Advanced pre-extraction method based on enhanced extraction of gas from horizontal wells with full coverage of working face

Abstract

The present invention discloses a method for pre-extraction of enhanced extraction by ground horizontal wells based on full coverage of working face gas, comprising determining the layout layer of the horizontal section in a U-shaped distal-end docking horizontal well group arranged along the direction of the working face; constructing a drainage vertical well, and completing the first drilling, second drilling and cementing of a directional horizontal well docked with the drainage vertical well; completing geological guidance drilling while drilling the third horizontal section, and adjusting the drilling trajectory in real time during the drilling process; completing cementing and completion of the entire well section of the directional horizontal well; performing segmented isolation on the horizontal section, mechanical isolation between segments and multi-cluster chemical temporary plugging and segmented fracturing construction on the target coal seam to form a three-dimensional volume fracture network; performing post-fracturing flowback and well washing operations to realize communication between the directional horizontal well and the drainage vertical well; completing pre-extraction of enhanced extraction by ground wells with full coverage of working face gas, and achieving the effect of achieving full coverage of coal mine working face gas and enhanced extraction and pre-extraction of ground horizontal wells through a single horizontal well.

Description

Technical Field

[0001] The present invention belongs to the technical field of ground gas extraction, in particular to a method for ground pre-extraction of gas from a coal mine working face, based on enhanced extraction of gas from a ground horizontal well with full coverage of gas from the working face. Background Art

[0002] my country's high-gas outburst mines are widely distributed and have abundant gas resources. Extracting gas from coal seams can not only effectively control coal mine gas disasters and ensure safe coal mine production, but also obtain a large amount of gas resources. At the same time, with the expansion of mine development and mining scale, gas disasters have seriously affected the mining and excavation succession and safe production of mines. Considering the high investment cost, long extraction time and high construction risk of underground coal mine gas extraction, the traditional underground through-layer and along-layer drilling pre-extraction of regional coal seam gas measures can no longer fully meet the needs of coal mine mining and excavation succession and safe production. At present, surface gas enhanced extraction and advanced pre-extraction have gradually become an effective way to control mine gas disasters. It not only reduces construction costs and ensures safe production, but also realizes the advanced control of mine gas, providing technical support for the rapid pre-extraction and elimination of gas outbursts in mine working faces and ensuring the continuity of coal mine mining.

[0003] The surface extraction technology has gradually shifted from the initial vertical well extraction to the horizontal well enhanced extraction. At the same time, with the development of fracturing production enhancement technology, the fracturing fracture mechanism has gradually changed from the long fracture fracturing theory to the volume fracturing technology of complex network fractures. The surface horizontal well extraction methods currently proposed have the following main defects: (1) The horizontal well location deployment and coal mine working face planning are not closely integrated, which cannot effectively solve the coal mine working face gas extraction problem and seriously affect the working face mining planning; (2) The horizontal section length of a single horizontal well is short and cannot fully cover the surface gas extraction demand of the entire working face. It is often necessary to design more than two surface horizontal wells to solve the surface gas extraction demand of the entire working face, which increases the construction investment and subsequent management costs; (3) The horizontal well extraction trajectory is difficult to control, and it is not suitable for soft coal seams, especially broken soft low permeability coal seams. When drilling between 0 and 2 meters above the coal seam roof, the wellbore trajectory is far away from the coal seam, which is not conducive to the expansion of the fracturing crack through the layer to connect the wellbore and the lower coal seam; (4) The control range of the single-stage fracturing crack in the horizontal well is limited, and there is a blind spot for gas extraction, which causes the risk of gas outburst during the mining process of the coal mine working face; (5) Conventional mechanical bridge plug segmented fracturing tools need to be lowered into the milling string after fracturing to drill and mill the bridge plug uniformly. The construction steps are complicated, the cycle is long, the cost is high, and there are certain construction risks; (6) The surface extraction production decays quickly and the stable production time is short, resulting in problems such as low gas production per well and low surface gas extraction rate. Summary of the Invention

[0004] In response to the defects and shortcomings in the existing technology, the present invention provides a method for advanced pre-extraction of gas based on full coverage of working face gas by ground horizontal wells, so as to solve the technical problem in the existing technology that it is impossible to achieve effective full coverage of coal mine working face gas and advanced pre-extraction of gas by ground horizontal wells through a single horizontal well.

[0005] In order to achieve the above object, the present invention adopts the following technical solutions:

[0006] The advanced pre-drainage method based on the enhanced drainage of ground horizontal wells with full coverage of working face gas includes the following steps:

[0007] Step 1: Collect exploration data and mine data for the fully covered gas extraction area of ​​the working face, and determine the layout layer of the horizontal section of the U-shaped distal docking horizontal well group arranged along the working face based on the collected data;

[0008] Wherein, the U-shaped distally connected horizontal well group includes a drainage and production vertical well and a directional horizontal well, and the horizontal connecting section between the drainage and production vertical well and the directional horizontal well is a horizontal section;

[0009] Step 2: constructing a vertical drainage well, and completing the first drilling, second drilling, and cementing of a directional horizontal well connected to the vertical drainage well;

[0010] Step 3: Complete the geosteering drilling while drilling the three-opening horizontal section, and adjust the drilling trajectory in real time during the drilling process so that the wellbore trajectory of the horizontal well is located in the layout layer described in step 1;

[0011] Step 4: Complete the cementing and completion of the entire well section of the directional horizontal well;

[0012] Step 5: Seal the horizontal section in sections, implement mechanical isolation between sections and perform multi-cluster chemical temporary plugging and staged fracturing on the target coal seam to form a three-dimensional volume fracture network;

[0013] Step 6: Perform post-pressure flowback and well flushing operations to achieve communication between the directional horizontal well and the drainage and production vertical well;

[0014] Step 7: Complete the full coverage of ground gas extraction and advance pre-extraction at the working face.

[0015] The present invention also has the following technical features:

[0016] The layout layers of the horizontal section of the U-shaped distal docking horizontal well group described in step 1 specifically include:

[0017] When the coal seam is a soft coal seam, the layout layer of the horizontal section is the coal seam roof;

[0018] When the coal seam is a hard coal seam, the layout layer of the horizontal section is the coal seam.

[0019] Furthermore, the step 3 of adjusting the drilling trajectory in real time during the drilling process so that the drilling trajectory is located in the layout layer described in step 1 specifically includes:

[0020] When the horizontal section is laid out in a coal seam, the drilling trajectory is adjusted based on the drilling data obtained in real time by geosteering logging while drilling to control the horizontal wellbore trajectory in the coal seam;

[0021] When the horizontal section is located at the coal seam roof, drilling data is obtained in real time through geosteering logging while drilling and multi-point coal exploration. Then, the coal exploration spacing, the vertical distance from the coal point to the horizontal plane where the coal exploration side drilling point is located, and the vertical distance from the coal exploration side drilling point to the top of the coal seam are calculated. Based on the calculated results, the drilling trajectory is adjusted in real time to control the vertical distance between the horizontal wellbore trajectory and the top of the coal seam to be 0 to 2 meters.

[0022] Furthermore, the coal exploration interval is determined by the following formula:

[0023]

[0024] Where:

[0025] L is the coal exploration distance, in m;

[0026] S i is the drilling depth of the i-th drilling point during the side drilling coal exploration process, in meters, and i is a positive integer;

[0027] α i is the well inclination angle of the i-th drilling point during sidetracking coal exploration, in degrees;

[0028] n is the number of drilling points in the side drilling coal exploration process, and n is a positive integer greater than 1.

[0029] Furthermore, the vertical distance from the coal-seeking point to the horizontal plane where the coal sidetracking point is located is calculated by the following formula:

[0030]

[0031] Where:

[0032] H B It is the vertical distance from the coal point to the horizontal plane where the coal exploration side drilling point is located, in meters;

[0033] S i is the drilling depth of the i-th drilling point during the side drilling coal exploration process, in meters, and i is a positive integer;

[0034] α i is the well inclination angle of the i-th drilling point during sidetracking coal exploration, in degrees;

[0035] n is the number of drilling points in the side drilling coal exploration process, and n is a positive integer greater than 1.

[0036] Furthermore, the vertical distance from the coal exploration sidetracking point to the top boundary of the coal seam is determined by the following formula:

[0037] When the coal seam roof is a downward-dipping coal seam roof,

[0038] H A =H B -Ltanβ

[0039] When the coal seam roof is an up-dip coal seam roof,

[0040] H A =H B +Ltanβ

[0041] Where:

[0042] H A It is the vertical distance between the side drilling point and the top of the coal seam, in meters;

[0043] H B It is the vertical distance from the coal point to the horizontal plane where the coal exploration side drilling point is located, in meters;

[0044] L is the coal exploration distance, in m;

[0045] β is the apparent dip of the coal seam, in degrees.

[0046] Furthermore, the three-opening full-well section cementing and completion of the directional horizontal well described in step 4 includes: when the horizontal section of the directional horizontal well is a long horizontal section with a large vertical-to-horizontal ratio, a combined cementing string including a horizontal well rotary guide shoe, an anti-channeling string, and a floating joint collar is run into the horizontal well to perform three-opening full-well section cementing and completion of the horizontal well.

[0047] Furthermore, the inter-stage mechanical isolation and staged fracturing construction described in step 5 uses a low-temperature soluble fracturing bridge plug that can withstand a pressure of 70 MPa and can be completely dissolved within 144 hours.

[0048] Furthermore, in the intra-segment multi-cluster chemical temporary plugging fracturing construction described in step 5, the amount of water-soluble temporary plugging agent used in the fracturing crack opening is determined by the following formula:

[0049] G=0.0412×πH(d×Δd+Δd 2 )×ρ 视 ×(l+k)

[0050] Where:

[0051] G is the amount of water-soluble temporary plugging agent used for fracturing cracks, in kg;

[0052] H is the length of the perforation section, in m;

[0053] d is the outer diameter of the casing, in cm;

[0054] Δd is the filter cake thickness in cm;

[0055] ρ 视 The apparent density of the water-soluble temporary plugging diversion agent for seam openings is g / cm 3 ;

[0056] k is the ratio of embedded cracks, in %.

[0057] Furthermore, in the staged fracturing construction described in step 5, the fracturing fluid is active water fracturing fluid, the proppant is quartz sand, and the sand addition strength of the fracturing section is 10 to 20 m 3 / m, injection displacement is 10~16m 3 / min, average sand ratio is 10-15%, and pre-fluid ratio is greater than or equal to 40%;

[0058] When the horizontal section is located in a coal seam, the perforation before fracturing is to perform multi-cluster directional perforation in the horizontal direction of the coal seam. The operation parameters include: 89-type perforating gun, 102-type perforating charge, perforation density of 10 holes / meter, and perforation phase angles of 45° and 135° horizontally.

[0059] When the horizontal section is located at the coal seam roof, the perforation before fracturing is carried out by performing multi-cluster directional perforation vertically downward from the coal seam roof. The construction parameters include: 89-type perforating gun, 102-type perforating bullet, 10 holes / m perforation density, and 90° vertically downward perforation phase angle.

[0060] Compared with the prior art, the present invention has the following beneficial technical effects:

[0061] (1) The method of the present invention closely combines the layout of horizontal wells with the planning of coal mine working faces, and can achieve the goal of a single horizontal well group completely covering the ground gas extraction needs of the entire working face, ensuring the precise control of the horizontal section eye trajectory of the horizontal well. It not only effectively solves the gas disaster problem of the coal mine working face, ensures the mining and excavation succession and safe production of the mine, reduces construction investment and subsequent management costs, and thus effectively ensures the high yield, stable production and high extraction rate of the horizontal well.

[0062] (2) In the method of the present invention, the horizontal section wellbore trajectory in the soft coal seam, especially the broken soft low-permeability coal seam, is controlled to be between 0 and 2 m away from the coal seam roof. Through the geological guidance logging while drilling and multi-point coal exploration wellbore trajectory control, the distance between the wellbore trajectory and the coal seam roof is ensured to be accurately controlled, which is conducive to the subsequent fracturing cracks penetrating the layer to connect the wellbore and the lower coal seam.

[0063] (3) The combined cementing string structure used in the cementing method of the present invention can effectively ensure the cementing quality of the entire horizontal well section and provide protection for subsequent fracturing operations.

[0064] (4) The method of the present invention adopts a segmented fracturing process that combines mechanical isolation between segments with temporary chemical plugging of multiple clusters within the segment, which is conducive to achieving the dense volume fracturing transformation effect of horizontal wells and forming a three-dimensional volume fracture network, thereby achieving gas extraction without blind spots in the coal mine working face and ensuring safe mining of the coal mine working face.

[0065] (5) The present invention adopts a low-temperature soluble fracturing bridge plug made of coalbed methane, which can reduce the drilling and milling process after fracturing, shorten the construction period, and reduce the construction cost and risk. BRIEF DESCRIPTION OF THE DRAWINGS

[0066] Figure 1 This is a construction flow chart of the present invention;

[0067] Figure 2 This is a schematic diagram of the wellbore trajectory control for geosteering logging while drilling + multi-point coal exploration;

[0068] Figure 3 This is a schematic diagram of the relationship between the side drilling coal positions in the down-dip coal seam;

[0069] Figure 4 (a) is the fracture distribution diagram of multi-cluster general fracturing in horizontal wells;

[0070] Figure 4 (b) Fracture distribution diagram of multi-cluster chemical temporary plugging volume fracturing in horizontal wells;

[0071] Figure 5 This is the effect diagram of multi-cluster chemical temporary plugging and staged fracturing in horizontal wells;

[0072] Figure 6 (a) Schematic diagram of the coverage of conventional horizontal well fracturing and extraction;

[0073] Figure 6 (b) is a schematic diagram of the coverage of the temporary plugging and fractured horizontal well enhanced extraction according to the present invention;

[0074] Figure 7 This is a comparison chart of the extraction effects of a conventional fractured horizontal well and a temporary plugging fractured horizontal well according to the present invention.

[0075] 1-coal seam roof, 2-coal seam, 3-directional horizontal well, 4-drainage vertical well, 5-horizontal section, 6-coal exploration branch hole, 7-horizontal wellhead, 8-horizontal well landing point, 9-drainage vertical wellhead, 10-working face, 11-tunnel, 12-bridge plug, 13-hydraulic fracturing fracture, 14-fracture gas extraction area, 15-gas extraction blind area, 16-secondary fractures formed by temporary plugging and fracturing; A-coal exploration side drilling point; B-coal sighting point. DETAILED DESCRIPTION

[0076] The embodiments described below are only some of the embodiments of the present invention, not all of the embodiments, and do not limit the present invention in any form. Any technical solution that utilizes this embodiment, including simple changes to this embodiment, falls within the scope of protection of the present invention.

[0077] The technical terms involved in the present invention are explained as follows:

[0078] U-shaped remote-end docking horizontal well group: includes a drainage and production vertical well and a directional horizontal well. The horizontal connecting section between the drainage and production vertical well and the directional horizontal well is the horizontal section.

[0079] Soft coal seam: A coal seam with a solidity coefficient of less than 1.0 is a soft coal seam; a coal seam with a solidity coefficient of 0.1 to 0.5 and a permeability coefficient of 10 -3 ~10m 2 / MPa 2 .d (equivalent to a permeability of 2.5×10 -5 ~2.5×10 -1 The coal seam of mD) is a broken, soft and low-permeability coal seam.

[0080] Hard coal seam: A coal seam with a solidity coefficient ≥1.0 is a hard coal seam.

[0081] Full coverage gas extraction from the working face: For gas control in coal mine working faces, through ground horizontal well drilling and intensive volume fracturing transformation, full coverage gas extraction based on the coal mine working face is achieved to achieve no gas extraction blind spots in the working face.

[0082] Drilling distance: the distance from the drill bit to the coal-rock interface along the drilling direction.

[0083] Vertical distance: the vertical distance from the drill bit to the coal-rock interface.

[0084] Horizontal well vertical ratio: the ratio of the horizontal projection length of a horizontal well to its vertical depth.

[0085] Inter-segment mechanical isolation: Applicable to casing cementing completion methods, mechanical isolation is used in the horizontal section of the horizontal well casing to achieve segmented fracturing. Mechanical isolation segmented fracturing of horizontal wells is to use bridge plugs to seal and isolate the wellbore in the horizontal well section, and then implement perforation fracturing to form multiple artificial fractures, thereby improving the productivity of a single well.

[0086] Intra-segment multi-cluster chemical temporary plugging fracturing: After the horizontal well casing is mechanically isolated to achieve intra-segment isolation, multi-cluster perforation is performed within the segment. The perforation segment at the lowest stress is first fractured to form a fracturing crack. Then, a chemical temporary plugging agent is added to plug the crack opened in the early stage. The fracturing is continued to open new fracturing cracks, making the fracturing cracks more complex and forming a volume fracturing crack effect, thereby increasing the discharge area and improving the degree of reservoir transformation.

[0087] Side drilling for coal exploration: During the geological guidance drilling while drilling in the horizontal section of a horizontal well, in order to accurately control the wellbore trajectory, the coal seam position is detected by side drilling downward by lowering the wellbore.

[0088] The present invention will be described in detail below with reference to the accompanying drawings and specific embodiments.

[0089] Example

[0090] In accordance with the above technical solution, the following specific embodiments of the present invention are given. It should be noted that the present invention is not limited to the following specific embodiments, and all equivalent modifications made on the basis of the technical solution of this application fall within the scope of protection of the present invention. The present invention is further described in detail below with reference to the embodiments.

[0091] like Figure 1 As shown, this embodiment provides a method for enhanced extraction and advance pre-extraction based on a horizontal well with full coverage of working face gas, the method comprising the following steps:

[0092] Step 1: Collect exploration data and mine data for the full gas extraction coverage area of ​​the working face. Based on the collected data, determine the layout layer of the horizontal section of the U-shaped distal docking horizontal well group arranged along the working face. Closely integrating the layout of the horizontal wells with the planning of the coal mine working face can achieve the surface gas extraction requirement of fully covering the entire working face with a single horizontal well group.

[0093] The exploration data collected in this embodiment include the lithology, thickness, burial depth, natural gamma, and resistivity of the coal seam and its roof.

[0094] Wherein, the U-shaped distally connected horizontal well group includes a drainage and production vertical well and a directional horizontal well, and the horizontal connecting section between the drainage and production vertical well and the directional horizontal well is a horizontal section;

[0095] When the coal seam is a soft coal seam, especially a broken, soft and low-permeability coal seam, in order to ensure effective drilling of the horizontal section and to consider that the migration of gas and water in the later drainage process is not affected by coal powder blockage, the layout layer of the horizontal section is the coal seam roof. The horizontal section is arranged in the coal seam roof. The hydraulic fracture can be extended through the interface between the coal seam and the coal seam roof, thereby communicating with the coal seam below and providing a channel for coalbed methane to enter the wellbore.

[0096] When the coal seam is a hard coal seam, the layout layer of the horizontal section is the coal seam.

[0097] Step 2: constructing a vertical drainage well, and completing the first drilling, second drilling, and cementing of a horizontal well connected to the vertical drainage well;

[0098] Step 3: Complete the geosteering drilling while drilling the three-opening horizontal section, and adjust the drilling trajectory in real time during the drilling process so that the wellbore trajectory of the horizontal well is located in the layout layer described in step 1;

[0099] like Figure 2 As shown, in this embodiment, the geosteering logging while drilling technology is used during the horizontal section drilling process to monitor the resistivity and natural gamma and other parameters of the horizontal section rock formation in real time. At the same time, the information such as rock cuttings, drilling time and gas logging and the three-dimensional geological model data such as burial depth, natural gamma and resistivity established in the early stage are combined to ensure the precise control of the horizontal section wellbore trajectory to the greatest extent.

[0100] As a preferred solution of this embodiment, when the horizontal section is arranged in a coal seam, the drilling trajectory is adjusted according to the drilling data obtained in real time by the geosteering logging while drilling, so as to control the horizontal wellbore trajectory in the coal seam;

[0101] When the horizontal section is located in the coal seam roof, real-time drilling data is acquired through geosteering logging while drilling and multi-point coal exploration. The team then calculates the coal exploration spacing, the vertical distance from the coal point to the horizontal plane containing the coal exploration sidetracking point, and the vertical distance from the coal exploration sidetracking point to the coal seam top. Based on these calculations, the drilling trajectory is adjusted in real time to maintain a vertical distance between the horizontal wellbore trajectory and the coal seam top of 0 to 2 meters. Precise control of the distance between the wellbore trajectory and the coal seam top facilitates the subsequent propagation of fractures through the layers, connecting the wellbore and the underlying coal seam.

[0102] In this embodiment, when the layout layer of the horizontal section is the coal seam roof, on the basis of the geological guidance logging while drilling, the top boundary of the coal seam is explored by multiple well inclination reductions, and the coal exploration spacing, the vertical distance from the coal point to the horizontal plane where the coal exploration side drilling point is located, and the vertical distance from the coal exploration side drilling point to the top boundary of the coal seam are calculated. The drilling trajectory is adjusted in real time according to the calculated results to achieve the purpose of accurately controlling the horizontal wellbore trajectory.

[0103] like Figure 3 As shown, during the process of drilling the down-dip coal seam roof, side drilling is performed to explore the coal and control the wellbore trajectory. From the side drilling point A, the well is lowered to the coal point B to encounter the coal seam. The coal exploration spacing L and the vertical distance H between the side drilling point A and the top boundary of the coal seam are determined. A , according to the coal exploration spacing L and the vertical distance H between the coal exploration side drilling point A and the top boundary of the coal seam A To adjust the horizontal wellbore trajectory in real time.

[0104] Specifically include:

[0105] The coal exploration spacing is determined by the following formula:

[0106]

[0107] Where:

[0108] L is the coal exploration distance, in m;

[0109] S i is the drilling depth of the i-th drilling point during the side drilling coal exploration process, in meters, and i is a positive integer;

[0110] α i is the well inclination angle of the i-th drilling point during sidetracking coal exploration, in degrees;

[0111] n is the number of drilling points in the side drilling coal exploration process, and n is a positive integer greater than 1.

[0112] As a preferred solution of this embodiment, the vertical distance from the coal-viewing point to the horizontal plane where the coal exploration sidetracking point is located is calculated by the following formula:

[0113]

[0114] Where:

[0115] H B It is the vertical distance from the coal point to the horizontal plane where the coal exploration side drilling point is located, in meters;

[0116] S i is the drilling depth of the i-th drilling point during the side drilling coal exploration process, in meters, and i is a positive integer;

[0117] α i is the well inclination angle of the i-th drilling point during side drilling coal exploration, in degrees;

[0118] n is the number of drilling points in the side drilling coal exploration process, and n is a positive integer greater than 1.

[0119] As a preferred solution of this embodiment, the vertical distance from the coal exploration sidetracking point to the top boundary of the coal seam is determined by the following formula:

[0120] When the coal seam roof is a downward-dipping coal seam roof,

[0121] H A =H B -Ltanβ

[0122] When the coal seam roof is an up-dip coal seam roof,

[0123] H A =H B +Ltanβ

[0124] Where:

[0125] H A It is the vertical distance between the side drilling point and the top of the coal seam, in meters;

[0126] HB It is the vertical distance from the coal point to the horizontal plane where the coal exploration side drilling point is located, in meters;

[0127] L is the coal exploration distance, in m;

[0128] β is the apparent dip of the coal seam, in degrees.

[0129] When H A In the range of 0 to 2 m, the drill bit is withdrawn to the sidetracking point and normal directional drilling is continued along the original drilling direction.

[0130] When H A When the drilling depth is >2m, the drill bit is withdrawn to the horizontal section trajectory of 0 to 2m from the top boundary of the coal seam in front of the side drilling point, and the wellbore is lowered and directional drilling is carried out forward on the basis of the original drilling trajectory, and the horizontal section trajectory is adjusted to be controlled within the vertical distance range of 0 to 2m from the top boundary of the coal seam.

[0131] Step 4: Complete the cementing and completion of the entire well section of the directional horizontal well;

[0132] As a preferred solution of this embodiment, during cementing, for horizontal sections with large vertical-to-horizontal ratios, a combined cementing string should be run in when cementing directional horizontal wells. The combined cementing string string includes, in sequence: a rotary guide shoe (drillable) + an anti-channeling string (short casing + drillable blind plug + external packer + long casing + screen + float collar (drillable) + check valve + shut-in valve) + casing string + floating joint collar + casing string + jointing joint. The rotary guide shoe at the front end of the cementing string is run to a point 0 to 0.5 m from the docking point between the horizontal well and the vertical well at the end of the rotary guide shoe. The adopted combined cementing string structure can effectively ensure the cementing quality of the entire horizontal well section and provide protection for subsequent fracturing operations.

[0133] The rotary guide shoe changes the flow pattern of the bottomhole drilling fluid by rotating, reducing friction during casing installation, improving the drilling fluid's cuttings-carrying capacity, preventing insertion into the formation, and resolving problems such as wellbore shrinkage and formation collapse, effectively improving casing running efficiency. The anti-channeling cementing string prevents cement slurry from entering the vertical wellbore cavity. The casing is designed with a blind plug to prevent cement slurry from entering the vertical wellbore cavity. An external packer is designed outside the casing to isolate the annulus outside the casing, preventing cement slurry from entering the vertical wellbore cavity. A floating collar ensures the safe running of casing in horizontal wells with long vertical-to-horizontal ratios. By adding a floating collar to the casing string, the buoyancy of the air or low-density drilling fluid trapped between the floating collar and the casing shoe is utilized during the early stages of casing running to reduce friction between the wellbore wall and the casing during running, thereby achieving safe casing running. After the casing is lowered into the rear section, the casing above the floating coupling is filled with mud (weighted mud) to make the vertical section of the casing as heavy as possible, thereby increasing the thrust of the casing's own weight on the lower casing and ensuring that the casing is safely lowered to the predetermined position. The drillable blind plug is used to isolate the passage between the casing and the vertical wellbore, preventing cement slurry from entering the vertical wellbore from the casing; the external packer is used to isolate the outer annulus of the casing after being lowered to a position near the docking point, preventing the cement slurry in the outer annulus of the casing from communicating with the docking well; the casing short section is connected to a drillable one-way valve and a shut-in valve at both ends to prevent the cementing liquid from flowing back through the one-way valve and the shut-in valve; the screen is used as a cement slurry passage between the inner and outer annuli of the casing.

[0134] Step 5: Separately isolate the horizontal section, implement mechanical isolation between sections and implement multi-cluster chemical temporary plugging and staged fracturing on the target coal seam to achieve intensive volume fracturing stimulation of the horizontal well and form a three-dimensional volume fracture network;

[0135] During the fracturing construction process, the horizontal section is segmented and isolated, and mechanical isolation between segments and multi-cluster chemical temporary plugging segmented fracturing construction is implemented towards the coal seam to achieve the effect of intensive volume fracturing transformation of the horizontal well and form a three-dimensional volume fracture network.

[0136] When the horizontal section is located in a coal seam, the perforation before fracturing is to perform multi-cluster directional perforation in the horizontal direction of the coal seam. The operation parameters include: 89-type perforating gun, 102-type perforating charge, perforation density of 10 holes / meter, and perforation phase angles of 45° and 135° horizontally.

[0137] When the horizontal section is located at the coal seam roof, the perforation before fracturing is carried out by performing multi-cluster directional perforation vertically downward from the coal seam roof. The construction parameters include: 89-type perforating gun, 102-type perforating bullet, 10 holes / m perforation density, and 90° vertically downward perforation phase angle.

[0138] The fracturing construction parameters during the fracturing construction process include: the fracturing fluid is active water fracturing fluid, the proppant is quartz sand, and the sand addition strength of the fracturing section is 10-20m 3 / m, injection displacement is 10~16m 3 / min, the average sand ratio is 10-15%, and the pre-fluid ratio is greater than or equal to 40%.

[0139] The backward fracturing method is used to complete the volume fracturing transformation of the entire horizontal well section step by section until the fracturing construction of the entire well section is completed.

[0140] As a preferred solution of this embodiment, a low-temperature soluble fracturing bridge plug capable of withstanding a pressure of 70 MPa and completely dissolving within 144 hours is employed in interstage mechanical isolation fracturing. Compared to conventional horizontal well mechanical bridge plug staged fracturing, this low-temperature soluble bridge plug is primarily made of a soluble magnesium alloy. Under conditions of a 1% KCl active water fracturing solution at 30°C, it can withstand a pressure of 70 MPa and completely dissolve within 144 hours. It features post-fracturing dissolution, a large drift diameter, low residue, and the elimination of drill plugs.

[0141] like Figure 4 and Figure 5 As shown in the figure, compared with conventional horizontal well fracturing and extraction technology, the inter-stage mechanical isolation + intra-stage multi-cluster chemical temporary plugging staged fracturing technology can achieve the effect of intensive volume fracturing transformation of horizontal wells, which is conducive to achieving the effect of intensive volume fracturing transformation of horizontal wells.

[0142] like Figure 6 As shown in the figure, compared with the fracturing and extraction coverage of conventional horizontal wells, the multi-cluster chemical temporary plugging segmented fracturing construction within the segment adopts a high-strength, degradable, low-temperature, water-soluble chemical temporary plugging agent suitable for the low-temperature and low-pressure (temperature ≤ 30°, pressure ≤ 25 MPa) reservoir characteristics of coalbed methane. The chemical temporary plugging agent is used to temporarily plug the cracks at the fracture mouth and within the fracture, forming new main fractures and branch fractures within the fracture, thereby forming a complex network of fractures and obtaining a larger transformation volume, thereby achieving gas extraction without blind spots in the coal mine working face and ensuring safe production of the coal mine working face.

[0143] Among them, the calculation formula for the amount of chemical temporary plugging agent for seam opening is:

[0144] G=0.0412×πH(d×Δd+Δd 2 )×p 视 ×(1+k)

[0145] Where:

[0146] G is the dosage of temporary sealing agent for seam opening, in kg;

[0147] H is the length of the perforation section, in m;

[0148] d is the outer diameter of the casing, in cm;

[0149] Δd is the filter cake thickness, in cm;

[0150] ρ 视 The apparent density of the water-soluble temporary plugging diversion agent for seam openings is g / cm 3 ;

[0151] k is the ratio of embedded cracks, in %.

[0152] The calculation formula for pumping displacement during chemical temporary plugging agent injection construction is:

[0153]

[0154] Where:

[0155] V s Temporary plugging agent pumping displacement, unit is m 3 / min;

[0156] ρ p is the density of the particle in g / cm 3 ;

[0157] P f is the density of the body in g / cm 3 ;

[0158] g is the acceleration due to gravity, in m / s 2 ;

[0159] μ is the viscosity of the liquid, in Pa·s;

[0160] d p is the diameter of the particle, in mm.

[0161] Step 6: Perform post-pressure flowback and well flushing operations to achieve communication between the directional horizontal well and the drainage and production vertical well;

[0162] Specifically include:

[0163] After completing the staged fracturing construction, the well is opened to the vertical well section, and clean water with a volume 1.5 times that of the horizontal wellbore is circulated for well washing operations to achieve communication between the horizontal well and the vertical well for drainage and production, ensuring the channel for gas and water migration during the later drainage and production period;

[0164] Perform circulating well washing operations on the horizontal wellbore and observe the return fluid at the outlet until the water quality at the inlet and outlet is consistent and the outlet liquid is clean and free of impurities and dirt, then stop the well washing operation.

[0165] Step 7: Complete full coverage of ground gas extraction and advance pre-extraction to ensure safe production of the coal mine working face.

[0166] This embodiment uses intelligent and refined drainage and gas production technology to achieve "slow, controlled, and stable" drainage and gas production. This technology enables real-time monitoring, intelligent identification, data collection, remote transmission, and remote automatic control, effectively ensuring high and stable production and high extraction rates in horizontal wells. This allows for full-coverage, ground-based, enhanced gas extraction and advanced pre-extraction from the working face, ensuring safe production at the coal mine working face.

[0167] Application Example 1:

[0168] In accordance with the above technical solution, in this embodiment, the target mining area is a mining area in Huaibei. The Huaibei mining area has developed Carboniferous and Permian coal measures, with many coal seams, and most of them are medium-thick coal seams. The mining area is a high-gas, double-burst mine. The No. 8 coal seam in the mining area is generally soft, strong, poorly permeable, high in gas content, and high in gas pressure. The investment cost of underground gas extraction is high, the extraction time is long, and the construction risk is high. With the development of mines and the expansion of mining scale, gas disasters have seriously affected the mining and excavation succession and safe production of mines. The traditional underground through-layer drilling pre-extraction of regional coal seam gas measures can no longer fully meet the needs of coal mine safety production.

[0169] Therefore, a method based on full coverage of working face gas and enhanced pre-extraction by ground horizontal wells is adopted. Through a single horizontal well, effective full coverage of coal mine working face gas and enhanced pre-extraction by ground horizontal wells are achieved, thereby ensuring safe production in coal mines.

[0170] Step 1: Since the coal seam has a solidity coefficient of approximately 0.32 and a permeability of 0.02 to 0.08 mD, indicating a typical crushed, soft, and low-permeability coal seam, the horizontal section of the U-shaped distally docked horizontal well group laid along the working face is located at the roof of the down-dip coal seam. The vertical distance between the horizontal wellbore trajectory and the top boundary of the down-dip coal seam is controlled to be 0 to 2 m.

[0171] A U-shaped distally connected horizontal well group is used, including a drainage and production vertical well and a directional horizontal well, and the horizontal connecting section between the drainage and production vertical well and the directional horizontal well is a horizontal section.

[0172] Step 2: Construct a vertical well for drainage and production. In this application example, the vertical well adopts a two-wellbore structure. The second drilling is completed to a position 50m below the coal seam, with a completed well depth of 850m. After drilling is completed, a large-diameter production casing with a diameter of 177.8mm is run and cemented. A fiberglass reinforced plastic casing is run at 767.05-774.95m at the top boundary of the 8th coal seam. To facilitate docking with the horizontal well, a hole is expanded and created at 770-773.5m with a hole diameter of 0.5m.

[0173] Step 3: Complete geosteering while drilling the horizontal section of the third spud. Before landing the second spud, construct an inclined pilot well to detect the coal seam position to achieve precise control of the landing point during horizontal drilling of the horizontal well. After determining the guide layer position, fill the pilot well. After sidetracking to the landing point, install 244.5mm diameter casing and cement the well. The second spud is completed and the well is drilled to a depth of 930 meters.

[0174] The 8th coal seam is buried at a depth of 770m. The horizontal well layout covers the entire working face length of 1500m. The second opening and deflection radius is 280m. The third opening and completion depth of the horizontal well is 2430m. The horizontal well position-vertical ratio reaches 2.3:1.

[0175] During the three-step drilling of the horizontal well, the drilling data was obtained in real time by using the LWD geosteering logging + multi-point coal exploration wellbore trajectory control technology to adjust the horizontal wellbore trajectory in real time. When the drilling trajectory reached 1300m (point A), side drilling was carried out to explore the coal. The side drilling branched out at 1380m (point B) and explored the 8-coal roof. According to the LWD drilling data, the coal exploration spacing L was 78m and H was 1. B The vertical distance H from the side drilling point A to the top of the coal seam is calculated to be 5.9m. At this time, the apparent inclination angle of the coal seam drilled in the downward direction of the coal seam is 2°. A The drill bit is adjusted to be withdrawn to 1250m and the well is lowered and directional drilling is carried out forward, and the horizontal section trajectory is controlled within the vertical distance range of 0 to 2m from the top boundary of the coal seam.

[0176] Step 4: Complete the cementing and completion of the three-well full-well section of the directional horizontal well with a long horizontal section and a large vertical ratio;

[0177] In this application example, since the horizontal well has a vertical-to-vertical ratio of 2.3:1, the technical issues of casing and full-well cementing in horizontal wells with large vertical-to-vertical ratios are addressed. By optimizing the cementing string, a combined cementing string consisting of a rotary guide shoe, anti-channeling string, and a floating collar is run into the horizontal well to complete the three-stage cementing and completion of the full-well section of the horizontal well.

[0178] Step 5: Using large-scale, high-volume fracturing technology; during the fracturing process, the horizontal section is segmented and isolated, mechanical isolation between segments is implemented toward the coal seam, and multi-cluster chemical temporary plugging and segmented fracturing is performed within the segment;

[0179] The horizontal well was completed at a depth of 2,430 m with a 1,500-m horizontal section. The fracturing stages were spaced 75 m apart, with three temporary plugging perforation clusters within each section, approximately 20 m apart. A total of 60 fracturing clusters were performed in 20 sections of the horizontal well.

[0180] Perforating parameters were selected as follows: perforating gun type 89, perforating charge type 102, perforating density 10 holes / m, perforating phase angle vertically downward; 3 clusters of perforations were perforated in each section, and each cluster had a perforation area of ​​2 m.

[0181] Fracturing parameter selection: The fracturing fluid is active water fracturing fluid, the fracturing fluid formula is: clean water + 1% KCl + 0.05% fungicide, the proppant is quartz sand, and the sand addition intensity of the fracturing section is 100m 3 / section, injection displacement is 14m 3 / min, the average sand ratio is about 12%, and the pre-fluid ratio is 40%.

[0182] During staged fracturing, low-temperature soluble fracturing bridge plugs are used as isolation between fracturing stages. At 30°C and using a 1% KCl active water fracturing solution, they can withstand a pressure of 70 MPa and dissolve completely within 144 hours. Using a pullback fracturing method, volumetric fracturing stimulation is completed stage by stage throughout the entire horizontal well until the entire well is fully fractured.

[0183] The intra-segment multi-cluster chemical temporary plugging fracturing technology uses high-strength, degradable, low-temperature, water-soluble chemical temporary plugging agents to temporarily plug the cracks at the fracture mouth and within the fractures, forming new main fractures and branch fractures within the fractures, thereby forming a complex network of fractures and obtaining a larger reconstruction volume.

[0184] The dosage of water-soluble chemical temporary plugging agent for seam opening is calculated by the formula: H = 3m, d = 13.9cm, Δd = 13cm, ρ 视 =1.2g / cm 3 , k = 60%. A low-temperature water-soluble chemical temporary plugging agent at 30°C was selected. The joint temporary plugging agent combination mainly consisted of particles of 1-3 mm and 3-5 mm. The temporary plugging agent ratio was 1:1. The calculated dosage of temporary plugging agent for each cluster of joints perforated was 260 kg.

[0185] The temporary plugging agent combination in the seam is mainly composed of 20-60 mesh and 1-3mm particle size, the temporary plugging agent ratio is 1:2, the temporary plugging agent dosage is 300kg, and the optimized water-soluble chemical temporary plugging agent pumping displacement is 1.0-2.5m 3 / min. Post-fracturing crack monitoring: The half-length of the main fracture is 120m, and branch fractures are formed within the fracture, which can achieve full gas coverage of the working face. Figure 6 -b as shown.

[0186] Step 6: After the staged fracturing construction, flowback and well washing operations are carried out to achieve communication between the horizontal well and the vertical well for drainage and production, ensuring the channel for gas and water migration during the later drainage and production period;

[0187] Step 7: Complete the advanced pre-extraction of ground-enhanced gas extraction at the working face.

[0188] Install screw pump drainage and production devices and intelligent drainage and production equipment to carry out "slow, controlled and stable" intelligent and refined drainage and gas production, and realize the advanced pre-extraction of ground gas intensification at the working face.

[0189] like Figure 7As shown, in the Huaibei mining area of ​​this application example, conventional surface horizontal well fracturing and extraction and surface horizontal well enhanced extraction engineering practices using the method of the present invention were carried out, and the same number of fracturing operations were carried out within the same working face range. The results showed that the maximum gas production of a single surface horizontal well using the method of the present invention was twice the maximum gas production of a single surface horizontal well using conventional fracturing, achieving good extraction effects.

[0190] The method of the present invention not only effectively solves the problem of gas disasters in coal mine working faces, ensures mining and excavation succession and safe production in mines, reduces construction investment and subsequent management costs, but also effectively ensures high production, stable production and high extraction rate of horizontal wells.

[0191] The preferred embodiments of the present disclosure are described in detail above in conjunction with the accompanying drawings. However, the present disclosure is not limited to the specific details of the above embodiments. Within the technical concept of the present disclosure, various simple modifications can be made to the technical solutions of the present disclosure, and these simple modifications all fall within the scope of protection of the present disclosure.

[0192] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any appropriate manner without contradiction. In order to avoid unnecessary repetition, the present disclosure will not further describe various possible combinations.

[0193] In addition, the various embodiments of the present disclosure may be arbitrarily combined, and as long as they do not violate the concept of the present disclosure, they should also be regarded as the contents disclosed by the present disclosure.

Claims

1. Based on the advanced pre-extraction method of enhanced extraction of gas from horizontal wells with full coverage of working face, the method is characterized by: The method comprises the following steps: Step 1: Collect exploration data and mine data for the fully covered gas extraction area of ​​the working face, and determine the layout layer of the horizontal section of the U-shaped distal docking horizontal well group arranged along the working face based on the collected data; Wherein, the U-shaped distally connected horizontal well group includes a drainage and production vertical well and a directional horizontal well, and the horizontal connecting section between the drainage and production vertical well and the directional horizontal well is a horizontal section; Step 2: constructing a vertical drainage well, and completing the first drilling, second drilling, and cementing of a directional horizontal well connected to the vertical drainage well; Step 3: Complete the geosteering drilling while drilling the three-opening horizontal section, and adjust the drilling trajectory in real time during the drilling process so that the wellbore trajectory of the horizontal well is located in the layout layer described in step 1; Step 4: Complete the cementing and completion of the entire well section of the directional horizontal well; Step 5: Seal the horizontal section in sections, implement mechanical isolation between sections and perform multi-cluster chemical temporary plugging and staged fracturing on the target coal seam to form a three-dimensional volume fracture network; Step 6: Perform post-pressure flowback and well flushing operations to achieve communication between the directional horizontal well and the drainage and production vertical well; Step 7: Complete the ground-based intensified extraction and pre-extraction of gas from the working face; The step 3 of adjusting the drilling trajectory in real time during the drilling process so that the drilling trajectory is located in the layout layer described in step 1 specifically includes: When the horizontal section is laid out in a coal seam, the drilling trajectory is adjusted based on the drilling data obtained in real time by geosteering logging while drilling to control the horizontal wellbore trajectory in the coal seam; When the horizontal section is located at the coal seam roof, drilling data is acquired in real time through geosteering logging while drilling and multi-point coal exploration. The coal exploration interval, the vertical distance from the coal point to the horizontal plane where the coal exploration sidetracking point is located, and the vertical distance from the coal exploration sidetracking point to the coal seam top are calculated. The drilling trajectory is adjusted in real time based on the calculated results to control the vertical distance between the horizontal wellbore trajectory and the coal seam top to be 0 to 2 meters. The coal exploration spacing is determined by the following formula: Where: L is the coal exploration distance, in m; S i is the drilling depth of the i-th drilling point during the side drilling coal exploration process, in meters, and i is a positive integer; α i is the well inclination angle of the i-th drilling point during sidetracking coal exploration, in degrees; n is the number of drilling points in the side drilling coal exploration process, and n is a positive integer greater than 1.

2. The method for enhanced extraction and pre-extraction of horizontal wells based on full coverage of working face gas according to claim 1, characterized in that: The layout layers of the horizontal section of the U-shaped distal docking horizontal well group described in step 1 specifically include: When the coal seam is a soft coal seam, the layout layer of the horizontal section is the coal seam roof; When the coal seam is a hard coal seam, the layout layer of the horizontal section is the coal seam.

3. The method for enhanced extraction and pre-extraction of horizontal wells based on full coverage of working face gas according to claim 1, characterized in that: The vertical distance from the coal point to the horizontal plane where the coal exploration sidetracking point is located is calculated by the following formula: Where: H B It is the vertical distance from the coal point to the horizontal plane where the coal exploration side drilling point is located, in meters; S i is the drilling depth of the i-th drilling point during the side drilling coal exploration process, in meters, and i is a positive integer; α i is the well inclination angle of the i-th drilling point during sidetracking coal exploration, in degrees; n is the number of drilling points in the side drilling coal exploration process, and n is a positive integer greater than 1.

4. The method for enhanced extraction and pre-extraction of horizontal wells based on full coverage of working face gas according to claim 1, characterized in that: The vertical distance from the coal exploration sidetracking point to the top of the coal seam is determined by the following formula: When the coal seam roof is a downward-dipping coal seam roof, H A =H B -Ltanβ When the coal seam roof is an up-dip coal seam roof, H A =H B +Ltanβ Where: H A It is the vertical distance between the side drilling point and the top of the coal seam, in meters; H B It is the vertical distance from the coal point to the horizontal plane where the coal exploration side drilling point is located, in meters; L is the coal exploration distance, in m; β is the apparent dip of the coal seam, in degrees.

5. The method for enhanced extraction and pre-extraction of horizontal wells based on full coverage of working face gas according to claim 1, characterized in that: The three-well full-section cementing and completion of the directional horizontal well described in step 4 includes: when the horizontal section of the directional horizontal well is a long horizontal section with a large vertical ratio, a combined cementing string including a horizontal well rotary guide shoe, an anti-channeling string, and a floating joint collar is run into the horizontal well to perform three-well full-section cementing and completion of the horizontal well.

6. The method for enhanced extraction and pre-extraction of horizontal wells based on full coverage of working face gas according to claim 1, characterized in that: The inter-stage mechanical isolation and staged fracturing construction described in step 5 uses a low-temperature soluble fracturing bridge plug that can withstand a pressure of 70 MPa and can be completely dissolved within 144 hours.

7. The method for enhanced extraction and pre-extraction of horizontal wells based on full coverage of working face gas according to claim 1, characterized in that: In the intra-segment multi-cluster chemical temporary plugging fracturing construction described in step 5, the amount of water-soluble temporary plugging agent used for the fracturing crack opening is determined by the following formula: G=0.0412×πH(d×Δd+Δd 2 )×ρ 视 ×(1+k) Where: G is the amount of water-soluble temporary plugging agent used for fracturing cracks, in kg; H is the length of the perforation section, in m; d is the outer diameter of the casing, in cm; Δd is the filter cake thickness in cm; ρ 视 The apparent density of the water-soluble temporary plugging diversion agent for seam openings is g / cm 3 ; k is the ratio of embedded cracks, in %.

8. The method for enhanced extraction and pre-extraction of horizontal wells based on full coverage of working face gas according to claim 1, characterized in that: In the staged fracturing construction described in step 5, the fracturing fluid is active water fracturing fluid, the proppant is quartz sand, and the sand addition strength of the fracturing section is 10 to 20 m 3 / m, injection displacement is 10~16m 3 / min, average sand ratio is 10-15%, and pre-fluid ratio is greater than or equal to 40%; When the horizontal section is located in a coal seam, the perforation before fracturing is to perform multi-cluster directional perforation in the horizontal direction of the coal seam. The operation parameters include: 89-type perforating gun, 102-type perforating charge, perforation density of 10 holes / meter, and perforation phase angles of 45° and 135° horizontally. When the horizontal section is located at the coal seam roof, the perforation before fracturing is carried out by performing multi-cluster directional perforation vertically downward from the coal seam roof. The construction parameters include: 89-type perforating gun, 102-type perforating bullet, 10 holes / m perforation density, and 90° vertically downward perforation phase angle.

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