Quantitative evaluation device and method for shale oil permeability increase in oxidation and thermal stress environment

Abstract

The present application relates to unconventional oil and gas development technical field, it is a kind of shale oil oxidation, thermal stress environment in the quantitative evaluation device and method of increasing penetration, the former includes the triaxial core holder being arranged in thermostat and the confining pressure medium injection system, oxidation medium injection system, detection medium injection system, gas collector, upstream storage tank, downstream storage tank, chromatograph and acoustic emission sensor being arranged at interval outside thermostat.This application can simulate the dynamic multi-field coupling physical simulation system of formation real working condition, through acquisition pressure, product component, acoustic signal and nuclear magnetic relaxation data, use the mathematical model of pore permeability dynamic inversion of pressure pulse attenuation method, integrate acoustic emission RA- AF seismic source identification and nuclear magnetic fractal evaluation, analyze the multi-field coupling effect of thermal field, flow field, force field and chemical field generated in air injection process, and the improvement degree of oxidation expansion to shale permeability and pore structure is quantitatively evaluated.

Description

Technical Field

[0001] This invention relates to the field of unconventional oil and gas development technology, and is a quantitative evaluation device and method for permeability enhancement in shale oil under oxidation and thermal stress environments. Background Technology

[0002] Against the backdrop of global energy demand transformation, medium- and low-maturity shale oil has become a core area for unconventional energy development due to its enormous resource potential. However, unlike the widely developed light, high-maturity shale oil in North America, a large number of medium- and low-maturity shale reservoirs exist globally, situated within dense matrices. These reservoirs present extremely high geological and physicochemical development barriers: on the one hand, the rock skeleton is extremely dense with very low porosity, and permeability is typically at the nano-Darcy to micro-Darcy levels, resulting in extremely high fluid flow resistance; on the other hand, the organic matter within the pores is mostly in the form of solid kerogen or extremely high-viscosity heavy oil, which has almost no mobility under original formation conditions. Traditional horizontal well combined with volumetric fracturing "cold production" technology often faces the dilemma of extremely rapid initial production decline and ultimately less than 10% recovery rate because it cannot improve matrix permeability and fluid viscosity at the microscale.

[0003] To overcome this bottleneck, in-situ refining technology has emerged. The core logic of this technology lies in actively injecting energy into the underground reservoir to induce the pyrolysis of kerogen, converting it into light liquid and gaseous hydrocarbons. Among numerous heating processes, air injection in-situ refining has shown disruptive potential. This process injects air into the preheated reservoir, utilizing the exothermic oxidation reaction (including low-temperature and high-temperature oxidation) between oxygen and organic matter to achieve thermal self-sufficiency and gas-driven fluid flow.

[0004] Oxidation and pyrolysis reactions instantaneously generate a large number of high-pressure gaseous products within micropores. Due to the ultra-low permeability of the shale matrix, these gases cannot migrate rapidly, thus generating intense gas phase expansion pressure in a local confined space. When this pressure overcomes external geostress and exceeds the tensile strength of the rock, physical expansion and cracking will occur inside the shale, generating a dense network of microcracks. This phenomenon is called "oxidative expansion cracking".

[0005] However, in-situ shale oil upgrading occurs in extreme deep-earth environments, and the evolution of microfractures is controlled by the complex coupling of temperature, chemical, and stress fields. Traditional direct observation methods (such as optical microscopes) cannot provide real-time, in-situ quantitative characterization during the experiment. Summary of the Invention

[0006] This invention provides a quantitative evaluation device and method for permeability enhancement in shale oil under oxidation and thermal stress environments, overcoming the shortcomings of the prior art. It can effectively solve the problem that the evolution of microcracks cannot be quantitatively characterized in real time and in situ during the existing in-situ shale oil upgrading process.

[0007] One of the technical solutions of this invention is achieved through the following measures: a quantitative evaluation device for permeability enhancement in shale oil oxidation and thermal stress environments, comprising a triaxial core holder installed inside a constant temperature chamber, and a confining pressure medium injection system, an oxidation medium injection system, a detection medium injection system, a gas collector, an upstream storage tank, a downstream storage tank, a chromatograph, and an acoustic emission sensor spaced apart outside the constant temperature chamber. A first confining pressure pipeline is fixedly connected between the outlet of the confining pressure medium injection system and the confining pressure inlet of the triaxial core holder, and a first confining pressure control valve is installed on the first confining pressure pipeline. A mixing pipeline is fixedly connected between the outlet of the oxidation medium injection system and the axial inlet of the triaxial core holder, and a first mixing control valve is installed on the mixing pipeline. A sampling pipeline is fixedly connected between the axial outlet of the triaxial core holder and the gas collector for sampling. A back pressure valve is installed on the pipeline. A separation pipeline is fixedly connected between the gas collector and the test port of the chromatograph. A sampling valve is installed on the separation pipeline. A first detection pipeline is fixedly connected between the outlet of the detection medium injection system and the radial inlet of the triaxial core holder. A first detection control valve is installed on the first detection pipeline. A first connecting pipeline is fixedly connected between the upstream storage tank and the first radial outlet of the triaxial core holder. A first regulating valve is installed on the first connecting pipeline. A second connecting pipeline is fixedly connected between the downstream storage tank and the second radial outlet of the triaxial core holder. A second regulating valve is installed on the second connecting pipeline. Several sensing windows are spaced apart on the outside of the triaxial core holder. An acoustic emission sensor is installed in each acoustic sensing window. All acoustic emission sensors are connected to a PLC. The PLC is connected to a host computer.

[0008] The following are further optimizations and / or improvements to one of the above-mentioned technical solutions: The confining pressure medium injection system mentioned above may include a confining pressure storage tank and a confining pressure delivery pump. A first confining pressure pipeline is fixedly connected between the outlet of the confining pressure storage tank and the inlet of the confining pressure delivery pump. A second confining pressure pipeline is fixedly connected between the outlet of the confining pressure delivery pump and the confining pressure inlet of the triaxial core holder. A first pressure gauge is installed on the second confining pressure pipeline. The oxidation medium injection system includes an air tank, a nitrogen tank, an air delivery pump, a nitrogen delivery pump, and a gas mixer. The outlet of the air tank is fixedly connected to the inlet of the air delivery pump. An air input pipeline is fixedly connected between the outlet of the air delivery pump and the first inlet of the gas mixer. A first control valve and a first mass flow controller are installed at intervals along the medium flow direction on the air input pipeline. The outlet of the nitrogen tank is fixedly connected to the inlet of the nitrogen delivery pump. A nitrogen input pipeline is fixedly connected between the outlet of the nitrogen delivery pump and the second inlet of the gas mixer. A second control valve and a second mass flow controller are installed at intervals along the medium flow direction on the nitrogen input pipeline. The mixing pipeline is fixedly connected between the outlet of the gas mixer and the axial inlet of the triaxial core holder. A second mixing control valve is installed on the mixing pipeline corresponding to the position between the first mixing control valve and the gas mixer. The detection medium injection system includes a helium tank and a helium delivery pump. A first detection pipeline is fixedly connected between the outlet of the helium tank and the inlet of the helium delivery pump. A second detection pipeline is fixedly connected between the outlet of the helium delivery pump and the radial inlet of the triaxial core holder. A second pressure gauge is installed on the second detection pipeline.

[0009] The above may also include an air injection pump and an electric heating jacket. A first preheating pipeline is fixedly connected between the mixing pipeline at the position between the first mixing control valve and the second mixing control valve and the inlet of the air injection pump. A second preheating pipeline is fixedly connected between the mixing pipeline at the position between the first preheating pipeline and the first mixing control valve and the outlet of the air injection pump. An electric heating jacket is installed on the outside of the mixing pipeline between the first preheating pipeline and the axial inlet of the triaxial core holder, on the outside of the first preheating pipeline, on the outside of the second preheating pipeline, and on the outside of the triaxial core holder.

[0010] The above may also include a controller and a distributed optical fiber temperature sensor. The triaxial core holder is equipped with a distributed optical fiber temperature sensor, which is connected to the controller. The triaxial core holder is equipped with a permeation component at both ends of the distributed optical fiber temperature sensor. The permeation component includes a pad and a guide plate.

[0011] A third pressure gauge may be installed on the first connecting pipeline between the upstream storage tank and the first regulating valve, and a fourth pressure gauge may be installed on the second connecting pipeline between the downstream storage tank and the second regulating valve.

[0012] The second technical solution of the present invention is achieved through the following measures: a quantitative evaluation method for permeability enhancement in shale oil under oxidation and thermal stress environments, comprising the following steps: S1, Construct a comparison database, including: S11, Select the shale in the target block; S12, prepare the first core sample in columnar shape from the shale in step S11, and obtain the initial matrix permeability of the first core sample; S13, Prepare a second core sample from the remaining shale in step S12, and obtain the organic matter abundance of the second core sample. S14, Obtain the transverse relaxation spectrum of the first core sample using nuclear magnetic resonance and set a reference point; S2, re-extracting the first core sample, constructing the experimental environment, including: S21, Place the first core sample into the triaxial core holder; S22, Install a sealing sleeve on the outside of the first core sample; S23, Install guide permeation components on both ends of the first core sample; S24, Multiple acoustic emission sensors are spaced apart on the outside of the triaxial core holder; S3 simulates deep reservoir conditions, including: S31, simulating triaxial geostress; S32, the back pressure value of the sampling pipeline is adjusted to the simulated formation pore pressure through the back pressure valve; S4, activates ignition, including: S41, inert gas is continuously injected into the triaxial core holder through the oxidation medium injection system for purging protection; S42, preheat the mixing pipeline to the set range; S5, injecting an oxidizing medium to capture thermal fronts, including: S51, the oxidation medium is mixed according to multiple set proportions; S52, stop the inert gas injection, inject multiple sets of oxidizing media into the triaxial core holder and react inside the first core sample, collect and plot the three-dimensional spatiotemporal evolution curve of the temperature corresponding to each set ratio of oxidizing media. S53 captures the advance of thermal fronts by tracking the movement of the exothermic peak as the temperature surges from the outside to the inside. S6, Obtain the physical signals and chemical composition of the internal reaction of the first core sample, including: S61 processes the signals captured by all acoustic emission sensors and extracts time-domain and frequency-domain characteristic parameters. S62, sampling is performed at set time intervals, and the component concentrations of the mixed gas are determined by a chromatograph; S7, gas-stopped dormancy, inversion of microscopic porosity and permeability structure, including: S71, the reaction gas in the first core sample was evacuated using a vacuum pump; S72, the detection medium is injected into the triaxial core holder through the detection medium injection system until the pressure reaches the preset value and then the first detection control valve is closed. S73, inject detection medium into the upstream storage tank until the pressure in the upstream storage tank rises to the set value; S74, open the back pressure valve, record the pressure difference change data at both ends of the first core sample, and at the same time record the density change data of the detection medium; S8, After the triaxial core holder is unloaded, the fracture characteristics of the first core sample are obtained, including: S81, slowly reduce the temperature of the sealing sleeve, the axial stress of the first core sample, and the confining pressure of the first core sample; S82, After the first core sample is taken out, it is placed in the vacuum saturation device to make the first core sample completely fluid saturated. S83, Obtain the transverse relaxation spectrum of the first core sample in step S82; S84, perform CT scan to obtain the three-dimensional spatial distribution morphology, orientation connectivity probability and pore throat ratio of the internal fractures of the first core sample. S9, Evaluation of the permeability enhancement of the first core sample, including: S91, Obtain the pressure difference attenuation coefficient based on the pressure difference change data at both ends of the first core sample in step S74: S92, the absolute equivalent permeability of the first core sample was calculated based on the pressure difference attenuation coefficient; S93, compare the absolute equivalent permeability in step S92 with the initial matrix permeability in step S11 to determine whether gas injection oxidation can create physical cracks in the first core sample. S94, calculate the total effective pore volume inside the first core sample; S95, calculate the effective interconnected porosity based on the total effective pore volume in step S94; S96, Obtain the fractal dimension based on the transverse relaxation spectrum in step S83; S97, evaluate the degree of oxidative expansion-induced cracking effect and crack network density based on fractal dimension; S98, Calculate the rise angle coefficient and the average frequency of the waveform based on the time domain and frequency domain characteristic parameters in step S61; S99, based on the rise angle coefficient and waveform average frequency, determine whether the high temperature and high pressure gas that instantly accumulates due to chemical oxidation inside the first core sample can cause the rock grains to open and tear apart, and determine whether the energy-gathering gas explosion expansion of the phase change gas can achieve physical transformation of the modified and compacted shale.

[0013] The following are further optimizations and / or improvements to the second technical solution of the above invention: Step S12 above involves preparing a columnar first core sample from the shale obtained in step S11, and acquiring the initial matrix permeability of the first core sample, including: S121, Prepare the first core sample in columnar shape from the shale in step S11; S122, the initial effective porosity of the first core sample was determined using the helium expansion method; S123, the initial matrix permeability of the first core sample was obtained using the pulse decay method; Step S13: Prepare a second core sample from the remaining shale from step S12, and obtain the organic matter abundance of the second core sample, including: S131, after crushing the remaining shale in step S12, a second core sample is prepared, and the total organic carbon content is determined. S132, the second core sample was pyrolyzed to obtain the highest pyrolysis peak temperature, free hydrocarbons and cracked hydrocarbons parameters; S133, Determine the initial kerogen type and thermal maturity of the second core sample based on the highest pyrolysis peak temperature, free hydrocarbon and cracked hydrocarbon parameters in step S132. S134, using X-ray diffraction and X-ray fluorescence spectroscopy to determine the initial mass percentage of brittle minerals and clay minerals.

[0014] Step S31 above, simulating triaxial geostress, includes: S311, the confining pressure medium is injected into the triaxial core holder through the confining pressure medium injection system, and the same confining pressure and transverse stress are applied to the outside of the first core sample until the confining pressure reaches the set radial confining pressure. The pressure increase rate of the confining pressure is less than 0.5 MPa / min. S312, apply axial stress to the left end face of the first core sample until the axial stress reaches the set axial stress, and the set axial stress is greater than the set radial confining pressure. In step S42 above, the mixing pipeline is preheated to a set range, specifically: the mixing pipeline is preheated to between 300°C and 450°C at a preheating rate of less than 10°C / min.

[0015] Step S91 above, obtaining the pressure difference attenuation coefficient based on the pressure difference change data at both ends of the first core sample in step S74, includes: S911, convert the pressure difference-time series data at both ends of the first core sample from step S74 into... For the scatter coordinates of time t, where, Let be the instantaneous pressure difference at time t, in MPa; The pressure difference between the upstream storage tank and the downstream storage tank when the pressure rises to the set value in step S73, in MPa; S912, the least squares method is used to perform linear fitting on the scattered point coordinates in step S91, the slope of the fitted line obtained after linear fitting is determined, and the slope of the fitted line is used as the pressure difference attenuation coefficient.

[0016] In step S92 above, the absolute equivalent permeability of the first core sample is calculated according to the following formula: In the above formula, k is the absolute equivalent permeability, and m 2 ; This is the differential pressure attenuation coefficient; ρ is the dynamic viscosity coefficient of the probe medium, mPa·s; L is the length of the first core sample, m; c is the isothermal composite compressibility coefficient of the probe medium, MPa -1 A represents the effective cross-sectional area through which the fluid passes in the first core sample, in meters. 2 ; The absolute effective volume of the upstream storage tank is expressed in cm. 3 ; The absolute effective volume of the gas collector is in cm³. 3 ; The formula for calculating the total effective pore volume in step S94 is as follows: In the above formula, The total effective pore volume is expressed in cm³. 3 ; The absolute effective volume of the upstream storage tank is expressed in cm. 3 ; The absolute effective volume of the gas collector is in cm³. 3 ; The density of the upstream storage tank before injecting the detection medium into the upstream storage tank in step S73, in g / cm³. 3 ; The density of the medium (g / cm³) was measured when the pressure was constant after the reaction within the triaxial core holder. 3 ; The density of the detection medium in step S73 when the pressure in the upstream storage tank rises to the set value, in g / cm³. 3 ; The formula for calculating the effective interconnected porosity in step S95 is as follows: ; In the above formula, To effectively connect porosity; The total effective pore volume is expressed in cm³. 3 ; The total volume of the first core sample is in cm³. 3 .

[0017] The formula for calculating the fractal dimension in step S96 is: In the above formula, V is the cumulative pore volume fraction at a certain moment in the transverse relaxation spectrum; D is the fractal dimension. The transverse relaxation time in the transverse relaxation spectrum is greater than 0.1 ms; It is a constant. The maximum value; C is a constant.

[0018] This application is capable of simulating a dynamic multi-field coupled physical simulation system that simulates real formation conditions. By collecting temperature, pressure, product composition, acoustic signals, and nuclear magnetic resonance relaxation data, it uses a mathematical model for dynamic inversion of porosity and permeability using the pressure pulse attenuation method. It integrates acoustic emission (RA-AF) source identification and nuclear magnetic resonance fractal evaluation to analyze the multi-field coupling effects of thermal, flow, force, and chemical fields generated during air injection and quantitatively evaluate the degree of improvement of oxidative expansion on shale permeability and pore structure.

[0019] High-frequency acoustic emission sensors can monitor rock fracture signals in real time. Combined with the RA-AF method, it can be used to determine whether the fracture is tensile or shear fracture. Before and after the experiment, nuclear magnetic resonance instruments are used to obtain the transverse relaxation spectrum of the sample and observe the evolution of the pore structure from matrix points to fracture network. The pressure, temperature, acoustic emission signals and nuclear magnetic resonance data are sorted out and combined inversion is performed through a multi-field coupling model of thermal field, flow field, force field and chemical field. Finally, a quantitative evaluation of the effect of "air injection" on physical fracturing of shale is achieved. Attached Figure Description

[0020] Appendix Figure 1 These are schematic diagrams of the main structure of embodiments one to five of the present invention.

[0021] The codes in the attached diagram are as follows: 1 is a constant temperature chamber, 2 is a triaxial core holder, 3 is a gas collector, 4 is an upstream storage tank, 5 is a downstream storage tank, 6 is a chromatograph, 7 is an acoustic emission sensor, 8 is the first confining pressure pipeline, 9 is the first confining pressure control valve, 10 is a mixing pipeline, 11 is the first mixing control valve, 12 is a sampling pipeline, 13 is a back pressure valve, 14 is a separation pipeline, 15 is a sampling valve, 16 is the first detection pipeline, 17 is the first detection control valve, 18 is the first connecting pipeline, 19 is the second connecting pipeline, 20 is the first regulating valve, 21 is the second regulating valve, 22 is the confining pressure storage tank, 23 is the confining pressure transfer pump, 24 is the second confining pressure pipeline, 25 is the first pressure gauge, 26 is an air tank, 27 is a nitrogen tank, 28 is an air transfer pump, and 29 is... Nitrogen delivery pump, 30 is a gas mixer, 31 is an air input line, 32 is a nitrogen input line, 33 is a first control valve, 34 is a second control valve, 35 is a first mass flow controller, 36 is a second mass flow controller, 37 is a helium tank, 38 is a helium delivery pump, 39 is a second detection line, 40 is a second pressure gauge, 41 is an injection pump, 42 is an electric heating jacket, 43 is a first preheating line, 44 is a second preheating line, 45 is a first preheating control valve, 46 is a second preheating control valve, 47 is a controller, 48 is a distributed fiber optic temperature sensor, 49 is a pad, 50 is a guide plate, 51 is a third pressure gauge, 52 is a fourth pressure gauge, 53 is a sealing sleeve, 54 is a first core sample, and 55 is a second mixing control valve. Detailed Implementation

[0022] The present invention is not limited to the following embodiments, and the specific implementation can be determined according to the technical solution of the present invention and the actual situation.

[0023] In this invention, for ease of description, the description of the relative positions of the components is based on the appendix to the specification. Figure 1 The layout is described using a diagrammatic method, such as the positional relationships of front, back, top, bottom, left, and right, which are based on the instructions attached. Figure 1 The orientation of the layout is determined by the direction of the map.

[0024] The present invention will be further described below with reference to embodiments and accompanying drawings: Example 1: As shown in the attached document Figure 1 As shown, the quantitative evaluation device for permeability enhancement in shale oil oxidation and thermal stress environment includes a triaxial core holder 2 installed in a constant temperature chamber 1, and a confining pressure medium injection system, an oxidation medium injection system, a detection medium injection system, a gas collector 3, an upstream storage tank 4, a downstream storage tank 5, a chromatograph 6, and an acoustic emission sensor 7, which are spaced apart outside the constant temperature chamber 1. A first confining pressure pipeline 8 is fixedly connected between the outlet of the confining pressure medium injection system and the confining pressure inlet of the triaxial core holder 2, and a first confining pressure control valve 9 is installed on the first confining pressure pipeline 8. A mixing pipeline 10 is fixedly connected between the outlet of the oxidation medium injection system and the axial inlet of the triaxial core holder 2. A first mixing control valve 11 is installed on the mixing pipeline 10. A sampling pipeline 12 is fixedly connected between the axial outlet of the triaxial core holder 2 and the gas collector 3. A back pressure valve 13 is installed on the sampling line 12. A separation line 14 is fixedly connected between the gas collector 3 and the test port of the chromatograph 6. A sampling valve 15 is installed on the separation line 14. A first detection pipeline 16 is fixedly connected between the outlet of the detection medium injection system and the radial inlet of the triaxial core holder 2, and a first detection control valve 17 is installed on the first detection pipeline 16. A first connecting pipeline is fixedly connected between the upstream storage tank 4 and the first radial outlet of the triaxial core holder 2, and a first regulating valve 20 is installed on the first connecting pipeline; A second connecting pipeline 19 is fixedly connected between the downstream storage tank 5 and the second radial outlet of the triaxial core holder 2, and a second regulating valve 21 is installed on the second connecting pipeline 19; The three-axis core holder 2 has several sensing windows spaced apart on its outer side. Each acoustic sensing window is equipped with an acoustic emission sensor 7. All acoustic emission sensors 7 are connected to a PLC, which is connected to a host computer.

[0025] The triaxial core holder 2 is a known technology, such as the triaxial core holder for overburden testing described in Chinese patent document CN110057686A. The triaxial core holder 2 can hold the sample and seal the cylindrical or end face of the sample. The radial inlet, confining pressure inlet, axial inlet, and axial outlet of the triaxial core holder 2 are all connected to the inner cavity. The acoustic emission sensor 7 is a high-frequency acoustic emission sensor. All acoustic emission sensors 7 are connected to the PLC, and the PLC is connected to the host computer, so that acoustic signals can be acquired.

[0026] Based on the physicochemical mechanism of oxidative expansion-induced fracturing, namely preheating ignition, gas expansion and energy accumulation, thermal stress damage, and mineral phase transformation degradation, this application utilizes a dynamic multi-field coupled simulation system to simulate real formation conditions. This system acquires temperature, pressure, product composition, acoustic signals, and nuclear magnetic resonance relaxation data. A mathematical model for dynamic inversion of porosity and permeability is developed using the pressure pulse attenuation method. This model integrates acoustic emission (RA-AF) source identification and nuclear magnetic resonance fractal evaluation to analyze the multi-field coupling effects of thermal, flow, force, and chemical fields generated during air injection, and quantitatively evaluates the degree to which oxidative expansion improves shale permeability and pore structure.

[0027] Acoustic emission sensor 7 can monitor rock fracture signals in real time. Combined with the RA-AF method, it can determine whether the fracture is tensile or shear fracture. Before and after the experiment, the transverse relaxation spectrum of the sample is obtained by nuclear magnetic resonance instrument to observe the evolution of pore structure from matrix point to fracture network. The pressure, temperature, acoustic emission signal and nuclear magnetic resonance data are sorted out and combined inversion is performed by multi-field coupling model of thermal field, flow field, force field and chemical field to finally realize the quantitative evaluation of the effect of "air injection" on physical fracturing of shale.

[0028] The quantitative evaluation device for permeability enhancement in shale oil oxidation and thermal stress environments can be further optimized and / or improved according to actual needs: Example 2: As an optimization of the above examples, as shown in the appendix. Figure 1 As shown, the confining pressure medium injection system includes a confining pressure storage tank 22 and a confining pressure delivery pump 23. A first confining pressure pipeline 8 is fixedly connected between the outlet of the confining pressure storage tank 22 and the inlet of the confining pressure delivery pump 23. A second confining pressure pipeline 24 is fixedly connected between the outlet of the confining pressure delivery pump 23 and the confining pressure inlet of the triaxial core holder 2. A first pressure gauge 25 is installed on the second confining pressure pipeline 24. The oxidation medium injection system includes an air tank 26, a nitrogen tank 27, an air delivery pump 28, a nitrogen delivery pump 29, and a gas mixer 30. The outlet of the air tank 26 is fixedly connected to the inlet of the air delivery pump 28. An air input pipeline 31 is fixedly connected between the outlet of the air delivery pump 28 and the first inlet of the gas mixer 30. A first control valve 33 and a first mass flow controller 35 are installed at intervals along the medium flow direction on the air input pipeline 31. The outlet of nitrogen tank 27 is fixedly connected to the inlet of nitrogen delivery pump 29. The outlet of nitrogen delivery pump 29 is fixedly connected to the second inlet of gas mixer 30 via nitrogen input pipeline 32. Second control valves 34 and second mass flow controllers 36 are installed at intervals along the medium flow direction on nitrogen input pipeline 32. The mixing pipeline 10 is fixedly connected between the outlet of the gas mixer 30 and the axial inlet of the triaxial core holder 2. A second mixing control valve 55 is installed on the mixing pipeline 10 at the position between the first mixing control valve 11 and the gas mixer 30. The detection medium injection system includes a helium tank 37 and a helium delivery pump 38. A first detection pipeline 16 is fixedly connected between the outlet of the helium tank 37 and the inlet of the helium delivery pump 38. A second detection pipeline 39 is fixedly connected between the outlet of the helium delivery pump 38 and the radial inlet of the triaxial core holder 2. A second pressure gauge 40 is installed on the second detection pipeline 39.

[0029] According to requirements, both the first control valve 33 and the second control valve 34 are pressure reducing valves; the first mass flow controller 35 and the second mass flow controller 36 are existing known technologies; the air delivery pump 28 and the nitrogen delivery pump 29 are existing known high-pressure air pumps; and the first pressure gauge 25, the second pressure gauge 40, and the second pressure gauge 40 are all existing known pressure transmitters, and all are connected to the PLC. The oxidation medium injection system delivers gas to the gas mixer 30 through the air tank 26, the nitrogen tank 27, the air delivery pump 28, and the nitrogen delivery pump 29. The gas mixer 30 can adjust the oxygen concentration to 21%-100%. The first mass flow controller 35 and the second mass flow controller 36 can adjust the gas injection rate to simulate different gas injection conditions. Nitrogen gas is injected through the delivery pump to apply axial pressure to the sample in the triaxial core holder 2, and liquid medium is input through the confining pressure delivery pump 23 to apply confining pressure to the sample in the triaxial core holder 2, so as to simulate the underground stress state of the sample.

[0030] Example 3: As an optimization of the above examples, as shown in the appendix. Figure 1 As shown, it also includes an air injection pump 41 and an electric heating jacket 42. A first preheating pipeline 43 is fixedly connected between the mixing pipeline 10, which corresponds to the position between the first mixing control valve 11 and the second mixing control valve 55, and the inlet of the air injection pump 41. A second preheating pipeline 44 is fixedly connected between the mixing pipeline 10, which corresponds to the position between the first preheating pipeline 43 and the first mixing control valve 11, and the outlet of the air injection pump 41. An electric heating jacket 42 is installed on the outside of the mixing pipeline 10, the outside of the first preheating pipeline 43, the outside of the second preheating pipeline 44, and the outside of the triaxial core holder 2, corresponding to the axial inlet of the triaxial core holder 2.

[0031] As required, a first preheating control valve 45 is installed on the first preheating pipeline 43, and a second preheating control valve 46 is installed on the second preheating pipeline 44. The electric heating jacket 42 is connected to a PLC. During the experiment, the mixed gas can be preheated to the oxidation reaction trigger temperature (generally 300℃-450℃) within the pipeline of the electric heating jacket 42, ensuring that the mixed gas can cross the reaction activation energy barrier when entering the sample, thus meeting the experimental conditions.

[0032] Example 4: As an optimization of the above examples, as shown in the appendix. Figure 1 As shown, it also includes a controller 47 and a distributed optical fiber temperature sensor 48. The triaxial core holder 2 is equipped with a distributed optical fiber temperature sensor 48, which is connected to the controller 47. The triaxial core holder 2 is equipped with a permeation component at both ends of the distributed optical fiber temperature sensor 48. The permeation component includes a pad 49 and a guide plate 50.

[0033] The distributed fiber optic temperature sensor 48 and controller 47 are existing known technologies, such as a temperature-sensing fiber optic cable and a distributed fiber optic temperature measurement host connected together. The controller 47 is connected to the PLC to facilitate the acquisition of temperature change data of the sample during the experiment, so as to capture the advancement process of the oxidation thermal front. The pad 49 is a highly permeable porous sintered metal pad (porous metal sintered plate), and the guide plate 50 is a microchannel guide plate. This can evenly disperse the injected linear airflow into a planar laminar flow, ensuring that the oxidation medium penetrates and advances evenly on the end face of the core sample.

[0034] Example 5: As an optimization of the above examples, as shown in the appendix. Figure 1 As shown, a third pressure gauge 51 is installed on the first connecting pipeline between the upstream storage tank 4 and the first regulating valve 20, and a fourth pressure gauge 52 is installed on the second connecting pipeline 19 between the downstream storage tank 5 and the second regulating valve 21.

[0035] According to the requirements, the third pressure gauge 51 and the fourth pressure gauge 52 are both existing and known pressure transmitters. Both the third pressure gauge 51 and the fourth pressure gauge 52 are connected to the PLC, so that the pressure value of the upstream storage tank 4 and the pressure value of the downstream storage tank 5 can be collected in real time and the pressure difference between the upstream storage tank 4 and the downstream storage tank 5 can be calculated. This facilitates the control of the pressure in the upstream storage tank 4 and the downstream storage tank 5, thereby facilitating the control of the pressure at both ends of the inner chamber of the triaxial core holder 2, and also facilitates the acquisition of the pressure difference between the upstream storage tank 4 and the downstream storage tank 5. With the cooperation of the upstream storage tank 4 and the downstream storage tank 5, the dynamic changes of permeability and porosity can be measured by the pulse attenuation method.

[0036] Example 6: As attached Figure 1 As shown, the quantitative evaluation method for permeability enhancement in shale oil under oxidation and thermal stress environments includes the following steps: S1, Construct a comparison database, including: S11, Select the shale in the target block; S12, prepare the first core sample 54 in columnar shape from the shale in step S11, and obtain the initial matrix permeability of the first core sample 54. S13, Prepare a second core sample from the remaining shale in step S12, and obtain the organic matter abundance of the second core sample. S14, obtain the transverse nuclear magnetic resonance relaxation spectrum of the first core sample 54, and set the reference point; S2, reprinted from core sample 54, describes the construction of the experimental environment, including: S21, Place the first core sample 54 into the triaxial core holder 2; S22, Install a sealing sleeve 53 on the outside of the first core sample 54; S23, install guide permeation components on both ends of the first core sample 54; S24, Multiple acoustic emission sensors 7 are spaced apart on the outside of the triaxial core holder 2; S3 simulates deep reservoir conditions, including: S31, simulating triaxial geostress; S32, the back pressure value of the sampling pipeline 12 is adjusted to the simulated formation pore pressure through the back pressure valve 13; S4, activates ignition, including: S41, inert gas is continuously injected into the triaxial core holder 2 through the oxidation medium injection system for purging protection; S42, preheat the mixing line 10 to the set range; S5, injecting an oxidizing medium to capture thermal fronts, including: S51, the oxidation medium is mixed according to multiple set proportions; S52, stop the inert gas injection, inject multiple sets of oxidizing media into the triaxial core holder 2 and react inside the first core sample 54, collect and plot the three-dimensional spatiotemporal evolution curve of the temperature corresponding to each set ratio of oxidizing media. S53 captures the advance of thermal fronts by tracking the movement of the exothermic peak as the temperature surges from the outside to the inside. S6, Obtain the physical signals and chemical composition of the internal reaction of the first core sample 54, including: S61, process the signals captured by all acoustic emission sensors 7, and extract time-domain and frequency-domain characteristic parameters; S62, sampling is performed at set time intervals, and the component concentrations of the mixed gas are determined by chromatograph 6; S7, gas-stopped dormancy, inversion of microscopic porosity and permeability structure, including: S71, the reaction gas inside the first core sample 54 was evacuated using a vacuum pump. S72, the detection medium is injected into the triaxial core holder 2 through the detection medium injection system until the pressure reaches the preset value and then the first detection control valve 17 is closed. S73, inject detection medium into upstream storage tank 4 until the pressure in upstream storage tank 4 rises to the set value; S74, open back pressure valve 13, record the pressure difference change data at both ends of the first core sample 54, and at the same time record the density change data of the detection medium; S8, after the triaxial core holder 2 is unloaded, the crack characteristics of the first core sample 54 are obtained, including: S81, slowly reduce the temperature of the sealing sleeve 53, the axial stress of the first core sample 54, and the confining pressure of the first core sample 54; S82, after taking out the first core sample 54, put it into the vacuum saturation device to make the first core sample 54 completely fluid saturated. S83, Obtain the transverse relaxation spectrum of the first core sample 54 in step S82; S84, perform CT scan to obtain the three-dimensional spatial distribution morphology, orientation connectivity probability and pore throat ratio of the internal cracks in the first core sample 54. S9, an evaluation of the permeability enhancement of the first core sample 54, including: S91, Obtain the pressure difference attenuation coefficient based on the pressure difference change data at both ends of the first core sample 54 in step S74: S92, the absolute equivalent permeability of the first core sample 54 was calculated based on the pressure difference attenuation coefficient; S93, compare the absolute equivalent permeability in step S92 with the initial matrix permeability in step S11 to determine whether gas injection oxidation can create physical cracks in the first core sample 54. S94, calculate the total effective pore volume inside the first core sample 54; S95, calculate the effective interconnected porosity based on the total effective pore volume in step S94; S96, Obtain the fractal dimension based on the transverse relaxation spectrum in step S83; S97, evaluate the degree of oxidative expansion-induced cracking effect and crack network density based on fractal dimension; S98, Calculate the rise angle coefficient and the average frequency of the waveform based on the time domain and frequency domain characteristic parameters in step S61; S99, based on the rise angle coefficient and the average frequency of the waveform, determine whether the high-temperature and high-pressure gas that instantly accumulates inside the first core sample 54 due to chemical oxidation can cause the rock grains to open and tear apart, and determine whether the energy-gathering gas explosion expansion of the phase change gas can achieve physical transformation of the modified and compacted shale.

[0037] The specific steps of the quantitative evaluation method for permeability enhancement in shale oil oxidation and thermal stress environments include: S1. Before the experiment, the multidimensional baseline parameters of the rock samples were fully calibrated, and a comparison database was constructed, including: S11, Select shale from the target block: Prepare representative core samples for medium- to low-maturity shale from the target block; S12, cut and extract the drilled shale, prepare the first core sample 54 in columnar shape from the shale in step S11, and obtain the initial matrix permeability of the first core sample 54. S13. Prepare a second core sample from the remaining shale in step S12 and obtain the organic matter abundance of the second core sample. Organic matter abundance refers to the amount of organic matter contained in sediments (rocks), which is an important parameter for evaluating the hydrocarbon generation potential of source rocks. It is often expressed by parameters such as total organic carbon (TOC), hydrocarbon generation potential (S1+S2), and pyrolytic hydrocarbons. S14. High-resolution X-ray micro-CT three-dimensional panoramic scanning of the dried first core sample 54 in its initial state and nuclear magnetic resonance transverse relaxation spectrum (T2 spectrum) after complete fluid saturation were acquired to obtain the geometric information of the original pores and matrix, clearly distinguish the pore phase and matrix phase, construct a pore network model, and quantify the topological parameters (establish the original spatial topological distribution model of matrix nanopores) as a reference zero point to determine whether macroscopic cracks are generated by subsequent oxidation expansion.

[0038] S2, reprinted from core sample 54, describes the construction of the experimental environment, including: S21, Place the first core sample 54 into the triaxial core holder 2: Carefully and slowly push the cylindrical first core sample 54, which has been dried under constant weight and measured parameters, into the center of the test chamber of the triaxial core holder 2. S22, Install a sealing sleeve 53 on the outside of the first core sample 54: Based on the expected maximum oxidation reaction temperature range of this batch of experiments, select a matching high-temperature resistant sealing sleeve 53. If simulating shallow reservoirs or mild low-temperature oxidation modification (preset maximum oxidation reaction temperature < 400℃), the high-temperature resistant sealing sleeve 53 is made of special high-temperature resistant fluororubber or polyether ether ketone (PEEK) heat-shrinkable material, and the first core sample 54 is wrapped in the special high-temperature resistant fluororubber or polyether ether ketone (PEEK) heat-shrinkable material; if simulating deep extreme high-temperature oxidation (preset oxidation reaction temperature in the range of 400℃-800℃), at this time the polymer will be completely melted and carbonized, the high-temperature resistant sealing sleeve 53 is made of annealed thin-walled copper tube or flexible graphite sleeve, and the first core sample 54 is wrapped in the annealed thin-walled copper tube or flexible graphite sleeve for a hard seal of metal wrapping to ensure sealing performance at high temperatures; S23, install guide permeation components on both ends of the first core sample 54: first place porous sintered metal pads 49 on the left and right ends of the first core sample 54, and then place microchannel guide plates 50 to ensure that the injected linear airflow is evenly dispersed into planar laminar flow, and to ensure that the oxidizing medium is evenly permeated and advanced on the end face of the first core sample 54. S24, Multiple acoustic emission sensors 7 are spaced apart on the outside of the triaxial core holder 2: Eight outward-facing acoustic sensing windows are set on the outer wall of the triaxial core holder 2 corresponding to the first core sample 54. The eight outward-facing acoustic sensing windows are spaced apart (in this embodiment, they are spirally distributed). Then, a layer of high-temperature resistant industrial petroleum jelly is uniformly coated inside the acoustic sensing windows as an acoustic coupling agent to remove tiny air bubbles at the contact interface. Subsequently, an acoustic emission sensor 7 is installed in each acoustic sensing window (the acoustic emission sensor 7 is a broadband acoustic emission sensor, mainly used to detect acoustic emission signals such as crack propagation and leakage inside the material. Its frequency response range is wide, usually from 20kHz to 1MHz, and its sensitivity reaches -70dB re1V / μPa). This ensures that the piezoelectric ceramic shell of the acoustic emission sensor 7 is electrically insulated from the triaxial core holder 2 to prevent electromagnetic interference (EMI) generated by the heating current and the operation of the motor of the delivery pump from mixing into the acoustic signal of rock fracture.

[0039] S3 simulates deep reservoir conditions, including: S31, Simulate triaxial geostress: Apply confining pressure, axial stress and transverse stress to the first core sample 54 to construct and restore the true triaxial geostress boundary of the underground reservoir of the first core sample 54. S32, the back pressure value of sampling pipeline 12 is adjusted to the simulated formation pore pressure through back pressure valve 13: Open back pressure valve 13 and set the back pressure value to the simulated formation pore pressure. This set back pressure value must be higher than the saturated vapor pressure of the gas in the triaxial core holder 2 at the experimental extreme temperature. The setting of the back pressure value, on the one hand, ensures that the light liquid hydrocarbons generated by pyrolysis in the pore system can be maintained in a supercritical or liquid stable phase, preventing abrupt phase changes that cause abnormal volume shrinkage; on the other hand, it forms a strong fluid barrier, which can effectively prevent the surge of mixed gas generated by gas injection and oxidation from freely and rapidly escaping outward, forcing the high-pressure gas to accumulate in the extremely low-permeability dense matrix, providing the necessary pressure accumulation bed for the subsequent "gas wedge energy fracturing" effect.

[0040] S4, activates ignition, including: S41, inert gas is continuously injected into the triaxial core holder 2 through the oxidation medium injection system for purging protection; S42, preheat the mixing line 10 to the set range; At normal temperature and the original formation temperature (usually less than 150°C), medium- to low-maturity shale is extremely stable and will not undergo spontaneous chain oxidation even with the injection of high concentrations of oxygen. Therefore, an external heat source is necessary to assist the first core sample 54 in overcoming the chemical activation energy barrier of kerogen oxidation.

[0041] S5, injecting an oxidizing medium to capture thermal fronts, including: S51, the oxidation medium is mixed according to multiple set proportions; S52, stop the inert gas injection, inject multiple sets of oxidizing media into the triaxial core holder 2 and react inside the first core sample 54, collect and plot the three-dimensional spatiotemporal evolution curve of the temperature corresponding to each set ratio of oxidizing media. S53 captures the advance of thermal fronts by tracking the movement of the exothermic peak as the temperature surges from the outside to the inside. When the local temperature inside the first core sample 54 reaches the preset oxidation reaction trigger threshold, the first core sample 54 enters the core stage of multi-physics field coupled in-situ remediation simulation.

[0042] By adjusting the first control valve 33, the first mass flow controller 35 (MFC), the second control valve 34, and the second mass flow controller 36 (MFC) according to the evaluation scheme requirements through the gas mixer 30, air and high-purity oxygen / nitrogen are mixed in a predetermined ratio to achieve stepped distribution of the injected oxygen concentration. To evaluate the impact of oxygen concentration on fracturing intensity, a gradient comparison group is formed by setting the ratio: for example, the volume percentage of oxygen in the injected gas is successively set to 21% (simulating natural air injection), 50%, 70%, and 100% (pure oxygen injection) under extreme fracturing conditions.

[0043] Start the air delivery pump 28 and nitrogen delivery pump 29 to continuously and stably introduce the prepared mixed oxidizing gas into the interior of the first core sample 54, which is under high temperature and high pressure. The injection gas flow rate needs to be adaptively matched according to the initial matrix permeability of the first core sample 54 (the initial matrix permeability is the Nadars level permeability obtained in step S12) to prevent the pressure at the injection end from exploding instantly.

[0044] As active oxygen molecules gradually penetrated into the interior of the first core sample 54 and came into close contact with the solid macromolecular kerogen and residual heavy oil, a violent exothermic oxidation reaction was instantly triggered. The first to occur was the low-temperature oxidation (LTO) pathway, which generates oxygen-containing active intermediates such as alcohols, aldehydes, and ketones. This was followed by a rapid transition to high-temperature oxidation (HTO), which caused the long chains of kerogen to break down, generating liquid oil and gas, and under sufficient oxygen support, underwent deep and complete combustion to generate large amounts of CO2, CO, and H2O.

[0045] Distributed fiber optic temperature sensors 48, located on the surface of the first core sample 54, collect temperature data in real time. The PLC and host computer generate a three-dimensional spatiotemporal evolution curve of temperature based on the temperature data. By tracking the movement trajectory of the exothermic peak that surges from the outside to the inside, the process of the incubation, formation, and advancement of the "high-temperature oxidation heat front" driven by the latent heat of violent chemical reaction in the dense matrix is ​​captured.

[0046] S6, Obtain the physical signals and chemical composition of the internal reaction of the first core sample 54, including: S61, process the signals captured by all acoustic emission sensors 7, and extract time-domain and frequency-domain characteristic parameters; S62, sampling is performed at set time intervals, and the component concentrations of the mixed gas are determined by chromatograph 6; As gas oxidation occurs and the thermal front advances, a physical phase transition and mechanical collapse process are taking place inside the first core sample 54 due to the violent chemical reaction that generates gas. It is necessary to record indirect dynamic evidence of the fracturing process.

[0047] High-frequency acoustic emission (AE) non-destructive dynamic monitoring: All acoustic emission sensors 7 are activated, and the high-frequency transient elastic waves released when the high-pressure gas in the first core sample 54 accumulates and expands, causing the local pore pressure to instantly exceed the tensile strength of the first core sample 54 and induce microcrack initiation are continuously captured by the acoustic emission sensors 7. Then, the high-frequency transient elastic waves are pre-amplified with low noise and bandpass filtered, and the time domain and frequency domain characteristic parameters of each rupture event are extracted in real time using the trigger threshold. The time domain and frequency domain characteristic parameters include peak amplitude, rise time, duration, absolute energy and ring count.

[0048] Chromatograph 6 online sampling analysis: Using sampling valve 15, the concentration of components in the released mixed gas is determined at set time intervals (e.g., once every 10 minutes during the period of intense oxidation, and once every 30 minutes or 1 hour during the period of stable oxidation).

[0049] Chromatograph 6 uses high-purity helium as the carrier gas and utilizes a high-resolution chromatographic column such as HP-PLOT Q for separation.

[0050] The TCD (thermal conductivity detector) channel of chromatograph 6 is responsible for capturing the concentration jumps of permanent gases such as CO2, CO, and H2 in the mixed gas, which serves as the core indicator for judging the intensity of the oxidation combustion reaction, oxygen consumption rate, and carbon-oxygen conversion rate.

[0051] The FID (Flame Ionization Detector) channel of Chromatograph 6 is responsible for quantifying the production concentration of C1-C6 (methane to hexane) light gaseous alkanes, alkenes, and even trace amounts of sulfur- or nitrogen-containing heterocyclic organic compounds (such as thiols and pyridines).

[0052] By comprehensively analyzing the data evolution of these two channels, the dynamic pyrolysis rate of solid kerogen transforming into mobile fluid (liquid / gas hydrocarbons) can be assessed. The superposition relationship between the gas product generation rate and local pressure reflects, from the underlying logic of material balance, the intensity of the "gas explosion" expansion inside core sample 54.

[0053] S7, gas-stopped dormancy, inversion of microscopic porosity and permeability structure, including: S71, the reaction gas inside the first core sample 54 was evacuated using a vacuum pump. S72, the detection medium is injected into the triaxial core holder 2 through the detection medium injection system until the pressure reaches the preset value and then the first detection control valve 17 is closed. S73, inject detection medium into upstream storage tank 4 until the pressure in upstream storage tank 4 rises to the set value; S74, open back pressure valve 13, record the pressure difference change data at both ends of the first core sample 54, and at the same time record the density change data of the detection medium; When gas injection reaches the predetermined time point, or when the internal temperature field of the first core sample 54 gradually decreases and approaches equilibrium, and the downstream chromatograph 6 shows a significant exponential decrease in hydrocarbon gas yield, it indicates that the oxidation potential at this stage has been exhausted. At this point, the injection of mixed gas is stopped, and the micropore permeability evaluation mode is started to quantitatively verify the physical fracturing effect.

[0054] Even with initial oxidation and fracturing, the overall equivalent permeability of the first core sample 54 remains extremely low (the equivalent permeability may increase from nano-Darcy to micro-Darcy). Traditional steady-state measurement methods based on stable flowmeters are completely ineffective and produce significant errors in this case. Therefore, this evaluation process employs a non-destructive, high-precision, and extremely short-duration transient pressure pulse decay method for dynamic porosity and permeability inversion.

[0055] First, a vacuum pump (which can be connected to the second preheating pipeline 44) is used to evacuate the residual oxidation gas in the triaxial core holder 2 and the first core sample 54. Then, a single-atom, non-adsorbent detection medium (such as high-purity helium) is injected into the triaxial core holder 2 through the detection medium injection system. This simultaneously pressurizes the upstream storage tank 4, the core pores of the first core sample 54, the downstream storage tank 5, and the triaxial core holder 2, slowly increasing the pressure to the preset value (reference saturation equilibrium pressure P). sat Then close the first detection control valve 17.

[0056] Subsequently, a small amount of high-pressure helium gas was injected instantaneously into the upstream storage tank 4 until the pressure in the upstream storage tank 4 rose to the set value, thus creating a step-like initial pressure difference between the upstream and downstream ends of the first core sample 54. (General initial differential pressure pulse) (Not exceeding 10% of the pressure setting value inside upstream storage tank 4).

[0057] Quickly open the back pressure valve 13 and continuously record the exponential curve data of the gradual dissipation and decay of the transient pressure difference between the upstream storage tank 4 and the downstream storage tank 5 over time (t); simultaneously record the slight changes in helium density inside the triaxial core holder 2 caused by pressure changes during this process. Stop the measurement when the triaxial core holder 2 reaches thermodynamic and pressure equilibrium again (this is the final helium density). ).

[0058] S8, after the triaxial core holder 2 is unloaded, the crack characteristics of the first core sample 54 are obtained, including: S81, slowly reduce the temperature of the sealing sleeve 53, the axial stress of the first core sample 54, and the confining pressure of the first core sample 54; S82, after taking out the first core sample 54, put it into the vacuum saturation device to make the first core sample 54 completely fluid saturated. S83, Obtain the transverse relaxation spectrum of the first core sample 54 in step S82; S84, X-ray three-dimensional micro-CT scanning was performed to obtain the three-dimensional spatial distribution morphology, orientation and connectivity probability of the internal cracks in the first core sample 54, as well as the pore throat ratio. After collecting and recording all in-situ data, the temperature of the sealing sleeve 53 (temperature inside the triaxial core holder 2) was slowly and gradually reduced. A small amount of high pressure was released from the internal pores of the first core sample 54 through the sampling valve 15. Finally, the radial confining pressure and axial stress of the first core sample 54 were simultaneously and evenly removed. Sudden pressure drops or rapid mechanical unloading were avoided to prevent unloading rebound cracks from interfering with the final analysis.

[0059] After removing the first core sample 54, it was carefully transferred to the nuclear magnetic resonance (NMR) and core analysis laboratory. It was brought back to 100% complete fluid saturation using a vacuum saturation device (a known technology), and then placed in an NMR coil to obtain the transverse relaxation spectrum (T2 spectrum) of the first core sample 54.

[0060] By comparing the transverse relaxation spectrum of the first core sample 54 before the experiment (obtained in step S14), the isolated single main peak in the pores (usually the central value is close to 0.1~1ms, representing nanoporous fluid that is firmly bound by capillary force) was observed.

[0061] If the transverse relaxation spectrum of the first core sample 54 obtained by placing it in the nuclear magnetic resonance coil shows a significant "drift to the right" phenomenon, and a continuous long relaxation sub-peak (or even the main peak shifts to this position) is clearly grown, spanning from 10 ms to 500 ms, then from the perspective of hydrogen proton magnetic resonance physics, it most directly confirms that the intense oxidative expansion effect has completely opened up the dense matrix, destroyed the nanopore walls, and formed a large-scale (micrometer to millimeter scale) truly interconnected microcrack network with macroscopic conductivity.

[0062] To obtain the final visual evidence, a high-resolution X-ray three-dimensional micro-CT scan was performed on the first core sample 54 after the experiment. The scan slices were superimposed and imported into a three-dimensional volume rendering visualization software for threshold segmentation and spatial binarization processing. The three-dimensional spatial distribution morphology, orientation connectivity probability and pore throat ratio of the microcrack network inside the first core sample 54 were presented intuitively and the results were calculated.

[0063] S9, an evaluation of the permeability enhancement of the first core sample 54, including: S91, Obtain the pressure difference attenuation coefficient based on the pressure difference change data at both ends of the first core sample 54 in step S74: S92, the absolute equivalent permeability of the first core sample 54 was calculated based on the pressure difference attenuation coefficient; S93, compare the absolute equivalent permeability in step S92 with the initial matrix permeability in step S11 to determine whether gas injection oxidation can create physical cracks in the first core sample 54. S94, calculate the total effective pore volume inside the first core sample 54; S95, calculate the effective interconnected porosity based on the total effective pore volume in step S94; S96, Obtain the fractal dimension based on the transverse relaxation spectrum in step S83; S97, evaluate the degree of oxidative expansion-induced cracking effect and crack network density based on fractal dimension; S98, Calculate the rise angle coefficient and the average frequency of the waveform based on the time domain and frequency domain characteristic parameters in step S61; S99, based on the rise angle coefficient and the average frequency of the waveform, determine whether the high-temperature and high-pressure gas that instantly accumulates inside the first core sample 54 due to chemical oxidation can cause the rock grains to open and tear apart, and determine whether the energy-gathering gas explosion expansion of the phase change gas can achieve physical transformation of the modified and compacted shale.

[0064] The data collected during the experiment (including pressure, temperature gradient, concentration of complex gas components, acoustic signals and NMR scan matrix) cannot be directly evaluated for the cracking effect in its original state. These data must be processed in real time, and decoupled and transformed into quantitative indicators for directly evaluating the "thermal stress infiltration effect" and its mechanism through physical and mathematical inversion algorithms.

[0065] Based on step S6, the time-domain and frequency-domain characteristic parameters of each rupture event are extracted. These parameters include peak amplitude, rise time, duration, absolute energy, and ring count. Two core mechanical ratio parameters are then calculated. Rise angle coefficient RA (reflecting waveform sluggishness) = signal rise time (time taken from break-off to peak) / maximum transient amplitude; The average frequency AF of the waveform (reflecting the intensity of energy release) = cumulative ring count (number of fluctuations crossing the threshold) / the complete duration of the signal.

[0066] When the high-temperature, high-pressure gas that instantly accumulates within the pores due to chemical oxidation triggers a significant local pore pressure gradient, causing the tensile circumferential stress on the micropore walls to exceed the inherent tensile strength of the rock, sudden opening and tearing separation occurs between the rock grains. This type of fracture does not require overcoming friction and can be completed instantaneously, releasing energy in the form of extremely high pulse peaks. The captured waveform characteristics are characterized by extremely short rise times and extremely high dominant frequencies. Therefore, in the two-dimensional feature scatter plot or clustering space constructed by the algorithm, the projections of these signals densely cluster in the quadrant where the extremely low RA axis region intersects with the extremely high AF axis region. The concentrated emergence of a large number of such signals during the gas injection oxidation period proves that the crack is caused by "gas wedge expansion-induced fracturing (tensile / tensional fracture)".

[0067] After high temperatures cause phase transformation degradation of some minerals and a significant weakening of rock mass strength, local frictional slippage occurs along the inherent weak zones of the rock's bedding under continuous compression by extremely high external pressure. Because this fracturing process is accompanied by prolonged and highly resistant crystal surface friction, energy release is relatively slow and gradual. Its waveform characteristics are characterized by a long rise time and a low average frequency. On the scatter plot, such event clusters are concentrated in the shear quadrant where high RA and low AF intersect. Time-series slice statistics were performed on a large number of AE signal clusters throughout the entire experimental period, calculating the cumulative ratio of the tensile event scatter plot to the shear event scatter plot over time. If it is found that in the stage where the local temperature reaches its extreme value and oxidation is most intense, the signal center overwhelmingly drifts towards the "tensile zone," it can be directly confirmed that the crack is caused by the "energy-gathering gas explosion expansion of internal phase-change gas" effect (shear / slip slippage crack).

[0068] This application reveals the "structural collapse" mechanism of shale tight matrix during gas injection oxidation, namely the physical origin of the transformation of solid organic matter into gaseous products and the induction of "gas explosion" expansion. An evaluation system is constructed, addressing the challenges of invisible and difficult-to-quantify fracture networks in deep-earth extreme environments, providing data support for evaluating whether air injection truly induces fractures. Real-time monitoring of dynamic evolution is achieved; through acoustic emission and online gas phase analysis, the critical moment of fracture initiation and its response to changes in injection intensity can be accurately captured. Scientific basis for process optimization is provided; through experimental comparisons under different oxygen concentrations and injection rates, optimal parameter suggestions are offered for the design of on-site gas injection projects.

[0069] The quantitative evaluation method for permeability enhancement in shale oil oxidation and thermal stress environments can be further optimized and / or improved according to actual needs: Example 7: As an optimization of the above examples, as shown in the appendix. Figure 1 As shown, step S12 involves preparing a columnar first core sample 54 from the shale from step S11, and obtaining the initial matrix permeability of the first core sample 54, including: S121, Prepare the first core sample 54 in columnar shape from the shale in step S11: For the medium and low maturity shale in the target block, cut the drilled shale and prepare the first core sample 54 in cylindrical shape. S122, The initial effective porosity of the first core sample 54 was determined by the helium expansion method: The first core sample 54 was placed under a set pressure condition, and its initial effective porosity was accurately determined by the Boyle's law helium expansion method. S123, then the initial matrix permeability of the first core sample 54 was obtained using the pulse decay method; Step S13: Prepare a second core sample from the remaining shale from step S12, and obtain the organic matter abundance of the second core sample, including: S131, After crushing the remaining shale in step S12, a second core sample is prepared and the total organic carbon content is determined: After crushing the adjacent scraps of shale remaining when cutting the first core sample 54 of the cylinder, the total organic carbon (TOC) content is determined to confirm its organic matter abundance. S132, the second core sample was pyrolyzed to obtain the highest pyrolysis peak temperature, free hydrocarbons and cracked hydrocarbons parameters: rock pyrolysis analysis was performed to obtain the highest pyrolysis peak temperature (Tmax), free hydrocarbons (S1) and cracked hydrocarbons (S2) parameters of the second core sample. S133, Determine the initial kerogen type and thermal maturity of the second core sample based on the highest pyrolysis peak temperature, free hydrocarbons and cracked hydrocarbons parameters in step S132: Determine the initial kerogen type (type I, type II or type III) and thermal maturity evolution stage based on the highest pyrolysis peak temperature (Tmax), free hydrocarbons (S1) and cracked hydrocarbons (S2) parameters of the second core sample. S134, Initial mass percentage of brittle minerals and clay minerals determined by X-ray diffraction and X-ray fluorescence spectroscopy: The initial mass percentage of brittle minerals such as quartz, feldspar, and carbonate rocks, as well as various clay minerals, was quantitatively determined by X-ray diffraction (XRD) and X-ray fluorescence spectroscopy (XRF).

[0070] Example 8: As an optimization of the above examples, as shown in the appendix Figure 1 As shown, step S31, simulating triaxial geostress, includes: S311, the confining pressure medium is injected into the triaxial core holder 2 through the confining pressure medium injection system, and the same confining pressure and transverse stress are applied to the outside of the first core sample 54 until the confining pressure reaches the set radial confining pressure. The pressure increase rate of the confining pressure is less than 0.5 MPa / min. The first confining pressure control valve 9 is opened, the confining pressure delivery pump 23 is started, and the confining pressure medium (the confining pressure medium is ultrapure water or high flash point hydraulic oil) is slowly pumped into the annular sealing cavity of the triaxial core holder 2, and the radial confining pressure is slowly increased and maintained at a loading rate of less than 0.5 MPa per minute. and transverse stress ( ); S312, apply axial stress to the left end face of the first core sample 54 until the axial stress reaches the set axial stress, which is greater than the set radial confining pressure. Immediately afterwards, inject oil or water into the triaxial core holder 2 (an independent liquid delivery pump can be used, with the outlet of the pump connected to the axial inlet of the triaxial holder; alternatively, an axial pressure system can be used to apply axial stress to the left end face of the first core sample 54; the axial pressure system includes a high-pressure pump, a storage tank, and an axial hydraulic cylinder located on the inner left side of the triaxial core holder; the triaxial core holder has a through-hole installation channel at the center of the left end; the cylinder body of the axial hydraulic cylinder is sealed and fixedly installed within the installation channel; the inlet of the high-pressure pump is connected to the storage tank; and the outlet of the high-pressure pump is connected to the inlet of the axial hydraulic cylinder via a high-pressure pipeline). During operation, the high-pressure pump draws hydraulic medium and continuously injects it into the rodless chamber of the axial hydraulic cylinder. The increase in pressure in the axial hydraulic cylinder drives the piston to move to the right. The movement of the piston in the axial hydraulic cylinder can be achieved by the action of the solenoid valve installed between the high-pressure pump and the axial hydraulic cylinder. A central tube with an outer diameter consistent with the first core sample 54 is fixed to the right end of the piston. The outer side of the central tube is provided with inlet holes that are connected inside and outside. The pad 49 and the guide plate 50 are both installed inside the central tube. In this way, after the piston drives the central tube to move, it acts on the left end face of the first core sample 54, applying axial stress to the left end face of the first core sample 54 until the axial stress reaches the set axial stress. The inlet holes facilitate the detection of the medium entering from the left end face of the first core sample 54, and smoothly apply axial deflection stress to the first core sample 54. This allows for the accurate construction and reconstruction of the true triaxial geostress boundary of the first core sample 54 in the underground reservoir. During the operation, it is essential to ensure that the confining pressure is always greater than the pore fluid pressure, and the application of triaxial geostress must be synchronized and carried out slowly to avoid premature shear failure of the first core sample 54 due to sudden changes in instantaneous stress difference. Example 9: As an optimization of the above embodiments, as shown in the appendix Figure 1 As shown, in step S42, the mixing pipeline 10 is preheated to a set range, specifically: the mixing pipeline 10 is preheated to between 300°C and 450°C at a preheating rate of less than 10°C / min.

[0071] Turn on the electric heating jacket 42 and adjust the heating process through the temperature controller 47 connected to the electric heating jacket 42: In order to prevent the excessively fast heating rate from generating a large temperature gradient inside the first core sample 54, causing severe uneven thermal expansion stress and resulting in non-oxidative cracking, the mixing pipeline 10 is preheated to between 300°C and 450°C at a preheating rate of less than 10°C / min. The preheating rate is usually set in a mild range of 0.5°C / min to 5°C / min for linear heating.

[0072] The final preheating target temperature is set between 300℃ and 450℃. The specific "ignition" trigger threshold temperature needs to be accurately calibrated in advance based on the exothermic peak values ​​obtained from kerogen pyrolysis kinetic experiments (such as thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC)) of adjacent samples in the same target block. During the preheating stage, the pores of the first core sample 54 are kept closed or purged with a small amount of inert gas (such as nitrogen or argon) to ensure that no premature low-temperature oxidation interference caused by trace amounts of oxygen occurs before reaching the target ignition temperature.

[0073] Example 10: As an optimization of the above example, step S91, obtaining the pressure difference attenuation coefficient based on the pressure difference change data at both ends of the first core sample 54 in step S74, includes: S911, convert the pressure difference-time series data at both ends of the first core sample 54 from step S74 into... For the scatter coordinates of time t, where, Let be the instantaneous pressure difference at time t, in MPa; The pressure difference between the upstream storage tank 4 and the downstream storage tank 5 when the pressure rises to the set value in step S73, in MPa; S912, the least squares method is used to perform linear fitting on the scattered point coordinates in step S91, the slope of the fitted line obtained after linear fitting is determined, and the slope of the fitted line is used as the pressure difference attenuation coefficient.

[0074] Because the seepage process of helium gas through the porous medium of a very low-permeability rock core is extremely slow, a system of partial differential equations was constructed based on Darcy's law for unsteady porous media and the equation of state for real gases. Solving this equation reveals the instantaneous pressure difference between the upstream and downstream of the system under given boundary conditions. It exhibits a natural exponential decay pattern with time t, and the mathematical model is as follows: ; in, Let be the instantaneous pressure difference at time t, in MPa; The pressure difference, in MPa, between the upstream storage tank 4 and the downstream storage tank 5 when the pressure rises to the set value in step S73. This is the differential pressure attenuation coefficient.

[0075] In the above model, the core inversion parameters This is the pressure differential attenuation coefficient. It is a comprehensive coefficient determined by the rock's own physical properties, fluid properties, and the geometric volume of the evaluation device, forming a bridge for solving unknown permeability: In the data processing, the extracted pressure difference-time series data is first converted into... Scattered coordinates for time t. The least squares method is used to... A linear fit is performed on the scatter plot coordinates of time t to obtain a fitted line. The absolute slope of the fitted line is then obtained, and this absolute slope is the pressure differential attenuation coefficient. .

[0076] Example 11: As an optimization of the above embodiment, in step S92, the absolute equivalent permeability of the first core sample 54 is calculated according to the following formula: In the above formula, k is the absolute equivalent permeability, and m 2 ; This is the differential pressure attenuation coefficient; ρ is the dynamic viscosity coefficient of the probe medium, mPa·s; L is the length of the first core sample 54, m; c is the isothermal comprehensive compressibility coefficient of the probe medium, MPa. -1 A represents the effective cross-sectional area through which fluid passes in the first core sample 54, in meters. 2 ; The absolute effective volume of upstream storage tank 4 is in cm³. 3 ; The absolute effective volume of gas collector 3 is in cm³. 3 .

[0077] The absolute equivalent permeability k of the first core sample 54 under the current modified state was calculated using the above formula. Comparing the inversion results before and after the experiment on the same core, it was found that the permeability exhibited an exponential or multi-order-of-magnitude increase (e.g., from an extremely dense 10...). -20 m 2 Explosiveness increased to 10 -15 m 2 This indicates that gas injection oxidation can create high-speed channels for physical fractures within a dense matrix (first core sample 54).

[0078] The formula for calculating the total effective pore volume in step S94 is as follows: In the above formula, The total effective pore volume is expressed in cm³. 3 ; The absolute effective volume of upstream storage tank 4 is in cm³. 3 ; The absolute effective volume of gas collector 3 is in cm³. 3 ; The density of the upstream storage tank 4 before injecting the detection medium into the upstream storage tank 4 in step S73, in g / cm³. 3 ; The density of the medium (g / cm³) was measured when the pressure was constant after the reaction inside the triaxial core holder 2.3 ; The density of the detection medium in step S73 when the pressure in the upstream storage tank 4 rises to the set value, in g / cm³. 3 .

[0079] The formula for calculating the effective interconnected porosity in step S95 is as follows: ; In the above formula, To effectively connect porosity; The total effective pore volume is expressed in cm³. 3 ; The total volume of the first core sample 54 is in cm³. 3 .

[0080] Effective connectivity porosity based on the mass conservation of the entire system ( Inversion Derivation: A single permeability index can only evaluate the fluid conductivity. To comprehensively quantify the size of the newly added reservoir space released by oxidation "structural collapse" and chemical pyrolysis inside the first core sample 54, the effective porosity after fracturing must be accurately calculated. Since conventional liquid saturation methods cannot penetrate these extremely small fractures, this evaluation method utilizes the absolute mass conservation law during the fully enclosed pulse decay test process. At three characteristic physical moments—before the pulse test, at the extremely short instant of pulse application, and at the complete decay equilibrium of the pulse—the total mass of helium molecules in the system must always be equal. Based on the gaseous matter balance equation, the total effective pore volume inside the core that actually participates in fluid exchange and flow can be solved. Subsequently, using measurements of the external geometric dimensions of the core, the relative proportion of effective interconnected porosity was finally calculated. .

[0081] This derivation process directly eliminates the interference of isolated dead pores that cannot conduct flow, and the obtained effective connectivity porosity... This directly represents the effective network space of reserves that the in-situ modification process can actually utilize.

[0082] The formula for calculating the fractal dimension in step S96 is: In the above formula, V is the cumulative pore volume fraction at a certain moment in the transverse relaxation spectrum; D is the fractal dimension. The transverse relaxation time in the transverse relaxation spectrum is greater than 0.1 ms; It is a constant. The maximum value; C is a constant.

[0083] To further quantify the heterogeneity, tortuosity, and topological complexity of the newly added crack network in three-dimensional space, this evaluation method introduces fractal geometry theory from nonlinear dynamics to process the data in the transverse relaxation spectrum (T2 spectrum) measured by nuclear magnetic resonance.

[0084] According to the theory of porous media based on nuclear magnetic resonance, the pore surface area and volume have a fractional proportional relationship. The fractal dimension D is obtained by extracting data from the transverse relaxation spectrum (T2 spectrum) and applying the above formula.

[0085] For three-dimensional Euclidean space, the theoretical range of fractal dimension D is strictly between 2 and 3. A fractal dimension of D of 2 represents a perfectly smooth, uniformly shaped, ideal spherical porous system, while a fractal dimension of D of 3 represents an extremely complex, rough-surfaced, chaotic system with numerous cracks of varying sizes.

[0086] By comparing the difference and tracing the drift trajectory of the fractal dimension D of the first core sample 54 before and after the experiment, extracted by computer, the degree of evolution of the fracture network from the original "dispersed, isolated, and structurally simple matrix spots" to "a highly complex network system with spanning multiple scales and extremely high connectivity" can be quantitatively assessed. Experimental results show that the more thorough the oxidative expansion-induced fracturing effect and the greater and more complex the microfracture network density, the more significantly the D value increases, infinitely approaching the limit value of 3.

[0087] The proposed mechanism and evaluation method for fracturing caused by oxidative expansion in shale oil air injection in this application is a system based on underlying physical mechanisms and cross-validated from multiple dimensions. By integrating high-temperature and high-pressure dynamic simulation, precise porosity-permeability inversion models, acoustic emission source identification, and nuclear magnetic resonance topological characterization, this application not only solves the technical challenge of the "invisible" fracturing effect during gas injection oxidation, but also provides quantitative evaluation standards and core supporting principles for the efficient in-situ development of medium- and low-maturity shale oil. The integrated design of this application is based on actual formation stress, fluid phase evolution, and chemical reaction thermodynamics, providing accurate and scientific decision-making basis for the petroleum industry to formulate in-situ reforming process schemes and evaluate reservoir stimulation effects.

[0088] The above technical features constitute various embodiments of the present invention, which have strong adaptability and implementation effect. Unnecessary technical features can be added or removed according to actual needs to meet the needs of different situations.

Claims

1. A quantitative evaluation method for permeability enhancement in shale oil under oxidation and thermal stress environments, characterized in that, The steps include the following: S1, Construct a comparison database, including: S11, Select the shale in the target block; S12, prepare the first core sample in columnar shape from the shale in step S11, and obtain the initial matrix permeability of the first core sample; S13, Prepare a second core sample from the remaining shale in step S12, and obtain the organic matter abundance of the second core sample. S14, Obtain the transverse relaxation spectrum of the first core sample using nuclear magnetic resonance and set a reference point; S2, reprinted from the first core sample, constructing the experimental environment, including: S21, Place the first core sample into the triaxial core holder; S22, Install a sealing sleeve on the outside of the first core sample; S23, Install guide permeation components on both ends of the first core sample; S24, Multiple acoustic emission sensors are spaced apart on the outside of the triaxial core holder; S3 simulates deep reservoir conditions, including: S31, simulating triaxial geostress; S32, the back pressure value of the sampling pipeline is adjusted to the simulated formation pore pressure through the back pressure valve; S4, activates ignition, including: S41, inert gas is continuously injected into the triaxial core holder through the oxidation medium injection system for purging protection; S42, preheat the mixing pipeline to the set range; S5, injecting an oxidizing medium to capture thermal fronts, including: S51, the oxidation medium is mixed according to multiple set proportions; S52, stop the inert gas injection, inject multiple sets of oxidizing media into the triaxial core holder and react inside the first core sample, collect and plot the three-dimensional spatiotemporal evolution curve of the temperature corresponding to each set ratio of oxidizing media. S53 captures the advance of thermal fronts by tracking the movement of the exothermic peak as the temperature surges from the outside to the inside. S6, Obtain the physical signals and chemical composition of the internal reaction of the first core sample, including: S61 processes the signals captured by all acoustic emission sensors and extracts time-domain and frequency-domain characteristic parameters. S62, sampling is performed at set time intervals, and the component concentrations of the mixed gas are determined by a chromatograph; S7, gas-stopped dormancy, inversion of microscopic porosity and permeability structure, including: S71, the reaction gas in the first core sample was evacuated using a vacuum pump; S72, the detection medium is injected into the triaxial core holder through the detection medium injection system until the pressure reaches the preset value and then the first detection control valve is closed. S73, inject detection medium into the upstream storage tank until the pressure in the upstream storage tank rises to the set value; S74, open the back pressure valve, record the pressure difference change data at both ends of the first core sample, and at the same time record the density change data of the detection medium; S8, After the triaxial core holder is unloaded, the fracture characteristics of the first core sample are obtained, including: S81, slowly reduce the temperature of the sealing sleeve, the axial stress of the first core sample, and the confining pressure of the first core sample; S82, After the first core sample is taken out, it is placed in a vacuum saturation device to make the first core sample fully fluid saturated. S83, Obtain the transverse relaxation spectrum of the first core sample in step S82; S84, perform CT scan to obtain the three-dimensional spatial distribution morphology, orientation connectivity probability and pore throat ratio of the internal fractures of the first core sample. S9, Evaluation of the permeability enhancement of the first core sample, including: S91, Obtain the pressure difference attenuation coefficient based on the pressure difference change data at both ends of the first core sample in step S74: S92, the absolute equivalent permeability of the first core sample was calculated based on the pressure difference attenuation coefficient; S93, compare the absolute equivalent permeability in step S92 with the initial matrix permeability in step S11 to determine whether gas injection oxidation can create physical cracks in the first core sample. S94, calculate the total effective pore volume inside the first core sample; S95, calculate the effective interconnected porosity based on the total effective pore volume in step S94; S96, Obtain the fractal dimension based on the transverse relaxation spectrum in step S83; S97, evaluate the degree of oxidative expansion-induced cracking effect and crack network density based on fractal dimension; S98, Calculate the rise angle coefficient and the average frequency of the waveform based on the time domain and frequency domain characteristic parameters in step S61; S99, based on the rise angle coefficient and the average frequency of the waveform, determine whether the high-temperature and high-pressure gas that instantly accumulates inside the first core sample due to chemical oxidation can cause the rock grains to open and tear apart, and determine whether the energy-gathering gas explosion expansion of the phase change gas can achieve physical transformation of the modified and compacted shale.

2. The quantitative evaluation method for permeability enhancement in shale oil under oxidation and thermal stress environments according to claim 1, characterized in that, A quantitative evaluation device for permeability enhancement in shale oil oxidation and thermal stress environments includes a triaxial core holder housed within a constant-temperature chamber, and confining pressure injection system, oxidation medium injection system, detection medium injection system, gas collector, upstream storage tank, downstream storage tank, chromatograph, and acoustic emission sensor spaced apart outside the chamber. A first confining pressure pipeline is fixedly connected between the outlet of the confining pressure injection system and the confining pressure inlet of the triaxial core holder, and a first confining pressure control valve is installed on the first confining pressure pipeline. A mixing pipeline is fixedly connected between the outlet of the oxidation medium injection system and the axial inlet of the triaxial core holder, and a first mixing control valve is installed on the mixing pipeline. A sampling pipeline is fixedly connected between the axial outlet of the triaxial core holder and the gas collector, and a back pressure valve is installed on the sampling pipeline. A separation pipeline is fixedly connected between the collector and the test port of the chromatograph, and a sampling valve is installed on the separation pipeline. A first detection pipeline is fixedly connected between the outlet of the detection medium injection system and the radial inlet of the triaxial core holder, and a first detection control valve is installed on the first detection pipeline. A first connecting pipeline is fixedly connected between the upstream storage tank and the first radial outlet of the triaxial core holder, and a first regulating valve is installed on the first connecting pipeline. A second connecting pipeline is fixedly connected between the downstream storage tank and the second radial outlet of the triaxial core holder, and a second regulating valve is installed on the second connecting pipeline. Several sensing windows are spaced apart on the outside of the triaxial core holder. An acoustic emission sensor is installed in each acoustic sensing window. All acoustic emission sensors are connected to a PLC, and the PLC is connected to a host computer.

3. The quantitative evaluation method for permeability enhancement in shale oil under oxidation and thermal stress environments according to claim 2, characterized in that, The confining pressure medium injection system includes a confining pressure storage tank and a confining pressure delivery pump. A first confining pressure pipeline is fixedly connected between the outlet of the confining pressure storage tank and the inlet of the confining pressure delivery pump. A second confining pressure pipeline is fixedly connected between the outlet of the confining pressure delivery pump and the confining pressure inlet of the triaxial core holder. A first pressure gauge is installed on the second confining pressure pipeline. The oxidation medium injection system includes an air tank, a nitrogen tank, an air delivery pump, a nitrogen delivery pump, and a gas mixer. The outlet of the air tank is fixedly connected to the inlet of the air delivery pump. An air input pipeline is fixedly connected between the outlet of the air delivery pump and the first inlet of the gas mixer. A first control valve and a first mass flow controller are installed at intervals along the medium flow direction on the air input pipeline. The outlet of the nitrogen tank is fixedly connected to the inlet of the nitrogen delivery pump. A nitrogen input pipeline is fixedly connected between the outlet of the nitrogen delivery pump and the second inlet of the gas mixer. A second control valve and a second mass flow controller are installed at intervals along the medium flow direction on the nitrogen input pipeline. The mixing pipeline is fixedly connected between the outlet of the gas mixer and the axial inlet of the triaxial core holder. A second mixing control valve is installed on the mixing pipeline corresponding to the position between the first mixing control valve and the gas mixer. The detection medium injection system includes a helium tank and a helium delivery pump. A first detection pipeline is fixedly connected between the outlet of the helium tank and the inlet of the helium delivery pump. A second detection pipeline is fixedly connected between the outlet of the helium delivery pump and the radial inlet of the triaxial core holder. A second pressure gauge is installed on the second detection pipeline.

4. The quantitative evaluation method for permeability enhancement in shale oil under oxidation and thermal stress environments according to claim 3, characterized in that, It also includes an air injection pump and an electric heating jacket. A first preheating pipeline is fixedly connected between the mixing pipeline at the position between the first mixing control valve and the second mixing control valve and the inlet of the air injection pump. A second preheating pipeline is fixedly connected between the mixing pipeline at the position between the first preheating pipeline and the first mixing control valve and the outlet of the air injection pump. Electric heating jackets are installed on the outside of the mixing pipeline between the first preheating pipeline and the axial inlet of the triaxial core holder, the outside of the first preheating pipeline, the outside of the second preheating pipeline, and the outside of the triaxial core holder.

5. The quantitative evaluation method for permeability enhancement in shale oil under oxidation and thermal stress environments according to claim 2, 3, or 4, characterized in that, It also includes a controller and a distributed fiber optic temperature sensor. The triaxial core holder is equipped with a distributed fiber optic temperature sensor, which is connected to the controller. The triaxial core holder is equipped with a permeation component at both ends of the distributed fiber optic temperature sensor. The permeation component includes a pad and a guide plate. Or / and, a third pressure gauge is installed on the first connecting pipeline between the upstream storage tank and the first regulating valve, and a fourth pressure gauge is installed on the second connecting pipeline between the downstream storage tank and the second regulating valve.

6. The quantitative evaluation method for permeability enhancement in shale oil under oxidation and thermal stress environments according to claim 1, characterized in that, Step S12 involves preparing a columnar first core sample from the shale obtained in step S11, and acquiring the initial matrix permeability of the first core sample, including: S121, Prepare the first core sample in columnar shape from the shale in step S11; S122, the initial effective porosity of the first core sample was determined using the helium expansion method; S123, the initial matrix permeability of the first core sample was obtained using the pulse decay method; Step S13: Prepare a second core sample from the remaining shale from step S12, and obtain the organic matter abundance of the second core sample, including: S131, after crushing the remaining shale in step S12, a second core sample is prepared, and the total organic carbon content is determined. S132, the second core sample was pyrolyzed to obtain the highest pyrolysis peak temperature, free hydrocarbons and cracked hydrocarbons parameters; S133, Determine the initial kerogen type and thermal maturity of the second core sample based on the highest pyrolysis peak temperature, free hydrocarbon and cracked hydrocarbon parameters in step S132. S134, using X-ray diffraction and X-ray fluorescence spectroscopy to determine the initial mass percentage of brittle minerals and clay minerals.

7. The quantitative evaluation method for permeability enhancement in shale oil under oxidation and thermal stress environments according to claim 1 or 6, characterized in that, Step S31, simulating triaxial geostress, includes: S311, the confining pressure medium is injected into the triaxial core holder through the confining pressure medium injection system, and the same confining pressure and transverse stress are applied to the outside of the first core sample until the confining pressure reaches the set radial confining pressure. The pressure increase rate of the confining pressure is less than 0.5 MPa / min. S312, apply axial stress to the left end face of the first core sample until the axial stress reaches the set axial stress, and the set axial stress is greater than the set radial confining pressure. Or / and, in step S42, preheat the mixing pipeline to a set range, specifically: preheat the mixing pipeline to between 300°C and 450°C at a preheating rate of less than 10°C / min.

8. The quantitative evaluation method for permeability enhancement in shale oil under oxidation and thermal stress environments according to claim 1 or 6, characterized in that, Step S91: Obtain the pressure difference attenuation coefficient based on the pressure difference change data at both ends of the first core sample from step S74, including: S911, convert the pressure difference-time series data at both ends of the first core sample from step S74 into... For the scatter coordinates of time t, where, Let be the instantaneous pressure difference at time t, in MPa; The pressure difference between the upstream storage tank and the downstream storage tank when the pressure rises to the set value in step S73, in MPa; S912, the least squares method is used to perform linear fitting on the scattered point coordinates in step S91, the slope of the fitted line obtained after linear fitting is determined, and the slope of the fitted line is used as the pressure difference attenuation coefficient.

9. The quantitative evaluation method for permeability enhancement in shale oil under oxidation and thermal stress environments according to claim 7, characterized in that, Step S91: Obtain the pressure difference attenuation coefficient based on the pressure difference change data at both ends of the first core sample from step S74, including: S911, convert the pressure difference-time series data at both ends of the first core sample from step S74 into... For the scatter coordinates of time t, where, Let be the instantaneous pressure difference at time t, in MPa; The pressure difference between the upstream storage tank and the downstream storage tank when the pressure rises to the set value in step S73, in MPa; S912, the least squares method is used to perform linear fitting on the scattered point coordinates in step S91, the slope of the fitted line obtained after linear fitting is determined, and the slope of the fitted line is used as the pressure difference attenuation coefficient.

10. The quantitative evaluation method for permeability enhancement in shale oil under oxidation and thermal stress environments according to claim 8, characterized in that, In step S92, the absolute equivalent permeability of the first core sample is calculated according to the following formula: In the above formula, For absolute equivalent penetration rate, m 2 ; This is the differential pressure attenuation coefficient; ρ is the dynamic viscosity coefficient of the probe medium, mPa·s; L is the length of the first core sample, m; c is the isothermal composite compressibility coefficient of the probe medium, MPa -1 A represents the effective cross-sectional area through which the fluid passes in the first core sample, in meters. 2 ; The absolute effective volume of the upstream storage tank is expressed in cm. 3 ; The absolute effective volume of the gas collector is in cm³. 3 ; The formula for calculating the total effective pore volume in step S94 is as follows: In the above formula, The total effective pore volume is expressed in cm³. 3 ; The absolute effective volume of the upstream storage tank is expressed in cm. 3 ; The absolute effective volume of the gas collector is in cm³. 3 ; The density of the upstream storage tank before injecting the detection medium into the upstream storage tank in step S73, in g / cm³. 3 ; The density of the medium (g / cm³) was measured when the pressure was constant after the reaction within the triaxial core holder. 3 ; The density of the detection medium in step S73 when the pressure in the upstream storage tank rises to the set value, in g / cm³. 3 ; The formula for calculating the effective interconnected porosity in step S95 is as follows: ； In the above formula, To effectively connect porosity; The total effective pore volume is expressed in cm³. 3 ; The total volume of the first core sample is in cm³. 3 ; The formula for calculating the fractal dimension in step S96 is: In the above formula, V is the cumulative pore volume fraction at a certain moment in the transverse relaxation spectrum; D is the fractal dimension. The transverse relaxation time in the transverse relaxation spectrum is greater than 0.1 ms; It is a constant. The maximum value; C is a constant.

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