A method for determining the lower limit of adjacent stratum sealing thickness in shale reservoirs

Abstract

The present invention discloses a method for determining the lower limit of the plugging thickness of adjacent strata in a shale reservoir, comprising: wrapping the side of a roof rock sample with a thermally insulating sealing material; arranging heating, pressurizing, and stressing devices and sensors on the bottom surface, including temperature, pressure, and strain sensors, with multiple groups of sensors arranged on the side at set intervals; heating the bottom of the rock sample to a first set temperature using a heating device; pressurizing the bottom to a first set pressure using a pressurizing device; applying stress to the bottom of the rock sample in steps from small to large to a first set stress using a stressing device, and stabilizing the stress until the measured values ​​of each sensor are stable; determining the lowest position where the rock sample temperature is not higher than a second set temperature, the pressure is not higher than a second set pressure, and the strain is not higher than a set strain based on the measured values ​​of the sensors; and then determining the lower limit of the roof plugging thickness; and similarly determining the lower limit of the bottom plate plugging thickness. This method can reasonably quantify the lower limit of the top and bottom plate plugging thickness of a shale reservoir through the joint simulation of temperature, pressure, and stress fields.

Description

Technical Field

[0001] The present invention relates to the fields of petroleum geology and shale reservoir mining technology, and in particular to a method for determining the lower limit of the sealing thickness of adjacent strata of a shale reservoir. Background Art

[0002] my country's medium- and low-maturity oil shale reserves hold enormous potential, and in-situ production technology is gaining increasing attention as an effective means of industrializing its extraction. In-situ production involves directly heating the underground shale reservoir, causing it to crack underground, with the resulting oil and gas extracted through production wells. Effective sealing of the overburden during in-situ production of shale reservoirs is a key factor in improving oil recovery. However, existing technologies lack effective methods for evaluating the sealing performance of the roof during in-situ production 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. Through a specific implementation method, a method for determining the lower limit of the sealing thickness of adjacent strata in a shale reservoir is provided. The method can reasonably quantify the lower limit of the sealing thickness of the shale reservoir roof through the joint simulation of the temperature field, pressure field and stress field.

[0004] An embodiment of the present invention provides a method for determining a lower limit of the sealing thickness of adjacent strata in a shale reservoir, comprising:

[0005] A roof rock sample is prepared using a coring section of an overlying stratum of a shale reservoir, and a side surface of the roof rock sample is wrapped with a heat-insulating sealing material. A first heating device, a first pressurizing device, a first stress device, and a group of first sensors are arranged on the bottom surface of the roof rock sample. Multiple groups of first sensors are arranged on the side surface of the roof rock sample at first set intervals, wherein the first sensors include a first temperature sensor, a first pressure sensor, and a first strain sensor.

[0006] The roof rock sample is heated by the first heating device until the temperature measured by the first temperature sensor at the bottom is a first set temperature, the roof rock sample is pressurized by the first pressurizing device until the pressure measured by the first pressure sensor at the bottom is a first set pressure, the first stress device is used to gradually apply stress to the bottom of the roof rock sample from small to large to the first set stress, and stabilize at the temperature, pressure, and stress until the change amplitude of the measured value of each first sensor is less than a set threshold, and the lowest position of the roof rock sample at which the temperature is not higher than the second set temperature, the pressure is not higher than the second set pressure, and the strain is not higher than the first set strain is determined based on the measured values ​​of the first sensors;

[0007] The lower limit of the roof plugging thickness of the shale reservoir is determined based on the distance between the position and 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 pressure is the fracture pressure of the shale reservoir, and the second set pressure is the fracture pressure of the overburden formation.

[0013] In some embodiments, the first set stress is the maximum principal stress underground at the burial 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.

[0014] In some embodiments, the length of the roof rock sample is not less than 500 cm.

[0015] In some embodiments, the first heating device is a one-way heating device;

[0016] The first heating device is located at the center of the bottom surface of the roof rock sample;

[0017] The area of ​​the bottom surface of the roof rock sample directly heated by the first heating device does not exceed 1 / 4 of the bottom surface area.

[0018] In some embodiments, the first set interval is set according to measurement accuracy requirements.

[0019] In some embodiments, further comprising:

[0020] A floor rock sample is prepared using a coring section of an underlying rock formation of a shale reservoir, and a side surface of the floor rock sample is wrapped with a heat-insulating sealing material. A second heating device, a second pressurizing device, a second stress device, and a group of second sensors are arranged on the top surface of the floor rock sample. Multiple groups of second sensors are arranged on the side surface of the floor rock sample at second set intervals, and the second sensors include a second temperature sensor, a second pressure sensor, and a second strain sensor.

[0021] 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, the bottom plate rock sample is pressurized by the second pressurizing device until the pressure measured by the second pressure sensor at the top is the second set pressure, 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, pressure, and stress until the change amplitude of the measured value of each second sensor is less than the set threshold value, and the highest position of the bottom plate rock sample is determined based on the measured values ​​of the second sensors at which the temperature is not higher than the third set temperature, the pressure is not higher than the third set pressure, and the strain is not higher than the second set strain;

[0022] The lower limit of the bottom plate plugging thickness of the shale reservoir is determined based on the distance between the position and the top surface.

[0023] In some embodiments, the third set temperature is the initial hydrocarbon production temperature of kerogen in the underlying rock formation;

[0024] The third set pressure is the fracture pressure of the underlying rock formation;

[0025] The second set stress is the maximum principal stress underground at the burial depth of the top surface of the bottom plate rock sample;

[0026] The second set strain is a critical damage strain value of the underlying rock formation.

[0027] The beneficial effects of the above technical solutions provided by the embodiments of the present invention include at least:

[0028] (1) The method for determining the lower limit of the plugging thickness of adjacent strata in a shale reservoir provided by an embodiment of the present invention comprises the following steps: heating a roof rock sample to a first set temperature using a first heating device, pressurizing the roof rock sample to a first set pressure using a first pressurizing device, and applying stress to the bottom of the roof rock sample step by step from small to large to the first set stress using a first stress device, and stabilizing the stress at the temperature, pressure, and stress until the measured values ​​of each sensor are stable. The lowest position where the temperature of the roof rock sample is not higher than a second set temperature, the pressure is not higher than a second set pressure, and the strain is not higher than the first set strain is determined based on the measured values ​​of the sensors; and the lower limit of the roof plugging thickness of the shale reservoir is determined based on the distance between the position and the bottom surface. The lower limit of the roof plugging thickness of the shale reservoir is determined by an experimental method based on the joint simulation of the temperature field, pressure field, and stress field, and the roof plugging conditions during the in-situ heating production of the shale reservoir are specifically quantified, which can effectively guide production and improve the economic benefits of in-situ heating production of shale oil and gas.

[0029] (2) The method for determining the lower limit of the sealing thickness of adjacent formations of a shale reservoir provided by an embodiment of the present invention is as follows: 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 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 mining process of the actual shale reservoir; the pressure at the bottom of the roof is kept constant at the fracture pressure of the shale reservoir, that is, the maximum pressure that may be encountered during the in-situ heating and mining process; stress is applied step by step from small to large to the bottom of the roof rock sample. The maximum subsurface principal stress at the depth of the surface is determined and stabilized at this stress, which is the maximum stress that may be experienced during in-situ heating and mining. Under the assumption that the roof bottom temperature is constant at the lowest temperature at which kerogen conversion reaches 90% in the shale reservoir, the pressure is constant at the shale reservoir fracture pressure, and the stress is constant at the maximum subsurface principal stress at the depth of the bottom surface, the lower limit of the roof plugging thickness is determined based on the lowest location where the roof rock sample temperature is no higher than the initial hydrocarbon production temperature of the overburden kerogen, the pressure is no higher than the overburden fracture pressure, and the strain is no higher than the critical damage strain value of the overburden fracture. Once the overburden begins to produce hydrocarbons, the kerogen material changes, leading to changes in the rock structure and destroying the original plugging properties. Therefore, the roof only has plugging properties below this temperature; the roof only has plugging properties below the overburden fracture pressure; and the roof only has plugging properties below the critical damage strain value of the overburden fracture. Therefore, the above temperature, pressure, stress, and strain settings ensure that the lower limit of the roof plugging thickness is reasonable and has strong production guidance significance.

[0030] (3) In the method for determining the lower limit of the sealing thickness of adjacent strata in a shale reservoir provided by an embodiment of the present invention, the first heating device is a unidirectional heating device, which saves 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.

[0031] (4) When studying the sealing properties of shale reservoirs, existing technologies often focus only on the sealing properties of the roof, while ignoring the sealing function of the floor. However, for in-situ heating and production of shale reservoirs, poor floor sealing performance will still lead to oil and gas loss, affecting the recovery rate. The method for determining the lower limit of the sealing thickness of adjacent strata in shale reservoirs provided by the embodiments of the present invention not only considers the sealing properties of the roof, but also fully considers the sealing properties of the floor, thus ensuring the reliability of the determination of the sealing performance and further providing a guarantee for improving the recovery rate.

[0032] Other features and advantages of the present invention will be described in the following description, and in part will become apparent from the description, or will be understood by practicing the present invention. The purposes 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.

[0033] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] 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:

[0035] Figure 1 This is a flow chart of a method for determining the lower limit of the sealing thickness of adjacent formations in a shale reservoir in Example 1 of the present invention;

[0036] Figure 2 This is a flow chart of a method for determining the lower limit of the sealing thickness of adjacent formations in a shale reservoir in Example 2 of the present invention;

[0037] Figure 3 This is a schematic diagram of the axial cross-section of the roof rock sample in Example 3 of the present invention;

[0038] Figure 4 This is a temperature field simulation diagram in Example 3 of the present invention;

[0039] Figure 5 This is a pressure field simulation diagram in Example 3 of the present invention;

[0040] Figure 6 This is a strain field simulation diagram in Example 3 of the present invention;

[0041] Figure 7 for Figure 4 Oil saturation variation diagram at the middle temperature line 200℃ and 220℃;

[0042] Figure 8 for Figure 5 Oil saturation variation diagram at the middle pressure line of 30MPa and 35MPa;

[0043] Figure 9 for Figure 6 Oil saturation variation diagram at the middle strain line of 10MPa and 25MPa. DETAILED DESCRIPTION

[0044] Exemplary embodiments of the present disclosure will be described in more detail below with reference to the accompanying drawings. Although 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. Rather, 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.

[0045] It should be understood that the terms described herein are intended only to describe particular embodiments and are not intended to limit the present invention. In addition, for numerical ranges herein, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Each smaller range between any intermediate value within a stated value or stated range and any other stated value or intermediate value within the stated range is also encompassed by the present invention. The upper and lower limits of these smaller ranges may be independently included or excluded within the scope.

[0046] Unless otherwise indicated, all technical and scientific terms used herein have the same meaning 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 any conflict with any incorporated document, the content of this specification shall prevail.

[0047] In the description of the present invention, it should be noted that the terms “include”, “including”, “have”, “contain”, etc. are all open terms, which mean including but not limited to.

[0048] During their work, the inventors discovered that the existing technology had the problem of difficulty in effectively evaluating the roof sealing performance during the heating and mining process of shale reservoirs. After further research and development, the inventors discovered that during the in-situ heating and mining process of shale reservoirs, the different heat conduction conditions of the roof and floor of the shale reservoir affect the different sealing thicknesses; the roof and floor are subjected to different stresses due to their different burial depths, which also affects the different sealing thicknesses; after the source rock is heated to a certain temperature, it begins to crack and generate hydrocarbons. The flow of hydrocarbon substances causes the roof and floor of the shale reservoir to be subjected to fluid pressure, which also affects the different sealing thicknesses. Therefore, the sealing thickness of the roof and floor can be reasonably determined through a joint simulation experiment of temperature field, pressure field and stress field. The embodiment of the present invention provides a method for determining the lower limit of the sealing thickness of adjacent strata of a shale reservoir, which can reasonably quantify the lower limit of the roof sealing thickness of a shale reservoir through the simulation of temperature field, pressure field and stress field.

[0049] Example 1

[0050] The first embodiment of the present invention provides a method for determining the lower limit of the sealing thickness of adjacent strata in a shale reservoir, referring to Figure 1 As shown, the following steps are included:

[0051] Step S11: Prepare a roof rock sample using a core section of the overlying rock formation of the shale reservoir, wrap the side of the roof rock sample with a thermal insulation and sealing material, arrange a first heating device, a first pressurizing device, a first stress device and a group of first sensors on the bottom surface of the roof rock sample, and arrange multiple groups of first sensors on the side of the roof rock sample at first set intervals.

[0052] The first sensor includes a first temperature sensor, a first pressure sensor, and a first strain sensor. The first temperature sensor, the first pressure sensor, and the first strain sensor arranged on the side of the rock sample have the same measurement position in the longitudinal direction.

[0053] Roof rock samples with the same cross-sectional area (eg, cylindrical with a diameter of 5 cm) are prepared using a core section of the overlying strata of the shale reservoir.

[0054] According to empirical data, the sealing thickness of the roof (mudstone roof) during in-situ heating mining of shale reservoirs is usually within 300 to 400 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 lower limit of the actual sealing thickness of the roof, resulting in experimental failure (the roof sealing thickness required for in-situ mining of shale cannot be measured).

[0055] The sides of the top rock sample are wrapped with thermal insulation material. The thermal insulation can prevent heat from being dissipated to the surroundings during the heating process. The sealing ensures that the fluid applied from the bottom of the rock sample during the fluid pressurization process cannot enter between the rock sample and the thermal insulation sealing material. The thermal insulation material needs to have a pressure resistance of not less than 80MPa.

[0056] The first pressurizing device may be a fluid pressurizing device; and the first stress device may be a triaxial stress testing device.

[0057] In some embodiments, the first heating device is a one-way heating device to save resources.

[0058] 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 an area of ​​the bottom surface of the top plate rock sample that does not exceed 1 / 4 of the bottom surface area, so that the heat source can be spread upward as much as possible.

[0059] Specifically, the bottom surface of the roof rock sample refers to the side closest to the shale reservoir at the corresponding original underground position.

[0060] The first temperature sensor, the first pressure sensor and the first strain sensor are arranged axially on the side of the roof rock sample. The first set interval of the arrangement is set according to the measurement accuracy requirement, usually at an interval of 10 cm.

[0061] 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 pressurizing device to pressurize the top plate rock sample to a first set pressure measured by the first pressure 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, pressure and stress until the change amplitude of the measured value of each first sensor is less than the set threshold value, and determine the lowest position where the temperature of the top plate rock sample is not higher than the second set temperature, the pressure is not higher than the second set pressure and the strain is not higher than the first set strain based on the measured values ​​of the first sensors.

[0062] 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.

[0063] The first set temperature can be determined by using a source rock thermal simulation experiment or a kerogen activation energy experiment.

[0064] For example, multiple samples of shale reservoirs are taken, and source rock thermal simulation experiments are conducted on each sample to measure the lowest temperature at which the kerogen conversion rate reaches a set conversion rate threshold, and the minimum value of the multiple measured minimum temperatures is determined as the first set temperature.

[0065] Furthermore, the first set temperature is the lowest temperature at which the kerogen conversion rate in the shale reservoir reaches 90%, which is usually 290-330°C.

[0066] The kerogen conversion rate reaches 90%. At this temperature, the reservoir is almost completely converted to hydrocarbons, achieving maximum oil and gas production. That is, this temperature is the highest temperature at which the reservoir can be heated during the in-situ heating and production process of actual shale reservoirs. Therefore, the setting of this temperature ensures the safety and rationality of the determined lower limit of the roof sealing thickness.

[0067] In some embodiments, the second set temperature is the initial hydrocarbon production temperature of kerogen in the overburden, which is typically 200-250°C.

[0068] The second set temperature can be determined by using a source rock thermal simulation experiment.

[0069] For example, multiple samples of the overlying rock formation are taken, and thermal simulation experiments of the source rock are performed on each sample 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.

[0070] In some embodiments, the first set pressure is the fracture pressure of the shale reservoir, and the second set pressure is the fracture pressure of the overburden formation, both of which can be determined through rock fracture pressure experiments.

[0071] The fracture pressure of a shale reservoir is generally about 50 MPa. The present embodiment is based on the premise that the overlying stratum of the shale reservoir is a mud shale formation, and the fracture pressure of the overlying stratum is generally about 30 MPa.

[0072] 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 layer, which can be determined through rock fracture experiments.

[0073] 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 overburden is determined; the fracture pressure P0 of the shale reservoir and the fracture pressure Px of the overburden are determined; the maximum underground 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 fracture of the overburden are determined.

[0074] In some embodiments, the minimum starting pressure (breakthrough pressure) Ps for 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.

[0075] The first heating device (heat source) is used to slowly heat the sample (no more than 20°C / day), with the maximum temperature of the heat source between 400 and 650°C. The power of the heat source is adjusted to keep the temperature at the bottom of the roof rock sample constant at T0. The first pressurizing device is used to pressurize the bottom of the roof rock sample, using fluid boosting at a boosting rate of no more than 300KPa / day (the specific value is flexibly set according to the on-site construction conditions), so that the pressure at the bottom of the roof rock sample is constant at P0. At the same time, the first stress device is used to gradually apply stress to the bottom of the roof rock sample, increasing by 1MPa for 5 minutes at a time, and finally applying a constant stress of Ex. Furthermore, the stress reaching Ex, the pressure reaching P0, and the temperature reaching T0 are achieved as synchronously as possible. The temperature is kept constant at T0, the pressure is kept constant at P0, and the stress is kept constant at Ex for at least 30 minutes until the variation of the measured values ​​of each sensor is less than the set threshold value, that is, after the temperature, pressure and strain are stable, the measured values ​​of each first temperature sensor, first pressure sensor and first strain sensor are collected. Since the temperature of the roof rock sample gradually decreases from bottom to top, the pressure gradually decreases from bottom to top, and the strain also gradually decreases from bottom to top, the measured values ​​of the first temperature sensor, first pressure sensor and first strain sensor can be collected in sequence from bottom to top until the currently collected temperature is not greater than Tx, the pressure is not greater than Px and the strain is not greater than εx. The lowest position of the roof rock sample where the temperature is not higher than Tx, the pressure is not higher than Px and the strain is not higher than εx is determined according to the position of the corresponding sensor.

[0076] 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.

[0077] Similarly, if the currently collected pressure is Px, the position of the corresponding first pressure sensor can be directly determined as the position where the roof rock sample pressure begins to drop to Px; if the currently collected pressure begins to be less than Px (the first pressure less than Px), based on the currently collected pressure and the previous collected pressure and the position of the current first pressure sensor and the position of the previous first pressure sensor, the second lowest position where the roof rock sample pressure is not higher than Px is determined by the proportional method.

[0078] 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 previous collected strain and the position of the current first strain sensor and the position of the previous first strain sensor, the third lowest position where the roof rock sample strain is not higher than εx is determined by the proportional method.

[0079] The higher of the first lowest position, the second lowest position and the second lowest position is used as the lowest position where the roof rock sample temperature is not higher than the second set temperature, the pressure is not higher than the second set pressure and the strain is not higher than the first set strain.

[0080] Step S13: determining the lower limit of the roof plugging thickness of the shale reservoir according to the distance between the position and the bottom surface.

[0081] The distance between this 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 can be used as the lower limit of the roof plugging thickness of the shale reservoir.

[0082] The method for determining the lower limit of the plugging thickness of adjacent strata in a shale reservoir provided in Example 1 of the present invention comprises: using a first heating device to heat a roof rock sample to a first set temperature, using a first pressurizing device to pressurize the roof rock sample to a first set pressure, and using a first stress device to gradually apply stress to the bottom of the roof rock sample from small to large to the first set stress, and stabilizing at this temperature, pressure, and stress until the measurement values ​​of each sensor are stable; determining the lowest position of the roof rock sample where the temperature is not higher than a second set temperature, the pressure is not higher than a second set pressure, and the strain is not higher than the first set strain based on the measurement values ​​of the sensors; and determining the lower limit of the roof plugging thickness of the shale reservoir based on the distance between this position and the bottom surface. By experimentally determining the lower limit of the roof plugging thickness of the shale reservoir based on the joint simulation of the temperature field, pressure field, and stress field, the roof plugging conditions during the 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.

[0083] In a method for determining the lower limit of the sealing thickness of adjacent formations in a shale reservoir provided in Example 1 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 at which 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 production of the actual shale reservoir; the pressure at the bottom of the roof is kept constant at the fracture pressure of the shale reservoir, that is, the maximum pressure that may be encountered during the in-situ heating and production; stress is applied step by step from small to large to the bottom of the roof rock sample. The maximum subsurface principal stress at the depth of the burial depth is determined and stabilized at this stress, which is the maximum stress that may be experienced during in-situ heating and mining. Under the assumption that the roof bottom temperature is constant at the lowest temperature at which kerogen conversion reaches 90% in the shale reservoir, the pressure is constant at the shale reservoir fracture pressure, and the stress is constant at the maximum subsurface principal stress at the bottom burial depth, the lower limit of the roof plugging thickness is determined based on the lowest location where the roof rock sample temperature is no higher than the initial hydrocarbon production temperature of the overburden kerogen, the pressure is no higher than the overburden fracture pressure, and the strain is no higher than the critical damage strain value for overburden fracture. Once the overburden begins to produce hydrocarbons, the kerogen material changes, leading to changes in the rock structure and destroying the original plugging properties. Therefore, the roof only has plugging properties below this temperature; the roof only has plugging properties below the overburden fracture pressure; and the roof only has plugging properties below the critical damage strain value for overburden fracture. Therefore, the above temperature, pressure, stress, and strain settings ensure that the lower limit of the roof plugging thickness is reasonable and has strong production guidance significance.

[0084] Example 2

[0085] The second embodiment of the present invention provides another method for determining the lower limit of the plugging thickness of adjacent formations in a shale reservoir, 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-mentioned embodiment 1 is still applicable here. For details, refer to Figure 2 As shown, the following steps are included:

[0086] 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 thermal insulation and sealing material, arrange a second heating device, a second pressurizing device, a second stress device and a group of second sensors on the top surface of the bottom plate rock sample, and arrange multiple groups of second sensors on the side of the bottom plate rock sample at second set intervals.

[0087] The second sensor includes a second temperature sensor, a second pressure sensor, and a second strain sensor. The second temperature sensor, the second pressure sensor, and the second strain sensor arranged on the side of the rock sample have the same measurement position in the longitudinal direction.

[0088] The second temperature sensor may be the same temperature sensor as the first temperature sensor. The "first" and "second" here are only used to distinguish whether the temperature sensor is set on the top plate rock sample or the bottom plate rock sample.

[0089] Similarly, the second pressure sensor can be the same pressure sensor as the first pressure sensor, and the "first" and "second" here are only used to distinguish whether the pressure sensor is set in the top plate rock sample or the bottom plate rock sample.

[0090] The second strain sensor may be the same strain sensor as the first strain sensor. The "first" and "second" here are only used to distinguish whether the strain sensor is set on the top plate rock sample or the bottom plate rock sample.

[0091] A bottom rock sample of the same cross-sectional area (e.g., cylindrical with a diameter of 5 cm) is prepared from a cored section of the underlying strata of the shale reservoir. The length (thickness) of the bottom rock sample is not less than 500 cm.

[0092] The second heating device can be the same heating device as the first heating device. The "first" and "second" here are just to distinguish whether the heating device is set on the bottom surface of the top plate rock sample or the top surface of the bottom plate rock sample.

[0093] The second pressurizing device can be a heating device that is the same as the first pressurizing device. The "first" and "second" here are only used to distinguish whether the pressurizing device is set on the bottom surface of the top plate rock sample or the top surface of the bottom plate rock sample.

[0094] 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 the top surface of the bottom plate rock sample.

[0095] The second heating device is located at the center of the top surface of the bottom plate rock sample. Further, the second heating device can directly heat the top surface of the bottom plate rock sample to an area not exceeding 1 / 4 of the top surface area, so that the heat source can be spread downward as much as possible.

[0096] Specifically, the top surface of the bottom plate rock sample refers to the side closest to the shale reservoir at the corresponding original underground position.

[0097] The second temperature sensor, the second pressure sensor and the second strain sensor are arranged axially on the side of the bottom plate rock sample. The second set interval is set according to the measurement accuracy requirement and can be consistent with the first set interval, usually 10 cm.

[0098] Step S22: using the second heating device to heat the bottom plate rock sample to the first set temperature measured by the second temperature sensor at the top, using the second pressurizing device to pressurize the bottom plate rock sample to the second set pressure measured by the second pressure sensor at the top, using the second stress device to apply stress to the top of the bottom plate rock sample step by step from small to large to the second set stress, and stabilize at the temperature, pressure and stress until the change amplitude of the measured value of each second sensor is less than the set threshold, and determine the highest position where the temperature of the bottom plate rock sample is not higher than the third set temperature, the pressure is not higher than the third set pressure and the strain is not higher than the second set strain based on the measured values ​​of the second sensors.

[0099] 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.

[0100] This application is based on the premise that the overlying and underlying rock layers of the shale reservoir are both mudstone formations. Therefore, if the rock properties of the overlying and underlying rock layers are basically the same, the initial hydrocarbon production temperature of kerogen in the overlying rock layer can also be approximated as the initial hydrocarbon production temperature of kerogen in the underlying rock layer.

[0101] In some embodiments, the third set pressure is the fracture pressure of the underlying rock formation, which can also be determined through rock fracture pressure experiments. Therefore, if the rock mechanical properties of the overburden and underlying rock formations are basically the same, the fracture pressure of the overburden formation can also be approximated as the fracture pressure of the underlying rock formation.

[0102] The second set stress is the maximum principal stress underground at the depth of burial of the top surface of the bottom plate rock sample, which is obtained by calculation.

[0103] The second set strain is the critical damage strain of the underlying rock stratum, which can also be determined through rock fracture experiments. Therefore, if the rock mechanical properties of the overburden and underlying rock strata are basically the same, the critical damage strain of the overburden stratum can also be approximated as the critical damage strain of the underlying rock stratum.

[0104] For example, with the third set temperature (Tx), the third set pressure (Px), the second set stress (Ex), and the second set strain (εx), the second heating device (heat source) is used to slowly heat the sample (no more than 20°C / day), with the maximum temperature of the heat source between 400°C and 650°C. The heat source power is adjusted to maintain a constant temperature of T0 at the top of the bottom plate rock sample. Simultaneously, the second pressurizing device is used to pressurize the top of the bottom plate rock sample, using fluid boosting at a rate of no more than 300 kPa / day (the specific value is flexibly set based on on-site construction conditions), to maintain a constant pressure of P0 at the top of the bottom plate rock sample. The second stress device is used to gradually apply stress to the top of the bottom plate rock sample, increasing it by 1 MPa for 5 minutes, until the final applied stress is constant at Ex. Furthermore, the pressure reaching P0, the stress reaching Ex, and the temperature reaching T0 are achieved simultaneously. The temperature is kept constant at T0, the pressure is kept constant at P0, and the stress is kept constant at Ex for at least 30 minutes until the variation of the measured values ​​of each sensor is less than the set threshold value. That is, after the temperature, pressure and strain are stable, the measured values ​​of each second temperature sensor, second pressure sensor and second strain sensor are collected. Since the temperature, pressure and strain of the bottom plate rock sample gradually decrease from the top to the bottom, the measurement values ​​of the second temperature sensor, second pressure sensor and second strain sensor can be collected in sequence from the top to the bottom until the currently collected temperature is not greater than Tx, the pressure is not greater than Px and the strain εx is not greater than Px. The highest position of the bottom plate rock sample where the temperature is not higher than Tx, the pressure is not greater than Px and the strain is not higher than εx is determined according to the position of the corresponding sensor.

[0105] 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 position of the current 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.

[0106] Similarly, if the currently collected pressure is Px, the position of the corresponding second pressure sensor can be directly determined as the position where the bottom plate rock sample pressure begins to drop to Px; if the currently collected pressure begins to be less than Px (the first pressure less than Px), based on the currently collected pressure and the previous collected pressure and the position of the current second pressure sensor and the position of the previous second pressure sensor, the second highest position where the bottom plate rock sample pressure is not higher than Px is determined by the proportional method.

[0107] If the currently collected strain is εx, the position of the corresponding second strain sensor can be directly determined as the position where the strain of the bottom plate rock sample 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 previous collected strain and the position of the current second strain sensor and the position of the previous second strain sensor, the third highest position where the strain of the bottom plate rock sample is not higher than εx is determined by the proportional method.

[0108] The lower of the first highest position, the second highest position and the second highest position is used as the highest position where the bottom plate rock sample temperature is not higher than the third set temperature, the pressure is not higher than the second set pressure, and the stress is not higher than the third set stress.

[0109] Step S23: determining the lower limit of the bottom plate plugging thickness of the shale reservoir according to the distance from the position to the top surface.

[0110] 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 a safety correction factor (greater than 1), and the product of the safety correction factor and the determined distance can be used as the lower limit of the bottom plate plugging thickness of the shale reservoir.

[0111] Existing research on the sealing properties of shale reservoirs often focuses solely on the sealing properties of the roof, while ignoring the sealing function of the floor. However, for in-situ heating and recovery of shale reservoirs, poor floor sealing performance can still lead to oil and gas loss, impacting recovery efficiency. The method for determining the lower limit of the sealing thickness of adjacent strata in a shale reservoir, provided in Example 2 of the present invention, fully considers the sealing properties of the floor, ensuring the reliability of the sealing performance determination and further guaranteeing an increase in recovery efficiency.

[0112] 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. Only when the top and bottom plate thicknesses of the shale reservoir both meet the corresponding lower limits of the plugging thickness can it be determined that the plugging requirements are met.

[0113] Example 3

[0114] A third embodiment of the present invention provides a specific application of a method for determining a lower limit of the roof plugging thickness of a shale reservoir, and verifies its accuracy through numerical simulation, including the following steps:

[0115] 1) The T0 (90% conversion temperature of kerogen) of the shale reservoir rock sample was measured to be 300°C.

[0116] 2) The Tx (initial hydrocarbon generation temperature of kerogen) of the roof rock sample was determined to be 200℃.

[0117] 3) The Po (fracture pressure) of the shale reservoir rock sample was measured to be 50 MPa.

[0118] 4) The Px (fracture pressure) of the roof rock sample was measured to be 30 MPa.

[0119] 5) Determine the stress Ex (maximum axial stress) of the reservoir rock sample to be 30 MPa.

[0120] 6) The critical damage strain value εx of the roof rock sample was determined to be 10 MPa.

[0121] 7) 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.

[0122] 8) Wrap the top rock sample with a pressure-resistant steel sleeve with a pressure resistance of not less than 80 MPa, and then wrap it with rock wool as an insulating material. Place the top rock sample in the experimental device. The sealing ensures that the fluid applied at the bottom of the sample cannot enter between the sample and the steel sleeve.

[0123] 7) Place a unidirectional heat source point at the bottom of the roof rock sample, arrange temperature sensors, pressure sensors and strain sensors starting from the bottom, and arrange several groups of temperature sensors, pressure sensors and strain sensors along the axial direction of the roof rock sample, with an interval of 10 cm.

[0124] 8) Heat the bottom of the roof sample with a unidirectional point heat source at a rate of 20°C / day, reaching a peak temperature of 300°C (T0). Fluid pressurize the bottom of the roof sample at a rate of 300 kPa / day, reaching a peak pressure of 50 MPa (Po). Apply a rigid stress at a rate of 1 MPa / 5 minutes to the bottom of the roof sample, reaching a peak stress of 30 MPa (Ex).

[0125] 9) After the bottom temperature of the roof rock sample is constant at T0, the pressure is constant at P0, and the stress is constant at Ex for 30 minutes (the measurement values ​​of each sensor are stable), the data of the roof rock sample temperature sensor, pressure sensor, and strain sensor are continuously collected.

[0126] 10) The distance from the position where the temperature Tx is measured and calculated to the bottom of the roof rock sample is 120 cm, the distance from the position where the pressure Px is measured and calculated to the thickness of the rock sample bottom is 110 cm, and the distance from the position where the strain εx is measured to the bottom of the rock sample is 120 cm. 120 cm is the lower limit of the roof sealing thickness.

[0127] 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, set the Px (fracture pressure) of the roof rock to 30 MPa, and set the critical damage strain value εx of the roof rock sample to 10 MPa.

[0128] 12) Keep the temperature at the bottom of the roof rock sample constant at T0 (300°C), the pressure constant at 50 MPa (P0), and the stress constant at Ex (30 MPa), complete the numerical simulation of the temperature field, pressure field, and stress field, and wait until the grid temperature, pressure, and strain are stable.

[0129] 13) See Figure 4 、 Figure 5 and Figure 6 As shown in the figure, they are the simulated temperature field, pressure field and strain field of the roof rock sample. Figure 4 Oil saturation at the Tx temperature line (200°C) (see Figure 7 There was no change during the entire simulation period, indicating that oil and gas were blocked at this location. Figure 5 Oil saturation at the Px pressure line (30 MPa) (see Figure 8 There was no change during the entire simulation period, indicating that oil and gas were blocked at this location. Figure 6 Oil saturation of the εx strain line (10 MPa) (see Figure 9 There was no change during the entire simulation period, indicating that oil and gas were blocked at this location.

[0130] 14) Observation Figure 4 Oil saturation at 220°C (see Figure 7 (As shown), obvious changes occurred during the entire simulation period, indicating that oil and gas were not blocked at this location. Figure 5 Oil saturation at the medium pressure line 35MPa (see Figure 8 (As shown), obvious changes occurred during the entire simulation period, indicating that oil and gas were not blocked at this location. Figure 6 Oil saturation at the middle strain line of 25 MPa (see Figure 9 During the entire simulation period, there are obvious changes, indicating that the oil and gas are not blocked at this location.

[0131] 15) The thickness of the Tx temperature line is 118 cm, the Px pressure line is 108 cm, and the εx strain line is 121 cm. A comprehensive comparison shows that a roof thickness of 121 cm meets the plugging requirements. The error between the numerical simulation results and the experimental results (120 cm) is approximately 0.01%, thus verifying the reliability of the experimental results.

[0132] It should be understood that the specific order or hierarchy of steps in the disclosed processes 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 the present disclosure. The accompanying method claims present elements of the various steps in an exemplary order and are not intended to be limited to the specific order or hierarchy described.

[0133] In the foregoing 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 embodiments of the claimed subject matter require more features than are expressly recited in each claim. On the contrary, as reflected in the appended claims, the invention comprises less than all the features of any individual disclosed embodiment. The appended claims are therefore hereby expressly incorporated into the detailed description, with each claim standing on its own as a separate preferred embodiment of the invention.

[0134] 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 may 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 encompassed in a manner similar to the term "including," as explained in terms of "including," used as a transitional word in the claims. In addition, any term "or" used in the specification of the claims is intended to mean "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 lower limit of the sealing thickness of adjacent strata in a shale reservoir, characterized in that: include: A roof rock sample is prepared using a coring section of an overlying stratum of a shale reservoir, and a side surface of the roof rock sample is wrapped with a heat-insulating sealing material. A first heating device, a first pressurizing device, a first stress device, and a group of first sensors are arranged on the bottom surface of the roof rock sample. Multiple groups of first sensors are arranged on the side surface of the roof rock sample at first set intervals, wherein the first sensors include a first temperature sensor, a first pressure sensor, and a first strain sensor. The roof rock sample is heated by the first heating device until the temperature measured by the first temperature sensor at the bottom is a first set temperature, the roof rock sample is pressurized by the first pressurizing device until the pressure measured by the first pressure sensor at the bottom is a first set pressure, the first stress device is used to gradually apply stress to the bottom of the roof rock sample from small to large to the first set stress, and stabilize at the temperature, pressure, and stress until the change amplitude of the measured value of each first sensor is less than a set threshold, and the lowest position of the roof rock sample at which the temperature is not higher than the second set temperature, the pressure is not higher than the second set pressure, and the strain is not higher than the first set strain is determined based on the measured values ​​of the first sensors; The lower limit of the roof plugging thickness of the shale reservoir is determined based on the distance between the position and the bottom surface.

2. The method according to claim 1, wherein 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, wherein 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, wherein The first set temperature is 290-330°C; the second set temperature is 200-250°C.

5. The method according to claim 3, wherein The first set pressure is the fracture pressure of the shale reservoir, and the second set pressure is the fracture pressure of the overburden formation.

6. The method according to claim 5, wherein The first set stress is the maximum underground principal stress at the depth of burial of the bottom surface of the roof rock sample; The first set strain is a critical damage strain value of the overburden formation.

7. The method according to claim 1, wherein The length of the roof rock sample is not less than 500 cm.

8. The method according to claim 1, wherein 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 roof rock sample; The area directly heated by the first heating device on the bottom surface of the roof rock sample does not exceed 1 / 4 of the bottom surface area.

9. The method according to claim 1, wherein The first set interval is set according to measurement accuracy requirements.

10. The method according to claim 1, wherein Also includes: A floor rock sample is prepared using a coring section of an underlying rock formation of a shale reservoir, and a side surface of the floor rock sample is wrapped with a heat-insulating sealing material. A second heating device, a second pressurizing device, a second stress device, and a group of second sensors are arranged on the top surface of the floor rock sample. Multiple groups of second sensors are arranged on the side surface of the floor rock sample at second set intervals, and the second sensors include a second temperature sensor, a second pressure sensor, and a second strain sensor. 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, the bottom plate rock sample is pressurized by the second pressurizing device until the pressure measured by the second pressure sensor at the top is the second set pressure, 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, pressure, and stress until the change amplitude of the measured value of each second sensor is less than the set threshold value, and the highest position of the bottom plate rock sample is determined based on the measured values ​​of the second sensors at which the temperature is not higher than the third set temperature, the pressure is not higher than the third set pressure, and the strain is not higher than the second set strain; The lower limit of the bottom plate plugging thickness of the shale reservoir is determined based on the distance between the position and the top surface.

11. The method according to claim 10, wherein The third set temperature is the initial hydrocarbon production temperature of kerogen in the underlying rock formation; The third set pressure is the fracture pressure of 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.

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