CN114439428B - Enhanced extraction method for coal bed gas horizontal well of coal group under goaf group - Google Patents
Enhanced extraction method for coal bed gas horizontal well of coal group under goaf group Download PDFInfo
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Abstract
The application discloses a method for strengthening extraction of coal bed gas horizontal wells of a group under a goaf penetrating group, which comprises the steps of determining a well track of the goaf penetrating group of an L-shaped horizontal well; determining the arrangement azimuth and average well deviation of a horizontal section of the horizontal well according to the minimum horizontal main stress direction of the goaf and the contour line of the lower coal group; determining a layout layer of a horizontal section of the horizontal well according to the distance between the top surface of the lower coal seam and the bottom surface of the adjacent goaf obtained through exploration, the firmness coefficient of the lower coal seam, the stress of the top plate of the lower coal seam and the stress of the bottom plate of the lower coal seam; completing the drilling and completion construction of the horizontal well of the coal seam of the lower group of the goaf group; determining perforation positions and fracturing segment positions of the horizontal segments of the horizontal well, and completing staged fracturing construction of the horizontal segments of the horizontal well; and after the horizontal well fracturing is completed, the blowout flowback and well flushing operation is carried out, and the coal bed gas drainage gas production is carried out. The method can efficiently penetrate the goaf group to realize large-scale and rapid extraction of the coal bed gas of the lower group, and has low construction risk and good extraction effect.
Description
Technical Field
The application belongs to the technical field of ground coal bed gas extraction, and particularly relates to a method for reinforcing extraction of coal bed gas horizontal wells of coal beds under a goaf group.
Background
The development of coal bed gas in mining areas has multiple economic and social benefits of relieving the situation of energy shortage, protecting the atmosphere environment, restraining coal mine gas disasters and the like. Along with the development of multi-coal-bed development mine coal exploitation, a huge goaf group is formed after the upper multi-coal-bed exploitation is finished, and the blocking influence is generated on the coal-bed gas extraction of the lower group coal, so that the coal-bed gas of the lower group coal of the goaf group of the extracted coal mine becomes an important technical problem of the coal and the coal-bed gas co-exploitation of the coal mining area in order to ensure the advanced pre-extraction and the continuous exploitation and utilization of coal-bed gas resources of the coal mine area. At present, the extraction of coal seam gas of the lower group coal is commonly performed by adopting a goaf penetrating straight well, and the method has the defects of large construction work amount, small single well control area, low yield and low extraction efficiency, and is difficult to achieve the requirement of efficiently penetrating the goaf group to realize large-scale and rapid reduction of the coal seam gas content of the lower group coal. Unused horizontal well extraction is mainly due to several reasons: (1) The goaf coal pillar distribution and stratum subsidence rule is complex, and the well positions and horizontal section positions of the horizontal well penetrating goaf groups are difficult to lay; (2) The drilling and completion difficulty of the horizontal well through the goaf group is high, the drilling leakage of the goaf section is serious, the plugging difficulty is high, the drilling efficiency is low, and the construction risk is high; (3) The upper goaf group has an important influence on horizontal well horizon layout of the lower coal seam.
Disclosure of Invention
Aiming at the defects and shortcomings in the prior art, the application provides a method for reinforcing extraction of coal bed gas of coal beds under a goaf penetrating group, which aims to solve the technical problem of low extraction efficiency of coal bed gas of coal beds under a goaf penetrating group in the prior art.
In order to achieve the above purpose, the application adopts the following technical scheme:
a method for enhanced extraction of coal bed gas of a group under a goaf group comprises the following steps:
step 1, acquiring exploration data of a target mining area, and determining a well track of an L-shaped horizontal well penetrating goaf group according to the exploration data;
step 2, determining the layout azimuth and average well deviation of a horizontal section of the horizontal well according to the minimum horizontal main stress direction of the goaf obtained by exploration and the contour line of the lower group coal;
step 3, determining the arrangement layer of the horizontal section of the horizontal well according to the distance between the top surface of the lower coal seam and the bottom surface of the adjacent goaf, the firmness coefficient of the lower coal seam, the stress of the top plate of the lower coal seam and the stress of the bottom plate of the lower coal seam, which are obtained through exploration:
step 4, completing the drilling and completion construction of the horizontal well of the coal seam of the lower group of the goaf group;
step 5, determining perforation positions and fracturing segment positions of the horizontal segment of the horizontal well, and then completing staged fracturing construction of the horizontal segment of the horizontal well;
and 6, after the horizontal well fracturing is completed, the blowout flowback and well flushing operation is carried out, and then the coal bed gas drainage and gas production are carried out.
The application also has the following technical characteristics:
further, determining the borehole trajectory of the L-shaped horizontal well goaf-penetrating group according to the exploration data specifically includes:
step 1.1, exploring to obtain the position of a protective coal pillar in each goaf, the thickness of a stope coal bed and the stope time;
step 1.2, determining a well track according to the position of a protective coal pillar in each goaf, the thickness of a stoping coal seam and the stoping time, arranging a horizontal well in an area with the stoping thickness of the coal seam less than 4m and the stoping time greater than 5 years, and enabling the horizontal distance between the intersection point of the perpendicular bisector of the vertical section of the well track and the horizontal line of the coal seam and the horizontal distance between the extension line of an adjacent coal pillar in each stoping layer to be not less than 20 times of the stoping thickness of the coal seam, wherein the adjacent coal pillar is the coal pillar adjacent to the vertical section of the well track.
Further, the determining the layout horizon of the horizontal well horizontal segment in step 3 specifically includes:
when the firmness coefficient of the lower group of coals is more than 1, the horizontal section of the horizontal well is arranged in the lower group of coal seams;
when the firmness coefficient of the lower group coal is less than 1, the vertical stress of the lower group coal bed and the lower group coal bed roof is more than the horizontal stress of the lower group coal bed and the lower group coal bed roof, the minimum horizontal main stress of the lower group coal bed roof is more than the minimum horizontal main stress of the lower group coal bed, and the distance between the lower group coal bed and the adjacent goaf is more than 2 times of the fracturing crack height simulation value of the horizontal well horizontal section, the horizontal well horizontal section is arranged in the roof stratum of the next adjacent lower group coal bed;
when the firmness coefficient of the lower group coal is less than 1, the vertical stress of the lower group coal bed and the lower group coal bed roof is more than the horizontal stress of the lower group coal bed and the lower group coal bed roof, the minimum horizontal main stress of the lower group coal bed roof is more than the minimum horizontal main stress of the lower group coal bed, and the distance between the lower group coal bed and the adjacent goaf is less than 2 times of the fracturing crack height simulation value of the horizontal well horizontal section, the horizontal well horizontal section is arranged in the bottom plate rock stratum of the next adjacent lower group coal bed.
Furthermore, the well bevel angle of the horizontal section of the horizontal well in the step 2 is 90-110 degrees.
Further, the well inclination angle of the horizontal section of the horizontal well in the step 2 is 100 °.
Furthermore, the construction of the drilling and completion of the coal seam horizontal well under the goaf penetrating group in step 4 specifically comprises adopting a three-well structure, and in the process of drilling and completion of the goaf penetrating group, sequentially lowering expansion pipes with gradually reduced diameters from top to bottom, wherein the diameter difference value of the adjacent expansion pipes is 20-25 mm.
Further, a rubber sealing element is arranged on the expansion pipe, and the position of the rubber sealing element in the expansion pipe is arranged in a rock stratum 5-10 m above a roof fracture zone and 5-10 m below a bottom drum fracture zone of each goaf in the goaf group.
Further, the technological parameters of the staged fracturing construction described in step 5 include:
when the horizontal well horizontal section is arranged on the top plate of the lower group of coal seams: adopting a vertical downward directional perforation mode, wherein the perforation penetration depth is more than 1m, adopting a sinking type propping agent, and the volume density is more than 1000kg/m 3 Finishing the penetrating layer fracturing construction by adopting optical sleeve injection;
when the horizontal section of the horizontal well is arranged in the lower group of coal seams, a horizontal and downward hydraulic directional sand blasting perforation mode is adopted, and a submerged propping agent with the volume density more than 1000kg/m is adopted 3 The fracturing construction is completed by adopting an oil pipe and annulus joint injection mode;
when the horizontal section of the horizontal well is arranged on the bottom plate of the lower group of coal beds, a vertical upward directional perforation mode is adopted, the perforation penetration depth is more than 1m, a floating type propping agent is adopted, and the volume density is 800-1000 kg/m 3 And finishing the penetrating layer fracturing construction by adopting the light sleeve injection.
Furthermore, in the drainage gas production operation in step 6, the pump hanging position is a vertical deep position of a connecting midpoint of a landing point target point of the horizontal well and a tail end target point of the horizontal well horizontal section, and the well inclination angle is less than 75 degrees.
Furthermore, in the blowout flow-back operation described in step 6, the blowout is started after the wellhead pressure of the horizontal well is lower than the closing pressure of the coal seam by 3MPa, and the initial blowout flow is 0.5m 3 The maximum discharge flow is less than 10.0m 3 /d/stage.
Compared with the prior art, the application has the beneficial technical effects that:
(1) According to different geological conditions of a target mining area and the extraction requirements of coal seam gas of the next group, the method can select the well track of the L-shaped horizontal well through goaf groups, the arrangement azimuth and average well inclination of the horizontal section of the horizontal well, so that the continuous through goaf well drilling and completion construction of the horizontal well is realized, the efficient arrangement of the horizontal wells of the strata of different goaf groups is completed, the method is beneficial to the improvement of the enhanced extraction effect of the coal seam gas horizontal well of the next group of the through goaf groups according to local conditions, the reduction of construction risks and the improvement of the enhanced extraction effect of the coal seam gas of the next group of the through goaf groups.
(2) According to the method, through the arrangement of the azimuth and the inclination angle of the horizontal section of the horizontal well, the vertical cracks formed by fracturing can be vertical to the shaft of the horizontal section of the horizontal well, so that the fracturing transformation and the drainage and gas production effects of the horizontal well are improved, the integral depressurization of the horizontal section of the horizontal well is realized, and the horizontal well is ensured to have higher productivity.
(3) According to the method, different staged fracturing processes are adopted for horizontal wells with different layout positions, so that the modification of the coalbed methane reservoir is realized, complex network cracks are formed in the staged fracturing process, and the single well yield can be effectively improved.
Drawings
FIG. 1 is a flow chart of the method of the present application;
FIG. 2 is a schematic view of the spatial position of the vertical section in the deployed position of the well site in the ground in accordance with the present application;
FIG. 3 is a schematic diagram of a horizontal well goaf group progressive plugging drilling and completion structure;
fig. 4 is a schematic diagram of enhanced drainage of a horizontal well of a coal seam of a lower group of through goaf groups.
FIG. 5 is a schematic diagram of enhanced drainage of a horizontal well through the roof strata of a coal seam under a goaf group.
FIG. 6 is a schematic diagram of enhanced drainage of a horizontal well through the floor of the coal seam in the goaf group.
FIG. 7 is a schematic diagram of the pumping position of the L-shaped horizontal well of the present application.
Reference numerals:
1-penetrating goaf group horizontal wells; 2-expanding the tube; roof strata of 3-lower group coal seam; 4-lower group coal seam; floor strata of 5-lower group coal seam; 6-upper group coal seam; 7-goaf; 8-fracturing the fracture.
The application is described in detail below with reference to the drawings and the detailed description.
Detailed Description
The application relates to a method for enhanced extraction of coal bed gas of a coal bed under a goaf group, which is used for extracting coal bed gas from the coal bed under the goaf group, and has the primary task of defining the top-bottom plate interface of the coal bed under the goaf group, the structure and position of the coal bed in the goaf group, and the secondary task of acquiring data such as the parameters of each goaf and the coal bed in the goaf group, the lithology, thickness, coal bed rock mechanical parameters, physical parameters and the like of the top plate or the bottom plate of the coal bed; the azimuth of the horizontal well is preferably distributed in parallel with the direction of the minimum horizontal main stress; determining the layout azimuth and average well deviation of the horizontal section of the horizontal well, and then finishing the drilling of the horizontal section of the horizontal well; and finally, carrying out directional perforation or multi-cluster directional perforation, and carrying out staged fracturing construction and drainage gas production of the coal bed gas of the lower group. The method achieves the purpose of strengthening extraction of the coal bed gas horizontal well of the group under the goaf through determining the well track of the goaf, selecting the extraction well position of the horizontal well and selecting the fracturing mode.
Technical terms related to the present application are explained as follows:
goaf group: refers to a stratum formed by a plurality of coal seam goafs after coal recovery.
Fracture height: refers to the height of a fracture formed above or below the horizontal leg wellbore of a horizontal well after fracturing.
Well bevel angle: the well inclination angle is used for indicating the inclination of the well track, and the well inclination angle refers to the included angle between the central axis of any point in the well track of the horizontal section of the horizontal well and the plumb line of the earth.
Roof slit band: the method refers to an interval in which an overlying strata forming a goaf after coal recovery is bent and deformed under the action of ground stress to generate cracks, and the overlying strata of the goaf is sequentially divided into a bending subsidence zone, a crack zone and a caving zone from top to bottom.
Bottom drum slit band: the coal mining method is characterized in that a floor rock stratum forming a goaf after coal mining is extruded and swelled to generate an interval of cracks under the action of ground stress, and an underlying stratum of the goaf is sequentially divided into a crushing zone, a crack zone and a bending sinking zone from top to bottom.
Wellbore trajectory: refers to the path a well has through from a surface wellhead location to a subsurface target area.
As shown in FIG. 2, A3 represents an area where the distance between the intersection point of the perpendicular bisector of the vertical section of the borehole track in the uppermost first goaf and the horizontal line of the coal seam is greater than 20 times the coal seam extraction thickness, A2 represents an area where the distance between the intersection point of the perpendicular bisector of the vertical section of the borehole track in the intermediate second goaf and the horizontal line of the coal seam is greater than 20 times the coal seam extraction thickness, A1 represents an area where the distance between the intersection point of the perpendicular bisector of the vertical section of the borehole track in the lowermost third goaf and the horizontal line of the coal seam is greater than 20 times the coal seam extraction thickness, and A is an overlapping area of three areas, namely, a setting area of the vertical section of the borehole track, and the vertical section of the borehole track should be set in the A area.
The following specific embodiments of the present application are given according to the above technical solutions, and it should be noted that the present application is not limited to the following specific embodiments, and all equivalent changes made on the basis of the technical solutions of the present application fall within the protection scope of the present application.
The present application will be described in further detail with reference to examples.
Example 1
In this example, a goaf group was selected at the Cheng Zhuang mine, and specific parameters of the goaf group were as follows:
the well field develops No. 3, no. 9 and No. 15 coal beds, wherein the thickness of the No. 3 coal bed is about 4m, the thickness of the No. 9 coal bed is about 2m, the thickness of the No. 15 coal bed is about 4m, the distance between the No. 15 coal bed and the No. 9 coal bed is 50-60 m, and the distance between the No. 15 coal bed and the No. 3 coal bed is about 100-110 m. Most of the No. 3 and No. 9 coal beds are mined, and the period of time after mining is 6 years. And when gas extraction of the No. 15 coal seam is carried out, the goaf of the No. 3 and No. 9 coal seams is required to be penetrated.
The embodiment provides a method for enhanced extraction of coal bed methane horizontal wells of coal groups under a goaf penetrating group, which comprises the following steps:
step 1, acquiring exploration data of a target mining area, and determining a well track of an L-shaped horizontal well penetrating goaf group according to the exploration data;
specifically, the exploration data of the target mining area collected in the embodiment includes: the method comprises the steps of (1) stratum inclination angle and tendency, ground stress direction of a region where a target mining area is located, seam roof/bottom plate contour of each group of coal, seam burial depth, seam thickness, stope time, seam firmness coefficient, seam roof bottom plate lithology, seam overlying strata lithology and thickness, seam mining back fracture zone development height, each coal layer protection coal pillar space position, seam roof rock layer thickness of a lower group of coal layers, longitudinal heights of all goafs above the lower group of coal layers, and testing the obtained fracture height design value of a horizontal well horizontal section.
The method for determining the well track of the L-shaped horizontal well penetrating goaf group according to the exploration data specifically comprises the following steps:
step 1.1, exploring to obtain the position of a protective coal pillar in each goaf, the thickness of a stope coal bed and the stope time;
and 1.2, determining a borehole track according to the position of a protective coal pillar in each goaf, the thickness of a stoping coal seam and the stoping time, arranging a horizontal well in an area with the stoping thickness of the coal seam less than 4m and the stoping time greater than 5 years, wherein the horizontal distance between the intersection point of the perpendicular bisector of the vertical section of the borehole track and the horizontal line of the coal seam and the horizontal distance between the extension line of an adjacent coal pillar in each stoping layer is not less than 20 times of the stoping thickness of the coal seam, and the adjacent coal pillar is the coal pillar adjacent to the vertical section of the borehole track so as to avoid a triangular area formed by downwards bending the coal pillar and a top plate.
In this embodiment, the purpose of selecting an L-shaped horizontal well is to reduce the number of times and the engineering amount of penetrating the goaf group in the well completion process, and reduce the construction cost and the construction risk.
Step 2, determining the layout azimuth and average well deviation of a horizontal section of the horizontal well according to the minimum horizontal main stress direction of the goaf obtained by exploration and the contour line of the lower group coal;
preferably, the horizontal section of the L-shaped horizontal well is parallel to the minimum horizontal main stress direction, and when the horizontal section shaft is arranged, the vertical distance between the tail end of the horizontal section shaft and the horizontal plane is larger than the vertical distance between the landing point of the horizontal section shaft and the reference plane, the well inclination angle of the horizontal section of the horizontal well is 100 degrees, and the vertical crack formed by later fracturing is vertical to the shaft of the horizontal section of the horizontal well, so that the fracturing transformation and drainage and gas production effects of the horizontal well are improved.
Step 3, determining the arrangement layer of the horizontal section of the horizontal well according to the distance between the top surface of the lower coal seam and the bottom surface of the adjacent goaf, the firmness coefficient of the lower coal seam, the stress of the top plate of the lower coal seam and the stress of the bottom plate of the lower coal seam, which are obtained through exploration:
as shown in fig. 4, when the firmness coefficient of the lower group coal is more than 1, the horizontal well horizontal section is arranged in the lower group coal seam;
as shown in fig. 5, when the robustness coefficient of the lower coal seam is less than 1, the vertical stress of the lower coal seam and the top plate of the lower coal seam is more than the horizontal stress of the lower coal seam and the top plate of the lower coal seam, the minimum horizontal main stress of the top plate of the lower coal seam is more than the minimum horizontal main stress of the coal seam of the lower coal seam, and the distance between the lower coal seam and the adjacent goaf is more than 2 times of the fracturing fracture height simulation value of the horizontal well horizontal segment, the horizontal well horizontal segment is arranged in the top plate rock stratum of the next adjacent lower coal seam;
as shown in fig. 6, when the lower coal seam firmness coefficient < 1, the vertical stress of the lower coal seam and the lower coal seam roof > the horizontal stress of the lower coal seam and the lower coal seam roof, the minimum horizontal main stress of the lower coal seam roof > the minimum horizontal main stress of the lower coal seam, and the distance between the lower coal seam and the adjacent goaf < the fracturing fracture height analog value of the horizontal well horizontal segment is 2 times, the horizontal well horizontal segment is arranged in the bottom plate rock stratum of the next lower coal seam.
And adopting Comsol Multiphysic simulation software to establish a numerical model of the horizontal well multi-section fracturing inter-section interference, simulating and analyzing the horizontal well fracturing inter-section interference law under different working conditions, determining the minimum section spacing H1 of the horizontal well section fracturing, and simultaneously obtaining the fracturing crack height design value of the horizontal well section.
In this embodiment, the horizontal well horizontal leg is deployed in coal seam No. 15, depending on the situation of the target mine.
Step 4, completing the drilling and completion construction of the horizontal well of the coal seam of the lower group of the goaf group;
specifically, in the process of drilling and completing a goaf group, expansion pipes with gradually reduced diameters are sequentially arranged in the horizontal well from top to bottom to seal a goaf leakage stratum, the diameter difference of adjacent expansion pipes is 20-25 mm, and the difference between the size of a drill bit penetrating through the next goaf and the inner diameter of the sealing expansion pipe of the upper goaf is 6-8 mm, so that the connection between the expansion pipes and the drill bit is realized, as shown in fig. 3.
As a preferable scheme of the embodiment, a horizontal well adopts a three-hole well structure, a drill bit with the diameter of 425mm is used for drilling into a stable bedrock for 5-10 m, then a surface casing with the diameter of 377mm is put into a J55 steel grade, and then cementing cement is returned to the ground; and drilling a drill bit with phi 311mm to about 50m above the stratum of the No. 3 coal seam goaf, adjusting drilling parameters, and comprising: 1.0-1.2 g/cm 3 The low-density slurry of (1), the rotating speed of 50-120 r/min, the rapid drilling of the fracture zone of the roof plate, the goaf and the bottom by the drilling pressure of less than 4tThe drum fracture zone leaks away from the formation. In the goaf group drilling completion process of penetrating the No. 3 coal seam and the No. 9 coal seam, sequentially downwards entering an expansion pipe with gradually reduced diameter from top to bottom, wherein the lower position of the rubber sealing element is arranged in a rock stratum 5-10 m above a roof fracture zone and 5-10 m below a bottom drum fracture zone of the No. 3 coal seam and the No. 9 coal seam goaf in the goaf group, and rubber on a pipe body of the expansion pipe is attached to the walls of the upper rock stratum and the lower rock stratum of a goaf layer section so as to realize the isolation of a goaf leakage stratum; until the packing construction of the whole goaf group is completed, then continuing to drill to a landing point of a horizontal well, putting a J55 steel grade and phi 193.7mm sleeve into the well, and returning well cementation cement paste to the ground; drilling a horizontal section of a horizontal well by using a drill bit with the diameter of phi 171.5mm, and putting a production sleeve with the diameter of phi 139.7mm into an N80 steel grade after finishing drilling; if the horizontal section of the horizontal well is arranged in the lower group of coal beds, the horizontal well adopts a casing running and well completion mode without well cementation, and if the horizontal section of the horizontal well is arranged on the top and bottom plates of the lower group of coal beds, the horizontal section of the horizontal well adopts a casing running and well completion mode; and then returning the cement slurry to the ground, and finishing the well drilling and completion construction.
Wherein, three open well tubular string adopts the showy sleeve pipe of running down, and showy sleeve pipe of running down includes: the floating collar and the casing string are arranged at the position 10-20 m in vertical depth above the landing site of the L-shaped horizontal well, mud is not poured into the casing below the floating collar in the casing running process, the casing string above the floating collar is filled with mud, the casing below the floating collar is hollow, floating centering of the casing in the horizontal well section is achieved, contact between the casing and the well wall in the casing running process is reduced, sliding friction resistance in the casing running process is reduced, and the casing is ensured to be smoothly run to the appointed depth.
Step 5, determining perforation positions and fracturing segment positions of the horizontal segment of the horizontal well, and then completing staged fracturing construction of the horizontal segment of the horizontal well;
when the horizontal well horizontal section is arranged on the top plate of the lower group of coal seams: adopting a vertical downward directional perforation mode, wherein the perforation penetration depth is more than 1m, adopting a sinking type propping agent, and the volume density is more than 1000kg/m 3 Finishing the penetrating layer fracturing construction by adopting optical sleeve injection; the construction discharge capacity reaches 8-15 m 3 /min, realizing large-displacement and large-scale additionSand, improving the fracturing reconstruction effect of the horizontal well.
When the horizontal section of the horizontal well is arranged in the lower group of coal seams, adopting a horizontal and downward hydraulic directional sand blasting perforation mode, and adopting an oil pipe and annulus joint injection mode to finish fracturing construction; the jet displacement is 1.5-2.5 m 3 Carrying out fracturing construction by adopting oil pipe and annular space combined injection, wherein the injection displacement of the oil pipe is 1.5-3.0 m 3 Annulus fracturing displacement is 4-7 m 3 Per min, total displacement of 5-10 m 3 A/min; realize large discharge capacity, add sand on a large scale, improve horizontal well fracturing transformation effect, reduce construction risk.
When the horizontal section of the horizontal well is arranged on the bottom plate of the lower group of coal beds, a vertical upward directional perforation mode is adopted, the perforation penetration depth is more than 1m, a floating type propping agent is adopted, and the volume density is 800-1000 kg/m 3 Finishing the penetrating layer fracturing construction by adopting the injection of the optical sleeve, wherein the construction discharge capacity reaches 8-15 m 3 And/min, realizing large-discharge and large-scale sand adding, and improving the fracturing transformation effect of the horizontal well.
In the embodiment, a horizontal and downward hydraulic directional sand blasting perforation mode is adopted, and an oil pipe and annulus combined injection mode is adopted to finish 8-section staged fracturing construction of the horizontal well; injection displacement of 2.2m 3 Carrying out fracturing construction by adopting oil pipe and annular space combined injection, wherein the injection displacement of the oil pipe is 1.8-2.7 m 3 /min, annular fracturing displacement 6.3m 3 Per min, total displacement of 8.2m 3 /min。
And 6, after the horizontal well fracturing is completed, the blowout flowback and well flushing operation is carried out, and then the coal bed gas drainage and gas production are carried out.
In the open flow flowback operation, open flow is started after the wellhead pressure of the horizontal well is lower than the closing pressure of the coal seam by 3MPa, and the initial open flow is 0.5m 3 The flow rate is gradually increased along with the pressure reduction, and the maximum discharge flow rate is less than 10.0m 3 /d/stage. The whole fracturing fluid flowback process always aims at controlling the coal bed without sand and coal dust. And flushing the horizontal well after the open flow is finished, so that the whole well section of the horizontal well is communicated.
Then the L-shaped horizontal well is fed into the anti-eccentric screw pump for drainage and gas production, as shown in fig. 7, the position of the screw pump fed into the L-shaped horizontal well is not lower than the vertical depth position of the midpoint of the connecting line between the landing point A of the horizontal well and the target point B of the tail end of the horizontal section, and the well inclination angle is smaller than 75 degrees, so that the risks of later drainage, sand and coal injection of the L-shaped horizontal well and pump burying are avoided, the reservoir pressure is reduced to the greatest extent, and the aim of large-area depressurization and desorption is fulfilled. As shown in fig. 7.
The preferred embodiments of the present application have been described in detail above with reference to the accompanying drawings, but the present application is not limited to the specific details of the above embodiments, and various simple modifications can be made to the technical solution of the present application within the scope of the technical concept of the present application, and all the simple modifications belong to the protection scope of the present application.
Moreover, any combination of the various embodiments of the application can be made without departing from the spirit of the application, which should also be considered as disclosed herein.
Claims (8)
1. The enhanced extraction method for the coal bed gas horizontal well of the group coal under the goaf group is characterized by comprising the following steps of:
step 1, acquiring exploration data of a target mining area, and determining a well track of an L-shaped horizontal well penetrating goaf group according to the exploration data;
step 2, determining the layout azimuth and average well deviation of a horizontal section of the horizontal well according to the minimum horizontal main stress direction of the goaf obtained by exploration and the contour line of the lower group coal;
step 3, determining the arrangement layer of the horizontal section of the horizontal well according to the distance between the top surface of the lower coal seam and the bottom surface of the adjacent goaf, the firmness coefficient of the lower coal seam, the stress of the top plate of the lower coal seam and the stress of the bottom plate of the lower coal seam, which are obtained through exploration:
step 4, completing the drilling and completion construction of the horizontal well of the coal seam of the lower group of the goaf group;
step 5, determining perforation positions and fracturing segment positions of the horizontal segment of the horizontal well, and then completing staged fracturing construction of the horizontal segment of the horizontal well;
step 6, after the horizontal well fracturing is completed, the blowout flowback and well flushing operation is carried out, and then the coal bed gas drainage and gas production are carried out;
the determining the borehole track of the L-shaped horizontal well goaf group according to the exploration data in the step 1 specifically comprises the following steps:
step 1.1, exploring to obtain the position of a protective coal pillar in each goaf, the thickness of a stope coal bed and the stope time;
step 1.2, determining a well track according to the position of a protective coal pillar in each goaf, the thickness of a stoping coal seam and the stoping time, arranging a horizontal well in a region with the stoping thickness of the coal seam less than 4m and the stoping time greater than 5 years, wherein the horizontal distance between the intersection point of the perpendicular bisector of the vertical section of the well track and the horizontal line of the coal seam and the horizontal distance between the extension line of an adjacent coal pillar in each stoping layer is not less than 20 times of the stoping thickness of the coal seam, and the adjacent coal pillar is the coal pillar adjacent to the vertical section of the well track;
the step 3 of determining the layout layer of the horizontal section of the horizontal well specifically includes:
when the firmness coefficient of the lower group of coals is more than 1, the horizontal section of the horizontal well is arranged in the lower group of coal seams;
when the firmness coefficient of the lower group coal is less than 1, the vertical stress of the lower group coal bed and the lower group coal bed roof is more than the horizontal stress of the lower group coal bed and the lower group coal bed roof, the minimum horizontal main stress of the lower group coal bed roof is more than the minimum horizontal main stress of the lower group coal bed, and the distance between the lower group coal bed and the adjacent goaf is more than 2 times of the fracturing crack height simulation value of the horizontal well horizontal section, the horizontal well horizontal section is arranged in the roof stratum of the next adjacent lower group coal bed;
when the firmness coefficient of the lower group coal is less than 1, the vertical stress of the lower group coal bed and the lower group coal bed roof is more than the horizontal stress of the lower group coal bed and the lower group coal bed roof, the minimum horizontal main stress of the lower group coal bed roof is more than the minimum horizontal main stress of the lower group coal bed, and the distance between the lower group coal bed and the adjacent goaf is less than 2 times of the fracturing crack height simulation value of the horizontal well horizontal section, the horizontal well horizontal section is arranged in the bottom plate rock stratum of the next adjacent lower group coal bed.
2. The method for enhanced drainage of coal bed methane horizontal wells under a goaf group according to claim 1, wherein the average well inclination of the horizontal well horizontal section in the step 2 is 90-110 °.
3. The method for enhanced drainage of coal seam gas horizontal wells in a coal seam gas under a goaf-penetrating group as claimed in claim 1, wherein the average well deviation of the horizontal well horizontal section in the step 2 is 100 °.
4. The method for enhanced drainage of coal bed methane horizontal wells under a goaf penetrating group as claimed in claim 1, wherein the construction of drilling and completion of the coal bed methane horizontal wells under the goaf penetrating group in step 4 specifically comprises adopting a three-well structure, and sequentially lowering expansion pipes with gradually reduced diameters from top to bottom in the process of drilling and completion of the goaf penetrating group, wherein the diameter difference between adjacent expansion pipes is 20-25 mm.
5. The enhanced drainage method of the coal bed methane horizontal well of the lower group of the goaf penetrating through the goaf group as claimed in claim 4, wherein a rubber sealing element is arranged on the expansion pipe, and the descending position of the rubber sealing element is arranged in a rock stratum 5-10 m above a roof fracture zone and 5-10 m below a bottom drum fracture zone of each goaf in the goaf group.
6. The method for enhanced drainage of coal bed methane horizontal wells under a through goaf group as claimed in claim 1, wherein the technological parameters of staged fracturing construction in step 5 include:
when the horizontal well horizontal section is arranged on the top plate of the lower group of coal seams: adopting a vertical downward directional perforation mode, wherein the perforation penetration depth is more than 1m, adopting a sinking type propping agent, and the volume density is more than 1000kg/m 3 Finishing the penetrating layer fracturing construction by adopting optical sleeve injection;
when the horizontal section of the horizontal well is arranged in the lower group of coal seams, a horizontal and downward hydraulic directional sand blasting perforation mode is adopted, and a submerged propping agent with the volume density more than 1000kg/m is adopted 3 The fracturing construction is completed by adopting an oil pipe and annulus joint injection mode;
when the horizontal section of the horizontal well is arranged on the bottom plate of the lower group of coal beds, a vertical upward directional perforation mode is adopted, the perforation penetration depth is more than 1m, and the coal is minedUsing floating propping agent with volume density of 800-1000 kg/m 3 And finishing the penetrating layer fracturing construction by adopting the light sleeve injection.
7. The method for enhanced drainage of coal seam gas horizontal wells in a coal seam gas under a goaf-penetrating group as claimed in claim 1, wherein in the drainage and gas production operation in step 6, the pump hanging position is a vertical deep position of a midpoint of a connecting line of a landing point of the horizontal well and a tail end target point of a horizontal section of the horizontal well, and the well inclination angle is less than 75 °.
8. The method for enhanced drainage of coal bed methane horizontal wells under a through goaf group as claimed in claim 1, wherein in the step 6, the open flow is started after the wellhead pressure of the horizontal well is lower than the closing pressure of the coal bed by 3MPa, and the initial open flow is 0.5m 3 The maximum discharge flow is less than 10.0m 3 /d/stage.
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