An experimental method and device for evaluating the effect of enhancing energy and permeability by thermal-assisted carbon dioxide huff and puff after fracturing in shale reservoirs

Abstract

The present 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 enhancement and permeability enhancement effects of thermal-assisted carbon dioxide huff and puff after fracturing in shale reservoirs. The experimental method includes the following steps: S1. Preparation of shale core samples: Select two shale cores from the same geological reservoir, one as the fractured core and the other as the matrix core; S2. Thermal-assisted CO2 huff and puff simulation experiment tests for the matrix core sample; Thermal-assisted CO2 huff and puff simulation experiment tests for the fractured core sample; Evaluate the energy enhancement efficiency of thermal-assisted CO2 huff and puff and the permeability enhancement effect on artificial fractures. This experimental method overcomes the limitations of the prior art in evaluating the energy enhancement and permeability enhancement effects of thermal-assisted supercritical CO2 on shale reservoirs, and can comprehensively and systematically evaluate the energy enhancement and permeability enhancement effects of CO2 on shale reservoirs during the thermal-assisted production process.

Description

Technical Field

[0001] The present invention belongs to the technical field of oil and gas field development engineering, and particularly relates to an experimental method and device for evaluating the energy enhancement and permeability enhancement effects of thermal-assisted carbon dioxide huff and puff after fracturing of shale reservoirs. Background Technique

[0002] At present, the development of shale reservoirs faces challenges such as low permeability, low porosity, and strong heterogeneity. The applicability of conventional enhanced oil recovery methods such as water flooding and polymer flooding in shale reservoirs is relatively low. The CO2 huff and puff technology has received extensive attention because it can enhance the fluidity of oil and gas and improve the oil recovery rate. Among them, the thermal-assisted CO2 huff and puff technology is an effective energy enhancement and permeability enhancement method for low-permeability shale reservoirs. By combining the thermal effect, it further strengthens the CO2 diffusion ability, reduces the viscosity of crude oil, and enhances the oil washing efficiency and energy enhancement effect of CO2. Therefore, this technology has important application potential in the energy enhancement development of shale reservoirs.

[0003] In experimental research, most current studies use CO2 huff and puff experiments under room temperature conditions to evaluate the change of reservoir permeability and production enhancement effect. In addition, some studies use high-temperature and high-pressure reactors or nuclear magnetic resonance and other means 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 - soaking stage - oil production stage, and do not involve the influence of temperature change on reservoir physical property 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 energy enhancement effect of CO2 huff and puff. Therefore, there is currently a lack of a systematic experimental evaluation method for the energy enhancement and permeability enhancement effects of CO2 huff and puff after fracturing of shale reservoirs.

[0005] In summary, it can be seen that currently, in the process of enhancing production by heat and mass transfer, there is a lack of effective experimental methods and experimental devices for systematically and comprehensively evaluating the energy enhancement and permeability enhancement effects of CO2 huff and puff. Summary of the Invention

[0006] The purpose of the present invention is to propose an experimental method and device for evaluating the energy enhancement and permeability enhancement effects of thermal-assisted carbon dioxide huff and puff after fracturing of shale reservoirs, which is used to study the energy enhancement and permeability enhancement mechanism of thermal-assisted supercritical CO2 for developing shale reservoirs. This experimental method overcomes the limitations of the prior art in evaluating the energy enhancement and permeability enhancement effects of thermal-assisted supercritical CO2 on shale reservoirs, and can comprehensively and systematically evaluate the energy enhancement and permeability enhancement effects of CO2 on shale reservoirs in the process of thermal-assisted production enhancement.

[0007] In the experimental method of the present invention, the increase in the permeability of the shale matrix by the CO2 - fracturing fluid - rock under the action of heat and mass transfer and the influence of the energy increase on the diversion capacity of the artificial fractures in the shale are comprehensively considered.

[0008] The specific technical solution is as follows:

[0009] An experimental method for evaluating the effect of heat - assisted carbon dioxide huff and puff on energy and permeability increase after fracturing in a shale reservoir, which comprises the following steps:

[0010] S1. Preparation of shale core samples:

[0011] First, select two shale cores from the same geological reservoir. After cleaning and drying, measure the basic physical properties of the two shale cores, including the original permeability of the shale cores. Select an organic solvent to clean the residual oil in the cores.

[0012] The permeability mentioned is the gas - measured permeability, which can be measured by the displacement method. If there are few internal micro - fractures in the selected shale core and the permeability is too small to be measured by the displacement method, the pressure pulse method can be used for measurement. For relevant methods, refer to the literature "Wang C L, Pan L H, 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".

[0013] Then, arbitrarily select one of the shale cores to create artificial fractures to obtain a fractured core; and correct the original permeability of the obtained fractured core to obtain the original permeability of the fractured core.

[0014] The other shale core serves as the matrix core, and the original permeability of the matrix core is the original permeability of the shale core in the basic physical properties mentioned above.

[0015] S2. Conduct heat - assisted CO2 huff and puff simulation experimental tests on the matrix core sample and the fractured core sample respectively:

[0016] Heat - assisted CO2 huff and puff simulation experimental test for the matrix core sample:

[0017] 1) After evacuating the matrix core in a reaction kettle, conduct the treatment of saturating the matrix core with an aqueous fracturing fluid.

[0018] 2) Inject CO2 into the reactor. Under the set experimental temperature and pressure conditions, the matrix core saturated with aqueous fracturing fluid interacts with CO2, and the interaction time is set as the soaking time of the experiment.

[0019] 3) After the interaction time of the matrix core ends, turn off the heating. Wait for the reactor to cool to room temperature, relieve the pressure, take out the matrix core and dry it.

[0020] 4) After the dried matrix core cools to room temperature, use the displacement method to measure the permeability of the matrix core after thermal-assisted CO2 huff and puff.

[0021] 5) Calculate the enhanced permeability level of the matrix by thermal-assisted CO2 huff and puff according to the following formula:

[0022] ;

[0023] In the formula, L m is the enhanced permeability level of the matrix by thermal-assisted CO2 huff and puff, %; K ma is the permeability of the matrix core after the action of CO2 at a certain temperature, mD; K 1 is the original permeability of the matrix core, mD.

[0024] Thermal-assisted CO2 huff and puff simulation experiment test for fractured core samples:

[0025] 1) First, evacuate and saturate the fractured core with formation simulated oil; then, inject CO2 into the fractured core until the CO2 is completely diffused into the core fractures.

[0026] During the CO2 injection process, the initial confining pressure is set as the confining pressure when measuring the original permeability of the fractured core in step S1. Subsequently, increase the inlet pressure of the core to make it equal to the inlet pressure when measuring the gas permeability. After gas appears at the outlet, maintain for a certain time to ensure that the CO2 is completely diffused into the core fractures. At this time, the fluid in the core fractures is CO2, and the fluid in the matrix is formation simulated oil.

[0027] 2) Gradually increase the CO2 inlet pressure and the confining pressure, 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 the confining pressure continues to increase to the original overburden pressure of the reservoir formation.

[0028] 3) After CO2 gas channeling occurs, use the displacement method to measure the permeability of the fractured core after depletion development.

[0029] 4) Calculate the damage index of the permeability of the fractured core after fracturing and depletion development according to the following formula:

[0030] ;

[0031] In the formula, E i is the permeability damage index of the fractured core, dimensionless; K f is the original permeability of the fractured core, mD; K fa is the permeability of the fractured core after depletion development, mD.

[0032] 5) Evaluate the energy enhancement efficiency of thermal-assisted CO2 huff and puff and the permeability enhancement effect on artificial fractures:

[0033] a. Inject a certain amount of CO2 into the fractured core at a constant pressure. Generally speaking, when simulating the CO2 huff and puff process in the field by experiment, the CO2 huff and puff pressure can be 5 - 10 MPa higher than the current reservoir production pressure.

[0034] b. After the inlet pressure and outlet pressure of the fractured core are stable, heat it to a certain temperature, shut in the well, and monitor and record the inlet pressure and outlet pressure of the fractured core during the shut-in process.

[0035] c. After the shut-in is completed, calculate the average pore pressure after thermal-assisted CO2 huff and puff shut-in according to the following formula:

[0036] ;

[0037] In the formula, P Hpa is the average pore pressure after thermal-assisted CO2 huff and puff shut-in, MPa; P Hin is the inlet pressure of the fractured core at the end of thermal-assisted CO2 huff and puff shut-in, MPa; P Hout is the outlet pressure of the fractured core at the end of thermal-assisted CO2 huff and puff shut-in, MPa.

[0038] d. Take the average pore pressure after shut-in as the outlet pressure of the fractured core, inject CO2, monitor and record the pressure difference at both ends and the CO2 flow rate at the outlet end, and calculate the permeability of the fractured core at the end of thermal-assisted CO2 huff and puff shut-in.

[0039] e. Calculate the energy enhancement efficiency of thermal-assisted CO2 huff and puff according to the following formula:

[0040] ;

[0041] In the formula, P o is the current reservoir production pressure, MPa; λ He is the energy enhancement efficiency of thermal-assisted CO2 huff and puff, %; P Hpais the average pore pressure after soaking during thermal-assisted CO2 huff and puff, MPa.

[0042] f. Calculate the enhanced permeability level of fractures during thermal-assisted CO2 huff and puff according to the following formula:

[0043] ;

[0044] In the formula, L Hf is the enhanced permeability level of fractures during thermal-assisted CO2 huff and puff, %; K Hf is the permeability of the fractured core at the end of soaking during thermal-assisted CO2 huff and puff, mD; K fa is the permeability of the fractured core after depletion development, mD.

[0045] In the present invention, the experimental method for evaluating the energy and permeability enhancement effects of thermal-assisted carbon dioxide huff and puff after fracturing in a shale reservoir further includes evaluating the improvement level of fracture aperture during thermal-assisted CO2 huff and puff. The specific operation is as follows:

[0046] First step, simulate ordinary CO2 huff and puff for the fractured core sample and evaluate its energy enhancement efficiency and permeability enhancement effect on artificial fractures:

[0047] a. First, inject a certain amount of CO2 into the fractured core at a constant pressure at room temperature. The injection amount of this CO2 is the same as the injection amount of CO2 used for soaking during the simulation of thermal-assisted CO2 huff and puff for the fractured core sample;

[0048] Then, soak the well and monitor and record the inlet pressure and outlet pressure of the fractured core during the soaking process.

[0049] b. After the soaking is completed, calculate the average pore pressure after soaking during ordinary CO2 huff and puff according to the following formula:

[0050] ;

[0051] In the formula, P pa is the average pore pressure after soaking during ordinary CO2 huff and puff, MPa; P in is the inlet pressure of the fractured core at the end of soaking during ordinary CO2 huff and puff, MPa; P out is the outlet pressure of the fractured core at the end of soaking during ordinary CO2 huff and puff, MPa.

[0052] c. Take the average pore pressure after soaking as the outlet pressure of the fractured core, inject CO2, monitor and record the pressure difference at both ends and the CO2 flow rate at the outlet end, and calculate the permeability of the fractured core at the end of soaking during ordinary CO2 huff and puff.

[0053] d. Calculate the energy enhancement efficiency of ordinary CO2 huff and puff according to the following formula:

[0054] ;

[0055] In the formula, λ e is the energy enhancement efficiency of ordinary CO2 huff and puff, %; P pa is the average pore pressure after soaking in ordinary CO2 huff and puff, MPa; P o is the current reservoir production pressure, MPa.

[0056] e. Calculate the fracture permeability enhancement level of ordinary CO2 huff and puff according to the following formula:

[0057] ;

[0058] In the formula, L f is the fracture permeability enhancement level of ordinary CO2 huff and puff, %; K cf is the permeability of the fracture core after soaking in ordinary CO2 huff and puff, mD; K fa is the permeability of the fracture core after depletion development, mD.

[0059] The second step is to compare the fracture aperture of thermal-assisted CO2 huff and puff with that of ordinary CO2 huff and puff:

[0060] During the thermal-assisted CO2 huff and puff process, if the matrix rock mainly relies on the dissolution effect of CO2 and fracturing fluid to enhance permeability, and the fracture core permeability enhancement is mainly caused by the increase in fracture aperture due to CO2 thermal expansion, calculate the fracture aperture increase index of thermal-assisted CO2 huff and puff according to the following formula:

[0061] ;

[0062] In the formula, E f is the fracture aperture increase index of thermal-assisted CO2 huff and puff, dimensionless; P pa is the average pore pressure after soaking in ordinary CO2 huff and puff, MPa; Z Hc is the CO2 compressibility factor under the temperature and pressure conditions of thermal-assisted CO2 huff and puff, dimensionless; T Hc is the experimental temperature of thermal-assisted CO2 huff and puff, K; Z c is the CO2 compressibility factor under the temperature and pressure conditions of ordinary CO2 huff and puff, dimensionless; T cis the temperature of the ordinary CO2 huff and puff experiment, K; P Hpa is the average pore pressure after soaking in the thermal-assisted CO2 huff and puff, MPa.

[0063] The above formula for calculating the fracture aperture increase index of thermal-assisted CO2 huff and puff is obtained through the following derivation process:

[0064] First, as described above, during the ordinary CO2 huff and puff and thermal-assisted CO2 huff and puff processes, the amount of CO2 in the fracture core system is equal. Therefore, according to the ideal gas law, the following formula can be obtained:

[0065] ;

[0066] In the formula, V c is the volume of CO2 at the end of soaking in the ordinary CO2 huff and puff, %; Z c is the CO2 compressibility factor under the temperature and pressure conditions of the ordinary CO2 huff and puff, dimensionless; R is the molar gas constant, J / (mol·K); T c is the temperature of the ordinary CO2 huff and puff experiment, K; V Hc is the volume of CO2 at the end of soaking in the thermal-assisted CO2 huff and puff, %; Z Hc is the CO2 compressibility factor under the temperature and pressure conditions of the thermal-assisted CO2 huff and puff, dimensionless; T Hc is the temperature of the thermal-assisted CO2 huff and puff experiment, K.

[0067] Furthermore, it can be deduced that: V Hc and V c The relationship between them is as follows: .

[0068] Assume that during the thermal-assisted CO2 huff and puff process, the matrix rock mainly relies on the dissolution effect of CO2 and fracturing fluid to enhance permeability, and the main reason for the increase in permeability of the fracture core is the increase in fracture aperture caused by the thermal expansion of CO2. Therefore, V Hc and V c The proportionality coefficient between them is defined as the fracture aperture increase index of thermal-assisted CO2, and thus the following can be obtained:

[0069] ;

[0070] In the formula, E fIt is the fracture aperture increase index of thermal-assisted CO2 huff and puff, dimensionless.

[0071] In the present invention, for the experimental method for evaluating the energy and permeability enhancement effects of thermal-assisted carbon dioxide huff and puff after fracturing in a shale reservoir, the basic physical properties of the shale core in step S1 further include length, diameter, dry weight, porosity, and core permeability.

[0072] In the present invention, for the experimental method for evaluating the energy and permeability enhancement effects of thermal-assisted carbon dioxide huff and puff after fracturing in a shale reservoir, the porosity of the shale core is measured by the dodecane saturation method, and the porosity is calculated according to the following formula: ;

[0073] In the formula, φ 1 is the porosity of the shale core, %; g s is the wet weight of the shale core saturated with dodecane, g; g d is the dry weight of the shale core, g; ρ D is the density of dodecane, g / cm 3 ; d is the diameter of the shale core, cm; l is the length of the shale core, cm.

[0074] In the present invention, for the experimental method for evaluating the energy and permeability enhancement effects of thermal-assisted carbon dioxide huff and puff after fracturing in a shale reservoir, the permeability (gas-measured permeability) corresponding to the core is calculated according to the following formula:

[0075] ;

[0076] In the formula, K is the permeability of the shale core, D; P 0 is the 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.

[0077] In the present invention, for the experimental method for evaluating the energy and permeability enhancement effects of thermal-assisted carbon dioxide huff and puff after fracturing in a shale reservoir, the fractured core in step S1 is artificially fractured by wire cutting or Brazilian splitting.

[0078] An apparatus for the experimental method of evaluating the effect of thermal-assisted carbon dioxide huff and puff on enhancing energy and permeability after fracturing in a shale reservoir, which includes a CO2 gas cylinder, a CO2 intermediate container, an aqueous fracturing fluid intermediate container, a reaction kettle, a drying oven and a core holder; wherein, both the CO2 intermediate container and the reaction kettle are provided with heating devices.

[0079] The CO2 gas cylinder is connected to a gas booster pump through a pipeline, and a No. I two-way valve is arranged on the outlet pipeline of the gas booster pump. The No. I two-way valve is connected to a No. I three-way pipeline; the No. I three-way is connected to a four-way through a pipeline.

[0080] A No. IV two-way valve is arranged on the pipeline at the top of the CO2 intermediate container, and the No. IV two-way valve is connected to the No. I three-way through a pipeline.

[0081] A No. II two-way valve is arranged on the pipeline at the bottom of the CO2 intermediate container, and the No. II two-way valve is connected to the displacement pump pipeline through a No. II three-way.

[0082] A No. V two-way valve is arranged on the pipeline at the top of the aqueous fracturing fluid intermediate container, and the No. V two-way valve is connected to the four-way through a pipeline.

[0083] A No. III two-way valve is arranged on the pipeline at the bottom of the aqueous fracturing fluid intermediate container, and the No. III two-way valve is connected to the displacement pump pipeline through a No. II three-way.

[0084] A No. VI two-way valve is arranged on the pipeline at the top of the reaction kettle, and the No. VI two-way valve is connected to the four-way through a pipeline.

[0085] A No. IV three-way is arranged on the pipeline at the bottom of the reaction kettle. One interface of the No. IV three-way is connected to the No. I back pressure valve pipeline through a No. VII two-way valve; the No. I back pressure valve is connected to the No. I hand pump pipeline, and a No. I pressure gauge is arranged at the outlet end of the No. I hand pump; the other interface of the No. IV three-way is connected to a vacuum pump pipeline through a No. X two-way valve.

[0086] A No. VIII two-way valve is arranged on the pipeline at the inlet end of the core holder. Among them, a No. II pressure gauge is arranged between the No. VIII two-way valve and the inlet end of the core holder; the No. VIII two-way valve is connected to the four-way pipeline through a No. III three-way, and a vent valve is connected to one interface of the No. III three-way.

[0087] A No. IX two-way valve is arranged on the pipeline at the outlet end of the core holder. Among them, a No. III pressure gauge is arranged between the No. IX two-way valve and the outlet end of the core holder; the No. IX two-way valve is connected to the No. II back pressure valve through a pipeline; the top of the No. II back pressure valve is connected to a gas flowmeter through a pipeline, and one side of the No. II back pressure valve is connected to the No. II hand pump through a pipeline, and a No. IV pressure gauge is arranged at the outlet end of the No. II hand pump.

[0088] One side of the core holder is connected to a hand pump No. III through a pipeline, and a pressure gauge No. V is provided at the outlet end of the hand pump No. III.

[0089] The beneficial effects of the present invention are as follows: The present invention innovatively designs an experimental method and device for evaluating the energy and permeability enhancement effects of thermal-assisted carbon dioxide huff and puff after fracturing in shale reservoirs. By combining various parameters such as temperature, pressure, and permeability, this method systematically simulates the fluid migration and rock response under the multi-field coupling effect during the thermal-assisted CO2 huff and puff process, comprehensively considering the energy enhancement effect and permeability change after CO2 injection, and can comprehensively evaluate the energy and permeability enhancement effects during the thermal-assisted CO2 huff and puff process, avoiding the limitation of traditional methods to the evaluation of a single factor. At the same time, by simulating the actual production environment of thermal-assisted CO2 huff and puff, factors such as pore pressure and fracture pressure in shale reservoirs are fully considered in the experiment, making the experimental results closer to the actual production situation and better reflecting the synergistic effect of the gas expansion effect and the heat and mass effect.

[0090] Compared with the prior art, the present invention can simulate the in-situ temperature environment of the reservoir during the experimental process. At the same time, by introducing the 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 thermal-assisted CO2 to improve the recovery rate of shale reservoirs. This method and device can not only accurately evaluate the CO2 energy enhancement effect under the heat and mass effect, but also evaluate the improvement amplitude of the thermal CO2 fluid effect on the shale matrix and fracture conductivity, realizing a comprehensive evaluation of the energy and permeability enhancement effects, providing a reliable experimental basis and data support for the thermal-assisted CO2 development of shale reservoirs, and thus facilitating the optimization of the extraction process of shale reservoirs.

[0091] In summary, the experimental method of the present invention has strong scalability and repeatability, can flexibly adjust experimental parameters according to different reservoir conditions, improves the adaptability and reliability of the evaluation experiment, and provides strong support for the efficient development of shale reservoirs. Description of the Drawings

[0092] Figure 1 It is a schematic diagram of an experimental device for evaluating the energy and permeability enhancement effects of thermal-assisted CO2 huff and puff after fracturing in a shale reservoir according to the present invention.

[0093] Figure 2 It is the inlet and outlet pressure curves during the soaking stage of ordinary (25°C) CO2 huff and puff of Core II.

[0094] Figure 3 It is the inlet and outlet pressure curves during the soaking stage of thermal-assisted (80°C) CO2 huff and puff of Core II.

[0095] 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 reaction kettle, 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 No. I, 21 is a three-way valve No. III, 22 is a vent valve, 23 is a two-way valve No. VIII, 24 is a pressure gauge No. II, 25 is a drying oven, 26 is a core holder, 27 is a fractured core sample, 28 is a pressure gauge No. III, 29 is a two-way valve No. IX, 30 is a back pressure valve No. II, 31 is a gas flow meter, 32 is a pressure gauge No. IV, 33 is a hand pump No. II, 34 is a pressure gauge No. V, 35 is a hand pump No. III, 36 is a constant temperature oven, 37 is a three-way valve No. IV, 38 is a two-way valve No. X, 39 is a vacuum pump. Specific implementation mode

[0096] The technical solution of the present invention will be described in detail below with reference to the accompanying drawings.

[0097] Example 1

[0098] A device for the experimental method for evaluating the effect of thermal-assisted CO2 huff and puff on enhancing energy and permeability after fracturing in the shale reservoir described in the present invention includes a CO2 gas cylinder 1, a CO2 intermediate container 9, an aqueous fracturing fluid intermediate container 10, a reaction kettle 16, a drying oven 25 and a core holder 26; among them, both the CO2 intermediate container 9 and the reaction kettle 16 are provided with heating devices.

[0099] The CO2 gas cylinder 1 is connected to the gas booster pump 2 through a pipeline, a two-way valve No. I 3 is arranged on the outlet pipeline of the gas booster pump 2, and the two-way valve No. I 3 is connected to the three-way valve No. I 4 through a pipeline; the three-way valve No. I 4 is connected to a four-way valve 13 through a pipeline.

[0100] A two-way valve No. IV 11 is arranged on the pipeline at the top of the CO2 intermediate container 9, and the two-way valve No. IV 11 is connected to the three-way valve No. I 4 through a pipeline.

[0101] A two-way valve No. II 7 is arranged on the pipeline at the bottom of the CO2 intermediate container 9, and the two-way valve No. II 7 is connected to the displacement pump 5 through the three-way valve No. II 6.

[0102] A two-way valve No. V 12 is arranged on the pipeline at the top of the aqueous fracturing fluid intermediate container 10, and the two-way valve No. V 12 is connected to the four-way valve 13 through a pipeline.

[0103] A two-way valve No. III 8 is provided on the pipeline at the bottom of the intermediate container 10 of the aqueous fracturing fluid. The two-way valve No. III 8 is connected to the pipeline of the displacement pump 5 through a three-way valve No. II 6.

[0104] A two-way valve No. VI 14 is provided on the pipeline at the top of the reactor 16. The two-way valve No. VI 14 is connected to the four-way valve 13 through a pipeline.

[0105] A three-way valve No. IV 37 is provided on the pipeline at the bottom of the reactor 16. One of the interfaces of the three-way valve No. IV 37 is connected to the pipeline of the backpressure valve No. I 18 through a two-way valve No. VII 17; the backpressure valve No. I 18 is connected to the hand pump No. I 20, 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 three-way valve No. IV 37 is connected to the vacuum pump 39 through a two-way valve No. X 38.

[0106] A two-way valve No. VIII 23 is provided on the pipeline at the inlet end of the core holder 26. Among them, a pressure gauge No. II 24 is provided between the two-way valve No. VIII 23 and the inlet end of the core holder 26; the two-way valve No. VIII 23 is connected to the four-way valve 13 through 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.

[0107] A two-way valve No. IX 29 is provided on the pipeline at the outlet end of the core holder 26. Among them, a pressure gauge No. III 28 is provided between the two-way valve No. IX 29 and the outlet end of the core holder 26; the two-way valve No. IX 29 is connected to the backpressure valve No. II 30 through a pipeline; the top of the backpressure valve No. II 30 is connected to a gas flowmeter 31 through a pipeline, and the middle part of the backpressure 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.

[0108] One side of the core holder 26 is connected to a hand pump No. III 35 through a pipeline, and a pressure gauge No. V 34 is provided at the outlet end of the hand pump No. III 35.

[0109] The described core holder 26 is placed in a constant temperature box 36. Among them, the pressure gauge No. II 24, the pressure gauge No. III 28, the two-way valve No. IX 29, the backpressure valve No. II 30, the gas flowmeter 31, the pressure gauge No. IV 32 and the hand pump No. II 33 connected to the core holder 26 are also placed in the constant temperature box 36.

[0110] I. Using the described device to simulate thermal-assisted CO2 huff and puff on the matrix core sample

[0111] 1) Vacuum pumping the matrix core: Place the matrix core sample 15 in the reactor 16, open the two-way valve No. X 38, and use the vacuum pump 39 to vacuum the matrix core sample 15 and the reactor 16.

[0112] Treat the matrix core by saturating it with the aqueous fracturing fluid: After the vacuum pumping is completed, 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 fracturing fluid in the intermediate container 10 of the aqueous fracturing fluid into the reaction kettle 16 at a certain pressure.

[0113] After the matrix core sample 15 is saturated with the fracturing fluid, the fracturing fluid in the reaction kettle 16 can be discharged through the two-way valve No. VII 17 and the backpressure valve No. I 18. At this time, the pressure of the backpressure valve No. I 18 is the atmospheric pressure, and at the same time, close the two-way valve No. III 8 and the two-way valve No. V 12.

[0114] 2) Inject CO2 and soak the well: Open the two-way valve No. I 3, and use the gas booster pump 2 to boost the CO2 in the CO2 gas cylinder 1 into the reaction kettle 16. After the boosting is completed, close the two-way valve No. I 3 and the two-way valve No. VI 14.

[0115] Heat the reaction kettle 16, and set the temperature to the experimental temperature. At the same time, use the hand pump No. I 20 to apply pressure to the backpressure valve No. I 18, and set the pressure of the backpressure valve No. I 18 to the CO2-rock interaction pressure, and its pressure value can be read from the pressure gauge No. I 19.

[0116] Open the two-way valve No. VII 17 to discharge the excess gas generated due to the volume expansion of CO2 caused by the temperature increase. Then start soaking the well to allow the matrix core sample 15 to interact with CO2.

[0117] 3) Take out the matrix core sample and dry it: When the matrix core sample 15 has interacted with CO2, turn off the heating to reduce the temperature of the reaction kettle 16 to room temperature, and then gradually reduce the pressure of the backpressure valve No. I 18 to discharge the gas.

[0118] Place the treated matrix core sample 15 in the drying oven 25 for drying.

[0119] 4) Measure the permeability of the matrix core after thermal-assisted CO2 huff and puff by the displacement method:

[0120] Place the dried matrix core sample 15 in the core holder 26, and use the hand pump No. III 35 to provide the confining pressure, and its pressure value can be read from the pressure gauge No. V 34.

[0121] Open the two-way valve No. I 3 and the two-way valve No. IV 11, use the gas booster pump 2 to inject CO2 into the CO2 intermediate container 9, and then close the two-way valve No. I 3.

[0122] Open the two-way valve No. II 7, the two-way valve No. VIII 23 and the two-way valve No. IX 29, and use the displacement pump 5 to displace CO2 into the core holder 26 at a constant pressure to measure the permeability of the matrix core after the action of CO2 at a certain temperature.

[0123] The inlet pressure and outlet pressure of the matrix core are read by the pressure gauge No. II 24 and the pressure gauge No. III 28 respectively. The gas flow rate under atmospheric pressure can be measured by the gas flowmeter 31. At this time, the pressure of the back pressure valve No. II 30 is set to atmospheric pressure.

[0124] II. Simulating thermal-assisted CO2 huff and puff on the fractured core sample using the device

[0125] 1) Place the fractured core sample 27 saturated with formation-simulating oil in the core holder 26, and use the displacement method to measure the original permeability of the fractured core. This method is the same as the measurement method of the aforementioned matrix core and will not be elaborated here.

[0126] 2) Gradually increase the displacement pressure of the displacement pump 5 and the confining pressure provided by the hand pump No. III 35, and keep the pressure difference between the two equal during this process. Until the displacement pressure of the displacement pump 5 reaches the production pressure of the current 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.

[0127] 3) Use the displacement method to measure the permeability of the fractured core sample 27 after depletion development at this time.

[0128] 4) Shut-in well: Close the two-way valve No. IX 29, adjust the displacement pump 5 to the constant flow injection mode, and inject a certain amount of CO2 into the fractured core sample 27.

[0129] Close the two-way valve No. VIII 23, open the thermostat 36 to heat the CO2 in the core holder 26 to the predetermined temperature, and monitor and record the values of the pressure gauge No. II 24 and the pressure gauge No. III 28 during the shut-in well process.

[0130] Subsequently, heat the CO2 in the CO2 intermediate container 9 so that its temperature is consistent with the temperature of the thermostat 36.

[0131] 5) When the shut-in well of the fractured core sample 27 ends, the hand pump No. II 33 sets the back pressure value of the back pressure valve No. II 30 to the average pore pressure at the end of the shut-in well.

[0132] Open the two-way valve No. VIII 23 and the two-way valve No. IX 29, and the displacement pump 5 injects at a constant pressure with a certain pressure difference. Use the gas flowmeter 31 to measure the CO2 flow rate under atmospheric pressure, and calculate the permeability of the fractured core sample 27 at the end of the thermal-assisted CO2 huff and puff shut-in well at this time.

[0133] Finally, close the incubator 36 and the CO2 intermediate container 9, and let them cool naturally to room temperature. Gradually reduce the pressure of the back-pressure valve No. II 30 to atmospheric pressure. The pressure at the front end of the core holder 26 can be relieved through the vent valve 22.

[0134] Example 2

[0135] The present invention will be further described below through specific application examples:

[0136] According to the experimental method described in the present invention, experiments are carried out using the device (as Figure 1 shown). The specific experimental steps are as follows:

[0137] S1. Preparation of shale core samples:

[0138] (1) The core used in this example is the shale core of the same geological reservoir in the GL block of the Daqing Oilfield. The residual oil in the core is cleaned with a mixed organic solvent (petroleum ether: ethanol = 1:1), and the oil washing time is 15 days. Then the core is dried, the temperature is set at 110 °C, and the time is 1 day. The basic physical properties of the two cores are shown in Table 1 below.

[0139] Table 1 Basic physical properties of the core

[0140]

[0141] The core used as the matrix core sample is named Core I, and the core used as the fractured core sample is named Core II.

[0142] (2) Artificial fractures are made on Core II by wire cutting, and the original permeability of the fractured Core II is corrected by the displacement method. The calculation formula is as follows:

[0143] ;

[0144] In the formula, K f is the original permeability of the fractured core, D; P 0 is the atmospheric pressure, 0.101 MPa; Q 0 is the flow rate under atmospheric pressure, measured as 0.5929 cm 3 / s; μ g is the gas viscosity, 0.02 mPa·s; P 入口 is the inlet pressure of Core II at this time, set at 0.301 MPa; P 出口 is the outlet pressure of Core II at this time, set at 0.101 MPa.

[0145] After calculation, the original permeability of Core II after creating fractures K f is 2.98×10 -3 D, that is, 2.98 mD.

[0146] S2. Conduct a thermal-assisted CO2 huff and puff simulation experiment test on Core I:

[0147] (1) Place Core I in the reactor 16, and use the vacuum pump 39 to evacuate Core I for 1 h.

[0148] 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 in the intermediate container 10 of the aqueous fracturing fluid (formulation composition: pure water + 8% KCl by mass concentration + 1.5‰ thickening agent by volume fraction) into the reactor 16 at a certain pressure and keep the pressure constant for 7 d.

[0149] (2) After Core I is saturated with the aqueous fracturing fluid, discharge the aqueous fracturing fluid through the two-way valve No. VII 17 and the back pressure valve No. I 18.

[0150] Open the two-way valve No. I 3, use the gas booster pump 2 to boost CO2 into the reactor 16, and set the acting pressure to 30 MPa. Set the temperature of the reactor 16 to 80 °C and the acting time to 3 h.

[0151] During this process, set the pressure of the back pressure valve No. I 18 to 30 MPa, open the two-way valve No. VII 17, and discharge the excess gas generated due to the volume expansion of CO2 caused by the temperature rise.

[0152] (3) After Core I acts for 3 h, turn off the heating, reduce the temperature of the reactor 16 to room temperature, relieve the pressure, take it out and place it in the drying oven 25 for drying.

[0153] (4) After Core I cools to room temperature, place Core I in the core holder 26, use the hand pump No. III 35 to provide a confining pressure of 3 MPa, and use the displacement pump 5 to displace CO2 at a constant pressure into the core holder 26 to measure the permeability. And calculate according to the following formula:

[0154] ;

[0155] In the formula, K ma is the permeability of the matrix core after the action of CO2 at a certain temperature, D; P 0 is the atmospheric pressure, 0.101 MPa; Q 0 is the flow rate under atmospheric pressure, measured as 0.02624 cm 3 / s; μg 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, which is set to 0.101 MPa.

[0156] The permeability of Core I after the action of thermal-assisted CO2 is calculated K ma is 0.005276 mD; Combining the data in Table 1, the original permeability of Core I K 1 is 0.00164 mD.

[0157] According to the formula: ; The permeability enhancement level of the matrix core sample Core I by thermal-assisted CO2 huff and puff is calculated L m is 221.70%, that is, the permeability of Core I has increased by 2.217 times.

[0158] S3. Conduct a general CO2 huff and puff simulation experiment test on Core II:

[0159] (1) Evacuate and saturate Core II with dodecane, then place Core II in the core holder 26, and use the gas booster pump 2 to boost the pressure of CO2 into the CO2 intermediate container 9. Use the displacement pump 5 to displace the CO2 in the CO2 intermediate container 9 into the core holder 26 at a certain pressure.

[0160] Gradually increase the displacement pressure and the confining pressure provided by the hand pump No. III 35 for the core holder 26, and keep the pressure difference between the displacement pressure and the confining pressure always equal to 3 MPa until the CO2 displacement pressure reaches the current reservoir production pressure ( P o ) 15 MPa.

[0161] (2) Inject CO2 at a constant pressure of 15 MPa using the displacement pump 5, and then continue to increase the confining pressure of the core holder 26 to 35 MPa (the original overburden pressure of the reservoir formation).

[0162] When CO2 gas channeling occurs, use the displacement method to measure the permeability of Core II after the development of the fractured core failure K fa . Calculate according to the following formula:

[0163] ;

[0164] In the formula, K fa is the permeability of the fractured core after the development of the core failure, D; P0 is the atmospheric pressure, 0.101 MPa; Q 0 is the flow rate under atmospheric pressure, measured as 1.3068 cm 3 / s; μ g is the gas viscosity, which is 0.02 mPa·s; P 入口 is the inlet pressure of Core II at this time, set to 18.5 MPa; P 出口 is the outlet pressure of Core II at this time, set to 15 MPa.

[0165] The permeability of Core II after depletion development is calculated to be K fa 0.00451 mD; combined with the original permeability of Core II measured and calculated in step S1(2) above K f = 2.98 mD, according to the formula: , the damage index of the fracture permeability of Core II after fracturing and depletion development is calculated E i is 0.9985.

[0166] (3) Use the displacement pump 5 to inject CO2 at a constant pressure of 22 MPa into Core II, and the temperature is set to 25 °C. When the inlet pressure and outlet pressure of Core II are stable, close the No. VIII two-way valve 23, monitor and record the values of the No. II pressure gauge 24 and the No. III pressure gauge 28 during the shut-in process, and the pressure curve is as Figure 2 shown.

[0167] During the experiment, the confining pressure needs to be higher than the internal system pressure of the core. Based on considering the pressure resistance value of the actual equipment and the pressure increase amplitude caused by the volume expansion of CO2 after heating, it is initially set to 22 MPa here, which is 7 MPa higher than the current reservoir production pressure.

[0168] After the shut-in is over, the inlet pressure of Core II P in and the outlet pressure P out are 18.78 MPa and 18.60 MPa respectively.

[0169] Calculate the average pore pressure after ordinary CO2 huff and puff shut-in according to the formula P pa : .

[0170] It is calculated that the average pore pressure after ordinary CO2 huff and puff shut-in P pa is 18.69 MPa.

[0171] Then, calculate the energy enhancement efficiency of ordinary CO2 huff and puff according to the formula λ e :

[0172] = =24.6%.

[0173] (4) Use the hand pump No. II 33 to provide a back pressure of 18.69 MPa for the back pressure valve No. II 30, and inject CO2 at a pressure of 22 MPa using the displacement pump 5. Record the flow rate at the outlet end as 2.5468 cm 3 / s.

[0174] Calculate the permeability of the fractured core at the end of the soaking period of ordinary CO2 huff and puff according to the following formula K cf :

[0175] ;

[0176] In the formula, K cf is the permeability of the fractured core at the end of the soaking period of ordinary CO2 huff and puff, mD; P 0 is the atmospheric pressure, 0.101 MPa; Q 0 is the flow rate under atmospheric pressure, measured as 2.5468 cm 3 / s; μ g is the gas viscosity, 0.02 mPa·s; P 入口 is the inlet pressure of core II at this time, set to 22 MPa; P 出口 is the outlet pressure of core II at this time, set to 18.69 MPa.

[0177] After calculation, the permeability of core II after depletion development is K cf 0.00765 mD.

[0178] Calculate the fracture permeability enhancement level of ordinary CO2 huff and puff according to the formula L f :

[0179] = =69.62%.

[0180] (5) Gradually reduce the pressures of the displacement pump 5 and the hand pump No. II 33 to 15 MPa (the current reservoir production pressure) and stabilize for a period of time. To prepare for the simulation of the thermal-assisted CO2 huff and puff experiment on core II.

[0181] S4. Conduct a thermal-assisted CO2 huff and puff simulation experiment test on Core II:

[0182] (1) Inject CO2 into Core II at a constant pressure of 22 MPa using the displacement pump 5. When the inlet pressure and outlet pressure of the core are stable, close the No. VIII two-way valve 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 period, and the pressure curve is as Figure 3 shown.

[0183] After the soaking period, the inlet pressure P Hin and outlet pressure P Hout of Core II are 27.05 MPa and 27.19 MPa respectively. Calculate the average pore pressure after thermal-assisted CO2 huff and puff soaking according to the formula P Hpa : .

[0184] After calculation, the average pore pressure P Hpa after thermal-assisted CO2 huff and puff soaking is 27.12 MPa.

[0185] Then, calculate the energy enhancement efficiency of thermal-assisted CO2 huff and puff according to the formula λ He :

[0186] = = 80.8%.

[0187] (2) Heat the CO2 in the CO2 intermediate container 9 to 80 °C, use the No. II hand pump 33 to set the back pressure value of the No. II back pressure valve 30 to 27.12 MPa, open the No. VIII two-way valve 23 and the No. IX two-way valve 29, and the displacement pump 5 injects CO2 at a constant pressure of 30 MPa. Use the gas flow meter 31 to measure the CO2 flow rate at atmospheric pressure as 35.77 cm 3 / s.

[0188] Calculate the permeability of the fractured core at the end of thermal-assisted CO2 huff and puff soaking according to the following formula K Hf :

[0189] ;

[0190] In the formula, K Hf is the permeability of the fractured core at the end of thermal-assisted CO2 huff and puff soaking, mD; P 0 is the atmospheric pressure, 0.101 MPa; Q0 is the flow rate under atmospheric pressure, measured as 35.77 cm 3 / s; μ g is the gas viscosity, which is 0.02 mPa·s; P 入口 is the inlet pressure of Core II at this time, set to 30 MPa; P 出口 is the outlet pressure of Core II at this time, set to 27.12 MPa

[0191] The permeability of Core II at the end of the soaking period of thermal-assisted CO2 huff and puff is obtained by calculation K Hf is 0.0879 mD.

[0192] Calculate the fracture permeability enhancement level of thermal-assisted CO2 huff and puff according to the formula L Hf :

[0193] = = 1849%.

[0194] Therefore, for Core II, the fracture permeability enhancement level of thermal-assisted CO2 huff and puff L Hf is 1849%, that is, the permeability of Core II has increased by 18.49 times.

[0195] (3) Close the thermostatic chamber 36 and the CO2 intermediate container 9, and let it cool naturally to room temperature. Gradually reduce the pressure of the back pressure valve No. II 30 by 5 MPa to atmospheric pressure. Use the vent valve 22 to release the pressure at the front end of the core holder 26 to complete the experimental test on the energy and permeability enhancement of Core II.

[0196] S5. Compare the fracture aperture of thermal-assisted CO2 huff and puff with that of ordinary CO2 huff and puff:

[0197] Assume that during the thermal-assisted CO2 huff and puff process, the main reason for the increase in the permeability of Core II is the increase in the fracture aperture caused by the thermal expansion of CO2.

[0198] Calculate the fracture aperture increase index of thermal-assisted CO2 huff and puff according to the following formula E f :

[0199] ;

[0200] In the formula, P pa = 18.69 MPa; Z Hc = 0.58; T Hc = 353.15 K;Z c = 0.35; T c = 298.15; P Hpa = 27.12 MPa.

[0201] Substituting into the calculation, the fracture aperture improvement index of Core II in the thermal-assisted CO2 huff and puff process E f is 1.353.

[0202] Therefore, compared with ordinary CO2 huff and puff, the fracture aperture in the thermal-assisted CO2 huff and puff process of Core II is 1.353 times that in 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 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; 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 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; 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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