Experimental method and device for evaluating heat-assisted carbon dioxide huff and puff energy-increasing and permeability-increasing effect after shale oil reservoir fracturing

Abstract

The invention belongs to the technical field of oil and gas field development engineering, and particularly relates to an experimental method and device for evaluating energy-increasing and permeation-increasing effects of thermal-assisted carbon dioxide huff and puff after shale oil reservoir fracturing. The experimental method comprises the following steps: S1, preparing a shale core sample: selecting two shale cores from the same geological reservoir, taking one as a fractured core and taking the other as a matrix core; s2, carrying out heat-assisted CO2 huff and puff simulation experiment test on the matrix rock core sample; carrying out a heat-assisted CO2 huff and puff simulation experiment test on the fractured rock core sample; and evaluating the energy increasing efficiency of the heat-assisted CO2 huff and puff and the permeation increasing effect on the artificial fracture. According to the experimental method, the limitation of evaluating the energy-increasing and permeability-increasing effect of the heat-assisted supercritical CO2 on the shale reservoir in the prior art is overcome, and the energy-increasing and permeability-increasing effect of the CO2 on the shale reservoir in the heat-assisted extraction process can be comprehensively and systematically evaluated.

Description

Technical Field

[0001] The invention belongs to the technical field of oil and gas field development engineering, and specifically relates to an experimental method and device for evaluating the energy and permeability enhancement effect of heat-assisted carbon dioxide huff and puff after shale oil reservoir fracturing. Background Art

[0002] At present, the development of shale oil reservoirs faces the challenges of low permeability, low porosity and strong heterogeneity. Conventional water flooding, polymer flooding and other methods of improving oil recovery are less applicable in shale oil reservoirs. CO2 huff-and-puff technology has attracted widespread attention because it can enhance oil and gas mobility and improve oil recovery. Among them, heat-assisted CO2 huff-and-puff technology is an effective energy-enhancing and permeability-enhancing method for low-permeability shale oil reservoirs. It further enhances the CO2 diffusion capacity by combining the thermal energy effect, reduces the viscosity of crude oil, and enhances the oil washing efficiency and energy-enhancing effect of CO2. Therefore, this technology has important application potential in the energy-enhancing development of shale oil reservoirs.

[0003] In terms of experimental research, most studies currently use CO2 huff-and-puff experiments under room temperature to evaluate reservoir permeability changes and oil recovery effects. In addition, some studies use high-temperature and high-pressure reactors or nuclear magnetic resonance to analyze the diffusion behavior of CO2 in shale pores, but lack a systematic analysis of the dynamic evolution of reservoir physical properties in different huff-and-puff stages, especially the CO2 injection stage-well soaking stage-oil production stage, and do not involve the impact of temperature changes on reservoir physical parameters.

[0004] On the other hand, some experimental methods only focus on the CO2 displacement efficiency, and fail to comprehensively consider key factors such as gas expansion effect, pore pressure change and permeability evolution, resulting in insufficient quantitative evaluation of the CO2 huff and puff energy enhancement effect. Therefore, there is currently a lack of systematic experimental evaluation methods for the energy enhancement and permeability enhancement effect of CO2 huff and puff after fracturing in shale oil reservoirs.

[0005] In summary, it can be seen that at present, in the process of thermal mass extraction, there is a lack of effective experimental methods and experimental equipment to systematically and comprehensively evaluate the energy-enhancing and permeability-enhancing effects of CO2 throughput. Summary of the invention

[0006] The purpose of the present invention is to propose an experimental method and device for evaluating the energy-enhancing and permeability-enhancing effect of heat-assisted carbon dioxide huff-and-puff after shale oil reservoir fracturing, which is used to study the energy-enhancing and permeability-enhancing mechanism of heat-assisted supercritical CO2 development of shale oil reservoirs. This experimental method overcomes the limitations of the existing technology in evaluating the energy-enhancing and permeability-enhancing effect of heat-assisted supercritical CO2 on shale reservoirs, and can comprehensively and systematically evaluate the effect of CO2 on the energy-enhancing and permeability-enhancing effect of shale reservoirs during the heat-assisted extraction process.

[0007] The experimental method described in the present invention comprehensively considers the effect of CO2-fracturing fluid-rock on the permeability enhancement of shale matrix under the action of heat and mass, and the effect of energy increase on the conductivity of shale artificial fractures.

[0008] The specific technical solutions are as follows: An experimental method for evaluating the effect of heat-assisted carbon dioxide huff and puff on energy and permeability enhancement after fracturing of a shale oil reservoir comprises the following steps: S1. Preparation of shale core samples: First, two shale cores from the same geological reservoir were selected, and after cleaning and drying, the basic physical properties of the two shale cores were measured, including the original permeability of the shale cores. An organic solvent was used to clean the residual oil in the cores.

[0009] The permeability is the gas permeability, which can be measured by displacement method. If the selected shale core has few internal microcracks and the permeability is too small to be tested by displacement method, the pressure pulse method can be used for measurement. The relevant method can be found in the literature "Wang CL, Pan LH, Zhao Y, et al. Analysis of the pressure-pulse propagation in rock: a new approach to simultaneously determine permeability, porosity, and adsorption capacity[J]. Rock Mechanics and Rock Engineering, 2019, 52: 4301-4317".

[0010] Then, one of the shale cores is selected to be artificially fractured to obtain a fracture core; and the original permeability of the obtained fracture core is corrected to obtain the original permeability of the fracture core.

[0011] Another shale core is used as a matrix core, wherein the original permeability of the matrix core is the original permeability of the shale core in the basic physical property parameters.

[0012] S2. Conduct heat-assisted CO2 huff-and-puff simulation test on matrix core samples and fracture core samples respectively: Thermally assisted CO2 huff and puff simulation test on matrix core samples: 1) After the matrix core is placed in a reactor and vacuumed, the matrix core is treated with saturated water-phase fracturing fluid.

[0013] 2) CO2 is injected into the reactor, and the matrix core saturated with water-phase fracturing fluid interacts with CO2 under the set experimental temperature and pressure conditions, and the action time is set to the experimental soaking time.

[0014] 3) After the matrix core action time is over, turn off the heating, wait for the reactor to cool to room temperature, release the pressure, take out the matrix core and dry it.

[0015] 4) After the dried matrix core is cooled to room temperature, the permeability of the matrix core after heat-assisted CO2 huff and puff is measured using the displacement method.

[0016] 5) Calculate the matrix permeability level of heat-assisted CO2 absorption and exhalation according to the following formula: ; In the formula, L m is the matrix permeability level of heat-assisted CO2 absorption and exhalation, %; K ma is the permeability of the matrix core after CO2 action at a certain temperature, mD; K 1 is the original permeability of the matrix core, mD.

[0017] Thermally assisted CO2 huff and puff simulation test on fracture core samples: 1) First, the fractured core is vacuumed to saturate the formation with simulated oil; then, CO2 is injected into the fractured core until CO2 is completely diffused into the core fractures.

[0018] During the CO2 injection process, the initial confining pressure is set to the confining pressure when measuring the original permeability of the fractured core in step S1. Then, the inlet pressure of the core is increased to be equal to the inlet pressure when measuring the gas permeability. When gas is seen at the outlet, it is maintained for a certain period of time to ensure that CO2 is completely diffused into the core fractures. At this time, the core fractures contain CO2, and the fluid in the matrix is ​​the formation simulated oil.

[0019] 2) Increase the CO2 inlet pressure and confining pressure step by step, and maintain the pressure difference between the CO2 inlet pressure and the confining pressure until the CO2 inlet pressure increases to the reservoir production pressure. Then, keep the CO2 inlet pressure constant and continue to increase the confining pressure to the original overburden pressure of the reservoir.

[0020] 3) After CO2 gas breakthrough, the permeability of the fractured rock after core depletion development is determined using the displacement method.

[0021] 4) Calculate the damage index of the depleted development fracture permeability after fracture core fracturing according to the following formula: ; In the formula, E i is the fracture core permeability damage index, dimensionless;K f is the original permeability of the fracture core, mD; K fa is the permeability after fracture core failure development, mD.

[0022] 5) Evaluate the energy enhancement efficiency of heat-assisted CO2 huff and puff and the permeability enhancement effect on artificial fractures: a. Inject a certain amount of CO2 into the fracture core at a constant pressure. Generally speaking, when simulating the on-site CO2 huff and puff process, the CO2 huff and puff pressure can be 5-10MPa higher than the current reservoir production pressure.

[0023] b. After the inlet pressure and outlet pressure of the fracture core are stable, heat it to a certain temperature, soak the well, and monitor and record the inlet pressure and outlet pressure of the fracture core during the soaking process.

[0024] c. After the well is soaked, the average pore pressure after the heat-assisted CO2 huff-and-puff soak is calculated according to the following formula: ; In the formula, P Hpa is the average pore pressure after heat-assisted CO2 huff-and-puff wellbore, MPa; P Hin is the inlet pressure of the fracture core at the end of the heat-assisted CO2 huff-and-puff well, MPa; P Hout The outlet pressure of the fractured core at the end of heat-assisted CO2 huff-and-puff wellbore, MPa.

[0025] d. Taking the average pore pressure after well soaking as the outlet pressure of the fracture core, inject CO2, monitor and record the pressure difference at both ends and the CO2 flow rate at the outlet, and calculate the permeability of the fracture core at the end of the heat-assisted CO2 well soaking.

[0026] e. Calculate the energy efficiency of thermally assisted CO2 throughput according to the following formula: ; In the formula, P o is the current reservoir production pressure, MPa; l He The efficiency of heat-assisted CO2 throughput, % P Hpa is the average pore pressure after heat-assisted CO2 huff-and-puff soaking, MPa.

[0027] f. Calculate the permeability enhancement level of thermally assisted CO2 stimulation fractures according to the following formula: ; In the formula, LHf is the fracture permeability enhancement level of heat-assisted CO2 huff and puff, %; K Hf is the permeability of the fracture core at the end of the heat-assisted CO2 huff-and-puff well, mD; K fa Permeability after fracture core failure development, mD.

[0028] In the present invention, the experimental method for evaluating the effect of heat-assisted carbon dioxide huff and puff on energy and permeability enhancement after shale oil reservoir fracturing also includes the evaluation of the level of improvement of fracture aperture by heat-assisted CO2 huff and puff, and the specific operation is as follows: The first step is to simulate the ordinary CO2 huff and puff for the fracture core sample and evaluate its energy enhancement efficiency and the permeability enhancement effect on the artificial fracture: a. First, a certain amount of CO2 is injected into the fracture core at a constant pressure at room temperature. The injection amount of CO2 is the same as the CO2 injection amount used for soaking the well when performing the heat-assisted CO2 huff-and-puff simulation on the fracture core sample; Then, the well is soaked, and the inlet pressure and outlet pressure of the fracture core are monitored and recorded during the soaking process.

[0029] b. After the well is soaked, calculate the average pore pressure after ordinary CO2 huff-and-puff soaking according to the following formula: ; In the formula, P pa is the average pore pressure after ordinary CO2 huff-and-puff well soaking, MPa; P in is the inlet pressure of the fracture core at the end of ordinary CO2 huff-and-puff well soaking, MPa; P out It is the outlet pressure of the fractured core at the end of ordinary CO2 huff-and-puff wellbore, MPa.

[0030] c. Take the average pore pressure after well soaking as the outlet pressure of the fracture core, inject CO2, monitor and record the pressure difference at both ends and the CO2 flow rate at the outlet, and calculate the permeability of the fracture core at the end of ordinary CO2 well soaking.

[0031] d. Calculate the energy efficiency of ordinary CO2 throughput according to the following formula: ; In the formula, l e The energy efficiency of ordinary CO2 throughput is %; P pa is the average pore pressure after ordinary CO2 huff-and-puff well soaking, MPa; P o is the current reservoir production pressure, MPa.

[0032] e. Calculate the permeability increase level of common CO2 stimulation fractures according to the following formula: ; In the formula, L f is the permeability increase level of ordinary CO2 stimulation fractures, %; K cf is the permeability of the fracture core at the end of the ordinary CO2 huff-and-puff well, mD; K fa Permeability after fracture core failure development, mD.

[0033] The second step is to compare the fracture opening of heat-assisted CO2 huff and puff and ordinary CO2 huff and puff: In the process of heat-assisted CO2 huff and puff, if the matrix rock mainly relies on the dissolution effect of CO2 and fracturing fluid to increase permeability, the permeability increase of the fracture core is mainly caused by the increase in fracture aperture due to the thermal expansion of CO2. The heat-assisted CO2 huff and puff fracture aperture improvement index is calculated according to the following formula: ; In the formula, E f is the thermal-assisted CO2 stimulation fracture aperture enhancement index, dimensionless; P pa is the average pore pressure after ordinary CO2 huff-and-puff well soaking, MPa; Z Hc is the CO2 compression factor under the temperature and pressure conditions of heat-assisted CO2 throughput, dimensionless; T Hc is the temperature of the heat-assisted CO2 huff-and-puff experiment, K; Z c is the CO2 compression factor under normal CO2 throughput temperature and pressure conditions, dimensionless; T c is the normal CO2 throughput test temperature, K; P Hpa is the average pore pressure after heat-assisted CO2 huff-and-puff soaking, MPa.

[0034] The above formula for calculating the thermally assisted CO2 huff and puff fracture aperture improvement index is obtained through the following derivation process: First, as mentioned above, in the process of ordinary CO2 huff and puff and heat-assisted CO2 huff and puff, the amount of CO2 in the fracture core system is equal, so the following formula can be obtained according to the gas state equation: ; In the formula, V c The volume of CO2 at the end of normal CO2 huff and puff well soaking, %; Z cis the CO2 compression factor under normal CO2 throughput temperature and pressure conditions, dimensionless; R is the molar gas constant, J / (mol·K); T c is the normal CO2 throughput test temperature, K; V Hc is the volume of CO2 at the end of heat-assisted CO2 huff and puff well shut-down, %; Z Hc is the CO2 compression factor under the temperature and pressure conditions of heat-assisted CO2 throughput, dimensionless; T Hc is the temperature of the heat-assisted CO2 huff-and-puff experiment, K.

[0035] It can be further inferred that: V Hc and V c The relationship between them is as follows: .

[0036] Assuming that during the heat-assisted CO2 huff and puff process, the matrix rock mainly relies on the dissolution effect of CO2 and fracturing fluid to increase permeability, and the main reason for the increased permeability of the fracture core is the increase in fracture aperture caused by the thermal expansion of CO2. V Hc and V c The proportional coefficient between them is defined as the thermally assisted CO2 crack aperture enhancement index, so it can be concluded that: ; In the formula, E f It is the fracture aperture enhancement index of heat-assisted CO2 stimulation, dimensionless.

[0037] In the present invention, the experimental method for evaluating the effect of heat-assisted carbon dioxide huff and puff to increase energy and permeability after shale oil reservoir fracturing, the basic physical properties of the shale core in step S1 also include length, diameter, dry weight, porosity and core permeability.

[0038] In the present invention, the experimental method for evaluating the effect of heat-assisted carbon dioxide huff and puff on energy and permeability enhancement after shale oil reservoir fracturing is described, wherein the porosity of the shale core is measured by the dodecane saturation method, and the porosity is calculated according to the following formula: ; In the formula, f 1 is the porosity of shale core, %; g s is the wet weight of shale core saturated with dodecane, g; g d is the dry weight of shale core, g; r D is the density of dodecane, g / cm3 ; d is the shale core diameter, cm; l is the length of shale core, cm.

[0039] In the present invention, the experimental method for evaluating the effect of heat-assisted carbon dioxide huff-and-puff energy and permeability enhancement after shale oil reservoir fracturing is to calculate the permeability (gas permeability) corresponding to the core according to the following formula: ; In the formula, K is the shale core permeability, D; P 0 is atmospheric pressure, 10 -1 MPa; Q 0 is the flow rate under atmospheric pressure, cm 3 / s; m g is the gas viscosity, mPa·s; P 入口 is the inlet pressure of the core, 10 -1 MPa; P 出口 is the outlet pressure of the core, 10 -1 MPa.

[0040] In the present invention, the experimental method for evaluating the effect of heat-assisted carbon dioxide huff and puff to increase energy and permeability after shale oil reservoir fracturing is described, wherein the fracture core in step S1 is artificially fractured by wire cutting or Babbitt splitting.

[0041] A device for evaluating the experimental method of heat-assisted carbon dioxide huff-and-puff energy and permeability enhancement after shale oil reservoir fracturing, comprising a CO2 gas cylinder, a CO2 intermediate container, an aqueous fracturing fluid intermediate container, a reactor, a drying box and a core holder; wherein the CO2 intermediate container and the reactor are both provided with a heating device.

[0042] The CO2 gas cylinder is connected to the gas booster pump through a pipeline. A two-way valve No. 1 is arranged on the outlet pipeline of the gas booster pump. The two-way valve No. 1 is connected to the three-way pipeline No. 1; the three-way pipeline No. 1 is connected to a four-way pipeline through a pipeline.

[0043] A two-way valve IV is provided on the pipeline at the top of the CO2 intermediate container, and the two-way valve IV is connected to the three-way valve I through a pipeline.

[0044] A two-way valve No. II is provided on the pipeline at the bottom of the CO2 intermediate container, and the two-way valve No. II is connected to the displacement pump pipeline through a three-way valve No. II.

[0045] A two-way valve No. V is arranged on the pipeline at the top of the intermediate container of the aqueous phase fracturing fluid, and the two-way valve No. V is connected to the four-way pipeline.

[0046] A two-way valve No. III is provided on the pipeline at the bottom of the intermediate container of the aqueous phase fracturing fluid, and the two-way valve No. III is connected to the displacement pump pipeline through a three-way valve No. II.

[0047] A two-way valve No. VI is arranged on the pipeline at the top of the reactor, and the two-way valve No. VI is connected to the four-way pipeline.

[0048] A tee No. IV is provided on the pipeline at the bottom of the reactor, one of the interfaces of the tee No. IV is connected to the back-pressure valve No. I pipeline via a two-way valve No. VII; the back-pressure valve No. I is connected to the hand pump No. I pipeline, and a pressure gauge No. I is provided at the outlet end of the hand pump No. I; the other interface of the tee No. IV is connected to a vacuum pump pipeline via a two-way valve No. X.

[0049] A two-way valve No. VIII is provided on the pipeline at the inlet end of the core clamp, wherein a pressure gauge No. II is provided between the two-way valve No. VIII and the inlet end of the core clamp; the two-way valve No. VIII is connected to the four-way pipeline via a three-way valve No. III, and a vent valve is connected to one of the interfaces of the three-way valve No. III.

[0050] A two-way valve No. IX is provided on the pipeline at the outlet end of the core clamp, wherein a pressure gauge No. III is provided between the two-way valve No. IX and the outlet end of the core clamp; the two-way valve No. IX is connected to the back pressure valve No. II through a pipeline; the top of the back pressure valve No. II is connected to a gas flow meter through a pipeline, one side of the back pressure valve No. II is connected to a hand pump No. II through a pipeline, and a pressure gauge No. IV is provided at the outlet end of the hand pump No. II.

[0051] One side of the core holder is connected to a hand pump III through a pipeline, and a pressure gauge V is provided at the outlet end of the hand pump III.

[0052] The beneficial effects of the present invention are as follows: the present invention innovatively designs an experimental method and device for evaluating the energy-enhancing and permeability-enhancing effects of heat-assisted carbon dioxide huff and puff after fracturing of shale oil reservoirs. The method combines multiple parameters such as temperature, pressure, and permeability to systematically simulate the fluid migration and rock response under multi-field coupling during the heat-assisted CO2 huff and puff process, and comprehensively considers the energy-enhancing effect and permeability change after CO2 injection, so as to comprehensively evaluate the energy-enhancing and permeability-enhancing effects during the heat-assisted CO2 huff and puff process, avoiding the evaluation of traditional methods that are limited to a single factor. At the same time, the present invention simulates the actual production environment of heat-assisted CO2 huff and puff, and fully considers factors such as pore pressure and fracture pressure of shale oil reservoirs in the experiment, so that the experimental results are closer to the actual production situation, and can better reflect the synergistic effect of gas expansion effect and thermal mass effect.

[0053] Compared with the prior art, the present invention can simulate the in-situ temperature environment of the reservoir during the experiment, and at the same time, by introducing gas expansion rate and pore pressure evolution parameters, the representativeness of the experimental results is improved, providing a scientific basis for optimizing the application of heat-assisted CO2 to improve the recovery rate of shale oil reservoirs. The method and device can not only accurately evaluate the CO2 energy enhancement effect under the action of heat and mass, but also evaluate the extent to which the thermal CO2 fluid enhances the conductivity of the shale matrix and fractures, and achieve a comprehensive evaluation of the energy enhancement and permeability enhancement effects, providing a reliable experimental basis and data support for the thermal-assisted CO2 development of shale oil reservoirs, thereby facilitating the optimization of the shale oil reservoir recovery process.

[0054] In summary, the experimental method of the present invention has strong scalability and repeatability, and can flexibly adjust the experimental parameters according to different reservoir conditions, thereby improving the adaptability and reliability of the evaluation experiment and providing strong support for the efficient development of shale oil reservoirs. BRIEF DESCRIPTION OF THE DRAWINGS

[0055] Figure 1 It is a schematic diagram of an experimental device for evaluating the effect of heat-assisted CO2 huff-and-puff energy and permeability enhancement after compression of shale oil reservoirs according to the present invention.

[0056] Figure 2 These are the inlet and outlet pressure curves of the normal (25°C) CO2 huff-and-puff wellbore stage of Core II.

[0057] Figure 3 These are the inlet and outlet pressure curves of the core II heat-assisted (80°C) CO2 huff-and-puff wellbore stage.

[0058] Among them, 1 is a CO2 gas cylinder, 2 is a gas booster pump, 3 is a two-way valve No. I, 4 is a three-way valve No. I, 5 is a displacement pump, 6 is a three-way valve No. II, 7 is a two-way valve No. II, 8 is a two-way valve No. III, 9 is a CO2 intermediate container, 10 is an aqueous fracturing fluid intermediate container, 11 is a two-way valve No. IV, 12 is a two-way valve No. V, 13 is a four-way valve, 14 is a two-way valve No. VI, 15 is a matrix core sample, 16 is a reactor, 17 is a two-way valve No. VII, 18 is a back pressure valve No. I, 19 is a pressure gauge No. I, 20 is a hand pump I No. 21 is three-way valve No. III, 22 is vent valve, 23 is two-way valve No. VIII, 24 is pressure gauge No. II, 25 is drying box, 26 is core holder, 27 is fracture core sample, 28 is pressure gauge No. III, 29 is two-way valve No. IX, 30 is back pressure valve No. II, 31 is gas flow meter, 32 is pressure gauge No. IV, 33 is hand pump No. II, 34 is pressure gauge No. V, 35 is hand pump No. III, 36 is constant temperature box, 37 is three-way valve No. IV, 38 is two-way valve No. X, 39 is vacuum pump. DETAILED DESCRIPTION

[0059] The technical solution of the present invention is described in detail below in conjunction with the accompanying drawings.

[0060] Example 1 A device for the experimental method for evaluating the effect of heat-assisted carbon dioxide injection and puffing to increase energy and permeability after shale oil reservoir fracturing as described in the present invention comprises a CO2 gas cylinder 1, a CO2 intermediate container 9, an aqueous fracturing fluid intermediate container 10, a reactor 16, a drying box 25 and a core clamp 26; wherein the CO2 intermediate container 9 and the reactor 16 are both provided with a heating device.

[0061] The CO2 gas cylinder 1 is connected to the gas booster pump 2 through a pipeline. A two-way valve No. 1 3 is provided on the outlet pipeline of the gas booster pump 2. The two-way valve No. 1 3 is connected to the three-way valve No. 1 4 pipeline; the three-way valve No. 1 4 is connected to a four-way valve 13 through a pipeline.

[0062] A two-way valve IV 11 is provided on the pipeline at the top of the CO2 intermediate container 9, and the two-way valve IV 11 is connected to the three-way valve I 4 through a pipeline.

[0063] A two-way valve II 7 is provided on the pipeline at the bottom of the CO2 intermediate container 9, and the two-way valve II 7 is connected to the pipeline of the displacement pump 5 through a three-way valve II 6.

[0064] A two-way valve No. V 12 is provided on the pipeline at the top of the aqueous phase fracturing fluid intermediate container 10, and the two-way valve No. V 12 is connected to the four-way valve 13 through a pipeline.

[0065] A two-way valve III 8 is provided on the pipeline at the bottom of the aqueous phase fracturing fluid intermediate container 10 , and the two-way valve III 8 is connected to the pipeline of the displacement pump 5 through a three-way valve II 6 .

[0066] A two-way valve VI 14 is provided on the pipeline at the top of the reactor 16 , and the two-way valve VI 14 is connected to the four-way valve 13 through a pipeline.

[0067] A tee No. IV 37 is provided on the pipeline at the bottom of the reactor 16, and one of the interfaces of the tee No. IV 37 is connected to the back-pressure valve No. I 18 pipeline via a two-way valve No. VII 17; the back-pressure valve No. I 18 is connected to the hand pump No. I 20 pipeline, and a pressure gauge No. I 19 is provided at the outlet end of the hand pump No. I 20; the other interface of the tee No. IV 37 is connected to the vacuum pump 39 pipeline via a two-way valve No. X 38.

[0068] A two-way valve No. VIII 23 is provided on the pipeline at the inlet end of the core clamp 26, wherein a pressure gauge No. II 24 is provided between the two-way valve No. VIII 23 and the inlet end of the core clamp 26; the two-way valve No. VIII 23 is connected to the four-way valve 13 through a pipeline via a three-way valve No. III 21, and a vent valve 22 is connected to one of the interfaces of the three-way valve No. III 21.

[0069] A two-way valve No. IX 29 is provided on the pipeline at the outlet end of the core clamp 26, wherein a pressure gauge No. III 28 is provided between the two-way valve No. IX 29 and the outlet end of the core clamp 26; the two-way valve No. IX 29 is connected to the back pressure valve No. II 30 through a pipeline; the top of the back pressure valve No. II 30 is connected to a gas flow meter 31 through a pipeline, the middle part of the back pressure valve No. II 30 is connected to a hand pump No. II 33 through a pipeline, and a pressure gauge No. IV 32 is provided at the outlet end of the hand pump No. II 33.

[0070] One side of the core holder 26 is connected to a hand pump III 35 through a pipeline, and a pressure gauge V 34 is provided at the outlet end of the hand pump III 35 .

[0071] The core holder 26 is placed in a thermostatic box 36. The pressure gauge II 24, pressure gauge III 28, two-way valve IX 29, back pressure valve II 30, gas flow meter 31, pressure gauge IV 32 and hand pump II 33 connected to the core holder 26 are also placed in the thermostatic box 36.

[0072] 1. Simulating heat-assisted CO2 huff and puff using the device on matrix core samples 1) Vacuuming the matrix core: placing the matrix core sample 15 in the reaction kettle 16, opening the two-way valve X 38, and using the vacuum pump 39 to vacuum the matrix core sample 15 and the reaction kettle 16.

[0073] The matrix core is treated with saturated water-phase fracturing fluid: after the vacuuming is completed, the two-way valve No. X 38 is closed, the two-way valve No. III 8, the two-way valve No. V 12 and the two-way valve No. VI 14 are opened, and the fracturing fluid in the water-phase fracturing fluid intermediate container 10 is injected into the reactor 16 at a certain pressure by using the displacement pump 5.

[0074] After the matrix core sample 15 is saturated with the fracturing fluid, the fracturing fluid in the reactor 16 can be discharged through the two-way valve VII 17 and the back pressure valve I 18. At this time, the pressure of the back pressure valve I 18 is atmospheric pressure, and the two-way valve III 8 and the two-way valve V 12 are closed at the same time.

[0075] 2) Inject CO2 and stew well: Open two-way valve No. I 3, and use gas booster pump 2 to pressurize CO2 in CO2 cylinder 1 into reactor 16. After the pressurization is completed, close two-way valve No. I 3 and two-way valve No. VI 14.

[0076] The reactor 16 is heated and the temperature is set to the experimental temperature. At the same time, a hand pump 20 is used to apply pressure to the back pressure valve 18, and the pressure of the back pressure valve 18 is set to the CO2-rock action pressure, and its pressure value can be read by the pressure gauge 19.

[0077] The two-way valve VII 17 is opened to discharge the excess gas generated by the volume expansion of CO2 due to the temperature increase, and then the well is soaked to allow the matrix core sample 15 to interact with CO2.

[0078] 3) Taking out the matrix core sample and drying it: After the matrix core sample 15 has finished reacting with CO2, turn off the heating to lower the temperature of the reactor 16 to room temperature, and then gradually reduce the pressure of the back pressure valve No. 18 to discharge the gas.

[0079] The matrix core sample 15 after the action is placed in a drying box 25 for drying.

[0080] 4) Displacement method to determine the permeability of matrix core after thermally assisted CO2 huff and puff: The dried matrix core sample 15 is placed in the core holder 26 , and a hand pump III 35 is used to provide a confining pressure, the pressure value of which can be read from a pressure gauge V 34 .

[0081] Open the two-way valve No. I 3 and the two-way valve No. IV 11, inject CO2 into the CO2 intermediate container 9 using the gas booster pump 2, and then close the two-way valve No. I 3.

[0082] Open two-way valve II 7, two-way valve VIII 23 and two-way valve IX 29, use displacement pump 5 to displace CO2 into core holder 26 at constant pressure, and measure the permeability of matrix core after CO2 action at a certain temperature.

[0083] The inlet pressure and outlet pressure of the matrix core are read out by pressure gauge II No. 24 and pressure gauge III No. 28 respectively, and the gas flow under atmospheric pressure can be measured by gas flow meter 31. At this time, the pressure of back pressure valve II No. 30 is set to atmospheric pressure.

[0084] 2. Using the device to simulate heat-assisted CO2 huff and puff on fracture core samples 1) The fracture core sample 27 saturated with formation simulated oil is placed in the core holder 26, and the original permeability of the fracture core is measured by the displacement method. This method is consistent with the measurement method of the matrix core mentioned above and will not be described in detail here.

[0085] 2) Gradually increase the displacement pressure of the displacement pump 5 and the confining pressure provided by the hand pump III 35, and keep the pressure difference between the two equal during the process, until the displacement pressure of the displacement pump 5 reaches the current production pressure of the reservoir, adjust the displacement pump 5 to the constant pressure mode, and then continue to increase the confining pressure to the overburden pressure of the reservoir.

[0086] 3) The displacement method was used to measure the permeability of the fracture core sample 27 after depletion development.

[0087] 4) Well soaking: close the two-way valve IX 29, adjust the displacement pump 5 to the constant flow injection mode, and inject a certain amount of CO2 into the fracture core sample 27.

[0088] Close the two-way valve No. VIII 23, open the thermostat 36 to heat the CO2 in the core holder 26 to a predetermined temperature, and monitor and record the values ​​of the pressure gauge No. II 24 and the pressure gauge No. III 28 during the soaking process.

[0089] The CO 2 in the CO 2 intermediate container 9 is then heated so that its temperature is consistent with the temperature of the constant temperature box 36 .

[0090] 5) When the soaking of the fracture core sample 27 is completed, the hand pump II 33 sets the back pressure value of the back pressure valve II 30 to the average pore pressure at the end of the soaking.

[0091] Open the two-way valve No. VIII 23 and the two-way valve No. IX 29, and use the displacement pump 5 to perform constant pressure injection at a certain pressure difference. Use the gas flowmeter 31 to measure the CO2 flow rate under atmospheric pressure, and calculate the permeability of the fracture core sample 27 after the thermal-assisted CO2 huff-and-puff well is completed.

[0092] Finally, the thermostatic box 36 and the CO2 intermediate container 9 are closed to allow them to cool naturally to room temperature, and the pressure of the back pressure valve II 30 is gradually reduced to atmospheric pressure. The pressure at the front end of the core clamp 26 can be released through the vent valve 22.

[0093] Example 2 The present invention will be further described below through specific application examples: According to the experimental method described in the present invention, using the device (such as Figure 1 The specific experimental steps are as follows: S1. Preparation of shale core samples: (1) The core used in this example is a shale core from the same geological reservoir in the GL block of Daqing Oilfield. The residual oil in the core was cleaned with a mixed organic solvent (petroleum ether: ethanol = 1:1) for 15 days. The core was then dried at 110°C for 1 day. The basic physical properties of the two cores are shown in Table 1 below.

[0094] Table 1 Core basic properties

[0095] The matrix core sample was named core I, and the fracture core sample was named core II.

[0096] (2) Artificially create fractures in core II by wire cutting, and use displacement method to correct the original permeability of the fractured core II. The calculation formula is as follows: ; In the formula, K f is the original permeability of the fracture core, D; P 0 is atmospheric pressure, 0.101MPa; Q 0 is the flow rate under atmospheric pressure, which is measured to be 0.5929 cm 3 / s; m g is the gas viscosity, which is 0.02 mPa·s; P 入口 The inlet pressure of core II at this time is set to 0.301 MPa; P 出口 At this time, the outlet pressure of core II is set to 0.101 MPa.

[0097] After calculation, the original permeability of core II after fracture creation is K f 2.98×10 -3 D, that is 2.98mD.

[0098] S2. Conduct heat-assisted CO2 huff-and-puff simulation test on core I: (1) The core I is placed in the reaction vessel 16 and the core I is evacuated by the vacuum pump 39 for 1 hour.

[0099] Then close the two-way valve No. X 38, open the two-way valve No. III 8, the two-way valve No. V 12 and the two-way valve No. VI 14, and use the displacement pump 5 to inject the aqueous fracturing fluid (formula composition: pure water + 8% KCl by mass concentration + 1.5‰ volume fraction of thickener) in the aqueous fracturing fluid intermediate container 10 into the reactor 16 at a certain pressure, and maintain the constant pressure for 7 days.

[0100] (2) After core I is saturated with water-phase fracturing fluid, the water-phase fracturing fluid is discharged through two-way valve No. VII 17 and back pressure valve No. I 18.

[0101] Open the two-way valve No. 1 3, and use the gas booster pump 2 to pressurize CO2 into the reactor 16, and the action pressure is set to 30 MPa. The temperature of the reactor 16 is set to 80° C., and the action time is 3 hours.

[0102] During this process, the pressure of the back pressure valve No. I 18 is set to 30 MPa, and the two-way valve No. VII 17 is opened to discharge the excess gas generated by the volume expansion of CO2 due to the increase in temperature.

[0103] (3) After the core I has been in the reaction chamber for 3 hours, the heating is turned off to lower the temperature of the reactor 16 to room temperature, the pressure is released, the core I is taken out and placed in a drying box 25 for drying.

[0104] (4) After the core I is cooled to room temperature, the core I is placed in the core holder 26, and a hand pump III 35 is used to provide a confining pressure of 3 MPa. The displacement pump 5 is used to displace CO2 into the core holder 26 at a constant pressure to measure the permeability. The permeability is calculated according to the following formula: ; In the formula, K ma is the permeability of the matrix core after CO2 action at a certain temperature, D; P 0 is atmospheric pressure, 0.101MPa; Q 0 is the flow rate under atmospheric pressure, which is measured to be 0.02624 cm 3 / s; m g is the gas viscosity, which is 0.02 mPa·s; P 入口 is the inlet pressure of core I, which is set to 1.5 MPa; P 出口 is the outlet pressure of core I, set to 0.101 MPa.

[0105] The permeability of core I after thermally assisted CO2 action was calculated. K ma is 0.005276 mD; combined with the data in Table 1, the original permeability of core I K 1 is 0.00164mD.

[0106] According to the formula: ; Calculate the permeability level of thermally assisted CO2 huff and puff matrix core sample core I L m It is 221.70%, that is, the permeability of core I increased by 2.217 times.

[0107] S3. Conduct common CO2 huff and puff simulation test on core II: (1) Core II is evacuated and saturated with dodecane, and then placed in a core holder 26. The gas booster pump 2 is used to pressurize CO2 into the CO2 intermediate container 9. The displacement pump 5 is used to displace the CO2 in the CO2 intermediate container 9 into the core holder 26 at a certain pressure.

[0108] The displacement pressure and the confining pressure provided by the hand pump III 35 to the core holder 26 are increased step by step, and the pressure difference between the displacement pressure and the confining pressure is always kept equal to 3 MPa, until the CO2 displacement pressure reaches the current reservoir production pressure ( P o ) 15MPa.

[0109] (2) CO2 is injected at a constant pressure of 15 MPa using the displacement pump 5, and then the confining pressure of the core holder 26 is continuously increased to 35 MPa (the original overburden pressure of the reservoir).

[0110] After CO2 gas breakthrough, the permeability of the fractured core II after core failure development was measured using the displacement method. K fa . Calculated according to the following formula: ; In the formula, K fa is the permeability after fracture core failure development, D; P 0 is atmospheric pressure, 0.101MPa; Q 0 is the flow rate at atmospheric pressure, which is measured to be 1.3068 cm 3 / s; m g is the gas viscosity, which is 0.02 mPa·s; P 入口 The inlet pressure of core II at this time is set to 18.5 MPa; P 出口 At this time, the outlet pressure of core II is set to 15 MPa.

[0111] The permeability of core II after depletion development was calculated. K fa is 0.00451 mD; combined with the original permeability of core II determined and calculated in step S1 (2) above K f =2.98mD, according to the formula: , the damage index of the depleted development fracture permeability of core II after fracturing is calculated E i is 0.9985.

[0112] (3) Use displacement pump 5 to inject 22 MPa of CO2 into core II at a constant pressure, and set the temperature to 25°C. When the inlet and outlet pressures of core II are stable, close two-way valve VIII 23, monitor and record the values ​​of pressure gauge II 24 and pressure gauge III 28 during the soaking process, and the pressure curve is as follows: Figure 2 shown.

[0113] During the experiment, the confining pressure needs to be higher than the system pressure in the core. Considering the pressure resistance of the actual equipment and the pressure increase due to the volume expansion of CO2 after heating, it is initially set to 22MPa, which is 7MPa higher than the current reservoir production pressure.

[0114] After the soaking is completed, the inlet pressure of core II Pin and outlet pressure P out They are 18.78MPa and 18.60MPa respectively.

[0115] Calculate the average pore pressure after ordinary CO2 huff and puff well according to the formula P pa : .

[0116] The average pore pressure after ordinary CO2 huff and puff well soaking is calculated. P pa It is 18.69MPa.

[0117] Then, calculate the energy efficiency of ordinary CO2 throughput according to the formula l e : = =24.6%.

[0118] (4) Use hand pump II 33 to provide 18.69 MPa back pressure for back pressure valve II 30, and use displacement pump 5 to inject CO2 at a pressure of 22 MPa. Record the outlet flow rate as 2.5468 cm 3 / s.

[0119] The permeability of the fracture core at the end of ordinary CO2 huff-and-puff wells is calculated according to the following formula K cf : ; In the formula, K cf is the permeability of the fracture core at the end of the ordinary CO2 huff-and-puff well, mD; P 0 is atmospheric pressure, 0.101MPa; Q 0 is the flow rate under atmospheric pressure, which is measured to be 2.5468cm 3 / s; m g is the gas viscosity, which is 0.02 mPa·s; P 入口 The inlet pressure of core II at this time is set to 22 MPa; P 出口 The outlet pressure of core II at this time is set to 18.69 MPa.

[0120] The permeability of core II after depletion development was calculated. K cf It is 0.00765mD.

[0121] Calculate the permeability increase level of common CO2 stimulation fractures according to the formulaL f : = =69.62%.

[0122] (5) Gradually reduce the pressure of displacement pump 5 and hand pump II 33 to 15 MPa (current reservoir production pressure) and stabilize it for a period of time to prepare for the thermal assisted CO2 huff-and-puff experiment on core II.

[0123] S4. Conduct heat-assisted CO2 huff-and-puff simulation test on core II: (1) Use displacement pump 5 to inject CO2 into core II at a constant pressure of 22 MPa. When the inlet pressure and outlet pressure of the core are stable, close the two-way valve VIII 23, open the thermostat 36 to heat the CO2 in the core holder 26 to 80°C, monitor and record the inlet pressure and outlet pressure of core II during the soaking process. The pressure curve is shown in Figure 2. Figure 3 shown.

[0124] After the soaking is completed, the inlet pressure of core II P Hin and outlet pressure P Hout The average pore pressure after heat-assisted CO2 huff and puff is calculated according to the formula: P Hpa : .

[0125] The average pore pressure after heat-assisted CO2 huff and puff well soaking was calculated. P Hpa It is 27.12MPa.

[0126] Then, the energy efficiency of thermally assisted CO2 throughput is calculated according to the formula: l He : = =80.8%.

[0127] (2) The CO2 in the CO2 intermediate container 9 is heated to 80°C. The back pressure value of the back pressure valve II 30 is set to 27.12 MPa using the hand pump II 33. The two-way valve VIII 23 and the two-way valve IX 29 are opened. The displacement pump 5 injects CO2 at a constant pressure of 30 MPa. The CO2 flow rate under atmospheric pressure is measured by the gas flow meter 31 and is 35.77 cm 3 / s.

[0128] The permeability of the fracture core at the end of thermal-assisted CO2 huff-and-puff well was calculated according to the following formula K Hf: ; In the formula, K Hf is the permeability of the fracture core at the end of the heat-assisted CO2 huff-and-puff well, mD; P 0 is atmospheric pressure, 0.101MPa; Q 0 is the flow rate under atmospheric pressure, which is measured to be 35.77 cm 3 / s; m g is the gas viscosity, which is 0.02 mPa·s; P 入口 The inlet pressure of core II at this time is set to 30 MPa; P 出口 The outlet pressure of core II at this time is set to 27.12 MPa The permeability of core II at the end of thermally assisted CO2 huff and puff was calculated. K Hf It is 0.0879mD.

[0129] Calculate the permeability enhancement level of thermally assisted CO2 stimulation fractures according to the formula L Hf : = =1849%.

[0130] Therefore, for core II, the permeability enhancement level of thermally assisted CO2 stimulation fractures is L Hf It is 1849%, that is, the permeability of core II increased by 18.49 times.

[0131] (3) Close the thermostat 36 and the CO2 intermediate container 9 and allow them to cool naturally to room temperature. Gradually reduce the pressure of the back pressure valve II 30 to atmospheric pressure at a gradient of 5 MPa. Use the vent valve 22 to release the pressure at the front end of the core holder 26 to complete the energy enhancement and permeability enhancement test of the core II.

[0132] S5. Compare the crack opening of heat-assisted CO2 huff and puff and ordinary CO2 huff and puff: It is assumed that the increase in the permeability of core II during the heat-assisted CO2 huff-and-puff process is mainly due to the increase in fracture aperture caused by the thermal expansion of CO2.

[0133] The thermal assisted CO2 stimulation fracture aperture improvement index was calculated according to the following formula: E f : ; In the formula, P pa =18.69MPa;Z Hc =0.58; T Hc =353.15K; Z c =0.35; T c =298.15; P Hpa =27.12MPa.

[0134] Substitute the calculated core II thermal assisted CO2 fracture aperture enhancement index into E f is 1.353.

[0135] Therefore, compared with the ordinary CO2 huff and puff, the fracture aperture of the core II thermal-assisted CO2 huff and puff process is 1.353 times that of the ordinary CO2 huff and puff process.

Claims

1. An experimental method for evaluating the effect of heat-assisted carbon dioxide huff and puff on energy and permeability enhancement after shale oil reservoir fracturing, characterized in that: The following steps are involved: S1. Preparation of shale core samples: Firstly, two shale cores from the same geological reservoir were selected, and after cleaning and drying, the basic physical properties of the two shale cores were measured, including the original permeability of the shale cores. Then, one of the shale cores is selected to be artificially fractured to obtain a fracture core; and the original permeability of the obtained fracture core is corrected to obtain the original permeability of the fracture core; Another shale core is used as a matrix core, wherein the original permeability of the matrix core is the original permeability of the shale core in the basic physical property parameters; S2. Conduct heat-assisted CO2 huff-and-puff simulation test on matrix core samples and fracture core samples respectively: Thermally assisted CO2 huff and puff simulation test on matrix core samples: 1) After the matrix core is placed in a reactor and vacuumed, the matrix core is treated with saturated water-phase fracturing fluid; 2) CO2 is injected into the reactor, and the matrix core saturated with water-phase fracturing fluid interacts with CO2 under the set experimental temperature and pressure conditions, and the action time is set to the experimental soaking time; 3) After the matrix core reaction time is over, turn off the heating, wait for the reactor to cool to room temperature, release the pressure, take out the matrix core and dry it; 4) After the dried matrix core is cooled to room temperature, the permeability of the matrix core after heat-assisted CO2 huff and puff is measured using the displacement method; 5) Calculate the matrix permeability level of heat-assisted CO2 absorption and exhalation according to the following formula: ； In the formula, L m is the matrix permeability level of heat-assisted CO2 injection, %; K ma is the permeability of the matrix core after CO2 action at a certain temperature, mD; K 1 is the original permeability of the matrix core, mD; Thermally assisted CO2 huff and puff simulation test on fracture core samples: 1) First, the fractured core is vacuumed to saturate the formation with simulated oil; then, CO2 is injected into the fractured core until the CO2 is completely diffused into the fractures of the core; 2) Increase the CO2 inlet pressure and confining pressure step by step, and maintain the pressure difference between the CO2 inlet pressure and the confining pressure until the CO2 inlet pressure increases to the reservoir production pressure, then keep the CO2 inlet pressure constant, and continue to increase the confining pressure to the original overburden pressure of the reservoir; 3) After CO2 gas breakthrough, the permeability of the fractured rock after core depletion development is determined using the displacement method; 4) Calculate the damage index of the depleted development fracture permeability after fracture core fracturing according to the following formula: ； In the formula, E i is the fracture core permeability damage index, dimensionless; K f is the original permeability of the fracture core, mD; K fa is the permeability after fracture core failure development, mD; 5) Evaluate the energy enhancement efficiency of heat-assisted CO2 huff and puff and the permeability enhancement effect on artificial fractures: a. Inject a certain amount of CO2 into the fracture core at constant pressure; b. After the inlet pressure and outlet pressure of the fracture core are stable, heat it to a certain temperature, soak the well, and monitor and record the inlet pressure and outlet pressure of the fracture core during the soaking process; c. After the well is soaked, the average pore pressure after the heat-assisted CO2 huff-and-puff soak is calculated according to the following formula: ； In the formula, P Hpa is the average pore pressure after heat-assisted CO2 huff-and-puff wellbore, MPa; P Hin is the inlet pressure of the fracture core at the end of the heat-assisted CO2 huff-and-puff well, MPa; P Hout The outlet pressure of the fractured core at the end of heat-assisted CO2 huff-and-puff wellbore, MPa; d. Taking the average pore pressure after well soaking as the outlet pressure of the fracture core, inject CO2, monitor and record the pressure difference at both ends and the CO2 flow rate at the outlet, and calculate the permeability of the fracture core at the end of the heat-assisted CO2 huff-and-puff well soaking; e. Calculate the energy efficiency of thermally assisted CO2 throughput according to the following formula: ； In the formula, P o is the current reservoir production pressure, MPa; λ He The efficiency of heat-assisted CO2 throughput, % P Hpa is the average pore pressure after heat-assisted CO2 huff-and-puff wellbore, MPa; f. Calculate the permeability enhancement level of thermally assisted CO2 stimulation fractures according to the following formula: ； In the formula, L Hf is the fracture permeability enhancement level of heat-assisted CO2 huff and puff, %; K Hf is the permeability of the fracture core at the end of the heat-assisted CO2 huff-and-puff well, mD; K fa Permeability after fracture core failure development, mD.

2. The experimental method for evaluating the effect of heat-assisted carbon dioxide huff and puff on energy and permeability enhancement after shale oil reservoir fracturing according to claim 1, characterized in that: It also includes the evaluation of the improvement level of fracture aperture by heat-assisted CO2 huff and puff. The specific operations are as follows: The first step is to simulate the common CO2 huff and puff for the fracture core sample and evaluate its energy enhancement efficiency and the permeability enhancement effect on the artificial fracture: a. First, a certain amount of CO2 is injected into the fracture core at a constant pressure at room temperature. The injection amount of CO2 is the same as the CO2 injection amount used for soaking the well when performing the heat-assisted CO2 huff-and-puff simulation on the fracture core sample; Then, the well is soaked, and the inlet pressure and outlet pressure of the fracture core are monitored and recorded during the soaking process; b. After the well is soaked, calculate the average pore pressure after ordinary CO2 huff-and-puff soaking according to the following formula: ； In the formula, P pa is the average pore pressure after ordinary CO2 huff-and-puff well soaking, MPa; P in is the inlet pressure of the fracture core at the end of ordinary CO2 huff-and-puff well soaking, MPa; P out The outlet pressure of the fractured core at the end of ordinary CO2 huff-and-puff well soaking, MPa; c. Taking the average pore pressure after well soaking as the outlet pressure of the fracture core, inject CO2, monitor and record the pressure difference at both ends and the CO2 flow rate at the outlet, and calculate the permeability of the fracture core after ordinary CO2 huff-and-puff well soaking; d. Calculate the energy efficiency of ordinary CO2 throughput according to the following formula: ； In the formula, λ e The energy efficiency of ordinary CO2 throughput is %; P pa is the average pore pressure after ordinary CO2 huff-and-puff well soaking, MPa; P o is the current reservoir production pressure, MPa; e. Calculate the permeability increase level of common CO2 stimulation fractures according to the following formula: ； In the formula, L f is the permeability increase level of common CO2 stimulation fractures, %; K cf is the permeability of the fracture core at the end of the ordinary CO2 huff-and-puff well, mD; K fa Permeability after fracture core failure development, mD; The second step is to compare the fracture opening of heat-assisted CO2 huff and puff and ordinary CO2 huff and puff: In the process of heat-assisted CO2 huff and puff, if the matrix rock mainly relies on the dissolution effect of CO2 and fracturing fluid to increase permeability, the permeability increase of the fracture core is mainly caused by the increase in fracture aperture due to the thermal expansion of CO2. The heat-assisted CO2 huff and puff fracture aperture improvement index is calculated according to the following formula: ； In the formula, E f is the thermal-assisted CO2 stimulation fracture aperture enhancement index, dimensionless; P pa is the average pore pressure after ordinary CO2 huff-and-puff well soaking, MPa; Z Hc is the CO2 compression factor under the temperature and pressure conditions of heat-assisted CO2 throughput, dimensionless; T Hc is the temperature of the heat-assisted CO2 huff-and-puff experiment, K; Z c is the CO2 compression factor under normal CO2 throughput temperature and pressure conditions, dimensionless; T c is the normal CO2 throughput test temperature, K; P Hpa is the average pore pressure after heat-assisted CO2 huff-and-puff soaking, MPa.

3. The experimental method for evaluating the effect of heat-assisted carbon dioxide huff and puff on energy and permeability enhancement after shale oil reservoir fracturing according to claim 1, characterized in that: The basic physical property parameters of the shale core in step S1 also include length, diameter, dry weight, porosity and core permeability.

4. The experimental method for evaluating the effect of heat-assisted carbon dioxide huff and puff on energy and permeability enhancement after shale oil reservoir fracturing according to claim 3, characterized in that: The porosity of the shale core is measured by the dodecane saturation method, and the porosity is calculated according to the following formula: ; In the formula, φ 1 is the porosity of shale core, %; g s is the wet weight of shale core saturated with dodecane, g; g d is the dry weight of shale core, g; ρ D is the density of dodecane, g / cm 3 ; d is the shale core diameter, cm; l is the length of shale core, cm.

5. The experimental method for evaluating the effect of heat-assisted carbon dioxide huff-and-puff energy and permeability enhancement after shale oil reservoir fracturing according to claim 1 or 2, characterized in that: The permeability corresponding to the core is calculated according to the following formula: ； In the formula, K is the shale core permeability, D; P 0 is atmospheric pressure, 10 -1 MPa; Q 0 is the flow rate under atmospheric pressure, cm 3 / s; μ g is the gas viscosity, mPa·s; P 入口 is the inlet pressure of the core, 10 -1 MPa; P 出口 is the outlet pressure of the core, 10 -1 MPa.

6. The experimental method for evaluating the effect of heat-assisted carbon dioxide huff and puff on energy and permeability enhancement after shale oil reservoir fracturing according to claim 1, characterized in that: The fractured core in step S1 is artificially fractured by wire cutting or Babbitt splitting.

7. A device for evaluating the experimental method of heat-assisted carbon dioxide huff-and-puff energy and permeability enhancement after shale oil reservoir fracturing as claimed in claim 1 or 2, characterized in that: It includes a CO2 gas cylinder, a CO2 intermediate container, an aqueous fracturing fluid intermediate container, a reactor, a drying box and a core holder; wherein the CO2 intermediate container and the reactor are both provided with a heating device; The CO2 gas cylinder is connected to the gas booster pump through a pipeline, and a two-way valve No. 1 is arranged on the outlet pipeline of the gas booster pump, and the two-way valve No. 1 is connected to the three-way pipeline No. 1; the three-way No. 1 is connected to a four-way through a pipeline; A two-way valve IV is provided on the pipeline at the top of the CO2 intermediate container, and the two-way valve IV is connected to the three-way valve I through a pipeline; A two-way valve No. II is provided on the pipeline at the bottom of the CO2 intermediate container, and the two-way valve No. II is connected to the displacement pump pipeline through a three-way valve No. II; A two-way valve No. V is provided on the pipeline at the top of the intermediate container of the aqueous phase fracturing fluid, and the two-way valve No. V is connected to the four-way pipeline; A two-way valve No. III is provided on the pipeline at the bottom of the intermediate container of the aqueous phase fracturing fluid, and the two-way valve No. III is connected to the displacement pump pipeline through a three-way valve No. II; A two-way valve No. VI is provided on the pipeline at the top of the reactor, and the two-way valve No. VI is connected to the four-way pipeline; A tee No. IV is provided on the pipeline at the bottom of the reactor, one of the interfaces of the tee No. IV is connected to the pipeline of the back pressure valve No. I via a two-way valve No. VII; the back pressure valve No. I is connected to the pipeline of the hand pump No. I, and a pressure gauge No. I is provided at the outlet end of the hand pump No. I; the other interface of the tee No. IV is connected to a vacuum pump pipeline via a two-way valve No. X; A two-way valve No. VIII is provided on the pipeline at the inlet end of the core holder, wherein a pressure gauge No. II is provided between the two-way valve No. VIII and the inlet end of the core holder; the two-way valve No. VIII is connected to the four-way pipeline via a three-way valve No. III, and a vent valve is connected to one of the interfaces of the three-way valve No. III; A two-way valve No. IX is provided on the pipeline at the outlet end of the core holder, wherein a pressure gauge No. III is provided between the two-way valve No. IX and the outlet end of the core holder; the two-way valve No. IX is connected to the back pressure valve No. II through a pipeline; the top of the back pressure valve No. II is connected to a gas flow meter through a pipeline, and one side of the back pressure valve No. II is connected to a hand pump No. II through a pipeline, and a pressure gauge No. IV is provided at the outlet end of the hand pump No. II; One side of the core holder is connected to a hand pump III through a pipeline, and a pressure gauge V is provided at the outlet end of the hand pump III.

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