Experimental Method for Exploring Horizontal Well Completion and Stimulation Technologies in High-Permeability Coal Reservoirs

Abstract

The present invention relates to an experimental method for exploring the completion and stimulation technology of horizontal wells in highly permeable coal reservoirs, including: prospecting highly permeable coal reservoirs; constructing at least two identical simulated coal seams in an experimental tank, and pre-burying pipelines in advance when constructing the coal seams; burying stress sensors at one end of the coal seams far from the pipelines; replacing the pre-buried pipelines with screen pipes in half of the coal seams, and replacing the pre-buried pipelines with simulated casings with directional openings in the other half of the coal seams; taking the two coal seams with screen pipes and simulated casings as an experimental object, and the screen pipes and simulated casings simulate horizontal wells, and experiments can be carried out on different length ratios of screen pipes and simulated casings in the coal seams; applying confining pressure and temperature to the experimental object, and perforating the coal seams by water jet through the openings of the simulated casings; fracturing through the screen pipes and simulated casings, and then recording the gas production and stress data; establishing a relationship between the different length ratios of the screen pipes and the simulated casings and the stress data of the coal seams to obtain the influence of the experiment on the coal seams.

Description

Technical Field

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

[0002] For high-permeability coalbed methane reservoirs, when designing their horizontal wells, initially, conventional casing completion was also adopted, followed by processes such as hydraulic fracturing stimulation, and then coalbed methane production. With the in-depth practice and research on high-permeability coal reservoirs, it has been found that by utilizing the high-permeability characteristics of coal reservoirs, using screen pipe completion and then fracturing can sometimes also obtain good gas production. The surface of the screen pipe is evenly and densely distributed with screen holes, eliminating the need for the technological steps of concrete cementing and well pipe perforation, which can save materials and reduce costs. However, the structures at different positions inside high-permeability coal reservoirs vary, and the adaptability to casings or screen pipes is not completely consistent. In order to fully develop coal reservoirs and obtain higher gas production, at present, the form of on-site development is adopted to explore how to use casings and screen pipes in combination. However, the entire process from on-site drilling, completion, perforation, fracturing to final gas production has a long construction period and high costs. How to simulate the completion and stimulation technology of horizontal wells in high-permeability coal reservoirs by experimental methods and simultaneously evaluate the gas production effects of two completion methods (casing and screen pipe) is a problem faced by those skilled in the art. Summary of the Invention

[0003] In view of the above problems, the present invention provides an experimental method for exploring the completion and stimulation technology of horizontal wells in high-permeability coal reservoirs, including the following steps:

[0004] S1: For high-permeability coal reservoirs, conduct geological exploration to obtain geological characteristics and structural data;

[0005] S2: According to the information data in step S1, construct at least two identical simulated coal seams in the experimental tank. When constructing the coal seams, pre-embed pipelines in advance to facilitate the subsequent arrangement of screen pipes and casings during gas production; evenly bury stress sensors at one end of the coal seam far from the pipelines to detect the influence of fracturing and gas production on the far end of the coal seam;

[0006] S3: In half of the number of coal seams, replace the pre-embedded pipelines with screen pipes, and in the other half of the number of coal seams, replace the pre-embedded pipelines with simulated casings with directional openings; the two coal seams with screen pipes and simulated casings are used as one experimental object. The screen pipes and simulated casings simulate horizontal wells, and experiments can be carried out on different length ratios of screen pipes and simulated casings in the coal seam;

[0007] S4: Apply the same experimental confining pressure and temperature to the experimental object, and use water jetting to perforate the coal seam through the openings of the simulated casing; then, conduct fracturing through the screen pipes and simulated casings, record the gas production volume, and simultaneously record the data of the stress sensors;

[0008] S5: Establish a curve relationship between the different length ratios of the screen pipe to the simulated casing and the average value of the stress data at the two ends of the coal seam, and obtain the influence of the separate fracturing and gas production of the screen pipe and the simulated casing on the coal seam.

[0009] In the present invention, a simulated coal seam is constructed in an experimental tank to simulate the fracturing and gas production processes of the coal seam. A pipe with directional openings is used to simulate the actual casing. When perforating, it is not necessary to penetrate the simulated casing. The simulated casing can be reused. When perforating, it can directly shoot at the coal seam, saving hydraulic energy and making the perforating operation easier to control. The present invention uses a water pressure jetting method with adjustable pressure to replace the traditional blasting perforation. The power of the blasting perforation is relatively large, and it is not suitable for small-scale laboratory experiments to operate explosives. 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 experimental tank. The water pipe and the jet head of the water pressure jetting are small in volume and have good safety. They can adjust the water pressure according to the experimental needs and are suitable for laboratory use.

[0010] During the operation in an actual coal reservoir, a horizontal well consists of a screen pipe and a casing. The screen pipe can be directly fractured without perforation, and the casing is fractured after perforation. After the screen pipe and the casing are fractured, gas production is carried out. It is found in the practical process that the different operation forms of the casing and the screen pipe will affect the gas production areas responsible for each other. This kind of influence is complex, and those skilled in the art have not yet studied this influence clearly. They only know that this influence is not conducive to the stability of gas production. At present, only field exploration can be carried out. The ends of the screen pipe and the casing that are close to each other are separated from each other, that is, a certain safety distance is set, so as to weaken or eliminate the influence of the screen pipe and the casing on each other.

[0011] The length of the horizontal well is several hundred meters, and the lengths of the casing and the screen pipe are also dozens of meters to one hundred meters. The above-mentioned safety distance may be more than ten meters to dozens of meters. In the present invention, simulation is carried out with an experimental tank. It is impossible to achieve a safety distance of more than ten meters to dozens of meters. Instead, the simulated casing and the screen pipe are separately buried in two coal seams under the same conditions, and then used as an experimental object for joint experiments to separately study the influences of the simulated casing and the screen pipe, and study the influence of the different length ratios of the screen pipe to the simulated casing on the overall gas production. The present invention selects the coal seam stress as an index to respectively reflect the influences of the fracturing and gas production of the simulated casing and the screen pipe on the coal seam.

[0012] Optionally, in step S1, geological exploration is carried out on the actual underground high-permeability coal reservoir, and combined with the previous exploration data, the geological information of the target coal reservoir is obtained. The geological information includes but is not limited to burial depth, seam 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 means.

[0013] 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;

[0014] 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.

[0015] 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.

[0016] Optionally, step S2 specifically includes:

[0017] (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;

[0018] 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;

[0019] (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;

[0020] (3) Remove the compaction plate, leave the partition plate in the test tank, and seal the test tank with the top cover.

[0021] 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.

[0022] 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.

[0023] Optionally, the simulation casing is a cylindrical hollow pipe, open at one end and closed at the other end, with at least one row of openings on its side for perforating, fracturing, and gas production in the coal seam. The arrangement direction of one row of openings is horizontal. Preferably, there are several rows of horizontal openings on the side of the simulation casing, and the included angle between two adjacent rows of openings is 60-90°, which is convenient for perforating, fracturing, and gas production in all directions of the coal seam. One end of the screen pipe is open and the other end is closed, and through holes are evenly distributed on the side.

[0024] Optionally, in step S3, remove the sealing plug at the through hole of the embedded pipeline, and insert the screen pipe or the simulation casing into the embedded pipeline from the open end of the embedded pipeline until one end of the screen pipe or the simulation casing reaches the closed end of the embedded pipeline; rotate and loosen the embedded pipeline, and withdraw the embedded pipeline from the experimental tank. When withdrawing, due to relative movement, the screen pipe or the simulation casing pushes open the end cover, and the screen pipe or the simulation casing remains inside the simulated coal seam; reinstall the sealing plug at the through hole, and connect the screen pipe or the simulation casing outside the experimental tank to the gas pipeline, so that the gas produced by the screen pipe or the simulation casing is transported to the detection device through the gas pipeline.

[0025] Optionally, in step S3, the partition plate evenly divides the whole compacted coal seam in the experimental tank into several simulated coal seams, preferably into an even number of simulated coal seams. The screen pipe is arranged in half of the coal seams, and the simulation casing is arranged in the other half of the coal seams. The two coal seams with the screen pipe and the simulation casing are used as an experimental object, and it is considered that the screen pipe and the simulation casing are combined to simulate the actual horizontal well, eliminating the disadvantage that due to the small size of the experimental tank, the screen pipe and the simulation casing are in the same simulated coal seam and have a large mutual influence, which is convenient for separately studying the influence of the fracturing gas production of the screen pipe and the simulation casing on gas production.

[0026] The screen pipe and the simulation casing in the experimental tank simulate a horizontal well. The sum of the lengths of the screen pipe and the simulation 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 smaller than the total length of an experimental object (i.e., the sum of the lengths of two simulated coal seams), and is more in line with the actual application situation of horizontal well coalbed methane extraction. The present invention can study the influence of different length ratios of the screen pipe and the simulation casing on the total gas production of an experimental object through multiple experiments. Each time an experiment is set with a length ratio of the screen pipe and the simulation casing, record the gas production of the first gas pipeline and the second gas pipeline in each experiment, and then add the two to obtain the total gas production.

[0027] Optionally, step S4 is specifically:

[0028] (4) Input methane gas into the coal seam through the screen pipe and the simulation casing until the coal seam is saturated with adsorbed methane;

[0029] Based on the information data in step S1, determine the experimental confining pressure and temperature, input hydraulic oil or gas into the oil and gas bladder, squeeze the coal seam to simulate the application of confining pressure, and heat the experimental tank to the experimental temperature;

[0030] (5) Simulate the input of a water pressure injection pipe into the casing, with the injection ports corresponding one by one to the openings of the simulated casing, and perform perforation using water pressure injection; then perform fracturing through the simulated casing, produce gas after fracturing, and output the produced methane through the second gas pipeline, record the gas production volume, and at the same time record the data of the stress sensors of the simulated coal seam;

[0031] (6) Perform fracturing through the screen pipe, produce gas after fracturing, output the produced methane through the first gas pipeline, record the gas production volume, and at the same time record the data of the stress sensors of the simulated coal seam;

[0032] The above steps (5) and (6) are executed simultaneously.

[0033] Optionally, in step S5, in each experiment, due to the different length ratios of the screen pipe to the simulated casing, the distances between the screen pipe and the corresponding sensor network are also different, and the stress influence caused by the operation of the screen pipe on the simulated coal seam changes with the change of the distance between the screen pipe and the corresponding sensor network. Similarly, the stress influence caused by the operation of the simulated casing on the simulated coal seam changes with the change of the distance between the simulated casing and the corresponding sensor network.

[0034] Further optionally, in one experiment, starting from the fracturing of the screen pipe until stable gas production, record the stress data detected by the corresponding stress sensors; using stable gas production as the dividing point, segment the stress data, and calculate the average value of the stress data in the stable gas production segment;

[0035] After multiple experiments, using the distance between the end of the screen pipe close to the sensor network and the sensor network as the X-axis data, and the average value of the stable gas production segment as the Y-axis data, obtain the screen pipe influence curve.

[0036] Further optionally, in one experiment, starting from the fracturing of the simulated casing until stable gas production, record the stress data detected by the corresponding stress sensors; using stable gas production as the dividing point, segment the stress data, and calculate the average value of the stress data in the stable gas production segment;

[0037] After multiple experiments, using 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 segment as the Y-axis data, obtain the simulated casing influence curve. Description of the Drawings

[0038] Figure 1 It is a schematic structural diagram of the experimental tank;

[0039] Figure 2 It is a schematic diagram of the compaction component;

[0040] Figure 3 It is a schematic diagram of embedded pipelines.

[0041] In the attached drawings, 1 - experimental tank, 2 - top cover, 3 - oil and gas bag, 4 - opening, 5 - embedded pipeline, 6 - simulated casing, 7 - screen pipe, 8 - compaction plate, 9 - partition plate, 10 - end cover. Specific implementation method

[0042] This embodiment provides an experimental method for exploring the completion and stimulation technology of horizontal wells in high - permeability coal reservoirs, including the following steps:

[0043] S1: For high - permeability coal reservoirs, conduct geological exploration to obtain geological characteristics and structural data;

[0044] S2: According to the information data in step S1, construct at least two identical simulated coal seams in the experimental tank 1. When constructing the coal seams, embed the pipeline 5 in advance to facilitate the subsequent arrangement of the screen pipe 7 and casing for gas production; uniformly bury stress sensors at one end of the coal seam away from the pipeline to detect the influence of fracturing and gas production on the far end of the coal seam;

[0045] S3: Replace the embedded pipeline 5 with the screen pipe 7 in half of the coal seams, and replace the embedded pipeline 5 with the simulated casing 6 with directional openings in the other half of the coal seams; The two coal seams with the screen pipe 7 and the simulated casing 6 are used as an experimental object. The screen pipe 7 and the simulated casing 6 simulate horizontal wells, and experiments can be carried out on different length ratios of the screen pipe 7 and the simulated casing 6 in the coal seam;

[0046] S4: Apply the same experimental confining pressure and temperature to the experimental object, and use water jet to perforate the coal seam through the openings of the simulated casing 6; Then, conduct fracturing through the screen pipe 7 and the simulated casing 6, record the gas production volume, and simultaneously record the data of the stress sensors;

[0047] S5: Establish a curve relationship between the different length ratios of the screen pipe 7 and the simulated casing 6 and the average value of the stress data at both ends of the two coal seams to obtain the influence of the separate fracturing and gas production of the screen pipe 7 and the simulated casing 6 on the coal seam.

[0048] In step S1, conduct geological exploration on the actual underground high - permeability coal reservoir, and combine with previous exploration data to obtain the geological information of the target coal reservoir. 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.

[0049] Such as Figures 1 - 3As 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;

[0050] 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 .

[0051] 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.

[0052] 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.

[0053] Step S2 is specifically as follows:

[0054] (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;

[0055] 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;

[0056] (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;

[0057] (3) Remove the compaction plate 8, leave the partition plate 9 in the experimental tank 1, and cover the top cover 2 to seal the experimental tank 1.

[0058] In step (1), first fill the matrix into the experimental tank 1. When the matrix reaches the height at the bottom of the preset embedded pipeline 5, insert the embedded pipeline 5 through the corresponding through-hole. According to the experimental requirements, adjust the length of each embedded pipeline 5 extending into the experimental tank 1. Then install a sealing plug at each through-hole to seal the gap between the through-hole and the embedded pipeline 5. Then continue to fill the matrix so that the matrix surrounds the embedded pipeline 5 until the matrix reaches the preset height.

[0059] When performing step (1), the oil and gas bags are not pressurized. When filling the matrix, after filling a certain thickness, compact it 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 voids or holes. Near the two vertical oil and gas bags, fill fine cinder and soil particles as much as possible to avoid damaging the oil and gas bags.

[0060] In step (1), each stress sensor is connected into a network by a sensing optical fiber 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 1 with a through-hole, and the other side of the sensing network faces the side of the experimental tank 1 with an oil and gas bag. The sensing network is close to the oil and gas bag, but there is a distance of 1 cm between the sensing network and the oil and gas bag. The matrix is filled between the sensing network and the oil and gas bag to avoid the pressure of the oil and gas bag 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.

[0061] In step (2), each partition plate 9 is opposite to the partition corresponding to the oil and gas bag on the vertical side of the experimental tank 1. Install a sealing strip on the side of the partition plate 9, and insert the partition plate 9 downward into the matrix. When the lower surface of the compaction plate 8 touches 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, and this distance is equal to the height by which the subsequent matrix will drop after being compacted, that is, the height of the partition plate 9 is equal to the height of the simulated coal seam after compaction.

[0062] In step (3), install a sealing strip on the top edge of the partition plate 9, and the top edge of the partition plate 9 is 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 touches the top surface of the simulated coal seam.

[0063] The embedded pipeline 5 is a cylindrical hollow pipe. One end of it outside the experimental tank 1 is open, and one end inside the experimental tank 1 is provided with an openable end cover 10 to close the embedded pipeline 5 and prevent the matrix from entering the embedded pipeline 5 when constructing the simulated coal seam.

[0064] The simulation casing 6 is a cylindrical hollow pipe, with four rows of openings 4 provided on its side for perforating, fracturing, and gas production in the coal seam. The arrangement direction of each row of openings 4 is horizontal, and the included angle between adjacent two rows of openings is 90°, facilitating perforating, fracturing, and gas production in all directions of the coal seam. The side of the screen pipe 7 is evenly and densely distributed with through holes.

[0065] In step S3, the replacement of the embedded pipeline 5 with the screen pipe 7 is specifically as follows: Remove the sealing plug at the through hole of the embedded pipeline 5, and from the open end of the embedded pipeline 5, send the screen pipe 7 into the embedded pipeline 5 until one end of the screen pipe 7 reaches the closed end of the embedded pipeline 5; Rotate and loosen the embedded pipeline 5, and withdraw the embedded pipeline 5 from the experimental tank 1; When withdrawing, due to relative movement, the screen pipe 7 pushes open the end cover 10, and the screen pipe 7 remains inside the simulated coal seam; Reinstall the sealing plug at the through hole, and connect the screen pipe 7 outside the experimental tank 1 to the first gas pipeline, so that the gas produced by the screen pipe 7 is transported to the detection device through the first gas pipeline.

[0066] In step S3, the replacement of the embedded pipeline 5 with the simulation casing 6 is specifically as follows: Remove the sealing plug at the through hole of the embedded pipeline 5, and from the open end of the embedded pipeline 5, send the simulation casing 6 into the embedded pipeline 5 until one end of the simulation casing 6 reaches the closed end of the embedded pipeline 5; Rotate and loosen the embedded pipeline 5, and withdraw the embedded pipeline 5 from the experimental tank 1; When withdrawing, due to relative movement, the simulation casing 6 pushes open the end cover 10, and the simulation casing 6 remains inside the simulated coal seam; Reinstall the sealing plug at the through hole, and connect the simulation casing 6 outside the experimental tank 1 to the second gas pipeline, so that the gas produced by the simulation casing 6 is transported to the detection device through the second gas pipeline.

[0067] In step S3, the partition plate 9 evenly divides the whole compacted coal seam in the experimental tank 1 into an even number of simulated coal seams.

[0068] Step S4 is specifically as follows:

[0069] (4) Input methane gas into the coal seam through the screen pipe 7 and the simulation casing 6 until the coal seam is saturated with adsorbed methane;

[0070] According to the information data in step S1, determine the experimental confining pressure and temperature, input hydraulic oil or gas into the oil and gas bag, and extrude the coal seam to simulate the application of confining pressure, and heat the experimental tank 1 to the experimental temperature;

[0071] (5) Input a water pressure injection pipe into the simulation casing 6, and the injection ports correspond one by one to the openings of the simulation casing 6, and use water pressure injection for perforating; Then, perform fracturing through the simulation casing 6, and after fracturing, perform gas production. The produced methane is output through the second gas pipeline, record the gas production volume, and at the same time record the data of the stress sensors of this simulated coal seam;

[0072] (6) Conduct fracturing through the screen pipe 7, and then produce gas after fracturing. The produced methane is output through the first gas pipeline. Record the gas production volume, and at the same time record the data of the stress sensors of the simulated coal seam.

[0073] The above steps (5) and (6) are executed simultaneously.

[0074] In step (4), several gas pipes are passed through the top cover 2 and inserted into the experimental tank 1, and the gas pipes are close to the end of the experimental tank 1 far from the screen pipe 7 and the simulated casing 6. The gas pipes correspond to each simulated coal seam one by one. When methane is input into the screen pipe 7 and the simulated casing 6, the excess methane is discharged from the experimental tank 1 through the gas pipes. When it is monitored that the methane gas volume input into the simulated coal seam is stably equal to the methane gas volume discharged from the gas pipes, it indicates that the simulated coal seam is saturated in adsorption.

[0075] The gas pipes pass through the top cover 2 and the separation part of the oil and gas bag on the top cover 2, and the passing positions are sealed to avoid air leakage. After the simulated coal seam is saturated in adsorption, the gas pipes are withdrawn and sealed again.

[0076] The operation parameters during 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 compared with the actual horizontal well. In this embodiment, the total length of the screen pipe 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 operation parameters of this embodiment are as follows: the fracturing sand volume is 0.53 m 3 , the liquid volume is 5.33 m 3 , the displacement is 0.053 m 3 / min, and the construction casing pressure is 0.133 MPa.

[0077] In step S5, in one experiment, starting from the fracturing of the screen pipe until stable gas production, record the stress data detected by the corresponding stress sensors; taking stable gas production as the separation point, segment the stress data, and calculate the average value of the stress data in the stable gas production segment;

[0078] After multiple experiments, taking the distance between the end of the screen pipe close to the sensor network and the sensor network as the X-axis data, and taking the average value of the stable gas production segment as the Y-axis data, the screen pipe influence curve is obtained after fitting.

[0079] In one experiment, starting from the fracturing of the simulated casing until stable gas production, record the stress data detected by the corresponding stress sensors; taking stable gas production as the separation point, segment the stress data, and calculate the average value of the stress data in the stable gas production segment;

[0080] After multiple experiments, 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 taking the average value of the stable gas production segment as the Y-axis data, the simulated casing influence curve is obtained.

[0081] During the experiment, confining pressure was also applied in the experimental tank. The stress data used to determine the safety distance was the value obtained by subtracting the confining pressure from the measured stress data. In this embodiment, 5 experiments were conducted, and the gas production volumes of the screen pipe and the simulated casing are shown in the following table.

[0082] Table 1 Lengths and stable gas production volumes of the screen pipe and the simulated casing in the experiment

[0083] 。

[0084] As can be seen from the above table, for different length ratios of the screen pipe and the simulated casing, the gas production volumes during stable gas production are different, and the gas production volumes of the screen pipe and the simulated casing in the fifth experiment are the largest. The present invention aims to provide an experimental method that can predict the gas production volumes of the screen pipe and the simulated casing at different length ratios through experiments.

[0085] Table 2 Data of the screen pipe and the simulated casing

[0086] 。

[0087] As can be seen from the above table, the influence curve of the screen pipe is y = -0.0094x + 0.269, R 2 = 0.9827. When x = 28.6 cm, y = 0 MPa. At this distance, the operation of the screen pipe has no influence on gas production. The influence curve of the simulated casing is y = -0.0098x + 0.301, R 2 = 0.9792. When x = 30.7 m, y = 0 MPa. At this distance, the operation of the simulated casing has no influence on gas production.

[0088] 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 pipe is zero (30.7 cm > 28.6 m). Therefore, the safety distance is 30.7 cm. The total length of the screen pipe and the simulated casing in the experimental tank is 160 cm, and the actual length of the simulated horizontal well is 300 m. Therefore, the simulated actual safety distance is 300×0.307 / 1.6 = 57.6 m.

Claims

1. An experimental method for exploring the completion and stimulation 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 holes; 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; In step S5, in one experiment, starting from the fracturing by the screen pipe and the fracturing by the simulated casing until the gas production is stable, the stress data detected by the corresponding stress sensors are recorded respectively; Taking stable gas production as the dividing point, the stress data is segmented, 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 and the simulated casing close to the sensor network and the sensor network was used as the X-axis data, and the average stress data of the stable gas production section was used as the Y-axis data, and the screen tube influence curve and the simulated casing influence curve were obtained respectively. The stress data used to determine the safety distance is the value obtained by subtracting the confining pressure from the measured stress data.

2. The experimental method for exploring the horizontal well completion and stimulation technology in highly permeable 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 stimulation technology of horizontal wells in high-permeability coal reservoirs according to claim 2, 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 horizontal well completion and stimulation technology in highly permeable coal reservoirs according to claim 3, 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 experimental tank, and cover the top cover to seal the experimental tank.

5. The experimental method for exploring the horizontal well completion and stimulation technology in highly permeable coal reservoirs according to claim 4, characterized in that In step (1), the stress sensors are connected into a network by sensing optical fibers to form a sensing network, and the stress sensors are evenly distributed. One side of the sensing network faces the side of the experimental tank with through holes, and the other side of the sensing network faces the side of the experimental tank with the oil and gas bladder, and the sensing network is close to the oil and gas bladder; 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 stimulation technology of horizontal wells in high-permeability coal reservoirs according to claim 1, characterized in that, The embedded pipeline is a cylindrical hollow pipe. One end of it outside the experimental tank is open, and one end inside the experimental tank is provided with an openable end cover to seal the embedded pipeline and prevent the matrix from entering the embedded pipeline when constructing the simulated coal seam. The simulation casing is a cylindrical hollow pipe, and at least one row of openings is provided on its side for perforating, fracturing, and gas production of the coal seam. The arrangement direction of one row of openings is horizontal; the side of the screen pipe is evenly and densely distributed with through holes.

7. The experimental method for exploring the horizontal well completion and stimulation technology in highly permeable coal reservoirs according to claim 6, characterized in that, In step S3, remove the sealing plug at the through hole of the embedded pipeline, and insert the screen pipe or the simulation casing into the embedded pipeline from the open end of the embedded pipeline until one end of the screen pipe or the simulation casing reaches the closed end of the embedded pipeline; rotate and loosen the embedded pipeline, and withdraw the embedded pipeline from the experimental tank; when withdrawing, due to relative movement, the screen pipe or the simulation casing pushes open the end cover, and the screen pipe or the simulation casing remains inside the simulated coal seam; reinstall the sealing plug at the through hole, and connect the screen pipe or the simulation casing outside the experimental tank to the gas pipeline, so that the produced gas of the screen pipe or the simulation casing is transported to the detection device through the gas pipeline.

8. The experimental method for exploring the completion and stimulation technology of horizontal wells in highly permeable coal reservoirs according to claim 2, characterized in that, Step S4 is specifically as follows: (4) Input methane gas into the coal seam through the screen pipe and the simulation casing until the coal seam is saturated with adsorbed methane. According to the information data in step S1, determine the experimental confining pressure and temperature, input hydraulic oil or gas into the oil and gas bladder, and squeeze the coal seam to simulate the application of confining pressure, and heat the experimental tank to the experimental temperature. (5) Input a water pressure injection pipe into the simulation casing, and the injection ports correspond to the openings of the simulation casing one by one, and use water pressure injection for perforating; then perform fracturing through the simulation casing, and after fracturing, perform gas production. The produced methane is output through the second gas pipeline, record the gas production volume, and at the same time record the data of the stress sensors of the simulated coal seam. (6) Perform fracturing through the screen pipe, and after fracturing, perform gas production. The produced methane is output through the first gas pipeline, record the gas production volume, and at the same time record the data of the stress sensors of the simulated coal seam. The above steps (5) and (6) are executed simultaneously.

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