Method for determining lower limit of plugging thickness of complex lithologic layer based on temperature field simulation

Abstract

The invention discloses a method for determining the lower limit of the plugging thickness of a complex lithologic layer based on temperature field simulation, 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 in a set range; respectively obtaining formulas for preparing siltstone and shale through experimental fitting; integrally forming and preparing a roof rock sample; arranging a heating device and temperature sensors on the bottom surface of the rock sample, and arranging a plurality of temperature sensors on the side surface of the rock sample at set intervals; heating the rock sample by using a heating device until the bottom temperature is a first set temperature, stabilizing the bottom temperature at the first set temperature until the measured value of each temperature sensor is stable, and determining the lowest position where the rock sample temperature is not higher than a second set temperature; determining the lower limit of the top plate plugging thickness according to the superposition relation and the position; and similarly, determining the bottom plate plugging thickness lower limit. According to the method, the lower limit of the plugging thickness of the top and bottom plates of the shale reservoir can be reasonably quantified by simplifying lithology and temperature field simulation.

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 lower limit of plugging thickness of a complex lithology layer based on temperature field simulation. 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 lower limit of the sealing thickness of a complex lithology layer based on temperature field simulation, which can reasonably quantify the lower limit of the sealing thickness of the shale reservoir top plate by simplifying the lithology and temperature field simulation methods.

[0006] The embodiment of the present invention provides a method for determining the lower limit of the plugging thickness of a complex lithology layer based on temperature field simulation, 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 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;

[0009] 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;

[0010] A first heating device and a first temperature sensor are arranged on the bottom surface of the roof rock sample, and a plurality of first temperature sensors are arranged on the side surface of the roof rock sample at a first set interval. The roof rock sample is heated by the first heating device until the measured temperature of the first temperature sensor at the bottom is a first set temperature, and is stabilized at this temperature until the variation amplitude of the measured values ​​of each first temperature sensor is less than a set threshold value. The lowest position where the temperature of the roof rock sample is not higher than the second set temperature is determined according to the measured value of the first temperature sensor, and the lower limit of the roof sealing thickness is determined according to the upper and lower overlapping relationship and the lowest position.

[0011] In some embodiments, the preparing a first formula of siltstone by experimental fitting based on measured properties of a plurality of siltstone samples comprises:

[0012] Measuring the particle size distribution, mineral composition 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;

[0013] 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 a siltstone sample, adjusting the current formula until the error between the porosity of the currently prepared siltstone sample and the corresponding average value meets the error threshold, thereby obtaining a first formula for preparing siltstone;

[0014] Accordingly, the second formula for preparing shale by experimental fitting based on the measured properties of the plurality of shale samples includes:

[0015] Measuring the particle size distribution, mineral composition, TOC, porosity and initial hydrocarbon production temperature of the rock samples of each shale layer within the set range, and obtaining the average values ​​of the corresponding parameters by thickness-weighted averaging;

[0016] The average values ​​of the particle size distribution of the shale layer and the average values ​​of the mineral composition are used as the current formula to prepare a shale sample, and the current formula is adjusted until the errors between the TOC, porosity and initial hydrocarbon production temperature of the kerogen of the currently prepared shale sample and the corresponding average values ​​meet the error threshold, thereby obtaining a second formula for preparing shale.

[0017] 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.

[0018] In some embodiments, the first set temperature is the lowest temperature at which the kerogen conversion rate in the shale reservoir reaches 90%.

[0019] In some embodiments, the second set temperature is an average value of the initial hydrocarbon production temperature of the kerogen of each shale sample within the set range of the overlying formation.

[0020] In some embodiments, the first heating device is a one-way heating device;

[0021] The first heating device is located at the center of the bottom surface of the top plate rock sample;

[0022] 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.

[0023] In some embodiments, if the upper and lower overlapping relationship is that the siltstone layer is on the upper side, determining the lower limit of the roof plugging thickness according to the upper and lower overlapping relationship and the lowest position includes:

[0024] If the lowest position is located in the mudstone layer of the roof rock sample, the distance from the lowest position to the bottom surface of the roof rock sample is determined as the lower limit of the roof plugging thickness;

[0025] If the lowest position is located in the siltstone layer of the roof rock sample, the method is ineffective.

[0026] In some embodiments, if the upper and lower overlapping relationship is that the siltstone layer is at the bottom, determining the lower limit of the roof plugging thickness according to the upper and lower overlapping relationship and the lowest position includes:

[0027] If the lowest position is located in the mudstone layer of the roof rock sample, the distance from the lowest position to the bottom surface of the roof rock sample is determined as the lower limit of the roof plugging thickness;

[0028] If the lowest position is located in the siltstone layer of the roof rock sample, the total thickness of the siltstone layer is determined as the lower limit of the roof sealing thickness.

[0029] In some embodiments, if the underlying rock formation of the shale reservoir is a mudstone formation, the method further includes executing the following step of determining the lower limit of the bottom plate plugging thickness:

[0030] A bottom plate rock sample is prepared by coring a coring section of an underlying rock formation of a shale reservoir, a side surface of the bottom plate rock sample is wrapped by a heat-insulating material that does not block pressure, a second heating device and a second temperature sensor are arranged on the top surface of the bottom plate rock sample, and a plurality of second temperature sensors are arranged on the side surface of the bottom plate rock sample at a second set interval;

[0031] The bottom plate rock sample is heated by the second heating device until the temperature measured by the second temperature sensor on the top is the first set temperature, and stabilized at this temperature until the measured temperature variation amplitude of each second temperature sensor is less than the set threshold value, and the highest position where the bottom plate rock sample temperature is not higher than the third set temperature is determined according to the measured temperature of each second temperature sensor;

[0032] 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.

[0033] In some embodiments, the third set temperature is the initial hydrocarbon production temperature of kerogen in the underlying rock formation.

[0034] In some embodiments, if the underlying rock layer of the shale reservoir is an interbedded layer of siltstone and mudstone, the method further includes executing the following step of determining the lower limit of the bottom plate plugging thickness:

[0035] 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;

[0036] preparing a third formula for siltstone by experimental fitting based on measured properties of a plurality of siltstone samples within the set range of the underlying rock formation, and preparing a fourth formula for shale by experimental fitting based on measured properties of a plurality of shale samples within the set range of the underlying rock formation;

[0037] 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;

[0038] A second heating device and a second temperature sensor are arranged on the top surface of the bottom plate rock sample, and multiple second temperature sensors are arranged on the side of the bottom plate rock sample at a second set interval. The second heating device is used to heat the bottom plate rock sample until the measured temperature of the second temperature sensor on the top is the first set temperature, and stabilize it at this temperature until the change amplitude of the measured value of each second temperature sensor is less than the set threshold value, and the highest position where the temperature of the bottom plate rock sample is not higher than the fourth set temperature is determined according to the measured value of the second temperature sensor, and based on the upper and lower overlapping relationship of the siltstone layer and the shale layer of the underlying rock stratum, the lower limit of the low plate plugging thickness is determined according to the highest position.

[0039] In some embodiments, the fourth set temperature is an average value of the initial hydrocarbon production temperatures of the kerogen of each shale sample within the set range of the underlying rock formation.

[0040] The beneficial effects of the above technical solution provided by the embodiment of the present invention include at least:

[0041] (1) The method for determining the lower limit of the plugging thickness of a complex lithology layer based on temperature field simulation provided by an embodiment of the present invention is to prepare a roof rock sample by integral molding, and to heat the roof rock sample by using a first heating device so that the measured temperature of the first temperature sensor at the bottom is stabilized at a first set temperature, until the measured temperatures of each first temperature sensor are stable, and the lowest position where the roof rock sample temperature is not higher than the second set temperature is determined according to the measured temperatures of each first temperature sensor; and the lower limit of the roof plugging thickness is determined according to the upper and lower overlapping relationship of the siltstone layer and the mudstone layer and the lowest position. The lower limit of the roof plugging thickness of the shale reservoir is determined based on the temperature field simulation by an experimental method, and the roof plugging conditions in the process of in-situ heating exploitation of the shale reservoir are specifically quantified, which can effectively guide production and improve the economic benefits of in-situ heating exploitation of shale oil and gas.

[0042] (2) The method for determining the lower limit of the plugging thickness of a complex lithology layer based on temperature field simulation provided by an embodiment of the present invention determines 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 according to the lithology vertical distribution characteristics of the overlying strata within a set range; obtains the formula for preparing siltstone and mudstone respectively through experimental fitting; and prepares the top plate rock sample by integral molding. 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 plugging thickness of the complex lithology top plate with interlayers of mudstone and siltstone can be realized.

[0043] (3) The method for determining the lower limit of the sealing thickness of a complex lithology layer based on temperature field simulation provided in an embodiment of the present invention is that during the experiment, the temperature of the bottom of the roof is kept constant at the lowest temperature at which the kerogen conversion rate in the reservoir reaches 90%. At this temperature, the reservoir almost completes the conversion to hydrocarbons and achieves maximum oil and gas production. That is, this temperature is the highest temperature at which the reservoir may be heated during the in-situ heating and exploitation of an actual shale reservoir. Therefore, the setting of this temperature ensures the safety and rationality of the determined lower limit of the roof sealing thickness.

[0044] (4) The method for determining the lower limit of the plugging thickness of a complex lithology layer based on temperature field simulation provided by an embodiment of the present invention determines the lower limit of the plugging thickness of the roof plate based on the fact that the bottom temperature of the roof plate is constant at the lowest temperature at which the kerogen conversion rate in the shale reservoir reaches a set conversion rate threshold, and the lower limit of the roof plate plugging thickness is determined according to the lowest position where the roof plate rock sample temperature is not higher than the initial hydrocarbon production temperature of the kerogen in the overlying rock formation. Once the overlying rock formation begins to produce hydrocarbons, the kerogen material changes, which in turn causes changes in the rock structure, destroying the original plugging properties. Therefore, only roof plates below this temperature have plugging properties. Therefore, the setting of this temperature ensures that the lower limit of the roof plate plugging thickness is determined to be reasonable, and has strong production guidance significance.

[0045] (5) In the method for determining the lower limit of the sealing thickness of a complex lithology layer based on temperature field simulation 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.

[0046] (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 lower limit of the sealing thickness of a complex lithology layer based on temperature field simulation provided by the embodiment of the present invention not only considers the sealing properties of the roof, but also fully considers the sealing properties of the floor, thereby ensuring the reliability of the determination of the sealing performance and further providing a guarantee for the improvement of the recovery rate.

[0047] 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.

[0048] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0049] 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:

[0050] Figure 1 This is a flow chart of a method for determining the lower limit of the plugging thickness of a complex lithology layer based on temperature field simulation in Embodiment 1 of the present invention;

[0051] Figure 2 This is a flow chart of a method for determining the lower limit of the plugging thickness of a complex lithology layer based on temperature field simulation in Embodiment 2 of the present invention;

[0052] Figure 3 This is a flow chart of a method for determining the lower limit of the plugging thickness of a complex lithology layer based on temperature field simulation in Embodiment 3 of the present invention;

[0053] Figure 4 This is a schematic diagram of the axial cross section of the roof rock sample in the fourth embodiment of the present invention;

[0054] Figure 5 This is a temperature field simulation diagram in the fourth embodiment of the present invention;

[0055] Figure 6 for Figure 5Oil saturation variation diagram at the middle temperature line 200℃ and 220℃. DETAILED DESCRIPTION

[0056] 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.

[0057] 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.

[0058] 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.

[0059] 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.

[0060] The inventors found in their work that the existing technology has the problem of difficulty in effectively evaluating the top plate plugging performance during the heating and exploitation of shale reservoirs. After further research and development, the inventors found that the difference in heat conduction between the top and bottom plates of the shale reservoir during the in-situ heating and exploitation of the shale reservoir determines the difference in its plugging thickness. Therefore, the plugging thickness of the top and bottom plates can be reasonably determined through the simulation experiment of the temperature field. In addition, it is generally believed that mud shale can produce a plugging effect during the in-situ mining of shale reservoirs, but the inventors found that the complex lithology of interlayers of mud shale and siltstone may also produce a plugging effect during the in-situ mining of shale reservoirs. The embodiment of the present invention provides a method for determining the lower limit of the plugging thickness of complex lithology layers based on temperature field simulation, which can reasonably quantify the lower limit of the plugging thickness of the top plate of the shale reservoir by simplifying the lithology and temperature field simulation methods.

[0061] Embodiment 1

[0062] Embodiment 1 of the present invention provides a method for determining the lower limit of the plugging thickness of a complex lithology layer based on temperature field simulation, referring to Figure 1 As shown, the following steps are included:

[0063] 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.

[0064] The complex lithology layer is the overlying stratum of the shale reservoir, which is interbedded with siltstone and mud shale.

[0065] According to empirical data, the plugging thickness of the roof during in-situ heating and 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 (the roof plugging thickness required for in-situ heating of shale cannot be measured). 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.

[0066] 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%), that is, the ratios of the two are equivalent, then the lower part within the set range is 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.

[0067] Step S12: 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.

[0068] In some embodiments, fitting of a first formula for preparing siltstone may include: measuring the particle size distribution, mineral composition and porosity 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 error between the porosity of the currently prepared siltstone sample and the corresponding average value meets an error threshold, thereby obtaining the first formula for preparing siltstone.

[0069] 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%).

[0070] In some embodiments, fitting of a second formula for preparing mudstone may include: measuring the particle size distribution, mineral composition, TOC, porosity and kerogen initial hydrocarbon production temperature of rock samples of each mudstone layer within a set range of the overlying formation, and obtaining the average values ​​of the corresponding parameters by thickness weighting; preparing mudstone samples using the average values ​​of the particle size distribution and the average values ​​of the mineral composition of the mudstone layer as the current formula, and adjusting the current formula until the errors between the TOC, porosity and kerogen initial hydrocarbon production temperature of the currently prepared mudstone sample and the corresponding average values ​​meet the error threshold, thereby obtaining the second formula for preparing mudstone.

[0071] Optionally, in the process of fitting the first formula and the second formula, the parameters used for calibration may not only include the above parameters, but also include fracture pressure, breakthrough pressure and critical damage strain value of fracture, etc. Correspondingly, the measurement results of natural samples of these parameters are obtained by obtaining the measurement results of corresponding rock samples through thickness-weighted averaging.

[0072] Step S13: 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.

[0073] Roof rock samples of the same cross-sectional area (eg, cylindrical with a diameter of 5 cm) may be prepared.

[0074] Taking the above setting range of 500 cm thickness as an example, the thickness of the roof rock sample is also 500 cm.

[0075] Furthermore, the sides of the roof rock sample are wrapped with a heat-insulating material that does not contain pressure. The heat insulation can prevent heat from being dissipated to the surroundings during the heating process; if there is no pressure, the pressure can be released outwards.

[0076] Step S14: arrange a first heating device and a first temperature sensor on the bottom surface of the roof rock sample, arrange multiple first temperature sensors on the side of the roof rock sample at a first set interval, use the first heating device to heat the roof rock sample until the measured temperature of the first temperature sensor at the bottom is the first set temperature, and stabilize at this temperature until the measured value change amplitude of each first temperature sensor is less than the set threshold value, determine the lowest position where the roof rock sample temperature is not higher than the second set temperature according to the measured value of the first temperature sensor, and determine the lower limit of the roof sealing thickness according to the upper and lower overlapping relationship and the lowest position.

[0077] In the embodiment of the present application, from bottom to top corresponds to from bottom to top.

[0078] In some embodiments, the first heating device is a unidirectional heating device to save resources.

[0079] 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.

[0080] The first temperature sensor is arranged axially on the side of the top plate 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.

[0081] 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.

[0082] The first set temperature can be determined by utilizing a source rock thermal simulation experiment or a kerogen activation energy experiment.

[0083] 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.

[0084] 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.

[0085] 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.

[0086] In some embodiments, the second set temperature is the average value of the initial hydrocarbon production temperature of the kerogen of each shale sample within the set range of the overlying formation, which is usually 200-250°C.

[0087] The initial hydrocarbon production temperature of kerogen in rock samples can be measured using thermal simulation experiments of source rocks.

[0088] On the basis that the temperature at the bottom of the roof is constant at the lowest temperature at which the kerogen conversion rate in the shale reservoir reaches the set conversion rate threshold, the lower limit of the roof plugging thickness is determined according to the lowest position where the roof rock sample temperature is not higher than the initial hydrocarbon production temperature of the kerogen in the overburden. Once the overburden begins to produce hydrocarbons, the kerogen material changes, which in turn causes changes in the rock structure, destroying the original plugging property. Therefore, only the roof below this temperature has plugging properties. Therefore, the setting of this temperature ensures that the lower limit of the roof plugging thickness is reasonable and has strong production guidance significance.

[0089] The first set temperature, ie, the lowest temperature T0 at which the kerogen conversion rate in the shale reservoir reaches 90%, is determined in the above manner, and the initial hydrocarbon production temperature Tx of the kerogen in the overlying rock formation is determined.

[0090] Use the first heating device (heat source) to heat slowly (not exceeding 20°C / day), with the maximum temperature of the heat source between 400 and 650°C. Adjust the heat source power to make the bottom temperature of the roof rock sample constant at T0, until the measured temperature change amplitude of each first temperature sensor is less than the set threshold, that is, after the temperature stabilizes, collect the measured temperature of each first temperature sensor. Since the temperature of the roof rock sample gradually decreases from bottom to top, the measured temperatures of the first temperature sensors can be collected from bottom to top in sequence until the currently collected temperature is Tx or not greater than Tx. Determine the lowest position where the roof rock sample temperature is not higher than the second set temperature based on the position of the corresponding first temperature sensor.

[0091] If the currently collected temperature is Tx, the position of the corresponding first temperature sensor can be directly determined as the position where the roof rock sample temperature begins to drop to Tx; if the currently collected temperature begins to be less than Tx (the first temperature less than Tx), based on the currently collected temperature and the previous collected temperature and the position of the current first temperature sensor and the position of the previous first temperature sensor, the lowest position where the roof rock sample temperature is not higher than Tx is determined by the proportional method.

[0092] In some embodiments, based on the upper and lower overlapping relationship of the siltstone layer and the mudstone layer, the lower limit of the roof plugging thickness is determined according to the lowest position where the roof rock sample temperature is not higher than the second set temperature, which may include the following two situations:

[0093] 1. The relationship between the upper and lower superposition is that the siltstone layer is on the upper

[0094] (1) If the lowest position is located in the mudstone layer of the roof rock sample, the distance from the lowest position to the bottom surface of the roof rock sample is determined as the lower limit of the roof plugging thickness.

[0095] (2) If the lowest position is located in the siltstone layer of the roof rock sample, the temperature field simulation method is invalid, and it is impossible to determine whether the overlying rock layer has sealing properties, and it is even more impossible to quantify the lower limit of the roof sealing thickness.

[0096] 2. The relationship between the upper and lower superposition is that the siltstone layer is at the bottom.

[0097] (1) If the lowest position is located in the mudstone layer of the roof rock sample, the distance from the lowest position to the bottom surface of the roof rock sample is determined as the lower limit of the roof plugging thickness.

[0098] (2) If the lowest position is located in the siltstone layer of the roof rock sample, because the mud shale layer is located above, the temperature in the mud shale layer must be lower than the second set temperature. As long as the thickness is higher than the total thickness of the siltstone layer, the mud shale layer above can produce a plugging effect. Therefore, the thickness of the siltstone layer of the roof rock sample is determined as the lower limit of the roof plugging thickness.

[0099] 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.

[0100] The method for determining the lower limit of the plugging thickness of a complex lithology layer based on temperature field simulation provided in the first embodiment of the present invention is to prepare a roof rock sample by integral molding, and to heat the roof rock sample by using a first heating device so that the measured temperature of the first temperature sensor at the bottom is stabilized at a first set temperature, until the measured temperature of each first temperature sensor is stable, and the lowest position where the temperature of the roof rock sample is not higher than the second set temperature is determined according to the measured temperature of each first temperature sensor; and the lower limit of the roof plugging thickness is determined according to the upper and lower overlapping relationship of the siltstone layer and the mudstone layer and the lowest position. The lower limit of the roof plugging thickness of the shale reservoir is determined based on the temperature field simulation by an experimental method, and the roof plugging conditions in the process of in-situ heating exploitation of the shale reservoir are specifically quantified, which can effectively guide production and improve the economic benefits of in-situ heating exploitation of shale oil and gas.

[0101] The method for determining the lower limit of the plugging thickness of a complex lithology layer based on temperature field simulation provided in Example 1 of the present invention determines 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 according to the lithology vertical distribution characteristics of the overlying strata within a set range; obtains the formula for preparing siltstone and mudstone respectively through experimental fitting; and prepares the top plate rock sample by integral molding. The prepared synthetic sample takes into account the properties of mudstone and siltstone, as well as the vertical superposition relationship between the two, and reasonably simplifies the sample, so that the determination of the lower limit of the plugging thickness of the complex lithology top plate with interlayers of mudstone and siltstone can be realized.

[0102] Embodiment 2

[0103] Embodiment 2 of the present invention provides another method for determining the lower limit of the plugging thickness of a complex lithology layer based on temperature field simulation, specifically a method for determining the lower limit of the bottom plate plugging thickness of a shale reservoir, which is applicable to the case where the underlying rock layer is a mudstone stratum. For details, refer to Figure 2 As shown, the following steps are included:

[0104] 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 non-pressure-holding insulating material, arrange a second heating device and a second temperature sensor on the top surface of the bottom plate rock sample, and arrange multiple second temperature sensors on the side of the bottom plate rock sample at a second set interval.

[0105] 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.

[0106] 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.

[0107] 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.

[0108] 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.

[0109] 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.

[0110] The second temperature sensor is arranged axially on the side of the bottom plate rock sample. The second set interval is set according to the measurement accuracy requirement and can be consistent with the first set interval, usually 10 cm.

[0111] Step S22: Use the second heating device to heat the bottom plate rock sample until the measured temperature of the second temperature sensor on the top is the first set temperature, and stabilize it at this temperature until the measured temperature change amplitude of each second temperature sensor is less than the set threshold value, and determine the highest position where the bottom plate rock sample temperature is not higher than the third set temperature based on the measured temperature of each second temperature sensor.

[0112] 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.

[0113] Use the second heating device (heat source) to heat slowly (not exceeding 20°C / day), with the maximum temperature of the heat source between 400 and 650°C. Adjust the heat source power to make the top temperature of the bottom plate rock sample constant T0, until the measured temperature change amplitude of each second temperature sensor is less than the set threshold, that is, after the temperature stabilizes, collect the measured temperature of each second temperature sensor. Since the temperature of the bottom plate rock sample gradually decreases from top to bottom, the measured temperatures of the second temperature sensors can be collected from top to bottom in sequence until the currently collected temperature is the third set temperature or starts to be less than the third set temperature. Determine the highest position where the bottom plate rock sample temperature is not higher than the third set temperature based on the position of the corresponding second temperature sensor.

[0114] Taking the third set temperature as Tx as an example, 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 highest position where the bottom plate rock sample temperature is not higher than Tx is determined by the proportional method.

[0115] 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.

[0116] 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.

[0117] Embodiment 3

[0118] Embodiment 3 of the present invention provides another method for determining the lower limit of the sealing thickness of a complex lithology layer based on temperature 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 a shale reservoir in the above embodiment 1 is still applicable here.

[0119] Specifically, refer to Figure 3 As shown, the following steps are included:

[0120] Step S31: 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.

[0121] 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.

[0122] Step S32: Based on the measured properties of multiple siltstone samples within the set range of the underlying rock formation, prepare a third formula for siltstone through experimental fitting, and based on the measured properties of multiple shale samples within the set range of the underlying rock formation, prepare a fourth formula for shale through experimental fitting.

[0123] Step S33: 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.

[0124] Step S34: arrange a second heating device and a second temperature sensor on the top surface of the bottom plate rock sample, arrange multiple second temperature sensors on the side of the bottom plate rock sample at a second set interval, use the second heating device to heat the bottom plate rock sample until the measured temperature of the second temperature sensor on the top is the first set temperature, and stabilize at this temperature until the measured value change amplitude of each second temperature sensor is less than the set threshold value, determine the highest position where the bottom plate rock sample temperature is not higher than the fourth set temperature according to the measured value of the second temperature sensor, and determine the lower limit of the low plate plugging thickness according to the highest position based on the upper and lower overlapping relationship.

[0125] The fourth set temperature is the average value of the initial hydrocarbon production temperature of the kerogen of the shale samples within the set range of the underlying rock formation.

[0126] When studying the sealing properties of shale reservoirs, the prior art often only focuses on the sealing properties of the top plate, while ignoring the sealing effect of the bottom plate. For in-situ heating and exploitation of shale reservoirs, poor bottom plate sealing performance will still lead to the loss of oil and gas, affecting the recovery rate. The method for determining the sealing thickness of complex lithology adjacent layers in shale reservoirs based on temperature simulation provided in the second and third embodiments of the present invention fully considers the sealing properties of the bottom plate, ensures the reliability of the determination of the sealing performance, and further provides a guarantee for the improvement of the recovery rate.

[0127] The above three embodiments can be applied separately; embodiment one and embodiment two can also be applied in combination, or embodiment one and embodiment three can be applied in combination, to determine both the lower limit of the top plate plugging thickness of the shale reservoir and the lower limit of the bottom plate plugging thickness of the shale reservoir. The top and bottom plate thicknesses of the shale reservoir both meet the corresponding lower limits of the plugging thickness, and then it is determined that the plugging requirements are met.

[0128] Embodiment 4

[0129] Embodiment 4 of the present invention provides a specific application of a method for determining a lower limit of the top plate plugging thickness of a shale reservoir, and verifies its accuracy through numerical simulation, including the following steps:

[0130] 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.

[0131] 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.

[0132] 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.

[0133] 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.

[0134] 5) According to the averaged parameter results, according to the superposition relationship and thickness, a roof rock sample containing a homogeneous siltstone layer and a homogeneous shale layer is synthesized at one time (the thickness of the shale layer is equal to 400 cm, and the thickness of the siltstone layer is equal to 100 cm. The cumulative deviation of the above parameters from the design value is not more than 15%, and the sample preparation is qualified. The roof rock sample is a cylinder with a diameter of 5 cm, see Figure 4 The figure shows a schematic cross-sectional view of the roof rock sample along the axial direction.

[0135] 6) The T0 of the reservoir rock sample was measured to be 300°C (90% conversion temperature of kerogen).

[0136] 7) The average Tx (initial hydrocarbon production temperature of kerogen) of rock samples in the shale layer was determined to be 200°C.

[0137] 8) Wrap the roof rock sample with rock wool as the insulation material, and the insulation material is not compressed. Place the wrapped roof rock sample in the experimental device. Place a unidirectional heat source point at the bottom of the roof rock sample, arrange temperature sensors from the bottom, and arrange several temperature sensors along the axial direction of the roof rock sample at intervals of 10 cm.

[0138] 9) The heat source is heated at a rate of 20°C / day, and the peak temperature is set to 300°C (T0).

[0139] 10) After the bottom of the roof rock sample is kept at a constant temperature of T0 for 30 minutes (the temperature measured by each temperature sensor reaches stability), the roof rock sample temperature sensor data is continuously collected. The distance from the position where the temperature Tx is measured to the bottom of the roof rock sample is 140 cm, which is the lower limit of the roof plugging thickness.

[0140] 11) A numerical model consistent with the sample and experimental conditions was established. The shale was on top and 400 cm thick. Its TOC, porosity, Tx, Px, εx, and mineral composition were the same as those of the artificial samples used in the experiment. The siltstone was on the bottom and 100 cm thick. Its porosity, Px, εx, and mineral composition were the same as those of the artificial samples used in the experiment. The kerogen activation energy parameters of the shale were set so that the Tx (initial hydrocarbon production temperature of the kerogen) of the roof rock sample was 200 °C.

[0141] 12) Keep the temperature at the bottom of the top rock sample constant at T0 (300°C), complete the numerical simulation of the temperature field, and wait for the grid temperature to stabilize.

[0142] 13) See Figure 5 The figure shows the simulated temperature field of the roof rock sample. Figure 5 Oil saturation at the Tx temperature line (200°C) (see Figure 6 There was no change in the whole simulation period, indicating that oil and gas were blocked at this location.

[0143] 14) Observation Figure 5 Oil saturation at 220°C (see Figure 6 During the whole simulation period, there are obvious changes, indicating that the oil and gas are not blocked at this location.

[0144] 15) The thickness of the Tx temperature line is 138 cm. The comparison proves that the top plate with a thickness of 138 cm meets the plugging requirements. The error between the numerical simulation results and the experimental results (140 cm) is 1.4%, so the numerical simulation verifies the reliability of the experimental results.

[0145] 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.

[0146] 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.

[0147] 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", "second", etc. are used for descriptive purposes and are not to be understood as indicating or implying relative importance.

Claims

1. A method for determining the lower limit of the plugging thickness of a complex lithology layer based on temperature field simulation, 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, characterized in that: The method comprises: 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 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; A first heating device and a first temperature sensor are arranged on the bottom surface of the roof rock sample, and a plurality of first temperature sensors are arranged on the side surface of the roof rock sample at a first set interval. The roof rock sample is heated by the first heating device until the measured temperature of the first temperature sensor at the bottom is a first set temperature, and is stabilized at this temperature until the variation amplitude of the measured values ​​of each first temperature sensor is less than a set threshold value. The lowest position where the temperature of the roof rock sample is not higher than the second set temperature is determined based on the measured value of the first temperature sensor, and the lower limit of the roof sealing thickness is determined based on the upper and lower overlapping relationship and the lowest position.

2. The method according to claim 1, 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 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 a siltstone sample, adjusting the current formula until the error between the porosity of the currently prepared siltstone sample and the corresponding average value meets the error threshold, thereby obtaining a first formula for preparing siltstone; Accordingly, the second formula for preparing shale by experimental fitting based on the measured properties of the plurality of shale samples includes: Measuring the particle size distribution, mineral composition, TOC, porosity and initial hydrocarbon production temperature of the rock samples of each shale layer within the set range, and obtaining the average values ​​of the corresponding parameters by thickness-weighted averaging; The average values ​​of the particle size distribution of the shale layer and the average values ​​of the mineral composition are used as the current formula to prepare a shale sample, and the current formula is adjusted until the errors between the TOC, porosity and initial hydrocarbon production temperature of the kerogen of the currently prepared shale sample and the corresponding average values ​​meet the error threshold, thereby obtaining a second formula for preparing shale.

3. The method according to claim 2, characterized in that The first set temperature is the lowest temperature at which the kerogen conversion rate in the shale reservoir reaches a set conversion rate threshold.

4. The method according to claim 3, characterized in that The first set temperature is the lowest temperature at which the kerogen conversion rate in the shale reservoir reaches 90%.

5. The method according to claim 3, characterized in that The second set temperature is the average value of the initial hydrocarbon production temperature of the kerogen of each shale sample within the set range of the overlying formation.

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

7. The method according to claim 1, characterized in that If the upper and lower overlapping relationship is that the siltstone layer is on the upper side, determining the lower limit of the roof plugging thickness according to the upper and lower overlapping relationship and the lowest position includes: If the lowest position is located in the mudstone layer of the roof rock sample, the distance from the lowest position to the bottom surface of the roof rock sample is determined as the lower limit of the roof plugging thickness; If the lowest position is located in the siltstone layer of the roof rock sample, the method is ineffective.

8. The method according to claim 7, characterized in that If the upper and lower overlapping relationship is that the siltstone layer is at the bottom, determining the lower limit of the roof plugging thickness according to the upper and lower overlapping relationship and the lowest position includes: If the lowest position is located in the mudstone layer of the roof rock sample, the distance from the lowest position to the bottom surface of the roof rock sample is determined as the lower limit of the roof plugging thickness; If the lowest position is located in the siltstone layer of the roof rock sample, the total thickness of the siltstone layer is determined as the lower limit of the roof sealing thickness.

9. 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, a side surface of the bottom plate rock sample is wrapped by a heat-insulating material that does not block pressure, a second heating device and a second temperature sensor are arranged on the top surface of the bottom plate rock sample, and a plurality of second temperature 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 on the top is the first set temperature, and stabilized at this temperature until the measured temperature variation amplitude of each second temperature sensor is less than the set threshold value, and the highest position where the bottom plate rock sample temperature is not higher than the third set temperature is determined according to the measured temperature of each second temperature sensor; The lower limit of the bottom plate plugging thickness of the shale reservoir is determined according to the distance between the position and the top surface.

10. The method according to claim 9, characterized in that The third set temperature is the initial hydrocarbon production temperature of kerogen in the underlying rock formation.

11. 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; preparing a third formula for siltstone by experimental fitting based on measured properties of a plurality of siltstone samples within the set range of the underlying rock formation, and preparing a fourth formula for shale by experimental fitting based on measured properties of a plurality of shale samples within the set range of the underlying rock formation; 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 and a second temperature sensor are arranged on the top surface of the bottom plate rock sample, and multiple second temperature sensors are arranged on the side of the bottom plate rock sample at a second set interval. The second heating device is used to heat the bottom plate rock sample until the measured temperature of the second temperature sensor on the top is the first set temperature, and stabilize it at this temperature until the change amplitude of the measured value of each second temperature sensor is less than the set threshold value, and the highest position where the temperature of the bottom plate rock sample is not higher than the fourth set temperature is determined according to the measured value of the second temperature sensor, and based on the overlapping relationship between the siltstone layer and the shale layer of the underlying rock stratum, the lower limit of the low plate plugging thickness is determined according to the highest position.

12. The method according to claim 11, characterized in that The fourth set temperature is the average value of the initial hydrocarbon production temperature of the kerogen of each shale sample within the set range of the underlying rock formation.

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