Method for determining plugging thickness required by shale reservoir in-situ exploitation

Abstract

The invention discloses a method for determining the plugging thickness required by shale reservoir in-situ exploitation, which comprises the following steps: if an adjacent layer of a shale reservoir is a shale layer or a silty rock layer and the minimum starting pressure is greater than the reservoir fracture pressure, preparing a rock sample by using an adjacent layer coring section; if the adjacent layer is the siltstone and shale interbed, preparing a rock sample according to the up-and-down superposition relation of the siltstone rock layer and the shale layer and the total thickness of the siltstone rock layer and the shale layer and the measurement property of the rock sample; heating and pressurizing the rock sample until the end surface is at a first set temperature and a first set pressure, applying stress to the rock sample step by step to the first set stress, stabilizing the temperature, the pressure and the stress until the measured values of the sensors on the side surface are stable, and determining the critical position of the rock sample meeting the requirements of the temperature, the pressure and the stress according to the measured values of the sensors; and taking the distance to the end surface as the lower limit of the adjacent layer plugging thickness. According to the method, the lower limit of the top and bottom plate plugging thickness is reasonably quantified through joint simulation of temperature, pressure and stress fields.

Description

Technical Field

[0001] The invention relates to the technical field of petroleum geology and shale reservoir exploitation, and in particular to a method for determining the plugging thickness required for in-situ exploitation 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 is increasingly gaining attention 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 is extracted through production wells.

[0003] In the same geological environment, the sealing strength of the caprock is highly correlated with the lithology. Caprocks of different lithologies are formed under various geological actions. According to the caprocks that have been explored so far, the lithologies are mainly gypsum, argillaceous rock and dense carbonate caprocks, and there are few examples of other lithologies being explored as caprocks.

[0004] Whether the overlying rock formation can be effectively sealed during the in-situ mining of shale reservoirs is one of the key factors to improve the recovery rate. The existing technology does not have an effective means to evaluate the roof sealing performance during the in-situ mining of shale reservoirs. Summary of the invention

[0005] 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 sealing thickness required for in-situ mining of shale reservoirs, which can reasonably quantify the lower limit of the sealing thickness of the shale reservoir roof through the joint simulation of temperature field, pressure field and stress field.

[0006] An embodiment of the present invention provides a method for determining the plugging thickness required for in-situ mining of a shale reservoir, comprising:

[0007] If it is determined that the adjacent layer of the shale reservoir is a mud shale layer, or the adjacent layer is a siltstone layer, and the minimum starting pressure of the siltstone layer is greater than the fracture pressure of the shale reservoir, the core section of the adjacent layer is used to prepare the rock sample;

[0008] If it is determined that the adjacent layers of the shale reservoir are interlayers of siltstone and mud shale, the vertical superposition relationship of the siltstone layer and the mud shale layer, and the total thickness of the siltstone layer and the total thickness of the mud shale layer are determined according to the lithology vertical distribution characteristics of the adjacent layers within the set range, and the rock samples are prepared by an integrated molding method in combination with the measured properties of multiple siltstone samples and multiple mud shale samples;

[0009] Arrange a heating device, a pressurizing device, a stress device and a group of sensors on the end surface of the rock sample close to the shale reservoir, and arrange multiple groups of sensors on the side of the rock sample at set intervals;

[0010] The heating device is used to heat the rock sample until the temperature measured by the temperature sensor at the end face is a first set temperature. The pressurizing device is used to pressurize the rock sample until the pressure measured by the pressure sensor at the end face is a first set pressure. The stress device is used to gradually apply stress to the rock sample from small to large to the first set stress, and stabilize at the temperature, pressure and stress until the variation amplitude of the measured values ​​of each sensor is less than the set threshold value. According to the measured values ​​of the sensors, the critical position of the rock sample that meets the temperature, pressure and stress requirements is determined, and the distance from the critical position to the end face is used as the lower limit of the adjacent layer plugging thickness.

[0011] In some embodiments, the method of combining the measured properties of a plurality of siltstone samples and a plurality of shale samples to prepare a rock sample by an integrated molding method includes:

[0012] Based on the measured properties of multiple siltstone samples, a first formula for siltstone is prepared by experimental fitting, and based on the measured properties of multiple shale samples, a second formula for shale is prepared by experimental fitting;

[0013] According to the upper and lower overlapping relationship, the total thickness of the siltstone layer and the total thickness of the shale layer, the first formula and the second formula, a rock sample is prepared by an integrated molding method.

[0014] In some embodiments, the preparing a first formula of siltstone by experimental fitting based on measured properties of a plurality of siltstone samples comprises:

[0015] The particle size distribution, mineral composition, fracture pressure, minimum starting pressure, fracture critical damage strain value and porosity of the rock samples of each siltstone layer within the set range of the adjacent layer are measured, and the average values ​​of the corresponding parameters are obtained by thickness-weighted averaging;

[0016] Taking the average values ​​of the grain size distribution and the average values ​​of the mineral composition of the siltstone layer as the current formula, preparing the siltstone sample, adjusting the current formula until the errors between the porosity, fracture pressure, fracture critical damage strain value and minimum starting pressure of the currently prepared siltstone sample and the corresponding average values ​​meet the error threshold, and obtaining the first formula for preparing the siltstone;

[0017] Accordingly, the second formula for preparing shale by experimental fitting based on the measured properties of the plurality of shale samples includes:

[0018] The particle size distribution, mineral composition, TOC, kerogen initial hydrocarbon production temperature, porosity, critical damage strain value and fracture pressure of the rock samples of each shale layer within the set range of the adjacent layer are measured, and the average value of the corresponding parameters is obtained by thickness-weighted averaging;

[0019] The average values ​​of the particle size distribution and the mineral composition of the shale layer are used as the current formula to prepare a shale sample, and the current formula is adjusted until the errors between the TOC, initial hydrocarbon production temperature of kerogen, porosity, critical damage strain value and rupture pressure of the currently prepared shale sample and the corresponding average values ​​meet the error threshold, thereby obtaining a second formula for preparing shale.

[0020] 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.

[0021] In some embodiments, the first set temperature is the lowest temperature at which the kerogen conversion rate in the shale reservoir reaches 90%.

[0022] In some embodiments, the first set pressure is the fracture pressure of the shale reservoir;

[0023] The first set stress is the maximum underground principal stress at the burial depth of the bottom surface of the rock sample, or the maximum underground principal stress at the burial depth of the top surface of the rock sample.

[0024] In some embodiments, if the adjacent layer is a shale layer, determining the critical position of the rock sample that meets the temperature, pressure and stress requirements includes:

[0025] Determine a critical position in the rock sample where the temperature is lower than the initial hydrocarbon production temperature of the kerogen of the adjacent layer, the pressure is lower than the fracture pressure of the adjacent layer, and the strain is lower than the critical damage strain value of the fracture of the adjacent layer.

[0026] In some embodiments, if the adjacent layer is a siltstone layer, determining the critical position of the rock sample that meets the temperature, pressure and stress requirements includes:

[0027] A critical position in the rock sample where the pressure is less than the fracture pressure of the adjacent layer and the strain is less than the fracture critical damage strain value of the adjacent layer is determined.

[0028] In some embodiments, the adjacent layer is an overlying stratum and / or an underlying stratum of the shale reservoir.

[0029] In some embodiments, if the adjacent layers are interbedded siltstone and shale, determining the critical position where the rock sample meets the temperature, pressure and stress requirements includes:

[0030] Based on the upper and lower superposition relationship of the siltstone layer and the shale layer in the adjacent layer, a critical position in the rock sample is determined where the temperature is lower than the initial hydrocarbon production temperature of the shale interlayer kerogen in the adjacent layer, the pressure is lower than the fracture pressure of the adjacent layer, and the strain is lower than the critical damage strain value of the fracture of the adjacent layer.

[0031] In some embodiments, if the adjacent layer is the overlying stratum of the shale reservoir, the upper and lower superposition relationship of the siltstone layer and the mud shale layer in the adjacent layer is that the siltstone layer is on top, the kerogen initial hydrocarbon production temperature of the mud shale layer in the adjacent layer is Tx, the fracture pressure of the adjacent layer is Px, and the fracture critical damage strain value of the adjacent layer is εx, the determining of the critical position of the rock sample that meets the temperature, pressure and stress requirements includes:

[0032] If the temperature in the shale layer drops to Tx, the pressure drops to Px and the strain drops to εx, the highest position among the position where the temperature is Tx, the position where the pressure is Px and the position where the strain is εx is determined as the critical position that meets the temperature, pressure and stress requirements;

[0033] If the temperature in the mudstone layer drops to Tx, but the pressure does not drop to Px and the strain does not drop to εx at the same time, if the minimum starting pressure of the siltstone layer is greater than the fracture pressure Pr of the shale reservoir, the higher position of the position where the pressure is Px and the position where the strain is εx is taken as the critical position that meets the temperature, pressure and stress requirements; if the minimum starting pressure of the siltstone layer is not greater than the fracture pressure Pr of the shale reservoir, it is determined that the rock sample cannot be plugged;

[0034] If the temperature in the shale layer is greater than Tx, the method is invalid.

[0035] In some embodiments, if the adjacent layer is the overlying stratum of the shale reservoir, the upper and lower superposition relationship of the siltstone layer and the mud shale layer in the adjacent layer is that the siltstone layer is at the bottom, the kerogen initial hydrocarbon production temperature of the mud shale layer in the adjacent layer is Tx, the fracture pressure of the adjacent layer is Px, and the fracture critical damage strain value of the adjacent layer is εx, the determining of the critical position where the rock sample meets the temperature, pressure and stress requirements includes:

[0036] If the temperature in the siltstone layer drops to Tx, the pressure drops to Px, and the strain drops to εx, the bottom of the shale layer is determined to be the critical position that meets the temperature, pressure, and stress requirements;

[0037] If the strain in the shale layer drops to εx, or the pressure drops to Px, or the temperature drops to Tx, the highest position among the position where the temperature is Tx, the position where the pressure is Px, and the position where the strain is εx is determined as the critical position that meets the temperature, pressure, and stress requirements.

[0038] The beneficial effects of the above technical solution provided by the embodiment of the present invention include at least:

[0039] (1) A method for determining the plugging thickness required for in-situ mining of a shale reservoir provided in an embodiment of the present invention first determines the lithology type of the adjacent layers of the shale reservoir. If the lithology is single, a rock sample is directly prepared through the coring section, that is, the prepared rock sample is a part of the real rock layer; if the shale is interlayered with siltstone and mudstone, a synthetic rock sample of superimposed siltstone and mudstone layers is prepared; a heating device is used to heat the rock sample and maintain the temperature near the end of the reservoir as a first set temperature; a pressurizing device is used to pressurize the rock sample and maintain the pressure near the end of the reservoir as a first set pressure; a stress device is used to gradually apply stress from small to large to the end of the rock sample to the first set stress, and stabilize it at the stress until the measured values ​​of each sensor are stable, and the critical position of the rock sample that meets the temperature, pressure and stress requirements is determined, and the distance from the critical position to the end face is used as the lower limit of the plugging thickness of the adjacent layer. The lower limit of the sealing thickness of the adjacent layers of the shale reservoir is determined by experimental methods based on the simulation of temperature field, pressure field and stress field. The sealing conditions of the adjacent layers during the in-situ mining of shale reservoirs are specifically quantified, which can effectively guide production and improve the economic benefits of in-situ mining of shale oil and gas.

[0040] (2) The method for determining the plugging thickness required for in-situ mining of shale reservoirs provided in an embodiment of the present invention determines the vertical superposition relationship between siltstone and mudstone layers, and the total thickness of siltstone and mudstone layers according to the lithology vertical distribution characteristics of adjacent layers of shale reservoirs within a set range, and prepares the top plate rock sample in one piece based on the measured properties of siltstone and mudstone. The prepared synthetic sample takes into account the properties of mudstone and siltstone, as well as the vertical superposition relationship between the two, and reasonably simplifies the sample, so that the determination of the lower limit of the plugging thickness of the complex lithology adjacent layers of mudstone and siltstone interlayers can be achieved.

[0041] (3) It is currently generally believed that only mudstone can effectively seal shale reservoirs during in-situ mining. The method for determining the sealing thickness required for in-situ mining of shale reservoirs provided in the embodiment of the present invention suggests that if the adjacent layer of the shale reservoir is a siltstone layer with a single lithology, or an interlayer of siltstone and mudstone, it may also produce a sealing effect during the in-situ mining of the shale reservoir, thereby broadening the exploration prospects of shale oil and gas.

[0042] (4) A method for determining the plugging thickness required for in-situ mining of a shale reservoir provided in an embodiment of the present invention comprises the following steps: during the experiment, the temperature of the rock sample near the end of the reservoir 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 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 mining of an actual shale reservoir; the pressure of the rock sample near the end of the reservoir 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 mining; stress is applied to the end of the rock sample near the reservoir step by step from small to large until the maximum principal stress underground at the bottom buried depth, and the stress is stabilized at this stress, that is, the maximum stress that may be encountered during the in-situ heating mining; on the basis that the temperature of the rock sample near the end of the reservoir 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 buried depth of the end, the lower limit of the top plate plugging thickness is determined according to the measurement value of the sensor. Therefore, the above settings of temperature, pressure, stress and strain ensure that the lower limit of the adjacent layer plugging thickness is reasonable and has strong production guidance significance.

[0043] (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 required sealing thickness for in-situ exploitation of shale reservoirs provided in 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.

[0044] 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.

[0045] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] 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:

[0047] Figure 1 This is a flow chart of a method for determining the plugging thickness required for in-situ mining of a shale reservoir in Embodiment 1 of the present invention;

[0048] Figure 2 This is a flow chart of a method for determining the plugging thickness required for in-situ mining of a shale reservoir in Embodiment 2 of the present invention;

[0049] Figure 3 This is a flow chart of a method for determining the plugging thickness required for in-situ mining of a shale reservoir in Embodiment 3 of the present invention;

[0050] 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;

[0051] Figure 5 This is a temperature field simulation diagram in the fourth embodiment of the present invention;

[0052] Figure 6 This is a pressure field simulation diagram in the fourth embodiment of the present invention;

[0053] Figure 7 This is a strain field simulation diagram in the fourth embodiment of the present invention;

[0054] Figure 8 for Figure 5 Oil saturation variation diagram at the middle temperature line 200℃ and 220℃;

[0055] Fig. 9 for Figure 6 Oil saturation variation diagram at the middle pressure line 20MPa and 25MPa;

[0056] Fig.10 for Figure 7 Oil saturation variation diagram at the middle strain line of 10MPa and 20MPa. DETAILED DESCRIPTION

[0057] 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.

[0058] 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.

[0059] 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.

[0060] 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.

[0061] 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 the different heat conduction conditions of the top plate and the bottom plate of the shale reservoir during the in-situ heating and exploitation of the shale reservoir affect the different plugging thicknesses; the top plate and the bottom plate are subjected to different stresses due to different burial depths, which also affects the different plugging 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 top plate and the bottom plate of the shale reservoir to be subjected to fluid pressure, which also affects the different plugging thicknesses. Therefore, the plugging thickness of the top plate and the bottom plate can be reasonably determined through the joint simulation experiment of temperature field, pressure field and stress field. In addition, it is generally believed that mud shale can produce a plugging effect in the in-situ exploitation of shale reservoirs, but the inventor found that the complex lithology of siltstone layer, or mud shale and siltstone interlayer, may also produce a plugging effect in the in-situ exploitation of shale reservoirs. The embodiment of the present invention provides a method for determining the plugging thickness required for in-situ mining of a shale reservoir, which can reasonably quantify the lower limit of the plugging thickness of adjacent layers of the shale reservoir by simulating temperature fields, pressure fields and stress fields.

[0062] Embodiment 1

[0063] Embodiment 1 of the present invention provides a method for determining the plugging thickness required for in-situ mining of a shale reservoir, referring to Figure 1 As shown, the following steps are included:

[0064] Step S11: If it is determined that the adjacent layer of the shale reservoir is a mudstone layer, or the adjacent layer is a siltstone layer, and the minimum starting pressure of the siltstone layer is greater than the fracture pressure of the shale reservoir, a rock sample is prepared using the coring section of the adjacent layer.

[0065] The adjacent layer is the overlying stratum and / or underlying stratum of the shale reservoir. That is, according to the actual research needs, the lower limit of the plugging thickness of the top plate of the shale reservoir is determined, or the lower limit of the plugging thickness of the bottom plate of the shale reservoir is determined, or the lower limit of the plugging thickness of the top and bottom plates of the shale reservoir is determined.

[0066] According to empirical data, the plugging thickness of the adjacent layer during the in-situ mining of shale reservoirs is usually within 300-400 centimeters, so the length (thickness) of the 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 plugging thickness, resulting in experimental failure (unable to measure the plugging thickness of the adjacent layer required for shale in-situ). That is, the range corresponding to the prepared rock sample is within the range of 500 cm in thickness. Preferably, for the overlying strata, the thickness is within 500 cm from the position closest to the top surface of the shale reservoir upward; for the underlying strata, the thickness is within 500 cm from the position closest to the bottom surface of the shale reservoir downward.

[0067] Step S12: If it is determined that the adjacent layers of the shale reservoir are interlayers of siltstone and mudstone, the upper and lower superposition relationship of the siltstone layer and the mudstone layer, and the total thickness of the siltstone layer and the total thickness of the mudstone layer are determined according to the longitudinal distribution characteristics of the lithology of the adjacent layers within the set range, and the rock samples are prepared by one-piece molding in combination with the measured properties of multiple siltstone samples and multiple mudstone samples.

[0068] Preferably, for the overlying strata, the setting range is within 500 cm in thickness from the position closest to the top surface of the shale reservoir; for the underlying strata, the setting range is within 500 cm in thickness from the position closest to the bottom surface of the shale reservoir.

[0069] Taking the determination of the upper and lower superposition relationship of the siltstone layer and the mud shale layer within the set range of the overlying strata as an example, the set range is divided into two parts, upper and lower, by an averaging method. If the cumulative thickness of the lower mud shale layer exceeds the first set ratio (for example, more than 60%), the superposition relationship is determined to be the mud shale layer at the bottom and the siltstone layer at the top; if the cumulative thickness of the lower mud shale layer is lower than the second set ratio (for example, lower than 40%), the superposition relationship is determined to be the mud shale layer at the top and the siltstone layer at the bottom; if the cumulative thickness of the lower mud shale layer is within the set ratio range (for example, 40% to 60%), the lower part within the set range is divided into two parts, upper and lower, by an averaging method, and the above method is repeated to determine the upper and lower superposition relationship of the siltstone layer and the mud shale layer.

[0070] The process of preparing a rock sample by one-piece molding may include the following steps:

[0071] Step S121: Based on the measured properties of multiple siltstone samples within the set range of adjacent layers, a first formula for siltstone is prepared by experimental fitting, and based on the measured properties of multiple shale samples within the set range of adjacent layers, a second formula for shale is prepared by experimental fitting.

[0072] In some embodiments, fitting of a first formula for preparing siltstone may include: measuring the particle size distribution, mineral composition, porosity, fracture pressure, critical fracture damage strain value, and minimum starting pressure of rock samples of each siltstone layer within a set range of adjacent formations, and obtaining the average values ​​of corresponding parameters by thickness-weighted averaging; preparing siltstone samples using the average values ​​of the particle size distribution and the average values ​​of the mineral composition of the siltstone layer as the current formula, and adjusting the current formula until the errors between the porosity, fracture pressure, critical fracture damage strain value, and minimum starting pressure of the currently prepared siltstone sample and the corresponding average values ​​meet an error threshold, thereby obtaining the first formula for preparing siltstone.

[0073] Small-size samples can be synthesized first, the porosity of the synthesized samples can be measured, and then calibrated with the measurement results of natural samples. Then, the current particle size distribution and mineral composition can be adjusted and optimized, and new artificial samples can be synthesized. Finally, the error between the measurement results of the synthetic samples and the natural samples does not exceed the error threshold (which can be set to 15%).

[0074] In some embodiments, fitting of a second formula for preparing mud shale may include: measuring the particle size distribution, mineral composition, TOC, kerogen initial hydrocarbon production temperature, porosity, critical damage strain value of fracture and fracture pressure of rock samples of each mud shale layer within a set range of the adjacent layer, and obtaining the average value of the corresponding parameters by thickness weighting; taking the average value of the particle size distribution and the average value of the mineral composition of the mud shale layer as the current formula, preparing a mud shale sample, adjusting the current formula until the errors between the TOC, kerogen initial hydrocarbon production temperature, porosity, critical damage strain value of fracture and fracture pressure of the currently prepared mud shale sample and the corresponding average values ​​all meet the error threshold, thereby obtaining the second formula for preparing mud shale.

[0075] Optionally, in the process of fitting the first formula and the second formula, the parameters used for calibration may include not only the above parameters but also other parameters. Correspondingly, the measurement results of natural samples of these parameters are obtained by measuring the measurement results of corresponding rock samples and averaging them by thickness weighted average.

[0076] Step S122: preparing a rock sample by an integrated molding method according to the upper and lower overlapping relationship, the total thickness of the siltstone layer and the total thickness of the shale layer, the first formula and the second formula.

[0077] The rock sample obtained in step S11 is a part of the real underground rock formation, and the rock sample obtained in step S12 is a synthetic simulated rock sample. Both can be rock samples with the same cross-sectional area (e.g., cylindrical with a diameter of 5 cm); preferably, the length (thickness) is 500 cm.

[0078] The sides of the rock sample are wrapped with heat-insulating materials to prevent heat from being dissipated to the surroundings during the heating process. The pressure resistance of the heat-insulating sealing material must be no less than 80MPa.

[0079] Step S13: Arrange a heating device, a pressurizing device, a stress device and a group of sensors on the end face of the rock sample close to the shale reservoir, and arrange multiple groups of sensors on the side face of the rock sample at set intervals.

[0080] The pressurizing device may be a fluid pressurizing device; and the stress device may be a triaxial stress testing device.

[0081] In some embodiments, the heating device is a one-way heating device to save resources.

[0082] The heating device is located at the center of the end face of the rock sample close to the shale reservoir. Furthermore, the direct heating area of ​​the end face by the heating device may not exceed 1 / 4 of the end face area, so that the heat source can be spread to the rock sample as much as possible.

[0083] A group of sensors arranged on the end face of the rock sample and each group of sensors arranged on the side face may include a temperature sensor, a pressure sensor and a strain sensor.

[0084] In some embodiments, if the adjacent layer is a siltstone layer, the temperature sensor may not be arranged on the side.

[0085] The first set interval of each set of sensors arranged on the side of the rock sample is set according to the measurement accuracy requirements, usually at an interval of 10 cm.

[0086] Each group of sensors (including temperature sensors, pressure sensors and strain sensors, or only pressure sensors and strain sensors) arranged on the side of the rock sample has the same measurement position in the longitudinal direction.

[0087] Step S14: using a heating device to heat the rock sample until the temperature measured by the temperature sensor at the end face is a first set temperature, using a pressurizing device to pressurize the rock sample until the pressure measured by the pressure sensor at the end face is a first set pressure, using a stress device to gradually apply stress to the rock sample from small to large to the first set stress, and stabilize at the temperature, pressure and stress until the variation amplitude of the measured values ​​of each sensor is less than the set threshold value, and according to the measured values ​​of the sensors, determine the critical position of the rock sample that meets the temperature, pressure and stress requirements, and use the distance from the critical position to the end face as the lower limit of the adjacent layer plugging thickness.

[0088] 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.

[0089] The first set temperature can be determined by utilizing a source rock thermal simulation experiment or a kerogen activation energy experiment.

[0090] 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.

[0091] 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.

[0092] 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.

[0093] In some embodiments, the first set pressure is the fracture pressure of the shale reservoir, which can be determined by a rock fracture pressure experiment; the first set stress is the maximum underground principal stress at the burial depth of the bottom surface of the top plate rock sample, or the maximum underground principal stress at the burial depth of the top surface of the bottom plate rock sample, which is obtained by calculation.

[0094] Taking the rock sample of the overlying strata (i.e., the roof rock sample) as an example, the set temperature, i.e., the lowest temperature T0 at which the kerogen conversion rate in the shale reservoir reaches 90%, is determined by the above method, the fracture pressure P0 of the shale reservoir is determined, and the maximum underground principal stress Ex at the burial depth of the bottom surface of the roof rock sample is determined.

[0095] Use a heating device (heat source) to heat slowly (no more than 20°C / day), with the maximum temperature of the heat source between 400 and 650°C, and adjust the heat source power to keep the temperature at the bottom of the top plate rock sample constant at T0; use a pressurizing device to pressurize the bottom of the top plate rock sample, use fluid to increase pressure, and the pressurization speed does not exceed 300KPa / day (the specific value is flexibly set according to the on-site construction situation) to keep the pressure at the bottom of the top plate rock sample constant at P0; at the same time, use a stress device 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 temperature, pressure and strain are stable, the measured values ​​of the first temperature sensor, the first pressure sensor and the 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, the first pressure sensor and the first strain sensor can be collected from bottom to top in sequence.

[0096] In the embodiment of the present application, from bottom to top corresponds to from bottom to top.

[0097] Before determining the lower limit of the adjacent layer plugging thickness, the following parameters need to be determined:

[0098] The initial hydrocarbon production temperature Tx of the kerogen in the adjacent shale layer is usually 200-250°C. It can be determined by thermal simulation experiments of source rocks;

[0099] The fracture pressure Px of the adjacent layer, if the adjacent layer is an interlayer of siltstone and shale, can be the average value of the fracture pressure of the siltstone layer and the shale layer after weighted average of the thickness;

[0100] The critical damage strain value εx of the adjacent layer, if the adjacent layer is an interlayer of siltstone and shale, can be the average value of the critical damage strain value of the siltstone layer and the shale layer after the thickness weighted average;

[0101] The minimum starting pressure Ps for oil and gas migration in the siltstone layer in the adjacent layer.

[0102] Determine the critical position where the rock sample meets the temperature, pressure and stress requirements. The specific methods vary depending on the lithology of the adjacent layers:

[0103] 1. If the adjacent layer is a shale layer

[0104] Determine the critical position of the rock sample that meets the temperature, pressure and stress requirements, including determining the critical position in the rock sample where the temperature is lower than the initial hydrocarbon production temperature of the kerogen in the adjacent layer, the pressure is lower than the fracture pressure of the adjacent layer, and the strain is lower than the critical damage strain value of the fracture of the adjacent layer.

[0105] (1) If the adjacent layer is the overlying stratum

[0106] Determine the position in the rock sample where the temperature is the initial hydrocarbon production temperature of the kerogen in the adjacent layer, the pressure is the fracture pressure of the adjacent layer, and the strain is the critical damage strain value of the fracture of the adjacent layer;

[0107] The highest position among the three determined positions is determined as the critical position where the rock sample meets the temperature, pressure and stress requirements.

[0108] (2) If the adjacent layer is the underlying stratum

[0109] Determine the position in the rock sample where the temperature is the initial hydrocarbon production temperature of the kerogen in the adjacent layer, the pressure is the fracture pressure of the adjacent layer, and the strain is the critical damage strain value of the fracture of the adjacent layer;

[0110] The lowest position among the three determined positions is determined as the critical position where the rock sample meets the temperature, pressure and stress requirements.

[0111] 2. If the adjacent layer is siltstone

[0112] Determine the critical position where the rock sample meets the temperature, pressure and stress requirements, including determining the critical position where the pressure in the adjacent layer is less than the fracture pressure of the adjacent layer and the strain is less than the critical damage strain value of the fracture of the adjacent layer.

[0113] (1) If the adjacent layer is the overlying stratum

[0114] Determine the position in the rock sample where the temperature is the initial hydrocarbon production temperature of the kerogen in the adjacent layer and the pressure is the fracture pressure of the adjacent layer;

[0115] The higher of the two determined positions is determined as the critical position where the rock sample meets the temperature, pressure and stress requirements.

[0116] (2) If the adjacent layer is the underlying stratum

[0117] Determine the position in the rock sample where the temperature is the initial hydrocarbon production temperature of the kerogen in the adjacent layer and the pressure is the fracture pressure of the adjacent layer;

[0118] The lower of the two determined positions is determined as the critical position where the rock sample meets the temperature, pressure and stress requirements.

[0119] 3. If the adjacent layers are interbedded with siltstone and shale

[0120] Determine the critical position of the rock sample that meets the temperature, pressure and stress requirements, including, based on the upper and lower superposition relationship of the siltstone layer and the shale layer in the adjacent layer, determine the critical position in the rock sample where the temperature is lower than the initial hydrocarbon production temperature of the kerogen in the shale interlayer in the adjacent layer, the pressure is lower than the fracture pressure of the adjacent layer, and the strain is lower than the critical damage strain value of the fracture of the adjacent layer.

[0121] Taking the overlying strata of the adjacent strata as an example, the following two situations can be included:

[0122] 1. The relationship between the upper and lower superposition is that the siltstone layer is on the upper

[0123] (1) If the temperature in the shale layer drops to Tx, the pressure drops to Px, and the strain drops to εx, the highest position among the position where the temperature is Tx, the position where the pressure is Px, and the position where the strain is εx is determined as the critical position that meets the temperature, pressure, and stress requirements;

[0124] (2) If the temperature in the mudstone layer drops to Tx, but the pressure does not drop to Px and the strain does not drop to εx at the same time, if the minimum starting pressure of the siltstone layer is greater than the fracture pressure Pr of the shale reservoir, the higher position of the position where the pressure is Px and the position where the strain is εx is taken as the critical position that meets the temperature, pressure and stress requirements; if the minimum starting pressure of the siltstone layer is not greater than the fracture pressure Pr of the shale reservoir, it is determined that the rock sample cannot be plugged;

[0125] (3) If the temperature in the shale layer is greater than Tx, the method is invalid.

[0126] 2. The relationship between the upper and lower superposition is that the siltstone layer is at the bottom.

[0127] (1) If the temperature in the siltstone layer drops to Tx, the pressure drops to Px, and the strain drops to εx, the bottom of the shale layer is determined to be the critical position that meets the temperature, pressure, and stress requirements;

[0128] (2) If the strain in the shale layer drops to εx, or the pressure drops to Px, or the temperature drops to Tx, the highest position among the position where the temperature is Tx, the position where the pressure is Px, and the position where the strain is εx is determined as the critical position that meets the temperature, pressure, and stress requirements.

[0129] In some embodiments, other factors affecting the plugging performance may be further considered to determine a safety correction factor (greater than 1), and the safety correction factor may be used to correct the lower limit of the roof plugging thickness determined above.

[0130] The method for determining the plugging thickness required for in-situ mining of a shale reservoir provided in Example 1 of the present invention first determines the lithology type of the adjacent layer of the shale reservoir. If it is a single lithology, a rock sample is directly prepared through the coring section, that is, the prepared rock sample is a part of the real rock layer; if it is an interlayer of siltstone and mudstone, a synthetic rock sample of superimposed siltstone layers and mudstone layers is prepared; a heating device is used to heat the rock sample and maintain the temperature near the end of the reservoir as a first set temperature, a pressurizing device is used to pressurize the rock sample and maintain the pressure near the end of the reservoir as a first set pressure, a stress device is used to gradually apply stress to the end of the rock sample from small to large to the first set stress, and stabilize at this stress until the measured values ​​of each sensor are stable, determine the critical position of the rock sample that meets the temperature, pressure and stress requirements, and use the distance from the critical position to the end face as the lower limit of the plugging thickness of the adjacent layer. The lower limit of the sealing thickness of the adjacent layers of the shale reservoir is determined by experimental methods based on the simulation of temperature field, pressure field and stress field. The sealing conditions of the adjacent layers during the in-situ mining of shale reservoirs are specifically quantified, which can effectively guide production and improve the economic benefits of in-situ mining of shale oil and gas.

[0131] The method for determining the plugging thickness required for in-situ mining of shale reservoirs provided in Example 1 of the present invention determines the vertical superposition relationship between siltstone layers and mudstone layers, and the total thickness of siltstone layers and mudstone layers according to the lithology vertical distribution characteristics of adjacent layers of shale reservoirs within a set range, and prepares the top plate rock sample in one piece based on the measured properties of siltstone and mudstone. The prepared synthetic sample takes into account the properties of mudstone and siltstone, as well as the vertical superposition relationship between the two, and reasonably simplifies the sample, so that the determination of the lower limit of the plugging thickness of the complex lithology adjacent layers of mudstone and siltstone interlayers can be achieved.

[0132] At present, it is generally believed that only mudstone can effectively seal the shale reservoir during in-situ mining. The method for determining the sealing thickness required for in-situ mining of shale reservoirs provided in Example 1 of the present invention proposes that if the adjacent layer of the shale reservoir is a siltstone layer with a single lithology, or an interlayer of siltstone and mudstone, it may also produce a sealing effect during the in-situ mining of the shale reservoir, thereby broadening the exploration prospects of shale oil and gas.

[0133] Embodiment 2

[0134] Embodiment 2 of the present invention provides another method for determining the sealing thickness required for in-situ mining of a shale reservoir, specifically a method for determining the lower limit of the bottom plate sealing thickness of a shale reservoir, wherein the underlying rock formation of the shale reservoir is a mudstone formation.

[0135] Specifically, refer to Figure 2 As shown, the following steps are included:

[0136] 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 heating device, a pressurizing device, a stress device and a group of sensors on the top surface of the bottom plate rock sample, and arrange multiple groups of sensors on the side of the bottom plate rock sample at set intervals.

[0137] Each group of sensors includes a temperature sensor, a pressure sensor and a strain sensor. The measurement positions of each group of temperature sensors, pressure sensors and strain sensors arranged on the side of the rock sample are consistent in the longitudinal direction.

[0138] 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.

[0139] The heating device is located at the center of the top surface of the bottom plate rock sample. Further, the heating device can heat the top surface of the bottom plate rock sample directly without exceeding 1 / 4 of the top surface area, so that the heat source can be spread downward as much as possible.

[0140] 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.

[0141] Each group of temperature sensors, pressure sensors and strain sensors are arranged axially on the side of the bottom plate rock sample, and the set interval of the arrangement is set according to the measurement accuracy requirements, usually at an interval of 10 cm.

[0142] Step S22: using a heating device to heat the bottom plate rock sample to a first set temperature measured by a top temperature sensor, using a pressurizing device to pressurize the bottom plate rock sample to a second set pressure measured by a top pressure sensor, using a 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 variation amplitude of the measured values ​​of each sensor is less than a set threshold, and determining the highest position at which the bottom plate 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 second set strain according to the measured values ​​of the sensors.

[0143] In some embodiments, the second set temperature is the initial hydrocarbon production temperature of kerogen in the underlying rock formation.

[0144] In some embodiments, the second 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.

[0145] 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.

[0146] 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.

[0147] Taking the second set temperature as Tx, the second set pressure as Px, the second set stress as Ex, and the second set strain as εx as an example, use a heating device (heat source) to slowly heat (no more than 20°C / day), the maximum temperature of the heat source is between 400 and 650°C, adjust the heat source power, and make the top temperature of the bottom plate rock sample constant at T0; at the same time, use a pressurizing device to pressurize the top of the bottom plate rock sample, use fluid pressurization, and the pressurization speed does not exceed 300KPa / day (the specific value is flexibly set according to the on-site construction situation) to make the top pressure of the bottom plate rock sample constant at P0; use a stress device 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 kept constant at T0, the pressure is kept constant at P0, and the stress is kept constant at Ex. They are kept 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 temperature sensor, pressure sensor and strain sensor are collected. Since the temperature of the bottom plate rock sample gradually decreases from the top to the bottom, the pressure gradually decreases from the top to the bottom, and the strain also gradually decreases from the top to the bottom, the measured values ​​of the temperature sensor, pressure sensor and strain sensor can be collected from the top to the 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.

[0148] If the currently collected temperature is Tx, the position of the corresponding 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 temperature sensor and the position of the previous temperature sensor, the first highest position where the bottom plate rock sample temperature is not higher than Tx is determined by the proportional method.

[0149] Similarly, if the currently collected pressure is Px, the position of the corresponding 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 pressure sensor and the position of the previous pressure sensor, the second highest position where the bottom plate rock sample pressure is not higher than Px is determined by the proportional method.

[0150] If the currently collected strain is εx, the position of the corresponding 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 strain sensor and the position of the previous strain sensor, the third highest position where the bottom plate rock sample strain is not higher than εx is determined by the proportional method.

[0151] 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 second set temperature, the pressure is not higher than the second set pressure, and the stress is not higher than the second set stress.

[0152] 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.

[0153] 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.

[0154] Embodiment 3

[0155] Embodiment 3 of the present invention provides another method for determining the plugging thickness required for in-situ mining of shale reservoirs, specifically a method for determining the lower limit of the bottom plate plugging thickness of shale reservoirs, wherein the underlying rock formation of the shale reservoir is a siltstone formation. It is determined whether the shale reservoir fracture pressure is less than the minimum starting pressure of the underlying siltstone formation; if so, the following bottom plate plugging thickness lower limit determination step is performed; if not, it is determined that the underlying formation does not have plugging properties during the in-situ mining of the shale reservoir.

[0156] For details, see Figure 3 As shown, the steps for determining the lower limit of the bottom plate plugging thickness include:

[0157] 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 heating device, a pressurizing device, a stress device and a temperature sensor, a pressure sensor and a strain sensor on the top surface of the bottom plate rock sample, and arrange multiple groups of pressure sensors and strain sensors on the side of the bottom plate rock sample at set intervals.

[0158] The measuring positions of each group of pressure sensors and strain sensors arranged on the side of the rock sample in the longitudinal direction are consistent.

[0159] 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.

[0160] The heating device is located at the center of the top surface of the bottom plate rock sample. Further, the heating device can heat the top surface of the bottom plate rock sample directly without exceeding 1 / 4 of the top surface area, so that the heat source can be spread downward as much as possible.

[0161] 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.

[0162] Each set of pressure sensors and strain sensors is arranged axially on the side of the bottom plate rock sample, and the set interval of the arrangement is set according to the measurement accuracy requirements, usually at an interval of 10 cm.

[0163] Step S32: using a heating device to heat the bottom plate rock sample to a first set temperature measured by a top temperature sensor, using a pressurizing device to pressurize the bottom plate rock sample to a second set pressure measured by a top pressure sensor, using a 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 pressure sensor and strain sensor is less than a set threshold value, and determining the highest position where the bottom plate rock sample pressure is not higher than the second set pressure and the strain is not higher than the second set strain based on the measured values ​​of the pressure sensor and the strain sensor.

[0164] In some embodiments, the second 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.

[0165] 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.

[0166] 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.

[0167] Taking the second set pressure as Px, the second set stress as Ex, and the second set strain as εx as an example, use a heating device (heat source) to slowly heat (no more than 20°C / day), the maximum temperature of the heat source is between 400 and 650°C, adjust the heat source power, and make the top temperature of the bottom plate rock sample constant T0; at the same time, use a pressurizing device to pressurize the top of the bottom plate rock sample, use fluid to increase pressure, and the increase 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 P0; use a stress device 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 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 pressure sensor and 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 pressure sensor and the 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.

[0168] If the currently collected pressure is Px, the position of the corresponding 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 pressure sensor and the position of the previous pressure sensor, the first highest position where the bottom plate rock sample pressure is not higher than Px is determined by the proportional method.

[0169] Similarly, if the currently collected strain is εx, the position of the corresponding 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), according to the currently collected strain and the previous strain collected and the position of the current strain sensor and the position of the previous strain sensor, the second highest position where the bottom plate rock sample strain is not higher than εx is determined by the proportional method.

[0170] 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.

[0171] 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.

[0172] 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.

[0173] 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 mining 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 sealing thickness required for in-situ mining of shale reservoirs provided in embodiments 2 and 3 of the present invention fully considers the sealing properties of the bottom plate, ensures the reliability of determining the sealing performance, and further provides a guarantee for improving the recovery rate.

[0174] The above three embodiments can be applied separately; embodiment one and embodiment two can also be applied in combination, or embodiment one and embodiment three can be applied in combination, to determine both the lower limit of the top plate plugging thickness of the shale reservoir and the lower limit of the bottom plate plugging thickness of the shale reservoir. The top and bottom plate thicknesses of the shale reservoir both meet the corresponding lower limits of the plugging thickness, and then it is determined that the plugging requirements are met.

[0175] Embodiment 4

[0176] 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:

[0177] 1) The total thickness of the siltstone layer and the total thickness of the shale layer in the overlying strata within the set range are counted respectively.

[0178] 2) The particle size distribution, mineral composition, initial kerogen hydrocarbon production temperature Tx, TOC, porosity Φ, fracture pressure Px, and critical damage strain value εx of different shale layer samples were measured respectively, and the average values ​​of the above parameters of the shale layer were calculated using the thickness weighted average method.

[0179] 3) The particle size distribution, mineral composition, porosity Φ, fracture pressure Px, and critical damage strain value εx of different siltstone layer samples were measured respectively, and the average values ​​of the above parameters of the siltstone layer were calculated using the thickness weighted average method.

[0180] 4) According to the geological conditions, the artificial samples in this experiment were determined to have a siltstone layer at the bottom and a shale layer at the top.

[0181] 5) According to the averaged parameter results, according to the superposition relationship and thickness, a roof rock sample containing a homogeneous siltstone layer and a homogeneous shale layer is synthesized at one time (the thickness of the shale layer is equal to 400 cm, and the thickness of the siltstone layer is equal to 100 cm. The cumulative deviation of the above parameters from the design value is not more than 15%, and the sample preparation is qualified. The roof rock sample is a cylinder with a diameter of 5 cm, see Figure 4 The figure shows a schematic cross-sectional view of the roof rock sample along the axial direction.

[0182] 6) Determine the T0 (kerogen 90% conversion temperature) of the reservoir rock sample at 300℃.

[0183] 7) The Tx (initial hydrocarbon production temperature of kerogen) of the mudstone roof rock sample was determined to be 200°C.

[0184] 8) The maximum stress Ex (maximum axial stress) of the reservoir rock sample was measured to be 30 MPa.

[0185] 9) The Px (fracture pressure) of the roof mudstone sample was measured to be 22 MPa, and the Px (fracture pressure) of the siltstone sample was 20 MPa. The fracture pressure of the entire roof rock sample was approximated to be 20 MPa.

[0186] 10) The critical damage strain value εx of the roof mudstone sample was determined to be 12MPa, and the critical damage strain value εx of the siltstone sample was 10MPa. The critical damage strain value εx of the entire roof rock sample was approximated to be 10MPa.

[0187] 11) 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. The sealing ensures that the fluid applied at the bottom of the sample cannot enter between the sample and the steel sleeve, and place the top plate rock sample into the experimental device.

[0188] 12) A unidirectional heat source point is placed at the bottom of the roof rock sample, and temperature sensors and strain sensors are arranged starting from the bottom. Several groups of temperature sensors and strain sensors are arranged along the axial direction of the roof rock sample, with an interval of 10 cm.

[0189] 13) 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). Fluid pressurization is applied to the bottom of the roof rock sample, with a pressurization rate of 300KPa / day and a pressure peak of 50MPa. 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).

[0190] 14) 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. After 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.

[0191] 15) The distance from the position where the temperature Tx is measured to the bottom of the roof rock sample is 140 cm, the distance from the position where the calculated pressure Px is measured to the thickness of the sample bottom is 170 cm, and the distance from the position where the strain εx is measured to the bottom of the roof rock sample is 180 cm, that is, 180 cm is the lower limit of the roof sealing thickness.

[0192] 16) A numerical model consistent with the sample and experimental conditions was established. The thickness of the mudstone was 400 cm, and its TOC, porosity, T0, Tx, P0, Px, Pr, εx, and mineral composition were the same as those of the artificial samples used in the experiment. The thickness of the siltstone was 100 cm, and its porosity, P0, Px, Ps, εx, and mineral composition were the same as those of the artificial samples used in the experiment. The kerogen activation energy parameters of the mudstone were set so that the Tx (initial hydrocarbon production temperature of the kerogen) of the roof rock sample was 200°C. The Px (fracture pressure) of the roof mudstone was set to 22 MPa, and the Px (fracture pressure) of the siltstone sample was set to 20 MPa. The critical damage strain value εx of the mudstone was set to 12 MPa. The critical damage strain value εx of the siltstone was set to 10 MPa.

[0193] 17) Keep the temperature at the bottom of the top rock sample constant at T0 (300°C), the pressure constant at P0 (50MPa), 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 temperature, pressure, and pressure change to stabilize.

[0194] 18) See Figure 5-7 As shown in the figure, they are the simulated temperature field, simulated pressure field and simulated strain field of the roof rock sample. Figure 5 Oil saturation at the Tx temperature line (200°C) (see Figure 8 There was no change in the entire simulation period, indicating that oil and gas were blocked at this location. Figure 6 Oil saturation at the Px pressure line (20 MPa) (see Fig. 9 There was no change in the entire simulation period, indicating that oil and gas were blocked at this location. Figure 7 Oil saturation at the medium strain line (10 MPa) (see Fig.10 There was no change in the whole simulation period, indicating that oil and gas were blocked at this location.

[0195] 19) Observation Figure 5 Oil saturation at 220°C (see Figure 8 (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 medium pressure line 25MPa (see Fig. 9(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 7 Oil saturation at the medium strain line of 20 MPa (see Fig.10 During the whole simulation period, there are obvious changes, indicating that the oil and gas are not blocked at this location.

[0196] 20) The thickness of the Tx temperature line is 145cm, the thickness of the Px pressure line is 176cm, and the thickness of the εx strain line is 179cm. The comprehensive comparison proves that the top plate with a thickness of 179cm meets the plugging requirements. The error between the numerical simulation results and the experimental results (180cm) is about 0.5%, so the numerical simulation verifies the reliability of the experimental results.

[0197] 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.

[0198] 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.

[0199] 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 plugging thickness required for in-situ mining of shale reservoirs, characterized in that: include: If it is determined that the adjacent layer of the shale reservoir is a mud shale layer, or the adjacent layer is a siltstone layer, and the minimum starting pressure of the siltstone layer is greater than the fracture pressure of the shale reservoir, the core section of the adjacent layer is used to prepare the rock sample; If it is determined that the adjacent layers of the shale reservoir are interlayers of siltstone and mud shale, the vertical superposition relationship of the siltstone layer and the mud shale layer, and the total thickness of the siltstone layer and the total thickness of the mud shale layer are determined according to the lithology vertical distribution characteristics of the adjacent layers within the set range, and the rock samples are prepared by an integrated molding method in combination with the measured properties of multiple siltstone samples and multiple mud shale samples; Arrange a heating device, a pressurizing device, a stress device and a group of sensors on the end surface of the rock sample close to the shale reservoir, and arrange multiple groups of sensors on the side of the rock sample at set intervals; The heating device is used to heat the rock sample until the temperature measured by the temperature sensor at the end face is a first set temperature. The pressurizing device is used to pressurize the rock sample until the pressure measured by the pressure sensor at the end face is a first set pressure. The stress device is used to gradually apply stress to the rock sample from small to large to the first set stress, and stabilize at the temperature, pressure and stress until the variation amplitude of the measured values ​​of each sensor is less than the set threshold value. According to the measured values ​​of the sensors, the critical position of the rock sample that meets the temperature, pressure and stress requirements is determined, and the distance from the critical position to the end face is used as the lower limit of the adjacent layer plugging thickness.

2. The method according to claim 1, characterized in that The method combines the measured properties of multiple siltstone samples and multiple shale samples to prepare rock samples by an integrated molding method, including: Based on the measured properties of multiple siltstone samples, a first formula for siltstone is prepared by experimental fitting, and based on the measured properties of multiple shale samples, a second formula for shale is prepared by experimental fitting; According to the upper and lower overlapping relationship, the total thickness of the siltstone layer and the total thickness of the shale layer, the first formula and the second formula, a rock sample is prepared by an integrated molding method.

3. The method according to claim 2, characterized in that The method of preparing a first formula of siltstone by experimental fitting based on measured properties of a plurality of siltstone samples comprises: The particle size distribution, mineral composition, fracture pressure, minimum starting pressure, fracture critical damage strain value and porosity of the rock samples of each siltstone layer within the set range of the adjacent layer are measured, and the average values ​​of the corresponding parameters are obtained by thickness-weighted averaging; Taking the average values ​​of the grain size distribution and the average values ​​of the mineral composition of the siltstone layer as the current formula, preparing the siltstone sample, adjusting the current formula until the errors between the porosity, fracture pressure, fracture critical damage strain value and minimum starting pressure of the currently prepared siltstone sample and the corresponding average values ​​meet the error threshold, and obtaining the first formula for preparing the siltstone; Accordingly, the second formula for preparing shale by experimental fitting based on the measured properties of the plurality of shale samples includes: The particle size distribution, mineral composition, TOC, kerogen initial hydrocarbon production temperature, porosity, critical damage strain value and fracture pressure of the rock samples of each shale layer within the set range of the adjacent layer are measured, and the average value of the corresponding parameters is obtained by thickness-weighted averaging; The average values ​​of the particle size distribution and the mineral composition of the shale layer are used as the current formula to prepare a shale sample, and the current formula is adjusted until the errors between the TOC, initial hydrocarbon production temperature of kerogen, porosity, critical damage strain value and rupture pressure of the currently prepared shale sample and the corresponding average values ​​meet the error threshold, thereby obtaining a second formula for preparing shale.

4. 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.

5. The method according to claim 4, characterized in that The first set temperature is the lowest temperature at which the kerogen conversion rate in the shale reservoir reaches 90%.

6. The method according to claim 5, characterized in that The first set pressure is the fracture pressure of the shale reservoir; The first set stress is the maximum underground principal stress at the burial depth of the bottom surface of the rock sample, or the maximum underground principal stress at the burial depth of the top surface of the rock sample.

7. The method according to claim 1, characterized in that If the adjacent layer is a shale layer, determining the critical position of the rock sample that meets the temperature, pressure and stress requirements includes: Determine a critical position in the rock sample where the temperature is lower than the initial hydrocarbon production temperature of the kerogen of the adjacent layer, the pressure is lower than the fracture pressure of the adjacent layer, and the strain is lower than the critical damage strain value of the fracture of the adjacent layer.

8. The method according to claim 1, characterized in that If the adjacent layer is a siltstone layer, determining the critical position of the rock sample that meets the temperature, pressure and stress requirements includes: A critical position in the rock sample where the pressure is less than the fracture pressure of the adjacent layer and the strain is less than the fracture critical damage strain value of the adjacent layer is determined.

9. The method according to any one of claims 1 to 8, characterized in that: The adjacent layers are the overlying strata and / or underlying strata of the shale reservoir.

10. The method according to claim 1, characterized in that If the adjacent layers are interbedded siltstone and shale, the step of determining the critical position where the rock sample meets the temperature, pressure and stress requirements includes: Based on the upper and lower superposition relationship of the siltstone layer and the shale layer in the adjacent layer, a critical position in the rock sample is determined where the temperature is lower than the initial hydrocarbon production temperature of the shale interlayer kerogen in the adjacent layer, the pressure is lower than the fracture pressure of the adjacent layer, and the strain is lower than the critical damage strain value of the fracture of the adjacent layer.

11. The method according to claim 10, characterized in that If the adjacent layer is the overlying stratum of the shale reservoir, the upper and lower superposition relationship of the siltstone layer and the mud shale layer in the adjacent layer is that the siltstone layer is on top, the kerogen initial hydrocarbon production temperature of the mud shale layer in the adjacent layer is Tx, the fracture pressure of the adjacent layer is Px, and the fracture critical damage strain value of the adjacent layer is εx, the critical position of determining that the rock sample meets the temperature, pressure and stress requirements includes: If the temperature in the shale layer drops to Tx, the pressure drops to Px and the strain drops to εx, the highest position among the position where the temperature is Tx, the position where the pressure is Px and the position where the strain is εx is determined as the critical position that meets the temperature, pressure and stress requirements; If the temperature in the mudstone layer drops to Tx, but the pressure does not drop to Px and the strain does not drop to εx at the same time, if the minimum starting pressure of the siltstone layer is greater than the fracture pressure Pr of the shale reservoir, the higher position of the position where the pressure is Px and the position where the strain is εx is taken as the critical position that meets the temperature, pressure and stress requirements; if the minimum starting pressure of the siltstone layer is not greater than the fracture pressure Pr of the shale reservoir, it is determined that the rock sample cannot be plugged; If the temperature in the shale layer is greater than Tx, the method is invalid.

12. The method according to claim 10, characterized in that If the adjacent layer is the overlying stratum of the shale reservoir, the upper and lower superposition relationship of the siltstone layer and the mud shale layer in the adjacent layer is that the siltstone layer is at the bottom, the kerogen initial hydrocarbon production temperature of the mud shale layer in the adjacent layer is Tx, the fracture pressure of the adjacent layer is Px, and the fracture critical damage strain value of the adjacent layer is εx, the critical position of determining that the rock sample meets the temperature, pressure and stress requirements includes: If the temperature in the siltstone layer drops to Tx, the pressure drops to Px, and the strain drops to εx, the bottom of the shale layer is determined to be the critical position that meets the temperature, pressure, and stress requirements; If the strain in the shale layer drops to εx, or the pressure drops to Px, or the temperature drops to Tx, the highest position among the position where the temperature is Tx, the position where the pressure is Px, and the position where the strain is εx is determined as the critical position that meets the temperature, pressure, and stress requirements.

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