Method for determining the sealing thickness of siltstone layer based on temperature-pressure field simulation

Abstract

The present invention discloses a method for determining the sealing thickness of a siltstone layer based on temperature-pressure field simulation, comprising: determining that the fracture pressure of a shale reservoir is less than the minimum starting pressure of an overlying siltstone layer, and executing the following steps: wrapping the side of a roof rock sample with a thermally insulating sealing material, arranging a heating and pressurizing device and temperature and pressure sensors on the bottom surface of the rock sample, and arranging multiple pressure sensors on the side of the rock sample at set intervals; heating the rock sample with a heating device to a set bottom temperature, and pressurizing the rock sample with a pressurizing device to a set bottom pressure, stabilizing the temperature and pressure until the measured values ​​of each sensor are stable, determining the lowest position where the rock sample pressure is no higher than a second set pressure based on the measured values ​​of the sensors; determining the lower limit of the roof sealing thickness based on the distance from this position to the bottom surface; and similarly determining the lower limit of the bottom sealing thickness. This method can reasonably quantify the lower limit of the top and bottom plate sealing thickness of a shale reservoir through the combined simulation of the temperature field and the pressure field.

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 layer based on temperature-pressure field simulation. Background Art

[0002] my country's medium- and low-maturity oil shale reserves hold enormous potential, and in-situ production technology is gaining increasing attention as an effective means of industrializing its extraction. In-situ production involves directly heating the underground shale reservoir, causing it to crack underground, with the resulting oil and gas extracted through production wells. Effective sealing of the overburden during in-situ production of shale reservoirs is a key factor in improving oil recovery. However, existing technologies lack effective methods for evaluating the sealing performance of the roof during in-situ production of shale reservoirs. Summary of the Invention

[0003] 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 a siltstone layer based on temperature-pressure field simulation is provided. The method can reasonably quantify the lower limit of the sealing thickness of the shale reservoir roof through the joint simulation of the temperature field and the pressure field.

[0004] An embodiment of the present invention provides a method for determining the sealing thickness of a siltstone layer based on temperature-pressure field simulation, comprising: if it is determined that the fracture pressure of a shale reservoir is less than the minimum starting pressure of a siltstone layer overlying the shale reservoir, performing the following steps:

[0005] A roof rock sample is prepared using a coring section of the overlying siltstone layer, and a side surface of the roof rock sample is wrapped with a heat-insulating sealing material. A first heating device, a first pressurizing device, a first temperature sensor, 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.

[0006] The roof rock sample is heated by the first heating device until the temperature measured by the first temperature sensor at the bottom is a first set temperature, and the roof rock sample is pressurized by the first pressurizing device until the pressure measured by the first pressure sensor at the bottom is a first set pressure, and stabilized at the temperature and pressure until the amplitude of the change in the measured value of each first pressure sensor is less than a set threshold, and 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 values ​​of the first pressure sensors;

[0007] 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.

[0008] 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.

[0009] In some embodiments, the first set temperature is the lowest temperature at which the kerogen conversion rate in the shale reservoir reaches 90%.

[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 overburden formation.

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

[0012] In some embodiments, the first heating device is a one-way heating device;

[0013] The first heating device is located at the center of the bottom surface of the roof rock sample;

[0014] The area of ​​the bottom surface of the roof rock sample directly heated by the first heating device does not exceed 1 / 4 of the bottom surface area.

[0015] In some embodiments, the first set interval is set according to measurement accuracy requirements.

[0016] In some embodiments, if the underlying rock formation of the shale reservoir is a mud shale formation, the method further includes:

[0017] A bottom plate rock sample is prepared using a coring section of an underlying rock formation of a shale reservoir, and a side surface of the bottom plate rock sample is wrapped with a heat-insulating sealing material. A second heating device, a second pressurizing device, a second temperature sensor, and a second pressure sensor are arranged on a top surface of the bottom plate rock sample. Multiple groups of second temperature sensors and second pressure sensors are arranged on the side surface of the bottom plate rock sample at second set intervals, with the measurement positions of each group of second temperature sensors and second pressure sensors being consistent in the longitudinal direction.

[0018] The bottom plate rock sample is heated by the second heating device until the temperature measured by the second temperature sensor at the top is the first set temperature, and the bottom plate rock sample is pressurized by the second pressurizing device until the pressure measured by the second pressure sensor at the top is the first set pressure, and stabilized at the temperature and pressure until the amplitude of the change in the measured value of each second temperature sensor and second pressure sensor is less than the set threshold value, and the highest position at which the temperature of the bottom plate rock sample is not higher than the third set temperature and the pressure is not higher than the third set pressure is determined based on the measured values ​​of the second temperature sensor and the second pressure sensor;

[0019] 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.

[0020] In some embodiments, if the underlying rock layer of the shale reservoir is an underlying siltstone layer, the method further includes determining whether the fracture pressure of the shale reservoir is less than the minimum starting pressure of the underlying siltstone layer. If so, performing the following steps:

[0021] A bottom plate rock sample is prepared using a coring section of an underlying rock formation of a shale reservoir, and a side surface of the bottom plate rock sample is wrapped with a heat-insulating sealing material. A second heating device, a second pressurizing device, a second temperature sensor, 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 heated by the second heating device until the temperature measured by the second temperature sensor at the top is the first set temperature, and the bottom plate rock sample is pressurized by the second pressurizing device until the pressure measured by the second pressure sensor at the top is the first set pressure, and stabilized at the temperature and pressure until the amplitude of the change in the measured value of each second pressure sensor is less than the set threshold value, and the highest position at which the pressure of the bottom plate rock sample is not higher than the third set pressure is determined based on the measured values ​​of each 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, the third set pressure is a fracture pressure of the underlying formation.

[0025] The beneficial effects of the above technical solutions provided by the embodiments of the present invention include at least:

[0026] (1) The method for determining the sealing thickness of a siltstone layer based on temperature-pressure field simulation provided by an embodiment of the present invention utilizes a first heating device to heat a roof rock sample and utilizes a first pressurizing device to pressurize the roof rock sample, so that the bottom temperature is stabilized at a first set temperature and the pressure is stabilized at a first set pressure until the measured values ​​of each sensor are stable. 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 values ​​of the sensors; 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. The lower limit of the roof sealing thickness of the shale reservoir is determined by experimental methods based on the joint simulation of the temperature field and the pressure field, and the roof sealing conditions during the in-situ heating production of the shale reservoir are specifically quantified, which can effectively guide production and improve the economic benefits of in-situ heating production of shale oil and gas.

[0027] (2) It is currently generally believed that only mud shale can effectively seal shale reservoirs during in-situ mining. The method for determining the sealing thickness of a siltstone layer based on temperature-pressure field simulation provided in the embodiment of the present invention proposes that if the overlying rock layer of a 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 a shale reservoir.

[0028] (3) The method for determining the sealing thickness of the siltstone layer based on the temperature-pressure field simulation provided by the 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 reaches the maximum oil and gas production, that is, this temperature is the highest temperature at which the reservoir may be heated during the in-situ heating and mining process of the actual shale reservoir; the pressure at the bottom of the roof is kept constant at the fracture pressure of the shale reservoir, that is, the maximum pressure that may be applied to the reservoir during the in-situ heating and mining process; on the basis of the temperature at the bottom of the roof being kept constant at the lowest temperature at which the kerogen conversion rate in the shale reservoir reaches 90% and the pressure being kept constant at the fracture pressure of the shale reservoir, the lower limit of the roof sealing thickness is determined according to the lowest position where the pressure is not higher than the fracture pressure of the overburden formation. Only the roof below the fracture pressure of the overburden formation has sealing properties. Therefore, the above-mentioned temperature and pressure settings ensure that the lower limit of the determined roof sealing thickness is reasonable and has strong production guidance significance.

[0029] (4) In the method for determining the sealing thickness of a siltstone layer based on temperature-pressure field simulation provided by an embodiment of the present invention, the first heating device is a unidirectional heating device, which saves 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.

[0030] (5) 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 heating and production of shale reservoirs, poor floor sealing performance can still lead to oil and gas loss, affecting the recovery rate. The method for determining the sealing thickness of a siltstone layer based on temperature-pressure field simulation provided in the embodiments of the present invention not only considers the sealing properties of the roof, but also fully considers the sealing properties of the floor, thus ensuring the reliability of the determination of the sealing performance and further providing a guarantee for improving the recovery rate.

[0031] 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.

[0032] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] 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:

[0034] Figure 1 This is a flow chart of a method for determining the sealing thickness of a siltstone layer based on temperature-pressure field simulation in Example 1 of the present invention;

[0035] Figure 2 This is a flow chart of a method for determining the sealing thickness of a siltstone layer based on temperature-pressure field simulation in Example 2 of the present invention;

[0036] Figure 3 This is a flow chart of a method for determining the sealing thickness of a siltstone layer based on temperature-pressure field simulation in Example 3 of the present invention;

[0037] Figure 4 This is a schematic diagram of the axial cross-section of the roof rock sample in Example 4 of the present invention;

[0038] Figure 5 This is a pressure field simulation diagram in Example 4 of the present invention;

[0039] Figure 6 for Figure 5 Oil saturation change diagram at the middle pressure line of 20MPa and 25MPa. DETAILED DESCRIPTION

[0040] 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.

[0041] 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.

[0042] 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.

[0043] 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.

[0044] The inventors found in their work that the existing technology has the problem of difficulty in effectively evaluating the roof sealing performance during the heating and mining process of shale reservoirs. After further research and development, the inventors found that during the in-situ heating and mining process of shale reservoirs, the source rock begins to crack and generate hydrocarbons after being heated to a certain temperature. The flow of hydrocarbon substances causes the roof and bottom plates of the shale reservoir to be affected by fluid pressure. In addition, the difference in heat conduction between the roof and bottom plates of the shale reservoir also affects the difference in their sealing thickness. Therefore, the sealing thickness of the roof and bottom plates can be reasonably determined through simulation experiments of temperature and pressure fields. The embodiment of the present invention provides a method for determining the sealing thickness of a siltstone layer based on temperature-pressure field simulation, which can reasonably quantify the lower limit of the roof sealing thickness of a shale reservoir through temperature and pressure field simulation methods.

[0045] Example 1

[0046] A first embodiment of the present invention provides a method for determining the sealing thickness of a siltstone layer based on temperature-pressure field simulation.

[0047] First, it is necessary to experimentally measure the shale reservoir fracture pressure and the minimum starting pressure (fracture pressure) for fluid migration in the overlying siltstone layer to determine whether the shale reservoir fracture pressure is less than the minimum starting pressure of the overlying siltstone layer. If so, perform the subsequent steps to determine the lower limit of the plugging thickness. If not, determine that the overlying siltstone layer does not have the sealing property during the in-situ mining process of the shale reservoir.

[0048] When data conditions permit, the minimum starting pressure of the overlying siltstone layer can be obtained by measuring the minimum starting pressure of at least 5 rock samples in the overlying siltstone layer (rock samples that are approximately uniformly distributed underground) and then calculating the average value; the fracture pressure of the shale reservoir needs to be obtained by measuring the fracture pressure of at least 3 rock samples in the shale reservoir (rock samples that are approximately uniformly distributed underground) and then calculating the average value.

[0049] The above measurements are performed under the initial temperature and pressure conditions of the corresponding formation.

[0050] It is currently generally believed that only mudstone can effectively seal shale reservoirs during in-situ mining. The method for determining the sealing thickness of a siltstone layer based on temperature-pressure field simulation provided in an embodiment of the present invention proposes that if the overlying rock layer of a shale reservoir is siltstone, a sealing effect can also be achieved during in-situ mining of a shale reservoir 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.

[0051] The specific process of determining the lower limit of the sealing thickness of the overlying siltstone layer is as follows: Figure 1 As shown, the following steps are included:

[0052] Step S11: Prepare a roof rock sample using the coring section of the overlying siltstone layer, wrap the side of the roof rock sample with a thermal insulation and sealing material, arrange a first heating device, a first pressurizing device, a first temperature sensor and a first pressure sensor on the bottom surface of the roof rock sample, and arrange multiple first pressure sensors on the side of the roof rock sample at a first set interval.

[0053] Roof rock samples with the same cross-sectional area (eg, cylindrical with a diameter of 5 cm) are prepared using a core section of the overlying strata of the shale reservoir.

[0054] According to empirical data, the sealing thickness of the roof during in-situ heating and 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 heating of shale).

[0055] The sides of the top rock sample are wrapped with thermal insulation sealing material. The thermal insulation can prevent heat from being dissipated to the surroundings during the heating process. The sealing ensures that the fluid applied from the bottom of the rock sample during the fluid pressurization process cannot enter between the rock sample and the thermal insulation sealing material. The thermal insulation sealing material needs to have a pressure resistance of not less than 80MPa.

[0056] The first pressurizing device is a fluid pressurizing device.

[0057] In some embodiments, the first heating device is a one-way heating device to save resources.

[0058] 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 an area of ​​the bottom surface of the top plate rock sample that does not exceed 1 / 4 of the bottom surface area, so that the heat source can be spread upward as much as possible.

[0059] Specifically, the bottom surface of the roof rock sample refers to the side closest to the shale reservoir at the corresponding original underground position.

[0060] 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.

[0061] Step S12: Use the first heating device to heat the top plate rock sample to the first set temperature measured by the first temperature sensor at the bottom, use the first pressurizing device to pressurize the top plate rock sample to the first set pressure measured by the first pressure sensor at the bottom, and stabilize at the temperature and pressure until the change amplitude of the measured value of each first pressure sensor is less than the set threshold value, and determine the lowest position where the pressure of the top plate rock sample is not higher than the second set pressure based on the measured value of the first pressure sensor.

[0062] 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.

[0063] The first set temperature can be determined by using a source rock thermal simulation experiment or a kerogen activation energy experiment.

[0064] For example, multiple samples of shale reservoirs are taken, and source rock thermal simulation experiments are conducted on each sample to measure the lowest temperature at which the kerogen conversion rate reaches a set conversion rate threshold, and the minimum value of the multiple measured minimum temperatures is determined as the first set temperature.

[0065] Furthermore, the first set temperature is the lowest temperature at which the kerogen conversion rate in the shale reservoir reaches 90%, which is usually 290-330°C.

[0066] The kerogen conversion rate reaches 90%. At this temperature, the reservoir is almost completely converted to hydrocarbons, achieving maximum oil and gas production. That is, this temperature is the highest temperature at which the reservoir can be heated during the in-situ heating and production process of actual shale reservoirs. Therefore, the setting of this temperature ensures the safety and rationality of the determined lower limit of the roof sealing thickness.

[0067] 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 overburden formation, both of which can be determined through rock fracture pressure experiments.

[0068] The fracture pressure of a shale reservoir is generally about 50 MPa. The present embodiment is based on the premise that the overlying stratum of the shale reservoir is a mud shale formation, and the fracture pressure of the overlying stratum is generally about 30 MPa.

[0069] 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 fracture pressure P0 of the shale reservoir and the fracture pressure Px of the overburden formation are determined.

[0070] Use the first heating device (heat source) to slowly heat the sample (no more than 20°C / day), with the maximum temperature between 400°C and 650°C. Adjust the heat source power to maintain a constant temperature at the bottom of the roof sample at T0. Simultaneously, use the first pressurizing device to pressurize the bottom of the roof sample using fluid at a rate not exceeding 300 kPa / day (the specific value is flexibly set based on on-site construction conditions) to maintain a constant pressure at the bottom of the roof sample at P0. Furthermore, strive to achieve simultaneous pressure and temperature at P0. Maintaining constant temperature at T0 and pressure at P0 for at least 30 minutes, until the fluctuation in the measured values ​​of each sensor is less than the set threshold (i.e., once the pressure stabilizes), collect the measured values ​​of each first pressure sensor. Since the pressure of the roof sample gradually decreases from bottom to top, collect the measured values ​​of the first pressure sensors sequentially from bottom to top until the currently collected pressure is no greater than Px. The lowest point where the roof sample pressure does not exceed Px is determined based on the position of the corresponding sensor.

[0071] If the currently collected pressure is Px, the position of the corresponding first pressure sensor can be directly determined as the position where the roof 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 first pressure sensor and the position of the previous first pressure sensor, the lowest position where the roof rock sample pressure is not higher than Px is determined by the proportional method.

[0072] 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.

[0073] 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.

[0074] The method for determining the sealing thickness of a siltstone layer based on temperature-pressure field simulation provided in Example 1 of the present invention utilizes a first heating device to heat a roof rock sample and utilizes a first pressurizing device to pressurize the roof rock sample, so that the bottom temperature stabilizes at a first set temperature and the pressure stabilizes at a first set pressure until the measured values ​​of each sensor stabilize. 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 values ​​of the sensors; 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 a shale reservoir based on the joint simulation of the temperature field and the pressure field, the roof sealing conditions during the in-situ heating and exploitation of shale reservoirs are specifically quantified, which can effectively guide production and improve the economic benefits of in-situ heating and exploitation of shale oil and gas.

[0075] The method for determining the sealing thickness of a siltstone layer based on temperature-pressure field simulation provided in Example 1 of the present invention is as follows: during the experiment, the temperature at the bottom of the roof is kept constant at the lowest temperature in the reservoir where the kerogen conversion rate reaches 90%. At this temperature, the reservoir almost completes the conversion to hydrocarbons and reaches maximum oil and gas production. That is, this temperature is the highest temperature that can be heated during the in-situ heating and production of an actual shale reservoir; the pressure at the bottom of the roof is kept constant at the fracture pressure of the shale reservoir, that is, the maximum pressure that can be applied to the reservoir during in-situ heating and production; based on the constant temperature at the bottom of the roof being the lowest temperature in the shale reservoir where the kerogen conversion rate reaches 90%, and the constant pressure being the fracture pressure of the shale reservoir, the lower limit of the roof sealing thickness is determined based on the lowest position where the pressure is not higher than the fracture pressure of the overburden formation. Only roofs below the fracture pressure of the overburden formation have sealing properties. Therefore, the above temperature and pressure settings ensure that the determined lower limit of the roof sealing thickness is reasonable and has strong production guidance significance.

[0076] Example 2

[0077] Embodiment 2 of the present invention provides another method for determining the sealing thickness of a siltstone layer based on temperature-pressure field simulation, specifically a method for determining the lower limit of the bottom plate sealing thickness of a shale reservoir, where the underlying rock layer of the shale reservoir is a mudstone formation.

[0078] Specifically, refer to Figure 2 As shown, the following steps are included:

[0079] Step S21: Prepare a bottom plate rock sample using the coring section of the underlying rock formation of the shale reservoir, wrap the side of the bottom plate rock sample with a thermal insulation sealing material, arrange a second heating device, a second pressurizing device, a second temperature sensor and a second pressure sensor on the top surface of the bottom plate rock sample, and arrange multiple groups of second temperature sensors and second pressure sensors on the side of the bottom plate rock sample at second set intervals.

[0080] The measurement positions of each group of second temperature sensors and second pressure sensors are consistent in the longitudinal direction.

[0081] The second temperature sensor may be the same temperature sensor as the first temperature sensor. The "first" and "second" here are only used to distinguish whether the temperature sensor is set on the top plate rock sample or the bottom plate rock sample.

[0082] Similarly, the second pressure sensor can 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.

[0083] 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.

[0084] The second heating device can be the same heating device as the first heating device. The "first" and "second" here are just to distinguish whether the heating device is set on the bottom surface of the top plate rock sample or the top surface of the bottom plate rock sample.

[0085] The second pressurizing device can be a heating device that is the same as the first pressurizing device. The "first" and "second" here are only used to distinguish whether the pressurizing device is set on the bottom surface of the top plate rock sample or the top surface of the bottom plate rock sample.

[0086] The second heating device is located at the center of the top surface of the bottom plate rock sample. Further, the second heating device can directly heat the top surface of the bottom plate rock sample to an area not exceeding 1 / 4 of the top surface area, so that the heat source can be spread downward as much as possible.

[0087] Specifically, the top surface of the bottom plate rock sample refers to the side closest to the shale reservoir at the corresponding original underground position.

[0088] The second temperature sensor and the second pressure sensor 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.

[0089] Step S22: Use the second heating device to heat the bottom plate rock sample to the first set temperature measured by the second temperature sensor on the top, and use the second pressurizing device to pressurize the bottom plate rock sample to the first set pressure measured by the second pressure sensor on the top, and stabilize at this temperature and pressure until the change amplitude of the measured values ​​of each second temperature sensor and second pressure sensor is less than the set threshold value, and determine the highest position where the temperature of the bottom plate rock sample is not higher than the third set temperature and the pressure is not higher than the third set pressure based on the measured values ​​of the second temperature sensor and the second pressure sensor.

[0090] In some embodiments, the third set temperature is the initial hydrocarbon production temperature of kerogen in the underlying rock formation.

[0091] This application is based on the premise that the overlying and underlying rock layers of the shale reservoir are both mudstone formations. Therefore, if the rock properties of the overlying and underlying rock layers are basically the same, the initial hydrocarbon production temperature of kerogen in the overlying rock layer can also be approximated as the initial hydrocarbon production temperature of kerogen in the underlying rock layer.

[0092] The third set pressure is the fracture pressure of the underlying rock formation, which can also be determined through rock fracture pressure experiments. Therefore, if the rock mechanical properties of the overburden and underlying rock formations are basically the same, the fracture pressure of the overburden formation can also be approximated as the fracture pressure of the underlying rock formation.

[0093] For example, using the third set temperature (Tx) and the third set pressure (Px), the second heating device (heat source) is used to slowly heat the sample (no more than 20°C / day), with the maximum temperature of the heat source between 400°C and 650°C. The heat source power is adjusted to maintain a constant temperature of T0 at the top of the bottom plate rock sample. Simultaneously, the second pressurizing device is used to pressurize the top of the bottom plate rock sample using fluid at a rate of no more than 300 kPa / day (the specific value is flexibly set based on on-site construction conditions) to maintain a constant pressure of P0 at the top of the bottom plate rock sample. Furthermore, the pressure P0 and the temperature T0 are achieved simultaneously as much as possible. The temperature is kept constant at T0 and the pressure is kept constant at P0 for at least 30 minutes until the change in the measured values ​​of each sensor is less than the set threshold value, that is, after the temperature and pressure are stable, the measured values ​​of each second temperature sensor and the second pressure sensor are collected. Since the temperature of the bottom plate rock sample gradually decreases from the top to the bottom, and the pressure also gradually decreases from the top to the bottom, the measured values ​​of the second temperature sensor and the second pressure sensor can be collected in sequence from the top to the bottom until the currently collected temperature is not greater than Tx and the pressure is not greater than Px. The highest position where the bottom plate rock sample temperature is not higher than Tx and the pressure is not higher than Px is determined according to the position of the corresponding sensor.

[0094] 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 position of the current second temperature sensor and the position of the previous second temperature sensor, the first highest position where the bottom plate rock sample temperature is not higher than Tx is determined by the proportional method.

[0095] Similarly, if the currently collected pressure is Px, the position of the corresponding second pressure sensor can be directly determined as the position where the bottom plate rock sample pressure begins to drop to Px; if the currently collected pressure begins to be less than Px (the first pressure less than Px), based on the currently collected pressure and the previous collected pressure and the position of the current second pressure sensor and the position of the previous second pressure sensor, the second highest position where the bottom plate rock sample pressure is not higher than Px is determined by the proportional method.

[0096] The lower of the first highest position and the second highest position is used as the highest position where the bottom plate rock sample temperature is not higher than the third set temperature and the pressure is not higher than the third set pressure.

[0097] 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.

[0098] The distance from this position to the top surface can be directly determined as the lower limit of the bottom plate plugging thickness of the shale reservoir; other factors affecting the plugging performance can also be further considered to determine a safety correction factor (greater than 1), and the product of the safety correction factor and the determined distance can be used as the lower limit of the bottom plate plugging thickness of the shale reservoir.

[0099] Example 3

[0100] Embodiment 3 of the present invention provides another method for determining the sealing thickness of a siltstone layer based on temperature-pressure field simulation, specifically a method for determining the lower limit of the bottom plate sealing thickness of a shale reservoir. The underlying rock layer of the shale reservoir is an underlying siltstone layer. The method for determining the lower limit of the top plate sealing thickness of the shale reservoir in the above embodiment 1 is still applicable here.

[0101] 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; if not, determine that the underlying formation does not have sealing properties during in-situ mining of the shale reservoir.

[0102] Specifically, refer to Figure 3 As shown, the following steps are included:

[0103] Step S31: Prepare a bottom plate rock sample using the coring section of the underlying rock formation of the shale reservoir, wrap the side of the bottom plate rock sample with a thermal insulation and sealing material, arrange a second heating device, a second pressurizing device, a second temperature sensor 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.

[0104] 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.

[0105] The second heating device is located at the center of the top surface of the bottom plate rock sample. Further, the second heating device can directly heat the top surface of the bottom plate rock sample to an area not exceeding 1 / 4 of the top surface area, so that the heat source can be spread downward as much as possible.

[0106] Specifically, the top surface of the bottom plate rock sample refers to the side closest to the shale reservoir at the corresponding original underground position.

[0107] 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.

[0108] Step S32: Use the second heating device to heat the bottom plate rock sample to the first set temperature measured by the second temperature sensor on the top, and use the second pressurizing device to pressurize the bottom plate rock sample to the first set pressure measured by the second pressure sensor on the top, and stabilize at this temperature and pressure until the change amplitude of the measured value 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 value of each second pressure sensor.

[0109] In some embodiments, the third set pressure is the fracture pressure of the underlying rock formation, which can also be determined through rock fracture pressure experiments. Therefore, if the rock mechanical properties of the overburden and underlying rock formations are basically the same, the fracture pressure of the overburden formation can also be approximated as the fracture pressure of the underlying rock formation.

[0110] For example, using the third set pressure as Px, slowly heat the sample using the second heating device (heat source) (no more than 20°C / day), with the maximum temperature between 400°C and 650°C. Adjust the heat source power to maintain a constant temperature at the top of the bottom plate sample, T0. Simultaneously, pressurize the top of the bottom plate sample using the second pressurizing device, using fluid boosting at a rate of no more than 300 kPa / day (the specific value is flexibly set based on on-site construction conditions), to maintain a constant pressure at P0. Furthermore, the pressure and temperature should be reached simultaneously. Maintaining both the temperature and pressure at T0 for at least 30 minutes, until the fluctuation in the measured values ​​of each sensor is less than the set threshold (i.e., once the pressure stabilizes), collect the measured values ​​of each second pressure sensor. Since the pressure of the bottom plate sample gradually decreases from the top to the bottom, the measured values ​​of the second pressure sensors can be collected sequentially from the top to the bottom until the currently collected pressure is no greater than Px. The highest point where the pressure of the bottom plate sample does not exceed Px is determined based on the position of the corresponding sensor.

[0111] 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.

[0112] Step S33: determining the lower limit of the bottom plate plugging thickness of the shale reservoir according to the distance from the position to the top surface.

[0113] The distance from this position to the top surface can be directly determined as the lower limit of the bottom plate plugging thickness of the shale reservoir; other factors affecting the plugging performance can also be further considered to determine a safety correction factor (greater than 1), and the product of the safety correction factor and the determined distance can be used as the lower limit of the bottom plate plugging thickness of the shale reservoir.

[0114] Existing research on the sealing properties of shale reservoirs often focuses solely on the sealing properties of the roof, while ignoring the sealing function of the floor. However, for in-situ heating and recovery of shale reservoirs, poor floor sealing performance can still lead to oil and gas loss, impacting recovery efficiency. The methods for determining the sealing thickness of siltstone layers based on temperature-pressure field simulation, provided in Examples 2 and 3 of the present invention, fully consider the sealing properties of the floor, ensuring the reliability of the sealing performance determination and further guaranteeing an increase in recovery efficiency.

[0115] The above-mentioned embodiments 1 to 3 can be applied individually; embodiment 1 can also be applied in combination with embodiment 2, or embodiment 1 can be applied in combination with embodiment 3, to determine both the lower limit of the top plate plugging thickness of the shale reservoir and the lower limit of the bottom plate plugging thickness of the shale reservoir. Only when the top and bottom plate thicknesses of the shale reservoir meet the corresponding lower limits of the plugging thickness can it be determined that the plugging requirements are met.

[0116] Example 4

[0117] A third embodiment of the present invention provides a specific application of a method for determining a lower limit of the roof plugging thickness of a shale reservoir, and verifies its accuracy through numerical simulation, including the following steps:

[0118] 1) The T0 (90% conversion temperature of kerogen) of the shale reservoir rock sample was measured to be 300°C.

[0119] 2) The Po (fracture pressure) of the shale reservoir rock sample was measured to be 50 MPa.

[0120] 3) The Px (fracture pressure) of the roof rock sample was measured to be 20 MPa.

[0121] 4) Prepare a cylindrical roof rock sample with a diameter of 5 cm and a length of 500 cm. Figure 4 The figure shows a schematic cross-sectional view of the roof rock sample along the axial direction.

[0122] 5) Wrap the top rock sample with a pressure-resistant steel sleeve with a pressure resistance of not less than 80 MPa, and then wrap it with rock wool as an insulating material. Place the top rock sample in the experimental device. The sealing ensures that the fluid applied at the bottom of the sample cannot enter between the sample and the steel sleeve.

[0123] 6) Place a unidirectional heat source point at the bottom of the roof rock sample, arrange a temperature sensor and a pressure sensor at the bottom, and arrange several pressure sensors along the axial direction of the roof rock sample at intervals of 10 cm.

[0124] 7) The bottom of the roof rock sample was heated and pressurized with fluid. The heating rate was 20°C / day, with a peak temperature of 300°C (T0). The pressurization rate was 300 kPa / day, with a peak pressure of 50 MPa (Po).

[0125] 8) The bottom temperature of the roof rock sample is constant at T0, and the pressure is constant at P0. After 30 minutes (the measurement values ​​of each sensor reach stability), the roof rock sample pressure sensor data is continuously collected.

[0126] 9) The thickness from the position where the pressure Px is measured to the bottom of the roof rock sample is 145 cm, so 145 cm is the lower limit of the roof sealing thickness.

[0127] 10) Establish a numerical model consistent with the roof rock sample and experimental conditions, and set the Px (fracture pressure) of the roof rock sample to 20 MPa.

[0128] 11) Keep the temperature at the bottom of the roof rock sample constant at T0 (300°C) and the pressure constant at P0 (50 MPa), complete the numerical simulation of the temperature field and pressure field, and wait for the grid pressure to stabilize.

[0129] 12) See Figure 5 The figure shows the simulated pressure field of the roof rock sample. Figure 5 Oil saturation at the Px pressure line (20 MPa) (see Figure 6 There was no change during the entire simulation period, indicating that oil and gas were blocked at this location.

[0130] 13) Observation Figure 5 Oil saturation at the medium pressure line 25MPa (see Figure 6 During the entire simulation period, there are obvious changes, indicating that the oil and gas are not blocked at this location.

[0131] 14) The thickness of the Px pressure line is 149 cm. A comprehensive comparison shows that a roof thickness of 149 cm meets the plugging requirements. The error between the numerical simulation results and the experimental results (145 cm) is approximately 2.8%, thus verifying the reliability of the experimental results.

[0132] 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.

[0133] 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.

[0134] 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 a siltstone layer based on temperature-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 a coring section of the overlying siltstone layer, and a side surface of the roof rock sample is wrapped with a heat-insulating sealing material. A first heating device, a first pressurizing device, a first temperature sensor, 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. The roof rock sample is heated by the first heating device until the temperature measured by the first temperature sensor at the bottom is a first set temperature, and the roof rock sample is pressurized by the first pressurizing device until the pressure measured by the first pressure sensor at the bottom is a first set pressure, and stabilized at the temperature and pressure until the amplitude of the change in the measured value of each first pressure sensor is less than a set threshold, and 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 values ​​of the first pressure sensors; 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 temperature is the lowest temperature at which the kerogen conversion rate in the shale reservoir reaches a set conversion rate threshold.

3. The method according to claim 2, wherein The first set temperature is the lowest temperature at which the kerogen conversion rate in the shale reservoir reaches 90%.

4. The method according to claim 3, 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.

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

6. The method according to claim 1, wherein 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 roof rock sample; The area of ​​the bottom surface of the roof 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, wherein The first set interval is set according to measurement accuracy requirements.

8. The method according to claim 1, wherein If the underlying rock layer of the shale reservoir is a mud shale formation, the following is also included: A bottom plate rock sample is prepared using a coring section of an underlying rock formation of a shale reservoir, and a side surface of the bottom plate rock sample is wrapped with a heat-insulating sealing material. A second heating device, a second pressurizing device, a second temperature sensor, and a second pressure sensor are arranged on a top surface of the bottom plate rock sample. Multiple groups of second temperature sensors and second pressure sensors are arranged on the side surface of the bottom plate rock sample at second set intervals, with the measurement positions of each group of second temperature sensors and second pressure sensors being consistent in the longitudinal direction. The bottom plate rock sample is heated by the second heating device until the temperature measured by the second temperature sensor at the top is the first set temperature, and the bottom plate rock sample is pressurized by the second pressurizing device until the pressure measured by the second pressure sensor at the top is the first set pressure, and stabilized at the temperature and pressure until the amplitude of the change in the measured value of each second temperature sensor and second pressure sensor is less than the set threshold value, and the highest position at which the temperature of the bottom plate rock sample is not higher than the third set temperature and the pressure is not higher than the third set pressure is determined based on the measured values ​​of the second temperature sensor and 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 method further includes determining whether the fracture pressure of the shale reservoir is less than the minimum starting pressure of the underlying siltstone layer. If so, executing the following steps: A bottom plate rock sample is prepared using a coring section of an underlying rock formation of a shale reservoir, and a side surface of the bottom plate rock sample is wrapped with a heat-insulating sealing material. A second heating device, a second pressurizing device, a second temperature sensor, 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 heated by the second heating device until the temperature measured by the second temperature sensor at the top is the first set temperature, and the bottom plate rock sample is pressurized by the second pressurizing device until the pressure measured by the second pressure sensor at the top is the first set pressure, and stabilized at the temperature and pressure until the amplitude of the change in the measured value of each second pressure sensor is less than the set threshold value, and the highest position at which the pressure of the bottom plate rock sample is not higher than the third set pressure is determined based on the measured values ​​of each second pressure sensor; The lower limit of the bottom plate sealing thickness of the shale reservoir is determined according to the distance between the position and the top surface.

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.

Images