Method and device for testing porosity of stratum under high-temperature and high-pressure conditions

Abstract

The invention relates to the technical field of pore testing in the oilfield exploration and development process, in particular to a method and device for testing the porosity of a stratum under the high-temperature and high-pressure condition, and the method comprises the steps: measuring the pressure in a constant volume vessel in real time, obtaining the volume of the constant volume vessel, and analyzing the pressure change before and after a control valve between the constant volume vessel and a core chamber is opened; obtaining the estimated pore volume by combining the volume of the constant volume vessel, obtaining the target pressure in the pressurizing process of the constant volume vessel, determining the permeation resistance characteristic value of the core in the core chamber, correcting the target pressure, calculating the first gas density, the second gas density and the third gas density of the constant volume vessel, and obtaining the actual pore volume of the core chamber. And obtaining the actual core skeleton volume of the sample chamber, and obtaining the porosity based on the actual pore volume and the actual core skeleton volume. Therefore, the accuracy of porosity testing is improved.

Description

Technical Field

[0001] The present application relates to the technical field of pore testing during oilfield exploration and development, and in particular to a porosity testing method and device under high-temperature and high-pressure conditions in a formation. Background Art

[0002] The reservoir space of shale directly affects the method, efficiency, and economics of oilfield production. Shale reservoir space is primarily composed of lamellae and matrix pores. Shale also contains a large amount of clay minerals, which easily form overpressure formations, and the pore pressure in the formations can reach very high levels. Porosity is one of the key parameters for reserve submission, and its test results directly determine the size of reserves. However, due to the deep burial depth, high formation pressure, and high formation temperature under formation conditions, and the high overburden pressure, high pore pressure, and high formation temperature, accurately obtaining porosity under high temperature and high pressure conditions in the formation is of great significance for reserve submission.

[0003] Traditional porosity measurement devices can only meet the measurement conditions of overburden pressure. The pore pressure and test temperature are relatively low, and cannot fully meet the measurement conditions under high temperature and high pressure conditions of the formation. In addition, the traditional porosity measurement method is the low-pressure gas expansion method, whose principle is based on the ideal gas state equation, but the applicable conditions of the ideal gas state equation are high temperature and low pressure. When measuring shale porosity, due to the high temperature and high pressure measurement environment, the results of the traditional ideal gas state equation measurement will produce large errors. Secondly, the traditional overburden porosity calculation assumes that the rock skeleton volume remains unchanged, and only the pore volume changes. However, in reality, the rock skeleton volume will also change, ultimately leading to inaccurate porosity test results. Summary of the Invention

[0004] In order to solve the above technical problems, the purpose of this application is to provide a method and device for testing porosity under high temperature and high pressure conditions of the formation. The technical solutions adopted are as follows:

[0005] In a first aspect, an embodiment of the present application provides a method for testing porosity of a formation under high temperature and high pressure conditions, the method comprising the following steps:

[0006] The porosity testing method is implemented by a porosity testing device, wherein the porosity testing device comprises a gas cylinder (1), fixed containers (8), (9), (10) of different volumes, a sample chamber (13), and a core chamber in a core holder (18), wherein the gas cylinder (1), fixed containers (8), (9), (10), sample chamber (13), and core holder (18) are connected in an arrangement order through a control valve; the porosity testing method comprises the following steps:

[0007] S1, real-time measurement of the gas pressure in the fixed container to obtain the volume of the fixed container;

[0008] S2, opening the control valve between the gas cylinder and any fixed container, closing the control valve between the any fixed container and the core chamber, evacuating the gas in the core chamber, then closing the control valve between the gas cylinder and the any fixed container, and opening the control valve between the any fixed container and the core chamber. This is recorded as the first opening of the control valve. The pressure changes before and after the opening of the control valve between the fixed container and the core chamber are analyzed, and the estimated pore volume is obtained based on the volume of the any fixed container.

[0009] S3, closing the control valve between the arbitrary fixed container and the core chamber; pressurizing the arbitrary fixed container to a target pressure, and reopening the control valve between the arbitrary fixed container and the core chamber after the pressurization is balanced; obtaining the target pressure based on a constant relationship between the total mass of gas in the arbitrary fixed container and the core chamber before and after pressurization by presetting a static pressure difference ratio before and after pressurization of the arbitrary fixed container and an estimated pore volume;

[0010] S4, analyzing the rate of decrease of the pressure of the any certain container during the first opening of the control valve to determine a permeation resistance characteristic value of the core in the core chamber; and correcting the target pressure based on the permeation resistance characteristic value;

[0011] S5, repeating step S2, after the pressure in the space of the any fixed container and the core chamber is balanced, obtaining a first gas density of the any fixed container based on the pressure measured in the any fixed container;

[0012] S6, repeating the pressurization process in step S3 based on the corrected target pressure, respectively obtaining a second gas density of the any fixed container after pressurization, and a third gas density of the any fixed container after the pressure is balanced by opening the control valve again after pressurization;

[0013] S7. Based on the constant relationship among the first gas density, the second gas density, the third gas density, and the total mass of the gas before and after pressurization, the actual pore volume of the core chamber is determined; accordingly, for the sample chamber, the same testing method as that of the core chamber is adopted to obtain the actual core skeleton volume of the sample chamber, and the porosity is obtained by combining the actual pore volume.

[0014] In one embodiment, determining the estimated pore volume includes:

[0015] Obtaining a first total mass of gas in any given container based on the pressure measured in the given container before the control valve is first opened, combined with the volume of the given container; and correspondingly, obtaining a second total mass of gas in the given container when the pressure is balanced after the control valve is first opened;

[0016] The difference between the total mass of the first gas and the total mass of the second gas is calculated to obtain the gas density of the fixed container when the pressure is balanced after the control valve is opened for the first time. The estimated pore volume is the ratio of the difference to the gas density of the fixed container.

[0017] In one embodiment, obtaining the target pressure includes:

[0018] Obtaining the gas density ρi1 corresponding to the pressure measured in any given container before pressurization, and obtaining the total gas mass M1 of the core chamber before the control valve is opened again after pressurization based on the gas density ρi1 and the estimated pore volume;

[0019] Assuming that the static pressure of any given container before the control valve is opened again after the pressurization is Pi2, and the static pressure of any given container after the control valve is opened again after the pressurization is Pi3, the pressure relationship is obtained based on the static pressure difference ratio;

[0020] The total mass of gas in the fixed container before reopening the control valve is obtained by using the gas density corresponding to the static pressure Pi2 and the volume of the fixed container, which is recorded as M2. Similarly, the total mass of gas in the core chamber and the fixed container after reopening the control valve is obtained by using the static pressure Pi3 and the estimated pore volume and the volume of the fixed container, which is recorded as M3.

[0021] The gas mass constant condition among M1, M2 and M3 is combined to obtain the target pressure corresponding to the static pressure Pi2.

[0022] In one embodiment, obtaining the pressure relationship based on the static pressure difference ratio includes:

[0023] The static pressure difference ratio is recorded as β, then

[0024] In one embodiment, the gas mass constant condition is M3=M1+M2.

[0025] In one embodiment, determining the characteristic value of the penetration resistance includes:

[0026] The pressure of any given container at all times between the first opening of the control valve and the closing of the control valve is obtained to form a pressure sequence, a frequency spectrum of the pressure sequence is obtained, the sum of each frequency and a preset value greater than 0 is calculated, the inverse of the sum is used as a weight, and the normalized results of the amplitudes corresponding to all frequencies are weighted and summed to obtain the characteristic value of the permeation resistance.

[0027] In one embodiment, the correcting the target pressure includes: increasing the target pressure by a preset multiple based on the permeability resistance characteristic value.

[0028] In one embodiment, determining the actual pore volume of the core chamber includes:

[0029] The difference between the second gas density and the third gas density is calculated and recorded as the first difference. The difference between the third gas density and the first gas density is calculated and recorded as the second difference. The ratio of the first difference to the second difference is calculated and recorded as the relative ratio. The actual pore volume is the product of the relative ratio and the volume of any given container.

[0030] In one embodiment, determining the porosity includes:

[0031] The sum of the actual pore volume and the actual core skeleton volume is calculated and recorded as the total core volume. The porosity is obtained based on the total core volume and the actual pore volume.

[0032] In one embodiment, the porosity is the ratio of the actual pore volume to the total volume of the core.

[0033] In the second aspect, an embodiment of the present application provides a porosity testing device under high temperature and high pressure conditions of a formation. The testing device is implemented based on the steps of any one of the porosity testing methods under high temperature and high pressure conditions of a formation. The testing device includes a gas supply system (27), a pressure safety system (35), a fixed container system (28), a core system (29), a vacuum system (30), a confining pressure system (31), and a constant temperature system (22).

[0034] In one embodiment, the gas supply system includes a gas cylinder and a gas booster pump, and the maximum test pressure of the gas supply system can be as low as 60MPa; the pressure safety system includes an alarm, an automatic pressure safety valve, an explosion-proof disk, and a safety box, and the pressure safety system is connected to the gas supply system and the fixed container system through a pipeline.

[0035] In one embodiment, the fixed container system includes three fixed containers of different volumes. The upper end of the fixed container system is connected to the gas supply system through a pipeline, and the pipeline is provided with a control valve and a pressure gauge; the lower end of the fixed container system is connected to the core system through a pipeline; and the fixed container system is placed in a constant temperature system.

[0036] In one embodiment, the core system includes a sample chamber and a core clamp, the upper end of the sample chamber is connected to the fixed container system through a pipeline, and a control valve and a differential pressure sensor are provided on the pipeline; the upper end of the sample chamber is also connected to the core clamp through a pipeline, and a control valve is provided on the pipeline; the upper end of the core clamp is connected to the fixed container system through a pipeline, and a control valve is provided on the pipeline; the confining pressure system includes a confining pressure pump and a pressure gauge, the confining pressure pump is connected to the core clamp through a pipeline, and a control valve and a pressure gauge are provided on the pipeline.

[0037] In one embodiment, the constant temperature system includes a heater and a constant temperature box; the vacuum system includes a vacuum pump and a pressure gauge, and the vacuum pump is connected to the core system through a pipeline, and the pipeline is provided with a control valve and a pressure gauge.

[0038] This application has at least the following beneficial effects:

[0039] The present application aims to solve the problem of large measurement errors in porosity measurement by the traditional gas expansion method under high temperature and high pressure conditions. First, the pressure changes before and after the opening of the control valve between the fixed container and the core chamber are analyzed, and the estimated pore volume is obtained in combination with the volume of any fixed container. Then, by controlling the pressurization operation of the fixed container, the target pressure is set during the pressurization process, thereby improving the accuracy of the target pressure of the pressurization, avoiding both the calculation error caused by the small static pressure difference value and the damage to the core structure caused by the excessive pressure difference between the fixed container and the core chamber; further, the permeability resistance characteristic value of the core in the core chamber is determined; based on the permeability The target pressure is corrected by using the resistance characteristic value, and the penetration resistance inside the core is characterized by the penetration resistance characteristic value. A higher target pressure is used for the core with large penetration resistance, so that the filling gas can quickly and completely fill the pores, avoiding measurement errors caused by insufficient pore filling, and further improving the accuracy of the target pressure setting; at the same time, compared with the traditional gas expansion method for measuring porosity, the present application avoids assuming that the environment is in an ideal gas state, so that the measurement accuracy of porosity can be maintained under high temperature and high pressure conditions, and will not be affected by the measurement interference of high-pressure environmental conditions, avoiding measurement errors, and improving the accuracy of porosity measurement.

[0040] The porosity testing device proposed in this application under high temperature and high pressure conditions of the formation can measure the pore volume and skeleton volume under the conditions of overburden pressure of 70MPa, pore pressure of 60MPa and temperature of 120°C, meeting the measurement requirements of porosity under high temperature and high pressure conditions of the formation; the calculation method of pore volume and skeleton volume using the law of conservation of mass solves the problem of inaccurate calculation results of conventional ideal gas state equation at high temperature and high pressure. The porosity testing device can measure both skeleton volume and pore volume, breaking through the limitation of traditional devices that can only measure a single volume; the porosity testing device has a special core holder suitable for high temperature and high pressure conditions, with multi-stage composite sealing technology, and the sealing material is made of perfluororubber material, which ensures effective sealing under high temperature; the gas supply system in the porosity testing device breaks through the problem of low pore pressure measurement of traditional porosity measuring devices, and realizes porosity measurement under pore pressure of 60MPa; and on the basis of conventional pressure gauges, a high-precision differential pressure sensor is added, and the test accuracy reaches 0.1KPa, which ensures the accuracy of the test results; the pressure safety system in the porosity testing device establishes a four-level insurance safety structure consisting of "alarm-pressure automatic safety valve-explosion-proof disk-pressure safety box" to ensure safety after gas pressurization. The alarm sends out an alarm signal when the gas pressure exceeds the maximum pressure. The automatic pressure safety valve automatically releases pressure after exceeding the maximum pressure. The explosion-proof disk releases pressure when the automatic pressure safety valve fails. The whole system is placed in a pressure safety box. The pressure safety box is resistant to high pressure and will not cause an explosion even if a leak occurs, thus ensuring safety. The fixed container system in the porosity testing device is suitable for measuring porosity in different ranges, breaking through the limitation of the single detection range of traditional devices and meeting the experimental testing needs of different samples. The constant temperature system in the porosity testing device has the advantages of small size and good constant temperature effect. A good dedicated constant temperature box has high constant temperature accuracy and better effect; the porosity testing device is installed with an explosion-proof and heat-resistant visual window, which adopts a large-angle explosion-proof and heat-resistant visual window for visualization, and the internal working status is clearly visible. The material adopts four layers of high-temperature and high-pressure explosion-proof tempered glass and an argon-injected structure, which is effectively pressure-resistant and temperature-resistant, ensuring the safety of high temperature and high pressure; the gas booster pump in the porosity testing device is controlled by a compression automatic compensation program, so that the flow accuracy of the gas booster pump remains stable when working under high pressure; the porosity testing device provides a high-speed storage medium for software operation control, and the software system runs fast and smoothly. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] In order to more clearly illustrate the technical solutions and advantages of the embodiments of the present application or the prior art, the following is a brief introduction to the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0042] Figure 1 A schematic diagram of a porosity testing device for formations under high temperature and high pressure conditions provided by one embodiment of the present application;

[0043] Figure 2 is a schematic diagram of sub-device 2;

[0044] Figure 3 is a schematic diagram of sub-device 4;

[0045] Figure 4 A flow chart of the steps of a porosity testing method under high temperature and high pressure conditions of a formation provided in one embodiment of the present application. DETAILED DESCRIPTION

[0046] To further illustrate the technical means and effectiveness of this application's objectives, the following, in conjunction with the accompanying drawings and preferred embodiments, details the specific implementation, structure, features, and effectiveness of a porosity testing method and apparatus for formations under high-temperature and high-pressure conditions proposed in this application. In the following description, references to different "one embodiment" or "another embodiment" do not necessarily refer to the same embodiment. Furthermore, specific features, structures, or characteristics of one or more embodiments may be combined in any suitable manner.

[0047] Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs.

[0048] The present application provides a porosity testing device under high temperature and high pressure conditions of the formation. The schematic diagram of the porosity testing device under high temperature and high pressure conditions of the formation is as follows: Figure 1 As shown, Figure 11-gas cylinder, 2-control valve, 3-gas booster pump, 4-control valve, 5-control valve, 6-control valve, 7-control valve, 8-fixed container, 9-fixed container, 10-fixed container, 11-pressure gauge, 12-control valve, 13-sample chamber, 14-control valve, 15-differential pressure sensor, 16-control valve, 17-control valve, 18-core holder, 19-confining pressure pump, 20-pressure gauge, 21-control valve, 22-constant temperature system, 23-vacuum pump, 24-pressure gauge, 25-control valve, 26-control valve, 27-gas supply system, 28-fixed container system, 29-core system, 30-vacuum system, 31-confining pressure system, 32-alarm, 33-automatic pressure safety valve, 34-explosion-proof disk, 35-pressure safety system, 36-control valve.

[0049] Figure 1 The system includes a gas supply system 27, a pressure safety system 35, a fixed container system 28, a core system 29, a vacuum system 30, a confining pressure system 31, and a constant temperature system 22. The gas supply system 27 primarily provides the test pressure required for porosity testing, namely the pore pressure. The maximum test pressure can reach as low as 60 MPa. It consists of two parts: a gas cylinder 1 and a gas booster pump 3. Gas cylinder 1 primarily provides low-pressure gas for testing, while gas booster pump 3 primarily increases the low-pressure gas to high pressure, enabling high-pressure testing with an accuracy of up to 0.1 kPa. The lower end of gas booster pump 3 is connected to gas cylinder 1 via a pipeline, which is equipped with a control valve 2 and a pressure gauge 11. The upper end of gas booster pump 3 is connected to pressure safety system 35 via a pipeline.

[0050] The main function of the pressure safety system 35 is to ensure safety under high-pressure conditions. It includes an alarm 32, an automatic pressure safety valve 33, and a burst-proof disk 34. The alarm 32, the automatic pressure safety valve 33, and the burst-proof disk 34 are placed in the pressure safety box. The pressure safety system 35 is connected to the gas supply system 27 and the fixed container system 28 through pipelines.

[0051] The main function of the fixed container system 28 is to store gas of the pressure required for the test and measure the volume. It includes three fixed containers 8, 9, and 10 of different volumes, which can be suitable for low-pore, medium-pore, and high-pore samples respectively to meet the measurement of samples of different porosity sizes; the upper end of the fixed container system 28 is connected to the gas supply system 27 through a pipeline, and the pipeline is provided with control valves 4, 5, 6, 7 and a pressure gauge; the lower end of the fixed container system 28 is connected to the core system 29 through a pipeline; the fixed container system 28 and the core system 29 are both placed in the constant temperature system 22.

[0052] The core system 29 mainly functions to place cores, and includes two parts: a sample chamber 13 and a core holder 18. The sample chamber 13 is mainly used to measure the rock skeleton volume, and the core holder 18 is used to measure the core pore volume. The upper end of the sample chamber 13 is connected to the fixed container system 28 via a pipeline, and a control valve 12, a control valve 36 and a differential pressure sensor 15 are provided on the pipeline. The upper end of the sample chamber 13 is also connected to the core holder 18 via a pipeline, and control valves 14 and 15 are provided on the pipeline. The upper end of the core holder 18 is connected to the fixed container system 28 via a pipeline, and a control valve 17 is provided on the pipeline.

[0053] The main function of the confining pressure system 31 is to apply the overburden pressure required for the test to the core holder 18, where the overburden pressure can reach 70 MPa. The confining pressure system 31 includes a confining pressure pump 19 and a pressure gauge 20. The confining pressure pump 19 is connected to the core holder 18 through a pipeline, and a control valve 21 and a pressure gauge 20 are provided on the pipeline.

[0054] The main function of the constant temperature system 22 is to heat and maintain the test temperature constant. The fixed containers (8), (9), (10), the sample chamber (13) and the core holder (18) are all placed in the constant temperature system.

[0055] The main function of the vacuum system 30 is to extract the air in the pipeline and the core system 29 to ensure accurate measurement results. It includes two parts: a vacuum pump 23 and a pressure gauge 24. The vacuum pump 23 is connected to the core system 29 through a pipeline, and the pipeline is provided with control valves 25, 26 and a pressure gauge 24.

[0056] The sample chamber 13 is referred to as sub-device 1, which can measure the volume of the skeleton. The sample chamber 13 for measuring the volume of the skeleton adopts a flange sealing structure to ensure sealing under high pressure conditions, and the sealing ring is made of perfluoroelastomer material with high temperature resistance.

[0057] The core holder 18 is recorded as sub-device 2. Sub-device 2 is a special core holder suitable for high temperature and high pressure conditions. The core holder is made of 316L stainless steel that is resistant to high temperature and high pressure. It has multi-stage sealing technology. The holder port adopts a three-stage composite sealing technology of double-threaded pressure cap sealing + inner and outer double-stage O-rings + sealing rubber sleeves. The O-rings and sealing rubber sleeves are made of perfluoroelastomer material, which has high temperature resistance and can reach 250°C, ensuring effective sealing under high temperature. The schematic diagram of sub-device 2 is shown in FIG. Figure 2 As shown, the size of the sub-device 2 is 491mm×98mm. Figure 2 The core is composed of a small pressure cap, a large pressure cap, a spacer, a taper sleeve, an O-ring, a core chamber, a rubber sleeve and a cylinder.

[0058] The differential pressure sensor 15 is recorded as sub-device 3. Sub-device 3 adopts a high-precision differential pressure sensor, which makes the test accuracy reach 0.1Kpa, ensuring the accuracy of the test results.

[0059] The constant temperature system 22 is recorded as sub-device 4. The schematic diagram of sub-device 4 is as follows: Figure 3 As shown, sub-device 4 utilizes an aluminum alloy thermostat with dimensions of 400mm (width x depth x height) x 400mm x 600mm (height x width x depth). Its compact design makes it easier to maintain a constant temperature. An opening is provided on the side of the thermostat for threading pipes and other connectors. The small opening ensures a constant temperature for the gas. The thermostat can heat up to 150°C with a temperature control accuracy of ±0.1°C. It utilizes internal hot air circulation technology using electric heating wires and a hot air blower. Sub-device 4 is computer-controlled and has a display screen. The temperature can be set and displayed in real time. It also has an automatic temperature control function. It automatically heats when the temperature falls below the set point and stops heating when the temperature is too high. The door seal of the thermostat is made of high-temperature and high-pressure resistant fluororubber. The thermostat is equipped with a high-temperature and high-pressure safety lock to effectively isolate the gas within the thermostat in the event of a leak, ensuring the safety of the experimenter. At the same time, the window of the constant temperature box uses a specially developed visual window and a built-in lighting system, so the internal working status is clearly visible; in addition, the visual window adopts a large-angle explosion-proof and heat-resistant visual window, and the material is four layers of high-temperature and high-pressure explosion-proof tempered glass + argon injection structure, which is effectively pressure-resistant and temperature-resistant, ensuring the safety of high temperature and high pressure.

[0060] The gas supply system 27 is recorded as sub-device 5. Sub-device 5 is a "double-boost and one-stabilize" pressure precision control system constructed by "gas source-boosting device-buffer tank". The gas booster pump is used to boost the pore fluid pressure to a minimum of 60MPa. In addition, a high-precision differential pressure sensor is added on the basis of a conventional pressure gauge. The pressure test accuracy reaches 0.1KPa, ensuring the accuracy of the test results.

[0061] Pressure safety system 35 is denoted as sub-device 6. Sub-device 6 utilizes a four-level safety structure consisting of an alarm, an automatic pressure safety valve, a bursting disk, and a pressure safety box, with layered controls. This ensures safety after gas pressurization. The alarm signals when gas pressure exceeds the maximum pressure, the automatic pressure safety valve automatically releases pressure after exceeding the maximum pressure, and the bursting disk releases pressure if the automatic pressure safety valve malfunctions. The entire system is housed in a pressure safety box, which is designed to withstand high pressures. Even a leak will not cause an explosion, ensuring safety.

[0062] The fixed container system 28 is recorded as sub-device 7. Sub-device 7 is designed with three different specifications of fixed containers with volumes of 10ml, 20ml and 40ml, which can be applied to low-pore, medium-pore and high-pore samples respectively. The porosity detection range is between 0.1% and 80%.

[0063] Confining pressure pump 19 is designated as sub-unit 8. Sub-unit 8 utilizes a high-precision constant-speed and constant-pressure pump controlled by an intelligent control system. Its flow rate range is 0.0001-30 ml / min, its maximum pressure is 70 MPa, and its pressure accuracy is 0.001 MPa. All operating parameters of the constant-speed and constant-pressure pump are displayed on the device's 10.2-inch LCD screen, which displays pressure, flow rate, and flow rate curves in real time. The device also features pressure measurement and overpressure and underpressure protection systems, ensuring safe and reliable operation. An automatic compression compensation program ensures stable flow rate accuracy even under high pressure.

[0064] Based on the same inventive concept as the above-mentioned device, the present invention also provides a method for testing porosity under high temperature and high pressure conditions. Figure 4 , the specific steps include:

[0065] S1, measure the gas pressure in the fixed container in real time to obtain the volume of the fixed container.

[0066] The porosity test steps in this embodiment are:

[0067] First, the thermostat in the porosity testing device is turned on and the temperature is set to the target temperature. In this embodiment, the target temperature is 20°C, but the implementer can set it according to the actual situation. The core chamber is responsible for clamping the core. The vacuum chamber is used to evacuate the core to remove the fluid inside the core. The gas cylinder is used to release gas into the fixed container and the core chamber so that the spaces in both are filled with isobaric gas, and then the spatial connection between the two chambers is cut off.

[0068] Secondly, the gas booster pump increases the pressure to the fixed container and waits for the pressure to stabilize;

[0069] Finally, open the valves of the fixed container and the core chamber to allow ventilation to both. Wait until the air pressure in the space stabilizes again, and calculate the volume of gas flowing from the fixed container to the core chamber based on the pressure change, and then infer the porosity of the rock mass in the core chamber.

[0070] Among them, the specific pressure of the fixed container needs to be controlled during the process of the gas booster pump boosting the pressure of the fixed container to meet the pore pressure required for the final pressure balance.

[0071] Therefore, the porosity measurement device in this embodiment has a pressure control problem, and the boost pressure needs to be controlled through intelligent control technology.

[0072] It should be noted that the gas contained in the gas cylinder 1 is helium. When the vacuum pump evacuates the core chamber, since it is technically difficult to achieve a complete vacuum in the core chamber, helium in the gas cylinder 1 is simultaneously introduced to change the gas composition inside the core chamber, so as to expel the non-helium components in the core chamber as much as possible, thereby reducing the influence of the complexity of the gas composition on the measurement results and avoiding measurement errors.

[0073] This embodiment uses pressure sensors to monitor the inflation conditions of the fixed container and the core chamber, and then uses intelligent control technology to control the boost pressure, specifically:

[0074] A pressure sensor is installed in the fixed container to measure the pressure data of the fixed container in real time. In this embodiment, the pressure data is recorded every 1 second.

[0075] At the same time, the volume of the fixed container in the porosity testing device is obtained through the intelligent control system.

[0076] The pressure sensor of this embodiment is installed in a fixed container. The environment in the fixed container is relatively stable, so the gas density and pressure show a positive correlation. To this end, this embodiment injects a known mass of gas into a pressure vessel with a volume scale, and realizes the pressurization process by compressing the volume, thereby obtaining the gas density under different pressures, that is, ρ = m / v, ρ is the gas density, m is the gas mass, and v is the gas volume. A limited number of experiments are used to obtain the gas density under different experimental conditions, and a relationship map of gas density and gas pressure is obtained. Fitting the relationship map of gas density and gas pressure through a limited number of experiments is a common technique for data processing, and this embodiment will not be described in detail here.

[0077] In the relationship diagram, the horizontal axis is pressure and the vertical axis is density. When using the relationship diagram, the pressure of a fixed container at time t is input, and the gas density ρi of the fixed container at time t can be output. t ; Taking the gas density of the fixed container at time t as input, the pressure of the fixed container at time t can be output.

[0078] At the same time, by setting the gas density ρi t Multiplying by the volume of the fixed container can get the gas mass Mi of the fixed container at time t t .

[0079] S2, open the control valve between the gas cylinder and any fixed container, close the control valve between the any fixed container and the core chamber, evacuate the gas in the core chamber, then close the control valve between the gas cylinder and the any fixed container, open the control valve between the any fixed container and the core chamber, record it as the first opening of the control valve, analyze the pressure changes before and after the control valve between the fixed container and the core chamber is opened, and combine it with the volume of the any fixed container to obtain the estimated pore volume.

[0080] In the test method of this embodiment, the measurement data mainly comes from the static pressure difference between the fixed container after the pressurization is completed and when it is opened. Therefore, the target pressure set for the pressurization is the main factor determining the static pressure difference between the fixed container before and after the pressurization, and it needs to be controlled carefully.

[0081] Based on this, this embodiment uses intelligent control technology to accurately control the target pressure, with the aim of reducing calculation errors during the porosity measurement process and ensuring fast and accurate measurement results.

[0082] In this embodiment, porosity measurement relies on the static pressure difference between the fixed container in two different states: the pressurized blocked state, i.e., before the valve is closed; and the pressurized open state, i.e., after the valve is opened. If the static pressure difference between these two states is too small, the data may be unclear and may be affected by system noise, thus affecting measurement accuracy.

[0083] This static pressure difference is usually achieved by controlling the target pressure. When the target pressure is too low, the pressure difference between the fixed container and the core chamber before the valve is opened is too small, and the static pressure difference before and after the valve is opened is also small, which makes the data easily masked by system noise, thereby causing porosity measurement errors.

[0084] Therefore, this embodiment obtains the target pressure by limiting the static pressure difference, and determines that when the pressure provided by the boosting device is less than the target pressure, the porosity measurement error will be caused due to the excessively small static pressure difference.

[0085] In this embodiment, the static pressure difference ratio is set to β=0.3%, which means that after the valve is opened in the boost blocking state, the static pressure of the fixed container system should be reduced to at least 1-β times the static pressure before the valve is opened to avoid measurement errors.

[0086] In this embodiment, the gas cylinder and the stationary container are initially in a connected state, while the core chamber and the stationary container are in a blocked state. At this time, the core chamber is evacuated to discharge shale oil, natural gas and other substances in the core chamber. At this time, the control valve between the gas cylinder and the stationary container is closed, and then the valve between the core chamber and the stationary container is opened, which is recorded as the first opening of the control valve, and the pressure measurement data of the stationary container is stabilized, and it is determined that the core chamber and the stationary container are in a pressure balance state at this time.

[0087] The core chamber undergoes a process of vacuuming and filling. During the filling process, the gas inside the core chamber comes from a fixed container. Therefore, the pore volume in the core chamber can be estimated by the outflowing gas from the fixed container. The estimation method is:

[0088] First, obtain the measured gas pressure of the predetermined container before the control valve is opened for the first time, use the relationship map to obtain the corresponding gas density, and calculate the multiplication result with the volume of the predetermined container to obtain the gas mass of the predetermined container before the control valve is opened for the first time.

[0089] The mass of the gas in the container before the control valve is opened for the first time is determined as the first total mass of the gas.

[0090] After the control valve is opened for the first time, based on the pressure value in the pressure equilibrium state, the same calculation method as before the control valve is opened for the first time is adopted to obtain the gas mass in the fixed container after the control valve is opened for the first time, which is determined as the second total gas mass.

[0091] Using the relationship diagram, the gas density of the fixed container when the pressure is balanced after the control valve is first opened is obtained, the difference between the total mass of the first gas and the total mass of the second gas is calculated, and the ratio of the difference to the gas density of the fixed container when the pressure is balanced is determined as the estimated pore volume.

[0092] Among them, the difference between the total mass of the first gas and the total mass of the second gas corresponds to the mass of the gas filled in the pores of the core chamber, and the gas density of the fixed container after the valve is opened for the first time corresponds to the gas density of the gas filled in the pores. Therefore, the preliminary pore volume can be estimated by comparing the two.

[0093] It should be noted that the estimated pore volume is calculated on the assumption that the core chamber is completely vacuumed after evacuation. However, it is difficult to evacuate the core chamber to a complete vacuum. Some helium still remains inside the core chamber after evacuation. Therefore, the pore volume obtained here can only be used as an estimated pore volume, which has a certain error from the actual pore volume.

[0094] S3, closing the control valve between the arbitrary fixed container and the core chamber; pressurizing the arbitrary fixed container to the target pressure, and reopening the control valve between the arbitrary fixed container and the core chamber after the pressurization is balanced; obtaining the target pressure based on the constant relationship between the total mass of gas in the arbitrary fixed container and the core chamber before and after pressurization by presetting the static pressure difference ratio before and after pressurization of the arbitrary fixed container and the estimated pore volume.

[0095] When the control valve is opened for the first time and the pressure measurement data of the fixed container is stable, the valve between the fixed container and the core chamber, i.e., the control valve, is closed. After closing the valve between the gas cylinder and the fixed container, and the valve between the fixed container and the core chamber, the fixed container is pressurized. After the pressure is increased to the target pressure, the valve between the fixed container and the core chamber is opened, which is recorded as the second valve opening.

[0096] In the device state before the second valve opening, the fixed container volume, the core chamber gas pressure, and the estimated pore volume can all be determined before pressurization, and the fixed container gas pressure corresponds to the target pressure of the pressurization process; if the static pressure difference after the second valve opening is stabilized is set to the static pressure difference ratio, the target pressure corresponding to the static pressure difference ratio can be inferred.

[0097] Therefore, based on this state transition relationship, this embodiment calculates the target pressure before boosting, specifically:

[0098] First, based on the gas pressure Pi1 of the fixed container before pressurization, the relationship map is used to obtain the gas density ρi1 of the fixed container before pressurization, the estimated pore volume Vr, and the volume Vi of the fixed container. Since the gas in the core chamber does not change before and after the pressurization of the fixed container before the second valve opening, the total gas mass M1 of the core chamber after pressurization is:

[0099] M1=ρi1×Vr(1)

[0100] It should be understood that before the valve is opened for the second time, the valves of the stator container and the core chamber are in a pressure equilibrium state when they are closed, so the gas density of the stator container can be used as the gas density of the core chamber.

[0101] Assuming that the static pressure before the second valve opening after the fixed container is pressurized is Pi2, and assuming that the static pressure after the second valve opening is Pi3, the pressure relationship is obtained according to the definition of the static pressure difference ratio:

[0102]

[0103] Then, using the pressure Pi2 of the fixed container as input, the relationship diagram is used to calculate the density of the fixed container after the output pressure is increased, which is ρi2. The total mass of gas in the fixed container at this time, M2, is:

[0104] M2=ρi2×Vi(3)

[0105] Finally, after the second valve opening, the total mass of gas in the core chamber and the fixed container, M3, is:

[0106] M3=ρi3×(Vi+Vr)(4)

[0107] Among them, before and after the second valve opening, the total mass of gas in the fixed container and the core chamber is the same, that is:

[0108] M3=M1+M2(5)

[0109] Therefore, by combining equations (1)(2)(3)(4)(5), we can calculate the gas density corresponding to the target pressure:

[0110]

[0111] Furthermore, the gas density ρi2 corresponding to the target pressure is used as input and calculated using the relational map, and the output is the target pressure Pi2.

[0112] The target pressure is calculated based on the estimated pore volume and the static pressure difference ratio. Using the target pressure as the minimum pressure and employing an intelligent control system to control the pressure increase ensures that the static pressure difference in the container before and after the second valve opening meets the static pressure difference ratio, thus avoiding calculation errors caused by an undersized static pressure difference.

[0113] At the same time, when the pressure increase is controlled by the intelligent control system, the pressure increase should be close to the target pressure to prevent the core structure from being damaged due to the large pressure difference between the fixed container and the core chamber.

[0114] By obtaining the target pressure, the intelligent control system can ensure that the target pressure is within a reasonable range, avoiding excessive pressure that damages the core structure, and preventing the measurement data from being masked by noise due to excessive pressure.

[0115] S4, analyzing the decreasing speed of the pressure of the arbitrary container during the first opening of the control valve to determine the permeation resistance characteristic value of the core in the core chamber; and correcting the target pressure based on the permeation resistance characteristic value.

[0116] Furthermore, due to the porosity of the pores in the core sample and the fact that cement between rock particles impedes gas flow, there is resistance to gas flow within the core, which is referred to as permeation resistance in this embodiment. Therefore, the intelligent control system should consider the influence of permeation resistance when controlling the target pressure.

[0117] Excessive permeability resistance will increase the overall time it takes for helium to fill the core after the valve is opened for the second time, which can easily cause the measurement time to be too long and may even prevent the gas from flowing into some accessible pores, resulting in measurement errors.

[0118] Before the valve is opened for the first time, the core chamber is in a vacuum state, so the static pressure difference between the core chamber and the fixed container is large; at this time, after the valve is opened, helium can quickly pass through the pores and cements and fill the core quickly; during the filling process, the pressure of the fixed container drops rapidly as a whole, but the rate of decrease is not uniform. This is because the internal structure of the core is complex. When facing large pores without cement, the gas fills quickly and the pressure of the fixed container drops quickly. When facing small pores or locations with cement, the gas fills slowly and the pressure of the fixed container drops slowly.

[0119] Therefore, this embodiment can judge the internal structure of the core by the change in the fixed container pressure after the valve is opened for the first time. The more severe the jitter of the fixed container pressure data when the valve is opened for the first time, the more cementing materials there are inside the core and the more complex the structure is. A higher fixed container target pressure is required to allow helium to quickly pass through the complex core structure to complete gas filling after the valve is opened for the second time.

[0120] Based on the above analysis, the permeability resistance characteristic value of the core in the core chamber is calculated, specifically:

[0121] Obtain the pressure values ​​measured at all times of the fixed container between the first opening of the control valve and the closing of the control valve, and form a pressure sequence in chronological order. Use the fast Fourier transform algorithm to obtain a spectrum of the pressure sequence, calculate the cumulative sum of the amplitudes corresponding to all frequencies in the spectrum, and calculate the ratio of the amplitude corresponding to each frequency in the spectrum to the cumulative sum as the normalized value of the amplitude corresponding to each frequency in the spectrum.

[0122] Among them, the fast Fourier transform algorithm is an existing well-known technology, and the specific process will not be described in detail. This embodiment only provides a frequency domain conversion algorithm and a normalization method. The implementer can choose other existing feasible frequency domain conversion algorithms and normalization methods according to actual conditions. This embodiment does not limit them here.

[0123] The specific calculation method of the penetration resistance characteristic value is:

[0124] Where δ is the characteristic value of the core's permeability resistance in the core chamber, γ k is the normalized value of the amplitude corresponding to the kth frequency in the spectrum of the pressure sequence, H k is the kth frequency in the spectrum diagram of the pressure sequence, K is the number of frequencies in the spectrum diagram of the pressure sequence, μ is a preset value greater than 0, and the denominator is 0. In this embodiment, μ=1, and the implementer can set it according to actual conditions.

[0125] The reciprocal of the frequency is used as the weight to perform weighted summation on the normalized amplitude in the spectrum. The smaller the characteristic value of the permeability resistance, the more concentrated the energy in the spectrum of the pressure sequence of the fixed container is in the high-frequency part, indicating that the pressure drop rate changes more unevenly when the valve is opened for the first time, and the more complex the core structure is. A higher target pressure is required before the valve is opened for the second time so that helium can quickly fill the core after the second valve opening.

[0126] Therefore, based on the permeation resistance characteristic value, the target pressure is corrected as follows:

[0127] Pr=Pi2×(ab×δ); wherein Pr is the corrected target pressure, recorded as the actual target pressure, Pi2 is the static pressure before the valve is opened for the second time after the container is pressurized, that is, the target pressure, recorded as the basic target pressure, δ is the permeability resistance characteristic value of the core in the core chamber, a is the first preset value, and b is the second preset value, wherein the first preset value is greater than the second preset value, and the difference between the first preset value and the second preset value is greater than or equal to 1, and the target pressure is expanded to ab to a times through the first preset value and the second preset value.

[0128] In this embodiment, a=40, b=39, which can be set by the implementer according to actual conditions, and this embodiment does not limit this.

[0129] Among them, the basic target pressure is the minimum value of the actual target pressure; the permeation resistance characteristic value is a coefficient ranging from 0 to 1. The smaller the permeation resistance characteristic value, the higher the actual target pressure needs to be set to ensure that helium can quickly fill the core; in this embodiment, the actual target pressure fluctuates between 1 and 40 times the basic target pressure. When the core structure is complex and a higher actual target pressure is required to dredge the internal structure of the core, selecting a higher actual target pressure helps helium to quickly fill the core, avoids the problem of core structure damage caused by excessive target pressure, the problem of measurement data being obscured by noise due to too low target pressure, and the problem of whether helium can quickly fill the pores, which helps to improve the accuracy of the final porosity test.

[0130] S5, repeating step S2, after the spatial pressure of the any fixed container and the core chamber is balanced, obtaining the first gas density of the any fixed container based on the pressure measured in the any fixed container.

[0131] Finally, this embodiment controls the porosity testing device to complete the porosity test. The specific process is as follows:

[0132] First, the gas cylinder, fixed container, and core chamber are three interconnected spaces. The control valve between the gas cylinder and fixed container is denoted as valve 1, and the control valve between the fixed container and core chamber is denoted as valve 2.

[0133] First open the first valve, close the second valve, and evacuate the core chamber;

[0134] Then, close the first valve and open the second valve. After the spatial pressure of the fixed container and the core chamber is balanced, the corresponding gas density ρ1 is obtained based on the pressure measured in the fixed container using the relationship diagram, which is recorded as the first gas density.

[0135] S6, repeating the pressurization process in step S3 based on the corrected target pressure, respectively obtaining the second gas density of any given container after pressurization, and the third gas density of any given container after the pressure is balanced by opening the control valve again after pressurization.

[0136] Next, close the second valve and pressurize the given container. The target pressure is the actual target pressure Pr calculated above, and wait for the pressurization to end. At this time, based on the actual target pressure Pr, the relationship diagram is used to obtain the gas density corresponding to the given container, which is ρ2, recorded as the second gas density.

[0137] Furthermore, the second valve is opened to allow the gas to penetrate naturally into the core chamber until equilibrium is reached. At this time, the gas density corresponding to the fixed container is ρ3, which is recorded as the third gas density.

[0138] S7. Based on the constant relationship among the first gas density, the second gas density, the third gas density, and the total mass of the gas before and after pressurization, the actual pore volume of the core chamber is determined. Accordingly, for the sample chamber, the same testing method as that of the core chamber is adopted to obtain the actual core skeleton volume of the sample chamber, and the porosity is obtained by combining the actual pore volume.

[0139] In this embodiment, the volume of the fixed container is recorded as Vi, and the actual pore volume is set as the unknown number Vx.

[0140] Based on the gas density ρ2 and the volume Vi of the fixed container, it can be calculated that after the pressurization in step S6 is completed, the gas mass C2 in the fixed container is C2 = ρ2 × Vi. Since the second valve is not opened at this time, the gas mass C3 in the core chamber is C3 = ρ1 × Vx.

[0141] After the second valve is opened in step S6, based on the gas density ρ3, the volume of the fixed container, and the actual pore volume Vx of the core chamber, the sum of the gas masses C4 in the fixed container and the core chamber can be expressed as C4 = ρ3 × (Vi + Vx);

[0142] Since no new gas is obtained after the pressurization is completed, the gas mass in the device is the same when the gas density ρ2 is obtained and when the gas density ρ3 is obtained. Therefore, C2+C3=C4; further deduction and calculation yield:

[0143] Vx is the actual pore volume. In this embodiment, ρ2-ρ3 is recorded as the first difference, and ρ3-ρ1 is recorded as the second difference. Recorded as relative ratio.

[0144] Since the core structure consists of two parts, one is the actual pore volume and the other is the actual core skeleton volume, accordingly, based on the gas cylinder, fixed container and sample chamber, the same operating steps of S1-S7 are used to obtain the actual core skeleton volume of the sample chamber; specifically, the core chamber in steps S1-S7 is replaced by the sample chamber.

[0145] The sum of the actual pore volume of the core chamber and the actual core skeleton volume of the sample chamber is calculated and recorded as the total core volume.

[0146] Finally, the specific calculation method of porosity in this embodiment is:

[0147] Where F is the measured porosity, Vx is the actual pore volume, and Vr is the total core volume.

[0148] Among them, the porosity measurement method adopted in this embodiment is different from the traditional gas expansion method. It does not assume that the gas in the device is in an ideal gas state. Instead, it completes the measurement based on the principle that the gas mass in the device is equal. This avoids the calculation error caused by the high-pressure environment not conforming to the ideal gas state during the measurement of the traditional gas expansion method, and obtains a more accurate porosity test result. At the same time, when performing porosity measurement, this embodiment controls the target pressure of the fixed container pressurization. During the control process, the basic target pressure is set to select a suitable pressure range, which not only avoids the problem of measurement data being masked by noise due to insufficient pressurization, but also avoids the problem of core structure being destroyed due to excessive pressurization. At the same time, the permeability resistance characteristic value is calculated to characterize the complexity of the internal structure of the core. The supercharging pressure is increased for cores with complex internal structures to avoid the problem of slow gas diffusion and long measurement time due to insufficient supercharging pressure.

[0149] It should be noted that the order in which the embodiments of the present application are presented is for illustrative purposes only and does not necessarily represent the superiority or inferiority of the embodiments. Furthermore, the foregoing descriptions of specific embodiments of this specification are provided. Furthermore, the processes depicted in the accompanying drawings do not necessarily require the specific order or sequential sequence shown to achieve the desired results. In certain embodiments, multitasking and parallel processing are also possible or may be advantageous.

[0150] The various embodiments in this specification are described in a progressive manner, and the same or similar parts between the various embodiments can be referred to each other. Each embodiment focuses on the differences from other embodiments.

[0151] The above description is only a preferred embodiment of the present application and is not intended to limit the present application. Any modifications, equivalent replacements, improvements, etc. made within the principles of the present application shall be included in the scope of protection of the present application.

Claims

1. A method for testing porosity of a formation under high temperature and high pressure conditions, characterized in that: The porosity testing method is implemented by a porosity testing device, wherein the porosity testing device comprises a gas cylinder (1), fixed containers (8), (9), (10) of different volumes, a sample chamber (13), and a core chamber in a core holder (18), wherein the gas cylinder (1), fixed containers (8), (9), (10), sample chamber (13), and core holder (18) are connected in an arrangement order through a control valve; the porosity testing method comprises the following steps: S1, real-time measurement of the gas pressure in the fixed container to obtain the volume of the fixed container; S2, opening the control valve between the gas cylinder and any fixed container, closing the control valve between the any fixed container and the core chamber, evacuating the gas in the core chamber, then closing the control valve between the gas cylinder and the any fixed container, and opening the control valve between the any fixed container and the core chamber. This is recorded as the first opening of the control valve. The pressure changes before and after the opening of the control valve between the fixed container and the core chamber are analyzed, and the estimated pore volume is obtained based on the volume of the any fixed container. S3, closing the control valve between the arbitrary fixed container and the core chamber; pressurizing the arbitrary fixed container to a target pressure, and reopening the control valve between the arbitrary fixed container and the core chamber after the pressurization is balanced; obtaining the target pressure based on a constant relationship between the total mass of gas in the arbitrary fixed container and the core chamber before and after pressurization by presetting a static pressure difference ratio before and after pressurization of the arbitrary fixed container and an estimated pore volume; S4, analyzing the rate of decrease of the pressure of the any certain container during the first opening of the control valve to determine a permeation resistance characteristic value of the core in the core chamber; and correcting the target pressure based on the permeation resistance characteristic value; S5, repeating step S2, after the pressure in the space of the any fixed container and the core chamber is balanced, obtaining a first gas density of the any fixed container based on the pressure measured in the any fixed container; S6, repeating the pressurization process in step S3 based on the corrected target pressure, respectively obtaining a second gas density of the any fixed container after pressurization, and a third gas density of the any fixed container after the pressure is balanced by opening the control valve again after pressurization; S7. Based on the constant relationship among the first gas density, the second gas density, the third gas density, and the total mass of the gas before and after pressurization, the actual pore volume of the core chamber is determined. Accordingly, for the sample chamber, the same testing method as that of the core chamber is adopted to obtain the actual core skeleton volume of the sample chamber, and the porosity is obtained by combining the actual pore volume.

2. The method for testing porosity of a formation under high temperature and high pressure conditions according to claim 1, characterized in that: The determination of the estimated pore volume includes: Obtaining a first total mass of gas in any given container based on the pressure measured in the given container before the control valve is first opened, combined with the volume of the given container; and correspondingly, obtaining a second total mass of gas in the given container when the pressure is balanced after the control valve is first opened; The difference between the total mass of the first gas and the total mass of the second gas is calculated to obtain the gas density of the fixed container when the pressure is balanced after the control valve is opened for the first time. The estimated pore volume is the ratio of the difference to the gas density of the fixed container.

3. The method for testing porosity of a formation under high temperature and high pressure conditions according to claim 1, wherein: The obtaining of the target pressure comprises: Obtaining the gas density ρi1 corresponding to the pressure measured in any given container before pressurization, and obtaining the total gas mass M1 of the core chamber before the control valve is opened again after pressurization based on the gas density ρi1 and the estimated pore volume; Assuming that the static pressure of any given container before the control valve is opened again after the pressurization is Pi2, and the static pressure of any given container after the control valve is opened again after the pressurization is Pi3, the pressure relationship is obtained based on the static pressure difference ratio; The total mass of gas in the fixed container before reopening the control valve is obtained by using the gas density corresponding to the static pressure Pi2 and the volume of the fixed container, which is recorded as M2. Similarly, the total mass of gas in the core chamber and the fixed container after reopening the control valve is obtained by using the static pressure Pi3 and the estimated pore volume and the volume of the fixed container, which is recorded as M3. The gas mass constant condition among M1, M2 and M3 is combined to obtain the target pressure corresponding to the static pressure Pi2.

4. The method for testing porosity of a formation under high temperature and high pressure conditions according to claim 3, wherein: The obtaining of the pressure relationship based on the static pressure difference ratio includes: The static pressure difference ratio is recorded as β, then 5. The method for testing porosity of a formation under high temperature and high pressure conditions according to claim 3, characterized in that: The constant gas mass condition is M3=M1+M2.

6. The method for testing porosity of a formation under high temperature and high pressure conditions according to claim 1, wherein: Determination of the characteristic value of the penetration resistance includes: The pressure of any given container at all times between the first opening of the control valve and the closing of the control valve is obtained to form a pressure sequence, a frequency spectrum of the pressure sequence is obtained, the sum of each frequency and a preset value greater than 0 is calculated, the inverse of the sum is used as a weight, and the normalized results of the amplitudes corresponding to all frequencies are weighted and summed to obtain the characteristic value of the permeation resistance.

7. The method for testing porosity of a formation under high temperature and high pressure conditions according to claim 1, characterized in that: The correcting of the target pressure includes: increasing the target pressure by a preset multiple based on the permeability resistance characteristic value.

8. The method for testing porosity of a formation under high temperature and high pressure conditions according to claim 1, wherein: Determining the actual pore volume of the core chamber includes: The difference between the second gas density and the third gas density is calculated and recorded as the first difference. The difference between the third gas density and the first gas density is calculated and recorded as the second difference. The ratio of the first difference to the second difference is calculated and recorded as the relative ratio. The actual pore volume is the product of the relative ratio and the volume of any given container.

9. The method for testing porosity of a formation under high temperature and high pressure conditions according to claim 1, wherein: The determination of the porosity includes: The sum of the actual pore volume and the actual core skeleton volume is calculated and recorded as the total core volume. The porosity is obtained based on the total core volume and the actual pore volume.

10. The method for testing porosity of a formation under high temperature and high pressure conditions according to claim 9, characterized in that: The porosity is the ratio of the actual pore volume to the total volume of the core.

11. A porosity testing device for formations under high temperature and high pressure conditions, the testing device being implemented based on the steps of a porosity testing method for formations under high temperature and high pressure conditions as claimed in any one of claims 1 to 10, characterized in that: The testing device comprises a gas supply system (27), a pressure safety system (35), a fixed container system (28), a core system (29), a vacuum system (30), a confining pressure system (31), and a constant temperature system (22).

12. The porosity testing device under high temperature and high pressure conditions of a formation according to claim 11, characterized in that: The gas supply system includes a gas cylinder and a gas booster pump, and the maximum test pressure of the gas supply system can reach as low as 60MPa; the pressure safety system includes an alarm, an automatic pressure safety valve, an explosion-proof disk, and a safety box. The pressure safety system is connected to the gas supply system and the fixed container system through pipelines.

13. The porosity testing device under high temperature and high pressure conditions of a formation according to claim 11, characterized in that: The fixed container system includes three fixed containers of different volumes. The upper end of the fixed container system is connected to the gas supply system through a pipeline, and a control valve and a pressure gauge are provided on the pipeline; the lower end of the fixed container system is connected to the core system through a pipeline; and the fixed container system is placed in a constant temperature system.

14. The porosity testing device for formations under high temperature and high pressure conditions according to claim 11, characterized in that: The core system includes a sample chamber and a core holder. The upper end of the sample chamber is connected to the fixed container system through a pipeline, and a control valve and a differential pressure sensor are provided on the pipeline; the upper end of the sample chamber is also connected to the core holder through a pipeline, and a control valve is provided on the pipeline; the upper end of the core holder is connected to the fixed container system through a pipeline, and a control valve is provided on the pipeline; the confining pressure system includes a confining pressure pump and a pressure gauge, and the confining pressure pump is connected to the core holder through a pipeline, and a control valve and a pressure gauge are provided on the pipeline.

15. The porosity testing device under high temperature and high pressure conditions of a formation according to claim 11, characterized in that: The constant temperature system includes a heater and a constant temperature box; the vacuum system includes a vacuum pump and a pressure gauge. The vacuum pump is connected to the core system through a pipeline, and a control valve and a pressure gauge are provided on the pipeline.

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