A method for determining the plugging thickness required for in-situ mining of shale reservoirs

Abstract

The present invention discloses a method for determining the sealing thickness required for in-situ mining of a shale reservoir, comprising: if the adjacent layer of the shale reservoir is a mud shale layer, or a siltstone layer and the minimum starting pressure is greater than the reservoir fracture pressure, using the adjacent layer coring section to prepare a rock sample; if the adjacent layer is an interbedded siltstone and mud shale layer, preparing a rock sample based on the upper and lower superposition relationship of the siltstone layer and the mud shale layer and the total thickness of the two layers, combined with the measured properties of the rock sample; heating and pressurizing the rock sample to a first set temperature and a first set pressure at the end face, applying stress to the rock sample step by step to the first set stress, and stabilizing at the temperature, pressure and stress until the measurement values ​​of the side sensors are stable, determining the critical position of the rock sample that meets the temperature, pressure and stress requirements based on the measurement values ​​of the sensors, and using the distance from the rock sample to the end face as the lower limit of the adjacent layer sealing thickness. The method reasonably quantifies the lower limit of the top and bottom plate sealing thickness through the joint simulation of temperature, pressure and stress fields.

Description

Technical Field

[0001] The present invention relates to the field of petroleum geology and shale reservoir mining technology, and in particular to a method for determining the plugging thickness required for in-situ mining of a shale reservoir. Background Art

[0002] my country's medium- to low-maturity oil shale reserves hold enormous potential, and in-situ mining technology, as an effective approach to industrializing its production, is gaining increasing attention. In-situ mining involves directly heating the shale reservoir underground, causing it to crack underground. The resulting oil and gas is then extracted through production wells.

[0003] Within the same geological environment, the sealing strength of the caprock is highly correlated with its lithology. Various geological processes form caprocks of varying lithologies. Based on the caprocks that have been explored to date, gypsum, argillaceous rock, and dense carbonate are the predominant lithologies, with few examples of other lithologies being explored as caprocks.

[0004] Whether the overburden can effectively seal shale reservoirs during in-situ mining is one of the key factors in improving oil recovery. However, there is no effective means to evaluate the roof sealing performance during 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. Through a specific implementation method, a method for determining the sealing thickness required for in-situ mining of shale reservoirs is provided. The method can reasonably quantify the lower limit of the sealing thickness of the shale reservoir roof through the joint simulation of the temperature field, pressure field and stress field.

[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 the adjacent layers of the shale reservoir are determined to be interbedded siltstone and mud shale, the vertical superposition relationship of the siltstone layer and the mud shale layer, as well as the total thickness of the siltstone layer and the mud shale layer are determined based on the lithologic vertical distribution characteristics of the adjacent layers within the set range. The rock samples are prepared by an integrated molding method based on 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 set of sensors on the end face of the rock sample close to the shale reservoir, and arrange multiple sets of sensors on the side face 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 apply stress to the rock sample step by step from small to large to the first set stress, and stabilize at the temperature, pressure and stress until the change amplitude of the measured value of each sensor is less than the set threshold value. Based on 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 sealing thickness.

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

[0012] Based on the measured properties of multiple siltstone samples, a first formula for siltstone is prepared by experimental fitting; 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, preparing a first formula of siltstone by experimental fitting based on measured properties of a plurality of siltstone samples comprises:

[0015] Measuring the particle size distribution, mineral composition, fracture pressure, minimum initiation pressure, fracture critical damage strain value and porosity of rock samples of each siltstone layer within the set range of the adjacent layer, and obtaining the average value of the corresponding parameters by thickness-weighted averaging;

[0016] Using the average values ​​of the grain size distribution and the average values ​​of the mineral composition of the siltstone layer as the current formula, a siltstone sample is prepared, and the current formula is adjusted until the errors between the porosity, fracture pressure, critical damage strain value, and minimum initiation pressure of the currently prepared siltstone sample and the corresponding average values ​​meet the error threshold, thereby obtaining a first formula for preparing 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] Measuring the particle size distribution, mineral composition, TOC, kerogen initial hydrocarbon generation temperature, porosity, critical damage strain value and fracture pressure of rock samples of each shale layer within the set range of the adjacent layer, and obtaining the average value of the corresponding parameters by thickness-weighted averaging;

[0019] A shale sample is prepared using the average values ​​of the particle size distribution and the average values ​​of the mineral composition of the shale layer as the current formula. The current formula is adjusted until the errors between the TOC, initial kerogen hydrocarbon production temperature, porosity, critical damage strain value, and fracture 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 underburden stratum of the shale reservoir.

[0029] In some embodiments, if the adjacent layers are interbedded siltstone and mud 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 mudstone 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 kerogen in the mudstone 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.

[0031] In some embodiments, if the adjacent layer is an overlying stratum of the shale reservoir, the siltstone layer and the mud shale layer in the adjacent layer have a vertical superposition relationship of the siltstone layer on top, the initial hydrocarbon production temperature of the kerogen in the mud shale layer in the adjacent layer is Tx, the fracture pressure of the adjacent layer is Px, and the critical damage strain value of the fracture of the adjacent layer is εx, determining 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 shale layer drops to Tx, but the pressure does not drop to Px and the strain does not drop to εx at the same time, and 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 used 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 an overlying stratum of the shale reservoir, the siltstone layer and the mud shale layer in the adjacent layer have an upper and lower superposition relationship of the siltstone layer at the bottom, the initial hydrocarbon production temperature of the kerogen in the mud shale layer in the adjacent layer is Tx, the fracture pressure of the adjacent layer is Px, and the critical damage strain value of the fracture of the adjacent layer is εx, determining the critical position of the rock sample that 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 to be the critical position that meets the temperature, pressure, and stress requirements.

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

[0039] (1) The method for determining the sealing thickness required for in-situ mining of a shale reservoir provided in an embodiment of the present invention first determines the lithologic type of the adjacent layers of the shale reservoir. If the lithologic type 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 siltstone and mud shale are interbedded, a synthetic rock sample of siltstone layers and mud shale layers is prepared; a heating device is used to heat the rock sample and maintain the temperature near the end of the reservoir at a first set temperature; a pressurizing device is used to pressurize the rock sample and maintain the pressure near the end of the reservoir at a first set pressure; a stress device is used to apply stress to the end of the rock sample step by step from small to large to the first set stress, and stabilize at the stress until the measurement 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 sealing thickness of the adjacent layer. Through experimental methods, the lower limit of the sealing thickness of the adjacent layers of the shale reservoir is determined 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 required plugging thickness 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, as well as the total thickness of the siltstone and mudstone layers, based on the lithologic vertical distribution characteristics of adjacent layers of the shale reservoir within a set range. Based on the measured properties of the siltstone and mudstone, a roof rock sample is prepared in one piece. The prepared synthetic sample takes into account both the properties of mudstone and siltstone, as well as their vertical superposition relationship, and rationally simplifies the sample, thereby enabling the determination of the lower limit of the plugging thickness of the complex lithologic adjacent layers of mudstone and siltstone interbeds.

[0041] (3) It is currently generally believed that only mud shale 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 proposes that if the adjacent layer of the shale reservoir is a siltstone layer with a single lithology, or an interbedded layer of siltstone and mud shale, 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) The method for determining the sealing thickness required for in-situ mining of shale reservoirs provided in an embodiment of the present invention is as follows: 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 the 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 to the maximum underground principal stress at the bottom buried depth, and 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 underground principal stress at the end buried depth, the lower limit of the roof sealing 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, existing technologies often only focus on the sealing properties of the roof, while ignoring the sealing function of the floor. However, for in-situ heating and production of shale reservoirs, poor floor sealing performance will still lead to oil and gas loss, affecting the recovery rate. The method for determining the required sealing thickness for in-situ production of shale reservoirs provided in the embodiments of the present invention not only considers the sealing properties of the roof, but also fully considers the sealing properties of the floor, thus ensuring the reliability of the determination of the sealing performance and further providing a guarantee for improving the recovery rate.

[0044] Other features and advantages of the present invention will be described in the following description, and in part will become apparent from the description, or will be understood by practicing the present invention. The purposes and other advantages of the present invention can be realized and obtained by the structures particularly pointed out in the written description, claims, and drawings.

[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 Example 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 Example 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 Example 3 of the present invention;

[0050] Figure 4 This is a schematic diagram of the axial cross-section of the roof rock sample in Example 4 of the present invention;

[0051] Figure 5 This is a temperature field simulation diagram in Example 4 of the present invention;

[0052] Figure 6 This is a pressure field simulation diagram in Example 4 of the present invention;

[0053] Figure 7 This is a strain field simulation diagram in Example 4 of the present invention;

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

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

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

[0057] Exemplary embodiments of the present disclosure will be described in more detail below with reference to the accompanying drawings. Although exemplary embodiments of the present disclosure are shown in the accompanying drawings, it should be understood that the present disclosure can be implemented in various forms and should not be limited by the embodiments set forth herein. Rather, these embodiments are provided to enable a more thorough understanding of the present disclosure and to fully convey the scope of the present disclosure to those skilled in the art.

[0058] It should be understood that the terms described herein are intended only to describe particular embodiments and are not intended to limit the present invention. In addition, for numerical ranges herein, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Each smaller range between any intermediate value within a stated value or stated range and any other stated value or intermediate value within the stated range is also encompassed by the present invention. The upper and lower limits of these smaller ranges may be independently included or excluded within the scope.

[0059] Unless otherwise indicated, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which the invention belongs. Although the present invention describes only preferred methods and materials, any methods and materials similar or equivalent to those described herein may also be used in the implementation or testing of the present invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials related to the documents. In the event of any conflict with any incorporated document, the content of this specification shall prevail.

[0060] In the description of the present invention, it should be noted that the terms “include”, “including”, “have”, “contain”, etc. are all open terms, which mean including but not limited to.

[0061] During their work, the inventors discovered that the existing technology had the problem of difficulty in effectively evaluating the roof sealing performance during the heating and mining process of shale reservoirs. After further research and development, the inventors found that due to the different heat conduction conditions of the roof and floor of the shale reservoir during the in-situ heating and mining process of the shale reservoir, the difference in their sealing thickness is affected; the roof and floor are subjected to different stresses due to their different burial depths, which also affects the difference in their sealing 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 roof and floor of the shale reservoir to be subjected to fluid pressure, which also affects the difference in their sealing thickness. Therefore, through the joint simulation experiment of temperature field, pressure field and stress field, the sealing thickness of the roof and floor can be reasonably determined. In addition, it is generally believed that only mud shale can produce a sealing effect during the in-situ mining of shale reservoirs. However, the inventors found that the complex lithology of siltstone layers, or interlayers of mud shale and siltstone, may also produce a sealing effect during the in-situ mining of shale reservoirs. An 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 the temperature field, pressure field and stress field.

[0062] Example 1

[0063] The first embodiment 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 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, a rock sample is prepared using the coring section of the adjacent layer.

[0065] The adjacent layers are the overlying and / or underlying strata of the shale reservoir. Specifically, the lower limit of the plugging thickness of the shale reservoir roof, the lower limit of the plugging thickness of the shale reservoir floor, or both the roof and floor of the shale reservoir is determined based on actual research needs.

[0066] According to empirical data, the sealing thickness of adjacent layers during in-situ mining of shale reservoirs is typically within 300-400 centimeters. Therefore, the length (thickness) of the rock sample should be no less than 500 cm. Any thicker increases the difficulty and cost of the experiment; any thinner will easily fall below the actual sealing thickness lower limit, resulting in experimental failure (unable to measure the adjacent layer sealing thickness required for shale in situ). That is, the range corresponding to the prepared rock sample thickness is within 500 cm. 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 interbedded siltstone and mud shale, the upper and lower superposition relationship of the siltstone layer and the mud shale layer, as well as the total thickness of the siltstone layer and the total thickness of the mud shale layer are determined based on the vertical distribution characteristics of the lithology of the adjacent layers within the set range. Combined with the measured properties of multiple siltstone samples and multiple mud shale samples, rock samples are prepared by one-piece molding.

[0068] Preferably, for the overlying strata, the setting range is within 500 cm of thickness from the position closest to the top surface of the shale reservoir; for the underlying strata, the setting range is within 500 cm of 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 rock samples by integral 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 of siltstone is prepared by experimental fitting; based on the measured properties of multiple shale samples within the set range of adjacent layers, a second formula of shale is prepared by experimental fitting.

[0072] In some embodiments, fitting the first formula for preparing siltstone may include: measuring the particle size distribution, mineral composition, porosity, fracture pressure, critical damage strain value for fracture, and minimum starting pressure of rock samples of each siltstone layer within a set range of adjacent formations, and obtaining the average value of the corresponding parameters by thickness-weighted averaging; preparing the siltstone sample using the average value of the particle size distribution and the average value 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 damage strain value for fracture, 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-sized samples can be synthesized first, the porosity of the synthesized samples can be measured, and the results can be 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 the 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 for 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; preparing mud shale samples using 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, and adjusting the current formula until the errors between the TOC, kerogen initial hydrocarbon production temperature, porosity, critical damage strain value for 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 and second formulas, 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 thickness-weighted averaging the measurement results of the corresponding rock samples.

[0076] Step S122: preparing a rock sample by integral molding 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 portion of an actual underground rock formation, while the rock sample obtained in step S12 is a synthetic simulated rock sample. Both samples can have the same cross-sectional area (e.g., a cylindrical shape with a diameter of 5 cm); preferably, their length (thickness) is 500 cm.

[0078] The sides of the rock sample are wrapped with heat-insulating material to prevent heat from being dissipated to the surroundings during heating. The pressure resistance of the heat-insulating 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 as far as possible into the rock sample.

[0083] The 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 set 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 change amplitude of the measured value of each sensor is less than the set threshold value, based on 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 using 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 conducted on each sample to measure the lowest temperature at which the kerogen conversion rate reaches a set conversion rate threshold, and the minimum value of the multiple measured minimum temperatures is determined as the first set temperature.

[0091] Furthermore, the first set temperature is the lowest temperature at which the kerogen conversion rate in the shale reservoir reaches 90%, which is usually 290-330°C.

[0092] The kerogen conversion rate reaches 90%. At this temperature, the reservoir is almost completely converted to hydrocarbons, achieving maximum oil and gas production. That is, this temperature is the highest temperature at which the reservoir can be heated during the in-situ heating and production process of actual shale reservoirs. Therefore, the setting of this temperature ensures the safety and rationality of the determined lower limit of the roof sealing thickness.

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

[0094] Taking the rock sample of the overlying stratum (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 slowly heat (no more than 20°C / day), with the maximum temperature of the heat source between 400 and 650°C. Adjust the heat source power to keep the temperature at the bottom of the roof rock sample constant at T0. Use a pressurizing device to pressurize the bottom of the roof rock sample, using fluid boosting at a boosting rate of no more than 300KPa / day (the specific value is flexibly set according to the on-site construction conditions) to keep the pressure at the bottom of the roof rock sample constant at P0. At the same time, use a stress device to gradually apply stress to the bottom of the roof rock sample, increasing by 1MPa for 5 minutes at a time, and finally applying a constant stress of Ex. Furthermore, try to achieve the simultaneous achievement of stress Ex, pressure P0, and temperature T0. The temperature T0, pressure P0, and stress Ex are kept constant for at least 30 minutes until the change in 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 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 interbed of siltstone and mud shale, can be the average value of the fracture pressure of the siltstone layer and the mud shale layer by weighted average of their thickness;

[0100] The critical damage strain value εx of the adjacent layer. If the adjacent layer is an interbed of siltstone and shale, it can be the average value of the thickness-weighted average of the critical damage strain values ​​of the siltstone layer and the shale layer;

[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 method varies 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 of the rock sample that meets the temperature, pressure and stress requirements, including determining the critical position in the adjacent layer 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.

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

[0114] Determine the location 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 location 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 mud 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 mud 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 mud 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 shale reservoir as an example, the following two situations can be included:

[0122] 1. The superposition relationship is that the siltstone layer is on top.

[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 positions where the temperature is Tx, the pressure is Px, and 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 superposition relationship 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 sealing 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 mud shale, a synthetic rock sample of superimposed siltstone layers and mud shale layers is prepared; a heating device is used to heat the rock sample and maintain it at a first set temperature near the end of the reservoir; a pressurizing device is used to pressurize the rock sample and maintain it at a first set pressure near the end of the reservoir; a stress device is used to apply stress to the end of the rock sample step by step from small to large to the first set stress, and stabilize it at this stress until the measurement 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 sealing thickness of the adjacent layer. Through experimental methods, the lower limit of the sealing thickness of the adjacent layers of the shale reservoir is determined 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 required plugging thickness for in-situ mining of shale reservoirs provided in Example 1 of the present invention determines the vertical superposition relationship of siltstone and mudstone layers, as well as the total thickness of the siltstone and mudstone layers, based on the lithologic vertical distribution characteristics of adjacent layers of the shale reservoir within a set range. Based on the measured properties of the siltstone and mudstone, a roof rock sample is prepared in one piece. The prepared synthetic sample takes into account both the properties of mudstone and siltstone, as well as their vertical superposition relationship, rationally simplifying the sample and enabling the determination of the lower limit of the plugging thickness for complex lithologic adjacent layers of interbedded mudstone and siltstone.

[0132] It is generally believed that only mud shale 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 Example 1 of the present invention suggests that if the adjacent layer of the shale reservoir is a siltstone layer with a single lithology, or an interbedded layer of siltstone and mud shale, 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] Example 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, where 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 thermal insulation and 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 set of sensors includes a temperature sensor, a pressure sensor, and a strain sensor. The temperature sensors, pressure sensors, and strain sensors of each set arranged on the side of the rock sample have the same measurement position in the longitudinal direction.

[0138] A bottom rock sample of the same cross-sectional area (e.g., cylindrical with a diameter of 5 cm) is prepared from a cored section of the underlying stratum of the shale reservoir. The length (thickness) of the bottom 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 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.

[0140] Specifically, the top surface of the bottom plate rock sample refers to the side closest to the shale reservoir at the corresponding original underground position.

[0141] Each set of temperature sensors, pressure sensors and strain sensors are arranged axially on the side of the bottom plate rock sample. The set interval 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 change amplitude of the measured values ​​of each sensor is less than the set threshold, and determining the highest position at which the temperature of the bottom plate rock sample is not higher than the second set temperature, the pressure is not higher than the second set pressure, and the strain is not higher than the second set strain based on 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 through rock fracture pressure experiments. Therefore, if the rock mechanical properties of the overburden and underlying rock formations are basically the same, the fracture pressure of the overburden formation can also be approximated as the fracture pressure of the underlying rock formation.

[0145] The second set stress is the maximum principal stress underground at the depth of burial of the top surface of the bottom plate rock sample, which is obtained through calculation.

[0146] The second set strain is the critical damage strain of the underlying rock stratum, which can also be determined through rock fracture experiments. Therefore, if the rock mechanical properties of the overburden and underlying rock strata are basically the same, the critical damage strain of the overburden stratum can also be approximated as the critical damage strain of the underlying rock stratum.

[0147] For example, with the second set temperature (Tx), the second set pressure (Px), the second set stress (Ex), and the second set strain (εx), a heating device (heat source) is used to slowly heat the sample (no more than 20°C / day), with the maximum temperature of the heat source between 400°C and 650°C. The heat source power is adjusted to maintain a constant temperature of T0 at the top of the bottom plate rock sample. Simultaneously, a pressurizing device is used to pressurize the top of the bottom plate rock sample, using fluid boosting at a rate of no more than 300 kPa / day (the specific value is flexibly set based on on-site construction conditions), to maintain a constant pressure of P0 at the top of the bottom plate rock sample. A stress device is used to gradually apply stress to the top of the bottom plate rock sample, increasing it by 1 MPa for 5 minutes, until the final applied stress is constant at Ex. Furthermore, the pressure reaching P0, the stress reaching Ex, and the temperature reaching T0 are achieved simultaneously. The temperature is kept constant at T0, the pressure is kept constant at P0, and the stress is kept constant at Ex for at least 30 minutes until the variation of the measured values ​​of each sensor is less than the set threshold value. That is, after the temperature, pressure and strain are stable, the measured values ​​of each 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 strain of the bottom plate rock sample begins to drop to εx; if the currently collected strain begins to be less than εx (the first strain less than εx), based on the currently collected strain and the previous collected strain and the position of the current strain sensor and the position of the previous strain sensor, the third highest position where the strain of the bottom plate rock sample is not higher than εx is determined by the proportional method.

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

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

[0154] Example 3

[0155] A third embodiment of the present invention provides another method for determining the required sealing thickness for in-situ mining of a shale reservoir, specifically a method for determining the lower limit of the floor sealing thickness for a shale reservoir, where the underlying stratum is a siltstone formation. The method determines whether the shale reservoir fracture pressure is less than the minimum triggering pressure of the underlying siltstone formation. If so, the following steps for determining the lower limit of the floor sealing thickness are performed. If not, the underlying stratum is determined to be unsealed during 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 sealing 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 thermal insulation and 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 measurement 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] A bottom rock sample of the same cross-sectional area (e.g., cylindrical with a diameter of 5 cm) is prepared from a cored section of the underlying stratum of the shale reservoir. The length (thickness) of the bottom 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 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.

[0161] Specifically, the top surface of the bottom plate rock sample refers to the side closest to the shale reservoir at the corresponding original underground position.

[0162] Each set of pressure sensors and strain sensors is arranged axially on the side of the bottom plate rock sample. The set interval 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 as measured by a top temperature sensor, using a pressurizing device to pressurize the bottom plate rock sample to a second set pressure as measured by a top pressure sensor, using a stress device 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 measured value changes of each pressure sensor and strain sensor are less than the set threshold, and determine the highest position where the pressure of the bottom plate rock sample 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 through rock fracture pressure experiments. Therefore, if the rock mechanical properties of the overburden and underlying rock formations are basically the same, the fracture pressure of the overburden formation can also be approximated as the fracture pressure of the underlying rock formation.

[0165] The second set stress is the maximum principal stress underground at the depth of burial of the top surface of the bottom plate rock sample, which is obtained through calculation.

[0166] The second set strain is the critical damage strain of the underlying rock stratum, which can also be determined through rock fracture experiments. Therefore, if the rock mechanical properties of the overburden and underlying rock strata are basically the same, the critical damage strain of the overburden stratum can also be approximated as the critical damage strain of the underlying rock stratum.

[0167] For example, with the second set pressure Px, the second set stress Ex, and the second set strain εx, a heating device (heat source) is used to slowly heat the sample (no more than 20°C / day), with the maximum temperature of the heat source between 400°C and 650°C. The heat source power is adjusted to maintain a constant temperature of T0 at the top of the bottom plate rock sample. Simultaneously, a pressurizing device is used to pressurize the top of the bottom plate rock sample, using fluid boosting at a rate of no more than 300 kPa / day (the specific value is flexibly set based on on-site construction conditions), to maintain a constant pressure of P0 at the top of the bottom plate rock sample. A stress device is used to gradually apply stress to the top of the bottom plate rock sample, increasing it by 1 MPa for 5 minutes, until the final applied stress is constant at Ex. Furthermore, the pressure reaching P0, the stress reaching Ex, and the temperature reaching T0 are achieved simultaneously. The temperature is kept constant at T0, the pressure is kept constant at P0, and the stress is kept constant at Ex for at least 30 minutes until the variation of the measured values ​​of each sensor is less than the set threshold value, that is, after the 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 strain sensor can be collected in sequence from the top to the bottom 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 strain of the bottom plate rock sample begins to drop to εx; if the currently collected strain begins to be less than εx (the first strain less than εx), based on the currently collected strain and the previous collected strain and the position of the current strain sensor and the position of the previous strain sensor, the second highest position where the strain of the bottom plate rock sample is not higher than εx is determined by the proportional method.

[0170] The lower of the first highest position and the second highest position is used 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: determining the lower limit of the bottom plate plugging thickness of the shale reservoir according to the distance from the position to the top surface.

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

[0173] Existing research on the sealing properties of shale reservoirs often focuses solely on the sealing properties of the roof, while ignoring the sealing function of the floor. However, for in-situ mining of shale reservoirs, poor floor sealing performance can still lead to oil and gas loss, impacting recovery efficiency. The methods for determining the required sealing thickness for in-situ mining of shale reservoirs, provided in Examples 2 and 3 of the present invention, fully consider the sealing properties of the floor, ensuring the reliability of the sealing performance determination and further guaranteeing an increase in recovery efficiency.

[0174] The above three embodiments can be applied individually; 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. Only when the top and bottom plate thicknesses of the shale reservoir both meet the corresponding lower limits of the plugging thickness can it be determined that the plugging requirements are met.

[0175] Example 4

[0176] A fourth embodiment of the present invention provides a specific application of a method for determining a lower limit of the roof plugging thickness of a shale reservoir, and verifies its accuracy through numerical simulation, including the following steps:

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

[0178] 2) The particle size distribution, mineral composition, initial kerogen hydrocarbon generation 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, based on the superposition relationship and thickness, a roof rock sample containing a homogeneous siltstone layer and a homogeneous mudstone layer is synthesized at one time (the mudstone layer thickness is equal to 400 cm, the siltstone layer thickness is equal to 100 cm, and the cumulative deviation of the above parameters from the design value does not exceed 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 (90% conversion temperature of kerogen) of the reservoir rock sample at 300℃.

[0183] 7) The Tx (initial hydrocarbon generation 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 approximately 20 MPa.

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

[0187] 11) Wrap the roof rock sample with a pressure-resistant steel sleeve with a pressure resistance of not less than 80 MPa, and then wrap it with rock wool as 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. Place the roof rock sample in the experimental device.

[0188] 12) Place a unidirectional heat source point at the bottom of the roof rock sample, arrange temperature sensors and strain sensors starting from the bottom, and arrange several groups of temperature sensors and strain sensors along the axial direction of the roof rock sample at intervals of 10 cm.

[0189] 13) Heat the bottom of the roof rock sample with a unidirectional point heat source at a rate of 20°C / day, with a peak temperature of 300°C (T0). Apply fluid pressure to the bottom of the roof rock sample at a rate of 300 kPa / day, with a peak pressure of 50 MPa. Apply a rigid stress to the bottom of the roof rock sample at a rate of 1 MPa / 5 minutes, with a peak stress of 30 MPa (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 (when 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 location where the temperature Tx is measured to the bottom of the roof rock sample is 140 cm, the distance from the location where the calculated pressure Px is measured to the thickness of the sample bottom is 170 cm, and the distance from the location 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 samples and experimental conditions was established. The mudstone was 400 cm thick, with the same TOC, porosity, T0, Tx, P0, Px, Pr, εx, and mineral composition as the artificial samples used in the experiment. The siltstone was 100 cm thick, with the same porosity, P0, Px, Ps, εx, and mineral composition as the artificial samples used in the experiment. The kerogen activation energy parameters for the mudstone were set so that the Tx (initial kerogen hydrocarbon production temperature) for the roof rock sample was 200°C. The Px (fracture pressure) for the roof mudstone was set to 22 MPa, and the Px (fracture pressure) for the siltstone sample was set to 20 MPa. The critical damage strain εx for the mudstone was set to 12 MPa. The critical damage strain εx for the siltstone was set to 10 MPa.

[0193] 17) Keep the temperature at the bottom of the roof rock sample constant at T0 (300°C), the pressure constant at P0 (50 MPa), and the stress constant at Ex (30 MPa), complete the numerical simulation of the temperature field, pressure field, and stress field, and wait until the grid temperature, pressure, and pressure deformation are stable.

[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 during 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 Figure 9 There was no change during 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 Figure 10 There was no change during the entire 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), obvious changes occurred during the entire simulation period, indicating that oil and gas were not blocked at this location. Figure 6 Oil saturation at the medium pressure line 25MPa (see Figure 9(As shown), obvious changes occurred during the entire simulation period, indicating that oil and gas were not blocked at this location. Figure 7 Oil saturation at the median strain line of 20 MPa (see Figure 10 During the entire 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 145 cm, the Px pressure line is 176 cm, and the εx strain line is 179 cm. A comprehensive comparison shows that a roof thickness of 179 cm meets the plugging requirements. The error between the numerical simulation results and the experimental results (180 cm) is approximately 0.5%, thus verifying the reliability of the experimental results.

[0197] It should be understood that the specific order or hierarchy of steps in the disclosed processes is an example of an exemplary method. Based on design preferences, it should be understood that the specific order or hierarchy of steps in the process can be rearranged without departing from the scope of the present disclosure. The accompanying method claims present elements of the various steps in an exemplary order and are not intended to be limited to the specific order or hierarchy described.

[0198] In the foregoing detailed description, various features are grouped together in a single embodiment to simplify the disclosure. This method of disclosure should not be interpreted as reflecting an intention that embodiments of the claimed subject matter require more features than are expressly recited in each claim. On the contrary, as reflected in the appended claims, the invention comprises less than all the features of any individual disclosed embodiment. The appended claims are therefore hereby expressly incorporated into the detailed description, with each claim standing on its own as a separate preferred embodiment of the invention.

[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 may be further combined and arranged. Therefore, the embodiments described herein are intended to cover all such changes, modifications and variations that fall within the scope of protection of the appended claims. In addition, with respect to the term "comprising" used in the specification or claims, the word is encompassed in a manner similar to the term "including," as explained in terms of "including," used as a transitional word in the claims. In addition, any term "or" used in the specification of the claims is intended to mean "non-exclusive or." The terms "first" and "second" are used for descriptive purposes and are not to be understood as indicating or implying relative importance.

Claims

1. A method for determining the 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 the adjacent layers of the shale reservoir are determined to be interbedded siltstone and mud shale, the vertical superposition relationship of the siltstone layer and the mud shale layer, as well as the total thickness of the siltstone layer and the mud shale layer are determined based on the lithologic vertical distribution characteristics of the adjacent layers within the set range. The rock samples are prepared by an integrated molding method based on the measured properties of multiple siltstone samples and multiple mud shale samples. Arrange a heating device, a pressurizing device, a stress device and a set of sensors on the end face of the rock sample close to the shale reservoir, and arrange multiple sets of sensors on the side face of the rock sample at set intervals; The rock sample is heated by the heating device until the temperature measured by the temperature sensor at the end face is a first set temperature. The rock sample is pressurized by the pressurizing device until the pressure measured by the pressure sensor at the end face is a first set pressure. The stress device is used to apply stress to the rock sample step by step from small to large to the first set stress, and stabilize at the temperature, pressure and stress until the change amplitude of the measured value of each sensor is less than the set threshold value. Based on 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 sealing thickness.

2. The method according to claim 1, wherein The method of combining the measured properties of multiple siltstone samples and multiple shale samples to prepare rock samples by an integrated molding method includes: Based on the measured properties of multiple siltstone samples, a first formula for siltstone is prepared by experimental fitting; 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, wherein The method of preparing a first formula of siltstone by experimental fitting based on measured properties of a plurality of siltstone samples comprises: Measuring the particle size distribution, mineral composition, fracture pressure, minimum initiation pressure, fracture critical damage strain value and porosity of rock samples of each siltstone layer within the set range of the adjacent layer, and obtaining the average value of the corresponding parameters by thickness-weighted averaging; Using the average values ​​of the grain size distribution and the average values ​​of the mineral composition of the siltstone layer as the current formula, a siltstone sample is prepared, and the current formula is adjusted until the errors between the porosity, fracture pressure, critical damage strain value, and minimum initiation pressure of the currently prepared siltstone sample and the corresponding average values ​​meet the error threshold, thereby obtaining a first formula for preparing siltstone; Accordingly, the second formula for preparing shale by experimental fitting based on the measured properties of the plurality of shale samples includes: Measuring the particle size distribution, mineral composition, TOC, kerogen initial hydrocarbon generation temperature, porosity, critical damage strain value and fracture pressure of rock samples of each shale layer within the set range of the adjacent layer, and obtaining the average value of the corresponding parameters by thickness-weighted averaging; A shale sample is prepared using the average values ​​of the particle size distribution and the average values ​​of the mineral composition of the shale layer as the current formula. The current formula is adjusted until the errors between the TOC, initial kerogen hydrocarbon production temperature, porosity, critical damage strain value, and fracture 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, wherein The first set temperature is the lowest temperature at which the kerogen conversion rate in the shale reservoir reaches a set conversion rate threshold.

5. The method according to claim 4, wherein 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, wherein 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, wherein 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, wherein 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, wherein: The adjacent layers are the overlying strata and / or underlying strata of the shale reservoir.

10. The method according to claim 1, wherein If the adjacent layers are interbedded siltstone and mud shale, 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 mudstone 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 kerogen in the mudstone 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.

11. The method according to claim 10, wherein If the adjacent layer is the overlying stratum of the shale reservoir, the siltstone layer and the mud shale layer in the adjacent layer have an upper and lower superposition relationship of the siltstone layer on top, the initial hydrocarbon production temperature of the kerogen in the mud shale layer in the adjacent layer is Tx, the fracture pressure of the adjacent layer is Px, and the critical damage strain value of the fracture of the adjacent layer is εx, determining the critical position of the rock sample that 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 shale layer drops to Tx, but the pressure does not drop to Px and the strain does not drop to εx at the same time, and 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 used 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, wherein If the adjacent layer is the overlying stratum of the shale reservoir, the siltstone layer and the mud shale layer in the adjacent layer have an upper and lower superposition relationship of the siltstone layer at the bottom, the initial hydrocarbon production temperature of the kerogen in 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, determining the critical position of the rock sample that 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 to be the critical position that meets the temperature, pressure, and stress requirements.

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