Method for determining adjacent layer plugging thickness of shale reservoir based on temperature stress field simulation

Abstract

The invention discloses a method for determining the adjacent layer plugging thickness of a shale reservoir based on temperature stress field simulation, which comprises the following steps: wrapping the side surface of a roof rock sample with a heat insulation material, arranging a heating and stress device and temperature and strain sensors on the bottom surface of the rock sample, and arranging a plurality of groups of temperature and strain sensors on the side surface of the rock sample according to a set interval; the heating device is used for heating the rock sample until the bottom temperature is a first set temperature, the stress device is used for applying stress to the bottom of the rock sample from small to large step by step to a first set stress, and the stress is stabilized at the temperature and the stress until the variation amplitude of the measured value of each sensor is smaller than a set threshold value; determining the lowest position where the rock sample temperature is not higher than the second set temperature and the strain is not higher than the first set strain according to the measured value of the sensor; determining the lower limit of the top plate plugging thickness according to the distance from the position to the bottom surface; and similarly, determining the bottom plate plugging thickness lower limit. According to the method, through joint simulation of a temperature field and a stress field, the lower limit of the plugging thickness of the shale reservoir top and bottom plates is reasonably quantified.

Description

Technical Field

[0001] The invention relates to the technical field of petroleum geology and shale reservoir exploitation, and in particular to a method for determining the adjacent layer plugging thickness of a shale reservoir based on temperature stress field simulation. Background Art

[0002] my country's medium- and low-maturity oil shale has huge resource potential, and in-situ mining technology has been increasingly valued by all walks of life as an effective way to achieve its industrialized mining. In-situ mining technology is to directly heat the underground shale reservoir to cause it to crack underground, and the generated oil and gas are extracted through production wells. Whether the overlying rock layer can be effectively blocked during the in-situ mining of shale reservoirs is one of the key factors in improving the recovery rate. The existing technology does not have an effective means to evaluate the roof blocking performance during the in-situ mining of shale reservoirs. Summary of the invention

[0003] In order to at least partially solve the above-mentioned technical problems existing in the prior art, the inventors have made the present invention, and through a specific implementation method, provide a method for determining the adjacent layer sealing thickness of a shale reservoir based on temperature stress field simulation, which can reasonably quantify the lower limit of the shale reservoir top plate sealing thickness through the joint simulation of temperature field and stress field.

[0004] An embodiment of the present invention provides a method for determining the plugging thickness of adjacent layers of a shale reservoir based on temperature stress field simulation, comprising:

[0005] A roof rock sample is prepared by coring a coring section of an overlying rock formation of a shale reservoir, and a side surface of the roof rock sample is wrapped with a heat-insulating material. A first heating device, a first stress device, a first temperature sensor, and a first strain sensor are arranged on the bottom surface of the roof rock sample, and multiple groups of first temperature sensors and first strain sensors are arranged on the side surface of the roof rock sample at a first set interval, and the measurement positions of each group of first temperature sensors and first strain sensors are consistent in the longitudinal direction;

[0006] The top plate rock sample is heated by the first heating device until the temperature measured by the first temperature sensor at the bottom is the first set temperature, and the first stress device is used to gradually apply stress to the bottom of the top plate rock sample from small to large to the first set stress, and stabilize at the temperature and the stress until the change amplitude of the measured values ​​of each first temperature sensor and the first strain sensor is less than the set threshold value, and the lowest position where the temperature of the top plate rock sample is not higher than the second set temperature and the strain is not higher than the first set strain is determined according to the measured values ​​of the first temperature sensor and the first strain sensor;

[0007] The lower limit of the roof plugging thickness of the shale reservoir is determined according to the distance from the position to the bottom surface.

[0008] In some embodiments, the first set temperature is the lowest temperature at which the kerogen conversion rate in the shale reservoir reaches a set conversion rate threshold;

[0009] The second set temperature is the initial hydrocarbon production temperature of kerogen in the overlying rock formation.

[0010] In some embodiments, the first set temperature is the lowest temperature at which the kerogen conversion rate in the shale reservoir reaches 90%.

[0011] In some embodiments, the first set temperature is 290-330°C; the second set temperature is 200-250°C.

[0012] In some embodiments, the first set stress is the maximum principal stress underground at the buried depth of the bottom surface of the roof rock sample; and the first set strain is the critical damage strain value of the overlying rock formation.

[0013] In some embodiments, the length of the roof rock sample is not less than 500 cm.

[0014] In some embodiments, the first heating device is a one-way heating device;

[0015] The first heating device is located at the center of the bottom surface of the top plate rock sample;

[0016] The area of ​​the bottom surface of the top plate rock sample directly heated by the first heating device does not exceed 1 / 4 of the bottom surface area.

[0017] In some embodiments, the first set interval is set according to measurement accuracy requirements.

[0018] In some embodiments, it also includes:

[0019] A bottom plate rock sample is prepared by coring a coring section of an underlying rock formation of a shale reservoir, and a side surface of the bottom plate rock sample is wrapped with a heat insulating material, and a second heating device, a second stress device, a second temperature sensor, and a second strain sensor are arranged on the top surface of the bottom plate rock sample, and a plurality of groups of second temperature sensors and second strain sensors are arranged on the side surface of the bottom plate rock sample at a second set interval, and the measurement positions of each group of second temperature sensors and second strain sensors are consistent in the longitudinal direction;

[0020] The bottom plate rock sample is heated by the second heating device until the temperature measured by the second temperature sensor at the top is the first set temperature, and the second stress device is used to gradually apply stress from small to large to the top of the bottom plate rock sample to the second set stress, and stabilize at the temperature and the stress until the variation amplitude of the measured values ​​of each second temperature sensor and the second strain sensor is less than the set threshold value, and the highest position where the temperature of the bottom plate rock sample is not higher than the third set temperature and the strain is not higher than the second set strain is determined according to the measured values ​​of the second temperature sensor and the second strain sensor;

[0021] The lower limit of the bottom plate plugging thickness of the shale reservoir is determined according to the distance between the position and the top surface.

[0022] In some embodiments, the third set temperature is the initial hydrocarbon production temperature of kerogen in the underlying rock formation;

[0023] The second set stress is the maximum principal stress underground at the burial depth of the top surface of the bottom plate rock sample;

[0024] The second set strain is a critical damage strain value of the underlying rock formation.

[0025] The beneficial effects of the above technical solution provided by the embodiment of the present invention include at least:

[0026] (1) The method for determining the plugging thickness of the adjacent layer of the shale reservoir based on the temperature stress field simulation provided by the embodiment of the present invention uses a first heating device to heat the top plate rock sample to a first set temperature, uses a first stress device to gradually apply stress to the bottom of the top plate rock sample from small to large to the first set stress, and stabilizes at this temperature and stress until the measurement values ​​of each sensor are stable, and determines the lowest position where the temperature of the top plate rock sample is not higher than the second set temperature and the strain is not higher than the first set strain according to the measurement values ​​of the sensors; and determines the lower limit of the top plate plugging thickness of the shale reservoir according to the distance between this position and the bottom surface. The lower limit of the top plate plugging thickness of the shale reservoir is determined by the experimental method based on the joint simulation of the temperature field and the stress field, and the top plate plugging conditions in the process of in-situ heating and exploitation of the shale reservoir are specifically quantified, which can effectively guide production and improve the economic benefits of in-situ heating and exploitation of shale oil and gas.

[0027] (2) The method for determining the adjacent layer plugging thickness of a shale reservoir based on temperature stress field simulation provided by an embodiment of the present invention, during the experiment, the temperature of the bottom of the roof is kept constant at the lowest temperature in the reservoir where the kerogen conversion rate reaches 90%. At this temperature, the reservoir almost completes the conversion to hydrocarbons and reaches the maximum oil and gas production, that is, this temperature is the highest temperature at which the reservoir may be heated during the in-situ heating and exploitation of the actual shale reservoir; stress is applied to the bottom of the roof rock sample step by step from small to large to the maximum underground principal stress at the bottom buried depth, and stabilized at this stress, that is, the maximum stress that may be experienced during the in-situ heating and exploitation; on the basis that the temperature of the bottom of the roof is kept constant at the lowest temperature in the shale reservoir where the kerogen conversion rate reaches 90%, and the stress is kept constant at the maximum underground principal stress at the bottom buried depth, the lower limit of the roof plugging thickness is determined according to the lowest position where the temperature of the roof rock sample is not higher than the initial hydrocarbon production temperature of the kerogen in the overlying rock formation, and the strain is not higher than the critical damage strain value of the overlying rock formation fracture. Once the overburden begins to produce hydrocarbons, the kerogen material changes, which in turn causes the rock structure to change, destroying the original sealing property. Therefore, only roofs below this temperature have sealing properties; at the same time, only roofs below the critical damage strain value of the overburden fracture have sealing properties. Therefore, the above-mentioned temperature, stress and strain settings ensure that the lower limit of the roof sealing thickness is reasonable and has strong production guidance significance.

[0028] (3) In the method for determining the adjacent layer plugging thickness of a shale reservoir based on temperature stress field simulation provided by an embodiment of the present invention, the first heating device is a unidirectional heating device to save resources; the heating position is located at the center, and the direct heating area of ​​the bottom surface of the top plate rock sample does not exceed 1 / 4 of the bottom surface area, so that the heat source can be spread upward as much as possible.

[0029] (4) When studying the sealing properties of shale reservoirs, the prior art often only focuses on the sealing properties of the roof, while ignoring the sealing effect of the floor. For in-situ heating and exploitation of shale reservoirs, poor sealing performance of the floor will still lead to the loss of oil and gas, affecting the recovery rate. The method for determining the adjacent layer sealing thickness of a shale reservoir based on temperature stress field simulation provided by the embodiment of the present invention not only considers the sealing properties of the roof, but also fully considers the sealing properties of the floor, thereby ensuring the reliability of the determination of the sealing performance and further providing a guarantee for the improvement of the recovery rate.

[0030] Other features and advantages of the present invention will be described in the following description, and partly become apparent from the description, or understood by practicing the present invention. The purpose and other advantages of the present invention can be realized and obtained by the structures particularly pointed out in the written description, claims, and drawings.

[0031] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] The accompanying drawings are used to provide a further understanding of the present invention and constitute a part of the specification. Together with the embodiments of the present invention, they are used to explain the present invention and do not constitute a limitation of the present invention. In the accompanying drawings:

[0033] Figure 1 This is a flow chart of a method for determining the plugging thickness of adjacent layers of a shale reservoir based on temperature stress field simulation in Embodiment 1 of the present invention;

[0034] Figure 2 This is a flow chart of a method for determining the plugging thickness of adjacent layers of a shale reservoir based on temperature stress field simulation in Embodiment 2 of the present invention;

[0035] Figure 3 This is a schematic diagram of the axial cross section of the roof rock sample in Example 3 of the present invention;

[0036] Figure 4 This is a temperature field simulation diagram in Embodiment 3 of the present invention;

[0037] Figure 5 This is a strain field simulation diagram in the third embodiment of the present invention;

[0038] Figure 6 for Figure 4 Oil saturation variation diagram at the middle temperature line 200℃ and 220℃;

[0039] Figure 7 for Figure 5 Oil saturation variation diagram at the middle strain line of 10MPa and 25MPa. DETAILED DESCRIPTION

[0040] The exemplary embodiments of the present disclosure will be described in more detail below with reference to the accompanying drawings. Although the exemplary embodiments of the present disclosure are shown in the accompanying drawings, it should be understood that the present disclosure can be implemented in various forms and should not be limited by the embodiments set forth herein. On the contrary, these embodiments are provided to enable a more thorough understanding of the present disclosure and to fully convey the scope of the present disclosure to those skilled in the art.

[0041] It should be understood that the terms described in the present invention are only for describing special embodiments and are not intended to limit the present invention. In addition, for the numerical range in the present invention, it should be understood that each intermediate value between the upper and lower limits of the scope is also specifically disclosed. Each smaller range between the intermediate value in any stated value or stated range and any other stated value or intermediate value in the described range is also included in the present invention. The upper and lower limits of these smaller ranges can be independently included or excluded in the scope.

[0042] Unless otherwise indicated, all technical and scientific terms used herein have the same meanings as commonly understood by those skilled in the art to which the invention belongs. Although the present invention describes only preferred methods and materials, any methods and materials similar or equivalent to those described herein may also be used in the implementation or testing of the present invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials related to the documents. In the event of a conflict with any incorporated document, the content of this specification shall prevail.

[0043] In the description of the present invention, it should be noted that the terms "include", "including", "have", "contain" and the like are open terms, meaning including but not limited to.

[0044] The inventor found in his work that it is difficult to effectively evaluate the plugging performance of the top plate in the process of heating and exploitation of shale reservoirs in the prior art. After further research and development, the inventor found that the different heat conduction conditions of the top plate and the bottom plate of the shale reservoir during the in-situ heating and exploitation of the shale reservoir affect the different plugging thicknesses. In addition, the top plate and the bottom plate are subjected to different stresses due to their different burial depths. Therefore, the plugging thickness of the top plate and the bottom plate can be reasonably determined through simulation experiments of temperature and stress fields. The embodiment of the present invention provides a method for determining the plugging thickness of the adjacent layer of a shale reservoir based on temperature and stress field simulation, which can reasonably quantify the lower limit of the plugging thickness of the top plate of a shale reservoir through the method of temperature and stress field simulation.

[0045] Embodiment 1

[0046] Embodiment 1 of the present invention provides a method for determining the plugging thickness of adjacent layers of a shale reservoir based on temperature stress field simulation, referring to Figure 1 As shown, the following steps are included:

[0047] Step S11: Prepare a roof rock sample using a coring section of the overlying rock strata of the shale reservoir, wrap the side of the roof rock sample with a heat-insulating material, arrange a first heating device, a first stress device, a first temperature sensor and a first strain sensor on the bottom surface of the roof rock sample, and arrange multiple groups of first temperature sensors and first strain sensors on the side of the roof rock sample at first set intervals.

[0048] The measuring positions of each set of the first temperature sensor and the first strain sensor are consistent in the longitudinal direction.

[0049] A coring section of the overlying strata of the shale reservoir is used to prepare a roof rock sample with the same cross-sectional area (eg, a cylindrical shape with a diameter of 5 cm).

[0050] According to empirical data, the sealing thickness of the roof (mudstone roof) during in-situ heating and exploitation of shale reservoirs is usually within three to four hundred centimeters. Therefore, the length (thickness) of the roof rock sample is set to be no less than 500 cm. If it is thicker, the experimental difficulty and cost will increase; if it is thinner, it will easily fall below the actual lower limit of the roof's sealing thickness, resulting in experimental failure (the roof sealing thickness required for in-situ heating of shale cannot be measured).

[0051] The sides of the roof rock sample are wrapped with heat-insulating material to prevent heat from being dissipated to the surroundings during heating. The pressure resistance of the heat-insulating material must be no less than 80MPa.

[0052] The first stress device may be a triaxial stress test device.

[0053] In some embodiments, the first heating device is a unidirectional heating device to save resources.

[0054] The first heating device is located at the center of the bottom surface of the top plate rock sample. Further, the first heating device can directly heat the bottom surface of the top plate rock sample to no more than 1 / 4 of the bottom surface area, so that the heat source can be spread upward as much as possible.

[0055] Specifically, the bottom surface of the roof rock sample refers to the side of the corresponding original underground position closest to the shale reservoir.

[0056] The first temperature sensor and the first strain sensor are arranged axially on the side of the roof rock sample, and the first set interval of the arrangement is set according to the measurement accuracy requirement, usually at an interval of 10 cm.

[0057] Step S12: using the first heating device to heat the top plate rock sample to a first set temperature measured by the first temperature sensor at the bottom, using the first stress device to gradually apply stress to the bottom of the top plate rock sample from small to large to the first set stress, and stabilize at the temperature and the stress until the measured value change amplitude of each first temperature sensor and the first strain sensor is less than the set threshold value, and determining the lowest position where the temperature of the top plate rock sample is not higher than the second set temperature and the strain is not higher than the first set strain according to the measured values ​​of the first temperature sensor and the first strain sensor.

[0058] In some embodiments, the first set temperature is the lowest temperature at which the kerogen conversion rate in the shale reservoir reaches a set conversion rate threshold.

[0059] The first set temperature can be determined by utilizing a source rock thermal simulation experiment or a kerogen activation energy experiment.

[0060] For example, multiple samples of shale reservoirs are taken, and source rock thermal simulation experiments are carried out respectively to measure the lowest temperature at which the kerogen conversion rate reaches a set conversion rate threshold, and the minimum value of the multiple minimum temperatures measured is determined as the first set temperature.

[0061] Furthermore, the first set temperature is the lowest temperature at which the kerogen conversion rate in the shale reservoir reaches 90%, usually 290-330°C.

[0062] The kerogen conversion rate reaches 90%. At this temperature, the reservoir almost completes the conversion to hydrocarbons and achieves maximum oil and gas production. That is, this temperature is the highest temperature at which the reservoir may be heated during the in-situ heating and exploitation of the actual shale reservoir. Therefore, the setting of this temperature ensures the safety and rationality of the lower limit of the roof plugging thickness.

[0063] In some embodiments, the second set temperature is the initial hydrocarbon production temperature of kerogen in the overlying rock formation, which is typically 200-250°C.

[0064] The second set temperature can be determined by using a source rock thermal simulation experiment.

[0065] For example, multiple samples of the overlying rock formation are taken, and thermal simulation experiments of the source rock are carried out respectively to measure the initial hydrocarbon production temperature of the kerogen, and the minimum value of the measured temperatures is determined as the second set temperature.

[0066] In some embodiments, the first set stress is the maximum principal stress underground at the depth of the bottom surface of the roof rock sample, which is obtained by calculation; the first set strain is the critical damage strain value of the overlying rock formation, which can be determined by a rock fracture experiment.

[0067] The first set temperature, i.e., the lowest temperature T0 at which the kerogen conversion rate in the shale reservoir reaches 90%, is determined in the above manner, the initial hydrocarbon production temperature Tx of the kerogen in the overlying rock formation is determined, the underground maximum principal stress Ex at the burial depth of the bottom surface of the roof rock sample and the critical damage strain value εx of the overlying rock formation are determined.

[0068] In some embodiments, the minimum starting pressure (breakthrough pressure) Ps of the fluid migration in the overburden is further determined. A prerequisite of the embodiments of the present application is that the minimum starting pressure Ps of the overburden is greater than the fracture pressure P0 of the shale reservoir.

[0069] The first heating device (heat source) is used to heat slowly (no more than 20°C / day), and the maximum temperature of the heat source is between 400 and 650°C. The power of the heat source is adjusted to make the temperature at the bottom of the roof rock sample constant at T0; at the same time, the first stress device is used to apply stress to the bottom of the roof rock sample step by step, and each increase of 1MPa can be constant for 5 minutes, and the final applied stress is constant at Ex. Further, the stress is made to reach Ex and the temperature reaches T0 synchronously as much as possible. The temperature is constant at T0 and the stress is constant at Ex, and it is stable for at least 30 minutes until the change amplitude of the measured values ​​of each sensor is less than the set threshold, that is, after the temperature and strain are stable, the measured values ​​of each first temperature sensor and the first strain sensor are collected. Since the temperature of the roof rock sample gradually decreases from bottom to top, and the strain also gradually decreases from bottom to top, the measured values ​​of the first temperature sensor and the first strain sensor can be collected from bottom to top in sequence until the currently collected temperature is not greater than Tx and the strain is not greater than εx. The lowest position where the temperature of the roof rock sample is not higher than Tx and the strain is not higher than εx is determined according to the position of the corresponding sensor.

[0070] If the currently collected temperature is Tx, the position of the corresponding first temperature sensor can be directly determined as the position where the roof rock sample temperature begins to drop to Tx; if the currently collected temperature begins to be less than Tx (the first temperature less than Tx), based on the currently collected temperature and the previous collected temperature and the position of the current first temperature sensor and the position of the previous first temperature sensor, the first lowest position where the roof rock sample temperature is not higher than Tx is determined by the proportional method.

[0071] Similarly, if the currently collected strain is εx, the position of the corresponding first strain sensor can be directly determined as the position where the roof rock sample strain begins to drop to εx; if the currently collected strain begins to be less than εx (the first strain less than εx), based on the currently collected strain and the last collected strain and the position of the current first strain sensor and the position of the last first strain sensor, the second lowest position where the roof rock sample strain is not higher than εx is determined by the proportional method.

[0072] The higher of the first lowest position and the second lowest position is taken as the lowest position where the temperature of the roof rock sample is not higher than the second set temperature and the strain is not higher than the first set strain.

[0073] Step S13: Determine the lower limit of the roof plugging thickness of the shale reservoir according to the distance between the position and the bottom surface.

[0074] The distance between the position and the bottom surface can be directly determined as the lower limit of the roof plugging thickness of the shale reservoir; other factors affecting the plugging performance can also be further considered to determine the safety correction factor (greater than 1), and the product of the safety correction factor and the determined distance is used as the lower limit of the roof plugging thickness of the shale reservoir.

[0075] The method for determining the plugging thickness of adjacent layers of a shale reservoir based on a temperature stress field simulation provided in the first embodiment of the present invention uses a first heating device to heat the top plate rock sample to a first set temperature, uses a first stress device to gradually apply stress to the bottom of the top plate rock sample from small to large to the first set stress, and stabilizes at the temperature and the stress until the measured values ​​of each sensor are stable, and determines the lowest position where the temperature of the top plate rock sample is not higher than the second set temperature and the strain is not higher than the first set strain according to the measured values ​​of the sensors; and determines the lower limit of the top plate plugging thickness of the shale reservoir according to the distance between the position and the bottom surface. The lower limit of the top plate plugging thickness of the shale reservoir is determined based on the joint simulation of the temperature field and the stress field through an experimental method, and the top plate plugging conditions in the process of in-situ heating and exploitation of the shale reservoir are specifically quantified, which can effectively guide production and improve the economic benefits of in-situ heating and exploitation of shale oil and gas.

[0076] The method for determining the plugging thickness of adjacent layers of a shale reservoir based on a temperature stress field simulation provided in the first embodiment of the present invention comprises the following steps: during the experiment, the temperature of the bottom of the roof is kept constant at the lowest temperature at which the kerogen conversion rate in the reservoir reaches 90%, at which the reservoir almost completes the conversion to hydrocarbon generation and reaches the maximum oil and gas production, that is, the temperature is the highest temperature at which the reservoir may be heated during the in-situ heating and exploitation of the actual shale reservoir; stress is applied step by step from small to large to the bottom of the roof rock sample to the maximum principal stress underground at the depth of the bottom surface burial, and stabilized at this stress, that is, the maximum stress that may be received during the in-situ heating and exploitation; on the basis that the temperature of the bottom of the roof is kept constant at the lowest temperature at which the kerogen conversion rate in the shale reservoir reaches 90%, and the stress is kept constant at the maximum principal stress underground at the depth of the bottom surface burial, the lower limit of the roof plugging thickness is determined according to the lowest position at which the temperature of the roof rock sample is not higher than the initial hydrocarbon production temperature of the kerogen in the overlying rock formation, and the strain is not higher than the critical damage strain value of the overlying rock formation fracture. Once the overburden begins to produce hydrocarbons, the kerogen material changes, which in turn causes the rock structure to change, destroying the original sealing property. Therefore, only roofs below this temperature have sealing properties; at the same time, only roofs below the critical damage strain value of the overburden fracture have sealing properties. Therefore, the above-mentioned temperature, stress and strain settings ensure that the lower limit of the roof sealing thickness is reasonable and has strong production guidance significance.

[0077] Embodiment 2

[0078] Embodiment 2 of the present invention provides another method for determining the plugging thickness of the adjacent layer of a shale reservoir based on temperature stress field simulation, specifically a method for determining the lower limit of the bottom plate plugging thickness of a shale reservoir. The method for determining the lower limit of the top plate plugging thickness of a shale reservoir in the above embodiment 1 is still applicable here. For details, refer to Figure 2 As shown, the following steps are included:

[0079] Step S21: Prepare a bottom plate rock sample using the coring section of the underlying rock formation of the shale reservoir, wrap the side of the bottom plate rock sample with a heat-insulating material, arrange a second heating device, a second stress device, a second temperature sensor and a second strain sensor on the top surface of the bottom plate rock sample, and arrange multiple groups of second temperature sensors and second strain sensors on the side of the bottom plate rock sample at second set intervals.

[0080] The measuring positions of each group of the second temperature sensors and the second strain sensors are consistent in the longitudinal direction.

[0081] The second temperature sensor may be the same temperature sensor as the first temperature sensor, and the "first" and "second" here are only used to distinguish whether the temperature sensor is set in the top plate rock sample or the bottom plate rock sample.

[0082] Similarly, the second strain sensor can be the same strain sensor as the first strain sensor, and the "first" and "second" here are just to distinguish whether it is a strain sensor set in the top plate rock sample or the bottom plate rock sample.

[0083] The bottom plate rock sample with the same cross-sectional area (e.g., cylindrical with a diameter of 5 cm) is prepared by coring the underlying rock formation of the shale reservoir. The length (thickness) of the bottom plate rock sample is not less than 500 cm.

[0084] The second heating device can be the same heating device as the first heating device, and the "first" and "second" here are just to distinguish whether the heating device is arranged on the bottom surface of the top plate rock sample or the top surface of the bottom plate rock sample.

[0085] The second stress device can be a heating device that is the same as the first stress device. The "first" and "second" here are only used to distinguish whether the stress device is set on the bottom surface of the top plate rock sample or on the top surface of the bottom plate rock sample.

[0086] The second heating device is located at the center of the top surface of the bottom plate rock sample. Further, the second heating device may directly heat the top surface of the bottom plate rock sample to no more than 1 / 4 of the top surface area, so that the heat source can be spread downward as much as possible.

[0087] Specifically, the top surface of the bottom plate rock sample refers to the side of the corresponding original underground position closest to the shale reservoir.

[0088] The second temperature sensor and the second strain sensor are arranged axially on the side of the bottom plate rock sample. The second set interval of the arrangement is set according to the measurement accuracy requirement and can be consistent with the first set interval, usually 10 cm.

[0089] Step S22: using the second heating device to heat the bottom plate rock sample until the measured temperature of the second temperature sensor at the top is the first set temperature, using the second stress device to gradually apply stress to the top of the bottom plate rock sample from small to large to the second set stress, and stabilize at this temperature and stress until the measured value change amplitude of each second temperature sensor and second strain sensor is less than the set threshold value, and determine the highest position where the bottom plate rock sample temperature is not higher than the third set temperature and the strain is not higher than the second set strain according to the measured values ​​of the second temperature sensor and the second strain sensor.

[0090] In some embodiments, the third set temperature is the initial hydrocarbon production temperature of kerogen in the underlying rock formation, and its determination method can refer to the determination of the second set temperature.

[0091] This application is based on the premise that the overlying and underlying rock formations of the shale reservoir are both mudstone formations. Therefore, if the rock properties of the overlying and underlying rock formations are basically the same, the initial hydrocarbon production temperature of kerogen in the overlying rock formation can also be approximated as the initial hydrocarbon production temperature of kerogen in the underlying rock formation.

[0092] The second set stress is the maximum principal stress underground at the buried depth of the top surface of the bottom plate rock sample, which is obtained by calculation.

[0093] The second set strain is the critical damage strain value of the underlying rock stratum, which can also be determined through rock fracture experiments. Therefore, if the rock mechanical properties of the overlying rock stratum and the underlying rock stratum are basically the same, the critical damage strain value of the overlying rock stratum can also be approximated as the critical damage strain value of the underlying rock stratum.

[0094] Taking the third set temperature as Tx, the second set stress as Ex, and the second set strain as εx as an example, the second heating device (heat source) is used to slowly heat (no more than 20°C / day), the maximum temperature of the heat source is between 400 and 650°C, and the heat source power is adjusted to make the top temperature of the bottom plate rock sample constant at T0; at the same time, the second stress device is used to gradually apply stress to the top of the bottom plate rock sample, and each increase of 1MPa can be constant for 5 minutes, so that the final applied stress is constant at Ex. Furthermore, try to make the stress reach Ex and the temperature reach T0 simultaneously. The temperature is constant T0 and the stress is constant Ex, and they are stable for at least 30 minutes until the change amplitude of the measured values ​​of each sensor is less than the set threshold, that is, after the temperature and strain are stable, the measured values ​​of each second temperature sensor and the second strain sensor are collected. Since the temperature of the bottom plate rock sample gradually decreases from the top to the bottom, the strain also gradually decreases from the top to the bottom, the measured values ​​of the second temperature sensor and the second strain sensor can be collected from the top to the bottom in sequence until the currently collected temperature is not greater than Tx and the strain εx is not greater than Px. The highest position where the bottom plate rock sample temperature is not higher than Tx and the strain is not higher than εx is determined according to the position of the corresponding sensor.

[0095] If the currently collected temperature is Tx, the position of the corresponding second temperature sensor can be directly determined as the position where the bottom plate rock sample temperature begins to drop to Tx; if the currently collected temperature begins to be less than Tx (the first temperature less than Tx), based on the currently collected temperature and the previous collected temperature and the current position of the second temperature sensor and the position of the previous second temperature sensor, the first highest position where the bottom plate rock sample temperature is not higher than Tx is determined by the proportional method.

[0096] Similarly, if the currently collected strain is εx, the position of the corresponding second strain sensor can be directly determined as the position where the bottom plate rock sample strain begins to drop to εxx; if the currently collected strain begins to be less than εx (the first strain less than εx), based on the currently collected strain and the last collected strain and the position of the current second strain sensor and the position of the last second strain sensor, the second highest position where the bottom plate rock sample strain is not higher than εx is determined by the proportional method.

[0097] The lower one of the first highest position and the second highest position is taken as the highest position where the bottom plate rock sample temperature is not higher than the third set temperature and the stress is not higher than the third set stress.

[0098] Step S23: Determine the lower limit of the bottom plate plugging thickness of the shale reservoir according to the distance from the position to the top surface.

[0099] The distance from this position to the top surface can be directly determined as the lower limit of the bottom plate plugging thickness of the shale reservoir; other factors affecting the plugging performance can also be further considered to determine the safety correction factor (greater than 1), and the product of the safety correction factor and the determined distance is used as the lower limit of the bottom plate plugging thickness of the shale reservoir.

[0100] When studying the sealing properties of shale reservoirs, the prior art often only focuses on the sealing properties of the top plate, while ignoring the sealing effect of the bottom plate. For in-situ heating and exploitation of shale reservoirs, poor bottom plate sealing performance will still lead to the loss of oil and gas, affecting the recovery rate. The method for determining the adjacent layer sealing thickness of a shale reservoir based on temperature stress field simulation provided in Example 2 of the present invention fully considers the sealing properties of the bottom plate, ensures the reliability of the determination of the sealing performance, and further provides a guarantee for the improvement of the recovery rate.

[0101] The above-mentioned embodiment 1 and embodiment 2 can be applied separately; or they can be applied in combination to determine both the lower limit of the top plate plugging thickness of the shale reservoir and the lower limit of the bottom plate plugging thickness of the shale reservoir. The top and bottom plate thicknesses of the shale reservoir both meet the corresponding lower limits of the plugging thickness, and then it is determined that the plugging requirements are met.

[0102] Embodiment 3

[0103] Embodiment 3 of the present invention provides a specific application of a method for determining a lower limit of the top plate plugging thickness of a shale reservoir, and verifies its accuracy through numerical simulation, including the following steps:

[0104] 1) The T0 (kerogen 90% conversion temperature) of the shale reservoir rock sample was measured to be 300°C.

[0105] 2) The Tx (initial hydrocarbon production temperature of kerogen) of the roof rock sample was measured to be 200℃.

[0106] 3) Determine the stress Ex (maximum axial stress) of the reservoir rock sample to be 30 MPa.

[0107] 4) The critical damage strain value εx of the roof rock sample was determined to be 10MPa.

[0108] 5) Prepare a cylindrical roof rock sample with a diameter of 5 cm and a length of 500 cm. Figure 3 The figure shows a schematic cross-sectional view of the roof rock sample along the axial direction.

[0109] 6) Rock wool is used as a heat-insulating material to wrap the roof rock sample, with a pressure resistance of not less than 80 MPa, and the roof rock sample is placed in the experimental device.

[0110] 7) A unidirectional heat source point is placed at the bottom of the roof rock sample, and temperature sensors and strain sensors are arranged starting from the bottom. Several groups of temperature sensors and strain sensors are arranged along the axial direction of the roof rock sample, with an interval of 10 cm.

[0111] 8) The bottom of the roof rock sample is heated with a unidirectional point heat source, the heat source is heated at a rate of 20°C / day, and the temperature peak is 300°C (T0). A rigid stress is applied to the bottom of the roof rock sample at a rate of 1MPa / 5 minutes, and the stress peak is 30MPa (Ex).

[0112] 9) The bottom temperature of the roof rock sample is constant at T0, and the stress is constant at Ex for 30 minutes (the measurement values ​​of each sensor are stable), and the temperature sensor and strain sensor data of the roof rock sample are continuously collected.

[0113] 10) The distance from the position where the temperature Tx is measured and calculated to the bottom of the roof rock sample is 110 cm, and the distance from the position where the strain εx is measured and calculated to the bottom of the roof rock sample is 120 cm, that is, the lower limit of the roof plugging thickness is 120 cm.

[0114] 11) Establish a numerical model consistent with the roof rock sample and experimental conditions, set the activation energy parameters in the chemical reaction, set the Tx (initial hydrocarbon production temperature of kerogen) of the roof rock sample to 200°C, and set the critical damage strain value εx of the roof rock sample to 10MPa.

[0115] 12) Keep the temperature at the bottom of the top rock sample constant at T0 (300°C) and the stress constant at Ex (30MPa), complete the numerical simulation of the temperature field and stress field, and wait for the grid temperature and strain to stabilize.

[0116] 13) See Figure 4 and Figure 5 As shown in Figure 2, they are the simulated temperature field and simulated strain field of the roof rock sample. Figure 4 Oil saturation at the Tx temperature line (200°C) (see Figure 6 There was no change in the entire simulation period, indicating that oil and gas were blocked at this location. Figure 5 Oil saturation of the εx strain line (10 MPa) (see Figure 7 There was no change in the whole simulation period, indicating that oil and gas were blocked at this location.

[0117] 14) Observation Figure 4 Oil saturation at 220°C (see Figure 6 (as shown in the figure), there are obvious changes in the entire simulation period, indicating that the oil and gas are not blocked at this location. Figure 5 Oil saturation at 25 MPa of the medium strain line (see Figure 7 During the whole simulation period, there are obvious changes, indicating that the oil and gas are not blocked at this location.

[0118] 15) The thickness of the Tx temperature line is 114cm, and the thickness of the εx strain line is 116cm. The comprehensive comparison proves that the top plate with a thickness of 116cm meets the plugging requirements. The error between the numerical simulation results and the experimental results (120cm) is about 3.3%, so the numerical simulation verifies the reliability of the experimental results.

[0119] It should be understood that the specific order or hierarchy of steps in the disclosed process is an example of an exemplary method. Based on design preferences, it should be understood that the specific order or hierarchy of steps in the process can be rearranged without departing from the scope of protection of the present disclosure. The attached method claims present the elements of the various steps in an exemplary order and are not intended to be limited to the specific order or hierarchy described.

[0120] In the above detailed description, various features are grouped together in a single embodiment to simplify the disclosure. This method of disclosure should not be interpreted as reflecting an intention that the embodiments of the claimed subject matter require more features than are clearly stated in each claim. On the contrary, as reflected in the appended claims, the invention is in a state of having less than all the features of the disclosed individual embodiments. Therefore, the appended claims are hereby expressly incorporated into the detailed description, with each claim standing on its own as a separate preferred embodiment of the invention.

[0121] The above description includes examples of one or more embodiments. Of course, it is impossible to describe all possible combinations of components or methods for the purpose of describing the above embodiments, but it should be recognized by those skilled in the art that the various embodiments can be further combined and arranged. Therefore, the embodiments described herein are intended to cover all such changes, modifications and variations that fall within the scope of protection of the appended claims. In addition, with respect to the term "comprising" used in the specification or claims, the word is covered in a manner similar to the term "including", just as "including," explained as a transitional word in the claims. In addition, any term "or" used in the specification of the claims is intended to represent "non-exclusive or". The terms "first" and "second" are used for descriptive purposes and are not to be understood as indicating or implying relative importance.

Claims

1. A method for determining the adjacent layer plugging thickness of a shale reservoir based on temperature stress field simulation, characterized in that: include: A roof rock sample is prepared by coring a coring section of an overlying rock formation of a shale reservoir, and a side surface of the roof rock sample is wrapped with a heat-insulating material. A first heating device, a first stress device, a first temperature sensor, and a first strain sensor are arranged on the bottom surface of the roof rock sample, and multiple groups of first temperature sensors and first strain sensors are arranged on the side surface of the roof rock sample at a first set interval, and the measurement positions of each group of first temperature sensors and first strain sensors are consistent in the longitudinal direction; The top plate rock sample is heated by the first heating device until the temperature measured by the first temperature sensor at the bottom is the first set temperature, and the first stress device is used to gradually apply stress to the bottom of the top plate rock sample from small to large to the first set stress, and stabilize at the temperature and the stress until the change amplitude of the measured values ​​of each first temperature sensor and the first strain sensor is less than the set threshold value, and the lowest position where the temperature of the top plate rock sample is not higher than the second set temperature and the strain is not higher than the first set strain is determined according to the measured values ​​of the first temperature sensor and the first strain sensor; The lower limit of the top plate plugging thickness of the shale reservoir is determined according to the distance from the position to the bottom surface.

2. The method according to claim 1, characterized in that The first set temperature is the lowest temperature at which the kerogen conversion rate in the shale reservoir reaches a set conversion rate threshold; The second set temperature is the initial hydrocarbon production temperature of kerogen in the overlying rock formation.

3. The method according to claim 2, characterized in that The first set temperature is the lowest temperature at which the kerogen conversion rate in the shale reservoir reaches 90%.

4. The method according to claim 3, characterized in that The first set temperature is 290-330°C; the second set temperature is 200-250°C.

5. The method according to claim 3, characterized in that The first set stress is the maximum principal stress underground at the buried depth of the bottom surface of the roof rock sample; The first set strain is a critical damage strain value of the overburden stratum.

6. The method according to claim 1, characterized in that The length of the roof rock sample is not less than 500 cm.

7. The method according to claim 1, characterized in that The first heating device is a one-way heating device; The first heating device is located at the center of the bottom surface of the top plate rock sample; The area of ​​the bottom surface of the top plate rock sample directly heated by the first heating device does not exceed 1 / 4 of the bottom surface area.

8. The method according to claim 1, characterized in that The first set interval is set according to the measurement accuracy requirement.

9. The method according to claim 1, characterized in that Also includes: A bottom plate rock sample is prepared by coring a coring section of an underlying rock formation of a shale reservoir, and a side surface of the bottom plate rock sample is wrapped with a heat insulating material, and a second heating device, a second stress device, a second temperature sensor, and a second strain sensor are arranged on the top surface of the bottom plate rock sample, and a plurality of groups of second temperature sensors and second strain sensors are arranged on the side surface of the bottom plate rock sample at a second set interval, and the measurement positions of each group of second temperature sensors and second strain sensors are consistent in the longitudinal direction; The bottom plate rock sample is heated by the second heating device until the temperature measured by the second temperature sensor at the top is the first set temperature, and the second stress device is used to gradually apply stress from small to large to the top of the bottom plate rock sample to the second set stress, and stabilize at the temperature and the stress until the variation amplitude of the measured values ​​of each second temperature sensor and the second strain sensor is less than the set threshold value, and the highest position where the temperature of the bottom plate rock sample is not higher than the third set temperature and the strain is not higher than the second set strain is determined according to the measured values ​​of the second temperature sensor and the second strain sensor; The lower limit of the bottom plate plugging thickness of the shale reservoir is determined according to the distance between the position and the top surface.

10. The method according to claim 9, characterized in that The third set temperature is the initial hydrocarbon production temperature of kerogen in the underlying rock formation; The second set stress is the maximum principal stress underground at the burial depth of the top surface of the bottom plate rock sample; The second set strain is a critical damage strain value of the underlying rock formation.

Images