Method for determining lower limit of siltstone adjacent layer plugging thickness of shale reservoir

Abstract

The invention discloses a siltstone adjacent layer plugging thickness lower limit determination method of a shale reservoir, which comprises the following steps: judging that the fracture pressure of the shale reservoir is smaller than the minimum starting pressure of an overlying siltstone rock layer, and executing the following steps: arranging heating, pressurizing and stress devices and temperature, pressure and strain sensors on the bottom surface of a roof rock sample; multiple groups of pressure and strain sensors are arranged on the side surface at set intervals; a heating device is used for heating the bottom of a rock sample to a set temperature, a pressurizing device is used for pressurizing the bottom to a first set pressure, a 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 stable until measured values of all sensors are stable; determining the lowest position where the rock sample pressure is not higher than the second set pressure and the strain is not higher than the set strain according to the measured value of the sensor; determining a roof plugging thickness lower limit; and similarly, determining the bottom plate plugging thickness lower limit. The method can reasonably quantify the lower limit of the top and bottom plate plugging thickness through temperature, pressure and stress field joint simulation.

Description

Technical Field

[0001] The invention relates to the technical fields of petroleum geology and shale reservoir exploitation, and in particular to a method for determining a lower limit of the sealing thickness of a siltstone adjacent layer of a shale reservoir. 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 lower limit of the sealing thickness of the siltstone adjacent layer of a shale reservoir, which can reasonably quantify the lower limit of the sealing thickness of the shale reservoir top plate through the joint simulation of the temperature field, pressure field and stress field.

[0004] The embodiment of the present invention provides a method for determining the lower limit of the plugging thickness of a siltstone adjacent layer of a shale reservoir, comprising: if it is determined that the fracture pressure of the shale reservoir is less than the minimum starting pressure of the overlying siltstone layer of the shale reservoir, executing the following steps:

[0005] A roof rock sample is prepared by using the coring section of the overlying siltstone layer, and the side of the roof rock sample is wrapped with a heat-insulating sealing material, and a first heating device, a first pressurizing device, a first stress device, a first temperature sensor, a first pressure sensor, and a first strain sensor are arranged on the bottom surface of the roof rock sample, and a plurality of groups of first pressure sensors and first strain sensors are arranged on the side of the roof rock sample at a first set interval;

[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 the 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 the first set pressure, the first stress device is used to gradually apply stress from small to large to the bottom of the roof rock sample to the first set stress, and stabilize at the temperature, the pressure and the stress until the measured value variation amplitude of each first pressure sensor and the first strain sensor is less than the set threshold value, and the lowest position of the roof rock sample at which the pressure is not higher than the second set pressure and the strain is not higher than the first set strain is determined according to the measured values ​​of the first pressure sensor and the first strain sensor;

[0007] 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.

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

[0010] 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.

[0011] 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.

[0012] In some embodiments, the length of the roof rock sample is not less than 500 cm.

[0013] In some embodiments, the first heating device is a one-way heating device;

[0014] The first heating device is located at the center of the bottom surface of the top plate rock sample;

[0015] 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.

[0016] In some embodiments, the first set interval is set according to measurement accuracy requirements.

[0017] In some embodiments, if the underlying rock formation of the shale reservoir is a mudstone formation, the method further includes executing the following step of determining the lower limit of the bottom plate plugging thickness:

[0018] 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 sealing material, and 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 bottom plate rock sample, and a plurality of groups of second sensors are arranged on the side surface of the bottom plate rock sample at a second set interval, wherein the second sensors include a second temperature sensor, a second pressure sensor, and a second strain sensor;

[0019] 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 variation amplitude of the measured values ​​of each second sensor is less than the set threshold, and the highest position of the bottom plate rock sample 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 is determined according to the measured values ​​of the second sensor;

[0020] 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.

[0021] In some embodiments, if the underlying rock layer of the shale reservoir is an underlying siltstone layer, it is determined whether the shale reservoir fracture pressure is less than the minimum starting pressure of the underlying siltstone layer; if so, the step of determining the lower limit of the bottom plate plugging thickness is performed:

[0022] A bottom plate rock sample is prepared by using a coring section of an underlying rock formation, and a side surface of the bottom plate rock sample is wrapped by using a heat-insulating sealing material, and a second heating device, a second pressurizing device, a second stress device, a second temperature sensor, a second pressure 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 pressure sensors and second strain sensors are arranged on the side surface of the bottom plate rock sample at a second set interval;

[0023] 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, the pressure and the stress until the measured value variation amplitude of each second pressure sensor and the second strain sensor is less than the set threshold value, and the highest position where the pressure of the bottom plate rock sample is not higher than the third set pressure and the strain is not higher than the second set strain is determined according to the measured values ​​of the second pressure sensor and the second strain sensor;

[0024] 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.

[0025] In some embodiments, the third set pressure is the fracture pressure of the underlying rock formation;

[0026] The second set stress is the maximum principal stress underground at the burial depth of the top surface of the bottom plate rock sample;

[0027] The second set strain is a critical damage strain value of the underlying rock formation.

[0028] The beneficial effects of the above technical solution provided by the embodiment of the present invention include at least:

[0029] (1) The method for determining the lower limit of the plugging thickness of the siltstone adjacent layer of the shale reservoir provided by the embodiment of the present invention is to use a first heating device to heat the top plate rock sample to a first set temperature, use a first pressurizing device to pressurize the top plate rock sample to a first set pressure, use 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 stabilize at the temperature, pressure and stress until the measured values ​​of each sensor are stable, and determine the lowest position where the pressure of the top plate rock sample is not higher than the second set pressure and the strain is not higher than the first set strain according to the measured values ​​of each sensor; and determine 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 by an experimental method based on the joint simulation of the temperature field, pressure field and stress field, and the top plate plugging conditions in the process of in-situ heating and exploitation of shale reservoirs are specifically quantified, which can effectively guide production and improve the economic benefits of in-situ heating and exploitation of shale oil and gas.

[0030] (2) It is currently generally believed that only mudstone can effectively seal shale during in-situ mining. The method for determining the lower limit of the sealing thickness of the siltstone adjacent layer of a shale reservoir provided in an embodiment of the present invention proposes that if the overlying rock layer of the shale reservoir is siltstone, as long as the minimum starting pressure (breakthrough pressure) is greater than the fracture pressure of the reservoir and the thickness meets the lower limit of the sealing thickness, it can also produce a sealing effect during the in-situ mining of the shale reservoir.

[0031] (3) A method for determining the lower limit of the plugging thickness of the siltstone adjacent layer of a shale reservoir provided in 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 at which the kerogen conversion rate reaches 90%. At this temperature, the reservoir almost completes the conversion to hydrocarbon generation 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; 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 exploitation; stresses are applied to the bottom of the roof rock sample step by step from small to large to the maximum principal stress underground at the bottom buried depth, and stabilized at this stress, that is, the maximum stress that may be encountered during the in-situ heating and exploitation; on the basis that the temperature at the bottom of the roof is kept constant at the lowest temperature in the shale reservoir at which the kerogen conversion rate reaches 90%, the pressure is kept constant at the fracture pressure of the shale reservoir, and the stress is kept constant at the maximum principal stress underground at the bottom buried depth, the lower limit of the roof plugging thickness is determined according to the lowest position where the pressure of the roof rock sample is not higher than the fracture pressure of the overlying rock formation and the strain is not higher than the critical damage strain value of the fracture of the overlying rock formation. Only roofs with a pressure lower than the fracture pressure of the overburden formation can have plugging properties; at the same time, only roofs with a strain value lower than the critical damage of the overburden formation can have plugging properties. Therefore, the above settings of temperature, pressure, stress and strain ensure that the lower limit of the roof plugging thickness is reasonable and has strong production guidance significance.

[0032] (4) In the method for determining the lower limit of the sealing thickness of the siltstone adjacent layer of the shale reservoir provided by the 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.

[0033] (5) 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 lower limit of the sealing thickness of the siltstone adjacent layer of the shale reservoir 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 improving the recovery rate.

[0034] 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.

[0035] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] 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:

[0037] Figure 1 This is a flow chart of a method for determining the lower limit of the plugging thickness of the siltstone adjacent layer of a shale reservoir in Example 1 of the present invention;

[0038] Figure 2 This is a flow chart of a method for determining the lower limit of the plugging thickness of the siltstone adjacent layer of a shale reservoir in Example 2 of the present invention;

[0039] Figure 3 This is a flow chart of a method for determining the lower limit of the plugging thickness of the siltstone adjacent layer of a shale reservoir in Example 3 of the present invention;

[0040] Figure 4 This is a schematic diagram of the axial cross section of the roof rock sample in the fourth embodiment of the present invention;

[0041] Figure 5 This is a pressure field simulation diagram in the fourth embodiment of the present invention;

[0042] Figure 6 This is a strain field simulation diagram in the fourth embodiment of the present invention;

[0043] Figure 7 for Figure 5 Oil saturation variation diagram at the middle pressure line 20MPa and 25MPa;

[0044] Figure 8 for Figure 6 Oil saturation variation diagram at the middle strain line of 10MPa and 15MPa. DETAILED DESCRIPTION

[0045] 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.

[0046] 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.

[0047] 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.

[0048] 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.

[0049] 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 existing technology. After further research and development, the inventor found that due to 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, the difference in the plugging thickness is affected; the top plate and the bottom plate are subjected to different stresses due to their different burial depths, which also affects the difference in their plugging thickness; after the source rock is heated to a certain temperature, it begins to crack and generate hydrocarbons. The flow of hydrocarbon substances causes the top plate and the bottom plate of the shale reservoir to be subjected to fluid pressure, which also affects the difference in their plugging thickness. Therefore, the plugging thickness of the top plate and the bottom plate can be reasonably determined through a joint simulation experiment of the temperature field, pressure field and stress field. The embodiment of the present invention provides a method for determining the lower limit of the plugging thickness of the siltstone adjacent layer of a shale reservoir, which can reasonably quantify the lower limit of the plugging thickness of the top plate of the shale reservoir through the method of simulating the temperature field, pressure field and stress field.

[0050] Embodiment 1

[0051] Embodiment 1 of the present invention provides a method for determining the lower limit of the sealing thickness of a siltstone adjacent layer in a shale reservoir.

[0052] First, it is necessary to experimentally measure the shale reservoir fracture pressure and the minimum starting pressure (fracture pressure) of the overlying siltstone layer to determine whether the shale reservoir fracture pressure is less than the minimum starting pressure of the overlying siltstone layer; if so, perform the subsequent steps to determine the lower limit of the plugging thickness; if not, determine that the overlying siltstone layer does not have the plugging property during the in-situ mining of the shale reservoir.

[0053] If conditions permit, the minimum starting pressure of the overlying siltstone layer needs to be obtained by measuring the minimum starting pressure of at least 5 rock samples (rock samples that are approximately evenly distributed underground) in the overlying siltstone layer, and then calculating the average value. The fracture pressure of the shale reservoir needs to be obtained by measuring the fracture pressure of at least 3 rock samples (rock samples that are approximately evenly distributed underground) in the shale reservoir, and then calculating the average value.

[0054] The above measurements are carried out under the initial temperature and pressure conditions of the corresponding formation.

[0055] At present, it is generally believed that only mud shale can effectively seal the shale reservoir during in-situ mining. The method for determining the lower limit of the sealing thickness of the siltstone layer based on temperature-stress field simulation provided in the embodiment of the present invention proposes that if the overlying rock layer of the shale reservoir is siltstone, as long as the minimum starting pressure (breakthrough pressure) is greater than the fracture pressure of the reservoir and the thickness meets the lower limit of the sealing thickness, a sealing effect can also be produced during the in-situ mining of the shale reservoir.

[0056] The specific determination process of the lower limit of the sealing thickness of the overlying siltstone layer is as follows: Figure 1 As shown, the following steps are included:

[0057] Step S11: Prepare a roof rock sample using the coring section of the overlying siltstone layer, wrap the side of the roof rock sample with a thermal insulation sealing material, arrange a first heating device, a first pressurizing device, a first stress device and a first temperature sensor, a first pressure sensor and a first strain sensor on the bottom surface of the roof rock sample, and arrange multiple groups of first pressure sensors and first strain sensors on the side of the roof rock sample at first set intervals.

[0058] The measurement positions of each group of first pressure sensors and first strain sensors in the longitudinal direction are consistent.

[0059] 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).

[0060] According to empirical data, the sealing thickness of the 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 lower limit of the actual sealing thickness of the roof, resulting in experimental failure (the roof sealing thickness required for in-situ shale mining cannot be measured).

[0061] 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 cannot enter between the rock sample and the thermal insulation sealing material during the fluid pressurization process. The thermal insulation material needs to have a pressure resistance of no less than 80MPa.

[0062] The first pressurizing device may be a fluid pressurizing device; and the first stress device may be a triaxial stress testing device.

[0063] In some embodiments, the first heating device is a unidirectional heating device to save resources.

[0064] 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.

[0065] Specifically, the bottom surface of the roof rock sample refers to the side of the corresponding original underground position closest to the shale reservoir.

[0066] The first pressure 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.

[0067] 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 measured value change amplitude of each first pressure sensor and first strain sensor is less than the set threshold value, and determine the lowest position where the pressure of the top plate rock sample is not higher than the second set pressure and the strain is not higher than the first set strain according to the measured values ​​of the first pressure sensor and the first strain sensor.

[0068] 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.

[0069] The first set temperature can be determined by utilizing a source rock thermal simulation experiment or a kerogen activation energy experiment.

[0070] 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.

[0071] 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.

[0072] 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.

[0073] 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.

[0074] 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.

[0075] The 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, as well as the fracture pressure P0 of the shale reservoir and the fracture pressure Px of the overlying rock formation, the underground maximum principal stress Ex at the buried depth of the bottom surface of the roof rock sample and the fracture critical damage strain value εx of the overlying rock formation are determined.

[0076] The first heating device (heat source) is used to heat slowly (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 top plate rock sample constant at T0. The first pressurizing device is used to pressurize the bottom of the top plate rock sample, and fluid is used for pressurization. The pressurization speed does not exceed 300KPa / day (the specific value is flexibly set according to the on-site construction conditions), so that the pressure at the bottom of the top plate rock sample is constant at P0. At the same time, the first stress device is used to apply stress to the bottom of the top plate 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. Furthermore, try to make the stress reach Ex, the pressure reach P0, and the temperature reach T0 simultaneously. The temperature is constant T0, the pressure is constant P0, and the stress is constant Ex. 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 pressure and strain are stable, the measured values ​​of the first pressure sensor and the first strain sensor are collected. Since the pressure of the roof rock sample gradually decreases from bottom to top, the strain also gradually decreases from bottom to top, the measured values ​​of the first pressure sensor and the first strain sensor can be collected from bottom to top in sequence until the currently collected pressure is not greater than Px and the strain is not greater than εx. The lowest position where the pressure of the roof rock sample is not higher than Px and the strain is not higher than εx is determined according to the position of the corresponding sensor.

[0077] 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 first lowest position where the roof rock sample pressure is not higher than Px is determined by the proportional method.

[0078] 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.

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

[0080] 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.

[0081] 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.

[0082] The method for determining the lower limit of the plugging thickness of the siltstone adjacent layer of the shale reservoir provided in the first embodiment of the present invention is to use a first heating device to heat the top plate rock sample to a set temperature, use a first pressurizing device to pressurize the top plate rock sample to a first set pressure, use 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 stabilize at the temperature, pressure and stress until the measured values ​​of each sensor are stable, and determine the lowest position where the pressure of the top plate rock sample is not higher than the second set pressure and the strain is not higher than the first set strain according to the measured values ​​of each sensor; and determine 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 by an experimental method based on the joint simulation of the temperature field, pressure field and stress field, and the top plate 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] The method for determining the lower limit of the plugging thickness of the siltstone adjacent layer of the shale reservoir 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; 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 exploitation; 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 bottom buried depth, and stabilized at this stress, that is, the maximum stress that may be encountered during the in-situ heating and exploitation; on the basis that the temperature at the bottom of the roof is kept constant at the lowest temperature at which the kerogen conversion rate in the shale reservoir reaches 90%, the pressure is kept constant at the fracture pressure of the shale reservoir, and the stress is kept constant at the maximum principal stress underground at the bottom buried depth, the lower limit of the roof plugging thickness is determined according to the lowest position where the pressure of the roof rock sample is not higher than the fracture pressure of the overlying rock formation and the strain is not higher than the critical damage strain value of the fracture of the overlying rock formation. Only roofs with a pressure lower than the fracture pressure of the overburden formation can have plugging properties; at the same time, only roofs with a strain value lower than the critical damage of the overburden formation can have plugging properties. Therefore, the above settings of temperature, pressure, stress and strain ensure that the lower limit of the roof plugging thickness is reasonable and has strong production guidance significance.

[0084] Embodiment 2

[0085] Embodiment 2 of the present invention provides another method for determining the lower limit of the plugging thickness of the siltstone adjacent layer of a shale reservoir, specifically a method for determining the lower limit of the bottom plate plugging thickness of a shale reservoir, wherein the underlying rock layer of the shale reservoir is a mudstone formation, specifically, 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 heat-insulating 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. Each group of the second temperature sensor, the second pressure sensor and the second strain sensor arranged on the side of the rock sample has the same measurement position in the longitudinal direction.

[0088] 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.

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

[0091] 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.

[0092] 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.

[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 arranged on the bottom surface of the top plate rock sample or on 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 on 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 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.

[0096] 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.

[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 of the arrangement is set according to the measurement accuracy requirement and can be consistent with the first set interval, usually 10 cm.

[0098] Step S22: using a second heating device to heat the bottom plate rock sample to a first set temperature at which the measured temperature of the second temperature sensor at the top is measured; using a second pressurizing device to pressurize the bottom plate rock sample to a second set pressure at which the measured pressure of the second pressure sensor at the top is measured; using a 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 the temperature, pressure and stress until the measured value variation amplitude of each second sensor is less than the set threshold value; determining the highest position at which the bottom plate rock sample 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 according to 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 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.

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

[0104] Taking the third set temperature as Tx, the third set pressure as Px, 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 pressurizing device is used to pressurize the top of the bottom plate rock sample, and the fluid is used for pressurization, and the pressurization speed does not exceed 300KPa / day (the specific value is flexibly set according to the on-site construction situation), so that the top pressure of the bottom plate rock sample is constant at P0; the second stress device is used to apply stress to the top of the bottom plate rock sample step by step, and each increase of 1MPa can be constant for 5 minutes, so that the final applied stress is constant at Ex. Further, try to make the pressure reach P0, the stress reach Ex, and the temperature reach T0 simultaneously. The temperature is constant at T0, the pressure is constant at P0, and the stress is constant at Ex. They are stable 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 of the bottom plate rock sample gradually decreases from top to bottom, the pressure gradually decreases from top to bottom, and the strain also gradually decreases from top to bottom, the measured values ​​of the second temperature sensor, second pressure sensor and second strain sensor can be collected from top to bottom in sequence 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 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.

[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 current position of the 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 bottom plate 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 strain collected and the position of the current second strain sensor and the position of the previous second strain sensor, the third highest position where the bottom plate rock sample strain 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: 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.

[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 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.

[0111] Embodiment 3

[0112] Embodiment 3 of the present invention provides another method for determining the lower limit of the sealing thickness of the siltstone adjacent layer of a shale reservoir, specifically, a method for determining the lower limit of the bottom plate sealing thickness of a shale reservoir. The underlying rock layer of the shale reservoir is an underlying siltstone layer. The method for determining the lower limit of the top plate sealing thickness of the shale reservoir in the above embodiment 1 is still applicable here.

[0113] Determine whether the shale reservoir fracture pressure is less than the minimum starting pressure of the underlying siltstone layer; if so, perform the following steps to determine the lower limit of the bottom plate plugging thickness; if not, determine that the underlying stratum does not have a plugging property during the in-situ mining of the shale reservoir.

[0114] Specifically, refer to Figure 3 As shown, the following steps are included:

[0115] Step S31: Prepare a bottom plate rock sample using the coring section of the underlying rock stratum, wrap the side of the bottom plate rock sample with a heat-insulating sealing material, arrange a second heating device, a second pressurizing device, a second stress device and a second temperature sensor, a second pressure sensor and a second strain sensor on the top surface of the bottom plate rock sample, and arrange multiple groups of second pressure sensors and second strain sensors on the side of the bottom plate rock sample at second set intervals.

[0116] The measuring positions of each group of second pressure sensors and second strain sensors arranged on the side of the rock sample in the longitudinal direction are consistent.

[0117] 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.

[0118] 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.

[0119] 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.

[0120] Each group of second pressure sensors and second strain sensors is 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.

[0121] Step S32: using a second heating device to heat the bottom plate rock sample to a first set temperature at which the measured temperature of the second temperature sensor at the top is measured; using a second pressurizing device to pressurize the bottom plate rock sample to a second set pressure at which the measured pressure of the second pressure sensor at the top is measured; using a 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 the temperature, the pressure, and the stress until the measured value changes of the second pressure sensor and the second strain sensor are all less than the set threshold value; determining the highest position at which the bottom plate rock sample 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 pressure sensor and the second strain sensor.

[0122] In some embodiments, the third set pressure is the fracture pressure of the underlying rock formation, which can also be determined by rock fracture pressure experiments. Therefore, if the rock mechanical properties of the overburden and the underlying rock formation are basically the same, the fracture pressure of the overburden can also be approximated as the fracture pressure of the underlying rock formation.

[0123] 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.

[0124] 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.

[0125] Taking the third set pressure as Px, 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 pressurizing device is used to pressurize the top of the bottom plate rock sample, and the fluid is used for pressurization, and the pressurization speed does not exceed 300KPa / day (the specific value is flexibly set according to the on-site construction situation), so that the top pressure of the bottom plate rock sample is constant at P0; the second stress device is used to apply stress to the top of the bottom plate rock sample step by step, and each increase of 1MPa can be constant for 5 minutes, so that the final applied stress is constant at Ex. Further, try to make the pressure reach P0, the stress reach Ex, and the temperature reach T0 simultaneously. The temperature is constant T0, the pressure is constant P0, and the stress is constant Ex. 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 pressure and strain are stable, the measured values ​​of each second pressure sensor and the second strain sensor are collected. Since the pressure 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 pressure sensor and the second strain sensor can be collected from the top to the bottom in sequence until the currently collected 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 pressure is not greater than Px and the strain is not higher than εx is determined according to the position of the corresponding sensor.

[0126] 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 current position of the second pressure sensor and the position of the previous second pressure sensor, the first highest position where the bottom plate rock sample pressure is not higher than Px is determined by the proportional method.

[0127] 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 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 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.

[0128] 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 pressure is not higher than the second set pressure and the stress is not higher than the third set stress.

[0129] Step S33: 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.

[0130] 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.

[0131] 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 lower limit of the sealing thickness of the siltstone adjacent layer of the shale reservoir provided in Examples 2 and 3 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.

[0132] The above-mentioned embodiments 1 to 3 can be applied separately; or they can be applied in combination, embodiment 1 is applied in combination with embodiment 2, or embodiment 1 is applied in combination with embodiment 3; 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 are determined, and 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.

[0133] Embodiment 4

[0134] Embodiment 4 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:

[0135] 1) The T0 (kerogen 90% conversion temperature) of the shale reservoir rock sample was measured to be 300°C.

[0136] 2) The Tx (initial hydrocarbon production temperature of kerogen) of the roof rock sample was measured to be 200℃.

[0137] 3) The Po (fracture pressure) of the shale reservoir rock sample was measured to be 50 MPa.

[0138] 4) The Px (fracture pressure) of the roof rock sample was measured to be 20 MPa.

[0139] 5) Determine the stress Ex (maximum axial stress) of the reservoir rock sample to be 30 MPa.

[0140] 6) The critical damage strain value εx of the roof rock sample was determined to be 10MPa.

[0141] 7) Prepare a cylindrical roof rock sample with a diameter of 5 cm and a length of 500 cm. Figure 4 The figure shows a schematic cross-sectional view of the roof rock sample along the axial direction.

[0142] 8) Wrap the top plate rock sample with a pressure-resistant steel sleeve with a pressure resistance of not less than 80Mpa, and then wrap it with rock wool as a heat-insulating material, and then place the top plate rock sample into 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.

[0143] 9) A unidirectional heat source point, a temperature sensor, a pressure sensor and a strain sensor are placed at the bottom of the roof rock sample, and several groups of pressure sensors and strain sensors are arranged along the axial direction of the roof rock sample, with an interval of 10 cm.

[0144] 10) The bottom of the roof rock sample is heated by a unidirectional point heat source, and the heat source is heated at a rate of 20°C / day, with a temperature peak of 300°C (T0). The bottom of the roof rock sample is pressurized by fluid, with a pressurization rate of 300KPa / day and a pressure peak of 50MPa (Po). A rigid stress is applied to the bottom of the roof rock sample at a rate of 1MPa / 5 minutes, with a stress peak of 30MPa (Ex).

[0145] 11) 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 pressure sensor and strain sensor data of the roof rock sample are continuously collected.

[0146] 12) The thickness from the location where the pressure Px is measured to the bottom of the sample is 150 cm, and the distance from the location where the strain εx is measured to the bottom of the roof rock sample is 165 cm. The measurement shows that 165 cm is the lower limit of the roof sealing thickness.

[0147] 13) A numerical model consistent with the roof rock sample and experimental conditions was established, Px of the roof rock was set to (fracture pressure) 30 MPa, and the critical damage strain value εx of the roof rock sample was set to 10 MPa.

[0148] 14) Keep the temperature at the bottom of the top rock sample constant at T0 (300°C), the pressure constant at 50MPa (P0), and the stress constant at Ex (30MPa), complete the numerical simulation of the temperature field, pressure field, and stress field, and wait for the grid pressure and strain to stabilize.

[0149] 15) See Figure 5 , Figure 6 As shown in Figure 2, they are the simulated pressure field and strain field of the roof rock sample. Figure 5 Oil saturation at the Px pressure line (20 MPa) (see Figure 7 There was no change in 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 8 There was no change in the whole simulation period, indicating that oil and gas were blocked at this location.

[0150] 16) Observation Figure 5 Oil saturation at medium pressure line 25MPa (see Figure 7 (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 6 Oil saturation at the median strain line of 15 MPa (see Figure 8 During the whole simulation period, there are obvious changes, indicating that the oil and gas are not blocked at this location.

[0151] 17) The thickness of the Px pressure line is 153cm, and the thickness of the εx strain line is 153cm. The comprehensive comparison proves that the top plate with a thickness of 153cm meets the plugging requirements. The error between the numerical simulation results and the experimental results (165cm) is about 5.8%, so the numerical simulation verifies the reliability of the experimental results.

[0152] 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.

[0153] 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.

[0154] 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 lower limit of the plugging thickness of the siltstone adjacent layer of a shale reservoir, characterized in that: If it is determined that the fracture pressure of the shale reservoir is less than the minimum starting pressure of the overlying siltstone layer of the shale reservoir, the following steps are performed: A roof rock sample is prepared by using the coring section of the overlying siltstone layer, and the side of the roof rock sample is wrapped with a heat-insulating sealing material, and a first heating device, a first pressurizing device, a first stress device, a first temperature sensor, a first pressure sensor, and a first strain sensor are arranged on the bottom surface of the roof rock sample, and a plurality of groups of first pressure sensors and first strain sensors are arranged on the side of the roof rock sample at a first set interval; The roof 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, the roof rock sample is pressurized by the first pressurizing device until the pressure measured by the first pressure sensor at the bottom is the first set pressure, the first stress device is used to gradually apply stress from small to large to the bottom of the roof rock sample to the first set stress, and stabilize at the temperature, the pressure and the stress until the measured value variation amplitude of each first pressure sensor and the first strain sensor is less than the set threshold value, and the lowest position of the roof rock sample at which the pressure is not higher than the second set pressure and the strain is not higher than the first set strain is determined according to the measured values ​​of the first pressure sensor and the first strain sensor; 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.

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.

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 pressure is the fracture pressure of the shale reservoir, and the second set pressure is the fracture pressure of the overburden formation.

5. The method according to claim 4, 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 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.

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

8. The method according to claim 1, characterized in that If the underlying rock layer of the shale reservoir is a mudstone formation, the method further includes executing the following step of determining the lower limit of the bottom plate plugging thickness: 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 sealing material, and 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 bottom plate rock sample, and a plurality of groups of second sensors are arranged on the side surface of the bottom plate rock sample at a second set interval, wherein 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 variation amplitude of the measured values ​​of each second sensor is less than the set threshold, and the highest position of the bottom plate rock sample 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 is determined according to the measured values ​​of the second 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.

9. The method according to claim 1, characterized in that If the underlying rock layer of the shale reservoir is an underlying siltstone layer, determine whether the shale reservoir fracture pressure is less than the minimum starting pressure of the underlying siltstone layer; if so, perform the step of determining the lower limit of the bottom plate plugging thickness: A bottom plate rock sample is prepared by using a coring section of an underlying rock formation, and a side surface of the bottom plate rock sample is wrapped by using a heat-insulating sealing material, and a second heating device, a second pressurizing device, a second stress device, a second temperature sensor, a second pressure 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 pressure sensors and second strain sensors are arranged on the side surface of the bottom plate rock sample at a second set interval; 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, the pressure and the stress until the measured value variation amplitude of each second pressure sensor and the second strain sensor is less than the set threshold value, and the highest position where the pressure of the bottom plate rock sample is not higher than the third set pressure and the strain is not higher than the second set strain is determined according to the measured values ​​of the second pressure 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 8 or 9, characterized in that 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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