Method for determining plugging thickness of complex lithologic layer based on simplified lithologic combination

Abstract

The invention discloses a method for determining the plugging thickness of a complex lithologic layer based on simplified lithologic combination, and the method comprises the steps: determining the vertical superposition relation of a silty rock layer and a shale layer and the total thickness of the silty rock layer and the shale layer according to the lithologic longitudinal distribution characteristics of an overlying stratum; integrally forming and preparing a roof rock sample by combining the properties of siltstone and shale; arranging a plurality of groups of temperature sensors, pressure sensors and strain sensors on the side surface of the rock sample at set intervals; heating the rock sample until the bottom temperature is the set temperature, pressurizing until the bottom pressure is the set pressure, applying stress to the bottom of the rock sample step by step from small to large until the set stress, and stabilizing at the temperature, the pressure and the stress until the measured value of the sensor is stable; determining the lower limit of the roof plugging thickness according to the measured value of each sensor and the up-and-down superposition relationship; and similarly, determining the bottom plate plugging thickness lower limit. According to the method, through simplified lithology and combined simulation of a temperature field, a pressure field and a stress field, the lower limit of the plugging thickness of the shale reservoir complex lithology roof and floor is reasonably quantified.

Description

Technical Field

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

[0006] The embodiment of the present invention provides a method for determining the sealing thickness of a complex lithology layer based on a simplified lithology combination, wherein the complex lithology layer is an overlying stratum of a shale reservoir, and the complex lithology layer is an interlayer of siltstone and mudstone, and the method comprises:

[0007] According to the lithology vertical distribution characteristics of the overlying strata within the set range, determine 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;

[0008] Based on the measured properties of the plurality of siltstone samples and the plurality of shale samples, and according to the upper and lower overlapping relationship and the total thickness of the siltstone layer and the total thickness of the shale layer, a roof rock sample is prepared by an integrated molding method;

[0009] A first heating device, a first pressurizing device, a first stress device and a group of first sensors are arranged on the bottom surface of the roof rock sample, and multiple groups of first sensors are arranged on the side of the roof rock sample at a first set interval, wherein the first sensor includes a first temperature sensor, a first pressure sensor and a first strain sensor; the roof rock sample is heated by the first heating device to a first set temperature at which the measured temperature of the first temperature sensor at the bottom is measured, the roof rock sample is pressurized by the first pressurizing device to a first set pressure at which the measured pressure of the first pressure sensor at the bottom is measured, and the first stress device is used to gradually apply stress to the bottom of the roof rock sample from small to large to a first set stress, and stabilize at the temperature, the pressure and the stress until the variation amplitude of the measured values ​​of each first sensor is less than the set threshold value, and the lower limit of the roof plugging thickness is determined according to the measured values ​​of the first sensors and the upper and lower overlapping relationship.

[0010] In some embodiments, the method of preparing the roof rock sample by an integrated molding method based on the measured properties of the plurality of siltstone samples and the plurality of shale samples and according to the upper and lower overlapping relationship and the total thickness of the siltstone layer and the total thickness of the shale layer includes:

[0011] 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;

[0012] 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 roof rock sample is prepared by an integrated molding method.

[0013] In some embodiments, the preparing a first formula of siltstone by experimental fitting based on measured properties of a plurality of siltstone samples comprises:

[0014] Measuring the particle size distribution, mineral composition, fracture pressure, minimum starting pressure, fracture critical damage strain value and porosity of rock samples of each siltstone layer within the set range of the overlying stratum, and obtaining the average value of the corresponding parameters by thickness-weighted averaging;

[0015] 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;

[0016] Accordingly, the second formula for preparing shale by experimental fitting based on the measured properties of the plurality of shale samples includes:

[0017] 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 are measured, and the average values ​​of the corresponding parameters are obtained by thickness-weighted averaging;

[0018] 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.

[0019] 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.

[0020] In some embodiments, the first set temperature is the lowest temperature at which the kerogen conversion rate in the shale reservoir reaches 90%.

[0021] In some embodiments, the first heating device is a one-way heating device;

[0022] The first heating device is located at the center of the bottom surface of the top plate rock sample;

[0023] The area of ​​the bottom surface of the top plate rock sample directly heated by the first heating device does not exceed 1 / 4 of the bottom surface area.

[0024] In some embodiments, the first set pressure is the fracture pressure of the shale reservoir; the first set stress is the maximum principal stress underground at the buried depth of the bottom surface of the roof rock sample.

[0025] In some embodiments, if the upper and lower stacking relationship is that the siltstone layer is on the upper side, the kerogen initial hydrocarbon production temperature of the shale layer in the top plate rock sample is Tx,

[0026] The fracture pressure of the roof rock sample is Px, the critical fracture damage strain value of the roof rock sample is εx, and the lower limit of the roof plugging thickness is determined according to the measurement value of the first sensor and the upper and lower superposition relationship, including:

[0027] If the temperature in the shale layer drops to Tx, the pressure drops to Px, and the strain drops to εx, determine 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, and determine the distance from the position to the bottom surface of the roof rock sample as the lower limit of the roof plugging thickness;

[0028] 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, and the minimum starting pressure of the siltstone layer is greater than the fracture pressure Pr of the shale reservoir, the distance from the higher position of the position where the pressure is Px and the position where the strain is εx to the bottom surface of the roof rock sample is determined as the lower limit of the roof plugging thickness; 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 roof rock sample cannot be plugged;

[0029] If the temperature in the shale layer is greater than Tx, the method is invalid.

[0030] In some embodiments, if the upper and lower superposition relationship is that the siltstone layer is at the bottom, the kerogen initial hydrocarbon production temperature of the shale layer in the roof rock sample is Tx, the fracture pressure of the roof rock sample is Px, and the critical damage strain value of the fracture of the roof rock sample is εx, the lower limit of the roof plugging thickness is determined according to the measurement value of the first sensor and the upper and lower superposition relationship, including:

[0031] If the temperature in the siltstone layer drops to Tx, the pressure drops to Px, and the strain drops to εx, the thickness of the siltstone layer is determined to be the lower limit of the roof plugging thickness;

[0032] If the strain in the shale layer drops to εx, or the pressure drops to Px, or the temperature drops to Tx, determine 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, and determine the distance from this position to the bottom surface of the roof rock sample as the lower limit of the roof sealing thickness.

[0033] The beneficial effects of the above technical solution provided by the embodiment of the present invention include at least:

[0034] (1) The method for determining the plugging thickness of a complex lithology layer based on a simplified lithology combination provided in an embodiment of the present invention is to prepare a roof rock sample by integral molding, heat the roof rock sample to a first set temperature using a first heating device, pressurize the roof rock sample to a first set pressure using a first pressurizing device, and apply stress to the bottom of the roof rock sample step by step from small to large to the first set stress using a first stress device, and stabilize at the temperature, pressure and stress until the measured values ​​of each sensor are stable, and determine the lower limit of the plugging thickness of the roof rock sample based on the measured values ​​of the sensors and the upper and lower overlapping relationship between the siltstone layer and the mudstone layer. The lower limit of the roof plugging thickness of the shale reservoir is determined by experimental methods based on the simulation of the temperature field, pressure field and stress field, and the roof plugging conditions during the in-situ exploitation of the shale reservoir are specifically quantified, which can effectively guide production and improve the economic benefits of in-situ exploitation of shale oil and gas.

[0035] (2) The method for determining the sealing thickness of a complex lithology layer based on a simplified lithology combination provided by an embodiment of the present invention determines the vertical superposition relationship between the siltstone layer and the mudstone layer, and the total thickness of the siltstone layer and the total thickness of the mudstone layer according to the lithology vertical distribution characteristics of the overlying strata within a set range, and prepares a roof rock sample in one piece based on the measured properties of the siltstone and mudstone. The prepared synthetic sample takes into account both the properties of mudstone and siltstone and the vertical superposition relationship between the two, and reasonably simplifies the sample, so that the determination of the lower limit of the sealing thickness of the complex lithology roof with interlayers of mudstone and siltstone can be achieved.

[0036] (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 of complex lithology layers based on simplified lithology combinations provided in the embodiments of the present invention suggests that if the overlying rock layer of the shale reservoir is 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.

[0037] (4) The method for determining the sealing thickness of a complex lithology layer based on a simplified lithology combination provided by an embodiment of the present invention, during the experiment, the temperature of the bottom of the roof is kept constant at the lowest temperature in the reservoir at which the kerogen conversion rate reaches 90%. At this temperature, the reservoir almost completes the conversion to hydrocarbon generation and reaches the maximum oil and gas production, that is, this temperature is the highest temperature at which the reservoir may be heated during the in-situ heating and exploitation of an actual shale reservoir; the pressure at the bottom of the roof is kept constant at the fracture pressure of the shale reservoir, that is, the maximum pressure that may be encountered during the in-situ heating and exploitation; stress is applied to the bottom of the roof rock sample step by step from small to large to the maximum principal stress underground at the depth of the bottom surface burial, and stabilized at this stress, that is, the maximum stress that may be encountered during the in-situ heating and exploitation; on the basis that the temperature at the bottom of the roof is kept constant at the lowest temperature in the shale reservoir at which the kerogen conversion rate reaches 90%, the pressure is kept constant at the fracture pressure of the shale reservoir, and the stress is kept constant at the maximum principal stress underground at the depth of the bottom surface burial, the lower limit of the roof sealing thickness is determined according to the measurement value of the sensor and the upper and lower overlapping relationship of the siltstone layer and the mudstone layer. Therefore, the above settings of temperature, pressure, stress and strain ensure that the lower limit of the roof plugging thickness is reasonable and has strong production guidance significance.

[0038] (5) In the method for determining the sealing thickness of a complex lithology layer based on a simplified lithology combination provided by an embodiment of the present invention, the first heating device is a unidirectional heating device to save resources; the heating position is located at the center, and the direct heating area of ​​the bottom surface of the top plate rock sample does not exceed 1 / 4 of the bottom surface area, so that the heat source can be spread upward as much as possible.

[0039] (6) 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 sealing thickness of a complex lithology layer based on a simplified lithology combination 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 the improvement of the recovery rate.

[0040] 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.

[0041] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] 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:

[0043] Figure 1 This is a flow chart of a method for determining the plugging thickness of a complex lithology layer based on a simplified lithology combination in Embodiment 1 of the present invention;

[0044] Figure 2 This is a flow chart of a method for determining the plugging thickness of a complex lithology layer based on a simplified lithology combination in Embodiment 2 of the present invention;

[0045] Figure 3 This is a flow chart of a method for determining the sealing thickness of a complex lithology layer based on a simplified lithology combination in Embodiment 3 of the present invention;

[0046] Figure 4 This is a flow chart of a method for determining the plugging thickness of a complex lithology layer based on a simplified lithology combination in Embodiment 4 of the present invention;

[0047] Figure 5 This is a schematic diagram of the axial cross section of the roof rock sample in Example 5 of the present invention;

[0048] Figure 6 This is a temperature field simulation diagram in Embodiment 5 of the present invention;

[0049] Figure 7 This is a pressure field simulation diagram in Embodiment 5 of the present invention;

[0050] Figure 8 This is a strain field simulation diagram in Embodiment 5 of the present invention;

[0051] Fig. 9 for Figure 6 Oil saturation variation diagram at the middle temperature line 200℃ and 220℃;

[0052] Fig.10 for Figure 7 Oil saturation variation diagram at the middle pressure line 20MPa and 25MPa;

[0053] Fig.11 for Figure 8 Oil saturation variation diagram at the middle strain line of 10MPa and 20MPa. DETAILED DESCRIPTION

[0054] 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.

[0055] 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.

[0056] 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.

[0057] 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.

[0058] 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 the interlayer of mud shale and siltstone 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 sealing thickness of a complex lithology layer based on a simplified lithology combination, which can reasonably quantify the lower limit of the top plate sealing thickness of a shale reservoir by simplifying the lithology and temperature field, pressure field and stress field simulation method.

[0059] Embodiment 1

[0060] Embodiment 1 of the present invention provides a method for determining the sealing thickness of a complex lithology layer based on a simplified lithology combination, referring to Figure 1 As shown, the following steps are included:

[0061] Step S11: Determine the vertical superposition relationship between the siltstone layer and the mudstone layer, and the total thickness of the siltstone layer and the total thickness of the mudstone layer according to the lithology vertical distribution characteristics of the overlying strata within a set range.

[0062] The complex lithology layer is the overlying stratum of the shale reservoir, which is interbedded with siltstone and mud shale.

[0063] According to empirical data, the plugging thickness of the roof during in-situ mining of shale reservoirs is usually within 300-400 cm, so the length (thickness) of the roof rock sample is set to be no less than 500 cm. If it is thicker, the experimental difficulty and cost will increase; if it is thinner, it will easily fall below the lower limit of the actual plugging thickness of the roof, resulting in experimental failure (unable to measure the required roof plugging thickness of shale in-situ). That is, the setting range of the overlying stratum is within the range of 500 cm in thickness, preferably, within the range of 500 cm in thickness from the position closest to the top surface of the shale reservoir upward.

[0064] The set range is divided into an upper and a lower part by an averaging method. If the cumulative thickness of the lower shale layer exceeds the first set ratio (for example, exceeding 60%), the superposition relationship is determined to be the shale layer at the bottom and the siltstone layer at the top; if the cumulative thickness of the lower shale layer is lower than the second set ratio (for example, lower than 40%), the superposition relationship is determined to be the shale layer at the top and the siltstone layer at the bottom; if the cumulative thickness of the lower shale layer is within the set ratio range (for example, 40% to 60%), the lower part within the set range is further divided into an upper and a lower part by an averaging method, and the above method is repeated to determine the upper and lower superposition relationship of the siltstone layer and the shale layer.

[0065] Step S12: Based on the measured properties of the plurality of siltstone samples and the plurality of shale samples, and according to the upper and lower overlapping relationship and the total thickness of the siltstone layer and the total thickness of the shale layer, a roof rock sample is prepared by an integrated molding method.

[0066] Step S121: Based on the measured properties of multiple siltstone samples, a first formula of siltstone is prepared by experimental fitting, and based on the measured properties of multiple shale samples, a second formula of shale is prepared by experimental fitting.

[0067] 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 the overlying stratum, and obtaining the average values ​​of the corresponding parameters by thickness-weighted averaging; preparing a siltstone sample 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.

[0068] 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%).

[0069] 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 overlying formation, and obtaining the average values ​​of the corresponding parameters by thickness weighting; taking the average values ​​of the particle size distribution and the average values ​​of the mineral composition of the mud shale layer as the current formula, preparing a mud shale sample, and 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 mud shale sample currently prepared and the corresponding average values ​​all meet the error threshold, thereby obtaining the second formula for preparing mud shale.

[0070] 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.

[0071] Step S122: preparing a roof 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.

[0072] Roof rock samples of the same cross-sectional area (eg, cylindrical with a diameter of 5 cm) may be prepared.

[0073] Taking the above setting range of 500 cm thickness as an example, the thickness of the roof rock sample is also 500 cm.

[0074] The sides of the roof rock sample are wrapped with heat-insulating materials. The heat insulation can prevent the 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.

[0075] Step S13: a first heating device, a first pressurizing device, a first stress device and a group of first sensors are arranged on the bottom surface of the roof rock sample, and multiple groups of first sensors are arranged on the side of the roof rock sample at a first set interval, wherein the first sensor includes a first temperature sensor, a first pressure sensor and a first strain sensor; the roof rock sample is heated by the first heating device to a first set temperature measured by the first temperature sensor at the bottom, the roof rock sample is pressurized by the first pressurizing device to a first set pressure measured by the first pressure sensor at the bottom, the first stress device is used to gradually apply stress to the bottom of the roof rock sample from small to large to a first set stress, and stabilize at the temperature, the pressure and the stress until the measured value variation amplitude of each first sensor is less than the set threshold value, and the lower limit of the roof plugging thickness is determined according to the measured value of the first sensor and the upper and lower overlapping relationship.

[0076] In the embodiment of the present application, from bottom to top corresponds to from bottom to top.

[0077] The measuring positions of each group of first temperature sensors, first pressure sensors and first strain sensors arranged on the side of the rock sample in the longitudinal direction are consistent.

[0078] The first pressurizing device may be a fluid pressurizing device; and the first stress device may be a triaxial stress testing device.

[0079] In some embodiments, the first heating device is a unidirectional heating device to save resources.

[0080] The first heating device is located at the center of the bottom surface of the top plate rock sample. Further, the first heating device can directly heat the bottom surface of the top plate rock sample to no more than 1 / 4 of the bottom surface area, so that the heat source can be spread upward as much as possible.

[0081] The first temperature sensor and the first strain sensor are arranged axially on the side of the roof rock sample, and the first set interval of the arrangement is set according to the measurement accuracy requirement, usually at an interval of 10 cm.

[0082] 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.

[0083] The first set temperature can be determined by utilizing a source rock thermal simulation experiment or a kerogen activation energy experiment.

[0084] 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.

[0085] 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.

[0086] 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.

[0087] 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 principal stress underground at the depth of the bottom surface of the roof rock sample, which is obtained by calculation.

[0088] The first set temperature, i.e., the lowest temperature T0 at which the kerogen conversion rate in the shale reservoir reaches 90%, is determined in the above manner, the fracture pressure P0 of the shale reservoir is determined, and the maximum underground principal stress Ex at the bottom burial depth of the roof rock sample is determined.

[0089] The first heating device (heat source) is used to heat slowly (no more than 20°C / day), with the maximum temperature of the heat source between 400 and 650°C. The power of the heat source is adjusted to keep the temperature at the bottom of the top plate rock sample constant at T0. The first pressurizing device is used to pressurize the bottom of the top plate rock sample, and fluid is used for pressurization. The pressurization speed does not exceed 300KPa / day (the specific value is flexibly set according to the on-site construction conditions), so that the pressure at the bottom of the top plate rock sample is constant at P0. At the same time, the first stress device is used to apply stress to the bottom of the top plate rock sample step by step, and each increase of 1MPa can be constant for 5 minutes, and the final applied stress is constant at Ex. Furthermore, try to make the stress reach Ex, the pressure reach P0, and the temperature reach T0 simultaneously. The temperature is constant T0, the pressure is constant P0, and the stress is constant Ex. They are stable for at least 30 minutes until the change amplitude of the measured values ​​of each sensor is less than the set threshold, that is, after the 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.

[0090] Before determining the lower limit of the top plate plugging thickness, the following parameters need to be determined:

[0091] The initial hydrocarbon production temperature Tx of the kerogen in the shale layer of the roof rock sample is usually 200-250°C. It can be determined by thermal simulation experiments of source rocks;

[0092] The fracture pressure Px of the roof rock sample can be the average value of the fracture pressures of the siltstone layer and the shale layer after weighted average of their thicknesses;

[0093] The critical damage strain value εx of the roof rock sample can be the average value of the critical damage strain value of the siltstone layer and the shale layer after the thickness weighted average;

[0094] The minimum starting pressure Ps for oil and gas migration in the siltstone layer in the roof rock sample.

[0095] In some embodiments, according to the measurement value of the first sensor and the vertical superposition relationship between the siltstone layer and the mudstone layer in the roof rock sample, the lower limit of the plugging thickness of the roof rock sample is determined to include the following two situations:

[0096] 1. The relationship between the upper and lower superposition is that the siltstone layer is on the upper

[0097] (1) If the temperature in the shale layer drops to Tx, the pressure drops to Px, and the strain drops to εx, determine 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, and determine the distance from this position to the bottom surface of the roof rock sample as the lower limit of the roof plugging thickness;

[0098] (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, and the minimum starting pressure of the siltstone layer is greater than the fracture pressure Pr of the shale reservoir, the distance from the higher position of the position where the pressure is Px and the position where the strain is εx to the bottom surface of the roof rock sample is determined as the lower limit of the roof plugging thickness; 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 roof rock sample cannot be plugged;

[0099] (3) If the temperature in the shale layer is greater than Tx, the method is invalid.

[0100] 2. The relationship between the upper and lower superposition is that the siltstone layer is at the bottom.

[0101] (1) If the temperature in the siltstone layer drops to Tx, the pressure drops to Px, and the strain drops to εx, the thickness of the siltstone layer is determined to be the lower limit of the roof plugging thickness;

[0102] (2) If the strain in the shale layer drops to εx, or the pressure drops to Px, or the temperature drops to Tx, determine 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, and determine the distance from this position to the bottom surface of the roof rock sample as the lower limit of the roof plugging thickness.

[0103] 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.

[0104] The method for determining the plugging thickness of a complex lithology layer based on a simplified lithology combination provided in the first embodiment of the present invention is to prepare a roof rock sample by integral molding, heat the roof rock sample to a first set temperature by a first heating device, pressurize the roof rock sample to a first set pressure by a first pressurizing device, and apply stress to the bottom of the roof rock sample step by step from small to large to the first set stress by a first stress device, and stabilize at the temperature, pressure and stress until the measured values ​​of each sensor are stable, and determine the lower limit of the plugging thickness of the roof rock sample based on the measured values ​​of the sensors and the upper and lower overlapping relationship between the siltstone layer and the mudstone layer. The lower limit of the roof plugging thickness of the shale reservoir is determined by experimental methods based on the simulation of the temperature field, pressure field and stress field, and the roof plugging conditions of the shale reservoir in situ process are specifically quantified, which can effectively guide production and improve the economic benefits of in-situ exploitation of shale oil and gas.

[0105] The method for determining the sealing thickness of a complex lithology layer based on a simplified lithology combination provided in Example 1 of the present invention determines the vertical 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 according to the lithology vertical distribution characteristics of the overlying strata within a set range, and prepares the roof rock sample in one piece based on the measured properties of the siltstone and mudstone. The prepared synthetic sample takes into account both the properties of mudstone and siltstone, and the vertical superposition relationship between the two, and reasonably simplifies the sample, so that the determination of the lower limit of the sealing thickness of the complex lithology roof with interlayers of mudstone and siltstone can be achieved.

[0106] 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 of a complex lithology layer based on a simplified lithology combination provided in Example 1 of the present invention suggests that if the overlying rock layer of the shale reservoir is 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.

[0107] Embodiment 2

[0108] Embodiment 2 of the present invention provides another method for determining the sealing thickness of a complex lithology layer based on a simplified lithology combination, specifically a method for determining the lower limit of the bottom plate sealing thickness of a shale reservoir, wherein the underlying rock layer of the shale reservoir is a mudstone formation.

[0109] Specifically, refer to Figure 2 As shown, the following steps are included:

[0110] Step S21: Prepare a bottom plate rock sample using the coring section of the underlying rock formation of the shale reservoir, wrap the side of the bottom plate rock sample with a heat-insulating sealing material, arrange a second heating device, a second pressurizing device, a second stress device and a group of second sensors on the top surface of the bottom plate rock sample, and arrange multiple groups of second sensors on the side of the bottom plate rock sample at second set intervals.

[0111] The second sensor includes a second temperature sensor, a second pressure sensor and a second strain sensor. The second temperature sensor, the second pressure sensor and the second strain sensor arranged on the side of the rock sample have the same measurement position in the longitudinal direction.

[0112] The second temperature sensor may be the same temperature sensor as the first temperature sensor, and the "first" and "second" here are only used to distinguish whether the temperature sensor is set in the top plate rock sample or the bottom plate rock sample.

[0113] Similarly, the second pressure sensor can be the same pressure sensor as the first pressure sensor, and the "first" and "second" here are just to distinguish whether the pressure sensor is set in the top plate rock sample or the bottom plate rock sample.

[0114] The second strain sensor may be the same strain sensor as the first strain sensor, and the "first" and "second" here are only used to distinguish whether the strain sensor is arranged in the top plate rock sample or the bottom plate rock sample.

[0115] 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.

[0116] The second heating device can be the same heating device as the first heating device, and the "first" and "second" here are just to distinguish whether the heating device is arranged on the bottom surface of the top plate rock sample or the top surface of the bottom plate rock sample.

[0117] The second pressurizing device can be a heating device that is the same as the first pressurizing device. The "first" and "second" here are only used to distinguish whether the pressurizing device is arranged on the bottom surface of the top plate rock sample or on the top surface of the bottom plate rock sample.

[0118] The second stress device can be a heating device that is the same as the first stress device. The "first" and "second" here are only used to distinguish whether the stress device is set on the bottom surface of the top plate rock sample or on the top surface of the bottom plate rock sample.

[0119] The second heating device is located at the center of the top surface of the bottom plate rock sample. Further, the second heating device may directly heat the top surface of the bottom plate rock sample to no more than 1 / 4 of the top surface area, so that the heat source can be spread downward as much as possible.

[0120] 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.

[0121] The second temperature sensor, the second pressure sensor and the second strain sensor are arranged axially on the side of the bottom plate rock sample. The second set interval of the arrangement is set according to the measurement accuracy requirement and can be consistent with the first set interval, usually 10 cm.

[0122] Step S22: using a second heating device to heat the bottom plate rock sample to a first set temperature at which the measured temperature of the second temperature sensor at the top is measured; using a second pressurizing device to pressurize the bottom plate rock sample to a second set pressure at which the measured pressure of the second pressure sensor at the top is measured; using a second stress device to gradually apply stress to the top of the bottom plate rock sample from small to large to the second set stress, and stabilize at the temperature, pressure and stress until the measured value variation amplitude of each second sensor is less than the set threshold value; determining the highest position at which the bottom plate rock sample temperature is not higher than the third set temperature, the pressure is not higher than the third set pressure and the strain is not higher than the second set strain according to the measured values ​​of the second sensors.

[0123] In some embodiments, the third set temperature is the initial hydrocarbon production temperature of kerogen in the underlying rock formation, and its determination method can refer to the determination of the second set temperature.

[0124] This application is based on the premise that the overlying and underlying rock formations of the shale reservoir are both mudstone formations. Therefore, if the rock properties of the overlying and underlying rock formations are basically the same, the initial hydrocarbon production temperature of kerogen in the overlying rock formation can also be approximated as the initial hydrocarbon production temperature of kerogen in the underlying rock formation.

[0125] In some embodiments, the third set pressure is the fracture pressure of the underlying rock formation, which can also be determined by rock fracture pressure experiments. Therefore, if the rock mechanical properties of the overburden and the underlying rock formation are basically the same, the fracture pressure of the overburden can also be approximated as the fracture pressure of the underlying rock formation.

[0126] 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.

[0127] 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.

[0128] Taking the third set temperature as Tx, the third set pressure as Px, the second set stress as Ex, and the second set strain as εx as an example, the second heating device (heat source) is used to slowly heat (no more than 20°C / day), the maximum temperature of the heat source is between 400 and 650°C, and the heat source power is adjusted to make the top temperature of the bottom plate rock sample constant at T0; at the same time, the second pressurizing device is used to pressurize the top of the bottom plate rock sample, and the fluid is used for pressurization, and the pressurization speed does not exceed 300KPa / day (the specific value is flexibly set according to the on-site construction situation), so that the top pressure of the bottom plate rock sample is constant at P0; the second stress device is used to apply stress to the top of the bottom plate rock sample step by step, and each increase of 1MPa can be constant for 5 minutes, so that the final applied stress is constant at Ex. Further, try to make the pressure reach P0, the stress reach Ex, and the temperature reach T0 synchronously. The temperature is constant at T0, the pressure is constant at P0, and the stress is constant at Ex. They are stable for at least 30 minutes until the variation of the measured values ​​of each sensor is less than the set threshold value, that is, after the temperature, pressure and strain are stable, the measured values ​​of each second temperature sensor, second pressure sensor and second strain sensor are collected. Since the temperature of the bottom plate rock sample gradually decreases from top to bottom, the pressure gradually decreases from top to bottom, and the strain also gradually decreases from top to bottom, the measured values ​​of the second temperature sensor, second pressure sensor and second strain sensor can be collected from top to bottom in sequence until the currently collected temperature is not greater than Tx, the pressure is not greater than Px, and the strain εx is not greater than Px. The highest position of the bottom plate rock sample where the temperature is not higher than Tx, the pressure is not greater than Px, and the strain is not higher than εx is determined according to the position of the corresponding sensor.

[0129] If the currently collected temperature is Tx, the position of the corresponding second temperature sensor can be directly determined as the position where the bottom plate rock sample temperature begins to drop to Tx; if the currently collected temperature begins to be less than Tx (the first temperature less than Tx), based on the currently collected temperature and the previous collected temperature and the current position of the second temperature sensor and the position of the previous second temperature sensor, the first highest position where the bottom plate rock sample temperature is not higher than Tx is determined by the proportional method.

[0130] Similarly, if the currently collected pressure is Px, the position of the corresponding second pressure sensor can be directly determined as the position where the bottom plate rock sample pressure begins to drop to Px; if the currently collected pressure begins to be less than Px (the first pressure less than Px), based on the currently collected pressure and the previous collected pressure and the current position of the second pressure sensor and the position of the previous second pressure sensor, the second highest position where the bottom plate rock sample pressure is not higher than Px is determined by the proportional method.

[0131] If the currently collected strain is εx, the position of the corresponding second strain sensor can be directly determined as the position where the bottom plate rock sample strain begins to drop to εx; if the currently collected strain begins to be less than εx (the first strain less than εx), based on the currently collected strain and the previous strain collected and the position of the current second strain sensor and the position of the previous second strain sensor, the third highest position where the bottom plate rock sample strain is not higher than εx is determined by the proportional method.

[0132] The lower of the first highest position, the second highest position and the second highest position is used as the highest position where the bottom plate rock sample temperature is not higher than the third set temperature, the pressure is not higher than the second set pressure, and the stress is not higher than the third set stress.

[0133] 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.

[0134] 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.

[0135] Embodiment 3

[0136] Embodiment 3 of the present invention provides another method for determining the sealing thickness of a complex lithology layer based on a simplified lithology combination, specifically a method for determining the lower limit of the bottom plate sealing thickness of a shale reservoir, wherein the underlying rock layer of the shale reservoir is a siltstone layer. Determine whether the fracture pressure of the shale reservoir is less than the minimum starting pressure of the underlying siltstone layer; if so, perform the following bottom plate sealing thickness lower limit determination step; if not, determine that the underlying stratum does not have sealing properties during the in-situ mining process of the shale reservoir.

[0137] For details, see Figure 3 As shown, the steps for determining the lower limit of the bottom plate plugging thickness include:

[0138] Step S31: Prepare a bottom plate rock sample using the coring section of the underlying rock stratum, wrap the side of the bottom plate rock sample with a heat-insulating sealing material, arrange a second heating device, a second pressurizing device, a second stress device and a second temperature sensor, a second pressure sensor and a second strain sensor on the top surface of the bottom plate rock sample, and arrange multiple groups of second pressure sensors and second strain sensors on the side of the bottom plate rock sample at second set intervals.

[0139] The measuring positions of each group of second pressure sensors and second strain sensors arranged on the side of the rock sample in the longitudinal direction are consistent.

[0140] 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.

[0141] The second heating device is located at the center of the top surface of the bottom plate rock sample. Further, the second heating device may directly heat the top surface of the bottom plate rock sample to no more than 1 / 4 of the top surface area, so that the heat source can be spread downward as much as possible.

[0142] 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.

[0143] The second pressure sensor and the second strain sensor are arranged axially on the side of the bottom plate rock sample. The second set interval of each group is set according to the measurement accuracy requirement and can be consistent with the first set interval, usually 10 cm.

[0144] Step S32: using a second heating device to heat the bottom plate rock sample to a first set temperature at which the measured temperature of the second temperature sensor at the top is measured; using a second pressurizing device to pressurize the bottom plate rock sample to a second set pressure at which the measured pressure of the second pressure sensor at the top is measured; using a second stress device to gradually apply stress to the top of the bottom plate rock sample from small to large to the second set stress, and stabilize at the temperature, the pressure, and the stress until the measured value changes of the second pressure sensor and the second strain sensor are all less than the set threshold value; determining the highest position at which the bottom plate rock sample pressure is not higher than the third set pressure and the strain is not higher than the second set strain based on the measured values ​​of the second pressure sensor and the second strain sensor.

[0145] In some embodiments, the third set pressure is the fracture pressure of the underlying rock formation, which can also be determined by rock fracture pressure experiments. Therefore, if the rock mechanical properties of the overburden and the underlying rock formation are basically the same, the fracture pressure of the overburden can also be approximated as the fracture pressure of the underlying rock formation.

[0146] 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.

[0147] 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.

[0148] Taking the third set pressure as Px, the second set stress as Ex, and the second set strain as εx as an example, the second heating device (heat source) is used to slowly heat (no more than 20°C / day), the maximum temperature of the heat source is between 400 and 650°C, and the heat source power is adjusted to make the top temperature of the bottom plate rock sample constant at T0; at the same time, the second pressurizing device is used to pressurize the top of the bottom plate rock sample, and the fluid is used for pressurization, and the pressurization speed does not exceed 300KPa / day (the specific value is flexibly set according to the on-site construction situation), so that the top pressure of the bottom plate rock sample is constant at P0; the second stress device is used to apply stress to the top of the bottom plate rock sample step by step, and each increase of 1MPa can be constant for 5 minutes, so that the final applied stress is constant at Ex. Further, try to make the pressure reach P0, the stress reach Ex, and the temperature reach T0 simultaneously. The temperature is constant T0, the pressure is constant P0, and the stress is constant Ex. They are stable for at least 30 minutes until the change amplitude of the measured values ​​of each sensor is less than the set threshold, that is, after the pressure and strain are stable, the measured values ​​of each second pressure sensor and the second strain sensor are collected. Since the pressure of the bottom plate rock sample gradually decreases from the top to the bottom, the strain also gradually decreases from the top to the bottom, the measured values ​​of the second pressure sensor and the second strain sensor can be collected from the top to the bottom in sequence until the currently collected pressure is not greater than Px and the strain εx is not greater than Px. The highest position of the bottom plate rock sample where the pressure is not greater than Px and the strain is not higher than εx is determined according to the position of the corresponding sensor.

[0149] If the currently collected pressure is Px, the position of the corresponding second pressure sensor can be directly determined as the position where the bottom plate rock sample pressure begins to drop to Px; if the currently collected pressure begins to be less than Px (the first pressure less than Px), based on the currently collected pressure and the previous collected pressure and the current position of the second pressure sensor and the position of the previous second pressure sensor, the first highest position where the bottom plate rock sample pressure is not higher than Px is determined by the proportional method.

[0150] Similarly, if the currently collected strain is εx, the position of the corresponding second strain sensor can be directly determined as the position where the bottom plate rock sample strain begins to drop to εx; if the currently collected strain begins to be less than εx (the first strain less than εx), based on the currently collected strain and the last collected strain and the position of the current second strain sensor and the position of the last second strain sensor, the second highest position where the bottom plate rock sample strain is not higher than εx is determined by the proportional method.

[0151] 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.

[0152] 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.

[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 4

[0155] Embodiment 4 of the present invention provides another method for determining the lower limit of the sealing thickness of complex lithology layers based on stress field simulation, specifically a method for determining the lower limit of the bottom plate sealing thickness of a shale reservoir, which is suitable for the case where the underlying rock layer of the shale reservoir is an interlayer of siltstone and mudstone. The method for determining the lower limit of the top plate sealing thickness of the shale reservoir in the above embodiment 1 is still applicable here.

[0156] Specifically, refer to Figure 4 As shown, the following steps are included:

[0157] Step S41: Determine the vertical superposition relationship between the siltstone layer and the mudstone layer, and the total thickness of the siltstone layer and the total thickness of the mudstone layer according to the lithology vertical distribution characteristics of the underlying rock layer within a set range.

[0158] The setting range of the underlying rock formation can be within a thickness range of 500 cm, preferably, within a thickness range of 500 cm downward from the position closest to the top surface of the shale reservoir.

[0159] Step S42: Based on the measured properties of multiple siltstone samples within the set range of the underlying rock formation, a third formula for siltstone is prepared by experimental fitting, and based on the measured properties of multiple shale samples within the set range of the underlying rock formation, a fourth formula for shale is prepared by experimental fitting.

[0160] Step S43: preparing a bottom plate rock sample by an integrated molding method according to the stacking relationship of the siltstone layer and the mudstone layer of the underlying rock layer, the total thickness of the siltstone layer and the total thickness of the mudstone layer, the third formula and the fourth formula.

[0161] Step S44: a second heating device, a second pressurizing device, a second stress device and a group of second sensors are arranged on the top surface of the bottom plate rock sample, and multiple groups of second sensors are arranged on the top surface of the bottom plate rock sample at second set intervals, wherein the second sensors include a second temperature sensor, a second pressure sensor and a second strain sensor; the bottom plate rock sample is heated by the second heating device to a first set temperature at the top by the second temperature sensor, the bottom plate rock sample is heated by the second pressurizing device to a second set pressure at the top by the second pressure sensor, and the top of the bottom plate rock sample is gradually stressed from small to large by the second stress device to the second set stress, and stabilized at the temperature, the pressure and the stress until the measured value variation amplitude of each second sensor is less than the set threshold value, and the lower limit of the bottom plate plugging thickness is determined according to the measured value of the second sensor and the upper and lower overlapping relationship between the siltstone layer and the shale layer of the bottom plate rock sample.

[0162] The execution process of step S44 can refer to the execution process of step S14, which will not be repeated here.

[0163] 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 of a complex lithology layer based on a simplified lithology combination provided in embodiments 2, 3 and 4 of the present invention fully considers the sealing properties of the bottom plate, ensures the reliability of the determination of the sealing performance, and further provides a guarantee for improving the recovery rate.

[0164] The above three embodiments can be applied separately; embodiment one can also be applied in combination with embodiment two, or embodiment one can be applied in combination with embodiment three, or embodiment one can be applied in combination with embodiment four, 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.

[0165] Embodiment 5

[0166] Embodiment 5 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:

[0167] 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.

[0168] 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.

[0169] 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.

[0170] 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.

[0171] 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 5 The figure shows a schematic cross-sectional view of the roof rock sample along the axial direction.

[0172] 6) Determine the T0 (kerogen 90% conversion temperature) of the reservoir rock sample at 300℃.

[0173] 7) The Tx (initial hydrocarbon production temperature of kerogen) of the mudstone roof rock sample was determined to be 200°C.

[0174] 8) The maximum stress Ex (maximum axial stress) of the reservoir rock sample was measured to be 30 MPa.

[0175] 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.

[0176] 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.

[0177] 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.

[0178] 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.

[0179] 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).

[0180] 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.

[0181] 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.

[0182] 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.

[0183] 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.

[0184] 18) See Figure 6-8 As shown in the figure, they are the simulated temperature field, simulated pressure field and simulated strain field of the roof rock sample. Figure 6 Oil saturation at the Tx temperature line (200°C) (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 Px pressure line (20 MPa) (see Fig.10 There was no change in the entire simulation period, indicating that oil and gas were blocked at this location. Figure 8Oil saturation at the medium strain line (10 MPa) (see Fig.11 There was no change in the whole simulation period, indicating that oil and gas were blocked at this location.

[0185] 19) Observation Figure 6 Oil saturation at 220°C (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 25 MPa of the medium pressure line (see Fig.10 (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 8 Oil saturation at the medium strain line of 20 MPa (see Fig.11 During the whole simulation period, there are obvious changes, indicating that the oil and gas are not blocked at this location.

[0186] 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. 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 is about 0.5%, so the numerical simulation verifies the reliability of the experimental results.

[0187] 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.

[0188] 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.

[0189] 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 sealing thickness of a complex lithology layer based on a simplified lithology combination, wherein the complex lithology layer is an overlying stratum of a shale reservoir, and the complex lithology layer is an interlayer of siltstone and mud shale, characterized in that: include: According to the lithology vertical distribution characteristics of the overlying strata within the set range, determine 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; Based on the measured properties of the plurality of siltstone samples and the plurality of shale samples, and according to the upper and lower overlapping relationship and the total thickness of the siltstone layer and the total thickness of the shale layer, a roof rock sample is prepared by an integrated molding method; A first heating device, a first pressurizing device, a first stress device and a group of first sensors are arranged on the bottom surface of the roof rock sample, and multiple groups of first sensors are arranged on the side of the roof rock sample at a first set interval, wherein the first sensor includes a first temperature sensor, a first pressure sensor and a first strain sensor; the roof rock sample is heated by the first heating device to a first set temperature at which the measured temperature of the first temperature sensor at the bottom is measured, the roof rock sample is pressurized by the first pressurizing device to a first set pressure at which the measured pressure of the first pressure sensor at the bottom is measured, and the first stress device is used to gradually apply stress to the bottom of the roof rock sample from small to large to a first set stress, and stabilize at the temperature, the pressure and the stress until the variation amplitude of the measured values ​​of each first sensor is less than the set threshold value, and the lower limit of the roof plugging thickness is determined according to the measured values ​​of the first sensors and the upper and lower overlapping relationship.

2. The method according to claim 1, characterized in that The method of preparing the roof rock sample by an integrated molding method based on the measured properties of the plurality of siltstone samples and the plurality of shale samples and according to the upper and lower overlapping relationship and the total thickness of the siltstone layer and the total thickness of the shale layer includes: 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 roof 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: Measuring the particle size distribution, mineral composition, fracture pressure, minimum starting pressure, fracture critical damage strain value and porosity of rock samples of each siltstone layer within the set range of the overlying stratum, and obtaining the average value of the corresponding parameters 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 are measured, and the average values ​​of the corresponding parameters are 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 buried depth of the bottom surface of the roof rock sample.

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

8. The method according to claim 1, characterized in that If the upper and lower superposition relationship is that the siltstone layer is on the upper side, the initial hydrocarbon production temperature of the kerogen of the shale layer in the roof rock sample is Tx, the fracture pressure of the roof rock sample is Px, and the critical damage strain value of the fracture of the roof rock sample is εx, the lower limit of the roof plugging thickness is determined according to the measurement value of the first sensor and the upper and lower superposition relationship, including: If the temperature in the shale layer drops to Tx, the pressure drops to Px, and the strain drops to εx, determine 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, and determine the distance from the position to the bottom surface of the roof rock sample as the lower limit of the roof plugging thickness; 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, and the minimum starting pressure of the siltstone layer is greater than the fracture pressure Pr of the shale reservoir, the distance from the higher position of the position where the pressure is Px and the position where the strain is εx to the bottom surface of the roof rock sample is determined as the lower limit of the roof plugging thickness; 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 roof rock sample cannot be plugged; If the temperature in the shale layer is greater than Tx, the method is invalid.

9. The method according to claim 1, characterized in that If the upper and lower superposition relationship is that the siltstone layer is at the bottom, the kerogen initial hydrocarbon production temperature of the shale layer in the roof rock sample is Tx, the fracture pressure of the roof rock sample is Px, and the critical damage strain value of the fracture of the roof rock sample is εx, the lower limit of the roof plugging thickness is determined according to the measurement value of the first sensor and the upper and lower superposition relationship, including: If the temperature in the siltstone layer drops to Tx, the pressure drops to Px, and the strain drops to εx, the thickness of the siltstone layer is determined to be the lower limit of the roof plugging thickness; If the strain in the shale layer drops to εx, or the pressure drops to Px, or the temperature drops to Tx, determine 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, and determine the distance from this position to the bottom surface of the roof rock sample as the lower limit of the roof sealing thickness.

10. The method according to claim 1, characterized in that If the underlying rock layer of the shale reservoir is a mudstone formation, the method further includes executing the following step of determining the lower limit of the bottom plate plugging thickness: A bottom plate rock sample is prepared by coring a coring section of an underlying rock formation of a shale reservoir, and a side surface of the bottom plate rock sample is wrapped with a heat-insulating sealing material, and a second heating device, a second pressurizing device, a second stress device, and a group of second sensors are arranged on the top surface of the bottom plate rock sample, and a plurality of groups of second sensors are arranged on the side surface of the bottom plate rock sample at a second set interval, wherein the second sensors include a second temperature sensor, a second pressure sensor, and a second strain sensor; The bottom plate rock sample is heated by the second heating device until the temperature measured by the second temperature sensor at the top is the first set temperature, the bottom plate rock sample is pressurized by the second pressurizing device until the pressure measured by the second pressure sensor at the top is the second set pressure, the second stress device is used to gradually apply stress from small to large to the top of the bottom plate rock sample to the second set stress, and stabilize at the temperature, pressure and stress until the variation amplitude of the measured values ​​of each second sensor is less than the set threshold, and the highest position of the bottom plate rock sample at which the temperature is not higher than the third set temperature, the pressure is not higher than the third set pressure and the strain is not higher than the second set strain is determined according to the measured values ​​of the second sensor; The lower limit of the bottom plate plugging thickness of the shale reservoir is determined according to the distance between the position and the top surface.

11. The method according to claim 1, characterized in that If the underlying rock layer of the shale reservoir is an underlying siltstone layer, the method further includes: determining whether the shale reservoir fracture pressure is less than the minimum starting pressure of the underlying siltstone layer; if so, executing the following bottom plate plugging thickness lower limit determination step: A bottom plate rock sample is prepared by using a coring section of an underlying rock formation, and a side surface of the bottom plate rock sample is wrapped by using a heat-insulating sealing material, and a second heating device, a second pressurizing device, a second stress device, a second temperature sensor, a second pressure sensor, and a second strain sensor are arranged on the top surface of the bottom plate rock sample, and a plurality of groups of second pressure sensors and second strain sensors are arranged on the side surface of the bottom plate rock sample at a second set interval; The bottom plate rock sample is heated by the second heating device until the temperature measured by the second temperature sensor at the top is the first set temperature, the bottom plate rock sample is pressurized by the second pressurizing device until the pressure measured by the second pressure sensor at the top is the second set pressure, the second stress device is used to gradually apply stress from small to large to the top of the bottom plate rock sample to the second set stress, and stabilize at the temperature, the pressure and the stress until the measured value variation amplitude of each second pressure sensor and the second strain sensor is less than the set threshold value, and the highest position where the pressure of the bottom plate rock sample is not higher than the third set pressure and the strain is not higher than the second set strain is determined according to the measured values ​​of the second pressure sensor and the second strain sensor; The lower limit of the bottom plate plugging thickness of the shale reservoir is determined according to the distance between the position and the top surface.

12. The method according to claim 10 or 11, characterized in that The third set pressure is the fracture pressure of the underlying rock formation; The second set strain is a critical damage strain value of the underlying rock formation; The second set stress is the maximum underground principal stress at the burial depth of the top surface of the bottom plate rock sample.

13. The method according to claim 1, characterized in that If the underlying rock layer of the shale reservoir is interbedded siltstone and mudstone, the method further includes executing the following step of determining the lower limit of the bottom plate plugging thickness: According to the lithology vertical distribution characteristics of the underlying rock layer within the set range, determine 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; Based on the measured properties of multiple siltstone samples within the set range of the underlying rock formation, a third formula for siltstone is prepared by experimental fitting, and based on the measured properties of multiple shale samples within the set range of the underlying rock formation, a fourth formula for shale is prepared by experimental fitting; According to the upper and lower overlapping relationship of the siltstone layer and the mud shale layer of the underlying rock layer, the total thickness of the siltstone layer and the total thickness of the mud shale layer, the third formula and the fourth formula, a bottom plate rock sample is prepared by an integrated molding method; A second heating device, a second pressurizing device, a second stress device and a group of second sensors are arranged on the top surface of the bottom plate rock sample, and multiple groups of second sensors are arranged on the top surface of the bottom plate rock sample at second set intervals, wherein the second sensors include a second temperature sensor, a second pressure sensor and a second strain sensor; the bottom plate rock sample is heated by the second heating device to a top temperature where the measured temperature of the second temperature sensor is the first set temperature; the bottom plate rock sample is heated by the second pressurizing device to a top pressure where the measured pressure of the second pressure sensor is the second set pressure; the second stress device is used to gradually apply stress to the top of the bottom plate rock sample from small to large to the second set stress, and the stress is stabilized at the temperature, the pressure and the stress until the measured value variation amplitude of each second sensor is less than the set threshold value; the lower limit of the bottom plate plugging thickness is determined according to the measured value of the second sensor and the upper and lower overlapping relationship between the siltstone layer and the shale layer of the bottom plate rock sample.

Images