Method for monitoring stress and deformation of oil and gas wells in cross-mining areas of coal, oil and gas overlap

Abstract

The present invention discloses a method for monitoring the stress and deformation of cross-mining oil and gas wells in coal, oil and gas overlapping areas. The method includes a method for arranging test wells and a method for arranging sensors. The test wells are installed according to the wellbore structure of the production or abandoned oil and gas wells in the mining area. During the dynamic advancement of the fully-mechanized mining face, the stress and deformation of the test wells in the coal mining face and the section coal pillars are monitored in real time by sensors installed in the test wells. Based on the stress and deformation monitoring data of the test wells and the observation results of the borehole television imaging device, the integrity of the production or abandoned oil and gas wells in the coal mining face and the section coal pillars is comprehensively evaluated. The present invention can not only effectively assess the risk of instability and leakage of production oil and gas wells affected by coal seam mining, but also provide useful ideas for the reasonable size design of protective coal pillars and section coal pillars for production oil and gas wells, and can provide a reference for the retention of protective coal pillars and section coal pillars for oil and gas wells.

Description

Technical Field

[0001] The invention relates to the technical field of exploration and design of oil and gas wells in coal, oil and gas overlapping areas, and in particular to a method for monitoring stress and deformation of cross-mining oil and gas wells in coal, oil and gas overlapping areas. Background Art

[0002] In recent years, cross-mining of multiple resources in overlapping coal, oil, and gas regions has become increasingly common. Due to the vertical overlap of coal and oil / natural gas resources, as well as their different development and utilization methods and characteristics, the safety, economy, efficiency, and coordinated development of mineral resources in these overlapping regions have gradually received increasing attention. Operating or abandoned oil and gas wells affected by coal seam mining are prone to instability and leakage risks. If toxic and hazardous gases generated within these wells flow into the mining face, they pose a significant threat to the safety of underground coal mine workers and severely restrict coal resource extraction. This not only complicates mine design and mining, impacting the technical and economic benefits of coal mining enterprises, but also poses a significant safety hazard to operating or abandoned oil and gas wells due to the mining of adjacent coal seams. Monitoring the stress and deformation of casing in operating or abandoned oil and gas wells within the impact zone of coal seam mining can significantly prevent damage to the casing during mining activities, which could result in the influx of toxic and hazardous gases from the wells into the mining face.

[0003] When there are producing or abandoned oil and gas wells at the coal mining face, it is usually necessary to leave a coal pillar to protect the oil and gas wells. If the coal pillar is too large, it will cause a waste of coal resources. If the coal pillar is too small, it will fail to play a protective role and damage the oil and gas wells. How to determine the reasonable size of the coal pillar is still without a unified standard.

[0004] Currently, the commonly used technical approach is to place instruments on the outside of the production well to monitor wellbore stress, deformation, and damage. However, cement sheaths exist between various types of casing. When the wellbore deforms, the cement sheath can offset some of the deformation. Therefore, the stress and deformation data monitored from the outside of the wellbore have large errors and cannot truly reflect the stress and deformation of the production casing. Since the production casing of the production well contains high-pressure fluid, it is impossible to place monitoring instruments inside the production casing of the production well. Since the waste gas oil and gas well has already been drilled, it is difficult to install monitoring instruments inside the production casing. Moreover, the waste gas oil and gas well is fixed in position, which cannot ensure a scientific comparison. Summary of the Invention

[0005] The present invention provides a method for monitoring the stress and deformation of cross-exploitation oil and gas wells in coal, oil and gas overlapping areas. By arranging test wells, the test wells are made to have the same wellbore structure and stress environment as production or waste gas oil and gas wells. By observing the stress and deformation conditions of the test wells, the stress and deformation conditions of production or waste gas wells can be scientifically evaluated.

[0006] The technical solution adopted by the present invention is a method for monitoring the stress and deformation of oil and gas wells in cross-mining of coal, oil and gas overlapping areas, including a method for arranging test wells and a method for arranging sensors, including the following steps:

[0007] S1: Install sensors on the inner wall of the production casing of the test well to monitor the stress and deformation of the test well;

[0008] S2: Select the location for the test well and drill the test well at the leading position of the coal mining face and within the section coal pillar;

[0009] S3: Construct and install test wells according to the wellbore structure of production or abandoned oil and gas wells in the mining area;

[0010] S4: During the dynamic advancement of the fully mechanized mining face, sensors installed in the test wells are used to monitor the stress and deformation of the coal mining face and the test wells in the section coal pillars in real time;

[0011] S5: When the monitored force or deformation data reaches the set value, the deformation degree of the test well affected by mining is observed in combination with the borehole television imaging device;

[0012] S6: The fully mechanized mining face continues to advance until the test well is destroyed, and the monitored force or deformation data of the test well is recorded;

[0013] S7: Based on the stress and deformation monitoring data of the test well and the observation results of the borehole television imager, a comprehensive assessment is made of the integrity of the producing or abandoned oil and gas wells in the coal mining face and the section coal pillar.

[0014] Preferably, in step S2, when arranging a test well at an advanced position of the coal mining face, the test well needs to be arranged outside the advanced influence range.

[0015] Preferably, in step S2, when arranging test wells in the segment coal pillar, three test wells are arranged along the width direction of the segment coal pillar, one of which is arranged in the middle of the segment coal pillar, and the other two test wells are symmetrically arranged on both sides of the middle test well.

[0016] Preferably, the wellbore of the test well passes through the coal seam floor, and the completion bottom of the test well is below the coal seam floor and above the oil and gas reservoir.

[0017] Preferably, the sensors include an axial stress sensor, a circumferential stress sensor and a displacement sensor.

[0018] Preferably, the circumferential stress sensor is arranged in an annular manner on the inner wall of the production casing, and the diameter of the annular ring is equal to the diameter of the inner wall of the production casing of the test well.

[0019] Preferably, multiple groups of the axial stress sensors and displacement sensors are longitudinally arranged on the inner wall of the production casing of the test well, and all the axial stress sensors are on the same axis, and all the displacement sensors are on the same axis.

[0020] Preferably, the axial stress sensor and displacement sensor are respectively installed on both sides of the intersection of the cross diameter of the production casing and the inner wall of the production casing, and the order of arranging the axial stress sensors and displacement sensors at the four intersections is consistent.

[0021] Preferably, in step S3, the wellbore structure includes, from outside to inside, a guide pipe, a surface casing, a coal seam protection casing, a technical casing, and a production casing, and cement rings are poured between each layer of casing as needed.

[0022] The beneficial effects of the present invention are as follows: by arranging test wells within the coal mining working face and the coal pillar of the section of the mining area, the stress and deformation of the test wells are monitored during the dynamic advancement of the working face, and the integrity of the oil and gas wells affected by coal seam mining in the coal, oil and gas superimposed area is effectively evaluated. In the present invention, the test well does not assume a production function, but its well body structure, construction process and other aspects are the same as the oil and gas wells being evaluated. There is no high-pressure fluid in the production casing of the test well, so the monitoring instrument can be arranged on the inner wall of the production casing. The monitoring results directly and accurately reflect the stress and deformation of the production casing of the test well during the dynamic advancement of the coal seam working face, thereby preventing the leakage of harmful gases, oil or water in the oil and gas wells into the mining working face or tunnel.

[0023] Because the test well does not undertake production functions, the coal mining face can be fully advanced during the test process, completely destroying the test well. This allows the stress and deformation data of the test well to be recorded from the beginning of stress to complete destruction, which is beneficial for determining the critical point of instability of the oil and gas well. By analyzing the stress and deformation monitoring data of the test well, it can provide a reference for the retention of protective coal pillars and section coal pillars for oil and gas wells, thereby improving the recovery rate of coal resources. Therefore, this method has important theoretical significance and engineering practical value. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 is a flow chart of the method of the present invention;

[0025] Figure 2 This is a schematic plan view of the layout of the test wells in an embodiment of the present invention;

[0026] Figure 3 Schematic diagram of the installation position of the sensor on the inner wall of the production casing of the test well in an embodiment of the present invention;

[0027] Figure 4 2. This is a cross-sectional diagram of the installation position of the sensor on the inner wall of the production casing of the test well according to an embodiment of the present invention;

[0028] Figure 5It is a schematic diagram of the test well body structure in an embodiment of the present invention.

[0029] In the figure, 1 is a test well in the coal mining face; 2 is a test well in the section coal pillar; 3 is the goaf; 4 is an auxiliary transport tunnel; 5 is the main transport tunnel; 6 is a circumferential stress sensor; 7 is an axial stress sensor; 8 is a displacement sensor; 9 is a production casing; 10 is a technical casing; 11 is a coal seam protection casing; 12 is a surface casing; 13 is a guide tube; 14 is a cement sheath; 15 is a completion well bottom; c, d are the spacing between the test wells in the section coal pillar; e is the width of the section coal pillar; m is the wellbore structure of the test well; n is the wellbore structure of the production or abandoned oil and gas well; L is the distance between the test well in the coal mining face and the fully mechanized mining face. DETAILED DESCRIPTION

[0030] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0031] Figure 1-Figure 5 The preferred embodiments of the present invention are presented, and the layout of the test well, the installation of the sensor, and the wellbore structure of the test well in the method of the present invention are respectively described in detail.

[0032] like Figure 1 As shown, the stress and deformation monitoring method for oil and gas wells in the cross-mining area of coal, oil and gas overlaps includes the following steps:

[0033] S1: If Figure 3 and Figure 4 As shown, since the test well is not responsible for production, sensors for monitoring the stress and deformation of the test well can be installed on the inner wall of the production casing of the test well. This method not only allows the observation of the stress and deformation of the production casing, but also avoids the problem of sensors being affected by the cement sheath when placed on the outer wall of the casing. In this embodiment, the sensors include axial stress sensors, circumferential stress sensors, and displacement sensors. The circumferential stress sensors are arranged in a ring on the inner wall of the production casing, with the diameter of the ring equal to that of the inner wall of the test well production casing. Multiple groups of axial stress sensors and displacement sensors are arranged longitudinally on the inner wall of the test well production casing.

[0034] The sensors monitor the stress and deformation of the test well, including axial stress, circumferential stress, and displacement of a certain point (section) of the test well casing. By monitoring the displacement change between two points (sections) of the test well casing in the XYZ directions, the casing deformation (tension, compression, shear, and extrusion) can be monitored. A reasonable distance is set between the axial stress sensor and the displacement sensor. They are installed on both sides of the intersection of the cross diameter of the production casing and the inner wall of the production casing. The axial stress sensors and displacement sensors at the four intersections are in the same order. In the longitudinal direction, all axial stress sensors and displacement sensors installed on the inner wall of the production casing are on the same axis. The axial stress sensors, displacement sensors, and circumferential stress sensors are at a certain distance from each other. The purpose of this setting is to make the monitoring results more reasonable and to make corresponding adjustments based on the actual situation on site.

[0035] S2: Select the location for the test well, such as Figure 2 As shown in the figure, the location of the test well arranged in the coal mining face is determined according to the advance influence distance of mining subsidence. The test well needs to be arranged outside the range of the advance influence distance, that is, the distance L between the test well arranged in the coal mining face and the fully mechanized mining face is greater than the advance influence distance. When the fully mechanized mining face dynamically advances and gradually approaches the test well, the stress and deformation data of the test well affected by coal seam mining can be monitored throughout the process, thereby accurately evaluating the integrity of the production or abandoned oil and gas wells in the coal mining face.

[0036] Because the leading stress is different from the lateral stress, and the segmental coal pillar is affected by the dual mining of the fully-mechanized mining faces on both sides, when laying out the segmental coal pillar test wells, three test wells are laid out along the width of the segmental coal pillar. One of the test wells is laid out in the middle of the segmental coal pillar, and the other two test wells are at the same distance from the middle test well, that is, c = d. When the fully-mechanized mining faces on both sides of the segmental coal pillar advance, the stress and deformation of the test wells are monitored and the data is recorded. Later, when designing coal seam mining in coal, oil, and gas superimposed mining areas, production or abandoned oil and gas wells within the segmental coal pillar can be planned in areas with low risk of instability and leakage. Step S2 and step S1 are not preceded by one another. Alternatively, the location for the test wells can be selected first, and then the sensors can be installed in the test wells.

[0037] S3: According to the well structure of the production or abandoned oil and gas wells to be evaluated in the mining area, the test wells are installed in the pre-selected locations, such as Figure 5 As shown, the wellbore structure includes the guide pipe, surface casing, coal seam protection casing, technical casing, production casing, and cement sheath. Test well completions are typically required to be within 1000 m below the coal seam floor. The spacing between the bottom ends of the coal seam protection casing, technical casing, and production casing and the coal seam floor depends on the depth of damage to the coal seam floor caused by mining under different coal seam conditions. This is primarily influenced by factors such as coal seam burial depth, mining height, and inclination. Vertically, the test well must be located within the impact range of coal seam mining. Figure 5Where m is the wellbore structure of the test well in the present invention, and n is the wellbore structure of the production or abandoned oil and gas well in actual engineering. The bottom of the test well does not need to be constructed to the oil and gas reservoir (usually at a depth of 2000-3000m, or even deeper), so the stress and deformation of the test well affected by coal seam mining can be monitored. The technical and economic costs of the test well in this method are greatly reduced compared to the production or abandoned oil and gas wells constructed to the oil and gas reservoir.

[0038] S4: During the dynamic advancement of the fully-mechanized mining face, sensors installed in the test wells monitor the stress and deformation of the coal mining face and the test wells within the section coal pillars in real time. During the test, the fully-mechanized mining face advances in full accordance with the actual mining rhythm. Specifically, as the fully-mechanized mining face advances, it gradually approaches the test wells located within the coal mining face or section coal pillars. When the sensors detect that the stress and deformation of the test wells are small, the daily advancement length of the fully-mechanized mining face remains unchanged. When the sensors detect that the stress and deformation growth rate of the test wells increases, the daily advancement length of the fully-mechanized mining face gradually decreases to prevent damage to the integrity of the test wells and provide a reasonable basis for the coal pillars reserved for oil and gas production wells within the coal mining face. This process continuously records the stress and deformation monitoring data of the test wells until the stress and deformation reach the tensile, shear, and extrusion strength thresholds of the test well casing.

[0039] S5: When the monitored stress or deformation data approaches or reaches the ultimate bearing capacity and deformation of the test well, the degree of deformation of the test well affected by mining shall be visually observed in combination with borehole television. Specifically, when the fully-mechanized mining face gradually approaches the test well, and the sensor monitors that the stress and deformation data of the test well approaches or reaches the ultimate bearing capacity and deformation of the test well, at least one borehole television shall be conducted daily to visually observe the degree of deformation of the test well affected by coal seam mining and whether there are axial cracks, shear failure and other casing damage on the inner wall of the production casing, and to assess whether there is a risk of instability and leakage in the production or abandoned oil and gas wells. When there are weak surfaces in the rock formations within the range of influence of coal seam mining, the number of daily borehole television tests on the test well shall be appropriately increased.

[0040] S6: The fully mechanized mining face continues to advance until the test well is destroyed, and the monitored stress or deformation data of the test well is recorded.

[0041] S7: Based on the analysis of stress and deformation monitoring data from test wells and borehole television observations, comprehensively assess the integrity of operating or abandoned oil and gas wells within the coal face and section coal pillars. Specifically, based on the analysis of stress and deformation monitoring data from test wells and borehole television observations, the principles for assessing the integrity of operating or abandoned oil and gas wells within the mining area are that the oil and gas well casing is intact and capable of continuous production, the stress and deformation do not reach the tensile, shear, and collapse strength thresholds of the test well casing, and there is no risk of instability or leakage.

[0042] While embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to these examples without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for monitoring stress and deformation of oil and gas wells in cross-mining areas of coal, oil and gas overlap, comprising the steps of arranging test wells and arranging sensors, characterized in that: The steps for arranging a test well include: S1: Install sensors on the inner wall of the production casing of the test well to monitor the stress and deformation of the test well; S2: Select the location for the test well and drill the test well at the leading position of the coal mining face and within the section coal pillar; S3: Construct and install test wells according to the wellbore structure of production or abandoned oil and gas wells in the mining area; S4: During the dynamic advancement of the fully mechanized mining face, sensors installed in the test wells are used to monitor the stress and deformation of the coal mining face and the test wells in the section coal pillars in real time; S5: When the monitored force or deformation data reaches the set value, the deformation degree of the test well affected by mining is observed in combination with the borehole television imaging device; S6: The fully mechanized mining face continues to advance until the test well is destroyed, and the monitored force or deformation data of the test well is recorded; S7: Based on the stress and deformation monitoring data of the test well and the observation results of the borehole TV imager, comprehensively evaluate the integrity of the producing or abandoned oil and gas wells in the coal face and the section coal pillar; The steps for placing sensors include: The sensors include an axial stress sensor, a circumferential stress sensor and a displacement sensor. The circumferential stress sensor is arranged in a ring manner on the inner wall of the production casing. The diameter of the ring is equal to the diameter of the inner wall of the production casing of the test well. The axial stress sensor and displacement sensor are respectively installed on both sides of the intersection of the cross diameter of the production casing and the inner wall of the production casing, and the order of arranging the axial stress sensors and displacement sensors at the four intersections is consistent.

2. The method for monitoring stress and deformation of oil and gas wells in cross-mining of coal, oil and gas overlapping areas according to claim 1 is characterized by: In step S2, when arranging a test well at an advanced position of the coal mining face, the test well needs to be arranged outside the advanced influence range.

3. The method for monitoring stress and deformation of oil and gas wells in cross-mining of coal, oil and gas overlapping areas according to claim 1 or 2, characterized in that: In step S2, when arranging test wells in the segment coal pillar, three test wells are arranged along the width direction of the segment coal pillar, one of which is arranged in the middle of the segment coal pillar, and the other two test wells are symmetrically arranged on both sides of the middle test well.

4. The method for monitoring stress and deformation of oil and gas wells in cross-mining of coal, oil and gas overlapping areas according to claim 1 is characterized by: The wellbore of the test well passes through the coal seam floor, and the bottom of the test well completion does not need to be constructed to the oil and gas reservoir.

5. The method for monitoring stress and deformation of oil and gas wells in cross-mining of coal, oil and gas overlapping areas according to claim 1 is characterized by: The axial stress sensors and displacement sensors are arranged in multiple groups longitudinally on the inner wall of the production casing of the test well. All the axial stress sensors are on the same axis, and all the displacement sensors are on the same axis.

6. The method for monitoring stress and deformation of oil and gas wells in cross-mining of coal, oil and gas overlapping areas according to claim 1 is characterized by: In step S3, the wellbore structure includes, from outside to inside, a guide pipe, a surface casing, a coal seam protection casing, a technical casing, and a production casing, and cement rings are poured between each layer of casing as needed.

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