Method and device for regulating and controlling supercritical state of supercritical carbon dioxide fracturing well bottom fluid

Abstract

The invention relates to the technical field of petroleum and natural gas well completion, and discloses a method and device for regulating and controlling the supercritical state of a supercritical carbon dioxide fracturing well bottom fluid. The method comprises the steps that liquid CO2 fluid in a liquid storage tank is sequentially heated, pressurized through a fracturing pump truck and then injected into a shaft, and the CO2 fluid at an inlet of the shaft reaches the preset temperature; the CO2 fluid at the preset temperature is in a supercritical state when passing through the shaft to reach the shaft bottom; when the temperature of the CO2 fluid at the inlet of the shaft is smaller than the preset temperature, the input power of the heating device is increased; and when the CO2 fluid temperature at the shaft inlet is higher than the preset temperature, the input power of the heating device is reduced. According to the method, the temperature of CO2 fluid near the well bottom in the whole fracturing process is kept about 32 DEG C, the situation that the proppant carrying capacity of supercritical CO2 is reduced due to the too high temperature is avoided, the situation that sedimentation of the proppant is accelerated due to the fact that a large section of supercritical CO2 fluid exists in a shaft is avoided, and meanwhile the cost for heating the low-temperature CO2 fluid on the ground is saved.

Description

Technical Field

[0001] The present invention relates to the technical field of oil and natural gas well completion, and in particular to a method and device for regulating the supercritical state of a supercritical carbon dioxide fracturing bottom hole fluid. Background Art

[0002] The principle of oil and gas well fracturing technology is to artificially apply external energy to underground oil and gas reservoirs in a short period of time to create cracks in the reservoirs, increase the flow channels of oil and gas, increase the output of oil and gas wells, and realize the economic development of oil and gas reservoirs. 2 As a medium for transferring external energy to the reservoir, CO 2 When it flows from the wellhead into the reservoir, it will enter a supercritical state. Compared with using water as a medium for energy transfer, supercritical carbon dioxide has lower surface tension, smaller viscosity and stronger diffusivity, making it easier to penetrate into the pores of the reservoir. Therefore, compared with hydraulic fracturing, supercritical carbon dioxide fracturing can reduce the reservoir fracture pressure, produce more tiny cracks, and form a more complex fracture network. In addition, for reservoirs with high clay mineral content, hydraulic fracturing can easily cause clay expansion, induce blockage of tiny pore throats, and damage the reservoir, while supercritical carbon dioxide will not cause clay mineral expansion. Supercritical carbon dioxide fracturing can also transfer some CO 2 Buried in the stratum, it is a green fracturing method.

[0003] During supercritical carbon dioxide fracturing operations, liquid CO 2 The fluid enters the booster pump from the storage tank, is slightly pressurized, and then transported to the sand mixing tank, where it is fully mixed with proppant and additives (if proppant is not transported during the fracturing stage, this step is omitted), and then is greatly pressurized by the fracturing pump truck and enters the wellbore after passing through the ground manifold. 2 It is a low temperature liquid, CO 2 As it flows to the bottom of the well, it exchanges heat with the formation and its temperature gradually rises. Existing studies have shown that in the early stages of fracturing operations, the CO 2 The temperature can reach or exceed the critical temperature of 31.1°C required for it to enter the supercritical state. 2 The pumping volume of the fluid is large, and after a certain period of time, the heat transfer of the formation around the wellbore is not enough to make the CO at the bottom of the well 2 The temperature reached 31.1°C, which means that the CO 2 It is not supercritical, so it is impossible to give full play to the advantages of supercritical carbon dioxide fracturing. Therefore, certain measures need to be taken to make the bottom CO2 in the whole fracturing process 2 The temperature of the fluid shall not be lower than 31.1°C. Summary of the invention

[0004] In order to solve the above problems, the present invention provides a method and device for controlling the supercritical state of supercritical carbon dioxide fracturing bottom fluid, which can control the supercritical state of the CO2 entering the well on the ground. 2 The fluid is heated to a certain temperature, so that the CO at the bottom of the well is 2 The fluid temperature is not less than 31.1°C, that is, the CO 2 The fluid is always in a supercritical state. The present invention provides the following technical solutions:

[0005] The present invention provides a method for controlling the supercritical state of a supercritical carbon dioxide fracturing bottom hole fluid, the method comprising:

[0006] Liquid CO in the tank 2 The fluid is heated by the heating device and pressurized by the fracturing pump truck before being injected into the wellbore. 2 The fluid temperature reaches the preset temperature;

[0007] At the preset temperature, CO 2 The fluid is in a supercritical state when it passes through the wellbore and reaches the bottom of the well;

[0008] When the wellbore entrance CO 2 When the fluid temperature is lower than the preset temperature, the input power of the heating device is increased;

[0009] When the wellbore entrance CO 2 When the fluid temperature is greater than the preset temperature, the input power of the heating device is reduced.

[0010] Furthermore, the method further comprises:

[0011] Liquid CO in the tank 2 The fluid is heated by the heating device in turn, mixed with proppant and additives in the sand mixing tank, and then pressurized by the fracturing pump truck and injected into the wellbore. 2 The fluid temperature reaches the preset temperature.

[0012] Further, determining the preset temperature includes the following steps:

[0013] Based on the basic data of the target fracturing well, a physical model of the wellbore and reservoir of the target fracturing well is constructed;

[0014] Based on the physical model of the wellbore and reservoir of the target fracturing well, a CO 2 Simulation model of fracturing fluid wellbore flow and heat transfer;

[0015] Based on CO 2 Simulation model of fracturing fluid wellbore flow and heat transfer to determine the bottom hole CO 2 It is the preset temperature corresponding to the supercritical state.

[0016] Furthermore, the basic data of the target fracturing well includes: geometric size data of the wellbore, the tubing in the well, and the cement sheath and the formation and their positional relationship.

[0017] Furthermore, based on the basic data of the target fracturing well, a physical model of the wellbore and reservoir of the target fracturing well is constructed, including:

[0018] Performing grid processing on the physical model of the wellbore and reservoir of the target fracturing well;

[0019] Based on CO 2 The physical property data of the fluid is used to determine the fluid boundary constraints and CO in the physical model of the target fracturing wellbore and reservoir. 2 The governing equations for fluid flow and heat transfer in the wellbore;

[0020] Based on the physical model of the wellbore and reservoir after gridding, fluid boundary constraints, and CO 2 The flow and heat transfer control equations of the fluid in the wellbore are used to construct the CO 2 Simulation model of fracturing fluid wellbore flow and heat transfer.

[0021] Furthermore, CO 2 The physical properties of the fluid include: density, viscosity, thermal conductivity, and specific heat capacity under temperature and pressure conditions.

[0022] Furthermore, the CO 2 The governing equations for fluid flow and heat transfer in the wellbore include:

[0023] Fluid CO in the central tube during heat extraction during fracturing 2 Heat transfer equation, energy equation in the heat exchange process between annular fluid and surrounding medium, and heat transfer equation within the formation.

[0024] Furthermore, the fluid CO in the central tube during the heat extraction process during fracturing 2 The heat transfer equation is:

[0025]

[0026] In the formula, ρ f1 is the density of the fluid in the center tube; A c1 is the cross-sectional area of ​​the flow channel in the center tube; C f1 is the specific heat capacity of the fluid in the central tube; T f1 is the fluid temperature in the center tube, is the derivative of the fluid temperature in the central tube; t is the fluid flow time, is the derivative with respect to time; Q 热对流1 is the heat convection of the fluid in the central tube; Q 热传导1 is the heat conduction of the fluid in the central tube; Q 摩擦热1is the friction heat between the fluid in the center tube and the tube wall; Q 1 is the heat exchange between the fluid in the center tube and the fluid in the annulus;

[0027]

[0028]

[0029]

[0030]

[0031] In the formula, u f1 is the flow velocity of the fluid in the central tube; is the divergence, is the divergence of the fluid temperature in the central tube; f1 is the thermal conductivity of the fluid in the central tube; f D1 is the Darcy friction factor of the fluid flowing in the center tube; d p1 is the hydraulic diameter of the center pipe; T f2 is the temperature of the fluid in the annulus; R 1 is the thermal resistance between the fluid in the center tube and the fluid in the annulus.

[0032] Furthermore, the energy equation in the heat exchange process between the annular fluid and the surrounding medium is expressed as follows:

[0033]

[0034] In the formula, ρ f2 is the density of the fluid in the annulus; A c2 is the cross-sectional area of ​​the flow channel in the annulus; C f2 is the specific heat capacity of the fluid in the annulus; T f2 is the fluid temperature in the annulus, is the derivative of the fluid temperature in the annulus; t is the fluid flow time, is the derivative with respect to time; Q 热对流2 is the thermal convection of the fluid in the annulus; Q 热传导2 is the heat conduction of the fluid in the annulus; Q 摩擦热2 is the friction heat between the fluid in the annulus and the pipe wall; Q 1 Q is the heat exchange between the fluid in the center tube and the fluid in the annulus; 2 is the heat exchange between the fluid in the annulus and the formation;

[0035]

[0036]

[0037]

[0038]

[0039] In the formula, u f2 is the flow velocity of the fluid in the annulus; is the divergence, is the divergence of the fluid temperature in the annulus; f2 is the thermal conductivity of the fluid in the annulus; f D2 is the Darcy friction factor of the fluid flow in the annulus; d p2 is the hydraulic diameter of the annulus; R 2 is the thermal resistance between the fluid in the annulus and the formation around the well; Ts is the formation temperature around the well.

[0040] Furthermore, the heat transfer equation in the formation is expressed as:

[0041]

[0042] Where, (ρC) eff and λ eff are the equivalent specific heat capacity and equivalent thermal conductivity of the formation respectively; t is the fluid flow time, is the derivative with respect to time; Ts is the formation temperature around the well, is the derivative of the formation temperature around the well, is the divergence of the formation temperature around the well; T f2 is the temperature of the fluid in the annulus; R 2 is the thermal resistance between the fluid in the annulus and the formation around the well;

[0043]

[0044] In the formula, is the porosity of the formation; ρ s is the density of the formation rock; C s is the specific heat capacity of the formation rock; ρ f3 is the density of the formation fluid; C f3 is the specific heat capacity of the formation fluid; s is the thermal conductivity of the formation rock; f3 is the thermal conductivity of the formation fluid.

[0045] Furthermore, based on CO 2 Simulation model of fracturing fluid wellbore flow and heat transfer to determine the bottom hole CO 2 The corresponding CO at the wellbore inlet when the fluid is in a supercritical state 2 Preset temperatures for fluids, including:

[0046] CO 2 Physical parameters, thermal conductivity parameters of wellbore and reservoir, and boundary conditions are input into CO 2The simulation model of fracturing fluid wellbore flow and heat transfer is iteratively solved to obtain the bottom hole CO 2 The corresponding CO at the wellbore inlet when the fluid is in a supercritical state 2 Fluid temperature;

[0047] Bottom-hole CO 2 When the fluid is in a supercritical state, the corresponding CO 2 The fluid temperature is the preset temperature.

[0048] The present invention also provides a device for controlling the supercritical state of supercritical carbon dioxide fracturing bottom fluid, which is used to control the supercritical state of CO2 before injection into the wellbore. 2 The fluid is heated, and the heated CO 2 The fluid is in a supercritical state when it enters the wellbore and reaches the bottom of the well;

[0049] The device comprises a booster pump, a heating device and a fracturing pump truck connected in sequence;

[0050] The booster pump is used to transfer the liquid CO 2 The fluid is pumped and pressurized and then transported to the heating device. It is also used to transfer the CO 2 The fluid is delivered to the fracturing pump truck.

[0051] The heating device is used to convert CO 2 Fluid heating;

[0052] Fracturing pump truck is used to transfer heated CO 2 The fluid is pressurized and injected into the wellbore, where CO 2 The fluid temperature is the preset temperature; the CO2 fluid reaching the preset temperature enters the wellbore and reaches the bottom of the well in a supercritical state;

[0053] The device further comprises a temperature sensor, which is arranged at the outlet of the heating device and at the inlet of the wellbore;

[0054] The temperature sensor is set at the outlet of the heating device to monitor the CO 2 The temperature of the fluid;

[0055] The temperature sensor is set at the entrance of the wellbore to monitor the CO 2 Fluid temperature; where,

[0056] When the wellbore entrance CO 2 When the fluid temperature is lower than the preset temperature, the input power of the heating device is increased;

[0057] When the wellbore entrance CO 2 When the fluid temperature is greater than the preset temperature, the input power of the heating device is reduced.

[0058] Furthermore, the device also includes a sand mixing tank, which is arranged between the heating device and the fracturing pump truck and is used to heat the CO2 heated to the temperature at the wellbore inlet. 2 The fluid is mixed with proppants and additives;

[0059] The fracturing pump truck is also used to receive CO mixed with proppant and additives. 2 fluid, and the CO 2 After the fluid is pressurized, it is injected into the wellbore, and CO 2 The fluid temperature is the preset temperature.

[0060] Technical effects and advantages of the present invention:

[0061] The control method of the present invention can increase the CO 2 The temperature of the fluid entering the well controls the CO near the bottom of the well. 2 The fluid is in a supercritical state throughout the fracturing stage, giving full play to the advantages of supercritical carbon dioxide technology.

[0062] The invention provides a method for injecting CO into a well. 2 The fluid temperature calculation process can solve the CO near the bottom of the well during the entire fracturing process. 2 The temperature of the fluid is maintained at about 32°C, which prevents the supercritical CO from being degraded due to excessive temperature. 2 The ability to carry proppant and avoid the presence of large sections of supercritical CO in the wellbore 2 fluid to accelerate proppant settling and save ground heating low-temperature CO 2 Cost of fluids.

[0063] The low temperature liquid CO of the present invention 2 The heating process can heat low-temperature CO in a relatively low-pressure environment because the heating timing is more appropriate. 2 fluid, improves heat exchange efficiency, reduces energy consumption and device material costs; can avoid CO 2 The fluid can wear or clog the heat exchange pipeline of the heating device, thereby increasing the service life of the heating device; the heating device can be supplied with liquid at a stable and high speed, which fully releases the potential of the heating device, improves the efficiency of a single heating device, and reduces the number of heating devices used and the total floor space.

[0064] The wellhead CO 2 Fluid temperature monitoring and control process, real-time measurement of CO at the outlet of the heating device and at the wellhead 2 Fluid temperature can be automatically controlled by software or manually adjusted to ensure CO 2 The fluid inlet temperature is consistent with the set value based on theoretical calculations.

[0065] Other features and advantages of the present invention will be described in the following description, and partly become obvious from the description, or be understood by implementing the present invention. The purpose and other advantages of the present invention can be realized and obtained by the structures pointed out in the description and the drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0066] Figure 1 It is a flow chart of a method for controlling the supercritical state of a supercritical carbon dioxide fracturing bottom hole fluid provided in an embodiment of the present application;

[0067] Figure 2 The cryogenic liquid CO provided in the embodiment of the present application 2 Schematic diagram of fluid floor heating process;

[0068] Figure 3 A flow chart for determining a preset temperature provided in an embodiment of the present application;

[0069] Figure 4 is an implementation flow chart of the supercritical state control method of bottom hole fluid provided in the embodiment of the present application;

[0070] Figure 5 The CO2 injection method provided in the embodiment of the present application 2 Schematic diagram of the fluid temperature calculation process. DETAILED DESCRIPTION

[0071] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0072] In order to solve the deficiencies of the prior art, the present invention discloses a method for controlling the supercritical state of a supercritical carbon dioxide fracturing bottom fluid, such as Figure 1 As shown, the method includes,

[0073] Liquid CO in the tank 2 The fluid is heated by the heating device and pressurized by the fracturing pump truck before being injected into the wellbore. 2 The fluid temperature reaches the preset temperature;

[0074] At the preset temperature, CO 2 The fluid is in a supercritical state when it enters the wellbore and reaches the bottom of the well;

[0075] When the wellbore entrance CO 2 When the fluid temperature is lower than the preset temperature, the input power of the heating device is increased;

[0076] When the wellbore entrance CO 2 When the fluid temperature is greater than the preset temperature, the input power of the heating device is reduced.

[0077] The basis for selecting 32℃ is: CO 2 The critical temperature and critical pressure of entering the supercritical state are 31.1℃ and 7.38MPa respectively. 2 The prerequisite is that the fluid pressure reaches 7.38MPa. The reason is that the fracture initiation pressure and extension pressure of the fracture reservoir are generally much higher than 7.38MPa. Therefore, it is only necessary to increase the bottom hole CO 2 The temperature of the fluid is maintained at no less than 31.1°C. In order to save low-temperature liquid CO 2 In order to save energy and reduce operating costs, it is more reasonable to set the target at 32°C. In addition, the higher the temperature of the supercritical carbon dioxide fluid, the lower its viscosity, which is less conducive to carrying proppant. Therefore, it is not advisable to excessively increase the viscosity of supercritical carbon dioxide. It is worth noting that it is not advisable to heat a large section of CO2 in the wellbore. 2 Heating the fluid to a supercritical state only requires the CO near the bottom of the well to 2 The fluid enters the supercritical state. 2 The viscosity is higher than that of supercritical CO 2 Therefore, its ability to carry proppant is better than supercritical CO 2 . CO in the wellbore 2 After the fluid changes from liquid to supercritical state, if there is a large section of CO 2 The liquid is in a supercritical state, and the proppant is easy to settle and fall below the fracturing point or accumulate near the fracturing point, which is not conducive to enhancing the conductivity of the fracture. 2 The liquid column length can reduce the CO 2 The temperature of the fluid saves ground heating costs.

[0078] In the present invention, low temperature liquid CO 2 Heating is bottom-hole CO 2 The key step in regulating the supercritical state of fluid. In order to facilitate storage and transportation, the CO used in supercritical carbon dioxide fracturing is 2 The raw material is in a low-temperature liquid state and needs to be heated to the calculated well entry temperature. The booster pump pumps the low-temperature liquid CO in the storage tank. 2 After being pumped and pressurized, it is transported to the heating device, where it reaches the set temperature after sufficient heat exchange. It then enters the sand mixing tank and is fully mixed with the proppant and additives. It is then greatly pressurized by the fracturing pump truck and finally flows through the surface manifold and is injected into the wellbore. If proppant pumping is not required at a certain stage of fracturing, the CO flowing out of the heating device 2The fluid directly enters the fracturing pump truck and enters the wellbore through the ground manifold.

[0079] CO 2 The heating time of the fluid (through the heating device) is between the low-pressure boosting (through the boosting pump) and the proppant and additive mixing (through the sand mixing tank) or the low-pressure boosting (through the boosting pump) and the high-pressure boosting (fracture pump truck). There are several advantages. First, the relatively low-pressure heat exchange can greatly reduce the performance requirements of the heat exchange pipeline in the heating device, such as strength, wall thickness, etc., thereby improving the heat exchange efficiency and reducing energy consumption and device material costs. Second, CO 2 After heating, it is mixed with proppant and additives, which can not only prevent high-velocity solid particles from colliding and wearing the heat exchange pipeline of the heating device, but also prevent solid particles from clogging the heat exchange pipeline, thus extending the service life of the heating device. 2 After being slightly pressurized by a booster pump and then entering the heating device, the liquid supply speed of the heating device can be increased, the potential of the heating device can be fully utilized, the efficiency of a single heating device can be improved, and the number of heating devices used and the total floor space can be reduced.

[0080] The heating method of the heating device can be a single heating method or a combined heating method, including but not limited to electric heating and gas combustion heating.

[0081] Wellhead CO 2 Fluid temperature (second predetermined temperature) monitoring and control is the bottom hole CO 2 An important guarantee for the regulation of supercritical state of fluid. 2 After the fluid flows out of the heating device, it needs to pass through the sand mixing tank, pressure pump truck and ground manifold. 2 The fluid will exchange heat with the external environment, and there will be a difference between its inlet temperature and the outlet temperature of the heating device, so this difference value needs to be monitored at all times. Temperature sensors are installed at the outlet of the heating device and the wellhead, and the temperature is displayed in real time on the heating device display.

[0082] In a specific embodiment of the present invention, cryogenic liquid CO 2 The low-temperature liquid CO is heated on the ground by a heating device. 2 Heat until CO enters the well 2 The fluid temperature is the preset temperature, and the process is as follows Figure 2 The booster pump 22 pumps the low-temperature liquid CO in the liquid storage tank 21 2 After being pumped and pressurized, it is transported to the heating device 23, and after sufficient heat exchange in the heating device 23, it reaches the set temperature, and then enters the sand mixing tank 24 to be fully mixed with the proppant and additives, and then greatly pressurized by the fracturing pump truck 25, and finally flows through the surface manifold and is injected into the wellbore 26. If there is no need to pump proppant at a certain stage of fracturing, the heated CO flowing out of the heating device 232 The fluid directly enters the fracturing pump truck 25 and enters the wellbore 26 through the surface manifold. 2 The state of the fluid after passing through the wellbore 26 and reaching the bottom of the well is a supercritical state.

[0083] In a specific embodiment of the present invention, Figure 3 As shown, determining the preset temperature includes the following steps:

[0084] Step S101: constructing a physical model of the wellbore and reservoir of the target fracturing well based on the basic data of the target fracturing well;

[0085] Step S1O2: Construct a CO2-based physical model of the target fracturing wellbore and reservoir. 2 Simulation model of fracturing fluid wellbore flow and heat transfer;

[0086] Step S103: Based on CO 2 Simulation model of fracturing fluid wellbore flow and heat transfer to determine the bottom hole CO 2 The corresponding CO in the supercritical state 2 The preset temperature of the fluid;

[0087] Step S104: When the temperature at the wellbore inlet is lower than the preset temperature, the input power of the heating device is increased; when the temperature at the wellbore inlet is higher than the preset temperature, the input power of the heating device is reduced.

[0088] In a specific embodiment of the present invention, in step S101: the basic data of the target fracturing well includes: geometric size data of the wellbore, the tubing in the well, and the cement sheath and the formation and their positional relationship.

[0089] In a specific embodiment of the present invention, the specific steps of step S102 are as follows:

[0090] Step S1021: gridding the physical model of the wellbore and reservoir of the target fracturing well;

[0091] Step S1O22: Based on CO 2 The physical property data of the fluid is used to determine the fluid boundary constraints and CO in the physical model of the target fracturing wellbore and reservoir. 2 The flow and heat transfer control equations of the fluid in the wellbore; among them, CO 2 The physical properties of the fluid include: density, viscosity, thermal conductivity, and specific heat capacity under temperature and pressure conditions.

[0092] Step S1023: Based on the physical model of the wellbore and reservoir after gridding, the fluid boundary constraints, and the CO 2 The flow and heat transfer control equations of the fluid in the wellbore are used to construct the CO 2Simulation model of fracturing fluid wellbore flow and heat transfer.

[0093] The fluid boundary constraints include the boundary conditions in the wellbore, the casing annulus and the formation. The boundary conditions in the wellbore include the pressure and displacement of the fluid at the wellhead, the displacement and temperature at the bottom of the well, and the displacement of the wellbore wall. In the embodiment of the present invention, the wellhead CO 2 Fluid displacement and pressure, bottom hole CO 2 The displacement and temperature of the fluid are numerically solved to obtain the required fluid temperature at the wellhead (i.e. the temperature required for heating and regulation) and the pressure of the bottom hole fluid, so as to judge whether the bottom hole fluid has reached the supercritical state (the supercritical state requires CO 2 The temperature of the fluid is not less than 31.1°C and the pressure is not less than 7.38MPa).

[0094] The CO 2 The flow and heat transfer control equations of the fluid in the wellbore include: the fluid CO in the central tube during the heat extraction process during fracturing 2 Heat transfer equation, energy equation in the heat exchange process between annular fluid and surrounding medium, and heat transfer equation within the formation.

[0095] Furthermore, the pipeline flow model is used to characterize the flow process in the wellbore center pipe. The mass conservation equation and momentum equation are as follows:

[0096]

[0097]

[0098] In the formula, A c1 is the cross-sectional area of ​​the flow channel in the central tube; ρ f1 is the density of the fluid in the central tube; t is the flow time of the fluid, is the derivative with respect to time; is the divergence; u f1 is the flow velocity of the fluid in the central tube; p w is the pressure of the fluid in the wellbore; f D1 is the Darcy friction factor of the fluid flowing in the center tube; d p1 is the hydraulic diameter of the center tube; g is the acceleration due to gravity. The second term on the right side of the second equation above is the pressure drop caused by the friction between the fluid and the tube wall, and the third term on the right side is the gravity of the fluid. D1 The table is calculated using the Churchill model:

[0099]

[0100] In the formula, e 1 Re is the surface roughness of the inner wall of the center tube; 1is the Reynolds number of the fluid in the center tube, and the calculation expression is as follows:

[0101]

[0102] Where, μf 1 is the viscosity of the fluid in the center tube.

[0103] Fluid CO in the central tube during heat extraction during fracturing 2 The heat transfer equation is:

[0104]

[0105] In the formula, ρ f1 is the density of the fluid in the central tube, A c1 is the cross-sectional area of ​​the flow channel in the center tube; C f1 is the specific heat capacity of the fluid in the central tube; T f1 is the fluid temperature in the center tube, is the derivative of the fluid temperature in the central tube; t is the fluid flow time, is the derivative with respect to time; Q 热对流1 is the heat convection of the fluid in the central tube; Q 热传导1 is the heat conduction of the fluid in the central tube; Q 摩擦热1 is the friction heat between the fluid in the center tube and the tube wall; Q 1 is the heat exchange between the fluid in the center tube and the fluid in the annulus;

[0106]

[0107]

[0108]

[0109]

[0110] In the formula, u f1 is the flow velocity of the fluid in the central tube; is the divergence, is the divergence of the fluid temperature in the central tube; f1 is the thermal conductivity of the fluid in the central tube; f D1 is the Darcy friction factor of the fluid flowing in the center tube; d p1 is the hydraulic diameter of the center pipe; T f2 is the temperature of the fluid in the annulus; R 1 is the thermal resistance between the fluid in the center tube and the fluid in the annulus; T f2 is the temperature of the fluid in the annulus; R 1 is the thermal resistance between the fluid in the center tube and the fluid in the annulus, and its calculation formula is:

[0111]

[0112] Where, d 1 is the inner diameter of the center tube; d 2 is the outer diameter of the center tube; m is the thermal conductivity of the central tube; h 1 h is the convective heat transfer coefficient between the fluid in the central tube and the central tube wall; 2 is the convective heat transfer coefficient between the annulus fluid and the center tube wall.

[0113] The expression of convective heat transfer coefficient is as follows:

[0114]

[0115]

[0116] Where N uwell1 is the Nusselt number of the fluid in the central tube; N uwell2 is the Nusselt number of the fluid in the annulus; f2 is the thermal conductivity of the fluid in the annulus; d p2 is the hydraulic diameter of the annulus. Under turbulent conditions, the Nusselt number can be calculated using the Gnielinski equation:

[0117]

[0118] or,

[0119]

[0120] In the formula, f D1 is the Darcy friction factor of the fluid flow in the center tube; Re 1 is the Reynolds number of the fluid in the central tube; Pr is the Prandtl number; f D2 is the Darcy friction factor of the fluid flow in the annulus; Re 2 is the Reynolds number of the fluid in the annulus, and the calculation expression is as follows:

[0121]

[0122] In the formula, ρ f2 is the density of the fluid in the annulus; u f2 is the flow velocity of the fluid in the annulus; μ f2 is the viscosity of the fluid in the annulus.

[0123] f D2 The Churchill model is also used for calculation:

[0124]

[0125] In the formula, e2 It is the average value of the surface roughness of the outer wall of the center tube and the inner wall of the casing.

[0126] According to the heat exchange process between the annular space fluid and the surrounding medium, the energy equation in the heat exchange process between the annular space fluid and the surrounding medium is expressed as follows:

[0127]

[0128] In the formula, ρ f2 is the density of the fluid in the annulus; A c2 is the cross-sectional area of ​​the flow channel in the annulus; C f2 is the specific heat capacity of the fluid in the annulus; T f2 is the fluid temperature in the annulus, is the derivative of the fluid temperature in the annulus; t is the fluid flow time, is the derivative with respect to time; Q 热对流2 is the thermal convection of the fluid in the annulus; Q 热传导2 is the heat conduction of the fluid in the annulus; Q 摩擦热2 is the friction heat between the fluid in the annulus and the pipe wall; Q 1 Q is the heat exchange between the fluid in the center tube and the fluid in the annulus; 2 is the heat exchange between the fluid in the annulus and the formation;

[0129]

[0130]

[0131]

[0132]

[0133] In the formula, u f2 is the flow velocity of the fluid in the annulus; is the divergence, is the divergence of the fluid temperature in the annulus; f2 is the thermal conductivity of the fluid in the annulus; f D2 is the Darcy friction factor of the fluid flow in the annulus; d p2 is the hydraulic diameter of the annulus; R 2 is the thermal resistance between the fluid in the annulus and the formation around the well; Ts is the formation temperature around the well.

[0134] According to the law of conservation of energy, the heat transfer equation in the formation can be expressed as:

[0135]

[0136] Where, (ρC) eff and λ effare the equivalent specific heat capacity and equivalent thermal conductivity of the formation respectively; t is the fluid flow time, is the derivative with respect to time; Ts is the formation temperature around the well, is the derivative of the formation temperature around the well, is the divergence of the formation temperature around the well; T f2 is the temperature of the fluid in the annulus; R 2 is the thermal resistance between the fluid in the annulus and the formation around the well;

[0137]

[0138]

[0139] In the formula, is the porosity of the formation; ρ s is the density of the formation rock; C s is the specific heat capacity of the formation rock; ρ f3 is the density of the formation fluid; C f3 is the specific heat capacity of the formation fluid; s is the thermal conductivity of the formation rock; f3 is the thermal conductivity of the formation fluid.

[0140]

[0141] Where, d 3 is the inner diameter of the annulus; d 4 is the outer diameter of the casing; d 5 h is the outer diameter of cement ring; 3 is the convective heat transfer coefficient between the fluid in the annulus and the casing wall, and its value is the same as h 2 Consistent; w is the thermal conductivity of the casing; c is the thermal conductivity of the cement sheath.

[0142] In a specific embodiment of the present invention, the specific steps of step S103 are as follows:

[0143] Step S1031: CO 2 Physical properties, thermal conductivity parameters of wellbore and reservoir are input into CO 2 The simulation model of fracturing fluid wellbore flow and heat transfer is iteratively solved to obtain the CO 2 The temperature of the fluid entering the well; this temperature can be automatically controlled by the ground heating device (according to the displacement and CO required for construction 2 The initial temperature of the cryogenic fluid automatically changes the heat transfer rate). Among them, the calculation of the inlet CO 2 Temperature (CO 2 The boundary conditions or initial conditions required for the calculation of the inlet CO 2Fluid displacement and pressure, bottom hole CO 2 Fluid displacement and temperature, etc.

[0144] Step S1032: Using bottom hole CO 2 The corresponding CO when the fluid is in a supercritical state 2 The temperature at the fluid inlet is the preset temperature. 2 After the fluid needs to reach the temperature, the inlet fluid CO required at the wellhead is obtained through numerical simulation calculation. 2 Therefore, by dynamically adjusting the heating device, the wellhead CO 2 The temperature of the fluid is slightly higher than the safe value. This can ensure that the bottom CO 2 The temperature at the inlet required for the fluid to be in a supercritical state prevents the wellhead temperature from being too high, which would increase costs.

[0145] In a specific embodiment of the present invention, for step 104: when the CO injected into the wellbore is calculated 2 The fluid temperature is lower than CO 2 When the temperature of the fluid itself is 2 The specific steps for heating the fluid to the target temperature are as follows:

[0146] The supercritical state control method of the supercritical carbon dioxide fracturing bottom fluid of the present invention can increase the CO 2 The temperature of the fluid entering the well controls the CO near the bottom of the well. 2 The fluid is in a supercritical state throughout the fracturing stage, giving full play to the supercritical CO 2 The advantages of technology.

[0147] The invention provides a method for injecting CO into a well. 2 The fluid temperature calculation process can solve the CO near the bottom of the well during the entire fracturing process. 2 The temperature of the fluid is maintained at about 32°C, which prevents the supercritical CO from being degraded due to excessive temperature. 2 The ability to carry proppant and avoid the presence of large sections of supercritical CO in the wellbore 2 fluid to accelerate proppant settling and save ground heating low-temperature CO 2 Cost of fluids.

[0148] The low temperature liquid CO of the present invention 2 The heating process can heat low-temperature CO in a relatively low-pressure environment because the heating timing is more appropriate. 2 fluid, improves heat exchange efficiency, reduces energy consumption and device material costs; can avoid CO 2The fluid can wear or clog the heat exchange pipeline of the heating device, thereby increasing the service life of the heating device; the heating device can be supplied with liquid at a stable and high speed, which fully releases the potential of the heating device, improves the efficiency of a single heating device, and reduces the number of heating devices used and the total floor space.

[0149] The wellhead CO 2 Fluid temperature monitoring and control process, real-time measurement of CO at the outlet of the heating device and at the wellhead 2 Fluid temperature can be automatically controlled by software or manually adjusted to ensure CO 2 The fluid inlet temperature is consistent with the set value based on theoretical calculations.

[0150] A device for controlling the supercritical state of the bottom fluid of supercritical carbon dioxide fracturing well is also provided. Figure 4 As shown, the device is used to inject CO 2 The fluid is heated, and the heated CO 2 The state of the fluid after entering the wellbore and reaching the bottom of the well is supercritical;

[0151] The device comprises a booster pump, a heating device and a fracturing pump truck connected in sequence;

[0152] The booster pump is used to transfer the liquid CO 2 The fluid is pumped and pressurized and then transported to the heating device. It is also used to transfer the CO 2 The fluid is delivered to the fracturing pump truck.

[0153] The heating device is used to convert CO 2 The fluid is heated to the wellbore inlet temperature;

[0154] The fracturing pump truck is used to heat the CO2 to the temperature at the wellbore entrance. 2 The fluid is pressurized and injected into the wellbore. CO 2 The fluid temperature is the preset temperature; the CO reaches the preset temperature 2 The fluid is in a supercritical state when it enters the wellbore and reaches the bottom of the well;

[0155] The device further comprises a temperature sensor, which is arranged at the outlet of the heating device and at the inlet of the wellbore;

[0156] The temperature sensor is set at the outlet of the heating device to monitor the CO 2 Whether the temperature of the fluid reaches the temperature at the wellbore entrance;

[0157] The temperature sensor is set at the entrance of the wellbore to monitor CO 2 Whether the temperature of the fluid reaches the preset temperature; wherein,

[0158] When the temperature at the wellbore inlet is lower than the preset temperature, the input power of the heating device is increased;

[0159] When the temperature at the wellbore inlet is greater than the preset temperature, the input power of the heating device is reduced.

[0160] The device also includes a sand mixing tank, which is arranged between the heating device and the fracturing pump truck and is used to heat the CO2 heated to the temperature at the wellbore inlet. 2 The fluid is mixed with proppants and additives;

[0161] The fracturing pump truck is also used to receive CO mixed with proppant and additives. 2 fluid, and the CO 2 After the fluid is pressurized, it is injected into the wellbore, and CO 2 The fluid temperature is the preset temperature.

[0162] The technical solution of the present invention will be further described below in conjunction with specific implementation methods.

[0163] The present invention provides a method for controlling the supercritical state of a bottom-hole fluid in supercritical carbon dioxide fracturing, comprising: 2 Fluid temperature calculation S1, cryogenic liquid CO 2 Heating S2, wellhead CO 2 Fluid temperature monitoring and control S3 and other steps, such as Figure 4 shown.

[0164] CO 2 The fluid temperature calculation step S1 consists of dividing the calculation model S11, establishing the control equation S12, substituting data for solution S13 and optimizing the wellbore temperature S14. Figure 5 As shown. Divide the calculation model S11: According to the basic data of the supercritical carbon dioxide fracturing operation well, establish the wellbore and reservoir model and divide the appropriate grid density; establish the control equation S12: establish CO 2 The governing equations for fluid flow and heat transfer in the wellbore; Substitute the data to solve S13: Substitute CO 2 The required calculation parameters such as physical property parameters, thermal conductivity parameters of wellbore and reservoir, etc., are iteratively solved for the CO 2 Fluid temperature and pressure change with well depth and time; Optimum well entry temperature S14: CO near the bottom of the well during the entire fracturing process 2 The target temperature is 32°C, and the lowest CO inlet temperature is selected. 2 Fluid temperature.

[0165] Cryogenic liquid CO 2 The heating step S2 is to heat the low temperature liquid CO 2Heating to the temperature of the CO2 fluid entering the well calculated by S1, the process is as follows Figure 5 The booster pump 22 pumps the low-temperature liquid CO in the liquid storage tank 21 2 After being pumped and pressurized, it is transported to the heating device 23, and after sufficient heat exchange in the heating device 23, it reaches the set temperature, and then enters the sand mixing tank 24 to be fully mixed with the proppant and additives, and then greatly pressurized by the fracturing pump truck 25, and finally flows through the surface manifold and is injected into the wellbore 26. If there is no need to pump proppant at a certain stage of fracturing, the CO flowing out of the heating device 23 2 The fluid directly enters the fracturing pump truck 25 and enters the wellbore 26 through the surface manifold.

[0166] The heating method of the heating device can be a single heating method or a combined heating method, including but not limited to electric heating and gas combustion heating.

[0167] Wellhead CO 2 Fluid temperature monitoring and control S3 step is used to accurately control wellhead CO 2 The temperature of the fluid. CO 2 After the fluid flows out of the heating device 23, it needs to pass through the sand mixing tank 24 and the pressure pump truck 25. 2 The fluid will exchange heat with the external environment, and there is a difference between the temperature at the wellbore 26 and the temperature at the outlet of the heating device 23. Therefore, this difference value needs to be monitored at all times. Temperature sensors are installed at the outlet of the heating device 23 and the inlet of the wellbore 26, and are displayed in real time on the display of the heating device 23. 2 If the temperature of the fluid at the outlet of the heating device 23 is lower than the temperature at the inlet of the wellbore 26, the input power of the heating device 23 is increased; if CO 2 If the temperature of the fluid at the outlet of the heating device 23 is higher than the temperature at the inlet of the wellbore 26, the input power of the heating device 23 is reduced. This function can be realized by manual operation or automatic control by software.

[0168] The supercritical state control method of the supercritical carbon dioxide fracturing bottom fluid of the present invention can increase the CO 2 The temperature of the fluid entering the well controls the CO near the bottom of the well. 2 The fluid is in a supercritical state throughout the fracturing stage, giving full play to the advantages of supercritical carbon dioxide technology.

[0169] The invention provides a method for injecting CO into a well. 2 The fluid temperature calculation process can solve the CO near the bottom of the well during the entire fracturing process. 2 The temperature of the fluid is maintained at about 32°C, which prevents the supercritical CO from being degraded due to excessive temperature. 2 The ability to carry proppant and avoid the presence of large sections of supercritical CO in the wellbore 2fluid to accelerate proppant settling and save ground heating low-temperature CO 2 Cost of fluids.

[0170] The low temperature liquid CO of the present invention 2 The heating process can heat low-temperature CO in a relatively low-pressure environment because the heating timing is more appropriate. 2 fluid, improves heat exchange efficiency, reduces energy consumption and device material costs; can avoid CO 2 The fluid can wear or clog the heat exchange pipeline of the heating device, thereby increasing the service life of the heating device; the heating device can be supplied with liquid at a stable and high speed, which fully releases the potential of the heating device, improves the efficiency of a single heating device, and reduces the number of heating devices used and the total floor space.

[0171] The wellhead CO 2 Fluid temperature monitoring and control process, real-time measurement of CO at the outlet of the heating device and at the wellhead 2 Fluid temperature can be automatically controlled by software or manually adjusted to ensure CO 2 The fluid inlet temperature is consistent with the set value based on theoretical calculations.

[0172] Finally, it should be noted that the above is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the aforementioned embodiments, it is still possible for those skilled in the art to modify the technical solutions described in the aforementioned embodiments or to make equivalent substitutions for some of the technical features therein. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for regulating the supercritical state of a supercritical carbon dioxide fracturing bottom hole fluid, characterized in that: The method comprises: The liquid CO2 fluid in the storage tank is heated by the heating device and pressurized by the fracturing pump truck before being injected into the wellbore, wherein the temperature of the CO2 fluid at the wellbore inlet reaches the preset temperature; The CO2 fluid at the preset temperature is in a supercritical state when it passes through the wellbore and reaches the bottom of the well; wherein, When the temperature of the CO2 fluid at the wellbore inlet is lower than the preset temperature, the input power of the heating device is increased; when the temperature of the CO2 fluid at the wellbore inlet is higher than the preset temperature, the input power of the heating device is reduced.

2. The method for controlling the supercritical state of supercritical carbon dioxide fracturing bottom hole fluid according to claim 1, characterized in that: The method further comprises: The liquid CO2 fluid in the storage tank is heated by the heating device in turn, mixed with the proppant and additives in the sand mixing tank, and then pressurized by the fracturing pump truck and injected into the wellbore. The temperature of the CO2 fluid at the wellbore inlet reaches the preset temperature.

3. The method for controlling the supercritical state of supercritical carbon dioxide fracturing bottom hole fluid according to claim 1 or 2, characterized in that: Determining the preset temperature includes the following steps: Based on the basic data of the target fracturing well, a physical model of the wellbore and reservoir of the target fracturing well is constructed; Based on the physical model of the target fracturing wellbore and reservoir, a simulation model of CO2 fracturing fluid wellbore flow and heat transfer is constructed; Based on the CO2 fracturing fluid wellbore flow and heat transfer simulation model, the preset temperature corresponding to the supercritical state of CO2 at the bottom of the well is determined.

4. The method for controlling the supercritical state of supercritical carbon dioxide fracturing bottom hole fluid according to claim 3, characterized in that: The basic data of the target fracturing well includes: geometric size data of the wellbore, the tubing in the well, and the cement sheath and the formation and their positional relationship.

5. The method for controlling the supercritical state of supercritical carbon dioxide fracturing bottom hole fluid according to claim 3, characterized in that: Based on the basic data of the target fracturing well, a physical model of the wellbore and reservoir of the target fracturing well is constructed, including: Performing grid processing on the physical model of the wellbore and reservoir of the target fracturing well; Based on the physical property data of CO2 fluid, determine the fluid boundary constraints in the physical model of the wellbore and reservoir of the target fracturing well, as well as the flow and heat transfer control equations of CO2 fluid in the wellbore; Based on the gridded physical model of the wellbore and reservoir, the fluid boundary constraints, and the flow and heat transfer control equations of the CO2 fluid in the wellbore, a simulation model of the wellbore flow and heat transfer of the CO2 fracturing fluid is constructed.

6. The method for controlling the supercritical state of supercritical carbon dioxide fracturing bottom hole fluid according to claim 5, characterized in that: The physical properties of CO2 fluid include: density, viscosity, thermal conductivity, and specific heat capacity under temperature and pressure conditions.

7. The method for controlling the supercritical state of supercritical carbon dioxide fracturing bottom hole fluid according to claim 5, characterized in that: The flow and heat transfer control equations of the CO2 fluid in the wellbore include: equation, and the heat transfer equation within the formation.

8. The method for controlling the supercritical state of supercritical carbon dioxide fracturing bottom hole fluid according to claim 7, characterized in that: The heat transfer equation of CO2 fluid in the central tube during the fracturing heat extraction process is: In the formula, ρ f1 is the density of the fluid in the center tube; A c1 is the cross-sectional area of ​​the flow channel in the center tube; C f1 is the specific heat capacity of the fluid in the central tube; T f1 is the fluid temperature in the center tube, is the derivative of the fluid temperature in the central tube; t is the fluid flow time, is the derivative with respect to time; Q 热对流1 is the heat convection of the fluid in the central tube; Q 热传导1 is the heat conduction of the fluid in the central tube; Q 摩擦热1 is the friction heat between the fluid in the center tube and the tube wall; Q1 is the heat exchange between the fluid in the center tube and the fluid in the annulus; where, In the formula, u f1 is the flow velocity of the fluid in the central tube; is the divergence, is the divergence of the fluid temperature in the central tube; f1 is the thermal conductivity of the fluid in the central tube; f D1 is the Darcy friction factor of the fluid flowing in the center tube; d p1 is the hydraulic diameter of the center pipe; T f2 is the temperature of the fluid in the annulus; R1 is the thermal resistance between the fluid in the center tube and the fluid in the annulus.

9. The method for controlling the supercritical state of supercritical carbon dioxide fracturing bottom hole fluid according to claim 7, characterized in that: The energy equation in the heat exchange process between the annular fluid and the surrounding medium is expressed as follows: In the formula, ρ f2 is the density of the fluid in the annulus; A c2 is the cross-sectional area of ​​the flow channel in the annulus; C f2 is the specific heat capacity of the fluid in the annulus; T f2 is the fluid temperature in the annulus, is the derivative of the fluid temperature in the annulus; t is the fluid flow time, is the derivative with respect to time; Q 热对流2 is the thermal convection of the fluid in the annulus; Q 热传导2 is the heat conduction of the fluid in the annulus; Q 摩擦热2 is the friction heat between the fluid in the annulus and the pipe wall; Q1 is the heat exchange between the fluid in the center pipe and the fluid in the annulus; Q2 is the heat exchange between the fluid in the annulus and the formation; where, In the formula, u f2 is the flow velocity of the fluid in the annulus; is the divergence, is the divergence of the fluid temperature in the annulus; f2 is the thermal conductivity of the fluid in the annulus; f D2 is the Darcy friction factor of the fluid flow in the annulus; d p2 is the hydraulic diameter of the annulus; R2 is the thermal resistance between the fluid in the annulus and the formation around the well; Ts is the formation temperature around the well.

10. The method for controlling the supercritical state of supercritical carbon dioxide fracturing bottom hole fluid according to claim 9, characterized in that: The heat transfer equation in the formation is expressed as: Where, (ρC) eff and λ eff are the equivalent specific heat capacity and equivalent thermal conductivity of the formation respectively; t is the fluid flow time, is the derivative with respect to time; Ts is the formation temperature around the well, is the derivative of the formation temperature around the well, is the divergence of the formation temperature around the well; T f2 is the temperature of the fluid in the annulus; R2 is the thermal resistance between the fluid in the annulus and the formation around the well; where, In the formula, is the porosity of the formation; ρ s is the density of the formation rock; C s is the specific heat capacity of the formation rock; ρ f3 is the density of the formation fluid; C f3 is the specific heat capacity of the formation fluid; s is the thermal conductivity of the formation rock; f3 is the thermal conductivity of the formation fluid.

11. The method for controlling the supercritical state of supercritical carbon dioxide fracturing bottom hole fluid according to claim 3, characterized in that: Based on the CO2 fracturing fluid wellbore flow and heat transfer simulation model, the preset temperature of the CO2 fluid at the wellbore inlet corresponding to the supercritical state of the bottom hole CO2 fluid is determined, including: The physical properties of CO2, thermal conductivity parameters of the wellbore and reservoir, and boundary conditions are input into the CO2 fracturing fluid wellbore flow and heat transfer simulation model for iterative solution to obtain the CO2 fluid temperature at the wellbore inlet corresponding to the supercritical state of the bottom hole CO2 fluid; When the CO2 fluid at the bottom of the well is in a supercritical state, the corresponding CO2 fluid temperature at the wellbore inlet is the preset temperature.

12. A device for controlling the supercritical state of bottom-hole fluid in supercritical carbon dioxide fracturing, characterized in that: The device is used to heat the CO2 fluid before injecting it into the wellbore, and the heated CO2 fluid is in a supercritical state when it enters the wellbore and reaches the bottom of the well; The device comprises a booster pump, a heating device and a fracturing pump truck connected in sequence; The booster pump is used to pump and pressurize the liquid CO2 fluid in the storage tank and then deliver it to the heating device, and is also used to deliver the CO2 fluid flowing out of the heating device to the fracturing pump truck; The heating device is used to heat the CO2 fluid; The fracturing pump truck is used to pressurize the heated CO2 fluid and inject it into the wellbore, wherein the temperature of the CO2 fluid at the wellbore inlet is a preset temperature; the CO2 fluid reaching the preset temperature enters the wellbore and reaches the bottom of the well in a supercritical state; The device further comprises a temperature sensor, which is arranged at the outlet of the heating device and at the inlet of the wellbore; The temperature sensor is arranged at the outlet of the heating device to monitor the temperature of the heated CO2 fluid; The temperature sensor is arranged at the entrance of the wellbore and is used to monitor the temperature of the CO2 fluid at the entrance of the wellbore; wherein, When the temperature of the CO2 fluid at the wellbore inlet is lower than the preset temperature, the input power of the heating device is increased; When the CO2 fluid temperature at the wellbore inlet is greater than the preset temperature, the input power of the heating device is reduced.

13. The device for controlling the supercritical state of supercritical carbon dioxide fracturing bottom hole fluid according to claim 12, characterized in that: The device also includes a sand mixing tank, which is arranged between the heating device and the fracturing pump truck and is used to mix the CO2 fluid heated to the temperature at the wellbore inlet with the proppant and the additive; The fracturing pump truck is also used to receive the CO2 fluid mixed with the proppant and the additive, and inject the CO2 fluid into the wellbore after pressurizing the CO2 fluid. The temperature of the CO2 fluid at the wellbore inlet is a preset temperature.

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