Controllable shock wave-based coalbed methane horizontal well stimulation method

Abstract

A controllable shock wave-based coalbed methane horizontal well stimulation method, comprising: S1: selecting a group of upward directional drilling construction sites in a downhole roadway of a horizontal well service mine, directional drilling target positions being respectively coalbeds (3) directly facing horizontal well perforations (2) at multiple positions from a horizontal well; S2: performing construction drilling on a target at A meters, and determining whether the drilling target enters a fracturing influence range and whether the drilling target is within a horizontal well drainage influence range; if the drilling target is within the fracturing influence range, performing controllable shock wave construction; and if the drilling target is not within the fracturing influence range, re-constructing other target positions until a target position within the fracturing influence range is found, and then stopping; and S3, executing S2, including construction drilling and determination, for each horizontal well perforation until target positions within the fracturing influence range corresponding to all the horizontal well perforations are found, and performing controllable shock wave construction. By means of the method, the production of a coalbed methane well is increased, a seepage channel is further expanded, and the production life of the coalbed methane well is prolonged.

Description

Coalbed Methane Horizontal Well Stimulation Method Based on Controllable Shock Waves Technical Field

[0001] This invention relates to the field of energy extraction, and more particularly to a method for enhancing production in horizontal coalbed methane wells. Background Technology

[0002] Coalbed methane (CBM) hazards pose a significant threat to coal mine safety in my country. With the continuous deepening of mining operations, CBM hazards have become increasingly severe. Furthermore, CBM is a major contributor to the greenhouse effect, with a greenhouse effect more than twenty times that of an equivalent volume of carbon dioxide. Extracting one cubic meter of CBM through drainage methods is equivalent to reducing carbon dioxide emissions by more than twenty cubic meters.

[0003] Currently, given the abundance of coal, scarcity of oil, and limited gas, coalbed methane (CBM) is a byproduct of coal mining. Increasing CBM development is beneficial for energy security. However, coal seams generally suffer from complex geological structures and poor permeability. Despite decades of continuous efforts, CBM production remains below expectations. In soft, low-permeability CBM wells, due to formation confining pressure and the inherent gas pressure of the coal seam, the fractures created by fracturing cannot be sustained, resulting in rapid exhaust decay and low production. While existing technologies include CN107956505A—a method for enhancing permeability in coal mine boreholes based on controllable shock wave technology—the lack of prior investigation during shock testing leads to poor shock effects and continued low production.

[0004] The information disclosed in this background section is intended only to enhance the understanding of the overall background of the invention and should not be construed as an admission or in any way implying that the information constitutes prior art known to those skilled in the art. Summary of the Invention

[0005] The technical problem to be solved by this invention is: how to solve the current problem of rapid decay and low production of coalbed methane.

[0006] The present invention solves the above-mentioned technical problems through the following technical means:

[0007] A method for enhancing coalbed methane production in horizontal wells based on controllable shock waves, comprising N horizontal well perforations in the horizontal section of the surface well, where N is an integer greater than 1, is characterized by the following steps:

[0008] S1: Select a set of upward directional drilling sites in the underground roadway of the horizontal well service mine. The target points of the directional drilling are the coal seams located at the distances from the horizontal well perforation point to the horizontal well, which are A meters, AB meters, A-2B meters, A-3B meters, and A-4B meters.

[0009] S2: First, drill a borehole at the target point A meters away. During the drilling process, determine whether it has entered the fracturing influence range. After the borehole enters the coal seam, determine whether it is within the horizontal well drainage influence range.

[0010] If the borehole target location is within the fracturing influence range, then controlled shock wave construction will be carried out;

[0011] If the target location of the borehole is not within the fracturing influence range, the drilling should be carried out again at the target location of AB meter, A-2B meter, A-3B meter, or A-4B meter until a target location within the fracturing influence range is found and then the drilling stops.

[0012] S3: For each horizontal well perforation, proceed with drilling and judgment according to step S2 until the target location of the fracturing influence range is found in all horizontal well perforations, and then carry out controlled shock wave construction.

[0013] Preferably, in step S2, the drilling method for the target point A meters is as follows: start drilling at a depth of 15-30 meters, install casing and wellhead sealing valve, and inject cement grout into the hole to seal it; after the cement solidifies, start drilling again to a distance of 1.5-2.5 meters from the bottom of the coal seam and end at a distance of 1.5-2.5 meters from the top of the coal seam after the borehole penetrates the coal.

[0014] Preferably, during the construction process, water samples and drill cuttings generated from the borehole are tested and analyzed to determine whether they have entered the fracturing influence range. If fracturing fluid is present in the water sample and fracturing sand is present in the drill cuttings, then they have entered the fracturing influence range. If fracturing fluid is not present in the water sample and fracturing sand is not present in the drill cuttings, then they have not entered the fracturing influence range.

[0015] Preferably, after the borehole enters the coal seam, a fixed-point sealed sample is taken, and the gas content of the coal sample is measured to determine whether it is within the influence range of horizontal well drainage. If the gas content in the coal sample decreases compared with the original gas content of the coal seam, it indicates that it has entered the influence range of horizontal well drainage. If the gas content in the coal sample does not change, it indicates that it has not entered the influence range of horizontal well drainage.

[0016] Preferably, the drilling sequence is as follows: first drill the hole at the target point A meter position; if it is determined that it has entered the fracturing influence range, then carry out controlled shock wave construction.

[0017] If the borehole at target point A meters does not enter the fracturing influence zone, there are two possibilities:

[0018] The first scenario: If it is determined that the coal seam is not within the range of the drainage impact, then the borehole should be redesigned with the target point located in the coal seam within the range of A-2B meters.

[0019] The second scenario: If the area is determined to be within the range of drainage but not within the range of fracturing, the borehole should be redesigned with the target point located within the AB meter range of the coal seam.

[0020] Preferably, after drilling at the target point A-2B meters, if it is determined that the area has entered the fracturing influence range, a controlled shock wave operation is carried out.

[0021] If it does not enter the fracturing influence zone, then there are two possibilities:

[0022] When it is determined that the borehole is not within the range of the impact of drainage, the borehole target point is the coal seam within the range of A-4B meters.

[0023] When it is determined that the area is within the scope of drainage but not within the scope of fracturing, the borehole is redesigned, and the target point of the borehole is located in the coal seam within the range of A-3B meters. The original borehole is then sealed and pressure is measured.

[0024] Preferably, when the borehole at the construction target point AB meters is determined to be within the fracturing influence range, a controllable shock wave construction shall be carried out.

[0025] If it does not enter the fracturing influence zone, then there are two possibilities:

[0026] When it is determined that the borehole is not within the range of the impact of drainage, the borehole target point is the coal seam within the range of A-3B meters.

[0027] When it is determined that the area is within the scope of drainage but not within the scope of fracturing, the borehole is redesigned, the target point of the borehole is the coal seam within the range of A-2B meters, and the original borehole is sealed and pressure is measured.

[0028] Continue drilling at target locations A-3B meters and A-4B meters until the target location within the fracturing influence range is found.

[0029] Preferably, the controlled shock wave construction method is as follows: After drilling, the controlled shock wave generator is sent into the formation where fracturing sand or fracturing fluid has been discovered using a drilling rig. The borehole sealing device is closed, and water is injected into the borehole through a pre-installed pipe. When the controlled shock wave generator detects that the water pressure has reached the set value, the shock wave operation is carried out.

[0030] Preferably, after the shock wave construction corresponding to a horizontal well perforation is completed, the changes in drainage parameters before and after the shock wave are examined.

[0031] If the instantaneous gas volume and casing pressure increase, it indicates that the shock wave is effective; the next horizontal well perforation point can continue to use shock wave intensity W for shock wave construction.

[0032] If the casing pressure decreases, it indicates that the shock wave intensity is too high. The next horizontal well perforation point can be constructed using shock wave with an intensity of 0.8W.

[0033] If the instantaneous gas volume and casing pressure do not change, the next horizontal well perforation point can be constructed using shock wave with a shock wave intensity of 1.2W.

[0034] Adjust the impact intensity promptly based on feedback to ensure the impact effect.

[0035] Preferably, before conducting shockwave construction operations, the surface well drainage personnel should be notified to pay close attention to drainage parameters such as bottom hole flowing pressure, casing pressure, and instantaneous gas production; if any abnormality occurs, the downhole construction personnel should be notified.

[0036] The advantages of this invention are:

[0037] The technical solution of this invention does not affect the surface coalbed methane well production during underground coal mine construction. By drilling directional boreholes into the fracturing influence range, controllable shock wave equipment is used to modify the fractures generated by surface well fracturing. The shock waves propagate through the fracturing fluid in the fractures, changing the coal seam pressure distribution, breaking down the barriers between fractures, and increasing the production of coalbed methane wells.

[0038] Adjust the target position for the next drilling operation based on whether it is within the fracturing influence range and the fracturing influence range, avoid blind construction, and improve drilling efficiency.

[0039] Adjust the impact intensity promptly based on feedback to ensure the impact effect. Attached Figure Description

[0040] Figure 1 is a schematic diagram of the structure of the coalbed methane horizontal well production enhancement method based on controllable shock wave according to an embodiment of the present invention;

[0041] Figure 2 is a schematic diagram of the drilling process according to an embodiment of the present invention;

[0042] Figure 3 is a flowchart illustrating the coalbed methane horizontal well production enhancement method based on controllable shock waves according to an embodiment of the present invention.

[0043] The following are labeled on the map: 1. Horizontal section of the surface well; 2. Perforation of the horizontal well; 3. Coal seams at different distances from the horizontal well; 4. Investigation hole in the fracturing influence zone; 5. Controllable shock wave drilling hole; 6. Core drilling section; 7. 2-meter line between the top and bottom plates of the coal seam. Detailed Implementation

[0044] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of 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 scope of protection of the present invention.

[0045] As shown in Figure 1, the horizontal section 1 of the surface well includes nine horizontal perforations 2. Fracturing is performed on these perforations 2 using high-pressure water flow to fracture and permeate the underground rock formations, increasing the permeability and flowability of oil and gas. Fracturing sand is then injected into the perforations. After fracturing, gas accumulates in the perforations 2, leading to the extraction of coalbed methane. It is necessary to verify and investigate where the gas can be extracted into the horizontal section 1 of the surface well. Therefore, this embodiment first aims to examine the fracturing influence range (the area where fracturing sand and fracturing fluid are located; the presence of fracturing sand or fracturing water indicates it is within the pressure influence range, otherwise it indicates it is not within the pressure influence range) and the horizontal well extraction influence range (whether the gas decreases; a decrease indicates it is within the extraction range, no decrease indicates it is not within the extraction range). The horizontal well extraction influence range is larger than the fracturing influence range. When within the fracturing influence range, controlled shock wave drilling can be performed to achieve enhanced oil recovery.

[0046] Specifically, the method for enhancing coalbed methane production in horizontal wells based on controllable shock waves includes the following steps:

[0047] Step S1: The underground roadway of the horizontal service mine is used as the construction point for upward directional drilling. The target points for directional drilling are the coal seams located at A meters, AB meters, A-2B meters, A-3B meters, and A-4B meters from the horizontal well perforation point (the horizontal well perforation point is the black dot in Figure 1). In this embodiment, the target points for directional drilling are the coal seams located at 70 meters, 60 meters, 50 meters, 40 meters, and 30 meters from the horizontal well perforation point (hereinafter referred to as the target point 70-meter position, target point 60-meter position, target point 50-meter position, target point 40-meter position, and target point 30-meter position).

[0048] The values ​​of A and B can also be selected according to the actual situation such as the thickness of the coal seam. In addition, this embodiment is not limited to the number of target points. That is to say, it can be extended to positions such as A-5B meters, A-6B meters, etc.

[0049] A can be 50-200 meters, and B can be 2-20 meters.

[0050] Step S2: First, construction is carried out at a position 70 meters from the target point. The first hole constructed is called fracturing influence zone investigation hole 4. The purpose is to investigate whether it is within the fracturing influence range. However, fracturing influence zone investigation hole 4 may eventually be consistent with controllable shock wave construction hole 5. If they are inconsistent, construction needs to be carried out again. Therefore, fracturing influence zone investigation hole 4 may not eventually be controllable shock wave construction hole 5.

[0051] As shown in Figure 2, during the drilling process: drilling starts at 20 meters, casing and wellhead sealing valve are installed, and cement grout is injected into the hole to seal it; after the cement solidifies, drilling resumes until the distance from the bottom of the coal seam to 2 meters and ends when the borehole passes through the coal seam to the top of the coal seam to 2 meters.

[0052] During the construction process, water samples and drill cuttings generated from the borehole are tested and analyzed; the concentration of K ions in the water samples (or other indicators) is measured and compared to determine whether fracturing fluid is present in the water; and the water content of the drill cuttings and the presence of fracturing sand are analyzed (the composition of suspected samples can be analyzed by spectral analysis) to determine whether the area has entered the fracturing influence range.

[0053] Simultaneously, after the borehole enters the coal seam, fixed-point sealed sampling is carried out to determine the gas content of the coal sample (comparative analysis of the original gas content of the coal seam) to determine whether it is within the influence range of horizontal well drainage. The determination of whether it has entered the influence range of fracturing and whether it is within the influence range of horizontal well drainage are carried out simultaneously during drilling.

[0054] Furthermore, if a large water inflow is detected during the drilling process, drilling should be stopped immediately, and if necessary, the gate valve should be closed to seal the borehole opening.

[0055] As mentioned above: first drill a hole 70 meters from the target point. If it is determined by fracturing fluid or fracturing water that the target has entered the fracturing influence range, then carry out controlled shock wave construction.

[0056] The controlled shock wave method involves the following steps: After drilling, a controlled shock wave generator is deployed to the layer where fracturing sand or fracturing fluid has been discovered using a drilling rig. The borehole sealing device is then closed, and water is injected into the borehole through a pre-installed pipe. The shock wave generator initiates the impact operation once it detects that the water pressure has reached the set value.

[0057] If the borehole at the target point 70 meters from the target does not enter the fracturing influence zone, there are two possibilities:

[0058] The first scenario: If it is determined that the horizontal well perforation is not within the scope of the drainage impact, then the instruction manual indicates that the fracturing of the horizontal well perforation has not affected the coal seam gas, which means that the current location is still far from the fracturing range. In this case, the borehole can be redesigned, and the target location of the borehole can be the coal seam within 50 meters of the target location (then proceed to step S21).

[0059] The second scenario: If it is determined that the area affected by drainage is not within the area affected by fracturing, then the instruction manual states that the fracturing of the horizontal well perforation does not affect the coal seam gas, but the current location is not far from the fracturing area. In this case, the borehole should be redesigned, and the target point of the borehole should be within 60 meters of the nearest target point in the coal seam.

[0060] Since the borehole at the 70-meter mark of the target point is no longer of any use, the borehole at the 70-meter mark of the target point will be sealed and pressure tested.

[0061] Step S21: After drilling at the 50-meter mark of the target point, if it is determined that the borehole has entered the fracturing influence range, controlled shock wave construction will be carried out; if it has not entered the fracturing influence range, there are two situations: if it is determined that the borehole is not within the drainage influence range, the borehole will be redesigned with the target point at the 30-meter mark of the coal seam (then proceed to step S24); if it is determined that the borehole is within the drainage influence range but not within the fracturing influence range, the borehole will be redesigned with the target point at the 40-meter mark of the coal seam (then proceed to step S23), and the original borehole will be sealed and pressure measured.

[0062] Step S22: When the borehole at the 60-meter target point is determined to be within the fracturing influence range, controlled shock wave construction is carried out; if it is not within the fracturing influence range, there are two situations: if it is determined to be outside the drainage influence range, the borehole is redesigned with the target point at the 40-meter range of the coal seam; if it is determined to be within the drainage influence range but outside the fracturing influence range, the borehole is redesigned with the target point at the 50-meter range of the coal seam, and the original borehole is sealed and pressure measured.

[0063] And so on:

[0064] Step S23: If the borehole at the 40-meter target point is determined to be within the fracturing influence range, controlled shock wave drilling will be carried out; if it is not within the fracturing influence range, there are two possibilities: if it is determined to be outside the drainage influence range, the borehole will be redesigned with the target point at the 20-meter coal seam; if it is determined to be within the drainage influence range but outside the fracturing influence range, the borehole will be redesigned with the target point at the 30-meter coal seam, and the original borehole will be sealed and pressure measured.

[0065] Step S24: If the borehole at the 30-meter mark of the target point is determined to be within the fracturing influence range, conduct controlled shock wave drilling; if it is determined to be outside the fracturing influence range, seal the borehole and measure the pressure.

[0066] S3: For each horizontal well perforation, proceed with drilling and judgment according to step S2 until the target location of the fracturing influence range is found in all horizontal well perforations, and then carry out controlled shock wave construction.

[0067] Furthermore, after the shockwave operation corresponding to a horizontal well perforation is completed, the changes in production parameters before and after the shockwave are examined. If the instantaneous gas volume and casing pressure increase, it indicates that the shockwave is effective. The shockwave intensity W is then used for the next horizontal well perforation point. If the casing pressure decreases, it indicates that the shockwave intensity is too high, and the shockwave intensity of 0.8W is used for the next horizontal well perforation point. If the instantaneous gas volume and casing pressure do not change, the shockwave intensity of 1.2W is used for the next horizontal well perforation point.

[0068] Before conducting shockwave construction operations, the surface well drainage personnel should be notified to pay close attention to drainage parameters such as bottom hole flowing pressure, casing pressure, and instantaneous gas production; if any abnormalities occur, the downhole construction personnel should be notified.

[0069] This embodiment demonstrates that underground construction in coal mines does not affect the production and drainage operations of surface coalbed methane wells. By drilling directional boreholes into the fracturing influence area, controlled shock wave equipment is used to modify the fractures generated by fracturing in surface wells. The shock waves propagate through the fracturing fluid in the fractures, altering the pressure distribution of the coal seam, breaking down the barriers between fractures, and increasing the production of coalbed methane wells.

[0070] 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 enhancing coalbed methane production in horizontal wells based on controllable shock waves, wherein the horizontal section of the surface well includes N horizontal well perforations, where N is an integer greater than 1, characterized in that... Includes the following steps: S1: Select a set of upward directional drilling sites in the underground roadway of the horizontal well service mine. The target points of the directional drilling are the coal seams located at the distances from the horizontal well perforation point to the horizontal well, which are A meters, AB meters, A-2B meters, A-3B meters, and A-4B meters. S2: First, drill a borehole at the target point A meters away. During the drilling process, determine whether it has entered the fracturing influence range. After the borehole enters the coal seam, determine whether it is within the horizontal well drainage influence range. If the borehole target location is within the fracturing influence range, then controlled shock wave construction will be carried out; If the target location of the borehole is not within the fracturing influence range, the drilling should be carried out again at the target location of AB meter, A-2B meter, A-3B meter, or A-4B meter until a target location within the fracturing influence range is found and then the drilling stops. S3: For each horizontal well perforation, proceed with drilling and judgment according to step S2 until the target location of the fracturing influence range is found in all horizontal well perforations, and then carry out controlled shock wave construction.

2. The method for enhancing coalbed methane production in horizontal wells based on controllable shock waves according to claim 1, characterized in that, In step S2, the drilling method for the target point A meters is as follows: start drilling at 15-30 meters, install casing and wellhead sealing valve, and inject cement grout into the hole to seal it; after the cement solidifies, start drilling again to 1.5-2.5 meters from the coal seam floor and end at 1.5-2.5 meters from the coal seam roof after the borehole penetrates the coal seam.

3. The method for enhancing coalbed methane production in horizontal wells based on controllable shock waves according to claim 1, characterized in that, During construction, water samples and drill cuttings generated from the borehole are tested and analyzed to determine whether they have entered the fracturing influence range. If fracturing fluid is present in the water sample and fracturing sand is present in the drill cuttings, then they have entered the fracturing influence range. If fracturing fluid is not present in the water sample and fracturing sand is not present in the drill cuttings, then they have not entered the fracturing influence range.

4. The method for enhancing coalbed methane production in horizontal wells based on controllable shock waves according to claim 1, characterized in that, After the borehole enters the coal seam, a fixed-point sealed sample is taken, and the gas content of the coal sample is measured to determine whether it is within the influence range of horizontal well drainage. If the gas content of the coal sample decreases when compared with the original gas content of the coal seam, it indicates that it has entered the influence range of horizontal well drainage. If the gas content of the coal sample does not change, it indicates that it has not entered the influence range of horizontal well drainage.

5. The method for enhancing coalbed methane production in horizontal wells based on controllable shock waves according to claim 1, characterized in that, The drilling sequence is as follows: first drill the hole at the target point A meter position; if it is determined that it has entered the fracturing influence range, then carry out controlled shock wave construction. If the borehole at target point A meters does not enter the fracturing influence zone, there are two possibilities: The first scenario: If it is determined that the coal seam is not within the range of the drainage impact, then the borehole should be redesigned with the target point located in the coal seam within the range of A-2B meters. The second scenario: If the area is determined to be within the range of drainage but not within the range of fracturing, the borehole should be redesigned with the target point located within the AB meter range of the coal seam.

6. The method for enhancing coalbed methane production in horizontal wells based on controllable shock waves according to claim 5, characterized in that, After drilling at the target point A-2B meters, if it is determined that the area has entered the fracturing influence range, controlled shock wave construction will be carried out. If it does not enter the fracturing influence zone, then there are two possibilities: When it is determined that the borehole is not within the range of the impact of drainage, the borehole target point is the coal seam within the range of A-4B meters. When it is determined that the area is within the scope of drainage but not within the scope of fracturing, the borehole is redesigned, and the target point of the borehole is located in the coal seam within the range of A-3B meters. The original borehole is then sealed and pressure is measured.

7. The method for enhancing coalbed methane production in horizontal wells based on controllable shock waves according to claim 5, characterized in that, When drilling at the target point AB meters is determined to be within the fracturing influence range, controlled shock wave construction shall be carried out. If it does not enter the fracturing influence zone, then there are two possibilities: When it is determined that the borehole is not within the range of the impact of drainage, the borehole target point is the coal seam within the range of A-3B meters. When it is determined that the area is within the scope of drainage but not within the scope of fracturing, the borehole is redesigned, the target point of the borehole is the coal seam within the range of A-2B meters, and the original borehole is sealed and pressure is measured. Continue drilling at target locations A-3B meters and A-4B meters until the target location within the fracturing influence range is found.

8. The method for enhancing coalbed methane production in horizontal wells based on controllable shock waves according to claim 6 or 7, characterized in that, The controlled shock wave method involves the following steps: After drilling, a controlled shock wave generator is deployed to the layer where fracturing sand or fracturing fluid has been discovered using a drilling rig. The borehole sealing device is then closed, and water is injected into the borehole through a pre-installed pipe. The shock wave generator initiates the impact operation once it detects that the water pressure has reached the set value.

9. The method for enhancing coalbed methane production in horizontal wells based on controllable shock waves according to claim 6 or 7, characterized in that, After the shock wave construction corresponding to a horizontal well perforation is completed, examine the changes in drainage parameters before and after the shock wave. If the instantaneous gas volume and casing pressure increase, it indicates that the shock wave is effective; the next horizontal well perforation point can continue to use shock wave intensity W for shock wave construction. If the casing pressure decreases, it indicates that the shock wave intensity is too high. The next horizontal well perforation point can be constructed using shock wave with an intensity of 0.8W. If the instantaneous gas volume and casing pressure do not change, the next horizontal well perforation point can be constructed using shock wave with a shock wave intensity of 1.2W.

10. The method for enhancing coalbed methane production in horizontal wells based on controllable shock waves according to claim 9, characterized in that, Before conducting shockwave construction operations, the surface well drainage personnel should be notified to pay close attention to drainage parameters such as bottom hole flowing pressure, casing pressure, and instantaneous gas production; if any abnormalities occur, the downhole construction personnel should be notified.

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