Method for identifying and plugging high-yield water layer section of combined-layer development coal-bed gas well

Abstract

The invention discloses a method for identifying and plugging a high-yield water layer section of a coal-bed gas well in combined development, and belongs to the technical field of coal-bed gas development. A coal-bed gas well with a second-opening well body structure is constructed from the ground, multiple target coal beds are subjected to separate layer fracturing from bottom to top, and wellhead pressure changes are analyzed to determine the communication condition of a shaft and a fracture structure; in the post-fracturing overflow releasing process, the change of chemical indexes of overflow liquid water is continuously monitored, and whether a high-yield water layer section exists or not is determined by comparing the change with the quality of injected fracturing liquid; and the position of the high-yield water layer section is judged by combining wellhead pressure and fracturing fluid water chemical index analysis. When the high-yield water layer section is located at the lowermost part of the shaft, permanent bridge plugs are arranged at the upper part and the lower part of the perforation layer section at the lowermost part for plugging; when the high-yield water layer section is located in the middle of the shaft, cement is injected into the lower double-packer oil pipe for plugging; and when the high-yield water layer section is located at the uppermost part of the shaft, the lower drillable bridge plug sleeve is plugged by cement. Therefore, accurate identification and efficient plugging of the high-yield water layer section are achieved, and the risk of abnormal high-yield water production in the drainage and mining process is remarkably reduced.

Description

Technical Field

[0001] The present invention relates to a method for identifying and plugging high-yield water layers in a combined-layer development coalbed methane well, in particular to a method for comprehensively identifying high-yield water layers in a combined-layer development coalbed methane vertical well or directional well by using fracturing wellhead pressure change data and overflow fluid water chemical index value data, and implementing corresponding bridge plugging or cement slurry plugging according to the location of the high-yield water layers, belonging to the technical field of in-situ coalbed methane surface development. Background Art

[0002] Large-scale development of coalbed methane can reduce the probability of coal mine gas accidents, reduce greenhouse gas emissions in coal mine production, and produce significant economic, environmental, safety and social benefits.

[0003] Since the abundance of coalbed methane resources in a single coal seam is relatively low, in order to increase the production of coalbed methane wells and the economic benefits of coalbed methane development, coal-measure multi-coal seam development areas need to adopt the coalbed methane multi-layer development method. At present, the specific process of coalbed methane multi-layer development in coal-measure multi-coal seam development areas is: construct coalbed methane vertical wells or directional wells on the ground, vertically pass through multiple coal seams in the coal-measure, cement after lowering production casing, perform perforation completion in the development coal seam section, and then use single-layer partial pressure or multi-layer fracturing to successively perform fracturing transformation on multiple coal seams, and finally conduct multi-layer development of coalbed methane resources in multiple coal seams by drainage and pressure reduction. However, under the conditions of multi-coal-seam coalbed methane joint development, due to the widespread development of fault structures near the fractured coal seams and their certain water conductivity, the artificial fractures formed in the hydraulic fracturing transformation of the coal seams are usually connected with the structural fractures, resulting in a significant enhancement in the fluid supply capacity of certain fractured coal seam sections in the joint-layer development coalbed methane wells. The large amount of formation water replenishment makes it difficult to drain the coalbed methane wells and reduce the pressure of the reservoir, which inhibits the expansion of the coal reservoir pressure drop funnel and the desorption of coalbed methane, resulting in the joint-layer development coalbed methane wells with continuously low gas production or long-term no gas production.

[0004] In order to suppress the adverse effects of high-yield water layers on coalbed methane development, it is necessary to accurately identify the location of high-yield water layers and take corresponding isolation or plugging measures to suppress the large amount of water production in high-yield water layers, so as to promote the continuous and stable depressurization of coal reservoirs and efficient production of coalbed methane during the drainage process. This requires the establishment of a method for identifying and plugging high-yield water layers in coalbed methane wells with combined development. However, for coalbed methane wells with combined development, due to the large number of coalbed methane producing layers and similar properties of produced fluids, a relatively accurate and reliable method for identifying high-yield water layers has not yet been established at home and abroad, and targeted measures cannot be taken to effectively plug high-yield water layers. As a result, a large number of high-yield water wells caused by unreasonable well location deployment have been scrapped due to the inability to effectively depressurize the reservoir, resulting in serious economic losses in the process of coalbed methane development. Summary of the invention

[0005] Technical problem: The purpose of the present invention is to overcome the problems that high-yield water-producing layers cannot be determined after hydraulic fracturing of multiple coal seams in a combined coalbed methane vertical well or directional well, and it is difficult to take targeted isolation or plugging measures for the high-yield water-producing layers according to the location of the high-yield water-producing layers. A method for identifying and plugging high-yield water-producing layers in combined coalbed methane wells is provided. The high-yield water-producing layers in combined coalbed methane vertical wells or directional wells are comprehensively identified by using the fracturing wellhead pressure change data and the water chemical index value data of the overflow fluid, and corresponding bridge plugging or cement slurry injection plugging is implemented according to the location of the high-yield water-producing layers.

[0006] Technical solution: In order to achieve the above-mentioned purpose, the present invention provides a method for identifying and plugging high-yield water layers in coalbed methane wells for multi-layer development, which is characterized by comprising the following steps:

[0007] (a) A coal-bed methane vertical well or directional well with a "second opening" wellbore structure is constructed on the ground, and hydraulic sand fracturing is performed on the lowest fracturing coal seam, the middle fracturing coal seam, and the uppermost fracturing coal seam in sequence from bottom to top;

[0008] (b) During the fracturing construction, continuously record the changes in the fracturing wellhead pressure, and continuously record the process of the fracturing wellhead pressure drop within 3 hours after the fracturing pump truck stops pumping, so as to determine whether the artificial fractures formed during the fracturing process of each coal seam are connected to the fracture structure around the wellbore;

[0009] (c) 24 hours after the completion of hydraulic fracturing, the overflow operation was carried out to continuously monitor the changes in the water chemical index values ​​of the overflow fluid and compare them with the water chemical index values ​​of the injected fracturing fluid, so as to determine whether there is a high-yield water layer in the coalbed methane well and the water-richness of the fractured coal seam; the tested water chemical index values ​​of the overflow fluid and the injected fracturing fluid include EC value, TDS value, salinity value, Cl - Concentration value;

[0010] (d) Comprehensively judge the connectivity of the fracture structure, the existence of high-yield water-producing layers, and the water-richness of the fractured coal seams by combining the changes in the fracturing wellhead pressure and the changes in the water chemical index values ​​of the overflow fluid, and identify the high-yield water-producing layers of the coalbed methane wells;

[0011] (e) When it is determined that there is a high-yield water layer section in the coalbed methane well, corresponding high-yield water layer section plugging measures are implemented according to the identification results of the location of the high-yield water layer section;

[0012] (f) After the high-yield water layer section is sealed, drilling, well clearing and well washing operations are carried out. After the drainage and production equipment is installed above and below the well, long-term drainage and gas production are carried out.

[0013] In step (a), the maximum well inclination of the directional well does not exceed 35° to ensure smooth downhole operations of segmented hydraulic pressure and high-yield water layer plugging; the vertical distance between the lowest fracturing coal seam and the middle fracturing coal seam is not less than 30m to ensure that there is a sand pocket of a set depth after the lowest fracturing coal seam is plugged.

[0014] In step (a), the staged hydraulic sand fracturing reconstruction adopts soluble bridge plug isolation to ensure that the bottom fractured coal seam, the middle fractured coal seam and the top fractured coal seam overflow to the wellhead simultaneously during the overflow process.

[0015] In step (b), the fracturing wellhead pressure has three changes during the fracturing construction process: first, the fracturing wellhead pressure is continuously slightly higher than the minimum principal stress of the fracturing coal seam, and the fracturing wellhead pressure drops rapidly after the fracturing pump truck stops pumping, gradually stabilizes within 3 hours after stopping the pump, and is maintained at a level slightly higher than the fracturing coal reservoir pressure. This fracturing wellhead pressure curve belongs to the artificial fracture and fault structure are not connected type fracturing curve; second, the fracturing wellhead pressure is continuously significantly lower than the minimum principal stress of the fracturing coal seam, and the fracturing wellhead pressure drops rapidly and stabilizes after the fracturing pump truck stops pumping, and is maintained at a level significantly lower than the coal reservoir pressure. This fracturing wellhead pressure curve belongs to the wellbore and structural fracture direct connection type fracturing curve; third, the fracturing wellhead pressure is higher in the early stage of the fracturing construction process, and then drops significantly to about 50% of the early stage, drops rapidly and stabilizes after stopping the pump, and is maintained at a level significantly lower than the coal reservoir pressure. This fracturing wellhead pressure curve belongs to the artificial fracture extension process connected structural fracture type fracturing curve.

[0016] In step (b), the method for judging whether the artificial fractures formed during the fracturing process of each coal seam are connected with the fracture structure around the wellbore is: when the fracturing curve type is a fracturing curve in which the artificial fractures are not connected with the fracture structure, it indicates that the artificial fractures generated during the fracturing process of the fracturing layer section are not connected with the fracture structure around the wellbore, and there is no possibility of high water production in the subsequent drainage process; when the fracturing curve type is a fracturing curve in which the wellbore is directly connected with the structural fracture or a fracturing curve in which the artificial fracture is connected with the structural fracture during the extension process, it indicates that the artificial fractures generated during the fracturing process of the fracturing layer section have been connected with the fracture structure around the wellbore, and there is a possibility of high water production in the subsequent drainage process.

[0017] In step (c), the changes in the water chemical index values ​​of the overflow fluid are monitored from the beginning of the overflow discharge to the end of the monitoring work when no overflow fluid is produced; the overflow fluid and fracturing fluid sampling method is to use a disposable sampling bottle with a volume of 250 ml, rinse the sampling bottle with the collected water sample 3 times, fill the entire bottle with the water sample when sampling, and conduct on-site tests on the water chemical index values ​​of the overflow fluid and the water chemical index values ​​of the injected fracturing fluid; the sampling and testing frequency of the overflow fluid water chemical index values ​​is once every 2 hours.

[0018] In step (c), the method for judging whether there is a high-water-yield layer section in the coalbed methane well and the water-richness of the fractured coal seam is as follows: when the water chemical index value of the overflow fluid measured during the overflow discharge is relatively stable and slightly lower than the water chemical index value of the injected fracturing fluid, which is about 90% of the water chemical index value of the injected fracturing fluid, then the curve is the water chemical index curve of the overflow fluid under the condition that there is no high-water-yield layer section and the water-richness of the fractured coal seam is weak, reflecting that there is no high-water-yield layer section and the water-richness of the fractured coal seam is weak in the coalbed methane vertical well or directional well, and there is no possibility of high water production in the subsequent drainage process; when the water chemical index value of the overflow fluid measured during the overflow discharge gradually decreases, and at the end of the overflow discharge, it drops to about 60% of the water chemical index value of the injected fracturing fluid, then the curve is no high-yield layer section. The water chemical index curve of the overflow fluid under the conditions of water layer section and medium water-richness of the fractured coal seam reflects that there is no high water-yield layer section in the coalbed methane vertical well or directional well and the water-richness of the fractured coal seam is medium, and there is no uncontrollable abnormally high water production in the subsequent drainage process; when the water chemical index value of the overflow fluid measured during the overflow discharge drops rapidly, and drops to less than 30% of the water chemical index value of the injected fracturing fluid at the end of the overflow discharge, then the curve is the water chemical index curve of the overflow fluid under the conditions of high water-yield layer section or strong water-richness of the fractured coal seam, reflecting that there is a high water-yield layer section in the coalbed methane vertical well or directional well or the water-richness of the fractured coal seam is strong, there is an uncontrollable abnormally high water production in the subsequent drainage process, and the high water-yield layer section sealing operation needs to be carried out before drainage of the coalbed methane vertical well or directional well.

[0019] In the steps, the method for identifying high water-yield layers is firstly to determine possible high water-yield layers according to the change curve of the fracturing wellhead pressure during the stratified fracturing of the combined development coalbed methane well, and the lower the stabilized fracturing wellhead pressure is, the greater the possibility of high water production in the fracturing layer; secondly, to determine whether there is a high water-yield layer in the coalbed methane vertical well or directional well according to the change curve of the water chemical index value of the overflow fluid during the overflow of the combined development coalbed methane well; if there is no high water-yield layer, no plugging operation is required; if there is a high water-yield layer, the position of the high water-yield layer in the coalbed methane vertical well or directional well is finally determined in combination with the judgment result of the high water production possibility of each fracturing layer by the fracturing wellhead pressure.

[0020] In step (e), the corresponding high-water-yield layer segment plugging measures are implemented respectively: when the lowest fractured coal seam is near the high-water-yield layer segment, a permanent bridge plug is inserted above the perforated layer segment of the lowest fractured coal seam to prevent the formation water produced near the lowest fractured coal seam from entering the wellbore, thereby reducing the water production capacity of the coalbed methane vertical well or directional well; when the middle fractured coal seam is near the high-water-yield layer segment, various oil pipes with upper and lower packers are lowered into the wellbore, and the surface passes through the screen pipe from the oil pipe. Inject G-grade oil well cement into the water-conducting fracture zone around the wellbore to seal the high-yield water-layer section. After the cement solidifies, the upper and lower packers are unsealed and the cement injection tubing is taken out. When the high-yield water-layer section is near the uppermost fractured coal seam, a drillable bridge plug is lowered into the wellbore for temporary isolation. G-grade oil well cement is injected from the wellhead into the water-conducting fracture zone around the wellbore by bare casing injection to seal the high-yield water-layer section, and clean water is used as the displacement fluid for displacement to reduce the difficulty of subsequent wellbore operations.

[0021] In step (f), the drilling, well cleaning and well washing operations are as follows: when the uppermost fractured coal seam is near a high-yield water layer and the plugging operation is carried out 72 hours later, the ground drilling rig carries out the drilling and plugging operation, and after the drilling and plugging, the well is cleaned and the well is cleaned to provide the wellbore conditions for subsequent long-term drainage; when the lowermost fractured coal seam is near a high-yield water layer and the plugging operation is carried out, the well cleaning and well washing operations are immediately carried out to provide the wellbore conditions for subsequent long-term drainage; when the middle fractured coal seam (11) is near a high-yield water layer and the plugging operation is carried out 72 hours later, the well cleaning and well washing operations are carried out to provide the wellbore conditions for subsequent long-term drainage.

[0022] Beneficial effect: Due to the adoption of the above technical scheme, the present invention overcomes the problems that high-yield water-producing layers cannot be determined after hydraulic fracturing of multiple coal seams in a combined coalbed methane vertical well or directional well, and it is difficult to take targeted isolation or plugging measures for the high-yield water-producing layers according to the location of the high-yield water-producing layers. A method for identifying and plugging high-yield water-producing layers in combined coalbed methane wells is proposed, and the high-yield water-producing layers in combined coalbed methane vertical wells or directional wells are comprehensively identified by using the fracturing wellhead pressure change data and the water chemical index value data of the overflow fluid, and corresponding bridge plug isolation or cement slurry injection plugging is implemented according to the location of the high-yield water-producing layers. First, determine the possible high-water-yield layer according to the type of curve change of the fracturing wellhead pressure during the stratified fracturing of the combined development coalbed methane well; secondly, determine whether there is a high-water-yield layer in the coalbed methane vertical well or directional well according to the type of curve change of the water chemical index value of the overflow fluid during the overflow of the combined development coalbed methane well; thirdly, if it is determined that there is a high-water-yield layer, determine the location of the high-water-yield layer in the coalbed methane vertical well or directional well in combination with the judgment result of the high water production possibility of each fracturing layer by the fracturing wellhead pressure; finally, implement the corresponding high-water-yield layer plugging measures according to the location identification result of the high-water-yield layer. The main advantages compared with the existing technology are:

[0023] 1) The existing technical methods cannot determine the high-yield water layer section after hydraulic fracturing of multiple coal seams in a vertical well or directional well for the combined development of coalbed methane. This technology uses the fracturing wellhead pressure change data and the water chemical index value data of the overflow fluid to comprehensively and accurately identify the high-yield water layer section of a vertical well or directional well for the combined development of coalbed methane;

[0024] 2) The existing technology cannot accurately identify the location of the high-yield water layer, so it is impossible to take targeted isolation or plugging measures to reduce the water production of the coalbed methane well. This technology can implement corresponding permanent bridge plug isolation of the bottom high-yield water layer and cement slurry plugging measures of the middle and upper high-yield water layer according to the accurate identification results of the location of the high-yield water layer;

[0025] 3) It can realize the resumption of production of coalbed methane wells with low gas production or no gas production in the coalbed methane layer development, and reduce the technical risks of coalbed methane vertical well and directional well development in multi-coal seam development areas;

[0026] 4) The isolation and plugging technology of high-yield water layers is simple, the project implementation cost is low, and the economic, environmental and social benefits are good. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] FIG. 1( a ) is a schematic diagram of step 1 of the method for plugging a high-yield water layer section in a coalbed methane well for multi-layer development according to the present invention.

[0028] FIG1( b ) is a schematic diagram of step 2 of the method for plugging a high-yield water layer section in a coalbed methane well for multi-layer development according to the present invention.

[0029] FIG. 1( c ) is a schematic diagram of step three of the method for plugging a high-yield water layer section in a coalbed methane well for multi-layer development according to the present invention.

[0030] Figure 2 This is a curve diagram of the change in fracturing wellhead pressure during the layered fracturing of a coalbed methane well in the combined layer development of the present invention.

[0031] Figure 3 The present invention provides a curve diagram of changes in water chemical index values ​​of overflow fluid during the overflow process of the coalbed methane well developed by the combined layer.

[0032] In the figure: 1-ground; 2-first opening hole; 3-surface casing; 4-first opening cementing cement ring; 5-second opening hole; 6-production casing; 7-second opening cementing cement ring; 8-wellhead; 9-annular steel plate; 10-lowest fracturing coal seam; 11-middle fracturing coal seam; 12-upper fracturing coal seam; 13-artificial well bottom; 14-well bottom sand settling; 15-perforated hole; 16-permanent bridge plug; 17-upper packer; 18-lower packer; 19-screen; 20-oil pipe; 21-drillable bridge plug; 22-cement slurry; 23-displacement of clean water; 24-fracturing construction time; 25-fracturing wellhead pressure; 26-fracturing construction stage section; 27-pressure monitoring stage after pump stop; 28-fracturing curve of artificial fractures not connected to fault structure; 29-fracturing curve of wellbore directly connected to structural fractures; 30-fracturing curve of artificial fractures connected to structural fractures during extension; 31-overflow time; 32-water chemical index value of overflow fluid; 33-water chemical index value of injected fracturing fluid; 34-water chemical index curve of overflow fluid under the condition of no high water-yielding layer section and weak water-richness of fractured coal seam; 35-water chemical index curve of overflow fluid under the condition of no high water-yielding layer section and medium water-richness of fractured coal seam; 36-water chemical index curve of overflow fluid under the condition of high water-yielding layer section or strong water-richness of fractured coal seam. DETAILED DESCRIPTION

[0033] The present invention will be further described below with reference to the embodiments in the accompanying drawings:

[0034] The method for identifying and plugging high-yield water layers in coalbed methane wells for multi-layer development of the present invention comprises the following specific steps:

[0035] (a) In a coalbed methane vertical well or directional well with a "two-opening" wellbore structure, hydraulic sand fracturing is performed on the lowest fractured coal seam 10, the middle fractured coal seam 11, and the uppermost fractured coal seam 12 from bottom to top; the maximum inclination of the directional well does not exceed 35° to ensure smooth downhole operations of segmented hydraulic pressure and high-yield water layer plugging; the vertical distance between the lowest fractured coal seam 10 and the middle fractured coal seam 11 is not less than 30m to ensure that a sand pocket of a certain depth exists after the lowest fractured coal seam 10 is plugged; soluble bridge plugs are used for segmented hydraulic sand fracturing to ensure that the lowest fractured coal seam 10, the middle fractured coal seam 11, and the uppermost fractured coal seam 12 can overflow to the wellhead 8 at the same time during the overflow process.

[0036] (b) During the fracturing construction process, the changes in the fracturing wellhead pressure 25 are continuously recorded, and the decline process of the fracturing wellhead pressure 25 is continuously recorded within 3 hours after the fracturing pump truck stops pumping, so as to judge whether the artificial fractures formed during the fracturing process of each coal seam are connected with the fracture structure around the wellbore; there are three possible changes in the fracturing wellhead pressure 25 during the fracturing construction process, one is that the fracturing wellhead pressure 25 is continuously slightly higher than the minimum principal stress of the fracturing coal seam, and the fracturing wellhead pressure 25 drops rapidly after the fracturing pump truck stops pumping, gradually stabilizes within 3 hours after stopping the pump, and maintains at a level slightly higher than the fracturing coal reservoir pressure. This fracturing wellhead pressure 25 curve belongs to the fracturing curve 28 of the artificial fracture and fracture structure not connected; the second is that the fracturing wellhead pressure 25 is continuously significantly lower than the minimum principal stress of the fracturing coal seam, and the fracturing wellhead pressure 25 drops rapidly and stabilizes after the fracturing pump truck stops pumping, and maintains at a level significantly lower than the coal reservoir pressure. This fracturing wellhead pressure 25 curve belongs to the type of fracturing that is directly connected to the wellbore and the structural fracture fracturing curve 29; thirdly, the fracturing wellhead pressure 25 is relatively high in the early stage of the fracturing construction process, and then drops significantly to about 50% of the early stage. After the pump is stopped, it drops rapidly and stabilizes, and is maintained at a level significantly lower than the coal reservoir pressure. This fracturing wellhead pressure 25 curve belongs to the fracturing curve 30 of the connected structural fracture type during the extension of the artificial fracture; the method for judging the connection between the artificial fractures formed in the fracturing process of each coal seam and the fracture structure around the wellbore, when the fracturing curve type is the fracturing curve 28 of the artificial fracture and the fracture structure not connected, it indicates that the artificial fractures generated in the fracturing process of the fracturing layer section are not connected with the fracture structure around the wellbore, and there is no possibility of high water production in the subsequent drainage process; when the fracturing curve type is the fracturing curve 29 of the direct connection between the wellbore and the structural fracture or the fracturing curve 30 of the connected structural fracture during the extension of the artificial fracture, it indicates that the artificial fractures generated in the fracturing process of the fracturing layer section have been connected with the fracture structure around the wellbore, and there is a possibility of high water production in the subsequent drainage process.

[0037] (c) 24 hours after the completion of the hydraulic fracturing construction, the overflow operation is carried out, and the changes in the water chemical index value 32 of the overflow fluid are continuously monitored, and compared with the water chemical index value 33 of the injected fracturing fluid, so as to judge whether there is a high-yield water layer section in the coalbed methane well and the water-richness of the fractured coal seam; the overflow fluid water chemical index value 32 is monitored from the beginning of the overflow discharge to the end when no overflow fluid is produced; the overflow fluid and fracturing fluid sampling method is to use a disposable sampling bottle with a volume of 250 ml, and the sampling bottle is rinsed 3 times with the collected water sample. When sampling, the water sample fills the entire bottle, and the overflow fluid water chemical index value 32 and the injected fracturing fluid water chemical index value 33 are tested on site; the tested overflow fluid water chemical index value 32 and the injected fracturing fluid water chemical index value 33 include EC value, TDS value, salinity value, Cl -concentration value; the sampling and testing frequency of the overflow fluid water chemical index value 32 is once every 2 hours; the method for judging whether there is a high water-yield layer section in the coalbed methane well and the water-richness of the fractured coal seam is that when the overflow fluid water chemical index value 32 measured during the overflow discharge is relatively stable and slightly lower than the injected fracturing fluid water chemical index value 33, which is about 90% of the injected fracturing fluid water chemical index value 33, then the curve is the overflow fluid water chemical index curve 34 under the condition that there is no high water-yield layer section and the water-richness of the fractured coal seam is weak, reflecting that there is no high water-yield layer section and the water-richness of the fractured coal seam is weak in the coalbed methane vertical well or directional well, and there is no possibility of high water production in the subsequent drainage process; when the overflow fluid water chemical index value 32 measured during the overflow discharge gradually decreases, and at the end of the overflow discharge, it drops to 6 of the injected fracturing fluid water chemical index value 33. 0%, then the curve is the overflow fluid water chemical index curve 35 under the condition that there is no high water-yield layer section and the water-richness of the fractured coal seam is medium, reflecting that there is no high water-yield layer section and the water-richness of the fractured coal seam is medium in the coalbed methane vertical well or directional well, and there is no uncontrollable abnormal high water production in the subsequent drainage process; when the overflow fluid water chemical index value 32 measured during the overflow discharge drops rapidly, and drops to less than 30% of the injected fracturing fluid water chemical index value 33 at the end of the overflow discharge, then the curve is the overflow fluid water chemical index curve 36 under the condition that there is a high water-yield layer section or the water-richness of the fractured coal seam is strong, reflecting that there is a high water-yield layer section or the water-richness of the fractured coal seam is strong in the coalbed methane vertical well or directional well, and there is an uncontrollable abnormal high water production in the subsequent drainage process, and the high water-yield layer section plugging operation needs to be carried out before the coalbed methane vertical well or directional well is drained.

[0038] (d) Comprehensively judging the connectivity of the fracture structure, the existence of high-water-yield layers, and the water-richness of the fractured coal seams by combining the changes in the fracturing wellhead pressure 25 and the changes in the water chemical index value 32 of the overflow fluid, and identifying the high-water-yield layers of the coalbed methane well; the method for identifying the high-water-yield layers is firstly to determine the possible high-water-yield layers according to the change curve of the fracturing wellhead pressure 25 during the stratified fracturing of the coalbed methane well in the combined development, and the lower the fracturing wellhead pressure 25 after stabilization, the greater the possibility of high water production in the fracturing layer; secondly, to determine whether there is a high-water-yield layer in the coalbed methane vertical well or directional well according to the change curve of the water chemical index value 32 of the overflow fluid during the overflow of the coalbed methane well in the combined development; if there is no high-water-yield layer, no plugging operation is required; if there is a high-water-yield layer, the position of the high-water-yield layer in the coalbed methane vertical well or directional well is finally determined in combination with the judgment result of the high-water production possibility of each fracturing layer by the fracturing wellhead pressure 25.

[0039] (e) When it is determined that there is a high-yield water layer section in the coalbed methane well, corresponding high-yield water layer section plugging measures are implemented according to the identification result of the location of the high-yield water layer section; the corresponding high-yield water layer section plugging measures are implemented respectively. When the vicinity of the lowest fractured coal seam 10 is a high-yield water layer section, a permanent bridge plug 16 is inserted above the perforated layer section of the lowest fractured coal seam 10 to plug it, so as to prevent the formation water produced near the lowest fractured coal seam 10 from entering the wellbore, thereby reducing the water production capacity of the coalbed methane vertical well or directional well; when the vicinity of the middle fractured coal seam 11 is a high-yield water layer section, various packers 17 are inserted into the wellbore with upper , the oil pipe 20 of the lower packer 18, and G-class oil well cement is injected from the oil pipe 20 through the screen pipe 19 into the water-conducting fracture zone around the wellbore on the ground to block the high-yield water layer section. After the cement solidifies, the upper packer 17 and the lower packer 18 are unsealed and the cement injection oil pipe 20 is taken out; when the high-yield water layer section is near the uppermost fractured coal seam 12, a drillable bridge plug 21 is lowered into the wellbore for temporary isolation, and G-class oil well cement is injected from the wellhead 8 on the ground into the water-conducting fracture zone around the wellbore by means of bare casing injection to block the high-yield water layer section, and clean water 23 is used as the displacement fluid for displacement to reduce the difficulty of subsequent wellbore operations.

[0040] (f) After the high-yield water layer section is sealed, drilling, well clearing and well washing operations are carried out, and drainage equipment is installed above and below the well for long-term drainage and gas production; the drilling, well clearing and well washing operations, when the vicinity of the uppermost fractured coal seam 12 is a high-yield water layer section and the sealing operation is carried out 72 hours later, the ground drilling rig carries out drilling and plugging operations, and the well is cleared and washed after drilling and plugging, so as to provide wellbore conditions for subsequent long-term drainage; when the vicinity of the lowermost fractured coal seam 10 is a high-yield water layer section and the sealing operation is carried out, the well clearing and well washing operations can be carried out immediately to provide wellbore conditions for subsequent long-term drainage; when the vicinity of the middle fractured coal seam 11 is a high-yield water layer section and the sealing operation is carried out 72 hours later, the well clearing and well washing operations can be carried out to provide wellbore conditions for subsequent long-term drainage.

Claims

1. A method for identifying and plugging high-yield water layers in coalbed methane wells with combined development, characterized in that The following steps are involved: (a) constructing a coalbed methane vertical well or directional well with a "two-opening" wellbore structure on the ground, and performing staged hydraulic sand fracturing transformation on the lowest fracturing coal seam (10), the middle fracturing coal seam (11), and the highest fracturing coal seam (12) in sequence from bottom to top; (b) During the fracturing construction process, the changes in the fracturing wellhead pressure (25) are continuously recorded, and the decline process of the fracturing wellhead pressure (25) is continuously recorded within 3 hours after the fracturing pump truck stops pumping, so as to judge whether the artificial fractures formed during the fracturing process of each coal seam are connected with the fracture structure around the wellbore; (c) 24 hours after the completion of hydraulic fracturing, the overflow operation is carried out, and the changes in the water chemical index value (32) of the overflow fluid are continuously monitored and compared with the water chemical index value (33) of the injected fracturing fluid to determine whether there is a high-yield water layer in the coalbed methane well and the water-richness of the fractured coal seam; the tested water chemical index values ​​(32) of the overflow fluid and the water chemical index values ​​(33) of the injected fracturing fluid include EC value, TDS value, salinity value, Cl - Concentration value; (d) Comprehensively judging the connectivity of the fracture structure, the existence of high-water-yielding layers, and the water-richness of the fractured coal seams by combining the changes in the fracturing wellhead pressure (25) and the changes in the water chemical index values ​​(32) of the overflow fluid, and identifying the high-water-yielding layers of the coalbed methane wells; (e) When it is determined that there is a high-yield water layer section in the coalbed methane well, corresponding high-yield water layer section plugging measures are implemented according to the identification results of the location of the high-yield water layer section; (f) After the high-yield water layer section is sealed, drilling, well clearing and well washing operations are carried out. After the drainage and production equipment is installed above and below the well, long-term drainage and gas production are carried out.

2. The method for identifying and plugging high-water-yield layers in coalbed methane wells for multi-layer development according to claim 1 is characterized by: In step (a), the maximum inclination of the directional well does not exceed 35° to ensure smooth downhole operations of segmented hydraulic pressure and high-yield water layer plugging; the vertical distance between the lowest fractured coal seam (10) and the middle fractured coal seam (11) is not less than 30m to ensure that a sand pocket of a set depth exists after the lowest fractured coal seam (10) is plugged.

3. The method for identifying and plugging high-yield water layers in coalbed methane wells for multi-layer development according to claim 1, characterized in that: In step (a), the segmented hydraulic sand fracturing transformation adopts soluble bridge plug isolation to ensure that the bottom fractured coal seam (10), the middle fractured coal seam (11) and the top fractured coal seam (12) overflow to the wellhead (8) at the same time during the overflow process.

4. The method for identifying and plugging high-water-yield layers in coalbed methane wells for multi-layer development according to claim 1 is characterized by: In step (b), the fracturing wellhead pressure (25) has three changes during the fracturing construction process: first, the fracturing wellhead pressure (25) continues to be slightly higher than the minimum principal stress of the fracturing coal seam, and the fracturing wellhead pressure (25) drops rapidly after the fracturing pump truck stops pumping, gradually stabilizes within 3 hours after stopping the pump, and maintains at a level slightly higher than the fracturing coal reservoir pressure. This fracturing wellhead pressure (25) curve belongs to the artificial fracture and fault structure unconnected fracturing curve (28); second, the fracturing wellhead pressure (25) continues to be significantly lower than the minimum principal stress of the fracturing coal seam, and After the fracturing pump truck stops pumping, the fracturing wellhead pressure (25) drops rapidly and stabilizes, and is maintained at a level significantly lower than the coal reservoir pressure. This fracturing wellhead pressure (25) curve belongs to the fracturing curve (29) of direct connection between the wellbore and the structural fracture. Third, the fracturing wellhead pressure (25) is relatively high in the early stage of the fracturing construction process, and then drops significantly to about 50% of the early stage. After stopping the pump, it drops rapidly and stabilizes, and is maintained at a level significantly lower than the coal reservoir pressure. This fracturing wellhead pressure (25) curve belongs to the fracturing curve (30) of connecting to the structural fracture during the extension process of the artificial fracture.

5. The method for identifying and plugging high-yield water-producing layers in coalbed methane wells for multi-layer development according to claim 1, characterized in that: In step (b), the method for judging whether the artificial fractures formed during the fracturing process of each coal seam are connected with the fracture structure around the wellbore is: when the fracturing curve type is a fracturing curve (28) in which the artificial fractures are not connected with the fracture structure, it indicates that the artificial fractures generated during the fracturing process of the fracturing layer segment are not connected with the fracture structure around the wellbore, and there is no possibility of high water production in the subsequent drainage process; when the fracturing curve type is a fracturing curve (29) in which the wellbore is directly connected with the structural fracture or a fracturing curve (30) in which the artificial fracture is connected with the structural fracture during the extension process, it indicates that the artificial fractures generated during the fracturing process of the fracturing layer segment are already connected with the fracture structure around the wellbore, and there is a possibility of high water production in the subsequent drainage process.

6. The method for identifying and plugging high-water-yield layers in coalbed methane wells for multi-layer development according to claim 1, characterized in that: In step (c), the change of the overflow liquid water chemical index value (32) is monitored from the beginning of the overflow discharge to the end of the monitoring work when no overflow liquid is produced; the overflow liquid and fracturing fluid sampling method is to use a disposable sampling bottle with a volume of 250 ml, rinse the sampling bottle with the collected water sample 3 times, fill the entire bottle with the water sample when sampling, and conduct on-site overflow liquid water chemical index value (32) and injected fracturing fluid water chemical index value (33) testing; the overflow liquid water chemical index value (32) sampling and testing frequency is once every 2 hours.

7. The method for identifying and plugging high-water-yield layers in coalbed methane wells for multi-layer development according to claim 1 is characterized by: In step (c), the method for judging whether there is a high water-yield layer section in the coalbed methane well and the water-richness of the fractured coalbed is as follows: when the overflow fluid water chemical index value (32) measured during the overflow discharge process is relatively stable and slightly lower than the injected fracturing fluid water chemical index value (33), which is about 90% of the injected fracturing fluid water chemical index value (33), then the curve is the overflow fluid water chemical index curve (34) under the condition that there is no high water-yield layer section and the water-richness of the fractured coalbed is weak, reflecting that there is no high water-yield layer section and the water-richness of the fractured coalbed in the coalbed methane vertical well or directional well, and there is no possibility of high water production in the subsequent drainage process; when the overflow fluid water chemical index value (32) measured during the overflow discharge process gradually decreases, and at the end of the overflow discharge, it decreases to about 60% of the injected fracturing fluid water chemical index value (33), then the curve It is the overflow fluid water chemical index curve (35) under the condition that there is no high water-yield layer section and the water-richness of the fractured coal seam is medium, reflecting that there is no high water-yield layer section and the water-richness of the fractured coal seam is medium in the coalbed methane vertical well or directional well, and there is no uncontrollable abnormal high water production in the subsequent drainage process; when the overflow fluid water chemical index value (32) measured during the overflow discharge process drops rapidly, and drops to less than 30% of the injected fracturing fluid water chemical index value (33) at the end of the overflow discharge, then the curve is the overflow fluid water chemical index curve (36) under the condition that there is a high water-yield layer section or the water-richness of the fractured coal seam is strong, reflecting that there is a high water-yield layer section or the water-richness of the fractured coal seam is strong in the coalbed methane vertical well or directional well, and there is an uncontrollable abnormal high water production in the subsequent drainage process, and the high water-yield layer section plugging operation needs to be carried out before the coalbed methane vertical well or directional well is drained.

8. The method for identifying and plugging high-water-yield layers in coalbed methane wells for multi-layer development according to claim 1, characterized in that: In step (d), the method for identifying high water-yield layers is as follows: first, the possible high water-yield layers are determined based on the variation curve of the fracturing wellhead pressure (25) during the stratified fracturing of the combined development coalbed methane well, and the lower the stabilized fracturing wellhead pressure (25), the greater the possibility of high water production in the fracturing layer; secondly, the presence of high water-yield layers in the coalbed methane vertical well or directional well is determined based on the variation curve of the water chemical index value (32) of the overflow fluid during the overflow of the combined development coalbed methane well; if there is no high water-yield layer, no plugging operation is required; if there is a high water-yield layer, the position of the high water-yield layer in the coalbed methane vertical well or directional well is finally determined based on the judgment result of the high water production possibility of each fracturing layer based on the fracturing wellhead pressure (25).

9. The method for identifying and plugging high-water-yield layers in coalbed methane wells for multi-layer development according to claim 1, characterized in that: In step (e), the corresponding high-water-yield layer segment plugging measures are respectively implemented: when the vicinity of the lowest fractured coal seam (10) is a high-water-yield layer segment, a permanent bridge plug (16) is inserted above the perforated layer segment of the lowest fractured coal seam (10) to plug the formation water produced near the lowest fractured coal seam (10) to prevent the formation water produced near the lowest fractured coal seam (10) from entering the wellbore, thereby reducing the water production capacity of the coalbed methane vertical well or directional well; when the vicinity of the middle fractured coal seam (11) is a high-water-yield layer segment, various oil pipes (20) with upper packers (17) and lower packers (18) are lowered into the wellbore, and the ground is connected to the oil pipe (20). The screen pipe (19) injects G-class oil well cement into the water-conducting fracture zone around the wellbore to seal the high-yield water layer section. After the cement solidifies, the upper packer (17) and the lower packer (18) are unsealed and the cement injection oil pipe (20) is taken out. When the uppermost fractured coal seam (12) is near the high-yield water layer section, a drillable bridge plug (21) is lowered into the wellbore for temporary isolation. The G-class oil well cement is injected into the water-conducting fracture zone around the wellbore from the wellhead (8) on the ground by means of bare casing injection to seal the high-yield water layer section, and clean water (23) is used as the displacement fluid for displacement to reduce the difficulty of subsequent wellbore operations.

10. The method for identifying and plugging high-water-yield layers in coalbed methane wells for multi-layer development according to claim 1, characterized in that: In step (f), the drilling, well cleaning and well washing operations are as follows: when the uppermost fractured coal seam (12) is near a high-yield water layer and the plugging operation is carried out 72 hours later, the ground drilling rig carries out the drilling and plugging operation, and after the drilling and plugging, the well is cleaned and the well is cleaned to provide the wellbore conditions for subsequent long-term drainage; when the lowermost fractured coal seam (10) is near a high-yield water layer and the plugging operation is carried out, the well cleaning and well washing operations are immediately carried out to provide the wellbore conditions for subsequent long-term drainage; when the middle fractured coal seam (11) is near a high-yield water layer and the plugging operation is carried out 72 hours later, the well cleaning and well washing operations are carried out to provide the wellbore conditions for subsequent long-term drainage.

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