A method for identifying and plugging high-yield water zones in coalbed methane wells with combined development

Abstract

The present invention discloses a method for identifying and sealing high-water-yield layers in coalbed methane wells with combined layer development, which belongs to the technical field of coalbed methane development. A coalbed methane well with a "second opening" wellbore structure is constructed by applying tools on the ground, and multiple target coal seams are fractured from bottom to top. The wellhead pressure changes are analyzed to determine the connectivity between the wellbore and the fracture structure. During the post-pressure overflow process, the water chemical index changes of the overflow fluid are continuously monitored, and the presence of a high-water-yield layer section is determined by comparing it with the water quality of the injected fracturing fluid. The location of the high-water-yield layer section is identified by comprehensively analyzing the wellhead pressure and the water chemical indexes of the fracturing fluid. When the high-water-yield layer section is at the bottom of the wellbore, a permanent bridge plug is inserted above the bottom perforated layer section for sealing. When the high-water-yield layer section is in the middle of the wellbore, a double packer oil pipe is lowered for cement sealing. When the high-water-yield layer section is at the top of the wellbore, a drillable bridge plug casing is lowered for cement sealing. This enables accurate identification and efficient sealing of the high-water-yield layer section, significantly reducing the risk of abnormally high water production during drainage and production.

Description

Technical Field

[0001] The present invention relates to a method for identifying and sealing high-water-yield layers in coalbed methane (CBM) wells developed in a combined layer, and in particular to a method for comprehensively identifying high-water-yield layers in CBM vertical or directional wells developed in a combined layer by utilizing 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-water-yield layers. The method belongs to the technical field of in-situ CBM 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 improve 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, run production casing and cement the well, perform perforation completion in the development coal seam section, then use single-layer partial pressure or multi-layer fracturing to successively perform fracturing transformation on multiple coal seams, and finally use drainage and pressure reduction to carry out multi-layer development of coalbed methane resources in multiple coal seams. However, under the conditions of multi-coal seam coalbed methane joint development, since the fault structure near the fractured coal seam is generally developed and has a certain water conductivity, the artificial fractures formed in the coal seam hydraulic fracturing transformation are usually connected with the structural fractures, resulting in a significant increase in the fluid supply capacity of certain fractured coal seam sections in the joint development coalbed methane wells. The large amount of formation water replenishment makes it difficult to drain the coalbed methane well 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 development coalbed methane wells having a continuously low gas production or no gas production for a long time.

[0004] To mitigate the adverse effects of high-water-yield intervals on coalbed methane (CBM) development, it is necessary to accurately identify their locations and implement appropriate isolation or plugging measures to suppress excessive water production. This, in turn, promotes sustained and stable depressurization of the coal reservoir and efficient CBM production during the production process. This necessitates the development of methods for identifying and plugging high-water-yield intervals in CBM wells developed in mixed layers. However, due to the large number of CBM producing layers and the similar properties of the produced fluids, a relatively accurate and reliable method for identifying high-water-yield intervals has not yet been established, both domestically and internationally. Consequently, targeted measures to effectively plug these high-water-yield intervals are not feasible. Consequently, a large number of high-water-yield wells resulting from inappropriate well placement have been abandoned due to the inability to effectively depressurize the reservoir, resulting in significant economic losses during CBM development. Summary of the Invention

[0005] Technical problem: The purpose of the present invention is to overcome the problems that high-yield water 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 layers according to the location of the high-yield water layers. A method for identifying and plugging high-yield water layers in a combined coalbed methane well is provided, which uses the fracturing wellhead pressure change data and the water chemical index value data of the overflow fluid to comprehensively identify the high-yield water layers in the combined coalbed methane vertical well or directional well, and implements corresponding bridge plug isolation or cement slurry injection plugging according to the location of the high-yield water layers.

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

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

[0008] (b) During the fracturing operation, 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, overflow discharge operation is carried out, and the changes in the water chemical index values ​​of the overflow fluid are continuously monitored and compared with the water chemical index values ​​of the injected fracturing fluid, so as to determine whether there is a high water-yielding 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-water-yielding 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-water-yielding layers of the coalbed methane wells;

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

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

[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 fractured coal seam and the middle fractured coal seam is not less than 30m to ensure that a sand pocket of a set depth exists after the lowest fractured coal seam is plugged.

[0014] In step (a), the staged hydraulic sand fracturing modification 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 maintains at a level slightly higher than the fracturing coal reservoir pressure. This fracturing wellhead pressure curve belongs to the artificial fracture and fracture structure non-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 maintains at a level significantly lower than the coal reservoir pressure. This fracturing wellhead pressure curve belongs to the type of fracturing curve in which the wellbore is directly connected to the structural fracture; 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. It drops rapidly and stabilizes after stopping the pump, and maintains at a level significantly lower than the coal reservoir pressure. This fracturing wellhead pressure curve belongs to the type of fracturing curve in which the structural fracture is connected during the extension of the artificial fracture.

[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 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 in which the wellbore is directly connected with the structural fracture or a fracturing curve in which the artificial fractures are 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.

[0017] In step (c), the changes in the water chemical index values ​​of the overflow fluid are monitored from the start 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 water sample when sampling, and conduct on-site water chemical index value tests of the overflow fluid and the injected fracturing fluid water chemical index value; the overflow fluid water chemical index value sampling and testing frequency 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 overflow fluid water chemical index curve under the conditions of no high-water-yield layer section and weak water-richness of the fractured coal seam, reflecting that there is no high-water-yield layer section and weak water-richness of the fractured coal seam 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-water-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 abnormal 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, and there is an uncontrollable abnormal high water production in the subsequent drainage process, and the high water-yield layer section needs to be sealed before drainage of the coalbed methane vertical well or directional well.

[0019] In the steps, the method for identifying high-water-yield layers is as follows: first, the possible high-water-yield layers are determined according to the curve of the change of the fracturing wellhead pressure during the stratified fracturing of the combined-layer development coalbed methane well, and the lower the fracturing wellhead pressure after stabilization, the greater the possibility of high water production in the fracturing layer; secondly, the existence of a high-water-yield layer in the coalbed methane vertical well or directional well is determined according to the curve of the change of the water chemical index value of the overflow fluid during the overflow of the combined-layer 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-yield possibility of each fracturing layer according to the fracturing wellhead pressure.

[0020] In step (e), the corresponding high-water-yield layer blocking measures are implemented respectively: when the low-est fractured coal seam is near the high-water-yield layer, a permanent bridge plug is inserted above the perforated layer of the low-est fractured coal seam to block the formation water produced near the low-est 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, 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. After the cement solidifies, the upper and lower packers are unsealed and the cementing oil pipe is removed. When the high-yield water layer 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, and clean water is used as the displacement fluid for over-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 drilling and plugging, the well is cleaned and the well is cleaned to provide 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 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 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 the high-yield water layer section 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 layer section according to the location of the high-yield water layer section. A method for identifying and plugging the high-yield water layer section of a combined coalbed methane well is proposed, which uses the fracturing wellhead pressure change data and the overflow fluid water chemical index value data to comprehensively identify the high-yield water layer section of a combined coalbed methane vertical well or directional well, and implements corresponding bridge plug isolation or cement slurry injection plugging according to the location of the high-yield water layer section. First, the possible high-water-yield layer is determined based on the type of curve change of the fracturing wellhead pressure during the stratified fracturing of the combined-layer development coalbed methane well; secondly, the presence of a high-water-yield layer in the coalbed methane vertical well or directional well is determined based on the type of curve change of the water chemical index value of the overflow fluid during the overflow of the combined-layer development coalbed methane well; thirdly, if it is determined that a high-water-yield layer exists, the location of the high-water-yield layer in the coalbed methane vertical well or directional well is determined based on the judgment result of the high water production possibility of each fracturing layer section based on the fracturing wellhead pressure; finally, based on the identification result of the location of the high-water-yield layer, corresponding high-water-yield layer plugging measures are implemented respectively. The main advantages compared with existing technologies are:

[0023] 1) Existing technical methods are unable to identify high-water-yielding layers after hydraulic fracturing of multiple coal seams in vertical or directional wells for combined coalbed methane development. This technology uses fracturing wellhead pressure change data and overflow fluid water chemical index data to comprehensively and accurately identify high-water-yielding layers in vertical or directional wells for combined coalbed methane development.

[0024] 2) Existing technologies cannot accurately identify the location of high-yield water layers, and therefore cannot take targeted isolation or plugging measures to reduce water production in coalbed methane wells. This technology can accurately identify the location of high-yield water layers and implement corresponding measures such as permanent bridge plugging of the bottom high-yield water layer and cement slurry plugging of the middle and upper high-yield water layers;

[0025] 3) It can restore production to coalbed methane wells with low gas production or even no gas production in coalbed methane layers, and reduce the technical risks of developing vertical and directional coalbed methane wells in areas with multiple coal seams;

[0026] 4) The isolation and plugging technology for 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] FIG1( a ) is a schematic diagram of step 1 of the method for plugging a high-yield water layer in a coalbed methane well for combined 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 in a coalbed methane well with combined layer development according to the present invention.

[0029] FIG1( c ) is a schematic diagram of step three of the method for plugging a high-yield water layer in a coalbed methane well with combined 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 developed in a multi-layer development according to the present invention.

[0031] Figure 3 This is a curve diagram of the changes in the water chemical index values ​​of the overflow fluid during the overflow process of the combined-layer development coalbed methane well of the present invention.

[0032] In the figure: 1-ground; 2-first opening hole; 3-surface casing; 4-first opening cement sheath; 5-second opening hole; 6-production casing; 7-second opening cement sheath; 8-wellhead; 9-annular steel plate; 10-lowest fractured coal seam; 11-middle fractured coal seam; 12-upper fractured coal seam; 13-artificial well bottom; 14-well bottom sand settling; 15-perforation hole; 16-permanent bridge plug; 17-upper packer; 18-lower packer; 19-screen; 20-tubing; 21-drillable bridge plug; 22-cement slurry; 23-displacement water; 24-fracturing operation time; 25-fracturing wellhead pressure; 26-fracturing operation stage Section; 27-pressure monitoring stage after pump stop; 28-fracturing curve of the type where artificial fractures are not connected to fault structures; 29-fracturing curve of the type where the wellbore is directly connected to structural fractures; 30-fracturing curve of the type where artificial fractures are 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 the 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 the 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 the 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 developed by combined layer development of the present invention comprises the following specific steps:

[0035] (a) A coalbed methane vertical well or directional well with a "two-opening" wellbore structure using ground tools is used to perform segmented hydraulic sand fracturing on the lowest fractured coal seam 10, the middle fractured coal seam 11, and the uppermost fractured coal seam 12 in sequence 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; a soluble bridge plug is 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 simultaneously during the overflow discharge 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, and this fracturing wellhead pressure 25 curve belongs to the artificial fracture and fracture structure non-connected type fracturing curve 28; 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, and this fracturing wellhead pressure 25 curve belongs to the wellbore directly connected type fracturing curve 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 artificial fracture extension process connected structural fracture type fracturing curve 30; the method for judging the connectivity 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 artificial fracture and fracture structure not connected type fracturing curve 28, 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 wellbore and structural fracture direct connection type fracturing curve 29 or the artificial fracture extension process connected structural fracture type fracturing curve 30, 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 overflow fluid water chemical index value 32 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 water-yielding 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, rinse the sampling bottle with the collected water sample 3 times, fill the entire bottle with water sample when sampling, and conduct on-site overflow fluid water chemical index value 32 and injected fracturing fluid water chemical index value 33 test; the tested overflow fluid water chemical index value 32 and injected fracturing fluid water chemical index value 33 include EC value, TDS value, salinity value, Cl value -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-yielding layer section in the coalbed methane well and the water-richness of the fractured coal seam, 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 conditions of no high water-yielding layer section and weak water-richness of the fractured coal seam, reflecting that there is no high water-yielding layer section and weak water-richness of the fractured coal seam 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 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 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 needs to be sealed before the drainage of the coalbed methane vertical well or directional well.

[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 seam 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 of 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 according to 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 and 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 , the oil pipe 20 of the lower packer 18, and G-grade oil well cement is injected into the water-conducting fracture zone around the wellbore from the oil pipe 20 through the screen pipe 19 on the ground to seal the high-yield water layer. After the cement solidifies, the upper packer 17 and the lower packer 18 are unsealed and the cementing oil pipe 20 is taken out; when the high-yield water layer is near the uppermost fractured coal seam 12, a drillable bridge plug 21 is lowered into the wellbore for temporary isolation, and G-grade 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, 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 cleaning and well washing operations are carried out, and long-term water drainage and gas production are carried out after drainage equipment is installed above and below the well; for the drilling, well cleaning and well washing operations, when the uppermost fractured coal seam 12 is near the 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 after drilling and plugging, the well is cleaned to provide wellbore conditions for subsequent long-term drainage; when the lowermost fractured coal seam 10 is near the high-yield water layer section and the sealing operation is carried out, well cleaning and well washing operations can be carried out immediately to provide wellbore conditions for subsequent long-term drainage; when the middle fractured coal seam 11 is near the high-yield water layer section and the sealing operation is carried out 72 hours later, well cleaning 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 segmented hydraulic sand fracturing transformation on the lowest fractured coal seam (10), the middle fractured coal seam (11), and the uppermost fractured coal seam (12) in sequence from bottom to top; the segmented hydraulic sand fracturing transformation adopts a soluble bridge plug for isolation to ensure that the lowest fractured coal seam (10), the middle fractured coal seam (11), and the uppermost fractured coal seam (12) overflow to the wellhead (8) simultaneously during the overflow process; (b) During the fracturing operation, continuously record the changes in the fracturing wellhead pressure (25), and continuously record the decline process of the fracturing wellhead pressure (25) 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; 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: when the overflow fluid water chemical index value (32) measured during the overflow discharge process tends to be stable and is lower than the injected fracturing fluid water chemical index value (33), which is 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 fracturing coalbed is weakly water-rich, reflecting that there is no high-water-yield layer section in the coalbed methane vertical well or directional well and the fracturing coalbed is weakly water-rich, 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 drops to 60% of the injected fracturing fluid water chemical index value (33) at the end of the overflow discharge, then the curve is no high-water-yield layer section. The overflow fluid water chemical index curve (35) under the condition of water layer section and medium water-rich fractured coal seam reflects that there is no high water-yielding layer section in the coalbed methane vertical well or directional well and the water-rich fractured coal seam is medium, 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, the curve is the overflow fluid water chemical index curve (36) under the condition of high water-yielding layer section or strong water-rich fractured coal seam, reflecting that there is a high water-yielding layer section or strong water-rich fractured coal seam 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-yielding layer section needs to be plugged before the coalbed methane vertical well or directional well is drained; (d) Comprehensively judging the connectivity of the fracture structure, the existence of high-water-yielding layers, and the water-richness of the fractured coal seam by combining the changes in the fracturing wellhead pressure (25) and the changes in the overflow fluid water chemical index value (32), and identifying the high-water-yielding layers of the coalbed methane well; (e) When it is determined that a high-yield water layer exists in a coalbed methane well, corresponding high-yield water layer plugging measures are implemented according to the identification results of the location of the high-yield water layer; (f) After the high-yield water layer is sealed, drilling, well cleaning 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 sealing high-water-yield layers in a coalbed methane well with combined development according to claim 1, characterized in that: In step (a), the maximum inclination of the directional well does not exceed 35 degrees to ensure that the segmented hydraulic pressure and high-yield water layer blocking downhole operations are carried out smoothly; the vertical distance between the lowest fractured coal seam (10) and the middle fractured coal seam (11) is not less than 30 meters to ensure that a sand pocket of a set depth exists after the lowest fractured coal seam (10) is blocked.

3. The method for identifying and plugging high-water-yield layers in a coalbed methane well with combined development according to claim 1, characterized in that: In step (b), the fracturing wellhead pressure (25) has three changes during the fracturing construction process: first, 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 the pump stops, 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) is continuously lower than the minimum principal stress of the fracturing coal seam. force, and after the fracturing pump truck stops pumping, the fracturing wellhead pressure (25) drops rapidly and stabilizes, and is maintained at a level 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 higher in the early stage of the fracturing construction process, and then drops to 50% of the early stage. After the pump is stopped, it drops rapidly and stabilizes, and is maintained at a level 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 of the artificial fracture.

4. The method for identifying and sealing high-water-yield layers in a coalbed methane well with combined development according to claim 1 is characterized by: 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 as follows: 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 during 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 have been connected with the fracture structure around the wellbore, and there is a possibility of high water production during the subsequent drainage process.

5. The method for identifying and sealing high-water-yield layers in a coalbed methane well with combined development according to claim 1 is characterized by: 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 three times, fill the entire bottle with the water sample when sampling, and conduct on-site testing of the overflow liquid water chemical index value (32) and the injected fracturing fluid water chemical index value (33); the sampling and testing frequency of the overflow liquid water chemical index value (32) is once every 2 hours.

6. The method for identifying and sealing high-water-yield layers in a coalbed methane well with combined development according to claim 1 is characterized by: In step (d), the method for identifying high-water-yield layers is to first determine the possible high-water-yield layers according to the variation curve of the fracturing wellhead pressure (25) during the stratified fracturing of the combined-layer development coalbed methane well, and the lower the fracturing wellhead pressure (25) after stabilization, the greater the possibility of high water production in the fracturing layer; secondly, determine whether there is a high-water-yield layer in the coalbed methane vertical well or directional well according to the variation curve of the water chemical index value (32) of the overflow fluid during the overflow of the combined-layer 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-yield possibility of each fracturing layer according to the fracturing wellhead pressure (25).

7. The method for identifying and sealing high-water-yield layers in a coalbed methane well with combined development according to claim 1, characterized in that: In step (e), the corresponding high-water-yield layer blocking measures are respectively implemented: when the lowermost fractured coal seam (10) is near a high-water-yield layer, a permanent bridge plug (16) is inserted above the perforated layer of the lowermost fractured coal seam (10) to block the formation water produced near the lowermost fractured coal seam (10) to prevent the formation water produced near the lowermost 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 middle fractured coal seam (11) is near a high-water-yield layer, an oil pipe (20) with an upper packer (17) and a lower packer (18) is inserted into the wellbore, and the surface is connected to the oil pipe (20). The screen pipe (19) injects G-grade oil well cement into the water-conducting fracture zone around the wellbore to seal the high-yield water layer. After the cement solidifies, the upper packer (17) and the lower packer (18) are unsealed and the cementing oil pipe (20) is taken out. When the high-yield water layer is near the uppermost fractured coal seam (12), a drillable bridge plug (21) is lowered into the wellbore for temporary isolation. The G-grade 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, and clean water (23) is used as the displacement fluid for displacement to reduce the difficulty of subsequent wellbore operations.

8. The method for identifying and sealing high-water-yield layers in a coalbed methane well with combined development according to claim 1 is characterized by: In step (f), the drilling, plugging, and well cleaning 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 dredged and cleaned to provide 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 cleaning operations are immediately carried out to provide 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 cleaning operations are carried out to provide wellbore conditions for subsequent long-term drainage.

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