A coalbed methane well drainage and gas production method and its application

Abstract

The present invention discloses a coalbed methane well drainage and gas production method and its application. The method includes five stages: rapid pressure drop, stable pressure drop, slow pressure drop to increase production, slight pressure drop to stabilize production, and production decline; or includes four stages: rapid pressure drop, slow pressure drop to increase production, slight pressure drop to stabilize production, and production decline; the gas production in the slow pressure drop to increase production stage reaches the optimal production allocation and enters the slight pressure drop to stabilize production stage. The coalbed methane well drainage and gas production method provided by the present invention has a reasonable division of drainage and production stages, can shorten drainage and production time, determine and control high and stable production for a long period of time, and thus improve the overall development efficiency.

Description

Technical Field

[0001] The present invention relates to the technical field of coalbed methane development, and in particular to a coalbed methane well drainage and gas production method and application thereof. Background Art

[0002] Coalbed methane well drainage control technology is known as the last key link in coalbed methane development.

[0003] The invention patent with application number CN201410532224.7 provides a method for draining coalbed methane from medium and high-rank coal. In the start-up phase, the first pressure reduction rate is used to drain water and reduce pressure. After reaching the reservoir pressure, the second pressure reduction rate is used to drain water and reduce pressure. After reaching the desorption pressure, the third pressure reduction rate is used to drain water and reduce pressure, and coalbed methane is drained.

[0004] The invention patent application number CN201510459826.9 provides a method for determining the drainage intensity of a coalbed methane well. In the single-phase flow stage, a first descent velocity of the dynamic liquid level is preset; the estimated total drainage time is determined based on the change from the initial bottomhole pressure to the critical desorption pressure; the predicted first bottomhole pressure generated by the wellbore liquid column is obtained based on the preset first descent velocity of the dynamic liquid level and the estimated total drainage time; the first descent velocity of the dynamic liquid level is adjusted according to the difference between the predicted first bottomhole pressure and the critical desorption pressure, and the dynamic liquid level descent velocity that makes the difference between the predicted first bottomhole pressure and the critical desorption pressure meet the error range is determined, and this velocity is determined as the drainage intensity in the single-phase flow stage. While ensuring high production and avoiding reservoir damage, the optimal drainage intensity calculation is achieved for the saturated single-phase water flow stage, the unsaturated single-phase water flow stage, and the gas-water two-phase flow stage of the coalbed methane well.

[0005] The invention patent with application number CN201510581003.3 provides a coalbed methane drainage method and equipment, which uses negative pressure equipment to atomize the bottom water and pump it out of the ground together with the coalbed methane, and then performs gas-liquid separation to obtain clean coalbed methane; the coalbed methane drainage equipment used includes a base, a power unit, a transmission mechanism, a control cabinet, a separation device, a compression device, a condensation device, an oil pipe and a water-carrying atomization device. The water-carrying atomization device is connected to the bottom of the gas well oil pipe. The power unit drives the compression device through the transmission mechanism, and uses the compression device to pump the coalbed methane-water mixture into the oil pipe and then into the separation device. The separated coalbed methane enters the compression device for compression, the condensation device for cooling, and then enters the gathering pipeline. The separated water and impurities are discharged through the sewage outlet.

[0006] The invention patent application number CN201710515847.7 provides a coalbed methane well drainage control method, including: opening all gas production valves, presetting a control cycle, and obtaining a measured value of the bottom hole flow pressure in each control cycle; obtaining the ideal value of the bottom hole flow pressure corresponding to each control cycle according to the drainage work system; for the same control cycle, comparing the measured value of the bottom hole flow pressure with the ideal value of the bottom hole flow pressure: if the difference between the two is less than or equal to 0.002MPa, greater than 0.002MPa and less than or equal to When the pressure is equal to 0.003MPa, greater than 0.003MPa and less than or equal to 0.004MPa, greater than 0.004MPa and less than or equal to 0.005MPa, greater than 0.005MPa and less than or equal to 0.01MPa, or greater than 0.01MPa and less than or equal to 0.05MPa, the frequency of the acquisition inverter is increased or decreased by 0.1Hz, 0.2Hz, 0.3Hz, 0.5Hz, 1Hz, or 2Hz, respectively, within the next adjacent control cycle. This method ensures stable and controllable bottomhole flow pressure, and keeps all gas production valves open, controlling only the bottomhole flow pressure. This method has high control accuracy, strong gas production capacity of the coalbed methane well, and low energy consumption.

[0007] The invention patent with application number CN201710641354.8 provides a coalbed methane well pressure-controlled drainage and gas production method and system, including: drainage with a first daily drainage volume, wherein the first daily drainage volume meets the need to remove mining interferences in the coal seam; while draining, injecting a pressure-replenishing medium to maintain the daily drop in bottomhole flow pressure at a first pressure difference value to avoid shrinkage and closure of pores and cracks in the coal seam.

[0008] The invention patent application number CN201810369229.0 provides a coalbed methane drainage method and system, including: controlling the conduction of the wellhead oil tree, gas production pipeline, and water production pipeline, and controlling the start of pumping through a control box; receiving the bottomhole flow pressure signal from the downhole pressure gauge collected at preset intervals through the control box; controlling the pumping unit to adjust the stroke rate through the control box based on the bottomhole flow pressure signal and the preset flow pressure variable; collecting the coalbed methane flow signal from the first flow meter at preset intervals; determining the gas production factor based on the bottomhole flow pressure signal and the coalbed methane flow signal; determining a simulated drainage pressure drop based on the gas production factor, current coalbed methane production, and planned coalbed methane production; and controlling the pumping unit to adjust the stroke rate through the control box based on the simulated drainage pressure drop. This method fully considers the impact of bottomhole flow pressure on coalbed methane production, improves the accuracy of gas regulation, and thus can ensure increased coalbed methane production. Summary of the Invention

[0009] The inventors discovered that after years of development and evolution, coalbed methane well drainage technology has basically gradually unified to rapid pressure reduction in the initial stage, and then switched to slow pressure reduction. However, how to increase production in the early stage of desorption? How to determine a reasonable production allocation? How to maintain high and stable production? These problems have been explored in practice, but have not been effectively solved. It is necessary to conduct research on flow pressure drop control, casing pressure control, adjustment of optimal production allocation, prevention of gas leakage from drainage water, etc., and formulate a reasonable control system in order to achieve high-efficiency, high-yield and stable production. However, the above six patents on coalbed methane drainage do not have a reasonable division of mining stages, so they cannot shorten the drainage time and control high and stable production for a long time.

[0010] In order to at least partially solve the above-mentioned technical problems existing in the prior art, the inventors have made the present invention, and through specific implementation methods, provide a coalbed methane well drainage and gas production method and its application, which can shorten the drainage time, determine and control high and stable production for a long time, and thus improve the overall development efficiency.

[0011] In a first aspect, an embodiment of the present invention provides a method for draining and producing gas from a coalbed methane well, comprising:

[0012] There are five stages: rapid pressure drop, stable pressure drop, slow pressure drop to increase production, slight pressure drop to stabilize production and production decline; or four stages: rapid pressure drop, slow pressure drop to increase production, stable production and production decline;

[0013] The gas production in the slow pressure drop and production increase stage reaches the optimal production allocation and enters the slight pressure drop and stable production stage.

[0014] In a second aspect, an embodiment of the present invention provides a coalbed methane mining method, comprising:

[0015] The gas producing wells in the coalbed methane reservoir are dewatered and gas produced according to the above-mentioned coalbed methane well dewatering and gas production method.

[0016] In a third aspect, an embodiment of the present invention provides an application of a coalbed methane well drainage and gas production method in a coalbed methane well, comprising:

[0017] The coalbed methane well is drained and gas produced according to the above-mentioned coalbed methane well drainage and gas production method.

[0018] The beneficial effects of the above technical solutions provided by the embodiments of the present invention include at least:

[0019] (1) The coalbed methane well drainage and gas production method provided by the embodiment of the present invention includes five stages: rapid pressure drop, stable pressure, slow pressure drop to increase production, slight pressure drop to stabilize production, and production decline, or includes four stages: rapid pressure drop, slow pressure drop to increase production, slight pressure drop to stabilize production, and production decline; the gas production in the slow pressure drop to increase production stage reaches the optimal production allocation and enters the slight pressure drop to stabilize production stage. In the rapid pressure drop stage, the maximum pressure difference of drainage is formed as soon as possible; on the basis of a large amount of drainage, the slow pressure drop to increase production stage is entered, and the pressure is slowly reduced to achieve a relatively fast production increase; the gas production reaches the optimal production allocation and enters the slight pressure drop to stabilize production stage, achieving a long period of high and stable production. Therefore, the coalbed methane well drainage and gas production method provided by the embodiment of the present invention can shorten the drainage time, determine and control a long period of high and stable production, and thus improve the overall development efficiency.

[0020] (2) The coalbed methane well drainage gas production method provided by the embodiment of the present invention, after the gas production reaches the predicted production allocation, promptly judges whether the gas production matching the predicted production allocation at this time is reasonable, determines the actual flow pressure drop according to the current production flow pressure value, determines the flow pressure slight drop according to the current production flow pressure value, the predicted depletion flow pressure value and the predicted stable production time, if the actual flow pressure drop is greater than the currently determined flow pressure slight drop, it means that the production allocation is too high, and the gas discharge volume should be appropriately adjusted down until the current actual flow pressure drop is equal to the currently determined flow pressure slight drop, and the current gas production is determined as the optimal production allocation, entering the slight drop flow pressure stable production stage; if the flow pressure drop is less than the currently determined flow pressure slight drop, it means that the production allocation can be further improved, and the optimal production allocation should be re-predicted, and the flow pressure should be continuously reduced to increase the gas production to the newly determined optimal production allocation. The reasonable determination of the optimal production allocation takes into account both the optimal output and the ability of the flow pressure to maintain sufficient space for long-term stable production period and pressure reduction when the actual production allocation is achieved; it avoids destructive mining that maintains high flow pressure and low production stability, or high gas production in a short period of time.

[0021] (3) The coalbed methane well drainage and gas production method provided by the embodiment of the present invention keeps the casing pressure lower than the set value of the drainage pump inlet pressure during the stages of slowly reducing the flow pressure to increase production, slightly reducing the flow pressure to stabilize production, and decreasing production, thereby avoiding waterline gas leakage and gas lock of the drainage and production equipment.

[0022] Other features and advantages of the present invention will be described in the following description, and in part will become apparent from the description, or will be understood by practicing the present invention. The purposes and other advantages of the present invention can be realized and obtained by the structures particularly pointed out in the written description, claims, and drawings.

[0023] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] The accompanying drawings are used to provide a further understanding of the present invention and constitute a part of the specification. Together with the embodiments of the present invention, they are used to explain the present invention and do not constitute a limitation of the present invention. In the accompanying drawings:

[0025] Figure 1 This is a process control diagram for drainage and gas production in a coalbed methane well in Example 1 of the present invention. DETAILED DESCRIPTION

[0026] Exemplary embodiments of the present disclosure will be described in more detail below with reference to the accompanying drawings. Although exemplary embodiments of the present disclosure are shown in the accompanying drawings, it should be understood that the present disclosure can be implemented in various forms and should not be limited by the embodiments set forth herein. Rather, these embodiments are provided to enable a more thorough understanding of the present disclosure and to fully convey the scope of the present disclosure to those skilled in the art.

[0027] It should be understood that the terms described herein are intended only to describe particular embodiments and are not intended to limit the present invention. In addition, for numerical ranges herein, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Each smaller range between any intermediate value within a stated value or stated range and any other stated value or intermediate value within the stated range is also encompassed by the present invention. The upper and lower limits of these smaller ranges may be independently included or excluded within the scope.

[0028] Unless otherwise indicated, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which the invention belongs. Although the present invention describes only preferred methods and materials, any methods and materials similar or equivalent to those described herein may also be used in the implementation or testing of the present invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials related to the documents. In the event of any conflict with any incorporated document, the content of this specification shall prevail.

[0029] In the description of the present invention, it should be noted that the terms “include”, “including”, “have”, “contain”, etc. are all open terms, which mean including but not limited to.

[0030] In order to solve the problem in the prior art that there is no reasonable division of mining stages in coalbed methane well drainage, which cannot shorten the drainage time and control high and stable production for a long time, the embodiment of the present invention provides a coalbed methane well drainage and gas production method and its application, which has a reasonable division of drainage stages, can shorten the drainage time, determine and control high and stable production for a long time, and thus improve the overall development efficiency.

[0031] Example 1

[0032] The first embodiment of the present invention provides a coalbed methane well drainage gas production method, referring to Figure 1 As shown, there are five stages in total, including the fast pressure drop stage ①, the stable pressure drop stage ②, the slow pressure drop stage ③, the slightly pressure drop stage ④ and the production decrease stage ⑤; or it only includes the fast pressure drop stage, the slow pressure drop stage ②, the stable production stage ③, the slightly pressure drop stage ④ and the production decrease stage.

[0033] The gas production in the slow pressure drop and production increase stage reaches the optimal production allocation and enters the slight pressure drop and stable production stage.

[0034] The first two (or one) stages focus on rapid drainage, while the last three stages focus on rapid production increases and long-term high and stable yields.

[0035] The rapid pressure drop phase creates the maximum drainage pressure differential as quickly as possible. Based on the large amount of drainage, the slow pressure drop phase begins, slowly reducing the pressure to achieve a relatively rapid production increase. Once gas production reaches optimal production, the slightly reduced pressure phase begins, achieving stable production, achieving high and stable production for a longer period. Therefore, the coalbed methane well drainage and gas production method provided by the embodiments of the present invention can shorten drainage time, determine and control high and stable production for a longer period, and thus improve the overall development efficiency.

[0036] The speed of flow pressure drop is controlled mainly by using a frequency converter to control the speed of operation of the drainage equipment, thereby changing the amount of water produced and achieving control of the flow pressure drop or stability.

[0037] The drainage and gas production methods in the above five mining stages are mainly suitable for gas wells in coalbed methane reservoirs with low permeability, low water content and little external water supply; for gas wells in coalbed methane reservoirs with high permeability, high water content or rich water supply, it is sufficient to directly reduce pressure and increase production. That is, the drainage and gas production process only requires four stages: rapid reduction of flow pressure, slow reduction of flow pressure to increase production, slight reduction of flow pressure to stabilize production and production reduction.

[0038] Example 2

[0039] The second embodiment of the present invention provides a specific implementation of a coalbed methane well drainage and gas production method, which includes five stages: rapid flow pressure reduction, stable flow pressure, slow flow pressure reduction to increase production, slight flow pressure reduction to stabilize production, and production reduction.

[0040] Before production, the coalbed methane well is analyzed, including the geological structure, hydrogeological conditions, well logging data, and fracturing curves of the coalbed methane well, to predict the desorption pressure, production allocation, stable production time, and depletion flow pressure value; during the production process, the desorption pressure is measured, the actual production allocation is adjusted, and the optimal production allocation is determined.

[0041] In the fast pressure drop stage, the maximum pressure difference of drainage is formed as soon as possible; in the steady pressure stage, as much water is drained as possible; on the basis of a large amount of drainage, the slow pressure drop and production increase stage is entered, and the pressure is slowly reduced to achieve a relatively fast production increase, while the casing pressure is controlled to be stable at a value lower than the design pressure level of the metering valve group; when the gas production reaches the optimal production allocation, the slight pressure drop and steady production stage is entered, and reasonable production allocation is obtained and stably controlled based on the predicted production allocation and the predicted stable production time, and the casing pressure is kept no higher than the casing pressure value during the production increase period and is kept above the set difference with the pump inlet pressure value, so as to achieve high and stable production for a long time; in the production decline stage, while maintaining the lowest pressure value, the difference between the casing pressure and the pump inlet pressure is maintained to continue production. Specifically:

[0042] 1. Rapid pressure drop stage.

[0043] See also Figure 1 The AB segment in .

[0044] Reduce the flow pressure according to the set rapid drop amplitude until the flow pressure drops to a value higher than the predicted desorption pressure set value.

[0045] Furthermore, the flow pressure is reduced at a rapid rate of 0.1 to 0.6 MPa / d.

[0046] Preferably, the flow pressure is reduced at a rapid rate of 0.5 MPa / d.

[0047] Further, the flow pressure is reduced according to the set rapid drop amplitude until the flow pressure drops to 0.1MPa to 0.5MPa higher than the predicted desorption pressure, preferably around 0.3MPa, and the daily water production reaches the maximum. The maximum daily water production in the rapid pressure drop stage is recorded.

[0048] Desorption pressure can be predicted by Figure 1 Flow pressure at point D.

[0049] 2. Steady flow and pressure stage.

[0050] See also Figure 1 The BC segment in .

[0051] Stabilize the flow pressure until the daily water production drops to the set water production value.

[0052] Furthermore, the flow pressure is stabilized until the daily water production is reduced to between one-third and one-quarter of the maximum daily water production in the fast pressure drop stage.

[0053] The flow pressure is stabilized. At this time, the flow pressure is higher than the predicted desorption pressure, so the water production can be maximized under the single-phase flow state.

[0054] 3. The stage of slowly reducing flow pressure and increasing production.

[0055] See also Figure 1 CE segment in.

[0056] Reduce the flow pressure according to the set slow-down amplitude until the casing pressure rises to the casing pressure set value and start to release gas. Stabilize the casing pressure, continue to reduce the flow pressure according to the slow-down amplitude, do not control the gas production, and release gas at high flow pressure to increase the gas production until the gas production reaches the predicted production allocation, and enter the stage of slightly reducing flow pressure and stabilizing production.

[0057] Furthermore, the flow pressure is reduced at a rate of 0.6 to 1.2 MPa per month.

[0058] Better yet, reduce the flow pressure at a rate of 1 MPa / month.

[0059] Further, when the casing pressure rises to 0.8-1.5 MPa, or when the casing pressure reaches 1 / 4-1 / 2 of the desorption pressure calculated by the isothermal adsorption curve under the current measured gas content, degassing begins.

[0060] More preferably, degassing begins when the casing pressure rises to 1 MPa, or when the casing pressure reaches 1 / 3 of the desorption pressure calculated using the isothermal adsorption curve under the current measured gas content.

[0061] See also Figure 1 During the process of “increasing production”, the flow pressure at point C changes from the stable pressure P C Reduce to the predicted desorption pressure P D At this time, the casing pressure begins to increase, and the servo electric valve is used to control the casing pressure at about 1MPa or about one-third of the desorption pressure calculated by the isothermal adsorption curve under the measured gas content (principle: not exceeding the design pressure of the metering valve group), until point H; when the casing pressure rises to the casing pressure set value, gas is released, coalbed methane begins to be produced, and the gas production begins to increase until point E, when the gas production reaches the predicted production.

[0062] Furthermore, the above-mentioned predicted production allocation is not necessarily the optimal production allocation. One of the purposes of the embodiment of the present invention is to achieve high and stable production for a long period of time. Therefore, obtaining the optimal production allocation and maintaining long-term stable production are key.

[0063] In some embodiments, after the gas production reaches the predicted production allocation, a short period of debugging (within 30 days) is also included to increase or decrease the optimal production allocation until the actual flow pressure drop matches the flow pressure drop.

[0064] Specifically, the current flow pressure value is recorded as the production flow pressure value, the actual flow pressure drop is determined according to the current production flow pressure value, and the flow pressure slight reduction amplitude is determined according to the current production flow pressure value, the predicted depletion flow pressure value and the predicted stable production time; it is judged whether the current actual flow pressure drop is greater than or less than the currently determined flow pressure slight reduction amplitude; if the current actual flow pressure drop is greater than the currently determined flow pressure slight reduction amplitude, the gas production is reduced, the current flow pressure value is recorded as the production flow pressure value, the actual flow pressure drop is determined according to the current production flow pressure value, and the flow pressure slight reduction amplitude is re-determined according to the current production flow pressure value, the predicted depletion flow pressure value and the predicted stable production time, and the judgment of whether the current actual flow pressure drop is greater than or less than the currently determined flow pressure slight reduction amplitude is returned until the current actual flow pressure drop is equal to the currently determined flow pressure slight reduction amplitude, and the current gas production is determined as the optimal production allocation; if the current actual flow pressure drop is less than the currently determined flow pressure slight reduction amplitude, the production allocation is re-predicted as the optimal production allocation, and the flow pressure is continued to be reduced until the current gas production is increased to the re-determined optimal production allocation.

[0065] After the gas production reaches the predicted allocation, it is promptly determined whether the gas production that matches the predicted allocation is reasonable. The actual pressure drop is determined based on the current peak flow pressure value. The pressure drop is then determined based on the current peak flow pressure value, the predicted depletion flow pressure value, and the predicted stable production time. If the actual pressure drop is greater than the currently determined pressure drop, it indicates that the allocation is too high, and the gas release rate should be appropriately reduced until the actual pressure drop equals the currently determined pressure drop. The current gas production is then determined as the optimal allocation, and the production phase with pressure drop and stable production begins. If the pressure drop is less than the currently determined pressure drop, it indicates that the allocation can be further increased, and the optimal allocation should be recalculated, and the pressure should be further reduced to increase the gas production to the newly determined optimal allocation. The reasonable determination of the optimal allocation takes into account both the optimal production and the sufficient pressure drop to maintain a long-term stable production period. This avoids destructive production practices such as maintaining high pressure and low production stability, or high gas production for a short period of time.

[0066] 4. Slightly reduced flow pressure and stable production stage.

[0067] See also Figure 1 EF segment in.

[0068] When the gas production reaches the optimal production allocation during the aforementioned slow pressure reduction phase, the current pressure is recorded as the peak pressure value. The micro-reduction margin is determined based on the peak pressure value, the predicted depletion pressure value, and the predicted stable production time. Specifically, the micro-reduction margin is calculated by dividing the difference between the peak pressure value and the predicted depletion pressure value by the predicted stable production time.

[0069] Reduce the flow pressure slightly and stabilize the gas production at the optimal production until the current flow pressure drops to the predicted depletion flow pressure.

[0070] Starting at point E, the servo electric valve controls gas production, while the frequency converter adjusts drainage parameters to ensure that the casing pressure meets two conditions simultaneously: it does not exceed the previously stable casing pressure (for example, 1 MPa), and the difference between the casing pressure and the pressure at the drainage pump inlet is no less than the set value (for example, no less than 20% of the pressure at the drainage pump inlet). This pressure control prevents the wellhead metering valve group from exceeding the design pressure and prevents gas cross-contamination in the downhole drainage pump. The servo electric valve and frequency converter work together to achieve these control objectives. The flow pressure value directs the frequency converter to control the operating parameters of the drainage equipment to maintain the casing pressure within the required range. The servo electric valve opening is controlled according to the gas production rate to ensure that the gas production is stable within the required range.

[0071] 5. The stage of decreasing output.

[0072] See also Figure 1 The FG segment in .

[0073] Stabilize the flow pressure and casing pressure until the current drainage and gas production no longer meets the set economic conditions.

[0074] Production continues under the predicted depletion flow pressure, and the gas production naturally decreases until the CBM well is shut down when it becomes uneconomical (unless effective production-increasing measures are taken, such as negative pressure pumping or reservoir reconstruction).

[0075] In some embodiments, during the aforementioned stages of slowly decreasing flow pressure to increase production, slightly decreasing flow pressure to stabilize production, and gradually decreasing production, the casing pressure is maintained below the set value of the drainage pump inlet pressure (with the set casing pressure value being no higher than the designed operating pressure of the metering valve group as a principle). This can prevent waterline gas blowby and gas lock in the drainage equipment.

[0076] Furthermore, the difference between the drainage pump inlet pressure and the casing pressure is maintained to be greater than or equal to 20% of the drainage pump inlet pressure.

[0077] Dewatering pump inlet pressure is determined using different methods for vertical, directional, and horizontal wells. For vertical or directional CBM wells, the dewatering pump inlet pressure is determined by combining the tubing structure data with the relationship between the coal seam and the downhole pressure gauge readings or dynamic liquid level test data. For L-shaped horizontal CBM wells, the dewatering pump inlet pressure is determined by converting the pressure gauge readings with the vertical depth relationship at the dewatering pump inlet. Horizontal wells with drainage caverns are treated as vertical wells.

[0078] The second embodiment of the present invention is based on the existing technology of rapid pressure reduction in the single-phase flow stage and large-scale drainage. According to the seepage theory of low-permeability reservoirs, the elastic energy of the desorbed gas is reasonably and effectively utilized to control the coalbed methane well to slowly reduce the flow pressure, effectively control the gas production rate of the low-permeability layer, quickly reach full production, and take a long period of high and stable production as the goal, to obtain the best production allocation and maintain long-term stable production, while avoiding waterline gas leakage and gas lock of drainage equipment.

[0079] Based on the inventive concept of the present invention, an embodiment of the present invention further provides a coalbed methane mining method, comprising:

[0080] The gas producing wells in the coalbed methane reservoir are dewatered and gas produced according to the above-mentioned coalbed methane well dewatering and gas production method.

[0081] Specifically, before implementing drainage and gas production in each well, the geological structure, hydrogeological conditions, well logging data, and fracturing curve of the coalbed methane well are analyzed to predict the desorption pressure, production allocation, preset stable production time, and preset depletion pressure value.

[0082] The above method is compiled into a drainage gas production control program, and the predicted desorption pressure, predicted production allocation, preset stable production time and preset depletion pressure value are input to output the following Figure 1 The drainage and gas production control diagram shown is used to guide the drainage and gas production process of coalbed methane wells.

[0083] Figure 1 In the diagram, A is the pumping start point, B is the pressure stabilization point, C is the point where the flowing pressure begins to slowly decrease, D is the desorption pressure point, E is the point where the production pressure reaches the specified level, F is the minimum pressure point, and G is the exhaustion point. The horizontal axis represents the production time; the vertical axis on the left represents the pressure value, specifically the flowing pressure or casing pressure; and the vertical axis on the right represents the gas production. Figure 1 The thicker solid line is the flow pressure change curve, the thinner solid line is the casing pressure change curve, and the dotted line is the gas volume (gas production) change curve.

[0084] The wellhead metering valve group of the coalbed methane well is installed with a servo electric regulating valve, an electronic pressure gauge is installed near the inlet of the underground drainage pump, and a variable frequency speed controller is installed on the drainage equipment. For coalbed methane wells that implement remote collection and automatic control, automatic control can be performed according to the above procedures. In special circumstances such as detection instrument failure and drainage equipment failure, early warning and manual intervention are implemented; for coalbed methane wells that do not implement remote collection and automatic control, manual adjustment and control are implemented according to the control chart output by the program, mainly including manual adjustment of the bleed valve to achieve casing pressure and gas production control, manual adjustment of the operating parameters of the drainage equipment to achieve flow pressure control, and adjustment at any time to ensure that all pressures and gas production are controlled within the design range. Especially at point E in the early stage of production, it is important to attach great importance to the repeated adjustment and determination of reasonable production allocation.

[0085] Based on the inventive concept of the present invention, an embodiment of the present invention further provides an application of a coalbed methane well drainage gas production method in a coalbed methane well, comprising:

[0086] The coalbed methane well is drained and gas produced according to the above-mentioned coalbed methane well drainage and gas production method.

[0087] It should be understood that the specific order or hierarchy of steps in the disclosed processes is an example of an exemplary method. Based on design preferences, it should be understood that the specific order or hierarchy of steps in the process can be rearranged without departing from the scope of the present disclosure. The accompanying method claims present elements of the various steps in an exemplary order and are not intended to be limited to the specific order or hierarchy described.

[0088] In the foregoing detailed description, various features are grouped together in a single embodiment to simplify the disclosure. This method of disclosure should not be interpreted as reflecting an intention that embodiments of the claimed subject matter require more features than are expressly recited in each claim. On the contrary, as reflected in the appended claims, the invention comprises less than all the features of any individual disclosed embodiment. The appended claims are therefore hereby expressly incorporated into the detailed description, with each claim standing on its own as a separate preferred embodiment of the invention.

[0089] The foregoing description includes examples of one or more embodiments. Of course, it is not possible to describe all possible combinations of components or methods for the purposes of describing the above embodiments, but one of ordinary skill in the art will recognize that the various embodiments may be further combined and arranged. Therefore, the embodiments described herein are intended to encompass all such changes, modifications and variations that fall within the scope of the appended claims. Furthermore, to the extent the term "comprising" is used in the specification or claims, the term is intended to be encompassed in a manner similar to the term "including," as explained in terms of "including," used as a transitional word in the claims. Furthermore, any use of the term "or" in the specification of the claims is intended to mean a "non-exclusive or."

Claims

1. A method for producing gas from a coalbed methane well by draining water, characterized in that: It includes five stages: rapid pressure drop, stable pressure drop, slow pressure drop to increase production, slight pressure drop to stabilize production and production decline; or four stages: rapid pressure drop, slow pressure drop to increase production, slight pressure drop to stabilize production and production decline; During the stage of slowly decreasing the flow pressure to increase production, the flow pressure is reduced according to the set slow-down range until the gas production reaches the predicted production; After the gas production reaches the predicted production, the current flow pressure value is recorded as the production flow pressure value. The actual flow pressure drop is determined based on the current production flow pressure value. The flow pressure drop is determined based on the current production flow pressure value, the predicted depletion flow pressure value, and the predicted stable production time. Determine whether the current actual flow pressure drop is greater than or less than the current determined flow pressure drop; If the current true flow pressure drop is greater than the currently determined flow pressure slight drop, reduce the gas production, record the current flow pressure value as the production flow pressure value, determine the true flow pressure drop based on the current production flow pressure value, re-determine the flow pressure slight drop based on the current production flow pressure value, the predicted depletion flow pressure value and the predicted stable production time, return to execute the judgment whether the current true flow pressure drop is greater than or less than the currently determined flow pressure slight drop, until the current true flow pressure drop is equal to the currently determined flow pressure slight drop, determine the current gas production as the optimal production allocation; if the current true flow pressure drop is less than the currently determined flow pressure slight drop, re-predict the production allocation as the optimal production allocation, continue to reduce the flow pressure until the current gas production is increased to the re-determined optimal production allocation; The gas production in the slow pressure drop and production increase stage reaches the optimal production allocation and enters the slight pressure drop and stable production stage.

2. The method according to claim 1, wherein The stage of slowly reducing flow pressure and increasing production specifically includes: Reduce the flow pressure according to the set slow-down range until the casing pressure rises to the casing pressure set value and starts to deflate. After the casing pressure is stabilized, continue to reduce the flow pressure according to the said slow-down range.

3. The method according to claim 2, wherein When the casing pressure rises to the casing pressure setting value, deflation begins, specifically including: Degassing begins when the casing pressure rises to 0.8-1.5 MPa, or when the casing pressure reaches 1 / 4-1 / 2 of the desorption pressure calculated using the isothermal adsorption curve under the current measured gas content.

4. The method according to any one of claims 1 to 3, wherein: The reducing the flow pressure according to the set slow-down range specifically includes: reducing the flow pressure according to a slow-down range of 0.6 to 1.2 MPa / month.

5. The method according to claim 1, wherein Also includes: During the stages of slowly reducing the flow pressure to increase production, slightly reducing the flow pressure to stabilize production, and gradually decreasing production, the casing pressure is kept lower than the set value of the drainage pump inlet pressure.

6. The method according to claim 5, wherein Maintaining the casing pressure below the set value of the drainage pump inlet pressure specifically includes: Keep the difference between the drainage pump inlet pressure and the casing pressure greater than or equal to 20% of the drainage pump inlet pressure.

7. The method according to claim 1, wherein The rapid pressure drop stage specifically includes: Reduce the flow pressure according to the set rapid drop amplitude until the flow pressure drops to 0.1MPa~0.5MPa higher than the predicted desorption pressure.

8. The method according to claim 7, wherein Reducing the flow pressure according to the set rapid drop amplitude specifically includes: Reduce the flow pressure at a rapid rate of 0.1 to 0.6 MPa / d.

9. The method according to claim 1, wherein The steady flow and pressure stage specifically includes: Stabilize the flow pressure until the daily water production drops to the set water production value.

10. The method according to claim 9, wherein The daily water production is reduced to the set water production value, specifically including: The daily water production is reduced to between one third and one quarter of the maximum daily water production in the fast pressure drop stage.

11. The method according to claim 1, wherein The slightly reduced flow pressure and stable production stage specifically includes: When the gas production in the stage of slowly decreasing the flow pressure and increasing the production reaches the optimal production allocation, the current flow pressure value is recorded as the production-reaching flow pressure value, and the flow pressure slight reduction amplitude is determined based on the production-reaching flow pressure value, the predicted depletion flow pressure value, and the predicted stable production time; The flow pressure is reduced according to the flow pressure slight reduction range, and the gas production is stabilized at the optimal production allocation until the current flow pressure drops to the predicted depletion flow pressure value.

12. The method according to any one of claims 1 to 3 and 5 to 11, wherein The production decline stage specifically includes: Stabilize the flow pressure and casing pressure until the current drainage and gas production no longer meets the set economic conditions.

13. A coalbed methane mining method, characterized in that: include: The gas producing wells in the coalbed methane reservoir are drained and gas produced according to the coalbed methane well water drainage and gas production method according to any one of claims 1 to 12.

14. Application of a coalbed methane well drainage gas production method in a coalbed methane well, characterized in that: include: The coalbed methane well is drained and gas produced according to the coalbed methane well drainage and gas production method according to any one of claims 1 to 12.

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