Method for determining supercritical co2 fracturing process under deep coal seam fluidization mining

Abstract

The application provides a deep coal seam fluidization mining lower supercritical CO2 fracturing process determination method, relates to the technical field of supercritical CO2 fracturing process determination method, and comprises the following steps: weighting and fusing the number of microseismic events and temperature disturbance values, and generating a comprehensive reconstruction intensity value of each depth unit; when performing a short-term pump test, continuously detecting the bottom hole pressure, drawing a bottom hole pressure-time square root relationship curve, and performing linear fitting by using a square root time method to obtain a dynamic filtration coefficient; constructing an effective displacement channel index, and drawing an effective displacement channel index change curve with cumulative injection amount; and weighting and fusing the microseismic events and temperature disturbance data on the depth unit, generating a comprehensive reconstruction intensity value, and providing a double confirmation index which can reflect both the crack initiation position and the CO2 diffusion range; by tracing the comprehensive reconstruction intensity value change curve with the cumulative injection amount, the black box fracturing process is converted into a visual profile management.

Description

Technical Field

[0001] This invention relates to the technical field of methods for determining supercritical CO2 fracturing processes, specifically to methods for determining supercritical CO2 fracturing processes under fluidized coal seam mining. Background Technology

[0002] Supercritical CO2 fracturing is a cutting-edge technology for deep coalbed methane development. It utilizes the low viscosity, high diffusivity, and strong adsorption and replacement capacity of supercritical CO2 to effectively modify coal seams and improve gas recovery. However, traditional methods typically rely on single indicators such as microseismic monitoring or pressure curve analysis to judge fracturing effectiveness. The number of microseismic events only reflects the rock fracture intensity but cannot characterize the formation of fluid seepage channels. Pressure curves also struggle to distinguish between phase deviations and anomalies caused by formation filtration, making misjudgments possible with single indicators. Existing process adjustments largely depend on engineer experience and lack quantitative control criteria, especially in key areas such as determining whether CO2 is in an ideal supercritical state and whether filtration is too rapid, making real-time adaptive control difficult.

[0003] In the prior art, patent application CN119981821A discloses a method for selecting a first CO2 fracturing process based on the geological parameters of the target reservoir; selecting a first fracture propagation model of the target reservoir using a preset fracturing sand plugging judgment model; and determining the sand plugging risk level when fracturing the target reservoir using the first CO2 fracturing process based on the first fracture propagation model of the target reservoir and the proppant particle size corresponding to the first CO2 fracturing process. However, this method failed to achieve the core functions of this application, such as real-time fusion of multi-source data during fracturing, joint dynamic diagnosis of phase state and filtration loss, continuous tracking of the effective displacement channel index, and graded closed-loop control based on the index change curve. Therefore, it cannot meet the actual needs for real-time optimization and adaptive control of the fracturing process in supercritical CO2 fluidized bed mining of deep coal seams. Thus, a method for determining the supercritical CO2 fracturing process in fluidized bed mining of deep coal seams is urgently needed.

[0004] The information disclosed in the background section is only intended to enhance the understanding of the background of this disclosure, and therefore may include information that does not constitute prior art known to those skilled in the art. Summary of the Invention

[0005] The purpose of this invention is to provide a method for determining the supercritical CO2 fracturing process under fluidized bed mining of deep coal seams, so as to solve the problems mentioned in the background art.

[0006] To achieve the above objectives, the present invention provides the following technical solution: The method for determining the supercritical CO2 fracturing process under fluidized bed mining of deep coal seams includes the following specific steps: S1: Divide the target injection well into depths and set depth units at equal intervals. Collect injection flow rate, vibration data and temperature data of each depth unit at a fixed sampling frequency. Based on the vibration data, use the energy ratio method to automatically detect micro-vibration events. At the same time, compare the temperature data with the initial temperature to generate the temperature disturbance value of each depth unit at each sampling time. S2: Taking the current sampling time as the end point, trace back a time window of a preset fixed duration as the current time window, and count the number of microseismic events and the average temperature disturbance value of each depth unit along the target injection well within the current time window. Determine the comprehensive transformation intensity value of each depth unit based on the number of microseismic events and the average temperature disturbance value. S3: During the supercritical CO2 pumping process, the bottom hole pressure and bottom hole temperature are continuously collected to calculate the phase deviation index. During the short-term pump stop test, the bottom hole pressure is continuously monitored, the bottom hole pressure and time square root relationship curve is plotted, and the dynamic filtration coefficient is obtained by linear fitting using the square root time method. S4: Adjust the phase adjustment strategy according to the phase deviation index and dynamic filtration coefficient; based on the injection displacement, further obtain the cumulative injection amount of supercritical CO2, and construct the effective displacement channel index according to the comprehensive modification intensity value and the phase deviation index, and plot the curve of the effective displacement channel index with the cumulative injection amount, and make corresponding adjustments to the phase adjustment strategy based on the curve.

[0007] Furthermore, the specific steps of S1 are as follows: The starting and ending depths of the target injection well are determined, and the wellbore is divided into several continuous depth units at equal intervals along the depth direction, with each depth unit corresponding to a depth interval; a fixed sampling time interval is set to generate a discrete sampling time sequence; vibration signals and temperature data of each depth unit are collected synchronously at each sampling time to form a depth-time two-dimensional data matrix; The vibration data is bandpass filtered. Starting from the current sampling time, the data is traced back to the preset short time window length and long time window length respectively. The average value of the vibration data within the two time windows is calculated, and the ratio of the two values ​​is calculated. When the ratio exceeds the preset threshold, it is determined that a micro-vibration event has been triggered. The temperature perturbation value of each depth cell at each sampling time is generated by comparing the measured temperature data of the depth cell at the current sampling time with the initial temperature of the depth cell, calculating the absolute value of the difference between the two, and obtaining the temperature perturbation value at the current sampling time.

[0008] Furthermore, the comprehensive modification intensity value for each depth unit is determined, and the specific steps are as follows: Within the current time window, the number of microseismic events and the average temperature disturbance value are statistically analyzed for each depth unit along the target injection well. Based on these data, the comprehensive stimulation intensity value for each depth unit is determined using the following formula: in, This represents the maximum number of microseismic events across all depth elements within the current time window. Indicates the first Number of microseismic events per depth element within the current time window; Indicates the first The average temperature perturbation value of each depth cell within the current time window; This represents the maximum value of the average temperature perturbation value across all depth cells within the current time window. Indicates the first The comprehensive renovation intensity value of each depth unit within the current time window; This represents the weighting factor for microseismic events. This represents the temperature disturbance weighting factor. ; Indicates the depth cell index; Indicates the current time window.

[0009] Further, the phase deviation index is calculated, and the specific steps are as follows: During supercritical CO2 injection, the phase deviation index is calculated by continuously collecting bottom-hole pressure and temperature data. in, This indicates the bottom hole pressure at the current sampling time; This indicates the bottom-hole temperature at the current sampling time; , These represent the critical temperature and critical pressure of CO2, respectively. , These represent the temperature weighting coefficient and the pressure weighting coefficient, respectively. This represents the phase deviation index at the current sampling moment.

[0010] Furthermore, the logic for obtaining the dynamic filtering coefficient is as follows: When performing a short-stop pump test, plot the bottom hole pressure versus the square root of time. The relationship curve was obtained, and linear fitting was performed using the square root time method to obtain the fitting formula. in, Indicates the first Instantaneous bottom hole pressure at the start of the second pump stop test; Indicates the first In the second pump stop test, the absolute value of the slope of the fitted straight line; An index indicating the number of pump stop tests; Indicates the first During the second pump shutdown test, after the pump was shut down... The bottom hole pressure detected in seconds; Indicates from the first The time variable is the time from the start of the pump stop test, in seconds; Based on the absolute value of the slope of the fitted straight line, a dynamic filtering coefficient is constructed: in, This indicates the viscosity of the fracturing fluid under the current bottom hole temperature and pressure conditions. This indicates the overall permeability of the formation in the area affected by fracturing fluid loss; This indicates the overall equivalent porosity of the formation in the area affected by fracturing fluid loss; This represents the overall equivalent composite compressibility coefficient of the formation in the area affected by fracturing fluid loss; Indicates the first The dynamic filtration coefficient corresponding to the pump stop test.

[0011] Furthermore, based on the phase deviation index and the dynamic filtering coefficient, the phase adjustment strategy is adjusted accordingly, specifically as follows: when and When the increase compared to the previous pump shutdown test was less than 30%, it was determined that the bottom hole temperature and bottom hole pressure were close to the critical point, and the supercritical CO2 was in an ideal supercritical state, requiring no adjustment. when If the degree to which the CO2 at the bottom of the well deviates from the critical point exceeds the allowable range, the temperature of the injected CO2 and the pressure at the bottom of the well will be adjusted toward the critical point through the coordinated control of the surface heat exchange equipment and the pump injection rate. when and When the increase compared to the previous pump shutdown test is greater than or equal to 30%, it indicates that the fracturing fluid is rapidly leaking along natural fractures or high-permeability channels. In the next pumping procedure, a temporary plugging agent should be added to the slug. After adding the temporary plugging agent, the injection rate should be increased by 10% to 20% to help the temporary plugging agent penetrate deeper into the channel. If the concentration of the temporary plugging agent is continuously increased during consecutive preset pump stop tests, then the concentration should be gradually increased until... and When the value is increased to the preset range, the second scenario should be adjusted first.

[0012] Furthermore, an effective displacement channel index is constructed, and the specific steps are as follows: Based on the injection displacement, the cumulative injection displacement at each sampling moment within the statistical time window is summed to obtain the cumulative injection volume of supercritical CO2. Based on the comprehensive modification intensity value and the phase deviation index, an effective displacement channel index is constructed. in, This represents the total effective length of continuous depth units whose comprehensive renovation intensity value exceeds the set threshold within the current time window; This indicates the cumulative amount of supercritical CO2 injected within the current time window; Indicates the total effective length Within, the average value of the comprehensive transformation intensity of all depth units; This represents the average value of the phase deviation index at all sampling moments within the current time window; Indicates the current sampling time The effective displacement channel index; This indicates the increment in the total effective length of the current time window compared to the previous adjacent time window; This represents the increase in the cumulative injection amount of supercritical CO2 at the current sampling time compared to the initial sampling time within the current time window, where t represents the current sampling time.

[0013] Furthermore, adjustments are made accordingly based on the phase adjustment strategy of the change curve, specifically as follows: The effective displacement channel index is plotted in real time as a function of the cumulative injection amount of supercritical CO2. Based on the plot, the following tiered adjustment strategy is implemented: Taking the current sampling time and the previous sampling time as the end points respectively, trace back two consecutive time windows of the same duration, the current time window and the previous time window, and count the effective total length within the two time windows respectively. If the effective total length within the current time window is greater than the effective total length within the previous time window, and this relationship holds true for a finite number of consecutive adjacent time window pairs, then the effective total length is determined to be in a state of continuous growth. If the curve of the effective displacement channel index is in an upward phase for two consecutive sampling times, and the effective total length is in a state of continuous growth, or the growth rate of the average value of the comprehensive transformation intensity value compared with the average value of the comprehensive transformation intensity value of the previous sampling time exceeds the preset threshold, and maintains a positive growth trend over multiple consecutive sampling times in the past, the current phase adjustment strategy should be maintained. If the curve of the effective displacement channel index enters a plateau period and the profile shows that the effective well section no longer increases and the average value of the comprehensive stimulation intensity value tends to stabilize, then temporary blocking and diversion should be implemented in the depth unit where the comprehensive stimulation intensity value is 40% lower than the maximum value of the profile, forcing the fluid to enter a new layer and seeking a second increase in the effective displacement channel index. If the curve of the effective displacement channel index drops prematurely, and the profile shows a shortening of the effective total length, determine the cause in conjunction with step S3: If it is due to... If this results in the temperature of the injected CO2 being adjusted gradually until... Less than 0.2; if due to If the increase is ≥30% compared to the previous pump stop test, add a filtration loss reducer until... The increase compared to the previous pump shutdown test was less than 30%.

[0014] Compared with the prior art, the beneficial effects of the present invention are: This scheme generates a comprehensive stimulation intensity value by weighting and fusing the number of microseismic events with the average temperature disturbance, achieving a leap from "single-indicator monitoring" to "multi-source information fusion." Microseismic data reflects the fracture initiation location, while temperature disturbance reflects the CO2 diffusion range; the two complement each other for verification, significantly improving the reliability of judging the actual reservoir stimulation effect. The scheme introduces the phase deviation index and dynamic filtration coefficient as quantitative control indicators and establishes a clear hierarchical adjustment strategy, transforming process parameter adjustment from "experience-based judgment" to "indicator-driven," achieving real-time adaptive control of injection temperature and pressure, and avoiding phase-dependent... Stirring failure caused by state deviation or excessively rapid filtration; by constructing a comprehensive stimulation intensity profile along the wellbore depth direction, and constructing an effective displacement channel index based on the effective total length and average stimulation intensity, a profiled quantitative diagnosis of stimulation uniformity is achieved. This can accurately locate low-intensity "blind zones" and guide temporary plugging and redirection, effectively improving the vertical coverage of fracturing stimulation; a complete closed loop of "monitoring-diagnosis-control-re-monitoring" is formed. The change curve of the effective displacement channel index with the cumulative injection volume can reflect the effectiveness of the current process in real time. The plateau period triggers redirection, and the descent period is adjusted by attribution, realizing continuous optimization of the fracturing process. Attached Figure Description

[0015] Figure 1 This is a schematic diagram of the overall method flow of the present invention; Figure 2 This is a graph showing the relationship between bottom hole pressure and the corresponding phase deviation index. Detailed Implementation

[0016] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments.

[0017] It should be noted that, unless otherwise defined, the technical or scientific terms used in this invention should have the ordinary meaning understood by one of ordinary skill in the art to which this invention pertains. The terms "first," "second," and similar terms used in this invention do not indicate any order, quantity, or importance, but are merely used to distinguish different components. Terms such as "comprising" or "including" mean that the element or object preceding the word encompasses the elements or objects listed following the word and their equivalents, without excluding other elements or objects. Terms such as "connected" or "linked" are not limited to physical or mechanical connections, but can include electrical connections, whether direct or indirect. Terms such as "upper," "lower," "left," and "right" are used only to indicate relative positional relationships; when the absolute position of the described object changes, the relative positional relationship may also change accordingly.

[0018] Example: Please see Figures 1-2 The present invention provides a technical solution: The method for determining the supercritical CO2 fracturing process under fluidized bed mining of deep coal seams includes the following specific steps: S1: Divide the target injection well into depths and set depth units at equal intervals. Collect injection flow rate, vibration data and temperature data of each depth unit at a fixed sampling frequency. Based on the vibration data, use the energy ratio method to automatically detect micro-vibration events. At the same time, compare the temperature data with the initial temperature to generate the temperature disturbance value of each depth unit at each sampling time. In this embodiment, the specific steps of S1 are as follows: The starting and ending depths of the target injection well are determined, and the wellbore is divided into several continuous depth units at equal intervals along the depth direction, with each depth unit corresponding to a depth interval; a fixed sampling time interval is set to generate a discrete sampling time sequence; vibration signals and temperature data of each depth unit are collected synchronously at each sampling time to form a depth-time two-dimensional data matrix; The vibration data is bandpass filtered. Starting from the current sampling time, the data is traced back to the preset short time window length and long time window length respectively. The average value of the vibration data within the two time windows is calculated, and the ratio of the two values ​​is calculated. When the ratio exceeds the preset threshold, it is determined that a micro-vibration event has been triggered. The temperature perturbation value of each depth cell at each sampling time is generated by comparing the measured temperature data of the depth cell at the current sampling time with the initial temperature of the depth cell, calculating the absolute value of the difference between the two, and obtaining the temperature perturbation value at the current sampling time.

[0019] In the above process, "equal interval" refers to dividing the wellbore into depth units at the same distance intervals, such as every 1 meter or every 2 meters. Each depth unit corresponds to a fixed depth interval, ensuring that the granularity of the division is uniform throughout the well section, so as to allow for spatial alignment and comparison of monitoring data at different depth locations. "Fixed sampling time interval" refers to continuously collecting data on the time axis at a constant period, such as every 0.5 seconds or every 1 second, generating a discrete sampling time sequence with equal intervals. This ensures the comparability and real-time performance of data in the time domain and avoids trend misjudgment caused by uneven sampling step size. The preset short window length and long window length are two key time parameters for automatically detecting microseismic events using the energy ratio method. They are determined as follows: the short window length is usually 1 to 2 times the estimated duration of the microseismic event, for example, 0.05 to 0.1 seconds, to ensure that the short window can capture the main signal of the event; the long window length is 5 to 10 times the short window length, for example, 0.5 to 1 second, to characterize the energy level of the current background noise. Bandpass filtering is a digital signal processing operation performed on the acquired raw vibration data. Its purpose is to retain the effective signal within a specific frequency range related to the microseismic event, while suppressing low-frequency and high-frequency interference outside this range. In practice, firstly, based on the spectral characteristics of the microseismic events in the target injection well area, the lower and upper cutoff frequencies of the bandpass filter are determined. Typically, the lower cutoff frequency is set to 50Hz to 100Hz to filter out low-frequency noise generated by drilling machinery vibration, fluid flow, or surface activity, while the upper cutoff frequency is set to 500Hz to 1000Hz to suppress high-frequency electronic noise or environmental clutter. Then, digital filters such as infinite impulse response (IR) filters or finite impulse response (FIR) filters are used to process the raw vibration data sequence, allowing frequency components between the lower and upper cutoff frequencies to pass through with near-zero attenuation, while frequency components below the lower cutoff frequency and above the upper cutoff frequency are significantly attenuated. Step S1 achieves real-time automatic detection of microseismic events and synchronous quantification of temperature disturbances. Specifically, vibration signals and temperature data are synchronously collected at a fixed sampling frequency for each depth unit along the wellbore depth direction, forming a depth-time two-dimensional data matrix. After bandpass filtering of the vibration data, the energy ratio method of short and long time windows is used. When the ratio exceeds a preset threshold, a microseismic event is automatically determined to be triggered. This method can effectively suppress background noise interference and improve the accuracy and real-time performance of microseismic event identification. At the same time, the measured temperature data at the current sampling moment is compared with the initial temperature of the depth unit, and the absolute value of the difference is calculated as the temperature disturbance value, which quantitatively reflects the degree of temperature deviation of the depth unit after supercritical CO2 injection. The larger the temperature disturbance, the stronger the fluid activity or phase change at that location. Through a synchronous acquisition and processing framework based on deep unit grids, the originally independently monitored microseismic and temperature signals are unified under the same depth-time coordinate system, laying a spatiotemporally consistent data foundation for subsequent multi-source data fusion. The parallel calculation of automatic detection of microseismic events and temperature disturbance values ​​using the energy ratio method enables the system to simultaneously acquire microseismic information reflecting crack initiation and temperature information reflecting the CO2 diffusion range at each sampling moment. These two types of data, with different physical meanings and response mechanisms, complement each other. Microseismic events reflect the dynamic intensity of rock fracture, while temperature disturbances reflect the static range of fluid seepage. The combined use of the two can effectively distinguish between "effective modification" and "ineffective fracture," providing reliable data support for calculating the comprehensive modification intensity value in step S2.

[0020] S2: Taking the current sampling time as the end point, trace back a time window of a preset fixed duration as the current time window, and count the number of microseismic events and the average temperature disturbance value of each depth unit along the target injection well within the current time window. Determine the comprehensive transformation intensity value of each depth unit based on the number of microseismic events and the average temperature disturbance value. In this embodiment, the comprehensive modification intensity value of each depth unit is determined by the following steps: Within the current time window, the number of microseismic events and the average temperature disturbance value are statistically analyzed for each depth unit along the target injection well. Based on these data, the comprehensive stimulation intensity value for each depth unit is determined using the following formula: in, This represents the maximum number of microseismic events across all depth elements within the current time window. Indicates the first Number of microseismic events per depth element within the current time window; Indicates the first The average temperature perturbation value of each depth cell within the current time window; This represents the maximum value of the average temperature perturbation value across all depth cells within the current time window. Indicates the first The comprehensive renovation intensity value of each depth unit within the current time window; This represents the weighting factor for microseismic events. This represents the temperature disturbance weighting factor. ; Indicates the depth cell index; Indicates the current time window.

[0021] In the above process, the comprehensive renovation intensity value As the dependent variable, it specifically reflects the situation in the first... Each depth unit, the current time window The comprehensive fracturing effect within the unit is achieved by normalizing and weighting the number of microseismic events with different physical meanings and the average temperature disturbance, so that the degree of transformation of a single depth unit can be output in the form of a dimensionless quantitative index, providing a unified quantitative basis for the construction of the effective displacement channel index and the decision of temporary blocking and turning. In this formula, the dependent variable is... With two core independent variables, namely the normalized number of microseismic events and normalized temperature perturbation average Directly related, both are weighted by microseismic event weighting factors. and temperature perturbation weighting factor A linear weighted summation is performed, where the number of microseismic events reflects the activity of rock fracturing within the depth unit, and the average temperature perturbation reflects the supercritical... The intensity of temperature change caused by seepage, and the two factors together determine the overall intensity of the renovation project. Regarding the positive and negative correlation, the dependent variable... It is positively correlated with the normalized number of microseismic events and with the normalized average temperature disturbance, respectively; Microseismic event weighting factor and temperature perturbation weighting factor The values ​​of all values ​​are between 0 and 1, and satisfy the following conditions: ,in The recommended value range is 0.3 to 0.5. The recommended value range is 0.5 to 0.7. This range is set because temperature perturbation data reflects the supercritical temperature range. The actual diffusion range and the opening status of seepage channels can more directly characterize the connectivity of the effectively modified area. While the number of microseismic events reflects the activity level of rock fracturing, it may include some events where fracturing occurred but no effective seepage channels were formed. Therefore, the temperature disturbance term is given a slightly higher weight. This allows the comprehensive fracturing intensity value to more accurately reflect the actual fracturing effect; the specific value can be adjusted according to the geological characteristics of the block where the target injection well is located: for reservoirs with well-developed natural fractures, abundant microseismic signals but slow temperature response, the value can be appropriately increased. For example, a value of 0.5 can be used; for reservoirs with low permeability and sensitive temperature disturbances to fracturing fluid response, the value can be appropriately increased. If we take 0.7, we recommend using... , As the default value, this is used to achieve a balanced integration of microseismic events and temperature disturbances; The current time window refers to a time interval consisting of a preset fixed duration, ending at the current sampling time, used to statistically analyze the number of microseismic events and the average temperature disturbance for each depth unit within this period. The recommended length of the current time window is 5 to 15 minutes, determined as follows: If the time window is too short (less than 2 minutes), the number of microseismic events counted within a single window may be insufficient, leading to significant random fluctuations in the statistical results and poor stability of the overall fracturing intensity value; if the time window is too long (greater than 30 minutes), it cannot promptly reflect the dynamic changes in fracturing intensity during the fracturing process, resulting in a lag in the response of the effective displacement channel index to process adjustments; a window length of 5 to 15 minutes strikes a balance between statistical stability and response sensitivity: on the one hand, this duration is sufficient to capture a sufficient number of microseismic events, typically occurring at frequencies of several to dozens per minute in deep coal seams, ensuring statistical significance; on the other hand, this duration is much shorter than the total duration of fracturing operations, which is usually 60 to 120 minutes, enabling real-time tracking of fracturing trends.

[0022] S3: During the supercritical CO2 pumping process, the bottom hole pressure and bottom hole temperature are continuously collected to calculate the phase deviation index. During the short-term pump stop test, the bottom hole pressure is continuously monitored, the bottom hole pressure and time square root relationship curve is plotted, and the dynamic filtration coefficient is obtained by linear fitting using the square root time method. In this embodiment, the phase deviation index is calculated using the following steps: During supercritical CO2 injection, the phase deviation index is calculated by continuously collecting bottom-hole pressure and temperature data. in, This indicates the bottom hole pressure at the current sampling time; This indicates the bottom-hole temperature at the current sampling time; , These represent the critical temperature and critical pressure of CO2, respectively. , These represent the temperature weighting coefficient and the pressure weighting coefficient, respectively. This represents the phase deviation index at the current sampling moment.

[0023] In the above process, the phase deviation index As the dependent variable, it specifically reflects the current sampling time. supercritical at the bottom of the well The actual temperature and pressure conditions deviate from their critical point, i.e., the critical temperature. Critical pressure The comprehensive nature of this technology lies in its ability to transform deviations between temperature and pressure—two quantities with different dimensions and physical meanings—through normalized weighted summation into a dimensionless, real-time quantitative indicator used to determine the bottom of the well. Whether it is in an ideal supercritical state provides a unified quantitative criterion for triggering subsequent phase state adjustment strategies; In this formula, the dependent variable is... With the two core independent variables, namely the normalized temperature deviation term and normalized pressure deviation term Directly related, both are weighted by temperature coefficients. and pressure weighting coefficient A linear weighted summation is performed, where the temperature deviation term reflects the degree of deviation of the current bottom hole temperature from the critical temperature, and the pressure deviation term reflects the degree of deviation of the current bottom hole pressure from the critical pressure. Together, they determine the magnitude of the phase deviation index. The weighting coefficients can be adjusted according to the sensitivity of different coal seams to temperature and pressure. Regarding positive and negative correlations, the dependent variable They are positively correlated with the normalized temperature deviation term and the normalized pressure deviation term, respectively, meaning that the further the bottom hole temperature or pressure deviates from the critical point, the greater the phase deviation index; simultaneously, the temperature weighting coefficient... and pressure weighting coefficient The weight of each deviation term determines its contribution to the dependent variable; the larger the weight, the more significant the impact of that deviation term on the phase deviation index. When When it is smaller, it indicates the bottom of the well. Approaching the critical point, it is in an ideal supercritical state; when When it is larger, it indicates If it deviates far from the critical point, it may tend to be in a gaseous or liquid state, requiring the triggering of corresponding phase adjustment strategies. The critical temperature of CO2 and critical pressure It is an inherent thermophysical constant of CO2, determined according to internationally recognized standard values: critical temperature. Take 31.1℃, critical pressure Use 7.38 MPa; temperature weighting coefficient and pressure weighting coefficient The values ​​of all values ​​are between 0 and 1, and satisfy the following conditions: ,in The recommended value range is 0.3 to 0.5. The recommended value range is 0.5 to 0.7, and it is usually taken as... The reason for setting this range and relative magnitude is that: the effect of pressure on the density and viscosity of supercritical CO2 is more significant than that of temperature near the critical point; near the critical pressure of 7.38 MPa, small changes in pressure cause large fluctuations in density, while the effect of temperature changes is relatively mild; at the same time, the fluctuation range of bottom hole pressure during deep coal seam fracturing is usually wider than that of temperature fluctuation; therefore, giving a higher weight to the pressure deviation term can make the phase deviation index more sensitive to changes in actual working conditions, and can be adopted... , As the default value, it aims to achieve a balanced integration of temperature deviation and pressure deviation.

[0024] In the above embodiments, 20 sets of data on bottom hole pressure and corresponding phase deviation index are given to reflect the change of phase deviation index with changes in bottom hole pressure, as shown in Table 1: Table 1: Relationship between bottom hole pressure and corresponding phase deviation index In Table 1 above, given , , , , Under the condition that the bottom-hole temperature is fixed at 35℃, the phase deviation index increases symmetrically with the degree to which the bottom-hole pressure deviates from the critical pressure of 7.38 MPa. In the low-pressure section where the bottom-hole pressure gradually increases from 4.00 MPa to 7.38 MPa, the phase deviation index continuously decreases from 0.33 to a minimum value of 0.05, indicating that the closer the pressure is to the critical point, the more CO2 tends to the ideal supercritical state. In the high-pressure section where the bottom-hole pressure continues to increase from 7.38 MPa to 12 MPa, the phase deviation index... The index rose from 0.05 to 0.43, indicating that the greater the pressure deviation, the more liquid CO2 tends to be. When the bottom hole pressure is in the range of 6.20 MPa to 8.50 MPa, the phase deviation index is less than 0.2, indicating that the bottom hole CO2 is in an ideal supercritical state. When the bottom hole pressure is lower than 6.20 MPa or higher than 8.50 MPa, the phase deviation index is greater than or equal to 0.2, indicating that the deviation exceeds the allowable range and a phase adjustment strategy needs to be triggered to control the injection temperature and pressure towards the critical point. The corresponding pressure range is approximately 6.20~8.50 MPa, at which point the CO2 at the bottom of the well is determined to be in an ideal supercritical state.

[0025] The logic for obtaining the dynamic filtering coefficient is as follows: When performing a short-stop pump test, plot the bottom hole pressure versus the square root of time. The relationship curve was obtained, and linear fitting was performed using the square root time method to obtain the fitting formula. in, Indicates the first Instantaneous bottom hole pressure at the start of the second pump stop test; Indicates the first In the second pump stop test, the absolute value of the slope of the fitted straight line; An index indicating the number of pump stop tests; Indicates the first During the second pump shutdown test, after the pump was shut down... The bottom hole pressure detected in seconds; Indicates from the first The time variable is the time from the start of the pump stop test, in seconds; Based on the absolute value of the slope of the fitted straight line, a dynamic filtering coefficient is constructed: in, This indicates the viscosity of the fracturing fluid under the current bottom hole temperature and pressure conditions. This indicates the overall permeability of the formation in the area affected by fracturing fluid loss; This indicates the overall equivalent porosity of the formation in the area affected by fracturing fluid loss; This represents the overall equivalent composite compressibility coefficient of the formation in the area affected by fracturing fluid loss; Indicates the first The dynamic filtration coefficient corresponding to the pump stop test.

[0026] In the above process, the absolute value of the slope As an intermediate dependent variable, it specifically reflects the situation in the first... In the short-term pump stop test, the bottom hole pressure increased by the square root of the time after pump stoppage. The rate of decrease, its technical advantage lies in simplifying the pressure decay process after pump shutdown into a linear relationship, allowing the filtration intensity to be controlled by a single slope parameter. Intuitive representation: A higher value indicates a faster pressure drop, meaning greater fluid loss from fracturing to the formation. Based on this, the dynamic fluid loss coefficient... As the final dependent variable, it specifically reflects the first The comprehensive filtration capacity corresponding to the second pump stop test has the technical effect of increasing the measured slope. With formation physical properties, i.e. viscosity Overall penetration rate Overall equivalent porosity Equivalent comprehensive compression coefficient Combined, they are transformed into a filtration loss evaluation index with clear physical meaning, which is used to quantitatively determine whether the current filtration loss state is within a controllable range; Dependent variable With independent variable There is a positive correlation, meaning that the larger the absolute value of the slope of the fitted line, the larger the dynamic filtering coefficient; at the same time With viscosity Overall penetration rate Overall equivalent porosity Equivalent comprehensive compression coefficient product There is a negative correlation, that is, the stronger the overall resistance of the formation to filtration loss, the larger the product, and the smaller the dynamic filtration loss coefficient. Regarding positive and negative correlations: Enlargement leads to An increase indicates that the faster the pressure drops, the more severe the filtration loss; while , , , Increasing any parameter will cause Decrease, of which An increase indicates that the fracturing fluid viscosity is higher, the fluidity is worse, and the filtration is more difficult. An increase indicates higher formation permeability, more unobstructed filtration channels, and easier filtration. and Increased formation reservoir capacity leads to relatively slower filtration attenuation; Overall equivalent comprehensive compression coefficient This reflects the comprehensive reservoir capacity of the formation in the area affected by fracturing fluid loss under pressure changes, and uses regional empirical values ​​as... Engineering estimates, for example, for deep coal seams, i.e., burial depths of 2000m to 4000m, are typically taken as values ​​in the range of... to between; S4: Adjust the phase adjustment strategy according to the phase deviation index and dynamic filtration coefficient; based on the injection displacement, further obtain the cumulative injection amount of supercritical CO2, and construct the effective displacement channel index according to the comprehensive modification intensity value and the phase deviation index, and plot the curve of the effective displacement channel index with the cumulative injection amount, and make corresponding adjustments to the phase adjustment strategy based on the curve.

[0027] In this embodiment, the phase adjustment strategy is adjusted according to the phase deviation index and the dynamic filtering coefficient, specifically as follows: when and When the increase compared to the previous pump shutdown test was less than 30%, it was determined that the bottom hole temperature and bottom hole pressure were close to the critical point, and the supercritical CO2 was in an ideal supercritical state, requiring no adjustment. when If the degree to which the CO2 at the bottom of the well deviates from the critical point exceeds the allowable range, the temperature of the injected CO2 and the pressure at the bottom of the well will be adjusted toward the critical point through the coordinated control of the surface heat exchange equipment and the pump injection rate. when and When the increase compared to the previous pump shutdown test is greater than or equal to 30%, it indicates that the fracturing fluid is rapidly flowing out along natural fractures or high-permeability channels. In the next pumping procedure, a temporary plugging agent should be added to the slug. After adding the temporary plugging agent, the injection rate should be increased by 10% to 20% to help the temporary plugging agent penetrate deeper into the channel. If the concentration of the temporary plugging agent is continuously increased during consecutive preset pump stop tests, then the concentration should be gradually increased until... and When the value is increased to the preset range, the second scenario should be adjusted first.

[0028] In the above process, the phase deviation index and dynamic filtration coefficient are used as two independent control dimensions. By setting clear thresholds, fracturing conditions are divided into three states with different physical mechanisms: "normal phase and controllable filtration", "phase deviation-dominated", and "excessive filtration-dominated". Differentiated control actions are executed for each state, achieving decoupled diagnosis and precise intervention of phase deviation and excessive filtration. At the same time, by establishing a priority rule of "when the phase deviation index is greater than or equal to 0.2 and the dynamic filtration coefficient increases to a preset level, priority is given to phase adjustment", the erroneous temporary blocking operation is avoided when the filtration falsely increases due to phase deterioration, ensuring the physical correctness of the control logic. The number 0.2 serves as the dividing point for the phase deviation index. Its physical basis is as follows: when the bottom-hole temperature or pressure deviates from the critical point by about 15%, the temperature deviation term and the pressure deviation term can be calculated to be about 0.15 based on the critical temperature of 31℃ and the critical pressure of 7.38MPa. The weighted sum of the two is about 0.15 to 0.2. Therefore, 0.2 corresponds to the upper boundary of the bottom-hole carbon dioxide approaching the ideal supercritical state. A value less than 0.2 indicates that the combined degree of temperature and pressure deviation from the critical point is within 15%, and carbon dioxide has the ideal supercritical characteristics of high density, moderate viscosity and strong compressibility. The 30% threshold for the dynamic filtration coefficient increase is based on the following: During normal fracturing, due to the gradual opening of natural fractures or the slow expansion of filtration channels, the dynamic filtration coefficient usually fluctuates naturally by 10% to 20% between two adjacent pump stop tests. Setting the threshold to 30% can effectively filter out normal fluctuations and avoid frequent false triggering of temporary plugging operations. At the same time, the 30% increase corresponds to the critical point of significant activation of filtration channels or formation of new filtration channels in engineering experience. Increasing the injection rate by 10% to 20% to assist the temporary plugging agent in reaching deeper sections of the channel is based on the premise that a low increase in rate is insufficient to push the temporary plugging agent through the near-wellbore filtration zone, while an excessively high increase may lead to over-dilution or bypassing of the target channel. Field tests have verified that a 10% to 20% increase can effectively push the temporary plugging agent to deeper sections of the filtration channel without significantly altering the net fracture pressure. The logic behind gradually increasing the concentration of the temporary plugging agent is that if the dynamic filtration coefficient continues to increase during multiple pump stop tests, it indicates that the current concentration of the temporary plugging agent is insufficient to effectively seal the filtration channel, necessitating a gradual increase in concentration to avoid accidental blockage caused by excessively high concentrations at once. The preset range can be set to 50%. That is, when the phase deviation index is greater than or equal to 0.2 and the increase in dynamic filtration coefficient compared with the previous pump stop test is greater than or equal to 50%, it is determined that the phase deviation is the root cause of the increased filtration, and the operation of adjusting the temperature and pressure towards the critical point is prioritized. When the phase deviation index is greater than or equal to 0.2 but the increase in dynamic filtration coefficient is less than 50%, it indicates that the phase deviation and the activation of the filtration channel have a combined effect, and temperature and pressure regulation and temporary blocking measures need to be implemented simultaneously.

[0029] The specific steps for constructing an effective displacement channel index are as follows: Based on the injection displacement, the cumulative injection displacement at each sampling moment within the statistical time window is summed to obtain the cumulative injection volume of supercritical CO2. Based on the comprehensive modification intensity value and the phase deviation index, an effective displacement channel index is constructed. in, This represents the total effective length of continuous depth units whose comprehensive renovation intensity value exceeds the set threshold within the current time window; This indicates the cumulative amount of supercritical CO2 injected within the current time window; Indicates the total effective length Within, the average value of the comprehensive transformation intensity of all depth units; This represents the average value of the phase deviation index at all sampling moments within the current time window; Indicates the current sampling time The effective displacement channel index; This indicates the increment in the total effective length of the current time window compared to the previous adjacent time window; This represents the increase in the cumulative injection amount of supercritical CO2 at the current sampling time compared to the initial sampling time within the current time window, where t represents the current sampling time.

[0030] In the above process, the effective total length refers to the length of the longest continuous segment formed by continuous depth units whose comprehensive transformation intensity value exceeds the initial candidate threshold within a time window; if there is no continuous segment exceeding the threshold within the time window, the effective total length is zero; the values ​​corresponding to the top 30% to 50% quantiles in the comprehensive transformation intensity value ranking are selected as the initial candidate threshold, or the empirical default value of 0.3 can be used as the initial candidate threshold, that is, when the comprehensive transformation intensity value of the depth unit is greater than or equal to 0.3, it is determined to be effectively transformed.

[0031] Define the total effective length The core objective is to transform the discretely distributed comprehensive stimulation intensity value along the wellbore depth direction into a continuous stimulation range index with clear physical meaning, in order to quantitatively characterize the supercritical range within the current time window. The longitudinal extension of the effective seepage channels formed by fracturing; the advantages of doing so are: First, by using the length of the longest continuous segment among multiple unconnected segments exceeding the threshold as the effective total length, it avoids overestimating the actual connected modification range due to the existence of isolated short segments, ensuring the physical truth of the word "effective" in the effective displacement channel index, that is, only continuously distributed modification segments can form a complete fluid flow path; Second, the effective total length provides a quantitative basis for evaluating the longitudinal uniformity of fracturing modification, when Continuous growth indicates that the crack is constantly expanding into new layers, while stabilization suggests that the activatable area under the current injection mode has been fully modified, requiring temporary blocking and redirection to activate the unmodified "blind spots"; third, the effective total length directly participates in the effective displacement channel index. The calculation, and the marginal renovation item Together, they reflect the effective increase in modification length that can be brought about by the unit cumulative injection volume, enabling the index to sensitively capture the changing trend of modification efficiency. Effective Displacement Channel Index As the dependent variable, it specifically reflects the current sampling time. Unit cumulative injection of supercritical The technical effect of the integrated level of "effective modified volume" and "modification efficiency" is that it integrates four dimensions—effective total length, average comprehensive modification intensity, phase deviation degree, and marginal modification efficiency—into a dimensionless comprehensive evaluation index, which is used to judge the effectiveness of the current fracturing process in real time and provide a quantitative decision-making basis for the staged adjustment strategy. Dependent variable It consists of four core independent variables: total effective length Cumulative injection volume Average comprehensive renovation intensity Average phase deviation index and marginal items .in, This reflects the total length of well sections that have been effectively modified within the current time window. This reflects the investment made to achieve the desired effect of the renovation. Total amount, the ratio of the two It characterizes the "breadth of transformation" efficiency per unit injection volume; This reflects the ratio of the average stimulation intensity to the degree of phase deviation within the effective stimulated well section, characterizing the efficiency of "stimulation quality"; marginal term It reflects the effective total length increment that a unit of new injection can bring compared to the previous adjacent time window, representing the efficiency of "marginal transformation" and used to determine whether the transformation has entered a plateau or decline phase. Regarding positive and negative correlations, the dependent variable Respectively with the effective total length It is positively correlated with the average comprehensive renovation intensity. Positively correlated with marginal terms They are positively correlated; meanwhile, the dependent variable Respectively with cumulative injection volume A negative correlation exists, meaning that for the same effective total length, a smaller injection volume indicates higher efficiency, and the deviation index from the average phase state is also positive. A negative correlation indicates a greater deviation in phase, with a smaller exponent. Through combinations of the above positive and negative correlations... The system can comprehensively evaluate the efficiency of the current fracturing process: the rising phase indicates good marginal efficiency and the strategy should be maintained; the plateau phase indicates that the marginal efficiency is close to zero and temporary blocking and switching should be implemented; and premature decline indicates that the marginal efficiency is negative and attribution adjustments should be made in combination with phase state or filtration loss reasons.

[0032] The corresponding adjustments are made based on the phase adjustment strategy of the change curve, specifically as follows: The effective displacement channel index is plotted in real time as a function of the cumulative injection amount of supercritical CO2. Based on the plot, the following tiered adjustment strategy is implemented: Taking the current sampling time and the previous sampling time as the end points respectively, trace back two consecutive time windows of the same duration, the current time window and the previous time window, and count the effective total length within the two time windows respectively. If the effective total length within the current time window is greater than the effective total length within the previous time window, and this relationship holds true for a finite number of consecutive adjacent time window pairs, then the effective total length is determined to be in a state of continuous growth. If the curve of the effective displacement channel index is in an upward phase for two consecutive sampling times, and the effective total length is in a state of continuous growth, or the growth rate of the average value of the comprehensive transformation intensity value compared with the average value of the comprehensive transformation intensity value of the previous sampling time exceeds the preset threshold, and maintains a positive growth trend over multiple consecutive sampling times in the past, the current phase adjustment strategy should be maintained. If the curve of the effective displacement channel index enters a plateau period and the profile shows that the effective well section no longer increases and the average value of the comprehensive stimulation intensity value tends to stabilize, then temporary blocking and diversion should be implemented in the depth unit where the comprehensive stimulation intensity value is 40% lower than the maximum value of the profile, forcing the fluid to enter a new layer and seeking a second increase in the effective displacement channel index. If the curve of the effective displacement channel index drops prematurely, and the profile shows a shortening of the effective total length, determine the cause in conjunction with step S3: If it is due to... If this results in the temperature of the injected CO2 being adjusted gradually until... Less than 0.2; if due to If the increase is ≥30% compared to the previous pump stop test, add a filtration loss reducer until... The increase compared to the previous pump shutdown test was less than 30%.

[0033] In the above process, "profile" refers to the comprehensive stimulation intensity value plotted along the depth direction of the target injection well. The distribution curve or distribution map, where the horizontal axis is the depth cell index. That is, along the depth position of the wellbore, the vertical axis represents the comprehensive renovation intensity value of each depth unit within the current time window; By changing the benchmark for the effective total length from "the instantaneous value at a single sampling moment" to "the statistical value of two adjacent windows of equal time duration," false growth judgments caused by random fluctuations in microseismic events or instantaneous anomalies in temperature disturbances within a single sampling moment are eliminated, thus improving the noise resistance and statistical robustness of the effective total length growth trend identification. At the same time, requiring that "a finite number of consecutively preset adjacent time window pairs" all satisfy the growth relationship rather than satisfying it only once further eliminates the interference of short-term sporadic fluctuations on trend judgment, ensuring that the effective total length is only judged as continuously growing when it shows a continuous and stable expansion trend. The "preset threshold" refers to the critical growth rate used to determine whether the average value of the comprehensive fracturing intensity value shows a significant positive increase. Its determination method is as follows: First, by collecting historical construction data from multiple fracturing wells in the block where the target injection well is located, extract the actual growth rate data of the average comprehensive fracturing intensity value between two adjacent sampling times during the stage where the fracturing effect is good (i.e., the effective displacement channel index continuously rises and the final production increase is significant). Calculate the statistical distribution characteristics of these growth rates, such as the mean and standard deviation. Then, set the preset threshold to the 50% to 70% quantile of the average growth rate during these effective growth stages, or to the mean minus 0.5 times the standard deviation. This ensures that the threshold can filter out small growth rate fluctuations caused by random fluctuations or measurement noise (usually less than 2% to 3%), while also preventing the actual effective growth trend from being missed due to an excessively high threshold. Alternatively, an empirical default value of 5% can be used as the preset threshold, meaning that when the average increase in the comprehensive fracturing intensity value between adjacent sampling times exceeds 5%, it is considered a significant increase. When the curve of the effective displacement channel index enters a plateau phase and the profile shows that the effective well section is no longer growing and the average value of the comprehensive stimulation intensity value tends to stabilize, it is determined that the activatable near-wellbore area under the current injection mode has been fully stimulated. If injection continues in the original manner at this time, the newly added supercritical CO2 can only be ineffectively lost along the established dominant channels, which can neither expand the stimulated volume nor increase the stimulation intensity, resulting in the effective displacement channel index stagnating. Therefore, it is necessary to implement temporary blocking and diversion in depth units where the comprehensive stimulation intensity value is less than 40% of the maximum value of the profile, forcing the fluid into the new, insufficiently stimulated interval, reactivating the stimulation process to seek a secondary increase in the effective displacement channel index. After plotting the comprehensive modification intensity value profile along the depth direction within the current time window, identify those depth units whose comprehensive modification intensity value is less than 40% of the maximum comprehensive modification intensity value in the profile. These units represent areas that have not been fully modified or have not been modified at all. At the corresponding location of these depth units, inject a temporary plugging agent slug. Utilize the bridging effect formed by the plugging agent particles in the original high-permeability modified area to temporarily block the dominant channels that have been fully modified. This forces the subsequently injected supercritical CO2 to redirect into these low-intensity depth units, achieving a vertical expansion of the modification range and a secondary increase in the effective displacement channel index. Gradual adjustment of the injected CO2 temperature refers to the process where, when the phase deviation is determined to be too large (i.e., the phase deviation index is greater than or equal to 0.2) due to temperature deviation from the critical point, the injection temperature is gradually decreased or increased in a set temperature step, typically 2°C to 3°C. After each adjustment, the injection is stabilized for a period of time, such as 5 to 10 minutes, while continuously monitoring the trend of the phase deviation index. If the phase deviation index decreases after adjusting one step but still does not fall below 0.2, the adjustment continues in the same direction with the same step length. If the phase deviation index increases instead, the gradual adjustment is performed in the opposite direction, such as changing from decreasing to increasing the temperature. Through this successive approximation method, the injection temperature gradually approaches the critical temperature, i.e., around 31°C, until the phase deviation index drops below 0.2, restoring the ideal physical properties of supercritical CO2. The 40% threshold is based on the following: the maximum value of the profile represents the most fully modified depth unit. Setting the threshold to 40% can effectively identify depth units that are "significantly undermodified". These units are neither completely unmodified (0%) nor moderately modified (50% to 70%), but are in a state of "some fluid contact but no effective channel". These units are most easily reactivated by temporary blocking and redirection. If the threshold is set too high, such as 60%, temporary blocking and redirection will be performed too early, resulting in wasted resources. If the threshold is set too low, such as 20%, the redirection time will be delayed, resulting in an excessively long plateau period.

[0034] When the curve of the effective displacement channel index drops prematurely and the profile shows a shortening of the effective total length, it indicates a decline in fracturing efficiency rather than a natural plateau, and the cause must be addressed: If the drop is caused by phase deviation, i.e., the phase deviation index is greater than or equal to 0.2, it means that CO2 deteriorates due to deviation from the critical point, i.e., the viscosity is too low in the gaseous state, leading to filtration loss, and the compressibility is poor in the liquid state, leading to a decrease in fracture-creating capacity. In this case, adjusting the injection temperature stepwise until the phase is restored is the root cause of the problem; if the drop is caused by excessively rapid filtration loss, i.e., the increase in the dynamic filtration coefficient is greater than or equal to 30%, it means that the fracturing fluid is rapidly flowing out along natural fractures or high-permeability channels. In this case, adding a filtration-reducing agent to block the dominant channels is the direct way to block the loss path; The 30% threshold is based on the fact that the normal fluctuation range of the dynamic filtration loss coefficient between two adjacent pump stop tests is usually between 10% and 20%. Setting the threshold to 30% can effectively filter out normal fluctuations and avoid accidental triggering of the filtration loss reduction operation due to random fluctuations. At the same time, 30% corresponds to the critical point of significant activation of the filtration loss channel or the formation of a new filtration loss channel in engineering experience. Exceeding this value indicates that filtration loss has had a substantial negative impact on the modification and intervention is necessary. Adding a filtration loss reducer refers to adding a chemical slug with temporary plugging function to the fracturing fluid system in the next pumping procedure when the filtration loss is determined to be too rapid (i.e., the increase in the dynamic filtration loss coefficient compared to the previous pump stop test is greater than or equal to 30%) and the phase deviation index is normal. These filtration loss reducers are usually materials such as nanoparticles, biodegradable polymer fibers, or viscoelastic surfactants, with a particle size range of 0.1 micrometers to 1 millimeter. After the filtration loss reducer enters the formation with the fracturing fluid, it forms a bridge or filter cake at the entrance of natural fractures or high-permeability channels, temporarily blocking these advantageous filtration loss channels, thereby reducing the ineffective leakage of fracturing fluid into the formation, improving the fracture creation efficiency of the fracturing fluid, and forcing the fracture to extend to the far field.

[0035] The above formulas are all dimensionless calculations. The formulas are derived from software simulations based on a large amount of collected data to obtain the most recent real-world results. The preset parameters in the formulas are set by those skilled in the art according to the actual situation.

[0036] The above embodiments can be implemented, in whole or in part, by software, hardware, firmware, or any other combination thereof. When implemented in software, the above embodiments can be implemented, in whole or in part, as a computer program product. Those skilled in the art will recognize that the units and algorithm steps of the various examples described in conjunction with the embodiments disclosed herein can be implemented by electronic hardware, or a combination of computer software and electronic hardware. Whether these functions are implemented in hardware or software depends on the specific application and design constraints of the technical solution.

[0037] The units described as separate components may or may not be physically separate. The components shown as units may or may not be physical units; they may be located in one place or distributed across multiple network units. Some or all of the units can be selected to achieve the purpose of this embodiment, depending on actual needs.

[0038] The above description is merely a specific embodiment of this application, but the scope of protection of this application is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this application should be included within the scope of protection of this application.

Claims

1. A method for determining supercritical CO2 fracturing technology under fluidized bed mining of deep coal seams, characterized by the following steps: include: S1: Divide the target injection well into depths and set depth units at equal intervals. Collect injection flow rate, vibration data and temperature data of each depth unit at a fixed sampling frequency. Based on the vibration data, use the energy ratio method to automatically detect micro-vibration events. At the same time, compare the temperature data with the initial temperature to generate the temperature disturbance value of each depth unit at each sampling time. S2: Taking the current sampling time as the end point, trace back a time window of a preset fixed duration as the current time window, and count the number of microseismic events and the average temperature disturbance value of each depth unit along the target injection well within the current time window. Determine the comprehensive transformation intensity value of each depth unit based on the number of microseismic events and the average temperature disturbance value. S3: During the supercritical CO2 pumping process, the bottom hole pressure and bottom hole temperature are continuously collected to calculate the phase deviation index. During the short-term pump stop test, the bottom hole pressure is continuously monitored, the bottom hole pressure and time square root relationship curve is plotted, and the dynamic filtration coefficient is obtained by linear fitting using the square root time method. S4: Adjust the phase adjustment strategy according to the phase deviation index and dynamic filtration coefficient; based on the injection displacement, further obtain the cumulative injection amount of supercritical CO2, and construct the effective displacement channel index according to the comprehensive modification intensity value and the phase deviation index, and plot the curve of the effective displacement channel index with the cumulative injection amount, and make corresponding adjustments to the phase adjustment strategy based on the curve.

2. The method for determining the supercritical CO2 fracturing process under fluidized bed mining of deep coal seams according to claim 1, characterized in that, The specific steps of S1 are as follows: The starting and ending depths of the target injection well are determined, and the wellbore is divided into several continuous depth units at equal intervals along the depth direction, with each depth unit corresponding to a depth interval; a fixed sampling time interval is set to generate a discrete sampling time sequence; vibration signals and temperature data of each depth unit are collected synchronously at each sampling time to form a depth-time two-dimensional data matrix; Bandpass filtering is applied to the vibration data. Starting from the current sampling time, the preset short time window length and long time window length are traced back respectively. The average value of the vibration data within the two time windows is calculated, and the ratio between the two is calculated. When this ratio exceeds a preset threshold, it is determined that a micro-seismic event has been triggered. The temperature perturbation value of each depth cell at each sampling time is generated by comparing the measured temperature data of the depth cell at the current sampling time with the initial temperature of the depth cell, calculating the absolute value of the difference between the two, and obtaining the temperature perturbation value at the current sampling time.

3. The method for determining the supercritical CO2 fracturing process under fluidized bed mining of deep coal seams according to claim 1, characterized in that, The specific steps for determining the comprehensive retrofit intensity value for each depth element are as follows: Within the current time window, the number of microseismic events and the average temperature disturbance value are statistically analyzed for each depth unit along the target injection well. Based on these data, the comprehensive stimulation intensity value for each depth unit is determined using the following formula: in, This represents the maximum number of microseismic events across all depth elements within the current time window. Indicates the first Number of microseismic events per depth element within the current time window; Indicates the first The average temperature perturbation value of each depth cell within the current time window; This represents the maximum value of the average temperature perturbation value across all depth cells within the current time window. Indicates the first The comprehensive renovation intensity value of each depth unit within the current time window; This represents the weighting factor for microseismic events. This represents the temperature disturbance weighting factor. ; Indicates the depth cell index; Indicates the current time window.

4. The method for determining the supercritical CO2 fracturing process under fluidized bed mining of deep coal seams according to claim 1, characterized in that, The specific steps for calculating the phase deviation index are as follows: During supercritical CO2 injection, the phase deviation index is calculated by continuously collecting bottom-hole pressure and temperature data. in, This indicates the bottom hole pressure at the current sampling time; This indicates the bottom-hole temperature at the current sampling time; , These represent the critical temperature and critical pressure of CO2, respectively. , These represent the temperature weighting coefficient and the pressure weighting coefficient, respectively. This represents the phase deviation index at the current sampling moment.

5. The method for determining supercritical CO2 fracturing technology under fluidized bed mining of deep coal seams according to claim 4, characterized in that, The logic for obtaining the dynamic filtering coefficient is as follows: When performing a short-stop pump test, plot the bottom hole pressure versus the square root of time. The relationship curve was obtained, and linear fitting was performed using the square root time method to obtain the fitting formula. in, Indicates the first Instantaneous bottom hole pressure at the start of the second pump stop test; Indicates the first In the second pump stop test, the absolute value of the slope of the fitted straight line; An index indicating the number of pump stop tests; Indicates the first During the second pump shutdown test, after the pump was shut down... The bottom hole pressure detected in seconds; Indicates from the first The time variable is the time from the start of the pump stop test, in seconds; Based on the absolute value of the slope of the fitted straight line, a dynamic filtering coefficient is constructed: in, This indicates the viscosity of the fracturing fluid under the current bottom hole temperature and pressure conditions. This indicates the overall permeability of the formation in the area affected by fracturing fluid loss; This indicates the overall equivalent porosity of the formation in the area affected by fracturing fluid loss; This represents the overall equivalent composite compressibility coefficient of the formation in the area affected by fracturing fluid loss; Indicates the first The dynamic filtration coefficient corresponding to the pump stop test.

6. The method for determining supercritical CO2 fracturing technology under fluidized bed mining of deep coal seams according to claim 5, characterized in that, Based on the phase deviation index and the dynamic filtering coefficient, the phase adjustment strategy is adjusted accordingly, specifically as follows: when and When the increase compared to the previous pump shutdown test was less than 30%, it was determined that the bottom hole temperature and bottom hole pressure were close to the critical point, and the supercritical CO2 was in an ideal supercritical state, requiring no adjustment. when When it is determined that the degree to which the CO2 at the bottom of the well deviates from the critical point exceeds the allowable range, the temperature of the injected CO2 and the pressure at the bottom of the well are adjusted towards the critical point through the coordinated control of the surface heat exchange equipment and the pump injection rate. when and When the increase compared to the previous pump shutdown test is greater than or equal to 30%, it indicates that the fracturing fluid is rapidly flowing out along natural fractures or high-permeability channels. In the next pumping procedure, a temporary plugging agent should be added to the slug. After adding the temporary plugging agent, the injection rate should be increased by 10% to 20% to help the temporary plugging agent penetrate deeper into the channel. If the concentration of the temporary plugging agent is continuously increased during consecutive preset pump stop tests, then the concentration should be gradually increased until... and When the value is increased to the preset range, the second scenario should be adjusted first.

7. The method for determining the supercritical CO2 fracturing process under fluidized bed mining of deep coal seams according to claim 1, characterized in that, The specific steps for constructing an effective displacement channel index are as follows: Based on the injection displacement, the cumulative injection displacement at each sampling moment within the statistical time window is summed to obtain the cumulative injection volume of supercritical CO2. Based on the comprehensive modification intensity value and the phase deviation index, an effective displacement channel index is constructed. in, This represents the total effective length of continuous depth units whose comprehensive renovation intensity value exceeds the set threshold within the current time window; This indicates the cumulative amount of supercritical CO2 injected within the current time window; Indicates the total effective length Within, the average value of the comprehensive transformation intensity of all depth units; This represents the average value of the phase deviation index at all sampling moments within the current time window; Indicates the current sampling time The effective displacement channel index; This indicates the increment in the total effective length of the current time window compared to the previous adjacent time window; This represents the increase in the cumulative injection amount of supercritical CO2 at the current sampling time compared to the initial sampling time within the current time window; t represents the current sampling time.

8. The method for determining the supercritical CO2 fracturing process under fluidized bed mining of deep coal seams according to claim 7, characterized in that, The corresponding adjustments are made based on the phase adjustment strategy of the change curve, specifically as follows: The effective displacement channel index is plotted in real time as a function of the cumulative injection amount of supercritical CO2. Based on the plot, the following tiered adjustment strategy is implemented: Taking the current sampling time and the previous sampling time as the end points respectively, trace back two consecutive time windows of the same duration, the current time window and the previous time window, and count the effective total length within the two time windows respectively. If the effective total length within the current time window is greater than the effective total length within the previous time window, and this relationship holds true for a finite number of consecutive adjacent time window pairs, then the effective total length is determined to be in a state of continuous growth. If the curve of the effective displacement channel index is in an upward phase for two consecutive sampling times, and the effective total length is in a state of continuous growth, or the growth rate of the average value of the comprehensive transformation intensity value compared with the average value of the comprehensive transformation intensity value of the previous sampling time exceeds the preset threshold, and maintains a positive growth trend over multiple consecutive sampling times in the past, the current phase adjustment strategy should be maintained. If the curve of the effective displacement channel index enters a plateau period and the profile shows that the effective well section no longer increases and the average value of the comprehensive stimulation intensity value tends to stabilize, then temporary blocking and diversion should be implemented in the depth unit where the comprehensive stimulation intensity value is 40% lower than the maximum value of the profile, forcing the fluid to enter a new layer and seeking a second increase in the effective displacement channel index. If the curve of the effective displacement channel index drops prematurely, and the profile shows a shortening of the effective total length, determine the cause in conjunction with step S3: If it is due to... If this results in the temperature of the injected CO2 being adjusted gradually until... Less than 0.2; If because If the increase is ≥30% compared to the previous pump stop test, add a filtration loss reducer until... The increase compared to the previous pump shutdown test was less than 30%.

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