Experimental method for exploring well completion and transformation process of horizontal well in high-permeability coal reservoir

Abstract

The invention relates to an experimental method for exploring a well completion and transformation process of a horizontal well in a high-permeability coal reservoir. The experimental method comprises the following steps: exploring the high-permeability coal reservoir; at least two identical simulation coal seams are constructed in the experiment groove, and when the coal seams are constructed, pipelines are pre-buried in advance; burying a stress sensor at one end of the coal seam away from the pipeline; replacing the pre-buried pipeline with a screen pipe in a half of the coal seam, and replacing the pre-buried pipeline with a simulation sleeve with a directional hole in the other half of the coal seam; the two coal seams provided with the screen pipe and the simulation casing pipe serve as an experiment object, the screen pipe and the simulation casing pipe simulate a horizontal well, and experiments can be conducted on different length proportions of the screen pipe and the simulation casing pipe in the coal seams; confining pressure and temperature are applied to the experimental object, and perforation is conducted on the coal seam through the holes of the simulation casing pipe by means of water pressure injection; fracturing is conducted through the screen pipe and the simulation casing pipe, and then the gas production rate and stress data are recorded; and establishing a relationship between different length ratios of the screen pipe and the simulation casing pipe and stress data of the coal seam to obtain the influence of the experiment on the coal seam.

Description

Technical Field

[0001] The invention belongs to the technical field of horizontal well completion and transformation in coal reservoirs, and specifically relates to an experimental method for exploring horizontal well completion and transformation technology in high-permeability coal reservoirs. Background Art

[0002] For high-permeability coalbed methane reservoirs, when designing their horizontal wells, conventional casing completion was initially used, followed by hydraulic fracturing and other processes, and then coalbed methane mining. With the deepening of practice and research on high-permeability coal reservoirs, it was found that by utilizing the high permeability characteristics of coal reservoirs, using screen completion and then fracturing, sometimes a good gas production can be obtained. The screen surface is evenly and densely covered with screen holes, and there is no need for concrete cementing and well pipe perforation process steps, which can save materials and reduce costs. However, the structure of different positions inside the high-permeability coal reservoir will change, and the adaptability to casing or screen is not completely consistent. In order to fully develop the coal reservoir and obtain higher gas production, field development is currently used to explore how casing and screen can be used together. However, the entire process of field drilling, completion, perforation, fracturing and final gas production is long and the cost is too high. How to use experimental methods to simulate the horizontal well completion and transformation technology in high permeability coal reservoirs and simultaneously evaluate the gas production effects of two completion methods (casing and screen) is a problem faced by technical personnel in this field. Summary of the invention

[0003] In view of the above problems, the present invention provides an experimental method for exploring the completion and transformation technology of horizontal wells in high permeability coal reservoirs, comprising the following steps: S1: Conduct geological exploration for high permeability coal reservoirs to obtain geological characteristics and structural data; S2: Based on the information data of step S1, at least two identical simulated coal seams are constructed in the experimental tank. When constructing the coal seams, pipelines are pre-buried in advance to facilitate the subsequent arrangement of screens and casings for gas extraction; stress sensors are evenly buried at one end of the coal seam away from the pipeline to detect the impact of fracturing and gas production on the far end of the coal seam; S3: In half of the coal seams, the pre-buried pipes are replaced with screens, and in the other half of the coal seams, the pre-buried pipes are replaced with simulated casings with directional openings; the two coal seams with screens and simulated casings are used as an experimental object. The screens and simulated casings simulate horizontal wells, and different length ratios of the screens and simulated casings in the coal seams can be tested; S4: applying the same experimental confining pressure and temperature to the experimental object, and using water pressure jet to perforate the coal seam through the opening of the simulated casing; then, fracturing is performed through the screen and the simulated casing, and the gas production is recorded, and the data of the stress sensor is recorded at the same time; S5: Establish a curve relationship between different length ratios of the screen and the simulated casing and the average value of the stress data at the ends of the two coal seams to obtain the influence of the separate fracturing and gas production of the screen and the simulated casing on the coal seam.

[0004] The present invention constructs a simulated coal seam in an experimental tank to simulate the fracturing and gas production process of the coal seam. A pipe with directional openings is used to simulate the actual casing. When perforating, there is no need to shoot through the simulated casing. The simulated casing can be reused. When perforating, just shoot directly at the coal seam, which saves hydraulic energy and makes the perforating operation easier to control. The present invention uses a water pressure injection method with adjustable pressure to replace the traditional blasting perforation. The blasting perforation is powerful, and the operation of explosives is not suitable for small-scale laboratory experiments. The perforating device cannot be made very small and thin. The diameter of the simulated casing needs to adapt to the thickness of the perforating device, which limits the size of the simulated casing and the size of the experimental tank. The water pipe and the injection head of the water pressure injection are not large in size, have good safety, can adjust the water pressure according to the needs of the experiment, and are suitable for laboratory use.

[0005] When operating in an actual coal reservoir, a horizontal well consists of a screen and a casing. The screen can be directly fractured without perforating, and the casing is fractured after perforating. After the screen and casing are fractured, gas production can be carried out. In practice, it is found that different operating modes of the casing and the screen will have an impact on the gas production area responsible for each other. This impact is complex. Technical personnel in this field have not been able to study this impact clearly, and only know that this impact is not conducive to the stability of gas production. At present, we can only explore on the spot, moving the ends of the screen and the casing that are close to each other away from each other, that is, separating them by a certain safety distance, to weaken or eliminate the impact of the screen and the casing on each other.

[0006] The length of a horizontal well is several hundred meters, and the length of the casing and screen is also tens to hundreds of meters. The above-mentioned safety distance may be more than ten meters to several dozen meters. The present invention uses an experimental tank for simulation, which cannot achieve a safety distance of more than ten meters to several dozen meters. Instead, the simulated casing and screen are buried separately in two coal seams with the same conditions, and then they are experimented together as an experimental object to study the effects of the simulated casing and screen, and the effects of different length ratios of the screen and simulated casing on the overall gas production. The present invention selects coal seam stress as an indicator to reflect the effects of the simulated casing and screen fracturing and gas production on the coal seam.

[0007] Optionally, in step S1, geological exploration is conducted on the actual underground high-permeability coal reservoir, and combined with previous exploration data, geological information of the target coal reservoir is obtained, and the geological information includes but is not limited to burial depth, layer thickness, pressure, temperature, permeability, geological structure, rock and soil type, and fracture development. Step S1 can apply conventional exploration and remote sensing and seismic monitoring methods.

[0008] Optionally, the test tank is in a cubic shape with a detachable top cover on the top, and hollow oil and gas bags are respectively provided on the three inner side surfaces of the test tank on the three-dimensional surface, so that after being filled with oil or gas, the oil and gas bags are squeezed against other inner side surfaces opposite to the simulated coal seam to provide confining pressure for the simulated coal seam; A temperature control device is provided in the experimental tank to control the temperature in the experimental tank; a plurality of through holes are provided on the vertical side of the experimental tank where no oil and gas bag is provided, so that the embedded pipeline, simulation casing and screen tube can enter and exit the experimental tank.

[0009] Further optionally, the experimental tank is equipped with a compaction assembly, which includes a horizontal compaction plate and a plurality of vertical partition plates, wherein the partition plates are detachably connected to the bottom surface of the compaction plate and are parallel to each other, and the partition plates are used to separate two adjacent simulated coal seams.

[0010] Optionally, step S2 specifically includes: (1) According to the information data of step S1, a simulated coal seam matrix with the same components as the actual coal reservoir is prepared, wherein the matrix includes but is not limited to rock, stone, coal slag, and coal blocks, and the mixture is evenly mixed; According to the length of the simulated casing and screen tube predetermined in the experiment, the pre-buried pipe is inserted into the experimental tank through the through hole on the side wall of the experimental tank, and then the matrix is ​​evenly filled into the experimental tank; when filling the matrix, the stress sensor is arranged at the same time; (2) Compacting the coal seam using a compacting plate with a separator installed, using mechanical pressure or air pressure on the compacting plate to press the compacting plate downward, and inserting the separator into the matrix to form a number of simulated coal seams parallel to each other; (3) Remove the compaction plate, leave the partition plate in the test tank, and seal the test tank with the top cover.

[0011] Further optionally, in step (1), each stress sensor is connected by a sensing optical fiber to form a mesh to form a sensing network, and each stress sensor is evenly distributed, one side of the sensing network faces the side of the experimental tank with a through hole, and the other side of the sensing network faces the side of the experimental tank with an oil-gas bag, and the sensing network is close to the oil-gas bag; the sensing optical fiber passes through the experimental tank and is connected to an external stress detection and analysis device.

[0012] Optionally, the pre-buried pipe is a cylindrical hollow tube, one end of which is open outside the experimental tank, and the other end inside the experimental tank is provided with an openable end cover to close the pre-buried pipe and prevent the matrix from entering the pre-buried pipe when constructing the simulated coal seam.

[0013] Optionally, the simulated casing is a cylindrical hollow tube, one end of which is open and the other end is closed, and the side thereof is provided with at least one row of openings for perforating, fracturing and gas extraction of the coal seam, and the arrangement direction of one row of openings is horizontal; preferably, the side of the simulated casing is provided with several rows of horizontal openings, and the angle between two adjacent rows of openings is 60-90°, so as to facilitate perforating, fracturing and gas extraction in all directions of the coal seam. The screen tube is open at one end and closed at the other end, and the side thereof is evenly and densely covered with through holes.

[0014] Optionally, in step S3, the sealing plug at the through hole of the embedded pipe is removed, and the screen tube or the simulated casing is inserted into the embedded pipe from the open end of the embedded pipe until one end of the screen tube or the simulated casing reaches the closed end of the embedded pipe; the embedded pipe is rotated to loosen, and the embedded pipe is withdrawn from the experimental tank; when withdrawing, due to relative movement, the screen tube or the simulated casing pushes open the end cover, and the screen tube or the simulated casing remains inside the simulated coal seam; the sealing plug is reinstalled at the through hole, and the screen tube or the simulated casing outside the experimental tank is connected to the gas pipeline, so that the gas produced by the screen tube or the simulated casing is transported to the detection device by the gas pipeline.

[0015] Optionally, in step S3, the partition plate divides the entire compacted coal seam in the experimental tank into several simulated coal seams, preferably into an even number of simulated coal seams, half of the coal seams are provided with screens, and the other half of the coal seams are provided with simulated casings; the two coal seams with screens and simulated casings are taken as an experimental object, and the screen and simulated casing are considered to be a combination to simulate an actual horizontal well, thereby eliminating the disadvantage that the screen and simulated casing have a great influence on each other due to the small size of the experimental tank and the fact that they are in the same simulated coal seam, so as to facilitate the separate study of the influence of the screen and simulated casing on gas production by fracturing and gas production.

[0016] The sieve tube and the simulated casing in the experimental tank simulate the horizontal well, and the sum of the lengths of the sieve tube and the simulated casing in the experimental tank is not greater than the length of a simulated coal seam, which can ensure that the length of the simulated horizontal well is much less than the total length of an experimental object (i.e., the sum of the lengths of the two simulated coal seams), which is more in line with the application of coalbed methane mining in actual horizontal wells. The present invention can study the influence of different length ratios of the sieve tube and the simulated casing on the total gas production of an experimental object through multiple experiments, set a length ratio of the sieve tube and the simulated casing for each experiment, record the gas production of the first gas pipeline and the second gas pipeline for each experiment, and then add the two to get the total gas production.

[0017] Optionally, step S4 is specifically: (4) Introducing methane gas into the coal seam through the screen pipe and the simulated casing until the coal seam is saturated with methane; According to the information data of step S1, the experimental confining pressure and temperature are determined, hydraulic oil or gas is input into the oil-gas bag, the coal seam is squeezed to simulate the application of confining pressure, and the experimental tank is heated to the experimental temperature; (5) A water pressure jet pipe is input into the simulated casing, and the jet ports correspond to the openings of the simulated casing one by one, and perforation is performed by water pressure jet; then, fracturing is performed through the simulated casing, and gas is produced after fracturing. The produced methane is output through the second gas pipeline, and the gas production is recorded. At the same time, the data of the stress sensor of the simulated coal seam is recorded; (6) Fracturing is performed through a screen pipe, and gas is produced after fracturing. The produced methane is output through a first gas pipeline, and the gas production is recorded. At the same time, data of the stress sensor of the simulated coal seam is recorded; The above steps (5) and (6) are performed simultaneously.

[0018] Optionally, in step S5, in each experiment, due to the different length ratios between the screen and the simulated casing, the spacing between the screen and the corresponding sensor network is also different. The stress effect caused by the operation of the screen on the simulated coal seam varies with the change of the spacing between the screen and the corresponding sensor network. Similarly, the stress effect caused by the operation of the simulated casing on the simulated coal seam varies with the change of the spacing between the simulated casing and the corresponding sensor network.

[0019] Further optionally, in one experiment, from the start of fracturing by the screen pipe until stable gas production, stress data detected by the corresponding stress sensor is recorded; the stress data is segmented with stable gas production as a dividing point, and the average value of the stress data of the stable gas production section is calculated; After many experiments, the screen tube influence curve was obtained by taking the distance between the end of the screen tube close to the sensor network and the sensor network as the X-axis data and the average value of the stable gas production section as the Y-axis data.

[0020] Further optionally, in one experiment, starting from the implementation of fracturing in the simulated casing until stable gas production, the stress data detected by the corresponding stress sensor is recorded; the stress data is segmented with stable gas production as the dividing point, and the average value of the stress data of the stable gas production section is calculated; After many experiments, the simulated casing influence curve was obtained by taking the distance between the end of the simulated casing close to the sensor network and the sensor network as the X-axis data and the average value of the stable gas production section as the Y-axis data. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 It is the structural diagram of the experimental tank; Figure 2 is a schematic diagram of a compaction assembly; Figure 3 This is a schematic diagram of the buried pipeline.

[0022] In the attached drawings, 1-experimental tank, 2-top cover, 3-oil and gas bag, 4-opening, 5-buried pipeline, 6-simulated casing, 7-screen pipe, 8-compacting plate, 9-partition plate, and 10-end cover. DETAILED DESCRIPTION

[0023] This embodiment provides an experimental method for exploring the completion and transformation process of a horizontal well in a high permeability coal reservoir, comprising the following steps: S1: Conduct geological exploration for high permeability coal reservoirs to obtain geological characteristics and structural data; S2: According to the information data of step S1, at least two identical simulated coal seams are constructed in the experimental tank 1. When constructing the coal seams, the pipeline 5 is pre-buried in advance to facilitate the subsequent arrangement of the screen pipe 7 and the casing during gas production; stress sensors are evenly buried at one end of the coal seam away from the pipeline to detect the impact of fracturing and gas production on the far end of the coal seam; S3: In half of the coal seams, the pre-buried pipes 5 are replaced with screens 7, and in the other half of the coal seams, the pre-buried pipes 5 are replaced with simulated casings 6 with directional openings; the two coal seams provided with screens 7 and simulated casings 6 are used as an experimental object, and the screens 7 and simulated casings 6 simulate horizontal wells, so that different length ratios of the screens 7 and simulated casings 6 in the coal seams can be tested; S4: applying the same experimental confining pressure and temperature to the experimental object, and perforating the coal seam through the opening of the simulated casing 6 by using water pressure jet; then, fracturing is performed through the screen 7 and the simulated casing 6, and then the gas production is recorded, and the data of the stress sensor is recorded at the same time; S5: Establish a curve relationship between different length ratios of the screen 7 and the simulated casing 6 and the average value of the stress data at the two coal seam ends to obtain the influence of the separate fracturing and gas production of the screen 7 and the simulated casing 6 on the coal seam.

[0024] In step S1, geological exploration is conducted on the actual underground high-permeability coal reservoir, and then combined with previous exploration data, geological information of the target coal reservoir is obtained. The geological information includes but is not limited to burial depth, layer thickness, pressure, temperature, permeability, geological structure, rock and soil type, and fracture development.

[0025] like Figure 1-Figure 3 As shown, the experimental tank 1 is in a cubic shape, with a detachable top cover 2 on the top, and hollow oil and gas bags 3 are respectively provided on the three inner side surfaces of the experimental tank 1 on the three-dimensional surface, which are used for the oil and gas bags to squeeze each other with the other inner side surfaces opposite to the simulated coal seam after being filled with oil or gas, so as to provide confining pressure for the simulated coal seam; A temperature control device is provided in the experimental tank 1 for controlling the temperature in the experimental tank 1 ; a plurality of through holes are provided on the vertical side of the experimental tank 1 where no oil and gas bag is provided, so that the embedded pipeline 5 , the simulation casing 6 and the screen tube 7 can enter and exit the experimental tank 1 .

[0026] The experimental tank 1 is equipped with a compaction assembly, which includes a horizontal compaction plate 8 and a plurality of vertical partition plates 9. The partition plates 9 are detachably connected to the bottom surface of the compaction plate 8 and are parallel to each other. The partition plates 9 are used to separate two adjacent simulated coal seams.

[0027] As a specific implementation, the experimental tank 1 is a rectangular parallelepiped, and the lower surface of its top cover 2 is provided with an oil-gas bag, and two vertical side surfaces perpendicular to each other are respectively provided with an oil-gas bag; the oil-gas bag of the top cover 2 and the oil-gas bag of the side surface perpendicular to the partition plate 9 are divided into a plurality of sub-bags according to the position of the partition plate 9 in the experimental tank 1. For example, the plurality of sub-bags of the top cover 2 are parallel to each other, and the adjacent side surfaces of two adjacent sub-bags are close to or even in contact with each other, but not connected, so that the top of the partition plate 9 can be inserted between the two sub-bags, so that one sub-bag can press the corresponding top surface of the simulated coal seam; the plurality of sub-bags of the side surface perpendicular to the partition plate 9 are parallel to each other, and the adjacent side surfaces of two adjacent sub-bags are close to or even in contact with each other, but not connected, so that the side edge of the partition plate 9 can be inserted between the two sub-bags, so that one sub-bag can press the corresponding side surface of the simulated coal seam. The through hole of the experimental tank 1 is arranged on the vertical side surface where the oil-gas bag is not arranged.

[0028] Step S2 is specifically as follows: (1) According to the information data of step S1, a simulated coal seam matrix with the same components as the actual coal reservoir is prepared, wherein the matrix includes but is not limited to rock, stone, coal slag, and coal blocks, and the mixture is evenly mixed; According to the length of the simulated casing 6 and the screen tube 7 predetermined in the experiment, the pre-buried pipe 5 is inserted into the experimental tank 1 through the through hole of the side wall of the experimental tank 1, and then the matrix is ​​evenly filled into the experimental tank 1; when filling the matrix, the stress sensor is arranged at the same time; (2) Compacting the coal seam using a compacting plate 8 equipped with a partition plate 9, using mechanical pressure or air pressure above the compacting plate 8 to press the compacting plate 8 downward, and inserting the partition plate 9 into the matrix to form a plurality of simulated coal seams parallel to each other; (3) Remove the compacting plate 8, leave the partition plate 9 in the experimental tank 1, and cover the top cover 2 to seal the experimental tank 1.

[0029] In step (1), the matrix is ​​first loaded into the experimental tank 1. When the matrix reaches the preset height of the bottom of the pre-buried pipe 5, the pre-buried pipe 5 is inserted from the corresponding through hole. According to the experimental requirements, the length of each pre-buried pipe 5 extending into the experimental tank 1 is adjusted, and then a sealing plug is installed at each through hole to seal the gap between the through hole and the pre-buried pipe 5. Then, the matrix is ​​continued to be loaded so that the matrix surrounds the pre-buried pipe 5 until the matrix reaches the preset height.

[0030] When executing step (1), the oil and gas bags are not pressurized. When filling the matrix, a certain thickness is filled and compacted once with a separate pressing plate. This compaction operation can be manual or mechanical, and the compaction force is not large, so that the matrix particles are filled tightly to avoid large gaps or holes. Fill the area near the two vertical oil and gas bags with fine coal slag and soil particles as much as possible to avoid damaging the oil and gas bags.

[0031] In step (1), each stress sensor is connected by a sensing optical fiber to form a mesh, forming a sensing network, and each stress sensor is evenly distributed. One side of the sensing network faces the side of the experimental tank 1 provided with a through hole, and the other side of the sensing network faces the side of the experimental tank 1 provided with an oil-gas bag. The sensing network is close to the oil-gas bag, but there is a distance of 1 cm between the sensing network and the oil-gas bag. A matrix is ​​filled between the sensing network and the oil-gas bag to prevent the pressure of the oil-gas bag from affecting the stress sensor; the sensing optical fiber passes through the experimental tank 1 and is connected to an external stress detection and analysis device.

[0032] In step (2), each partition plate 9 is directly opposite to the partition corresponding to the oil-gas pocket on the vertical side of the experimental tank 1, and a sealing strip is installed on the side of the partition plate 9. The partition plate 9 is inserted downward into the matrix. When the lower surface of the compaction plate 8 contacts the upper surface of the matrix, there is a small distance between the bottom edge of the partition plate 9 and the bottom surface of the experimental tank 1. The distance is equal to the height of the subsequent matrix after compaction, that is, the height of the partition plate 9 is equal to the height of the simulated coal seam after compaction.

[0033] In step (3), a sealing strip is installed on the top edge of the partition plate 9, and the top edge of the partition plate 9 is directly opposite to the partition corresponding to the oil and gas bag of the top cover 2; the oil and gas bag of the top cover 2 contacts the top surface of the simulated coal seam.

[0034] The pre-buried pipe 5 is a cylindrical hollow tube, one end of which is open outside the experimental tank 1, and the other end inside the experimental tank 1 is provided with an openable end cover 10 to close the pre-buried pipe 5 to prevent the matrix from entering the pre-buried pipe 5 when constructing a simulated coal seam.

[0035] The simulated casing 6 is a cylindrical hollow tube, and four rows of openings 4 are arranged on its side for perforating, fracturing and gas extraction of the coal seam. The arrangement direction of each row of openings 4 is horizontal, and the angle between two adjacent rows of openings is 90°, which is convenient for perforating, fracturing and gas extraction in all directions of the coal seam. The side of the screen tube 7 is evenly and densely covered with through holes.

[0036] In step S3, the pre-buried pipe 5 is replaced by the sieve tube 7, specifically, the sealing plug at the through hole of the pre-buried pipe 5 is removed, and the sieve tube 7 is inserted into the pre-buried pipe 5 from the open end of the pre-buried pipe 5 until one end of the sieve tube 7 reaches the closed end of the pre-buried pipe 5; the pre-buried pipe 5 is rotated to loosen, and the pre-buried pipe 5 is withdrawn from the experimental tank 1; when withdrawing, due to the relative movement, the sieve tube 7 pushes open the end cover 10, and the sieve tube 7 remains inside the simulated coal seam; the sealing plug is reinstalled at the through hole, and the sieve tube 7 outside the experimental tank 1 is connected to the first gas pipeline, so that the gas produced by the sieve tube 7 is transported to the detection device by the first gas pipeline.

[0037] In step S3, the pre-buried pipe 5 is replaced with the simulated casing 6, specifically: the sealing plug of the pre-buried pipe 5 at the through hole is removed, and the simulated casing 6 is sent into the pre-buried pipe 5 from the open end of the pre-buried pipe 5 until one end of the simulated casing 6 reaches the closed end of the pre-buried pipe 5; the pre-buried pipe 5 is rotated to loosen, and the pre-buried pipe 5 is withdrawn from the experimental tank 1; when withdrawing, due to relative movement, the simulated casing 6 pushes open the end cover 10, and the simulated casing 6 remains inside the simulated coal seam; the sealing plug is reinstalled at the through hole, and the simulated casing 6 outside the experimental tank 1 is connected to the second gas pipeline, so that the gas produced by the simulated casing 6 is transported to the detection device by the second gas pipeline.

[0038] In step S3, the partition plate 9 divides the entire compacted coal seam in the test tank 1 into an even number of simulated coal seams.

[0039] Step S4 is specifically as follows: (4) methane gas is introduced into the coal seam through the screen pipe 7 and the simulated casing 6 until the coal seam is saturated with methane; According to the information data of step S1, the experimental confining pressure and temperature are determined, hydraulic oil or gas is input into the oil-gas bag, and the coal seam is squeezed to simulate the application of confining pressure, and the experimental tank 1 is heated to the experimental temperature; (5) A water pressure jet pipe is input into the simulated casing 6, and the jet ports correspond to the openings of the simulated casing 6 one by one, and perforation is performed by water pressure jet; then, fracturing is performed through the simulated casing 6, and gas is produced after fracturing. The produced methane is output through the second gas pipeline, and the gas production is recorded. At the same time, the data of the stress sensor of the simulated coal seam is recorded; (6) Fracturing is performed through the screen pipe 7, and gas is produced after fracturing. The produced methane is output through the first gas pipeline, and the gas production is recorded. At the same time, the data of the stress sensor of the simulated coal seam is recorded; The above steps (5) and (6) are performed simultaneously.

[0040] In step (4), a plurality of gas guide tubes are passed through the top cover 2 and inserted into the experimental tank 1, and the gas guide tubes are close to the end of the experimental tank 1 away from the screen tube 7 and the simulation casing 6, and the gas guide tubes correspond to each simulated coal seam one by one; when methane is input into the screen tube 7 and the simulation casing 6, the excess methane is discharged from the experimental tank 1 through the gas guide tubes. When the amount of methane input into the simulated coal seam is stably equal to the amount of methane discharged from the gas guide tubes, it indicates that the simulated coal seam is adsorbed saturated.

[0041] The air guide pipe passes through the partition between the top cover 2 and the oil-air bag on the top cover 2, and the passing position is sealed to prevent air leakage; after the simulated coal seam is adsorbed and saturated, the air guide pipe is withdrawn and sealed again.

[0042] The operating parameters of perforation, fracturing and gas production in steps (5) and (6) are determined according to the mining conditions of the actual coal seam and the reduction ratio of the experiment to the actual horizontal well. In this embodiment, the total length of the screen and the simulated casing in the experimental tank is 160 cm, the actual length of the simulated horizontal well is 300 m, and the reduction ratio is 1:187.5. The main operating parameters of this embodiment are: the amount of fracturing sand is 0.53 m 3 , liquid volume 5.33m 3 , displacement 0.053m 3 / min, construction casing pressure 0.133MPa.

[0043] In step S5, in one experiment, from the start of fracturing by the screen pipe until stable gas production, the stress data detected by the corresponding stress sensor is recorded; the stress data is segmented with stable gas production as the dividing point, and the average value of the stress data of the stable gas production section is calculated; After many experiments, the distance between the end of the screen tube close to the sensor network and the sensor network was used as the X-axis data, and the average value of the stable gas production section was used as the Y-axis data. After fitting, the screen tube influence curve was obtained.

[0044] In one experiment, starting from the fracturing of the simulated casing until the stable gas production, the stress data detected by the corresponding stress sensor is recorded; the stress data is segmented with the stable gas production as the dividing point, and the average value of the stress data of the stable gas production section is calculated; After many experiments, the simulated casing influence curve was obtained by taking the distance between the end of the simulated casing close to the sensor network and the sensor network as the X-axis data and the average value of the stable gas production section as the Y-axis data.

[0045] During the experiment, a confining pressure was also applied in the test tank, and the stress data used to determine the safety distance was the value obtained by subtracting the confining pressure from the measured stress data. This embodiment conducted 5 experiments, and the gas production of the screen pipe and the simulated casing was as shown in the following table.

[0046] Table 1 Length and stable gas production of screen tube and simulated casing in the experiment .

[0047] It can be seen from the above table that the gas production at stable gas production is different for different length ratios of the screen tube and the simulated casing, and the gas production of the screen tube and the simulated casing in the fifth experiment is the largest. The present invention aims to provide an experimental method that can predict the gas production of the screen tube and the simulated casing at different length ratios by experiment.

[0048] Table 2 Data of screen and simulated casing .

[0049] From the above table, we can see that the screen influence curve is y=-0.0094x+0.269, R 2=0.9827, when x=28.6cm, y=0MPa, at this distance, the effect of screen operation on gas production is zero. The simulated casing influence curve is y=-0.0098x+0.301, R 2 =0.9792, when x=30.7m, y=0MPa, at this distance, the effect of the simulated casing operation on gas production is zero.

[0050] In this embodiment, the distance when the influence of the simulated casing is zero is greater than the distance when the influence of the screen is zero (30.7cm>28.6m), so the safety distance is 30.7cm. The total length of the screen and the simulated casing in the experimental tank is 160cm, and the actual length of the simulated horizontal well is 300m. Therefore, the actual safety distance of the simulation is 300×0.307 / 1.6=57.6m.

Claims

1. An experimental method for exploring the completion and transformation technology of horizontal wells in high permeability coal reservoirs, characterized in that: The following steps are involved: S1: Conduct geological exploration for high permeability coal reservoirs to obtain geological characteristics and structural data; S2: Based on the information data of step S1, at least two identical simulated coal seams are constructed in the experimental tank. When constructing the coal seams, pipelines are pre-buried in advance; stress sensors are evenly buried at one end of the coal seam away from the pipeline to detect the effects of fracturing and gas production on the far end of the coal seam; S3: In half of the coal seams, the pre-buried pipes are replaced with screens, and in the other half of the coal seams, the pre-buried pipes are replaced with simulated casings with directional openings; the two coal seams with screens and simulated casings are used as an experimental object. The screens and simulated casings simulate horizontal wells, and different length ratios of the screens and simulated casings in the coal seams can be tested; S4: applying the same experimental confining pressure and temperature to the experimental object, and using water pressure jet to perforate the coal seam through the opening of the simulated casing; then, fracturing is performed through the screen and the simulated casing, and the gas production is recorded, and the data of the stress sensor is recorded at the same time; S5: Establish a curve relationship between different length ratios of the screen and the simulated casing and the average value of the stress data at the ends of the two coal seams to obtain the influence of the separate fracturing and gas production of the screen and the simulated casing on the coal seam.

2. The experimental method for exploring the completion and transformation technology of horizontal wells in high permeability coal reservoirs according to claim 1, characterized in that: The experimental tank is in the shape of a cube, with a detachable top cover on the top. The three inner sides of the experimental tank on the three-dimensional surface are respectively provided with hollow oil and gas bags, which are used to provide confining pressure for the simulated coal seam after being filled with oil or gas; a temperature control device is provided in the experimental tank to control the temperature in the experimental tank; The vertical side of the test tank where the oil and gas bag is not arranged is provided with a plurality of through holes, so that the pre-buried pipeline, the simulation casing and the screen tube can enter and exit the test tank.

3. The experimental method for exploring the completion and transformation technology of horizontal wells in high permeability coal reservoirs according to claim 2 is characterized in that: The experimental tank is equipped with a compaction assembly, which includes a horizontal compaction plate and a plurality of vertical partition plates. The partition plates are detachably connected to the bottom surface of the compaction plate and are parallel to each other. The partition plates are used to separate two adjacent simulated coal seams.

4. The experimental method for exploring the completion and transformation technology of horizontal wells in high permeability coal reservoirs according to claim 3 is characterized in that: Step S2 is specifically as follows: (1) According to the information data of step S1, a simulated coal seam matrix having the same components as the actual coal reservoir is prepared; According to the length of the simulated casing and screen tube predetermined in the experiment, the pre-buried pipe is inserted into the experimental tank through the through hole on the side wall of the experimental tank, and then the matrix is ​​evenly filled into the experimental tank; when filling the matrix, the stress sensor is arranged at the same time; (2) Compacting the coal seam using a compacting plate with a separator installed, using mechanical pressure or air pressure on the compacting plate to press the compacting plate downward, and inserting the separator into the matrix to form a number of simulated coal seams parallel to each other; (3) Remove the compaction plate, leave the partition plate in the test tank, and seal the test tank with the top cover.

5. The experimental method for exploring the completion and transformation technology of horizontal wells in high permeability coal reservoirs according to claim 4 is characterized in that: In step (1), each stress sensor is connected by a sensing optical fiber to form a mesh, forming a sensing network, and each stress sensor is evenly distributed. One side of the sensing network faces the side of the experimental tank with a through hole, and the other side of the sensing network faces the side of the experimental tank with an oil-gas bag. The sensing network is close to the oil-gas bag; the sensing optical fiber passes through the experimental tank and is connected to an external stress detection and analysis device.

6. The experimental method for exploring the completion and transformation technology of horizontal wells in high permeability coal reservoirs according to claim 1, characterized in that: The pre-buried pipe is a cylindrical hollow pipe, one end of which is open outside the experimental tank, and the other end inside the experimental tank is provided with an openable end cover to close the pre-buried pipe and prevent the matrix from entering the pre-buried pipe when constructing the simulated coal seam; The simulated casing is a cylindrical hollow tube with at least one row of openings on its side for perforating, fracturing and gas extraction of coal seams, and the arrangement direction of the row of openings is horizontal; the side of the screen tube is evenly and densely covered with through holes.

7. The experimental method for exploring the completion and transformation technology of horizontal wells in high permeability coal reservoirs according to claim 6, characterized in that: In step S3, the sealing plug of the embedded pipe at the through hole is removed, and the screen tube or the simulated casing is sent into the embedded pipe from the open end of the embedded pipe until one end of the screen tube or the simulated casing reaches the closed end of the embedded pipe; the embedded pipe is rotated to loosen, and the embedded pipe is withdrawn from the experimental tank; when withdrawing, due to the relative movement, the screen tube or the simulated casing pushes open the end cover, and the screen tube or the simulated casing remains inside the simulated coal seam; the sealing plug is reinstalled at the through hole, and the screen tube or the simulated casing outside the experimental tank is connected to the gas pipeline, so that the gas produced by the screen tube or the simulated casing is transported to the detection device by the gas pipeline.

8. The experimental method for exploring the completion and transformation technology of horizontal wells in high permeability coal reservoirs according to claim 1, characterized in that: Step S4 is specifically as follows: (4) Introducing methane gas into the coal seam through the screen pipe and the simulated casing until the coal seam is saturated with methane; According to the information data of step S1, the experimental confining pressure and temperature are determined, hydraulic oil or gas is input into the oil-gas bag, the coal seam is squeezed to simulate the application of confining pressure, and the experimental tank is heated to the experimental temperature; (5) A water pressure jet pipe is input into the simulated casing, and the jet ports correspond to the openings of the simulated casing one by one, and perforation is performed by water pressure jet; then, fracturing is performed through the simulated casing, and gas is produced after fracturing. The produced methane is output through the second gas pipeline, and the gas production is recorded. At the same time, the data of the stress sensor of the simulated coal seam is recorded; (6) Fracturing is performed through a screen pipe, and gas is produced after fracturing. The produced methane is output through a first gas pipeline, and the gas production is recorded. At the same time, data of the stress sensor of the simulated coal seam is recorded; The above steps (5) and (6) are performed simultaneously.

9. The experimental method for exploring the completion and transformation technology of horizontal wells in high permeability coal reservoirs according to claim 1, characterized in that: In step S5, in one experiment, from the start of fracturing by the screen pipe until stable gas production, the stress data detected by the corresponding stress sensor is recorded; the stress data is segmented with stable gas production as the dividing point, and the average value of the stress data of the stable gas production section is calculated; After many experiments, the screen tube influence curve was obtained by taking the distance between the end of the screen tube close to the sensor network and the sensor network as the X-axis data and the average value of the stable gas production section as the Y-axis data.

10. The experimental method for exploring the completion and transformation technology of horizontal wells in high permeability coal reservoirs according to claim 1, characterized in that: In step S5, in one experiment, starting from the implementation of fracturing in the simulated casing until stable gas production, the stress data detected by the corresponding stress sensor is recorded; the stress data is segmented with stable gas production as the dividing point, and the average value of the stress data of the stable gas production section is calculated; After many experiments, the simulated casing influence curve was obtained by taking the distance between the end of the simulated casing close to the sensor network and the sensor network as the X-axis data and the average value of the stable gas production section as the Y-axis data.

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