfonated asphalt + 11.5% to 12.5% ​​potassium chloride + 11.5% to 12.5% ​​sodium chloride + 0.3% to 0.5% shale inhibitor + 1% to 1.5% complex aluminum inhibitor + 0.1% to 0.5% film-forming agent + barite powder, the remainder is saturated brine, and the specific amount of barite powder is determined according to the specific gravity required on site.

[0015] The embodiment of the present invention also discloses a method for constructing drilling fluid, which is used to construct the drilling fluid, comprising the following steps:

[0016] Step 1: Measure the performance of a single drilling fluid material in different proportions in fresh water, unsaturated brine and saturated brine. The measured properties include apparent viscosity, plastic viscosity, dynamic shear force, dynamic plastic ratio, initial shear ratio, final shear ratio, filtration loss and pH value. Select the drilling fluid material based on the measured data and determine the addition ratio range of the drilling fluid material.

[0017] Taking polyanionic cellulose (PAC-LV) as an example, its performance in fresh water and salt water at different ratios is shown in Table 1. It can be seen from Table 1 that the viscosity of polyanionic cellulose increases with the increase of the addition ratio. Its viscosity increases in saturated salt water while reducing the filtration loss. Therefore, polyanionic cellulose is selected as the thickener in the drilling fluid.

[0018]

[0019] According to the same method as above, all drilling fluid materials are selected and the addition ratio range of the drilling fluid materials is determined. The final addition ratio range of the drilling fluid materials is shown in Table 2.

[0020]

[0021] Step 2, using a solution of saturated brine + 0.1% to 0.2% caustic soda + 0.1% to 0.2% soda ash + 3% to 5% bentonite as the base slurry, measuring the drilling fluid properties of different dosage ratio combinations of various drilling fluid materials, the measured properties include density, apparent viscosity, plastic viscosity, dynamic shear force, dynamic plastic ratio, initial cutting and final cutting ratio, filtration loss and pH value, determining the optimal dosage ratio of the drilling fluid based on the measured data, and determining the amount of barite powder to be added based on the optimal dosage ratio of the drilling fluid and the specific gravity required on site.

[0022] The following example uses saturated salt water + 0.1% caustic soda + 0.2% soda ash + 4% bentonite as the base slurry to measure the drilling fluid properties of drilling fluid materials with different addition ratio combinations. The experimental data of 5 groups of experiments are shown in Table 3.

[0023]

[0024] The dosage ratios of the drilling fluid materials in each group of experiments are as follows:

[0025] Experiment 1: 0.75% salt-resistant and high-temperature-resistant fluid loss reducer + 0.5% modified starch + 0.8% salt-resistant copolymer + 0.5% polyanionic cellulose + 1% sulfonated asphalt + 0.1% film-forming agent + 12% potassium chloride + 12% sodium chloride + 1% complex aluminum inhibitor + 0.3% shale inhibitor + 2% cationic emulsified asphalt.

[0026] Experiment 2: 0.75% salt-resistant and high-temperature-resistant fluid loss reducer + 0.5% modified starch + 0.8% salt-resistant copolymer + 0.6% polyanionic cellulose + 1% sulfonated asphalt + 0.2% film-forming agent + 12% potassium chloride + 12% sodium chloride + 1% complex aluminum inhibitor + 0.3% shale inhibitor + 2% cationic emulsified asphalt.

[0027] Experiment 3: 0.5% salt-resistant and high-temperature-resistant fluid loss reducer + 1% modified starch + 0.8% salt-resistant copolymer + 0.6% polyanionic cellulose + 1% sulfonated asphalt + 0.3% film-forming agent + 12% potassium chloride + 12% sodium chloride + 1% complex aluminum inhibitor + 0.3% shale inhibitor + 2% cationic emulsified asphalt.

[0028] Experiment 4: 0.75% salt-resistant and high-temperature-resistant fluid loss reducer + 1% modified starch + 0.8% salt-resistant copolymer + 0.6% polyanionic cellulose + 1% sulfonated asphalt + 0.3% film-forming agent + 12% potassium chloride + 12% sodium chloride + 1% complex aluminum inhibitor + 0.3% shale inhibitor + 2% cationic emulsified asphalt.

[0029] Experiment 5: 0.75% salt-resistant and high-temperature-resistant fluid loss reducer + 1% modified starch + 0.8% salt-resistant copolymer + 1% polyanionic cellulose + 1% sulfonated asphalt + 0.5% film-forming agent + 12% potassium chloride + 12% sodium chloride + 1% complex aluminum inhibitor + 0.3% shale inhibitor + 2% cationic emulsified asphalt.

[0030] In step 1 and step 2, the measuring instruments used include a mixer, a density meter, a six-speed rotational viscometer, a medium-pressure filter loss meter, and a mud cake viscosity coefficient tester.

[0031] The embodiment of the present invention also discloses a method for drilling along a coal seam, which uses the drilling fluid, including sequentially drilling a first vertical well section, drilling a second connecting well section, and drilling a third horizontal well section; before the third drilling, the drilling fluid is prepared as the third drilling fluid and fully hydrated, and the second drilling fluid is first used to penetrate the casing and cementing cement; before the third drilling is about to enter the coal seam, the hydrated third drilling fluid is used for full circulation until the borehole is filled with the third drilling fluid.

[0032] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the aforementioned embodiments, it should be understood by those skilled in the art that the technical solutions described in the aforementioned embodiments may still be modified, or some of the technical features thereof may be replaced by equivalents. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A drilling fluid, characterized in that: The invention comprises the following components by mass fraction: 0.1% to 0.2% caustic soda + 0.1% to 0.2% soda ash + 3% to 5% bentonite + 0.5% to 1% salt-resistant and high-temperature-resistant fluid loss reducer + 0.5% to 1% modified starch + 0.5% to 1% polyanionic cellulose + 0.5% to 1% salt-resistant copolymer + 2% to 3% cationic emulsified asphalt + 0.5% to 1% sulfonated asphalt + 11.5% to 12.5% ​​potassium chloride + 11.5% to 12.5% ​​sodium chloride + 0.3% to 0.5% shale inhibitor + 1% to 1.5% complex aluminum inhibitor + 0.1% to 0.5% film-forming agent + barite powder, and the balance is saturated brine.

2. A method for constructing a drilling fluid, for constructing the drilling fluid according to claim 1, characterized in that: The following steps are involved: Step 1: measuring the performance of a single drilling fluid material in different proportions in fresh water, unsaturated salt water and saturated salt water, selecting the drilling fluid material and determining the addition ratio range of the drilling fluid material according to the measurement data; Step 2: Using a solution of saturated brine + 0.1% to 0.2% caustic soda + 0.1% to 0.2% soda ash + 3% to 5% bentonite as the base slurry, measure the drilling fluid performance of different dosage ratio combinations of various drilling fluid materials, determine the optimal dosage ratio of the drilling fluid based on the measurement data, and determine the amount of barite powder to be added based on the optimal dosage ratio of the drilling fluid and the specific gravity required on site.

3. The method for constructing a drilling fluid according to claim 2, characterized in that: In step 1, the properties measured include apparent viscosity, plastic viscosity, dynamic shear force, dynamic plastic ratio, initial shear to final shear ratio, fluid loss and pH value.

4. The method for constructing a drilling fluid according to claim 2, characterized in that: In step 2, the properties measured include density, apparent viscosity, plastic viscosity, dynamic shear force, dynamic plastic ratio, initial shear to final shear ratio, fluid loss and pH value.

5. The method for constructing a drilling fluid according to claim 3 or 4, characterized in that: The measuring instruments used include a mixer, a density meter, a six-speed rotational viscometer, a medium-pressure filter loss meter and a mud cake viscosity coefficient tester.

6. A method for drilling along a coal seam, using the drilling fluid as claimed in claim 1, characterized in that: The method comprises the following steps: drilling a first vertical well section, drilling a second connecting well section and drilling a third horizontal well section in sequence; before the third drilling, the drilling fluid is prepared as the third drilling fluid and hydrated, and the second drilling fluid is used to penetrate the casing and cementing cement; before the third drilling is about to enter the coal seam, the hydrated third drilling fluid is circulated until the borehole is filled with the third drilling fluid.

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