A method and device for testing porosity under high temperature and high pressure conditions of a stratum

Abstract

The application relates to the technical field of pore testing in the process of oilfield exploration and development, in particular to a porosity testing method and device under high-temperature and high-pressure conditions of a formation, which comprises the following steps: measuring the pressure in a constant container in real time, obtaining the volume of the constant container, analyzing the pressure change before and after the opening of a control valve between the constant container and a core chamber, combining the volume of the constant container to obtain an estimated pore volume, obtaining a target pressure in the pressurization process of the constant container, determining the permeation resistance characteristic value of a 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 container, obtaining the actual pore volume of the core chamber, correspondingly, obtaining the actual core skeleton volume of a 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 in the process of oilfield exploration and development, and particularly relates to a method and device for testing porosity under high temperature and high pressure conditions of a formation. BACKGROUND

[0002] The reservoir space of shale directly affects the mode, efficiency and economy of oilfield exploitation, and the reservoir space of shale is mainly based on the shale cleat and matrix pore, and shale contains a large amount of clay minerals, which is easy to form an overpressure formation, and the pore pressure of the formation can be very high. The porosity is one of the key parameters for submitting reserves, and the test result directly determines the size of the reserves. However, due to the high formation depth, high formation pressure and high formation temperature under the formation condition, and the formation environment is high overburden pressure, high pore pressure and high formation temperature, it is of great significance to accurately obtain the porosity under the high temperature and high pressure conditions of the formation for submitting reserves.

[0003] The traditional porosity measuring device can only meet the measurement condition of the overburden pressure, the pore pressure and the test temperature are relatively low, and cannot completely meet the measurement condition under the high temperature and high pressure conditions of the formation. In addition, the traditional porosity measurement method is a low-pressure gas expansion method, and the principle is based on the ideal gas state equation. However, the applicable condition of the ideal gas state equation is high temperature and low pressure. When the shale porosity is measured, the measurement environment is high temperature and high pressure, and the measurement result of the traditional ideal gas state equation will have a large error. In addition, the rock skeleton volume is assumed to be unchanged when the traditional overburden porosity is calculated, and only the pore volume changes. However, in fact, the rock skeleton volume will also change, and finally the porosity test result is inaccurate. SUMMARY

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

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

[0006] The porosity test method is realized by a porosity test device, and the porosity test device comprises a gas cylinder (1), constant volume containers (8), (9) and (10) with different volumes, a sample chamber (13) and a core chamber in a core holder (18). The gas cylinder (1), the constant volume containers (8), (9) and (10), the sample chamber (13) and the core holder (18) are connected in sequence by control valves. The porosity test method comprises the following steps:

[0007] S1, measuring the gas pressure in the constant volume container in real time to obtain the volume of the constant volume container;

[0008] S2, opening the control valve between the gas cylinder and the constant volume container, closing the control valve between the constant volume container and the core chamber, vacuumizing the gas in the core chamber, then closing the control valve between the gas cylinder and the constant volume container, opening the control valve between the constant volume container and the core chamber, which is recorded as the first time of opening the control valve, analyzing the pressure change before and after the control valve between the constant volume container and the core chamber is opened, and combining the volume of the constant volume container to obtain the estimated pore volume;

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

[0010] S4, analyzing the pressure drop rate of the constant volume container during the first time of opening the control valve to determine the permeation resistance characteristic value of the core in the core chamber; correcting the target pressure based on the permeation resistance characteristic value;

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

[0012] S6, repeating the pressurization process in step S3 based on the corrected target pressure, respectively obtaining the second gas density of the constant volume container after pressurization, and the third gas density of the constant volume container after the control valve is opened again after pressurization and pressure balance;

[0013] S7, determining the actual pore volume of the core chamber based on the first gas density, the second gas density, the third gas density, and the constant relationship between the total mass of the gas before and after pressurization; correspondingly, the actual core skeleton volume of the sample chamber is obtained by using the same test method as the core chamber, and the porosity is obtained by combining the actual pore volume.

[0014] In one embodiment, the determination of the estimated pore volume comprises:

[0015] obtaining the first total mass of gas of the constant volume container based on the measured pressure of the constant volume container before the control valve is opened for the first time, and combining the volume of the constant volume container; and correspondingly, obtaining the second total mass of gas of the constant volume container when the pressure is balanced after the control valve is opened for the first time;

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

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

[0018] A gas density ρi1 corresponding to the measured pressure of the constant volume container before pressurization is obtained, and based on the gas density ρi1 and the estimated pore volume, a total gas mass M1 of the core chamber before the control valve is opened again after pressurization is obtained.

[0019] The static pressure of the constant volume container before the control valve is opened again after pressurization is Pi2, and the static pressure of the constant volume container after the control valve is opened again after pressurization is Pi3, and the pressure relationship is obtained based on the static pressure difference ratio.

[0020] The total gas mass of the constant volume container before the control valve is opened again is obtained by using the gas density corresponding to the static pressure Pi2 in combination with the volume of the constant volume container, and is denoted as M2; correspondingly, the total gas mass of the core chamber and the constant volume container after the control valve is opened again is obtained by using the static pressure Pi3 in combination with the estimated pore volume and the volume of the constant volume container, and is denoted as M3.

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

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

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

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

[0025] In one embodiment, the determination of the permeation resistance characteristic value comprises:

[0026] A pressure sequence is obtained by obtaining all pressures of the constant volume container at all times from when the control valve is opened for the first time to when the control valve is closed, a frequency spectrum diagram of the pressure sequence is obtained, a sum value of each frequency and a preset value greater than 0 is calculated, the reciprocal of the sum value is taken as a weight, and a weighted sum of normalization results of all frequency corresponding amplitudes is obtained to obtain the permeation resistance characteristic value.

[0027] In one embodiment, the correction of the target pressure comprises: based on the permeation resistance characteristic value, the target pressure is enlarged by a preset multiple.

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

[0029] calculating a difference between the second gas density and the third gas density, denoted as a first difference, calculating a difference between the third gas density and the first gas density, denoted as a second difference, calculating a ratio of the first difference to the second difference, denoted as a relative ratio, and the actual pore volume is a product of the relative ratio and the volume of the constant volume vessel.

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

[0031] calculating a sum of the actual pore volume and the actual core skeleton volume, denoted as a total core volume, and obtaining the porosity based on the total core volume and the actual pore volume.

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

[0033] In a second aspect, the embodiments of the present application provide a porosity testing device under high temperature and high pressure conditions of a formation, which is implemented based on any one of the steps of the porosity testing method under high temperature and high pressure conditions of the formation. The testing device comprises a gas supply system (27), a pressure safety system (35), a constant volume vessel system (28), a core system (29), a vacuum pumping system (30), a confining pressure system (31), and a constant temperature system (22).

[0034] In one embodiment, the gas supply system comprises a gas cylinder and a gas booster pump, and the maximum testing pressure of the gas supply system is at least 60 MPa. The pressure safety system comprises an alarm, an automatic pressure safety valve, an explosion-proof sheet, and a safety tank, and is connected to the gas supply system and the constant volume vessel system through pipelines.

[0035] In one embodiment, the constant volume vessel system comprises three constant volume vessels with different volumes. The upper end of the constant volume vessel system is connected to the gas supply system through a pipeline, and a control valve and a pressure gauge are arranged on the pipeline. The lower end of the constant volume vessel system is connected to the core system through a pipeline. The constant volume vessel system is placed in the constant temperature system.

[0036] In one embodiment, the core system includes a sample chamber and a core holder, the upper end of the sample chamber is connected to the constant volume system through a pipeline, and a control valve and a differential pressure sensor are arranged 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 arranged on the pipeline; the upper end of the core holder is connected to the constant volume system through a pipeline, and a control valve is arranged 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 arranged on the pipeline.

[0037] In one embodiment, the constant temperature system includes a heater and an incubator; 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 a control valve and a pressure gauge are arranged on the pipeline.

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

[0039] The present application aims to solve the problem of large measurement error of traditional gas expansion method for measuring porosity under high temperature and high pressure conditions. First, the pressure change before and after the opening of the control valve between the constant volume vessel and the core chamber is analyzed, and the estimated pore volume is obtained in combination with the volume of the constant volume vessel. Then, by controlling the pressurization operation of the constant volume vessel, the target pressure is set during the pressurization process, which improves the accuracy of the target pressure of the pressurization. This avoids both the calculation error caused by the small value of the static pressure difference and the destruction of the core structure caused by the large pressure difference between the constant volume vessel and the core chamber. Further, the permeation resistance characteristic value of the core in the core chamber is determined. Based on the permeation resistance characteristic value, the target pressure is corrected. The permeation resistance characteristic value represents the permeation resistance inside the core. For cores with high permeation resistance, a higher target pressure is used to enable the filling gas to 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 the assumption of ideal gas state, so it can maintain the measurement accuracy of porosity under high temperature and high pressure conditions, and will not be affected by the measurement interference of high pressure environment conditions, avoiding measurement error and improving the accuracy of porosity measurement.

[0040] The porosity testing device under high temperature and high pressure of stratum can realize the measurement of pore volume and skeleton volume under the condition of overburden pressure 70 MPa, pore pressure 60 MPa and temperature 120 DEG C, and meets the measurement requirement of porosity under high temperature and high pressure of stratum. The calculation method of pore volume and skeleton volume calculated by mass conservation law solves the problem of inaccurate calculation result of high temperature and high pressure by conventional ideal gas state equation. The porosity testing device can measure both skeleton volume and pore volume, breaking the limitation of traditional device that can only measure single volume. The porosity testing device has a special core holder suitable for high temperature and high pressure condition, and has multi-stage composite sealing technology. The sealing material is made of perfluoro rubber material, which ensures effective sealing under high temperature. The gas supply system of the porosity testing device breaks the problem of low pore pressure measurement of traditional porosity measurement device, and realizes the measurement of porosity under the condition of pore pressure 60 MPa. On the basis of conventional pressure gauge, high-precision differential pressure sensor is added, and the test precision reaches 0.1 KPa, which ensures the accuracy of test result. The pressure safety system of the porosity testing device establishes four-level insurance safety structure composed of alarm, automatic pressure safety valve, explosion-proof sheet and pressure safety tank, which ensures the safety after gas pressurization. The alarm sends an alarm signal when the gas pressure exceeds the maximum pressure. The automatic pressure safety valve automatically releases pressure when the pressure exceeds the maximum pressure. The explosion-proof sheet releases pressure when the automatic pressure safety valve fails. The whole system is placed in the pressure safety tank, which has high pressure resistance and will not cause explosion even if leakage occurs, ensuring safety. The constant volume system of the porosity testing device is suitable for the measurement of porosity in different ranges, breaking the limitation of single detection range of traditional device, and meeting the experimental test demand of different samples. The constant temperature system of the porosity testing device has a special constant temperature box with small volume and good constant temperature effect, high constant temperature precision and better effect. The porosity testing device is provided with explosion-proof temperature-resistant visual window. The visual angle is large, the internal working state is clear and visible, the material is four-layer high-temperature-resistant high-pressure explosion-proof tempered glass and argon injection structure, which effectively resists pressure and temperature, and ensures the safety of high temperature and high pressure. The gas pressurizing pump of the porosity testing device adopts compression automatic compensation program control, so that the flow accuracy of the gas pressurizing pump remains stable when working under high pressure. The porosity testing device provides software running control high-speed storage medium, and the software system runs fast and smoothly. BRIEF DESCRIPTION OF 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 drawings needed to be used in the embodiments or prior art description will be briefly introduced. Obviously, the drawings in the following description are only some embodiments of the present application, and for those skilled in the art, other drawings can be obtained without creative labor based on these drawings.

[0042] Figure 1 A schematic diagram of a porosity testing device under high temperature and high pressure conditions of a formation is provided for an embodiment of the present application.

[0043] Figure 2 A schematic diagram of a sub-device 2 is provided.

[0044] Figure 3 A schematic diagram of a sub-device 4 is provided.

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

[0046] In order to further illustrate the technical means and effects adopted by the present application to achieve the predetermined purposes, the specific embodiments, structures, features and effects of a porosity testing method and device under high temperature and high pressure conditions of a formation according to the present application are described in detail as follows. In the following description, different "one embodiment" or "another embodiment" do not necessarily refer to the same embodiment. In addition, the specific features, structures or characteristics in one or more embodiments can be combined in any suitable form.

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

[0048] The present application provides a porosity testing device under high temperature and high pressure conditions of a formation, and a schematic diagram of the porosity testing device under high temperature and high pressure conditions of a formation is shown in Figure 1 wherein, Figure 11 - gas cylinder, 2 - control valve, 3 - gas booster pump, 4 - control valve, 5 - control valve, 6 - control valve, 7 - control valve, 8 - constant volume vessel, 9 - constant volume vessel, 10 - constant volume vessel, 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 - constant volume vessel system, 29 - core system, 30 - vacuum system, 31 - confining pressure system, 32 - alarm, 33 - pressure automatic safety valve, 34 - rupture disc, 35 - pressure safety system, 36 - control valve.

[0049] Figure 1 The system includes a gas supply system 27, a pressure safety system 35, a constant volume vessel system 28, a core system 29, a vacuum system 30, a confining pressure system 31, and a constant temperature system 22. The main function of the gas supply system 27 is to provide the test pressure required for porosity testing, i.e. pore pressure, with a maximum test pressure of up to 60 MPa, including a gas cylinder 1 and a gas booster pump 3. The gas cylinder 1 mainly provides low-pressure gas for testing, and the gas booster pump 3 mainly increases the low-pressure gas to high pressure to achieve high-pressure testing with an accuracy of 0.1 KPa. The lower end of the gas booster pump 3 is connected to the gas cylinder 1 through a pipeline, and the pipeline is provided with a control valve 2 and a pressure gauge 11. The upper end of the gas booster pump 3 is connected to the pressure safety system 35 through a pipeline.

[0050] The main function of the pressure safety system 35 is to ensure safety under high pressure, including an alarm 32, a pressure automatic safety valve 33, and a rupture disc 34. The alarm 32, the pressure automatic safety valve 33, and the rupture disc 34 are placed in a pressure safety tank, and the pressure safety system 35 is connected to the gas supply system 27 and the constant volume vessel system 28 through a pipeline.

[0051] The main function of the constant volume vessel system 28 is to store the pressure gas required for testing and measure the volume, including three constant volume vessels 8, 9, and 10 with different volumes, which can be respectively applied to low-porosity, medium-porosity, and high-porosity samples to meet the measurement of samples with different porosities. The upper end of the constant volume vessel system 28 is connected to the gas supply system 27 through a pipeline, and the pipeline is provided with control valves 4, 5, 6, and 7 and a pressure gauge. The lower end of the constant volume vessel system 28 is connected to the core system 29 through a pipeline. The constant volume vessel system 28 and the core system 29 are placed in the constant temperature system 22.

[0052] The core system 29 mainly functions to place the core, including two parts of the sample chamber 13 and the core holder 18; the sample chamber 13 is mainly used to measure the volume of the rock skeleton, and the core holder 18 is used to measure the pore volume of the core; the upper end of the sample chamber 13 is connected with the constant volume system 28 through a pipeline, and the pipeline is provided with a control valve 12, a control valve 36 and a differential pressure sensor 15; the upper end of the sample chamber 13 is also connected with the core holder 18 through a pipeline, and the pipeline is provided with control valves 14 and 15; the upper end of the core holder 18 is connected with the constant volume system 28 through a pipeline, and the pipeline is provided with a control valve 17.

[0053] The confining pressure system 31 mainly functions to apply the overburden pressure required for the test to the core holder 18, wherein the overburden pressure can reach 70 MPa; the confining pressure system 31 includes a confining pressure pump 19 and a pressure gauge 20, and the confining pressure pump 19 is connected with the core holder 18 through a pipeline, and the pipeline is provided with a control valve 21 and the pressure gauge 20.

[0054] The constant temperature system 22 mainly functions to heat and keep the test temperature constant, and the constant volume vessels (8), (9) and (10), the sample chamber (13) and the core holder (18) are all placed in the constant temperature system.

[0055] The vacuum system 30 mainly functions to extract the air in the pipeline and the core system 29, so as to ensure the accuracy of the measurement results, and includes two parts of a vacuum pump 23 and a pressure gauge 24; the vacuum pump 23 is connected with the core system 29 through a pipeline, and the pipeline is provided with control valves 25 and 26 and the pressure gauge 24.

[0056] The sample chamber 13 is recorded as a sub-device 1, and the sub-device 1 can realize the measurement of the skeleton volume. The sample chamber 13 for measuring the skeleton volume adopts a flange sealing structure, which ensures the sealing property under high pressure, and the sealing ring adopts a perfluorinated rubber material, which has high temperature resistance.

[0057] The core holder 18 is recorded as a sub-device 2, and the 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 material with high temperature and high pressure resistance, has multi-stage sealing technology, and the holder port adopts double-threaded cap sealing + inner and outer double-stage O-ring + sealing rubber sleeve three-stage composite sealing technology. The O-ring and the sealing rubber sleeve are made of perfluorinated rubber material, which has high temperature resistance and can resist a temperature of 250℃, thereby ensuring effective sealing under high temperature. The sub-device 2 is shown in the schematic view of the sub-device 2 as shown in the schematic view of the sub-device 2. Figure 2 The size of the sub-device 2 is 491mm x 98mm, Figure 2 The core holder 18 is recorded as a sub-device 2, and the 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 material with high temperature and high pressure resistance, has multi-stage sealing technology, and the holder port adopts double-threaded cap sealing + inner and outer double-stage O-ring + sealing rubber sleeve three-stage composite sealing technology. The O-ring and the sealing rubber sleeve are made of perfluorinated rubber material, which has high temperature resistance and can resist a temperature of 250℃, thereby ensuring effective sealing under high temperature. The sub-device 2 is shown in the schematic view of the sub-device 2.

[0058] The differential pressure sensor 15 is referred to as sub-device 3. Sub-device 3 uses a high-precision differential pressure sensor, which enables the test accuracy to reach 0.1 kPa, thus ensuring the accuracy of the test results.

[0059] The constant temperature system 22 is referred to as sub-device 4, and the schematic diagram of sub-device 4 is shown below. Figure 3 As shown, sub-device 4 is a thermostat chamber made of aluminum alloy, with dimensions of 400mm x 400mm x 600mm (width x depth x height). Its compact design facilitates temperature control. An opening on the side of the chamber allows for the passage of pipes and other connecting components; the small opening ensures effective temperature control of the gas. The thermostat chamber can reach 150℃ with a temperature control accuracy of ±0.1℃, employing internal hot air circulation technology with electric heating wire and hot air blower. Sub-device 4 is computer-controlled and displays a screen, allowing for real-time temperature setting and display. It also features automatic temperature control, automatically heating when the temperature falls below the set point and stopping heating when the temperature is too high. The chamber door is sealed with high-temperature, high-pressure resistant fluororubber. The chamber is equipped with a high-temperature, high-pressure safety lock to effectively isolate gas within the chamber in the event of a leak, ensuring the safety of personnel. Meanwhile, the constant temperature chamber uses a specially developed viewing window with a built-in lighting system, making the internal working status clearly visible. In addition, the viewing window adopts a large-angle explosion-proof and temperature-resistant design, and the material is made of four layers of high-temperature and high-pressure explosion-proof tempered glass with an argon-filled structure, which effectively resists pressure and temperature, ensuring the safety of high temperature and high pressure.

[0060] The gas supply system 27 is referred to as sub-device 5. Sub-device 5 is a "dual boosting and one stabilizing" pressure precision control system constructed from "gas source-pressurization device-buffer tank". The gas booster pump pressurizes the pore fluid to a minimum pressure of 60MPa. In addition, a high-precision differential pressure sensor is added to the conventional pressure gauge, and the pressure test accuracy reaches 0.1KPa, ensuring the accuracy of the test results.

[0061] The pressure safety system 35 is designated as sub-device 6. Sub-device 6 establishes a four-level safety structure consisting of an alarm, an automatic pressure safety valve, an explosion-proof diaphragm, and a pressure safety box, with each level providing control. This ensures safety after gas pressurization. The alarm issues a signal when the gas pressure exceeds the maximum pressure; the automatic pressure safety valve automatically releases pressure when the maximum pressure is exceeded; and the explosion-proof diaphragm releases pressure when the automatic pressure safety valve malfunctions. The entire system is housed in a pressure safety box, which is pressure-resistant and will not cause an explosion even in the event of a leak, thus ensuring safety.

[0062] The fixed container system 28 is referred to 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 used for samples with low porosity, medium porosity and high porosity, respectively, and the porosity detection range is between 0.1% and 80%.

[0063] The confining pressure pump 19 is denoted as a sub-device 8, which adopts a high-precision constant-speed constant-pressure pump controlled by an intelligent control system, with a flow rate range of 0.0001-30 ml / min, a maximum pressure of 70 MPa, and a pressure accuracy of 0.001 MPa. All operating parameters of the constant-speed constant-pressure pump are displayed on a 10.2-inch liquid crystal display screen configured on the device, which can display the pressure, flow rate, and flow rate change curve in real time, has a pressure measurement and overpressure / underpressure protection system, and is safe and reliable in operation; and has a compression automatic compensation program control, so that the flow rate accuracy remains stable when the pump works at high pressure.

[0064] Based on the same inventive concept as the above device, the present embodiment also provides a porosity testing method under high temperature and high pressure conditions of a formation, and a step flowchart is shown in Figure 4 , and the specific steps include:

[0065] S1, measuring the gas pressure in the constant-volume container in real time to obtain the volume of the constant-volume container.

[0066] The testing steps of porosity in the present embodiment are as follows:

[0067] First, open the thermostat in the porosity testing device, and set the temperature to the target temperature, which is 20℃ in the present embodiment, and 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 vacuumize the core to remove the fluid inside the core; the gas cylinder is used to release gas to the constant-volume container and the core chamber, so that the space in the two chambers is filled with isobaric gas, and then the space connection between the two chambers is cut off;

[0068] Second, the gas booster pump is used to pressurize the constant-volume container, and the pressurization is waited to be stable.

[0069] Finally, the valves of the constant-volume container and the core chamber are opened to ventilate the two chambers, and the space gas pressure is stabilized again, and the gas volume flowing from the constant-volume container to the core chamber is calculated through the change of the gas pressure, and then the porosity of the rock mass in the core chamber is calculated.

[0070] In the process of pressurization of the gas booster pump to the constant-volume container, the specific pressure of the constant-volume container needs to be controlled to meet the pore pressure required when the final pressure balance is achieved.

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

[0072] It is particularly pointed out that the gas loaded in the gas cylinder 1 is helium; when the vacuum pump is used to vacuumize the core chamber, it is difficult to achieve complete vacuumization of the core chamber in technology, so the helium in the gas cylinder 1 is simultaneously introduced to change the gas composition in the core chamber, so as to discharge the non-helium gas composition in the core chamber as much as possible, thereby reducing the influence of the complexity of the gas composition on the measurement result and avoiding measurement errors.

[0073] The embodiment monitors the inflation of the constant volume container and the core chamber through the pressure sensor, and then controls the pressurization pressure through intelligent control technology, specifically:

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

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

[0076] The pressure sensor of the embodiment is installed in the constant volume container, and the environment in the constant volume container is relatively stable, so the gas density and the pressure present a positive correlation. For this, the embodiment injects a known mass of gas into the pressure container with a volume scale, realizes the pressurization process through the compression volume, and obtains 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. The gas density under different experimental conditions is obtained through a limited number of experiments, and the relationship map of the gas density and the gas pressure is obtained. The relationship map of the gas density and the gas pressure is fitted through a limited number of experiments, which is a common data processing technology, and the embodiment will not be described in detail.

[0077] The horizontal axis in the relationship map is the pressure, and the vertical axis is the density. When using the relationship map, the constant volume container pressure at time t is input, and the constant volume container gas density ρi t at time t can be output. The constant volume container gas density at time t is input, and the constant volume container pressure at time t can be output.

[0078] At the same time, the constant volume container gas density ρi t multiplied by the constant volume container volume can obtain the constant volume container gas mass Mi t at time t.

[0079] S2, open the control valve between the gas cylinder and the constant volume container, close the control valve between the constant volume container and the core chamber, vacuumize the gas in the core chamber, then close the control valve between the gas cylinder and the constant volume container, open the control valve between the constant volume container and the core chamber, record it as the first time to open the control valve, analyze the pressure change before and after the control valve between the constant volume container and the core chamber is opened, and obtain the estimated pore volume combined with the volume of the constant volume container.

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

[0081] Therefore, the embodiment adopts intelligent control technology to accurately control the target pressure, so as to reduce the calculation error in the porosity measurement process and ensure the rapid and accurate measurement result.

[0082] In the embodiment, the porosity measurement relies on the static pressure difference of the constant container in two different states: the pressurization blocking state, i.e., before the valve is closed; and the pressurization connection state, i.e., after the valve is opened. If the static pressure difference in the two states is too small, the data can be disturbed by system noise due to insufficient obviousness, thereby affecting the accuracy of the measurement.

[0083] The static pressure difference is usually achieved by controlling the target pressure. When the target pressure is too low, the pressure difference between the constant container and the core chamber before the valve is opened is too small, and thus the static pressure difference of the constant container before and after the valve is opened is also small, which causes the data to be easily covered by system noise, thereby causing the measurement error of the porosity.

[0084] Therefore, the embodiment obtains the target pressure by limiting the static pressure difference. When the pressure provided by the pressurization device is less than the target pressure, the porosity measurement error is caused due to the too small static pressure difference.

[0085] In the embodiment, the static pressure difference ratio is set to β = 0.3%, which represents that, after the valve is opened in the pressurization blocking state, the static pressure of the constant container system should be decreased to (1-β) times of that before the valve is opened, so as to avoid the measurement error.

[0086] In the embodiment, the gas cylinder and the constant container are initially in the connection state, and the core chamber and the constant container are in the blocking state. At this time, the core chamber is vacuumized 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 constant container is closed, and the valve between the core chamber and the constant container is opened, which is recorded as the first opening of the control valve, and the pressure measurement data of the constant container is waited to be stable, so as to determine that the core chamber and the constant container are in the pressure balance state at this time.

[0087] The core chamber undergoes the vacuumization and filling processes. In the filling process, the gas in the core chamber comes from the constant container, and thus the pore volume in the core chamber can be estimated by the outflow gas of the constant container. The estimation method is as follows:

[0088] Firstly, the measured gas pressure of the constant container before the first opening of the control valve is obtained, the corresponding gas density is obtained by using the relational diagram, and the multiplication result of the gas density and the volume of the constant container is calculated to obtain the gas mass of the constant container before the first opening of the control valve.

[0089] The gas mass of the constant container before the first opening of the control valve is determined as the first total gas mass.

[0090] For the first time after opening the control valve, based on the pressure balance state pressure value, the same calculation method as before the first time opening the control valve is used to obtain the gas mass of the constant volume container after the first time opening the control valve, and is determined as the second total gas mass.

[0091] The relationship between the two is that the first gas total mass and the second gas total mass correspond to the gas mass filled in the core chamber pores, and the constant volume container gas density after the first valve opening corresponds to the gas density of the gas filled in the pores, so the two can estimate the preliminary pore volume.

[0092] Therefore, the difference between the first gas total mass and the second gas total mass corresponds to the gas mass filled in the core chamber pores, and the constant volume container gas density after the first valve opening corresponds to the gas density of the gas filled in the pores, so the two can estimate the preliminary pore volume.

[0093] It is particularly pointed out that the estimation of the pore volume assumes that the core chamber is completely vacuumed after being pumped, but it is difficult to achieve complete vacuuming, and some helium remains in the core chamber after being pumped. Therefore, the pore volume obtained here can only be used as an estimated pore volume, and there is a certain error with the actual pore volume.

[0094] S3, close the control valve between the constant volume container and the core chamber; pressurize the constant volume container to the target pressure, and open the control valve between the constant volume container and the core chamber again after the pressure balance; based on the constant relationship between the total gas mass of the constant volume container and the core chamber before and after pressurization, the target pressure is obtained by presetting the static pressure difference ratio before and after pressurization of the constant volume container and the estimated pore volume.

[0095] In the first time of opening the control valve and waiting for the pressure measurement data of the constant volume container to be stable, the valve between the constant volume container and the core chamber, i.e. the control valve, is closed, and the valve between the cylinder and the constant volume container and the valve between the constant volume container and the core chamber are closed. After pressurizing the constant volume container to the target pressure, the valve between the constant volume container and the core chamber is opened, which is recorded as the second time of opening the valve.

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

[0097] Therefore, based on the state transition relationship, the target pressure is calculated before pressurization, which is specifically:

[0098] Firstly, based on the constant volume gas pressure Pi1 before pressurization, the constant volume gas density ρi1 before pressurization is obtained by using the relationship map, and the estimated pore volume Vr and the constant volume Vi are obtained. Since the gas in the core chamber does not change before and after the constant volume is pressurized before the second valve opening, the total mass of the gas in the core chamber after pressurization M1 is:

[0099] M1= ρi1×Vr (1)

[0100] It should be understood that before the second valve opening, the valve of the constant volume and the core chamber is closed in pressure balance, so the gas density of the constant volume can be used as the gas density of the core chamber.

[0101] Assuming that the static pressure of the constant volume before the second valve opening after pressurization is Pi2, and the static pressure of the constant volume 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, taking the pressure Pi2 of the constant volume as input, the corresponding constant volume density ρi2 after pressurization is calculated by using the relationship map, and the total mass of the gas in the constant volume at this time M2 is:

[0104] M2= ρi2×Vi (3)

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

[0106] M3= ρi3×(Vi+Vr) (4)

[0107] Wherein, the total mass of the gas in the constant volume and the core chamber is the same before and after the second valve opening, that is:

[0108] M3= M1+ M2 (5)

[0109] Therefore, by solving equations (1), (2), (3), (4) and (5), the gas density corresponding to the target pressure can be calculated:

[0110]

[0111] Further, taking the gas density ρi2 corresponding to the target pressure as input, the target pressure Pi2 is calculated by using the relationship map.

[0112] Wherein, the target pressure is calculated based on the estimated pore volume and the static pressure difference ratio. If the target pressure is used as the minimum pressure and the intelligent control system is used to control the pressurization, the static pressure difference of the constant volume before and after the second valve opening can meet the static pressure difference ratio, and the calculation error caused by the too small static pressure difference can be avoided.

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

[0114] Through the target pressure, the intelligent control system can ensure that the target pressure is in a reasonable range, avoid damaging the core structure due to too large pressure, and avoid the measured data being covered by noise due to too small pressure.

[0115] S4, during the process of opening the control valve for the first time, the falling speed of the pressure of the constant container is analyzed to determine the permeation resistance characteristic value of the core in the core chamber; and the target pressure is corrected based on the permeation resistance characteristic value.

[0116] Further, due to the pore effect of the pores in the core sample and the cementation between the particles in the rock stratum which hinders the gas flow, there is a resistance to the gas flow in the core, which is referred to as permeation resistance in the embodiment. Therefore, the intelligent control system should consider the influence of the permeation resistance when controlling the target pressure.

[0117] If the permeation resistance is too large, the overall time for the helium to fill the core after the valve is opened for the second time is increased, that is, it is easy to cause the measurement time to be too long, and even the gas cannot flow into some accessible pores, causing measurement error.

[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 constant container is large; at this time, after the valve is opened, the helium can quickly pass through the pores and the cementation and quickly fill the core; during the filling process, the pressure of the constant container falls rapidly as a whole, but the falling speed is not uniform, because the internal structure of the core is complex, when facing a large pore without cementation, the gas fills quickly and the pressure of the constant container falls rapidly, while when facing a small pore or a position with cementation, the gas fills slowly and the pressure of the constant container falls slowly.

[0119] Therefore, the embodiment can determine the internal structure of the core through the change of the pressure of the constant container after the valve is opened for the first time, the more the cementation in the core and the more complex the structure, the more the pressure of the constant container fluctuates when the valve is opened for the first time, and the higher the target pressure of the constant container is required to make the helium quickly pass through the complex core structure to complete the gas filling after the valve is opened for the second time.

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

[0121] Obtaining the pressure values measured at all moments of the constant volume container between the first opening of the control valve to the closing of the control valve, and composing a pressure sequence in time sequence, using fast Fourier transform algorithm to obtain the frequency spectrum of the pressure sequence, calculating the cumulative sum of the amplitude corresponding to all frequencies in the frequency spectrum, and calculating the ratio of the amplitude corresponding to each frequency in the frequency spectrum to the cumulative sum as the normalized value of the amplitude corresponding to each frequency in the frequency spectrum.

[0122] Among them, the fast Fourier transform algorithm is a known technology, and the specific process will not be repeated, and the embodiment only provides a frequency domain conversion algorithm and a normalization method, and the implementer can select other feasible frequency domain conversion algorithms and normalization methods according to actual conditions, which is not limited in the embodiment.

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

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

[0125] Among them, the normalized amplitude in the frequency spectrum is weighted and summed with the reciprocal of the frequency as the weight, the smaller the permeation resistance characteristic value, the more concentrated the energy in the high frequency part in the frequency spectrum of the pressure sequence of the constant volume container, the more uneven the pressure drop speed when the valve is first opened, and the more complex the core structure. Before the second time the valve is opened, a higher target pressure is needed to enable the helium to quickly fill the core after the second time the valve is opened.

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

[0127] Pr = Pi2×(a-b×δ); in the formula, Pr is the corrected target pressure, which is the actual target pressure, Pi2 is the static pressure before the second time the valve is opened after the constant volume container is pressurized, that is, the target pressure, which is the basic target pressure, δ is the permeation resistance characteristic value of the core in the core chamber, a is a first preset value, and b is a second preset value. 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. The target pressure is expanded to a-b to a times through the first preset value and the second preset value.

[0128] In the embodiment, a = 40 and b = 39, and the implementer can set them according to actual conditions, which is not limited in the embodiment.

[0129] Wherein, the basic target pressure is the minimum value of the actual target pressure; the permeation resistance characteristic value is a coefficient with a value between 0 and 1, the smaller the permeation resistance characteristic value, the higher the actual target pressure needs to be set to ensure that the helium can quickly fill the core; the actual target pressure in this embodiment fluctuates between 1 to 40 times of the basic target pressure, when the core structure is complex and needs a higher actual target pressure to dredge the internal structure of the core, selecting a higher actual target pressure helps the helium to quickly fill the core, avoiding the problems of core structure damage caused by too large target pressure, the problem of measurement data being covered by noise caused by too small target pressure, and the problem of whether the helium can quickly fill the pores, which helps the final porosity test accuracy.

[0130] S5, repeating step S2, after the space pressure of the constant container and the core chamber is balanced, the first gas density of the constant container is obtained based on the pressure measured by the constant container.

[0131] Finally, this embodiment controls the porosity testing device to complete the porosity test, and the specific process is:

[0132] Firstly, the gas cylinder, the constant container and the core chamber are three connectable spaces, the control valve between the gas cylinder and the constant container is referred to as the first valve, and the control valve between the constant container and the core chamber is referred to as the second valve.

[0133] First, open the first valve, close the second valve, and vacuum the core chamber.

[0134] Then, close the first valve, open the second valve, and wait for the space pressure of the constant container and the core chamber to balance, at this time, the corresponding gas density ρ1 is obtained based on the pressure measured by the constant container, which is referred to as the first gas density.

[0135] S6, based on the corrected target pressure, repeat the pressurization process in step S3 to obtain the second gas density of the constant container after pressurization, and the third gas density of the constant container after the control valve is opened again after pressurization and pressure balance.

[0136] Secondly, close the second valve, pressurize the constant container, the target pressure is the actual target pressure Pr calculated above, and wait for the pressurization to end, at this time, the corresponding gas density ρ2 of the constant container is obtained based on the actual target pressure Pr, which is referred to as the second gas density.

[0137] Further, open the second valve to allow the gas to naturally penetrate into the core chamber until equilibrium is reached, at this time, the corresponding gas density ρ3 of the constant container is obtained, which is referred to as the third gas density.

[0138] S7, determining the actual pore volume of the core chamber based on the first gas density, the second gas density, the third gas density, and the constant relationship of the total mass of the gas before and after pressurization; correspondingly, for the sample chamber, the same test method as the core chamber is used to obtain the actual core skeleton volume of the sample chamber, and the actual pore volume is combined to obtain the porosity.

[0139] In the embodiment, the constant volume is denoted as Vi, and the actual pore volume is denoted as unknown Vx.

[0140] Based on the gas density p2 and the volume Vi of the constant volume container, the gas mass C2 in the constant volume container after the pressurization ends in step S6 can be calculated as C2 = p2 x Vi, and since the second valve is not opened at this time, the gas mass C3 of the core chamber is C3 = p1 x Vx.

[0141] After the second valve is opened in step S6, based on the gas density p3 and the volume of the constant volume container and the actual pore volume Vx of the core chamber, the sum C4 of the gas masses of the constant volume container and the core chamber can be represented as C4 = p3 x (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 p2 is obtained and when the gas density p3 is obtained, so: C2 + C3 = C4; and further calculation is derived to obtain:

[0143] Vx is the actual pore volume, in the embodiment, p2-p3 is denoted as the first difference, and p3-p1 is denoted as the second difference, which is denoted as the relative ratio.

[0144] Since the core structure is composed of two parts, one is the actual pore volume, and the other is the actual core skeleton volume, correspondingly, based on the gas cylinder, the constant volume container and the sample chamber, the same operation steps of S1-S7 can be 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 denoted as the total volume of the core.

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

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

[0148] The porosity measurement method used in the embodiment is different from the traditional gas expansion method. The gas in the device is not assumed to be in an ideal gas state, but the measurement is completed based on the principle of equal gas mass in the device, avoiding the calculation error caused by the non-ideal gas state in the high-pressure environment in the traditional gas expansion method, and obtaining more accurate porosity test results. At the same time, when measuring the porosity, the embodiment controls the target pressure of the constant volume vessel. In the control process, the basic target pressure is set to select an appropriate pressure range, which avoids the problem that the measurement data is covered by noise due to insufficient pressurization, and also avoids the problem that the core structure is damaged due to excessive pressurization. At the same time, the permeation resistance characteristic value is calculated to represent the complexity of the internal structure of the core. The pressurization pressure of the core with complex internal structure is increased to avoid the problem that the gas diffusion is slow and the measurement time is too long due to insufficient pressurization pressure.

[0149] It should be noted that the above-mentioned sequence of the embodiments of the present application is only for description, and does not represent the advantages and disadvantages of the embodiments. The above describes specific embodiments of the present specification. In addition, the processes depicted in the drawings do not necessarily require the specific order or continuous order shown to achieve the desired results. In some embodiments, multi-task processing and parallel processing are possible or can be advantageous.

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

[0151] The above only describes the preferred embodiments of the present application, and does not limit the present application. Any modification, equivalent replacement, improvement, etc. within the principles of the present application shall be included in the protection scope of the present application.

Claims

1. A method for testing porosity under high temperature and high pressure conditions of a formation, characterized by, The porosity test method is realized by a porosity test device, wherein the porosity test device comprises a gas cylinder (1), constant volume containers (8), (9), (10), a sample chamber (13), and a core chamber in a core holder (18), wherein the gas cylinder (1), the constant volume containers (8), (9), (10), the sample chamber (13), and the core holder (18) are connected in sequence by control valves; the porosity test method comprises the following steps: S1, measuring the gas pressure in the constant volume container in real time to obtain the volume of the constant volume container; S2, opening the control valve between the gas cylinder and the constant volume container, closing the control valve between the constant volume container and the core chamber, vacuumizing the gas in the core chamber, then closing the control valve between the gas cylinder and the constant volume container, opening the control valve between the constant volume container and the core chamber, which is recorded as the first time of opening the control valve, analyzing the pressure change before and after the control valve between the constant volume container and the core chamber is opened, and combining the volume of the constant volume container to obtain the estimated pore volume; S3, closing the control valve between the constant volume container and the core chamber; pressurizing the constant volume container to a target pressure, opening the control valve between the constant volume container and the core chamber again after pressure equilibrium; obtaining the target pressure based on the constant relationship between the total mass of the gas in the constant volume container and the core chamber before and after pressurization by presetting the static pressure difference ratio before and after pressurization of the constant volume container and the estimated pore volume; S4, analyzing the pressure drop speed of the constant volume container during the first time of opening the control valve to determine the permeation resistance characteristic value of the core in the core chamber; correcting the target pressure based on the permeation resistance characteristic value; S5, repeating step S2, obtaining the first gas density of the constant volume container based on the measured pressure of the constant volume container after the space pressure between the constant volume container and the core chamber is balanced; S6, repeating the pressurization process in step S3 based on the corrected target pressure to obtain the second gas density of the constant volume container after pressurization and the third gas density of the constant volume container after the control valve is opened again after pressure equilibrium after pressurization; S7, determining the actual pore volume of the core chamber based on the first gas density, the second gas density, the third gas density, and the constant relationship between the total mass of the gas before and after pressurization; accordingly, the same test method as that for the core chamber is used to obtain the actual core skeleton volume of the sample chamber, and the porosity is obtained in combination with the actual pore volume.

2. The method for testing the porosity under the high temperature and high pressure conditions of the earth formation according to claim 1, wherein, The determination of the estimated pore volume comprises: obtaining the first total mass of gas of the constant volume container based on the measured pressure of the constant volume container before the control valve is opened for the first time, and combining the volume of the constant volume container; accordingly, obtaining the second total mass of gas of the constant volume container when the pressure is balanced after the control valve is opened for the first time. The difference between the first total gas mass and the second total gas mass is calculated to obtain the gas density of the constant volume container at the pressure balance after the control valve is opened for the first time, and the estimated pore volume is a ratio of the difference and the gas density of the constant volume container.

3. The method of testing porosity under high temperature and high pressure conditions of a subterranean formation of claim 1, wherein, The target pressure is obtained by: The gas density ρi1 corresponding to the measured pressure of the constant volume container before pressurization is obtained, and the total gas mass M1 of the core chamber before the control valve is opened again after pressurization is obtained based on the gas density ρi1 and the estimated pore volume. The static pressure of the constant volume container before the control valve is opened again after pressurization is Pi2, and the static pressure of the constant volume container after the control valve is opened again after pressurization is Pi3, and the pressure relationship is obtained based on the static pressure difference ratio. The total gas mass of the constant volume container before the control valve is opened again is obtained by using the gas density corresponding to the static pressure Pi2 and combining the volume of the constant volume container, and is denoted as M2; correspondingly, the total gas mass of the core chamber and the constant volume container after the control valve is opened again is obtained by using the static pressure Pi3, combining the estimated pore volume and the volume of the constant volume container, and is denoted as M3. The target pressure corresponding to the static pressure Pi2 is obtained based on the gas mass constant condition among M1, M2 and M3.

4. The method of testing porosity under high temperature and high pressure conditions of a subterranean formation of claim 3, wherein, The pressure relationship is obtained based on the static pressure difference ratio, including: Let the ratio of the static pressure difference be denoted by β, then 5. The method of testing porosity under high temperature and high pressure conditions of a subterranean formation of claim 3, wherein, The gas mass constant condition is M3=M1+M2.

6. The method of testing porosity under high temperature and high pressure conditions of a subterranean formation of claim 1, wherein, The determination of the permeation resistance characteristic value includes: The pressures of the constant volume container at all times between the first time when the control valve is opened and the time when the control valve is closed are obtained to form a pressure sequence, a frequency spectrum diagram of the pressure sequence is obtained, a sum of each frequency and a preset value greater than 0 is calculated, and the reciprocal of the sum is used as a weight to perform weighted summation on the normalization results of the amplitudes corresponding to all frequencies, so as to obtain the permeation resistance characteristic value.

7. The method of testing porosity under high temperature and high pressure conditions of a subterranean formation of claim 1, wherein, The target pressure is corrected by enlarging the target pressure by a preset multiple based on the permeation resistance characteristic value.

8. The method of testing porosity under high temperature and high pressure conditions of a subterranean formation of claim 1, wherein, The determination of the actual pore volume of the core chamber includes: A first difference value is calculated by calculating the difference between the second gas density and the third gas density, a second difference value is calculated by calculating the difference between the third gas density and the first gas density, a relative ratio is calculated by calculating the ratio of the first difference value and the second difference value, and the actual pore volume is a product of the relative ratio and the volume of the constant volume container.

9. The method of testing porosity under high temperature and high pressure conditions of a subterranean formation of claim 1, wherein, The determination of the porosity includes: A total volume of the core is calculated by calculating the sum of the actual pore volume and the actual core skeleton volume, and the porosity is obtained based on the total volume of the core and the actual pore volume.

10. The method of testing porosity under high temperature and high pressure conditions of a subterranean formation of claim 9, wherein, The porosity is a ratio of the actual pore volume and the total volume of the core.

11. A device for testing porosity under high temperature and high pressure conditions of a formation, said device being implemented on the basis of the steps of the method for testing porosity under high temperature and high pressure conditions of a formation according to any one of claims 1 to 10, characterized in that, The test device includes a gas supply system (27), a pressure safety system (35), a constant volume container system (28), a core system (29), a vacuum pumping system (30), a confining pressure system (31), and a constant temperature system (22).

12. The apparatus of claim 11, wherein the apparatus is configured to be used in a formation having a temperature of at least 150 °C and a pressure of at least 10,000 psi. The gas supply system includes a gas cylinder and a gas booster pump, and the maximum test pressure of the gas supply system is at least 60 MPa; the pressure safety system includes an alarm, an automatic pressure safety valve, an explosion-proof sheet and a safety tank, and the pressure safety system is connected with the gas supply system and the constant volume system through pipelines.

13. The apparatus of claim 11, wherein the apparatus is configured to be used at high temperature and high pressure conditions of a formation. The constant volume system includes three constant volume vessels with different volumes, and the upper end of the constant volume system is connected with the gas supply system through a pipeline, and a control valve and a pressure gauge are arranged on the pipeline; the lower end of the constant volume system is connected with the core system through a pipeline; and the constant volume system is placed in a constant temperature system.

14. The apparatus of claim 11, wherein the apparatus is configured to be used at elevated temperature and pressure conditions of a subterranean formation. The core system includes a sample chamber and a core holder, the upper end of the sample chamber is connected with the constant volume system through a pipeline, and a control valve and a differential pressure sensor are arranged on the pipeline; the upper end of the sample chamber is also connected with the core holder through a pipeline, and a control valve is arranged on the pipeline; the upper end of the core holder is connected with the constant volume system through a pipeline, and a control valve is arranged on the pipeline; and the confining pressure system includes a confining pressure pump and a pressure gauge, and the confining pressure pump is connected with the core holder through a pipeline, and a control valve and a pressure gauge are arranged on the pipeline.

15. The apparatus of claim 11, wherein the apparatus is configured to be used at elevated temperature and pressure conditions of a subterranean formation. The constant temperature system includes a heater and a constant temperature box; and the vacuum system includes a vacuum pump and a pressure gauge, and the vacuum pump is connected with the core system through a pipeline, and a control valve and a pressure gauge are arranged on the pipeline.

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