Method for determining the thickness of the shale reservoir siltstone adjacent layer plugging based on pressure field simulation

Abstract

The application discloses a method for determining the shale reservoir siltstone adjacent layer plugging thickness based on pressure field simulation, comprising the following steps: if it is judged that the shale reservoir fracture pressure is less than the minimum starting pressure of the overlying siltstone layer, the following steps are executed: preparing a roof rock sample by using the overlying siltstone coring section, wrapping the roof rock sample by using a sealing material, arranging a pressurizing device and a pressure sensor on the bottom surface of the rock sample, and arranging a plurality of pressure sensors on the side surface of the roof rock sample at a set interval; pressurizing the roof rock sample to the bottom to a set pressure by using the pressurizing device, and stabilizing at the pressure until the change amplitude of the measurement values of all the pressure sensors is less than a set threshold value; determining the lowest position of the roof rock sample at which the pressure is not higher than a second set pressure according to the measurement values of the pressure sensors; determining the lower limit of the roof plugging thickness according to the distance from the position to the bottom surface; and determining the lower limit of the floor plugging thickness in the same way. The method can reasonably quantify the lower limit of the roof and floor plugging thickness of the shale reservoir by the method of pressure field simulation.

Description

Technical Field

[0001] The present invention relates to the technical fields of petroleum geology and shale reservoir mining, and in particular to a method for determining the sealing thickness of a siltstone adjacent layer in a shale reservoir based on pressure field simulation. Background Art

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

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

[0004] Whether the overlying rock layer can effectively seal the shale reservoir during in-situ mining (whether a caprock can be formed) is one of the key factors in improving the recovery rate. However, there is no effective method to evaluate the roof sealing performance during in-situ mining of shale reservoirs. Summary of the Invention

[0005] In order to at least partially solve the above-mentioned technical problems existing in the prior art, the inventors have made the present invention. Through specific implementation methods, a method for determining the sealing thickness of the siltstone adjacent layer in a shale reservoir based on pressure field simulation is provided. The method can reasonably quantify the lower limit of the sealing thickness of the shale reservoir roof through the pressure field simulation method.

[0006] An embodiment of the present invention provides a method for determining the sealing thickness of a siltstone adjacent layer in a shale reservoir based on pressure field simulation, comprising: if it is determined that the fracture pressure of the shale reservoir is less than the minimum starting pressure of the overlying siltstone layer of the shale reservoir, performing the following steps:

[0007] A roof rock sample is prepared using the coring section of the overlying siltstone layer, a side surface of the roof rock sample is wrapped with a sealing material, a first pressurizing device and a first pressure sensor are arranged on the bottom surface of the roof rock sample, and a plurality of first pressure sensors are arranged on the side surface of the roof rock sample at first set intervals;

[0008] Using the first pressurizing device to pressurize the roof rock sample until the pressure measured by the first pressure sensor at the bottom reaches a first set pressure, and stabilizing the pressure at this pressure until the amplitude of the pressure change measured by each first pressure sensor is less than a set threshold, and determining the lowest position where the pressure of the roof rock sample is no higher than the second set pressure based on the pressure measured by the first pressure sensor;

[0009] The lower limit of the roof plugging thickness of the shale reservoir is determined based on the distance between the position and the bottom surface.

[0010] In some embodiments, the first set pressure is the fracture pressure of the shale reservoir, and the second set pressure is the fracture pressure of the overlying siltstone layer.

[0011] In some embodiments, the length of the roof rock sample is not less than 500 cm.

[0012] In some embodiments, the first pressurizing device is a fluid pressurizing device.

[0013] In some embodiments, the first set interval is set according to measurement accuracy requirements.

[0014] In some embodiments, determining the lowest position where the roof rock sample pressure is not higher than the second set pressure based on the measured pressure of each first pressure sensor includes:

[0015] The measured pressures of the first pressure sensors are collected in order from bottom to top. If the currently collected pressure is the second set pressure, the position of the corresponding first pressure sensor is determined as the lowest position where the roof rock sample pressure is not higher than the second set pressure.

[0016] If the currently collected pressure is the first pressure that is less than the second set pressure, the lowest position where the roof rock sample pressure is not higher than the second set pressure is determined by a proportional method based on the currently collected pressure and the previous collected pressure and the position of the current first pressure sensor and the position of the previous first pressure sensor, and the previous pressure is not equal to the second set pressure.

[0017] In some embodiments, determining the lower limit of the roof plugging thickness of the shale reservoir based on the distance from the position to the bottom surface includes:

[0018] The distance from the position to the bottom surface is determined as the lower limit of the roof plugging thickness of the shale reservoir; or,

[0019] The product of the safety correction factor and the distance from the position to the bottom surface is determined as the lower limit of the roof plugging thickness of the shale reservoir, and the safety correction factor is greater than 1.

[0020] In some embodiments, if the underlying rock formation of the shale reservoir is a mud shale formation, the method further includes performing the following step of determining the lower limit of the bottom plate plugging thickness:

[0021] A bottom plate rock sample is prepared using a coring section of an underlying rock formation of the shale reservoir, a side surface of the bottom plate rock sample is wrapped with a sealing material, a second pressurizing device and a second pressure sensor are arranged on a top surface of the bottom plate rock sample, and a plurality of second pressure sensors are arranged on the side surface of the bottom plate rock sample at second set intervals;

[0022] The bottom plate rock sample is pressurized by the second pressurizing device until the pressure measured by the second pressure sensor at the top reaches the first set pressure, and is stabilized at this pressure until the amplitude of the pressure change measured by each second pressure sensor is less than a set threshold, and the maximum position at which the bottom plate rock sample pressure is not higher than the third set pressure is determined based on the pressure measured by the second pressure sensor;

[0023] The lower limit of the bottom plate plugging thickness of the shale reservoir is determined based on the distance between the position and the top surface.

[0024] In some embodiments, if the underlying rock layer of the shale reservoir is an underlying siltstone layer, the method further includes:

[0025] Determining whether the shale reservoir fracture pressure is less than the minimum starting pressure of the underlying siltstone layer;

[0026] If so, execute the step of determining the lower limit of the bottom plate sealing thickness.

[0027] In some embodiments, the third set pressure is a fracture pressure of the underlying formation.

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

[0029] (1) The method provided in the embodiment of the present invention for determining the sealing thickness of the siltstone adjacent layer of a shale reservoir based on pressure field simulation uses a first pressurizing device to pressurize the roof rock sample so that the measured pressure of the first pressure sensor at the bottom stabilizes at the first set pressure until the measured pressure of each first pressure sensor stabilizes. The lowest position where the pressure of the roof rock sample is not higher than the second set pressure is determined based on the measured pressure of the first pressure sensor; and the lower limit of the roof sealing thickness of the shale reservoir is determined based on the distance between this position and the bottom surface. By experimentally determining the lower limit of the roof sealing thickness of the shale reservoir based on pressure field simulation, the roof sealing conditions during the in-situ mining of the shale reservoir are specifically quantified, which can effectively guide production and improve the economic benefits of in-situ mining of shale oil and gas.

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

[0031] (3) The method provided by the embodiment of the present invention for determining the sealing thickness of the siltstone adjacent layer in a shale reservoir based on pressure field simulation is as follows: during the experiment, the pressure at the bottom of the roof is kept constant at the shale reservoir fracture pressure, which is the highest pressure that may be applied to the reservoir during in-situ mining of the shale reservoir. Under the premise that the pressure at the bottom of the roof is kept constant at the shale reservoir fracture pressure, the lower limit of the roof sealing thickness of the shale reservoir is determined based on the lowest position where the pressure of the roof rock sample is not higher than the fracture pressure of the overlying siltstone layer. The setting of the two pressure values ​​ensures the safety and rationality of the determined lower limit of the roof sealing thickness.

[0032] (4) When studying the sealing properties of shale reservoirs, existing technologies often focus only on the sealing properties of the roof, while ignoring the sealing function of the floor. However, for in-situ mining of shale reservoirs, poor floor sealing performance will still lead to oil and gas loss, affecting the recovery rate. The method for determining the sealing thickness of the siltstone adjacent layer in a shale reservoir based on pressure 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, thus ensuring the reliability of the determination of the sealing performance and further providing a guarantee for improving the recovery rate.

[0033] Other features and advantages of the present invention will be described in the following description, and in part will become apparent from the description, or will be understood by practicing the present invention. The purposes and other advantages of the present invention can be realized and obtained by the structures particularly pointed out in the written description, claims, and drawings.

[0034] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] 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:

[0036] Figure 1 This is a flow chart of a method for determining the sealing thickness of the siltstone adjacent layer in a shale reservoir based on pressure field simulation in Example 1 of the present invention;

[0037] Figure 2This is a flow chart of a method for determining the sealing thickness of the siltstone adjacent layer in a shale reservoir based on pressure field simulation in Example 2 of the present invention;

[0038] Figure 3 This is a schematic diagram of the axial cross-section of the roof rock sample in Example 3 of the present invention;

[0039] Figure 4 This is a pressure field simulation diagram in Example 3 of the present invention;

[0040] Figure 5 for Figure 4 Oil saturation change diagram at the middle pressure line of 20MPa and 25MPa. DETAILED DESCRIPTION

[0041] Exemplary embodiments of the present disclosure will be described in more detail below with reference to the accompanying drawings. Although exemplary embodiments of the present disclosure are shown in the accompanying drawings, it should be understood that the present disclosure can be implemented in various forms and should not be limited by the embodiments set forth herein. Rather, these embodiments are provided to enable a more thorough understanding of the present disclosure and to fully convey the scope of the present disclosure to those skilled in the art.

[0042] It should be understood that the terms described herein are intended only to describe particular embodiments and are not intended to limit the present invention. In addition, for numerical ranges herein, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Each smaller range between any intermediate value within a stated value or stated range and any other stated value or intermediate value within the stated range is also encompassed by the present invention. The upper and lower limits of these smaller ranges may be independently included or excluded within the scope.

[0043] Unless otherwise indicated, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which the invention belongs. Although the present invention describes only preferred methods and materials, any methods and materials similar or equivalent to those described herein may also be used in the implementation or testing of the present invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials related to the documents. In the event of any conflict with any incorporated document, the content of this specification shall prevail.

[0044] In the description of the present invention, it should be noted that the terms “include”, “including”, “have”, “contain”, etc. are all open terms, which mean including but not limited to.

[0045] The inventors find that during in-situ exploitation of the shale reservoir, the source rock starts to crack and generate hydrocarbon after being heated to a certain pressure, the flow of the hydrocarbon makes the top plate and the bottom plate of the shale reservoir be affected by the fluid pressure, and therefore the lower limit of the sealing thickness of the top plate and the bottom plate can be reasonably determined through the simulation experiment of the pressure field. In addition, the inventors believe that the limitation of the lithology understanding of the cap rock limits the development of oil and gas exploration, and the siltstone may also become the cap rock during the in-situ exploitation of the shale reservoir under certain conditions.

[0046] The embodiment of the present application provides a method for determining the sealing thickness of the siltstone adjacent layer of the shale reservoir based on pressure field simulation, which can reasonably quantify the lower limit of the sealing thickness of the top plate of the shale reservoir through the method of pressure field simulation.

[0047] Embodiment one

[0048] The embodiment one of the present application provides a method for determining the sealing thickness of the siltstone adjacent layer of the shale reservoir based on pressure field simulation.

[0049] Firstly, the shale reservoir fracture pressure and the minimum starting pressure (fracture pressure) of the fluid migration of the overlying siltstone layer need to be measured through experiments to determine whether the shale reservoir fracture pressure is less than the minimum starting pressure of the overlying siltstone layer; if yes, the subsequent determination of the lower limit of the sealing thickness is performed; if no, it is determined that the overlying siltstone layer does not have sealing property during the in-situ exploitation of the shale reservoir.

[0050] The minimum starting pressure of the overlying siltstone layer needs to be measured by determining the minimum starting pressure of at least 5 or more rock samples (approximately uniformly distributed rock samples in the underground) in the overlying siltstone layer, and then taking the average value. The shale reservoir fracture pressure needs to be measured by determining the fracture pressure of at least 3 or more rock samples (approximately uniformly distributed rock samples in the underground) in the shale reservoir, and then taking the average value.

[0051] The above measurement is performed under the initial temperature and pressure conditions of the corresponding stratum.

[0052] The specific determination process of the lower limit of the sealing thickness of the overlying siltstone layer is shown in the following Figure 1 and includes the following steps:

[0053] Step S11: a top plate rock sample is prepared by using the coring section of the overlying rock layer of the shale reservoir, the side surface of the top plate rock sample is wrapped with a sealing material, a first pressure device and a first pressure sensor are arranged on the bottom surface of the top plate rock sample, and a plurality of first pressure sensors are arranged on the side surface of the top plate rock sample at a first set interval.

[0054] The top plate rock sample with the same cross-sectional area (for example, a cylindrical shape with a diameter of 5 cm) is prepared by using the coring section of the overlying rock layer of the shale reservoir.

[0055] According to empirical data, the sealing thickness of the roof during in-situ mining of shale reservoirs is usually within 300 to 400 centimeters. Therefore, the length (thickness) of the roof rock sample is set to be no less than 500 cm. Thicker length increases the difficulty and cost of the experiment; thinner length easily falls below the lower limit of the actual sealing thickness of the roof, resulting in experimental failure (unable to measure the roof sealing thickness required for in-situ mining of shale).

[0056] The sides of the top plate rock sample are wrapped with sealing material. The sealing property ensures that the fluid applied from the bottom of the rock sample cannot enter between the rock sample and the thermal insulation sealing material during the fluid pressurization process. The pressure resistance of the sealing material is required to be not less than 80MPa.

[0057] The first pressure sensors 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.

[0058] The bottom surface of the roof rock sample refers to the side closest to the shale reservoir at the corresponding original underground position.

[0059] The first pressurizing device is a fluid pressurizing device.

[0060] Step S12: Use the first pressurizing device to pressurize the roof rock sample until the measured pressure of the first pressure sensor at the bottom is the first set pressure, and stabilize it at this pressure until the measured pressure change amplitude of each first pressure sensor is less than the set threshold value, and determine the lowest position where the roof rock sample pressure is not higher than the second set pressure based on the measured pressure of the first pressure sensor.

[0061] In some embodiments, the first set pressure is the fracture pressure of the shale reservoir, and the second set pressure is the fracture pressure of the overlying siltstone layer, both of which can be determined through rock fracture pressure experiments.

[0062] The fracture pressure of shale reservoirs is usually around 50 MPa, and the fracture pressure of the overlying siltstone layer is usually around 20 MPa.

[0063] The first set pressure, ie, the shale reservoir fracture pressure P0, and the second set pressure, ie, the overlying siltstone layer fracture pressure Px, are determined in the above manner.

[0064] The bottom of the roof rock sample is pressurized by using a first pressurizing device, 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 roof rock sample is constant at P0 and is stable for at least 30 minutes until the change amplitude of the measured value of each sensor is less than the set threshold. That is, after the pressure is stable, the measured values ​​of each first pressure sensor are collected. Since the pressure of the roof rock sample gradually decreases from bottom to top, the measured values ​​of the first pressure sensors can be collected in sequence from bottom to top until the currently collected pressure is no greater than Px. The lowest position where the pressure of the roof rock sample is no higher than Px is determined according to the position of the corresponding sensor.

[0065] If the currently collected pressure is the second set pressure Px, the position of the corresponding first pressure sensor is directly determined as the lowest position where the roof rock sample pressure is not higher than Px; if the currently collected pressure begins to be less than Px (the first pressure less than Px), the lowest position where the roof rock sample pressure is not higher than Px is determined by the proportional method based on the currently collected pressure and the previous collected pressure and the position of the current first pressure sensor and the position of the previous first pressure sensor.

[0066] Step S13: determining the lower limit of the roof plugging thickness of the shale reservoir according to the distance between the position and the bottom surface.

[0067] The distance between this position and the bottom surface can be directly determined as the lower limit of the roof plugging thickness of the shale reservoir; other factors affecting the plugging performance can also be further considered to determine the safety correction factor (greater than 1), and the product of the safety correction factor and the determined distance can be used as the lower limit of the roof plugging thickness of the shale reservoir.

[0068] The method provided in Example 1 of the present invention for determining the sealing thickness of the siltstone adjacent layer in a shale reservoir based on pressure field simulation utilizes a first pressurizing device to pressurize the roof rock sample so that the measured pressure of the first pressure sensor at the bottom stabilizes at a first set pressure until the measured pressure of each first pressure sensor stabilizes. The lowest position where the pressure of the roof rock sample is not higher than the second set pressure is determined based on the measured pressure of the first pressure sensor; and the lower limit of the roof sealing thickness of the shale reservoir is determined based on the distance between this position and the bottom surface. By experimentally determining the lower limit of the roof sealing thickness of the shale reservoir based on pressure field simulation, the roof sealing conditions during the in-situ mining of the shale reservoir are specifically quantified, which can effectively guide production and improve the economic benefits of in-situ mining of shale oil and gas.

[0069] It is currently generally believed that only mud shale can effectively seal shale reservoirs during in-situ mining. The method provided in Example 1 of the present invention for determining the sealing thickness of siltstone adjacent layers in shale reservoirs based on pressure field simulation proposes that if the overlying rock layer of the shale reservoir is siltstone, as long as the minimum starting pressure (breakthrough pressure) is greater than the fracture pressure of the reservoir and the thickness meets the lower limit of the sealing thickness, a sealing effect can also be achieved during in-situ mining of the shale reservoir.

[0070] In a first embodiment of the present invention, a method for determining the sealing thickness of the adjacent siltstone layer in a shale reservoir based on pressure field simulation is provided. During the experiment, the pressure at the bottom of the roof is maintained constant at the shale reservoir fracture pressure, which is the highest pressure that can be applied to the reservoir during in-situ mining of the shale reservoir. Under the premise that the pressure at the bottom of the roof is constant at the shale reservoir fracture pressure, the lower limit of the roof sealing thickness of the shale reservoir is determined based on the lowest position where the pressure of the roof rock sample does not exceed the fracture pressure of the overlying siltstone layer. The setting of these two pressures ensures the safety and rationality of the determined lower limit of the roof sealing thickness.

[0071] Example 2

[0072] Embodiment 2 of the present invention provides another method for determining the sealing thickness of the siltstone adjacent layer of a shale reservoir based on pressure field simulation, specifically a method for determining the lower limit of the bottom plate sealing thickness of a shale reservoir. 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.

[0073] If the underlying rock layer of the shale reservoir is a mudstone formation, directly perform the following steps to determine the lower limit of the bottom plate plugging thickness; if the underlying rock layer of the shale reservoir is an underlying siltstone layer, determine whether the shale reservoir fracture pressure is less than the minimum starting pressure of the underlying siltstone layer; if so, perform the following steps to determine the lower limit of the bottom plate plugging thickness; if not, determine that the underlying formation does not have sealing properties during the in-situ mining of the shale reservoir.

[0074] Specifically, refer to Figure 2 As shown, determining the lower limit of the bottom plate plugging thickness includes the following steps:

[0075] 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 sealing material, arrange a second pressurizing device and a second pressure sensor on the top surface of the bottom plate rock sample, and arrange multiple second pressure sensors on the side of the bottom plate rock sample at a second set interval.

[0076] The second pressure sensor may be the same pressure sensor as the first pressure sensor, and the "first" and "second" here are only used to distinguish whether the pressure sensor is set in the top plate rock sample or the bottom plate rock sample.

[0077] A bottom rock sample of the same cross-sectional area (e.g., cylindrical with a diameter of 5 cm) is prepared from a cored section of the underlying stratum of the shale reservoir. The length (thickness) of the bottom rock sample is not less than 500 cm.

[0078] The second pressurizing device can be the same as the first pressurizing device. The "first" and "second" here are only used to distinguish whether the pressurizing device is set on the bottom surface of the top plate rock sample or the top surface of the bottom plate rock sample.

[0079] The second pressure sensors are 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.

[0080] Step S22: Use the second pressurizing device to pressurize the bottom plate rock sample until the measured pressure of the second pressure sensor at the top is the first set pressure, and stabilize at this pressure until the measured pressure change amplitude of each second pressure sensor is less than the set threshold value, and determine the highest position where the bottom plate rock sample pressure is not higher than the third set pressure based on the measured pressure of the second pressure sensor.

[0081] In some embodiments, the third set pressure is the fracture pressure of the underlying rock formation, and its determination method can refer to the determination of the second set pressure.

[0082] Taking the third set pressure as Px as an example, the second pressurizing device is used to pressurize the top of the bottom 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 top of the bottom plate rock sample is constant at P0 and stabilized for at least 30 minutes until the change amplitude of the measured value of each sensor is less than the set threshold. That is, after the pressure is stable, the measured values ​​of each second pressure sensor are collected. Since the pressure of the bottom plate rock sample gradually decreases from top to bottom, the measured values ​​of the second pressure sensors can be collected in sequence from top to bottom until the currently collected pressure is no greater than Px. The highest position where the pressure of the top plate rock sample is no higher than Px is determined according to the position of the corresponding sensor.

[0083] 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 position of the current second pressure sensor and the position of the previous second pressure sensor, the highest position where the bottom plate rock sample pressure is not higher than Px is determined by the proportional method.

[0084] Step S23: determining the lower limit of the bottom plate plugging thickness of the shale reservoir according to the distance from the position to the top surface.

[0085] The distance between the position and the top surface can be directly determined as the lower limit of the shale reservoir floor sealing thickness, or a safety correction factor (greater than 1) can be further determined by considering other sealing performance influencing factors, and the product of the safety correction factor and the determined distance is taken as the lower limit of the shale reservoir floor sealing thickness.

[0086] The prior art only focuses on the sealing of the top plate when studying the sealing of the shale reservoir, and ignores the sealing of the bottom plate. For in-situ mining of the shale reservoir, poor sealing performance of the bottom plate will still cause the loss of oil and gas and affect the recovery rate. The method for determining the siltstone adjacent layer sealing thickness of the shale reservoir based on pressure field simulation provided in Embodiment Two fully considers the sealing of the bottom plate, ensures the reliability of the sealing performance determination, and further provides a guarantee for improving the recovery rate.

[0087] Embodiments One and Two can be applied independently or in combination, that is, the lower limit of the shale reservoir top plate sealing thickness and the lower limit of the shale reservoir bottom plate sealing thickness are determined, and the thicknesses of the top plate and the bottom plate of the shale reservoir both satisfy the corresponding lower limit of the sealing thickness, so that the sealing requirement is met.

[0088] Embodiment Three

[0089] Embodiment Three of the present application provides a specific application of the method for determining the lower limit of the shale reservoir top plate sealing thickness, and the accuracy is verified by numerical simulation, including the following steps:

[0090] 1) The Po (fracturing pressure) of the shale reservoir rock sample is 50 MPa.

[0091] 2) The Px (fracturing pressure) of the top plate rock sample is 20 MPa.

[0092] 3) A cylindrical top plate rock sample with a diameter of 5 cm and a length of 500 cm is prepared. Referring to FIG. 1, which is a schematic view of the cross section of the top plate rock sample along the axial direction. Figure 3

[0093] 4) The top plate rock sample is wrapped with a pressure-resistant steel sleeve with a pressure resistance of not less than 80 MPa, and then wrapped with rock wool as a heat insulation material. Then, the top plate rock sample is placed in an experimental device, and the sealing property is ensured so that the fluid applied at the bottom of the sample cannot enter the space between the sample and the steel sleeve.

[0094] 5) A plurality of pressure sensors are arranged at intervals of 10 cm along the axial direction of the top plate rock sample from the bottom of the top plate rock sample.

[0095] 6) The bottom of the top plate rock sample is pressurized with a fluid, and the pressurization speed is 300 KPa / day, and the pressure peak value is 50 MPa (Po).

[0096] ​7) After the bottom pressure of the roof rock sample is constant at P0 for 30 minutes (the measurement values ​​of each sensor are stable), the roof rock sample pressure sensor data are continuously collected.

[0097] 10) The distance from the position where the pressure Px is measured to the bottom of the roof rock sample is 140 cm, which is the lower limit of the roof sealing thickness.

[0098] 11) Establish a numerical model consistent with the roof rock sample and experimental conditions, and set the Px (fracture pressure) of the roof rock to 20 MPa.

[0099] 12) Keep the pressure at the bottom of the roof rock sample constant at P0 (50 MPa), complete the numerical simulation of the pressure field, and wait for the grid temperature to stabilize.

[0100] 13) See Figure 4 The figure shows the simulated pressure field of the roof rock sample. Figure 4 Oil saturation at the Px pressure line (20 MPa) (see Figure 5 There was no change during the entire simulation period, indicating that oil and gas were blocked at this location.

[0101] 14) Observation Figure 4 Oil saturation at the medium pressure line 25MPa (see Figure 5 During the entire simulation period, there are obvious changes, indicating that the oil and gas are not blocked at this location.

[0102] 15) The thickness of the Px pressure line is 146 cm. Comparison shows that a roof thickness of 146 cm meets the plugging requirements. The error between the numerical simulation results and the experimental results (140 cm) is 4.3%, thus the numerical simulation verifies the reliability of the experimental results.

[0103] It should be understood that the specific order or hierarchy of steps in the disclosed processes is an example of an exemplary method. Based on design preferences, it should be understood that the specific order or hierarchy of steps in the process can be rearranged without departing from the scope of the present disclosure. The accompanying method claims present elements of the various steps in an exemplary order and are not intended to be limited to the specific order or hierarchy described.

[0104] In the foregoing detailed description, various features are grouped together in a single embodiment to simplify the disclosure. This method of disclosure should not be interpreted as reflecting an intention that embodiments of the claimed subject matter require more features than are expressly recited in each claim. On the contrary, as reflected in the appended claims, the invention comprises less than all the features of any individual disclosed embodiment. The appended claims are therefore hereby expressly incorporated into the detailed description, with each claim standing on its own as a separate preferred embodiment of the invention.

[0105] The above description includes examples of one or more embodiments. Of course, it is impossible to describe all possible combinations of components or methods for the purpose of describing the above embodiments, but it should be recognized by those skilled in the art that the various embodiments may be further combined and arranged. Therefore, the embodiments described herein are intended to cover all such changes, modifications and variations that fall within the scope of protection of the appended claims. In addition, with respect to the term "comprising" used in the specification or claims, the word is encompassed in a manner similar to the term "including," as explained in terms of "including," used as a transitional word in the claims. In addition, any term "or" used in the specification of the claims is intended to mean "non-exclusive or." The terms "first" and "second" are used for descriptive purposes and are not to be understood as indicating or implying relative importance.

Claims

1. A method for determining the sealing thickness of siltstone adjacent layers in shale reservoirs based on pressure field simulation, characterized in that: If it is determined that the fracture pressure of the shale reservoir is less than the minimum starting pressure of the siltstone layer overlying the shale reservoir, the following steps are performed: A roof rock sample is prepared using the coring section of the overlying siltstone layer, a side surface of the roof rock sample is wrapped with a sealing material, a first pressurizing device and a first pressure sensor are arranged on the bottom surface of the roof rock sample, and a plurality of first pressure sensors are arranged on the side surface of the roof rock sample at first set intervals; Using the first pressurizing device to pressurize the roof rock sample until the pressure measured by the first pressure sensor at the bottom reaches a first set pressure, and stabilizing the pressure at this pressure until the amplitude of the pressure change measured by each first pressure sensor is less than a set threshold, and determining the lowest position where the pressure of the roof rock sample is no higher than the second set pressure based on the pressure measured by the first pressure sensor; The lower limit of the roof plugging thickness of the shale reservoir is determined based on the distance between the position and the bottom surface.

2. The method according to claim 1, wherein The first set pressure is the fracture pressure of the shale reservoir, and the second set pressure is the fracture pressure of the overlying siltstone layer.

3. The method according to claim 1, wherein The length of the roof rock sample is not less than 500 cm.

4. The method according to claim 1, wherein The first pressurizing device is a fluid pressurizing device.

5. The method according to claim 1, wherein The first set interval is set according to measurement accuracy requirements.

6. The method according to claim 1, wherein The step of determining the lowest position where the roof rock sample pressure is not higher than the second set pressure according to the measured pressures of the first pressure sensors includes: The measured pressures of the first pressure sensors are collected in order from bottom to top. If the currently collected pressure is the second set pressure, the position of the corresponding first pressure sensor is determined as the lowest position where the roof rock sample pressure is not higher than the second set pressure. If the currently collected pressure is the first pressure that is less than the second set pressure, the lowest position where the roof rock sample pressure is not higher than the second set pressure is determined by a proportional method based on the currently collected pressure and the previous collected pressure and the position of the current first pressure sensor and the position of the previous first pressure sensor, and the previous pressure is not equal to the second set pressure.

7. The method according to claim 1, wherein Determining the lower limit of the roof plugging thickness of the shale reservoir based on the distance from the position to the bottom surface includes: The distance from the position to the bottom surface is determined as the lower limit of the roof plugging thickness of the shale reservoir; or, The product of the safety correction factor and the distance from the position to the bottom surface is determined as the lower limit of the roof plugging thickness of the shale reservoir, and the safety correction factor is greater than 1.

8. The method according to claim 1, wherein If the underlying rock layer of the shale reservoir is a mud shale formation, the method further includes performing the following steps of determining the lower limit of the bottom plate plugging thickness: A bottom plate rock sample is prepared using a coring section of an underlying rock formation of the shale reservoir, a side surface of the bottom plate rock sample is wrapped with a sealing material, a second pressurizing device and a second pressure sensor are arranged on a top surface of the bottom plate rock sample, and a plurality of second pressure sensors are arranged on the side surface of the bottom plate rock sample at second set intervals; The bottom plate rock sample is pressurized by the second pressurizing device until the pressure measured by the second pressure sensor at the top reaches the first set pressure, and is stabilized at this pressure until the amplitude of the pressure change measured by each second pressure sensor is less than a set threshold, and the maximum position at which the bottom plate rock sample pressure is not higher than the third set pressure is determined based on the pressure measured by the second pressure sensor; The lower limit of the bottom plate plugging thickness of the shale reservoir is determined based on the distance between the position and the top surface.

9. The method according to claim 8, wherein If the underlying rock layer of the shale reservoir is an underlying siltstone layer, the following also applies: Determining whether the shale reservoir fracture pressure is less than the minimum starting pressure of the underlying siltstone layer; If so, execute the step of determining the lower limit of the bottom plate sealing thickness.

10. The method according to claim 8 or 9, characterized in that The third set pressure is the fracture pressure of the underlying rock formation.

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