CO2 phase change fracturing evaluation method, device and electronic equipment

Abstract

The present invention discloses CO 2 The present invention relates to a method, device and electronic equipment for evaluating the phase change before fracturing, which belongs to the field of drilling technology for soil or rock. The method includes: determining CO 2 The expected values ​​of the parameters to be achieved by phase change fracturing are calculated using the formula and the preset release diameter, shear thickness and CO 2 The filling pressure is calculated based on the parameter prediction value. If the parameter prediction value meets the parameter expectation value, the preset release diameter, shear thickness and CO 2 The filling pressure of CO 2 Phase change fracturing, otherwise adjust the preset release diameter, shear thickness and CO 2 The filling pressure is adjusted, and the parameter prediction value is recalculated until it meets the parameter expected value. 2 The implementation plan of phase change fracturing technology is more reasonable, reducing blindness in implementation, reducing costs and improving safety; the evaluation results also help to select appropriate equipment and protective measures, as well as determine the scope of phase change fracturing cracks, thereby better guiding experiments and construction.

Description

Technical Field

[0001] The present invention relates to the technical field of soil layer or rock drilling, and in particular to an evaluation method, device and electronic equipment before CO2 phase change fracturing. Background Art

[0002] Compared with traditional CO2 enhanced oil recovery technology, CO2 phase change fracturing technology is an emerging reservoir transformation technology. Injecting CO2 into the reservoir at high pressure and high displacement during the fracturing stage can effectively improve the ability of CO2 to affect the nano-scale pore throats of shale. Relying on the artificial fractures caused by CO2 phase change, the scope of CO2 action can be greatly increased, and the effects of oil recovery and carbon sequestration can be enhanced. However, CO2 phase change fracturing is still an emerging technology, and various experimental explorations are urgently needed, and its equipment and solutions must be optimized and improved in order to achieve field application as soon as possible. At present, due to high risks, strong uncontrollability and difficulty in evaluating the effect, the development and application of CO2 phase change fracturing technology are subject to certain restrictions. Summary of the invention

[0003] In order to solve the problems existing in the prior art, the present invention provides the following technical solutions.

[0004] The first aspect of the present invention provides a method for evaluating CO2 phase change fracturing before fracturing, comprising:

[0005] Determine the expected values ​​of parameters to be achieved by CO2 phase change fracturing, wherein the expected values ​​of parameters include an expected value of phase change cracks, an expected value of phase change peak load, and an expected value of temperature when the phase change load drops to zero;

[0006] The parameter prediction values ​​are calculated using the following formula and the preset release diameter, shear sheet thickness and CO2 filling pressure, and the parameter prediction values ​​include the phase change crack prediction value, the phase change peak load prediction value and the temperature prediction value when the phase change load drops to zero:

[0007] ；

[0008] ；

[0009] ；

[0010] ；

[0011] ；

[0012] ；

[0013] ；

[0014] ；

[0015] in, is the blasting strength; To release the caliber; is the shear sheet thickness; is the predicted value of phase change peak load; The preset filling pressure of CO2; is the predicted value of the initial load of phase change; is the predicted value of the drop time of the phase change load; is the predicted temperature when the phase change load reaches the peak value; is the predicted temperature when the phase change load drops to zero; is the predicted value of phase change crack; is the radius of the prefabricated hole; is the natural base; is the tensile strength; is the stress wave propagation velocity; is Young's modulus; is Poisson’s ratio; is the density;

[0016] The parameter prediction value is compared with the parameter expected value. If the parameter prediction value meets the parameter expected value, CO2 phase change fracturing is performed according to the preset release diameter, shear plate thickness and CO2 filling pressure. If the parameter prediction value does not meet the parameter expected value, the preset release diameter, shear plate thickness and CO2 filling pressure are adjusted, and the parameter prediction value is recalculated until it meets the parameter expected value.

[0017] Preferably, the evaluation method further comprises: obtaining experimental data of the nanoindentation experiment, and calculating the mechanical parameters of the rock according to the experimental data, wherein the mechanical parameters include Young's modulus and tensile strength .

[0018] Preferably, the mechanical parameters of the rock are calculated based on the experimental data using the following formula:

[0019] ;

[0020] ;

[0021] ;

[0022] ;

[0023] ;

[0024] ;

[0025] ;

[0026] ;

[0027] ;

[0028] ;

[0029] In the formula, is the contact stiffness; is the external load; is the penetration depth; is the contact depth; is the maximum depth; is the maximum load; is the first constant related to the indenter geometry; is the contact area; is the contact hardness; is Young's modulus; is the second constant related to the indenter geometry; The energy lost in the pure plastic stage; is the pure elastic energy during the pressing process; is the residual depth; is the total energy during the pressing process; is the crack fracture energy; is the critical energy release rate; is the fracture toughness of rock, is the tensile strength; is the ratio of pi.

[0030] A second aspect of the present invention provides a CO2 phase change fracturing pre-evaluation device, comprising:

[0031] A parameter expected value determination module is used to determine the parameter expected values ​​to be achieved by CO2 phase change fracturing, wherein the parameter expected values ​​include the phase change crack expected value, the phase change peak load expected value, and the temperature expected value when the phase change load drops to zero;

[0032] The parameter prediction value calculation module is used to calculate the parameter prediction value using the following formula and the preset release diameter, shear sheet thickness and CO2 filling pressure, wherein the parameter prediction value includes the phase change crack prediction value, the phase change peak load prediction value and the temperature prediction value when the phase change load drops to zero:

[0033] ；

[0034] ；

[0035] ；

[0036] ；

[0037] ；

[0038] ；

[0039] ；

[0040] ;

[0041] in, is the blasting strength; To release the caliber; is the shear sheet thickness; is the predicted value of phase change peak load; The preset filling pressure of CO2; is the predicted value of the initial load of phase change; is the predicted value of the drop time of the phase change load; is the predicted temperature when the phase change load reaches the peak value; is the predicted temperature when the phase change load drops to zero; is the predicted value of phase change crack; is the radius of the prefabricated hole; is the natural base; is the tensile strength; is the stress wave propagation velocity; is Young's modulus; is Poisson's ratio; is the density;

[0042] A comparison and evaluation module is used to compare the parameter prediction value with the parameter expected value. If the parameter prediction value meets the parameter expected value, CO2 phase change fracturing is performed according to the preset release diameter, shear plate thickness and CO2 filling pressure; if the parameter prediction value does not meet the parameter expected value, the preset release diameter, shear plate thickness and CO2 filling pressure are adjusted, and the parameter prediction value is recalculated until it meets the parameter expected value.

[0043] Preferably, the evaluation device further comprises a mechanical parameter acquisition module, which is used to: obtain experimental data of the nanoindentation experiment and calculate the mechanical parameters of the rock according to the experimental data, wherein the mechanical parameters include Young's modulus and tensile strength .

[0044] Preferably, the mechanical parameters of the rock are calculated based on the experimental data using the following formula:

[0045] ;

[0046] ;

[0047] ;

[0048] ;

[0049] ;

[0050] ;

[0051] ;

[0052] ;

[0053] ;

[0054] ;

[0055] In the formula, is the contact stiffness; is the external load; is the penetration depth; is the contact depth; is the maximum depth; is the maximum load; is the first constant related to the indenter geometry; is the contact area; is the contact hardness; is Young's modulus; is the second constant related to the indenter geometry; The energy lost in the pure plastic stage; is the pure elastic energy during the pressing process; is the residual depth; is the total energy during the pressing process; is the crack fracture energy; is the critical energy release rate; is the fracture toughness of rock, is the tensile strength; is the ratio of pi.

[0056] A third aspect of the present invention provides a memory storing a plurality of instructions, wherein the instructions are used to implement the CO2 phase change pre-fracturing assessment method as described in the first aspect.

[0057] A fourth aspect of the present invention provides an electronic device, comprising a processor and a memory connected to the processor, wherein the memory stores a plurality of instructions, and the instructions can be loaded and executed by the processor so that the processor can execute the CO2 phase change fracturing pre-evaluation method as described in the first aspect.

[0058] The beneficial effects of the present invention are as follows: the evaluation method, device and electronic device provided by the present invention before CO2 phase change fracturing can predict and evaluate the key parameters for the implementation of CO2 phase change fracturing technology, such as blasting intensity, phase change cracks, phase change peak load, phase change initial load, temperature when the phase change load drops to zero, temperature when the phase change load reaches the peak value and the decline time of the phase change load before the implementation of CO2 phase change fracturing technology; if the predicted values ​​of these key parameters do not meet the expected values ​​set in the early stage, the preset implementation plan can be changed to re-evaluate the key parameters until the predicted values ​​obtained meet the expected values ​​set in the early stage. Thereby, the implementation plan of CO2 phase change fracturing technology is more reasonable, less blind, lower costs and improve safety; the evaluation results are also helpful in selecting appropriate equipment and protective measures, as well as judging the scope of phase change fracturing cracks, so as to better guide experiments and construction. BRIEF DESCRIPTION OF THE DRAWINGS

[0059] Figure 1 This is a schematic diagram of the process of the evaluation method before CO2 phase change fracturing according to the present invention;

[0060] Figure 2 is a schematic diagram of a nanoindentation curve in a specific embodiment;

[0061] Figure 3 is a schematic diagram of boundary conditions of a simulation model in a specific embodiment;

[0062] Figure 4 is a schematic diagram of the development of simulated cracks in a specific embodiment;

[0063] Figure 5 It is a schematic diagram of a CO2 phase change fracturing experimental device in a specific embodiment;

[0064] Figure 6 It is a schematic diagram of the CO2 phase change load-time curve in a specific embodiment;

[0065] Figure 7 It is a schematic diagram of the definition of some parameters described in the present invention;

[0066] Figure 8 This is a schematic diagram of the functional structure of the CO2 phase change fracturing evaluation device of the present invention. DETAILED DESCRIPTION

[0067] In order to better understand the above technical solution, the above technical solution will be described in detail below in conjunction with the accompanying drawings and specific implementation methods.

[0068] The method provided by the present invention can be implemented in the following terminal environment, and the terminal may include one or more of the following components: a processor, a memory, and a display screen. The memory stores at least one instruction, and the instruction is loaded and executed by the processor to implement the method described in the following embodiment.

[0069] The processor may include one or more processing cores. The processor uses various interfaces and lines to connect various parts of the entire terminal, and executes various functions of the terminal and processes data by running or executing instructions, programs, code sets or instruction sets stored in the memory, and calling data stored in the memory.

[0070] The memory may include random access memory (RAM) or read-only memory (ROM). The memory may be used to store instructions, programs, codes, code sets or instructions.

[0071] The display screen is used to display the user interface of each application.

[0072] In addition, those skilled in the art can understand that the structure of the above terminal does not constitute a limitation on the terminal, and the terminal may include more or fewer components, or combine certain components, or arrange the components differently. For example, the terminal also includes components such as a radio frequency circuit, an input unit, a sensor, an audio circuit, and a power supply, which will not be described in detail here.

[0073] Embodiment 1

[0074] like Figure 1 As shown, an embodiment of the present invention provides a method for evaluating CO2 phase change fracturing before fracturing, comprising:

[0075] S101, determining expected parameter values ​​to be achieved by CO2 phase change fracturing, wherein the expected parameter values ​​include an expected phase change crack value, an expected phase change peak load value, and an expected temperature value when the phase change load drops to zero;

[0076] S102, using the following formula and the preset release diameter, shear sheet thickness and CO2 filling pressure to calculate parameter prediction values, the parameter prediction values ​​including the phase change crack prediction value, the phase change peak load prediction value and the temperature prediction value when the phase change load drops to zero:

[0077] ；

[0078] ；

[0079] ；

[0080] ；

[0081] ；

[0082] ；

[0083] ；

[0084] ;

[0085] in, is the blasting strength; To release the caliber; is the shear sheet thickness; is the predicted value of phase change peak load; The preset filling pressure of CO2; is the predicted value of the initial load of phase change; is the predicted value of the drop time of the phase change load; is the predicted temperature when the phase change load reaches the peak value; is the predicted temperature when the phase change load drops to zero; is the predicted value of phase change crack; is the radius of the prefabricated hole; is the natural base; is the tensile strength; is the stress wave propagation velocity; is Young's modulus; is Poisson’s ratio; is the density;

[0086] S103, comparing the parameter prediction value with the parameter expected value. If the parameter prediction value meets the parameter expected value, CO2 phase change fracturing is performed according to the preset release diameter, shear plate thickness and CO2 filling pressure. If the parameter prediction value does not meet the parameter expected value, the preset release diameter, shear plate thickness and CO2 filling pressure are adjusted, and the parameter prediction value is recalculated until it meets the parameter expected value.

[0087] In a preferred embodiment of the present invention, the evaluation method may further include: obtaining experimental data of the nanoindentation experiment, and calculating the mechanical parameters of the rock according to the experimental data, wherein the mechanical parameters include Young's modulus and tensile strength .

[0088] The mechanical parameters of the rock can be calculated based on the experimental data using the following formula:

[0089] ;

[0090] ;

[0091] ;

[0092] ;

[0093] ;

[0094] ;

[0095] ;

[0096] ;

[0097] ;

[0098] ;

[0099] In the formula, is the contact stiffness; is the external load; is the penetration depth; is the contact depth; is the maximum depth; is the maximum load; is the first constant related to the indenter geometry; is the contact area; is the contact hardness; is Young's modulus; is the second constant related to the indenter geometry; The energy lost in the pure plastic stage; is the pure elastic energy during the pressing process; is the residual depth; is the total energy during the pressing process; is the crack fracture energy; is the critical energy release rate; is the fracture toughness of rock, is the tensile strength; is the ratio of pi. Specific embodiments

[0101] The objectives of the CO2 phase change fracturing experiment were determined, including the expected values ​​of some key parameters to be achieved, among which the expected value of the phase change crack was greater than 1m, the expected value of the phase change peak load was greater than 30MPa, and the expected value of the temperature when the phase change load dropped to zero was less than 360K.

[0102] The CO2 phase change fracturing experiment plan presets: the release diameter is 24mm, the shear piece thickness is 1mm, and the CO2 filling pressure is 12MPa.

[0103] First, a mechanical experiment is carried out to obtain experimental data, and the mechanical parameters of the rock are calculated based on the experimental data. In this embodiment, a nanoindentation experiment is selected. The main steps of the nanoindentation experiment include: selecting a square dot matrix on the surface of the sample, and performing a nanoindentation experiment on each point; in the experiment, the external load is initially increased linearly at a loading rate of 200μN / s, and maintained for 2s after reaching the maximum load of 1000μN, at which time the indentation depth reaches the maximum; after that, the indenter begins to unload at a rate of 200μN / s. In a preferred embodiment of the present invention, before the nanoindentation experiment on the sample is carried out, the following steps are further included: cutting the sample into small pieces of a preset size, selecting the cross section to be polished, and polishing it with sandpaper from coarse to fine; then fixing the sample on a polisher, and polishing it with a high-energy argon ion beam to polish the roughness of the loading surface to the micron level. Obtain nanoindentation experimental data and draw a nanoindentation curve (such as Figure 2 ) and then calculate to get 2.89GPa, is 34.71N / m, 0.32 , 2.2MPa, It is 0.02m.

[0104] Then, the parameter prediction values ​​are calculated based on the preset release diameter, shear plate thickness, CO2 filling pressure and rock mechanics parameters obtained by experimental calculation.

[0105] According to the formula: , and BS is obtained to be 36.52MPa.

[0106] According to the formula: , FS is obtained to be 49.59 MPa, which meets the expected value of phase change peak load.

[0107] According to the formula: , HS is obtained to be 17.59MPa.

[0108] because 32MPa, greater than 30MPa, application formula: ,

[0109] The obtained value of t is 97.89 ms.

[0110] According to the formula: , to obtain is 324.88K,

[0111] According to the formula: , to obtain It is 353.63K, which meets the requirement that the temperature is less than 360K when the phase change load drops to zero.

[0112] Get FS and After that, according to the formula: , to obtain It is 1.183m, which meets the requirement that the expected value of phase change cracks is greater than 1m.

[0113] Through calculation and comparison, it can be known that the parameter prediction values ​​are consistent with the parameter expected values. The CO2 phase change fracturing experiment can be carried out according to the preset experimental plan: the release diameter size is 24mm, the shear piece thickness is 1mm, and the CO2 filling pressure is 12MPa.

[0114] In order to verify the effectiveness of the solution of the present invention, a numerical simulation model can be established based on the fracture phase field method. The fracture phase field method is very accurate and effective in predicting crack development. The model used can be a commonly used model in the industry. In the numerical simulation model, a circular hole model is used to explore the crack development. Among them, the sample size can be a 4m diameter disk with a prefabricated circular hole in the middle with a diameter of 2mm, such as Figure 3 As shown. In the model simulation, according to the results of the nanoindentation experiment, the Young's modulus can be set to 2.89GPa, the Poisson's ratio can be set to 0.3, and the fracture energy can be set to 34.71N / m. The pressure of loading from the prefabricated circular hole in the middle is set to HZ to simulate the impact process of the load formed after the release of CO2 on the sample. HZ is calculated according to the following formula:

[0115] ;

[0116] Among them, HZ is the loading pressure set during simulation, is the time variable; is the decreasing rate constant, which is taken as 400; is the duration of the initial load of phase change of CO2 after release, Finally, the length of the simulated crack is 1.13m, and the development of the simulated crack can be shown as follows: Figure 4As shown. The error between the simulated crack and the predicted value of phase change crack 1.183m is 4.6%. It can be seen that the present invention is effective in predicting the length of phase change cracks. Therefore, the present invention can design the filling pressure and other conditions in advance according to the target fracture length before construction or experiment to achieve effective transformation.

[0117] In addition, this embodiment uses a CO2 phase change fracturing experimental device to collect relevant data. The CO2 phase change fracturing experimental device can use a common device in the art, such as Figure 5 As shown, it mainly includes:

[0118] (1) Gas source: Ensure that the experiment has a high-purity (99%) source of liquid carbon dioxide, and the temperature of the carbon dioxide can be kept constant using a simple temperature controller.

[0119] (2) Liquid storage tube: It is mainly made of a 1.4m long (inner diameter 40mm, thickness 6mm) 304 grade stainless steel. Its maximum and minimum allowable temperatures are 1600°C and -152°C respectively. The compression and heating of liquid carbon dioxide are carried out inside the liquid storage tube. The maximum working pressure of the experimental device is 350MPa.

[0120] (3) Injection module: mainly includes the injection valve, which controls the initial filling pressure of liquid carbon dioxide and sets the filling pressure value required for the experiment.

[0121] (4) Heating module: It includes a heating rod and a heating starter, which can quickly raise the temperature in the liquid storage tube to 750°C. The heating module is designed to instantly generate a temperature in the liquid storage tube that is sufficient for liquid carbon dioxide to undergo a BLEVE (Boiling Liquid Extending Vapor Cloud Explosion).

[0122] (5) Energy release module: Located at the junction of the release tube and the liquid storage tube, it adjusts the bursting pressure through shear plates of different thicknesses and different release calibers (the diameter of the release tube, CO2 is released from the outlet of the release tube).

[0123] (6) Computer data acquisition module: mainly includes signal cables, pressure sensors and temperature sensors.

[0124] The release aperture size of the experimental device is 24mm, the thickness of the shear plate is 1mm, and the experiment is carried out when the filling pressure of CO2 is 12MPa. Carbon dioxide is filled into the CO2 phase change experimental device according to the filling pressure. Pressure sensors and temperature sensors are set at the energy release plate to detect temperature and pressure changes during the experiment. After the carbon dioxide is filled, the heating starter is started to make the heating rod work, and the carbon dioxide inside the liquid storage tube boils rapidly and is released from the outlet of the release tube. During this period, the relevant experimental data are monitored with the help of pressure sensors and temperature sensors: the size of the burst strength is 36.5MPa, the size of the phase change peak load of CO2 after release is 46.2MPa, the size of the initial phase change load of CO2 after release is 17MPa, the decline time of the phase change load is 105ms, the temperature when the phase change load reaches the peak value (that is, the size of the phase change peak load) is 319.13K, and the temperature when the phase change load drops to zero is 351.1K, and the curve of pressure (phase change load) changing with time is obtained as shown in the figure. Figure 6 shown.

[0125] By comparing the parameter values ​​obtained by monitoring the actual CO2 phase change fracturing experiment with the parameter values ​​calculated using the method of the present invention, it can be seen that the parameter values ​​calculated using the method of the present invention are more consistent with the parameter values ​​monitored at the experimental site, with a smaller error, indicating that the implementation plan is evaluated or adjusted before CO2 phase change fracturing according to the method of the present invention, and the implementation plan is implemented on site according to the evaluated implementation plan, and the expected effect can be obtained. Therefore, the technical solution provided by the present invention can remove the limitations on the development and application of CO2 phase change fracturing technology.

[0126] It should be noted that some of the parameter prediction values ​​involved in the present invention ( , and ) can be found in Figure 7 understand.

[0127] Embodiment 2

[0128] like Figure 8 As shown, the embodiment of the present invention provides a functional module architecture that is completely consistent with the method flow of the first embodiment, that is, the embodiment of the present invention also provides a CO2 phase change fracturing pre-evaluation device, including:

[0129] The parameter expected value determination module 801 is used to determine the parameter expected values ​​to be achieved by the CO2 phase change fracturing, wherein the parameter expected values ​​include the phase change crack expected value, the phase change peak load expected value, and the temperature expected value when the phase change load drops to zero;

[0130] The parameter prediction value calculation module 802 is used to calculate the parameter prediction value using the following formula and the preset release diameter, shear sheet thickness and CO2 filling pressure, wherein the parameter prediction value includes the phase change crack prediction value, the phase change peak load prediction value and the temperature prediction value when the phase change load drops to zero:

[0131] ；

[0132] ；

[0133] ；

[0134] ；

[0135] ；

[0136] ；

[0137] ；

[0138] ;

[0139] in, is the blasting strength; To release the caliber; is the shear sheet thickness; is the predicted value of phase change peak load; The preset filling pressure of CO2; is the predicted value of the initial load of phase change; is the predicted value of the drop time of the phase change load; is the predicted temperature when the phase change load reaches the peak value; is the predicted temperature when the phase change load drops to zero; is the predicted value of phase change crack; is the radius of the prefabricated hole; is the natural base; is the tensile strength; is the stress wave propagation velocity; is Young's modulus; is Poisson's ratio; is the density;

[0140] The comparison and evaluation module 803 is used to compare the parameter prediction value with the parameter expected value. If the parameter prediction value meets the parameter expected value, CO2 phase change fracturing is performed according to the preset release diameter, shear plate thickness and CO2 filling pressure; if the parameter prediction value does not meet the parameter expected value, the preset release diameter, shear plate thickness and CO2 filling pressure are adjusted, and the parameter prediction value is recalculated until it meets the parameter expected value.

[0141] Furthermore, the evaluation device may also include a mechanical parameter acquisition module 204, which is used to: obtain experimental data of the nanoindentation experiment and calculate the mechanical parameters of the rock according to the experimental data. The mechanical parameters include Young's modulus and tensile strength .

[0142] The mechanical parameters of the rock can be calculated based on the experimental data using the following formula:

[0143] ;

[0144] ;

[0145] ;

[0146] ;

[0147] ;

[0148] ;

[0149] ;

[0150] ;

[0151] ;

[0152] ;

[0153] In the formula, is the contact stiffness; is the external load; is the penetration depth; is the contact depth; is the maximum depth; is the maximum load; is the first constant related to the indenter geometry; is the contact area; is the contact hardness; is Young's modulus; is the second constant related to the indenter geometry; The energy lost in the pure plastic stage; is the pure elastic energy during the pressing process; is the residual depth; is the total energy during the pressing process; is the crack fracture energy; is the critical energy release rate; is the fracture toughness of rock, is the tensile strength; is the ratio of pi.

[0154] The device can be implemented by the CO2 phase change pre-fracturing evaluation method provided in the above-mentioned embodiment 1. The specific implementation method can be found in the description of embodiment 1 and will not be repeated here.

[0155] The present invention also provides a memory storing a plurality of instructions, wherein the instructions are used to implement the CO2 phase change pre-fracturing assessment method as described in the first embodiment.

[0156] The present invention also provides an electronic device, comprising a processor and a memory connected to the processor, wherein the memory stores a plurality of instructions, and the instructions can be loaded and executed by the processor so that the processor can execute the CO2 phase change pre-fracturing assessment method as described in Example 1.

[0157] Although preferred embodiments of the present invention have been described, additional changes and modifications may be made to these embodiments by those skilled in the art once the basic inventive concepts are known. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments and all changes and modifications that fall within the scope of the present invention. Obviously, those skilled in the art may make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention is also intended to include these modifications and variations.

Claims

1. A method for evaluating CO2 phase change fracturing before fracturing, characterized in that: include: Determine the expected values ​​of parameters to be achieved by CO2 phase change fracturing, wherein the expected values ​​of parameters include an expected value of phase change cracks, an expected value of phase change peak load, and an expected value of temperature when the phase change load drops to zero; The parameter prediction values ​​are calculated using the following formula and the preset release diameter, shear sheet thickness and CO2 filling pressure, and the parameter prediction values ​​include the phase change crack prediction value, the phase change peak load prediction value and the temperature prediction value when the phase change load drops to zero: ； ； ； ； ； ； ； ； in, is the blasting strength; To release the caliber; is the shear sheet thickness; is the predicted value of phase change peak load; The preset filling pressure of CO2; is the predicted value of the initial load of phase change; is the predicted value of the drop time of the phase change load; is the predicted temperature when the phase change load reaches the peak value; is the predicted temperature when the phase change load drops to zero; is the predicted value of phase change crack; is the radius of the prefabricated hole; is the natural base; is the tensile strength; is the stress wave propagation velocity; is Young's modulus; is Poisson's ratio; is the density; The parameter prediction value is compared with the parameter expected value. If the parameter prediction value meets the parameter expected value, CO2 phase change fracturing is performed according to the preset release diameter, shear plate thickness and CO2 filling pressure. If the parameter prediction value does not meet the parameter expected value, the preset release diameter, shear plate thickness and CO2 filling pressure are adjusted, and the parameter prediction value is recalculated until it meets the parameter expected value.

2. The CO2 phase change fracturing evaluation method according to claim 1, characterized in that: The evaluation method further includes: obtaining experimental data of the nanoindentation experiment, and calculating the mechanical parameters of the rock according to the experimental data, wherein the mechanical parameters include Young's modulus and tensile strength .

3. The CO2 phase change fracturing evaluation method according to claim 2, characterized in that: The mechanical parameters of rock are calculated based on experimental data using the following formula: ； ； ； ； ； ； ； ； ； ； In the formula, is the contact stiffness; is the external load; is the penetration depth; is the contact depth; is the maximum depth; is the maximum load; is the first constant related to the indenter geometry; is the contact area; is the contact hardness; is Young's modulus; is the second constant related to the indenter geometry; The energy lost in the pure plastic stage; is the pure elastic energy during the pressing process; is the residual depth; is the total energy during the pressing process; is the crack fracture energy; is the critical energy release rate; is the fracture toughness of rock, is the tensile strength; is the ratio of pi.

4. A CO2 phase change fracturing pre-evaluation device, characterized in that: include: A parameter expected value determination module is used to determine the parameter expected values ​​to be achieved by CO2 phase change fracturing, wherein the parameter expected values ​​include the phase change crack expected value, the phase change peak load expected value, and the temperature expected value when the phase change load drops to zero; The parameter prediction value calculation module is used to calculate the parameter prediction value using the following formula and the preset release diameter, shear sheet thickness and CO2 filling pressure, wherein the parameter prediction value includes the phase change crack prediction value, the phase change peak load prediction value and the temperature prediction value when the phase change load drops to zero: ； ； ； ； ； ； ； ； in, is the blasting strength; To release the caliber; is the shear sheet thickness; is the predicted value of phase change peak load; The preset filling pressure of CO2; is the predicted value of the initial load of phase change; is the predicted value of the drop time of the phase change load; is the predicted temperature when the phase change load reaches the peak value; is the predicted temperature when the phase change load drops to zero; is the predicted value of phase change crack; is the radius of the prefabricated hole; is the natural base; is the tensile strength; is the stress wave propagation velocity; is Young's modulus; is Poisson's ratio; is the density; A comparison and evaluation module is used to compare the parameter prediction value with the parameter expected value. If the parameter prediction value meets the parameter expected value, CO2 phase change fracturing is performed according to the preset release diameter, shear plate thickness and CO2 filling pressure; if the parameter prediction value does not meet the parameter expected value, the preset release diameter, shear plate thickness and CO2 filling pressure are adjusted, and the parameter prediction value is recalculated until it meets the parameter expected value.

5. The CO2 phase change fracturing evaluation device according to claim 4, characterized in that: The evaluation device also includes a mechanical parameter acquisition module, which is used to: obtain experimental data of the nanoindentation experiment and calculate the mechanical parameters of the rock according to the experimental data. The mechanical parameters include Young's modulus and tensile strength .

6. The CO2 phase change fracturing evaluation device according to claim 5, characterized in that: The mechanical parameters of rock are calculated based on experimental data using the following formula: ； ； ； ； ； ； ； ； ； ； In the formula, is the contact stiffness; is the external load; is the penetration depth; is the contact depth; is the maximum depth; is the maximum load; is the first constant related to the indenter geometry; is the contact area; is the contact hardness; is Young's modulus; is the second constant related to the indenter geometry; The energy lost in the pure plastic stage; is the pure elastic energy during the pressing process; is the residual depth; is the total energy during the pressing process; is the crack fracture energy; is the critical energy release rate; is the fracture toughness of rock, is the tensile strength; is the ratio of pi.

7. A memory, characterized in that: A plurality of instructions are stored, and the instructions are used to implement the CO2 phase change pre-fracturing evaluation method as described in any one of claims 1-3.

8. An electronic device, characterized in that: It comprises a processor and a memory connected to the processor, wherein the memory stores a plurality of instructions, and the instructions can be loaded and executed by the processor, so that the processor can execute the CO2 phase change pre-fracturing assessment method as described in any one of claims 1-3.

Images