A method for constructing a horizontal well along a coal seam

Abstract

The application discloses a kind of horizontal well construction methods along coal seam, it is related to coal mine ground drilling field, comprising the following steps: construction one open well section, construction two open well section, construction three open well section;Before the three open well section drilling, according to surrounding borehole and coal seam mining situation, using geological software modeling expects coal seam profile and three open well section design trajectory;During the three open well section drilling, using wireless mud pulse directional instrument and azimuth gamma instrument while drilling monitoring coal seam variation and real drilling trajectory, according to monitoring data real-time adjustment drilling trajectory, keep drill bit in coal seam distance roof layer 0~2m range drilling.The application has the advantages that: ensure that horizontal well drilling trajectory control range and coal seam drilling rate meet the design requirements, and play a positive role in promoting the safety, efficient and green mining of coal mine.

Description

Technical Field

[0001] This invention relates to the field of coal mine surface drilling, and more particularly to a method for constructing horizontal wells along coal seams. Background Technology

[0002] Currently, gas control primarily relies on mining protective layers and pre-drainage through underground boreholes, supplemented by surface wells in mining-affected areas. In areas where gas pressure exceeds 3 MPa, underground measures are not permitted, necessitating research into new gas control models to fundamentally address the problem. Some mines currently employ horizontal well pre-drainage; for example, patent document CN115749923A discloses a method for pre-drainage of gas through segmented fracturing of horizontal wells in combined mine-surface tunneling. However, existing horizontal well drilling methods, when applied to soft, low-permeability coal seams, suffer from several drawbacks: difficulty in controlling the wellbore trajectory and coal seam encounter rate during drilling, resulting in low safety and efficiency; poor formation stability, leading to coal seam collapse and rockfall; poor sand return from vibrating screens, resulting in sedimentation or cuttings accumulation during tripping; and high wellbore frictional resistance, hindering smooth casing installation. Summary of the Invention

[0003] The technical problem to be solved by this invention is to effectively control the wellbore trajectory and coal seam encounter rate during the drilling process of horizontal wells in soft, low-permeability coal seams.

[0004] This invention solves the above-mentioned technical problems through the following technical means: a method for constructing horizontal wells along coal seams, comprising the following steps:

[0005] Step 1: Construct the first well section, which is a vertical well section;

[0006] Step two: Construct the second well section, which includes a vertical well section and an arc-shaped well section;

[0007] Step 3: Construct the three-section well, which is a horizontal well section;

[0008] Before drilling the three-section well, geological software was used to model and predict the coal seam profile and the designed trajectory of the three-section well, based on the surrounding boreholes and coal seam mining conditions. During the drilling of the three-section well, wireless mud pulse orientation instruments and azimuth gamma instruments were used to monitor the changes in the coal seam and the actual drilling trajectory while drilling. The drilling trajectory was adjusted in real time based on the monitoring data to keep the drill bit drilling within a range of 0 to 2 meters from the roof layer of the coal seam.

[0009] As an optimized technical solution, the mud used in the third well section comprises the following components by mass fraction: 0.1%–0.2% caustic soda + 0.1%–0.2% soda ash + 3%–5% bentonite + 0.5%–1% salt-resistant and high-temperature-resistant fluid loss reducing agent + 0.5%–1% modified starch + 0.5%–1% polyanionic cellulose + 0.5%–1% salt-resistant copolymer + 2%–3% cationic emulsified asphalt + 0.5%–1% sulfonated asphalt + 11.5%–12.5% ​​potassium chloride + 11.5%–12.5% ​​sodium chloride + 0.3%–0.5% shale inhibitor + 1%–1.5% complexed aluminum inhibitor + 0.1%–0.5% film-forming agent + barite powder, with the balance being saturated brine.

[0010] As an optimized technical solution, the pumping rate for drilling the three-section well is 20-30 L / s.

[0011] As an optimized technical solution, the top drive rotation speed during drilling in the three-section well is 30-35 r / min.

[0012] As an optimized technical solution, the drilling speed of the three-section well drilling is 0.2 to 0.3 m / min.

[0013] As an optimized technical solution, the reaming method for drilling the three-section well is as follows: after the single-section directional drilling is completed, the pump flow rate is reduced to 10-12 L / s, the top drive rotation is stopped, the drill string is lifted for 2-3 m, and then reaming is performed at a reaming speed of less than 2 m / min.

[0014] As an optimized technical solution, during the drilling process of the three-section well, a short start is performed every 190-210m.

[0015] As an optimized technical solution, if the torque or pump pressure changes by more than 2 kN·m / Mpa, or the coal quantity changes abnormally during the drilling process of the three-section well, the drill string should be immediately lifted from the bottom of the hole, and drilling should continue only after the circulation is normal.

[0016] As an optimized technical solution, during the drilling of the three-section well, the mud specific gravity is controlled at 1.18 g / cm³. 3 above.

[0017] As an optimized technical solution, after drilling is completed, the casing is lowered into the three-section well by rotating the casing.

[0018] The advantages of this invention are:

[0019] 1. For horizontal well construction in soft, low-permeability coal seams, the use of measurement-while-drilling instruments for monitoring during drilling allows for real-time adjustment of the drilling trajectory. This ensures that the control range of the horizontal well drilling trajectory and the coal seam encounter rate meet design requirements, playing a positive role in ensuring safe, efficient, and green mining of coal mines.

[0020] 2. Drilling fluid materials were selected and their proportions determined through laboratory experiments. The dosage of relevant materials was optimized based on actual field performance, resulting in a mud system suitable for drilling soft, easily collapsing coal seams. This mud system exhibits: 1) Strong anti-collapse capabilities, effectively preventing coal seam collapse and spalling. The film-forming agent forms a film around the wellbore, preventing free water from entering the formation; asphalt-based materials seal and bond formation fissures, further improving formation stability. 2) Good carrying capacity, with good sand return on the vibrating screen, and no sedimentation or cuttings accumulation during tripping. 3) Good lubrication performance, effectively reducing frictional resistance. No special lubricant was added to this system; the emulsified asphalt and other components in the system also possess certain lubricating properties, resulting in stable torque and low frictional resistance during directional drilling, and smooth casing installation in the later stages.

[0021] 3. Explore drilling parameters such as pump flow rate, top drive speed, and drilling speed when drilling along coal seams, and supplement them with methods such as reaming, short starts, and abnormal handling to form a complete set of horizontal well drilling technology for soft and easily collapsible coal seams.

[0022] 4. The method of rotating the casing is adopted to achieve smooth casing installation in soft and easily collapsible coal seams. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of the well shaft structure according to an embodiment of the present invention.

[0024] Figure 2 This is a schematic diagram of the expected coal seam profile and the design trajectory of the three-section well section in an embodiment of the present invention.

[0025] Figure 3 This is a comparison diagram of the designed trajectory and the actual drilling trajectory of the well section in Embodiment 3 of the present invention. Detailed Implementation

[0026] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the protection scope of the present invention.

[0027] like Figure 1 As shown in the figure, an embodiment of the present invention discloses a method for constructing a horizontal well along a coal seam, comprising the following steps:

[0028] Step 1: Construct the first section of the well, which is a vertical well section.

[0029] Step 2: Construct the second well section 2, which includes a vertical well section and an arc-shaped well section.

[0030] Step 3: Construct section 3 of the three-section well, which is a horizontal section.

[0031] To match the existing drilling tools and adapt to high build-up rate drilling, the first well section 1 and the second well section 2 adopt the hole enlargement method to achieve the design hole diameter. The drilling tool combination is shown in Table 1.

[0032]

[0033]

[0034] Based on the characteristics of the coal seam, the well structure design, and the drilling process requirements, the technical difficulties of construction were fully assessed, and it was decided that a strong brine film-forming mud system would be adopted for the third section of the well. The mud performance requirements are shown in Table 2.

[0035]

[0036] The drilling mud used in section 3 of the third well comprises the following components by mass fraction: 0.1%–0.2% caustic soda + 0.1%–0.2% soda ash + 3%–5% bentonite + 0.5%–1% salt-resistant and high-temperature-resistant fluid loss reducing agent + 0.5%–1% modified starch + 0.5%–1% polyanionic cellulose (PAC-LV) + 0.5%–1% salt-resistant copolymer + 2%–3% cationic emulsified asphalt + 0.5%–1% sulfonated asphalt + 11.5%–12.5% ​​potassium chloride + 11.5%–12.5% ​​sodium chloride + 0.3%–0.5% shale inhibitor + 1%–1.5% complexed aluminum inhibitor + 0.1%–0.5% film-forming agent + barite powder, with the balance being saturated brine. The specific amount of barite powder used depends on the required specific gravity on site.

[0037] The mud system used in the third drilling section of the well achieved relatively ideal results, as detailed below:

[0038] 1) This mud system exhibits strong anti-collapse capabilities, effectively preventing coal seam collapse and rockfall. The film-forming agent forms a film around the wellbore, preventing free water from entering the formation; the bituminous materials seal and bond the formation's fissures, further improving formation stability.

[0039] 2) The mud system has good carrying capacity. During the construction of section 3 of the third well, the mud viscosity remained between 50 and 60 s, the sand return of the vibrating screen was good, and there was no sedimentation or cuttings accumulation during tripping in and out of the well.

[0040] 3) This mud system has good lubrication properties, effectively reducing frictional resistance. No special lubricant was added to this system; the emulsified asphalt and other components also possess certain lubricating properties. During directional drilling, torque remained stable, frictional resistance was low, and casing installation proceeded smoothly in the later stages.

[0041] The parameters and related requirements for drilling section 3 of the third well section are as follows:

[0042] 1) Pump flow rate is 20-30 L / s.

[0043] 2) The top drive speed is 30-35 r / min.

[0044] 3) The drilling speed is 0.2 to 0.3 m / min, and the drilling pressure is adjusted appropriately.

[0045] 4) The reaming method is as follows: After the single-root orientation is completed, the pump flow rate is reduced to 10-12 L / s, the top drive rotation is stopped, the drill is lifted for 2-3 m, and then the reaming is performed. The reaming speed is less than 2 m / min.

[0046] 5) During the drilling process, a short start should be performed every 190-210m.

[0047] 6) If, during the drilling process, the torque or pump pressure changes by more than 2 kN·m / Mpa, or there are abnormal changes in the amount of coal, immediately lift the drill bit away from the bottom of the hole and continue drilling only after the circulation is normal.

[0048] 7) During drilling, the mud specific gravity is controlled at 1.18 g / cm³. 3 above.

[0049] like Figure 2 As shown, before drilling the third section of the three-section well, based on the surrounding boreholes and coal seam mining conditions, geological software was used to model and predict the coal seam profile and the design trajectory of the third section of the well, including the design coal seam boundary 4, the design landing point of the second section of the well 5, the design trajectory of the third section of the well 6, and the design exploration area 7.

[0050] like Figure 3 As shown, during the drilling of section 3 of the third well section, wireless mud pulse directional instruments and azimuth gamma instruments were used to monitor the changes in the coal seam and the actual drilling trajectory 8. The monitoring points of the actual drilling trajectory 8 include the starting point 81 of the first coal seam encounter in the third well section, the ending point 82 of the first coal seam encounter in the third well section (roof exploration), the starting point 83 of the second coal seam encounter in the third well section, and the ending point 84 of the second coal seam encounter in the third well section. The drilling trajectory was adjusted in real time according to the monitoring data to keep the drill bit drilling within the range of 0 to 2m from the roof layer of the coal seam, ensuring that the control range of the drilling trajectory and the coal seam encounter rate meet the design requirements.

[0051] After drilling is completed, the casing is lowered into section 3 of the well using a rotating casing lowering method. Existing rotating casing lowering devices such as rotating guide shoes and rotating centralizers can be used.

[0052] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for constructing horizontal wells along coal seams, characterized in that: Includes the following steps: Step 1: Construct the first well section, which is a vertical well section; Step two: Construct the second well section, which includes a vertical well section and an arc-shaped well section; Step 3: Construct the three-section well, which is a horizontal well section; Before drilling the third section, based on the surrounding boreholes and coal seam recovery conditions, geological software was used to model and predict the coal seam profile and the designed trajectory of the third section. The trajectory included the coal seam boundary, the landing point of the second section, the trajectory of the third section, and the roof exploration area. During the drilling of the third section, wireless mud pulse orientation instruments and azimuth gamma instruments were used to monitor coal seam changes and the actual drilling trajectory while drilling. The drilling trajectory was adjusted in real time based on the monitoring data to keep the drill bit drilling within a range of 0 to 2 meters from the roof layer of the coal seam. The drilling parameters for the third section are as follows: pump flow rate of 20–30 L / s; top drive speed of 30–35 r / min; drilling speed of 0.2–0.3 m / min; reaming method: after single-section directional drilling is completed, the pump flow rate is reduced to 10–12 L / s, the top drive rotation is stopped, the drill string is lifted 2–3 m, and reaming is performed at a speed of less than 2 m / min; during drilling, a short start is performed every 190–210 m; if the torque or pump pressure changes by more than 2 kN·m / MPa, or if there are abnormal changes in coal quantity, the drill string is immediately lifted from the bottom of the hole, and drilling continues only after circulation returns to normal; mud specific gravity is controlled at 1.18 g / cm³. 3 above.

2. The method for constructing a horizontal well along a coal seam according to claim 1, characterized in that: The drilling mud used in the third well section comprises the following components by mass fraction: 0.1%–0.2% caustic soda + 0.1%–0.2% soda ash + 3%–5% bentonite + 0.5%–1% salt-resistant and high-temperature-resistant fluid loss reducing agent + 0.5%–1% modified starch + 0.5%–1% polyanionic cellulose + 0.5%–1% salt-resistant copolymer + 2%–3% cationic emulsified asphalt + 0.5%–1% sulfonated asphalt + 11.5%–12.5% ​​potassium chloride + 11.5%–12.5% ​​sodium chloride + 0.3%–0.5% shale inhibitor + 1%–1.5% complexed aluminum inhibitor + 0.1%–0.5% film-forming agent + barite powder, with the balance being saturated brine.

3. The method for constructing horizontal wells along coal seams according to claim 1, characterized in that: After drilling is completed, the casing is lowered into the three-section well using a rotating casing method.

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