A method and apparatus for controlling CO2 injection pressure

Abstract

The application provides a CO2 injection pressure control method and device. The method divides the CO2 injection process into multiple continuous injection periods, each injection period sequentially includes a pressure increasing stage and a pressure relief stage; in the pressure increasing stage of the current injection period, the injection pump is controlled to increase the injection pressure at a preset constant rate; in the corresponding pressure relief stage, the injection pump is controlled to stop pressure injection, the bottom hole pressure in the stage is continuously collected, and a logarithmic curve of the pressure change with time in the pressure increasing stage is generated by taking time as the horizontal coordinate and the logarithmic value of the bottom hole pressure as the vertical coordinate; based on the logarithmic curve and the logarithmic curve of the last injection period, the current dynamic fracturing pressure is determined, and based on the current dynamic fracturing pressure, the injection pressure in the pressure increasing stage of the next injection period is controlled. The method maximizes the injection efficiency under the premise of ensuring the safety of the caprock.

Description

Technical Field

[0001] This application relates to the field of CO2 capture, utilization and storage technology, and more specifically, to a method and apparatus for controlling CO2 injection pressure. Background Technology

[0002] In response to global climate change, CO2 utilization and geological storage technologies are receiving widespread attention. Among these, the current mainstream storage technology involves injecting captured CO2 from industrial emissions into deep saline aquifers or depleted oil and gas reservoirs via wellbore for long-term safe geological storage. The injection process essentially involves injecting high-pressure CO2 fluid into tight underground reservoirs. The core safety challenge lies in ensuring that the injection pressure remains consistently below the formation's fracturing pressure, thereby avoiding mechanical damage to the caprock, preventing CO2 leakage, and maintaining geological stability.

[0003] Currently, in CO2 geological storage injection operations, the main method for obtaining formation fracture pressure parameters relies on pre-operation geological exploration data. The specific process includes: rock mechanics experiments such as core drilling and laboratory core mechanics tests to determine rock tensile strength; calculating in-situ stress distribution using well logging data; and then statically estimating the formation fracture pressure using empirical formulas such as the Eaton method. In actual CO2 geological storage injection operations, operators set a fixed upper limit for safe injection pressure based on this pre-estimated fracture pressure value and control the injection process using a step-by-step pressure increase method. In some advanced practices, "injection-shut-in-pressure drop" tests are conducted periodically. By analyzing the pressure decay curve, the formation condition is indirectly assessed, serving as a reference for adjusting the injection pressure.

[0004] However, the existing CO2 injection pressure control technology mentioned above cannot monitor the dynamic changes of formation fracture pressure in real time during the injection process. As a result, the setting of the injection pressure can only rely on the static estimate before injection or the intermittent test results after shutting in the well, and cannot be dynamically adjusted according to the real-time feedback of rock mechanical response. Summary of the Invention

[0005] The purpose of this application is to provide a method and apparatus for controlling CO2 injection pressure, which can compare the logarithmic pressure curves of the pressure relief phase of adjacent injection cycles, realize the dynamic rupture pressure in real time, and adaptively adjust the injection pressure accordingly, so as to maximize the injection efficiency while ensuring the safety of the caprock.

[0006] Firstly, a method for controlling CO2 injection pressure is provided, which may include: The CO2 injection process is divided into multiple consecutive injection cycles, each of which includes a pressurization phase and a depressurization phase. During the pressurization phase of the current injection cycle, the injection pump is controlled to increase the injection pressure at a preset constant rate; during the corresponding depressurization phase, the injection pump is controlled to stop injecting pressure, and the bottom hole pressure during this phase is continuously collected. A logarithmic curve of pressure change over time during this phase is generated with time as the abscissa and the logarithm of the bottom hole pressure as the ordinate. Based on the logarithmic curve and the logarithmic curve of the previous injection cycle, the current dynamic rupture pressure is determined, and based on the current dynamic rupture pressure, the injection pressure in the pressurization phase of the next injection cycle is controlled.

[0007] In one possible implementation, the CO2 injection process is divided into multiple consecutive injection cycles, each of which includes a pressurization phase and a depressurization phase in sequence. Before the formal CO2 injection, a short-term test injection operation is performed. The injection is increased at a preset constant rate until the bottom hole pressure reaches the preset upper limit of the test injection. Then the injection is stopped and the total time for the bottom hole pressure to naturally decay to the initial static pressure is recorded. The duration of the pressurization phase during the injection test is determined as the duration of the pressurization phase in each injection cycle, and the total duration of the natural decay of the bottom hole pressure is determined as the duration of the depressurization phase in each injection cycle.

[0008] In one possible implementation, the current dynamic rupture pressure is determined from the logarithmic curve of the previous injection cycle and the logarithmic curve of the previous injection cycle, including: Overlay the logarithmic curve of the current injection cycle with the logarithmic curve of the previous injection cycle on the same time axis, calculate the sum of the areas of the closed regions enclosed by the two curves, and determine the sum of the areas as the current hysteresis loop area of ​​the current injection cycle. Compare the current hysteresis loop area of ​​the current injection cycle with the hysteresis loop area of ​​the previous injection cycle. If the increase ratio of the current hysteresis loop area to the hysteresis loop area of ​​the previous cycle exceeds a preset mutation threshold, then the bottom hole peak pressure is determined as the current dynamic fracture pressure.

[0009] In one possible implementation, the preset mutation threshold is obtained by means of: At the beginning of the injection process, take the M consecutive injection cycles before the current injection cycle, calculate the increase ratio of the hysteresis loop area between adjacent injection cycles, and determine the dynamically adjusted mutation threshold based on the arithmetic mean of the M-1 increase ratios. Afterwards, after every N consecutive injection cycles, the increase ratio of the hysteresis loop area between adjacent injection cycles in the N injection cycles is calculated, and the dynamically adjusted mutation threshold is determined based on the median value of the N-1 increase ratios. Where M is a positive integer not less than 3 and less than N; N is a positive integer not less than 5.

[0010] In one possible implementation, the injection pressure during the pressurization phase of the next injection cycle is controlled based on the current dynamic rupture pressure, including: Obtain the peak pressure actually reached during the pressurization phase of the current injection cycle; Calculate the absolute difference between the peak pressure and the current dynamic rupture pressure, and use half of the absolute difference as the safety offset. The upper limit of the injection pressure in the boosting phase of the next injection cycle is set to the difference between the current dynamic fracturing pressure and the safety offset, so that the bottom hole pressure is monitored in real time during the boosting phase of the next injection cycle, and the injection pump is controlled so that the bottom hole pressure never exceeds the upper limit of the injection pressure.

[0011] In one possible implementation, after detecting that the increase in the current hysteresis loop area relative to the previous cycle hysteresis loop area exceeds a preset abrupt change threshold, the method further includes: The duration of the pressurization phase and the duration of the depressurization phase in each subsequent injection cycle are proportionally shortened to a preset percentage of the original duration, and the minimum value of the total duration of the injection cycle after the shortening is not lower than the preset minimum response time.

[0012] In one possible implementation, the preset constant rate is set in the following ways: The starting time of the depressurization phase of the previous injection cycle is taken as the zero point. A continuous sampling interval is taken from the zero point as the initial segment. The duration of this sampling interval is less than a preset proportion of the total duration of the entire depressurization phase. Within the initial segment, the collected bottom hole pressure values ​​are linearly fitted with time as the horizontal axis and the logarithm of the bottom hole pressure as the vertical axis. The absolute value of the slope of the fitted line is taken as the absolute value of the slope of the initial segment. The absolute value is compared with a preset first slope threshold and a second slope threshold, wherein the first slope threshold is greater than the second slope threshold; If the absolute value is greater than the first slope threshold, the boost rate of the current injection cycle is reduced by a predetermined deceleration ratio; if the absolute value is less than the second slope threshold, the boost rate of the current injection cycle is increased by a predetermined acceleration ratio.

[0013] Secondly, a CO2 injection pressure control device is provided, which may include: The CO2 injection process is divided into multiple consecutive injection cycles, each of which includes a pressurization phase and a depressurization phase. The control unit is used to control the injection pump to increase the injection pressure at a preset constant rate during the pressurization phase of the current injection cycle; and to control the injection pump to stop injecting pressure during the corresponding depressurization phase, and to control the data acquisition module to continuously acquire the bottom hole pressure during that phase. The generation unit is used to generate a logarithmic curve of pressure change over time in this stage, with time as the horizontal axis and the logarithm of the bottom hole pressure as the vertical axis. The determination unit is used to determine the current dynamic rupture pressure based on the logarithmic curve of the current logarithmic curve and the logarithmic curve of the previous injection cycle. The control unit is also used to control the injection pressure during the pressurization phase of the next injection cycle based on the current dynamic rupture pressure.

[0014] Thirdly, an electronic device is provided, which includes a processor, a communication interface, a memory, and a communication bus, wherein the processor, the communication interface, and the memory communicate with each other through the communication bus; Memory, used to store computer programs; When a processor executes a program stored in memory, it implements any of the steps described in the first aspect above.

[0015] Fourthly, a computer-readable storage medium is provided, wherein a computer program is stored therein, and when executed by a processor, the computer program implements the steps of any of the methods described in the first aspect above.

[0016] The CO2 injection pressure control method and apparatus provided in this application divide the CO2 injection process into multiple consecutive injection cycles, each cycle including a pressurization phase and a depressurization phase. During the pressurization phase of the current injection cycle, the injection pump is controlled to increase the injection pressure at a preset constant rate. During the corresponding depressurization phase, the injection pump is controlled to stop injecting pressure, and the bottom hole pressure within this phase is continuously collected. A logarithmic curve of pressure versus time is generated, with time as the abscissa and the logarithmic value of the bottom hole pressure as the ordinate. Based on this logarithmic curve and the logarithmic curve of the previous injection cycle, the current dynamic fracturing pressure is determined, and based on the current dynamic fracturing pressure, the injection pressure in the pressurization phase of the next injection cycle is controlled. This method compares the pressure logarithmic curves of the depressurization phases of adjacent injection cycles to deduce the dynamic fracturing pressure in real time and adaptively adjust the injection pressure accordingly, maximizing injection efficiency while ensuring caprock safety. Attached Figure Description

[0017] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the embodiments of this application will be briefly introduced below. It should be understood that the following drawings only show some embodiments of this application and should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0018] Figure 1A flowchart illustrating a method for controlling CO2 injection pressure provided in an embodiment of this application; Figure 2 A schematic diagram of a CO2 injection pressure control device provided in an embodiment of this application; Figure 3 This is a schematic diagram of the structure of an electronic device provided in an embodiment of this application. Detailed Implementation

[0019] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of the embodiments. Based on the embodiments of this application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of this application. Unless otherwise defined, the technical or scientific terms used in this application should have the ordinary meaning understood by those skilled in the art. The terms "first," "second," and similar terms used in this application do not indicate any order, quantity, or importance, but are only used to distinguish different components. The terms "comprising" or "including," etc., mean that the element or object preceding the word covers the element or object listed after the word and its equivalents, but does not exclude other elements or objects. The terms "connection," "coupled," or "linked," etc., are not limited to physical or mechanical connections, but can include electrical connections, whether direct or indirect.

[0020] The hardware system relied upon by the CO2 injection pressure control method provided in this application embodiment includes: a CO2 injection pump, a downhole pressure gauge, a data acquisition module, a controller (industrial computer or PLC), and a storage unit. The outlet of the injection pump is connected to the wellhead of the injection well via a CO2 pipeline. The downhole pressure gauge is fixed to the bottom of the injection tubing at the target injection depth and is used to measure the bottom hole pressure in real time. The signal cable or wireless transmission module of the downhole pressure gauge is connected to the data acquisition module, and the output of the data acquisition module is connected to the controller. The control signal output of the controller is connected to the speed or pressure control port of the injection pump. The storage unit is used to save the acquired pressure time series, calculated intermediate parameters (such as hysteresis loop area, mutation threshold, etc.), and program instructions.

[0021] The preferred embodiments of this application are described below with reference to the accompanying drawings. It should be understood that the preferred embodiments described herein are for illustration and explanation only and are not intended to limit this application. Furthermore, the embodiments and features in the embodiments of this application can be combined with each other without conflict.

[0022] Figure 1This is a flowchart illustrating a method for controlling CO2 injection pressure according to an embodiment of this application. Figure 1 As shown, the method may include: Step S110: Divide the CO2 injection process into multiple consecutive injection cycles, each injection cycle including a pressurization stage and a depressurization stage.

[0023] The controller divides the CO2 injection process into multiple consecutive injection cycles, each cycle consisting of a pressurization phase and a depressurization phase. This division is automatically executed by the controller according to time logic: at the end of each cycle, the pressurization phase of the next cycle is automatically started.

[0024] Before the formal CO2 injection, the controller performs a short trial injection to determine the baseline cycle length. Specifically: The controller drives the injection pump to inject pressure at a preset constant rate (e.g., 0.1 MPa / min) while continuously collecting bottom hole pressure data.

[0025] When the bottom hole pressure reaches the preset upper limit of the injection test (such as 70% of the initial fracture pressure estimated based on geological exploration data), the controller immediately stops the injection pump.

[0026] Record the total time it takes for the bottomhole pressure to naturally decay to the initial static pressure (i.e., the original formation pressure before injection), denoted as . .

[0027] The time taken from the start of pressurization to reaching the upper limit of the test injection is denoted as . And determine the duration of the pressurization phase in each injection cycle during the formal injection; Determine the duration of the depressurization phase in each injection cycle.

[0028] In subsequent formal injections, all injection cycles used the aforementioned duration until the controller detected a significant change in formation condition, at which point the trial injection operation was re-executed. Trial injection calibration ensured that the cycle duration matched the pressure response characteristics of a specific formation, avoiding blindly setting cycles that could lead to incomplete observation of the pressure decay curve or wasted injection time.

[0029] Step S120: During the pressurization phase of the current injection cycle, control the injection pump to increase the injection pressure at a preset constant rate.

[0030] First, during the pressurization phase, the controller needs to pre-determine a preset constant rate. This rate is not a fixed value, but is dynamically adjusted based on the initial decay slope of the depressurization phase in the previous injection cycle, as detailed below: Obtain the absolute value of the slope of the initial segment of the pressure decay curve during the depressurization phase of the previous injection cycle. The initial segment is defined as follows: taking the start time of the depressurization phase as zero, a continuous sampling interval is taken starting from zero. The duration of this sampling interval is less than a preset proportion of the total duration of the entire depressurization phase (e.g., less than 20% of the total duration). This preset proportion can be pre-set by the operator or adaptively determined by the computer based on the sampling frequency (e.g., taking the first 10 sampling points).

[0031] Within this initial segment, in terms of time The x-axis represents the logarithmic value of the bottom hole pressure. Using the vertical axis as the ordinate, a least-squares linear fit is performed on the collected discrete values ​​of bottom-hole pressure to obtain a straight line, the slope of which is denoted as . The absolute value of the slope As the absolute value of the slope of the initial segment.

[0032] The controller has a preset first slope threshold. Second slope threshold ,and .Compare With these two thresholds: like This indicates that the pressure decay is too rapid (the formation has good permeability or low risk of fracturing), and the pressurization rate of the current injection cycle should be reduced by a predetermined rate reduction ratio (e.g., to 70% of the original rate).

[0033] like This indicates that the pressure decay is too slow (the formation is dense or the fracture pressure is close), so the pressurization rate of the current injection cycle should be increased by a predetermined rate increase ratio (e.g., to 120% of the original rate).

[0034] Otherwise, maintain the original rate.

[0035] This dynamic rate setting method matches the injection pressurization rate with the actual seepage capacity of the formation, maximizing injection efficiency under safe conditions, while avoiding approaching the fracture pressure too quickly due to an inappropriate rate.

[0036] Secondly, during the pressurization phase of the current injection cycle, the controller maintains a constant rate (denoted as ) as determined in the above manner. Control the injection pump to increase the injection pressure, and simultaneously continuously collect bottom hole pressure values ​​at a sampling frequency of no less than once per second. The controller monitors the pressure value in real time until the predetermined peak pressure (i.e., the pressure limit) of the injection cycle is reached. This occurs when the duration of the pressurization phase reaches the baseline duration. If the pressure reaches the upper limit prematurely, the pressurization phase ends, and the peak bottom-hole pressure reached at the end of this phase is recorded. It is stored in the storage unit for use in the next injection cycle.

[0037] Step S130: During the corresponding depressurization stage, control the injection pump to stop injecting pressure, continuously collect the bottom hole pressure during this stage, and generate a logarithmic curve of pressure change with time during this stage with time as the abscissa and the logarithm of the bottom hole pressure as the ordinate.

[0038] First, during the depressurization phase of each injection cycle, the controller issues a command to stop the injection pump from injecting pressure, and simultaneously begins continuously acquiring discrete pressure values ​​of the bottom hole pressure decaying over time. The sampling frequency is no less than once per second, and the acquisition duration covers the entire depressurization phase.

[0039] Then, for each time point collected... ( The corresponding bottom hole pressure value The controller performs the following calculations: Take the logarithm to the base 10: In terms of time x-axis The ordinate is the vertical axis, for discrete points. By performing a least-squares linear fit, a straight line is obtained. The equation of this line is: ,in The slope The intercept is given. This straight line is the pressure logarithm-time curve for this depressurization phase, that is, the logarithmic curve of pressure change over time.

[0040] The fitted curve can more clearly reflect the exponential law of pressure decay, transforming nonlinear decay into a linear relationship and eliminating the influence of pressure amplitude differences on the curve shape.

[0041] Step S140: Based on the logarithmic curve and the logarithmic curve of the previous injection cycle, determine the current dynamic rupture pressure, and based on the current dynamic rupture pressure, control the injection pressure in the pressurization phase of the next injection cycle.

[0042] It should be noted that the hysteresis loop area in this application refers to the area of ​​difference between the two pressure logarithmic-time curves of the decompression phases within a common time interval during adjacent injection cycles. This area of ​​difference characterizes the relative change in formation seepage characteristics between two adjacent injection cycles. When the area of ​​difference undergoes a sudden change, it indicates a degradation of formation fracture pressure.

[0043] First, the logarithmic curve of the current injection cycle is superimposed on the logarithmic curve of the previous injection cycle on the same time axis. The sum of the areas of the closed regions enclosed by the two curves is calculated, and this sum of areas is determined as the current hysteresis loop area of ​​the current injection cycle. Specifically, the controller will determine the current injection cycle (the...) The pressure logarithm-time curve generated during the depressurization phase of the cycle. Compared with the previous injection cycle (the first one) Corresponding curve of period) The curves are overlaid on the same time axis. Since the acquisition time intervals of the two curves may not be completely consistent (e.g., due to different depressurization times), the controller first extracts the common time interval. ,in Let this be the shorter of the two depressurization phases. Then, calculate the sum of the areas of the closed regions enclosed by the two curves within this common time interval, and determine this sum as the [missing value]. Area of ​​the hysteresis loop in the period The specific calculation formula is as follows: In the formula, the integrand is the absolute value of the difference between the ordinates of the two curves at the same time t, and the integral result is the area of ​​the region between the two curves (i.e., the total area of ​​the closed region). In discrete implementation, the trapezoidal rule or the rectangular rule is used to approximate the above integral.

[0044] Next, the current hysteresis loop area of ​​the current injection cycle is compared with the hysteresis loop area of ​​the previous injection cycle. If the increase in the current hysteresis loop area relative to the hysteresis loop area of ​​the previous injection cycle exceeds a preset abrupt change threshold, the bottom hole peak pressure is determined as the current dynamic fracturing pressure. Specifically, the controller compares the hysteresis loop area of ​​the current cycle. Hysteresis loop area compared to the previous injection cycle Calculate the increase ratio: ;like Exceeding the preset mutation threshold If so, it is determined that the dynamic fracturing pressure of the current formation has decreased to the bottom hole peak pressure reached at the end of the pressurization phase of the previous injection cycle. The following, and will be Determined as the current dynamic rupture pressure By utilizing abrupt changes in the hysteresis loop area as a precursor indicator of formation mechanical degradation, real-time tracking of dynamic fracturing pressure was achieved.

[0045] In some embodiments, the controller employs the following dual mechanism to obtain the mutation threshold: At the beginning of the injection process, take M consecutive injection cycles preceding the current injection cycle (preferred). The increase percentage of the hysteresis loop area during adjacent injection cycles is calculated, and a dynamically adjusted mutation threshold is determined based on the arithmetic mean of M-1 increase percentages. For example, the mutation threshold is obtained by multiplying the arithmetic mean of M-1 increase percentages by two. Then, after every N consecutive injection cycles (preferably...),... The algorithm calculates the percentage increase in the hysteresis loop area between adjacent injection cycles over N injection cycles, and determines a dynamically adjusted mutation threshold based on the median of N-1 percentage increases. For example, the current mutation threshold can be updated to 2.5 times this median value.

[0046] Where M is a positive integer not less than 3 and less than N; N is a positive integer not less than 3.

[0047] Furthermore, based on After determining the mutation threshold using an arithmetic mean of increasing proportions, the controller can also activate a threshold decay mechanism, specifically: Real-time monitoring of the hysteresis loop area in each injection cycle; when the hysteresis loop area in two consecutive injection cycles does not exceed the current mutation threshold (i.e., ... and ), and activate the decay mechanism.

[0048] Set the current mutation threshold Multiply by an attenuation factor less than 1 (like ), thus obtaining a new mutation threshold: .

[0049] The attenuation coefficient gradually decreases as the number of consecutive cycles without alarm triggering increases (i.e., each stable cycle is multiplied by a smaller coefficient, such as exponential attenuation), until it reaches the preset lower limit of attenuation. The decay stops when the time is right.

[0050] When the hysteresis loop area exceeds the current mutation threshold again, the mutation threshold is immediately reset to the original value calculated most recently based on the arithmetic mean or median (i.e., the value before decay), and the decay process restarts.

[0051] This mechanism enables the mutation threshold to automatically reduce its sensitivity during the formation's stable period, avoiding frequent false triggering of pressure adjustments due to normal minor fluctuations; while it can quickly restore high sensitivity when the risk of rupture is approaching, thus achieving dynamic optimization of the threshold through self-adaptation.

[0052] In some embodiments, to avoid false triggering due to noise or local disturbances, the controller also executes the following anti-false triggering logic: When the hysteresis loop area increases proportionally between two consecutive injection cycles and All exceed the current mutation threshold However, the difference between these two increases is less than the preset stable fluctuation threshold. (Right now When this occurs, the controller determines it as a suspicious event rather than a genuine drop in rupture pressure.

[0053] In this case, it is prohibited to update the current dynamic rupture pressure to the peak pressure of the previous injection cycle; the original dynamic rupture pressure should be maintained. Unchanged. Simultaneously, an alarm message indicating a questionable formation state is generated, instructing the computer to use 90% of the current pressure limit as the injection pressure limit for the next three injection cycles (i.e.,...). Perform confirmatory injection. After verification, re-inject based on the most recent... Each injection cycle calculates a sudden change threshold and continues normal judgment. This anti-false triggering logic effectively distinguishes between genuine formation fracture pressure drops and transient disturbances, avoiding unnecessary pressure reduction operations and maintaining injection efficiency.

[0054] Corresponding to the above method, embodiments of this application also provide a CO2 injection pressure control device, such as... Figure 2 As shown, the device includes: The CO2 injection process is divided into multiple consecutive injection cycles, each of which includes a pressurization phase and a depressurization phase. The control unit 210 is used to control the injection pump to increase the injection pressure at a preset constant rate during the pressurization phase of the current injection cycle; and to control the injection pump to stop injecting pressure during the corresponding depressurization phase, and to control the data acquisition module to continuously acquire the bottom hole pressure during the phase. The generation unit 220 is used to generate a logarithmic curve of pressure change over time in this stage, with time as the horizontal axis and the logarithm of the bottom hole pressure as the vertical axis. Determining unit 230 is used to determine the current dynamic rupture pressure based on the logarithmic curve and the logarithmic curve of the previous injection cycle; The control unit 210 is also used to control the injection pressure in the pressurization phase of the next injection cycle based on the current dynamic rupture pressure.

[0055] The functions of each functional unit of the CO2 injection pressure control device provided in the above embodiments of this application can be realized through the above methods and steps. Therefore, the specific working process and beneficial effects of each unit in the CO2 injection pressure control device provided in the embodiments of this application will not be repeated here.

[0056] This application also provides an electronic device, such as... Figure 3 As shown, it includes a processor 310, a communication interface 320, a memory 330, and a communication bus 340, wherein the processor 310, the communication interface 320, and the memory 330 communicate with each other through the communication bus 340.

[0057] Memory 330 is used to store computer programs; When the processor 310 executes the program stored in the memory 330, it performs the following steps: The CO2 injection process is divided into multiple consecutive injection cycles, each of which includes a pressurization phase and a depressurization phase. During the pressurization phase of the current injection cycle, the injection pump is controlled to increase the injection pressure at a preset constant rate; during the corresponding depressurization phase, the injection pump is controlled to stop injecting pressure, and the bottom hole pressure during this phase is continuously collected. A logarithmic curve of pressure change over time during this phase is generated with time as the abscissa and the logarithm of the bottom hole pressure as the ordinate. Based on the logarithmic curve and the logarithmic curve of the previous injection cycle, the current dynamic rupture pressure is determined, and based on the current dynamic rupture pressure, the injection pressure in the pressurization phase of the next injection cycle is controlled.

[0058] The communication bus mentioned above can be a Peripheral Component Interconnect (PCI) bus or an Extended Industry Standard Architecture (EISA) bus, etc. This communication bus can be divided into address bus, data bus, control bus, etc. For ease of illustration, only one thick line is used to represent it in the diagram, but this does not mean that there is only one bus or one type of bus.

[0059] The communication interface is used for communication between the aforementioned electronic devices and other devices.

[0060] The memory may include random access memory (RAM) or non-volatile memory (NVM), such as at least one disk storage device. Optionally, the memory may also be at least one storage device located remotely from the aforementioned processor.

[0061] The processors mentioned above can be general-purpose processors, including central processing units (CPUs), network processors (NPs), etc.; they can also be digital signal processors (DSPs), application-specific integrated circuits (ASICs), field-programmable gate arrays (FPGAs), or other programmable logic devices, discrete gate or transistor logic devices, or discrete hardware components.

[0062] The implementation methods and beneficial effects of the various components of the electronic device in the above embodiments for solving the problem can be found in [reference needed]. Figure 1 The steps in the illustrated embodiments are used to implement the electronic device. Therefore, the specific working process and beneficial effects of the electronic device provided in this application will not be repeated here.

[0063] In another embodiment provided in this application, a computer-readable storage medium is also provided, which stores instructions that, when executed on a computer, cause the computer to perform the CO2 injection pressure control method described in any of the above embodiments.

[0064] In another embodiment provided in this application, a computer program product containing instructions is also provided, which, when run on a computer, causes the computer to execute the CO2 injection pressure control method described in any of the above embodiments.

[0065] Those skilled in the art will understand that the embodiments in this application can be provided as methods, systems, or computer program products. Therefore, the embodiments in this application can take the form of a completely hardware embodiment, a completely software embodiment, or an embodiment combining software and hardware aspects. Furthermore, the embodiments in this application can take the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.

[0066] This application describes embodiments of methods, apparatus (systems), and computer program products according to embodiments of this application with reference to flowchart illustrations and / or block diagrams. It will be understood that each block of the flowchart illustrations and / or block diagrams, and combinations of blocks in the flowchart illustrations and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, special-purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, generate instructions for implementing the flowchart illustrations. Figure 1 One or more processes and / or boxes Figure 1 A device that provides the functions specified in one or more boxes.

[0067] These computer program instructions may also be stored in a computer-readable storage medium that can direct a computer or other programmable data processing device to function in a particular manner, such that the instructions stored in the computer-readable storage medium produce an article of manufacture including instruction means, which are implemented in a process Figure 1 One or more processes and / or boxes Figure 1 The function specified in one or more boxes.

[0068] These computer program instructions may also be loaded onto a computer or other programmable data processing equipment to cause a series of operational steps to be performed on the computer or other programmable equipment to produce a computer-implemented process, thereby providing instructions that execute on the computer or other programmable equipment for implementing the process. Figure 1 One or more processes and / or boxes Figure 1 The steps of the function specified in one or more boxes.

[0069] Although preferred embodiments have been described in this application, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments as well as all changes and modifications falling within the scope of the embodiments of this application.

[0070] Obviously, those skilled in the art can make various modifications and variations to the embodiments of this application without departing from the spirit and scope of the embodiments of this application. Therefore, if these modifications and variations to the embodiments of this application fall within the scope of the claims in this application and their equivalents, then this application also intends to include these modifications and variations.

Claims

1. A method for controlling CO2 injection pressure, characterized in that, The method includes: The CO2 injection process is divided into multiple consecutive injection cycles, each of which includes a pressurization phase and a depressurization phase. During the pressurization phase of the current injection cycle, the injection pump is controlled to increase the injection pressure at a preset constant rate; during the corresponding depressurization phase, the injection pump is controlled to stop injecting pressure, and the bottom hole pressure during this phase is continuously collected. A logarithmic curve of pressure change over time during the pressurization phase is generated with time as the abscissa and the logarithm of the bottom hole pressure as the ordinate. Based on the logarithmic curve and the logarithmic curve of the previous injection cycle, the current dynamic rupture pressure is determined, and based on the current dynamic rupture pressure, the injection pressure in the pressurization phase of the next injection cycle is controlled.

2. The method as described in claim 1, characterized in that, The CO2 injection process is divided into multiple consecutive injection cycles, each of which includes a pressurization phase and a depressurization phase. Before the formal CO2 injection, a short-term test injection operation is performed. The injection is increased at a preset constant rate until the bottom hole pressure reaches the preset upper limit of the test injection. Then the injection is stopped and the total time for the bottom hole pressure to naturally decay to the initial static pressure is recorded. The duration of the pressurization phase during the test injection process is determined as the duration of the pressurization phase in each injection cycle, and the total duration of the natural decay of the bottom hole pressure is determined as the duration of the depressurization phase in each injection cycle.

3. The method as described in claim 1, characterized in that, Based on the logarithmic curve of this injection cycle and the logarithmic curve of the previous injection cycle, the current dynamic rupture pressure is determined, including: Overlay the logarithmic curve of the current injection cycle with the logarithmic curve of the previous injection cycle on the same time axis, calculate the sum of the areas of the closed regions enclosed by the two curves, and determine the sum of the areas as the current hysteresis loop area of ​​the current injection cycle. Compare the current hysteresis loop area of ​​the current injection cycle with the hysteresis loop area of ​​the previous injection cycle. If the increase ratio of the current hysteresis loop area to the hysteresis loop area of ​​the previous cycle exceeds a preset mutation threshold, then the bottom hole peak pressure is determined as the current dynamic fracture pressure.

4. The method as described in claim 3, characterized in that, The method for obtaining the preset mutation threshold includes: At the beginning of the injection process, take the M consecutive injection cycles before the current injection cycle, calculate the increase ratio of the hysteresis loop area between adjacent injection cycles, and determine the dynamically adjusted mutation threshold based on the arithmetic mean of the M-1 increase ratios. Afterwards, after every N consecutive injection cycles, the increase ratio of the hysteresis loop area between adjacent injection cycles in the N injection cycles is calculated, and the dynamically adjusted mutation threshold is determined based on the median value of the N-1 increase ratios. Where M is a positive integer not less than 3 and less than N; N is a positive integer not less than 5.

5. The method as described in claim 1, characterized in that, Based on the current dynamic rupture pressure, control the injection pressure during the pressurization phase of the next injection cycle, including: Obtain the peak pressure actually reached during the pressurization phase of the current injection cycle; Calculate the absolute difference between the peak pressure and the current dynamic rupture pressure, and use half of the absolute difference as the safety offset. The upper limit of the injection pressure in the boosting phase of the next injection cycle is set to the difference between the current dynamic fracturing pressure and the safety offset, so that the bottom hole pressure is monitored in real time during the boosting phase of the next injection cycle, and the injection pump is controlled so that the bottom hole pressure never exceeds the upper limit of the injection pressure.

6. The method as described in claim 5, characterized in that, After detecting that the increase in the current hysteresis loop area relative to the previous cycle hysteresis loop area exceeds a preset abrupt change threshold, the method further includes: The duration of the pressurization phase and the duration of the depressurization phase in each subsequent injection cycle are proportionally shortened to a preset percentage of the original duration, and the minimum value of the total duration of the injection cycle after the shortening is not lower than the preset minimum response time.

7. The method as described in claim 1, characterized in that, The preset constant rate setting method includes: Take the start time of the depressurization phase of the previous injection cycle as the zero point, and take a continuous sampling interval from the zero point as the initial segment. The duration of this sampling interval is less than the preset proportion of the total duration of the entire depressurization phase. Within the initial segment, the collected bottom hole pressure values ​​are linearly fitted with time as the horizontal axis and the logarithm of the bottom hole pressure as the vertical axis. The absolute value of the slope of the fitted line is taken as the absolute value of the slope of the initial segment. The absolute value is compared with a preset first slope threshold and a second slope threshold, wherein the first slope threshold is greater than the second slope threshold; If the absolute value is greater than the first slope threshold, the boost rate of the current injection cycle is reduced by a predetermined deceleration ratio; if the absolute value is less than the second slope threshold, the boost rate of the current injection cycle is increased by a predetermined acceleration ratio.

8. A device for controlling CO2 injection pressure, characterized in that, The device includes: The CO2 injection process is divided into multiple consecutive injection cycles, each of which includes a pressurization phase and a depressurization phase. The control unit is used to control the injection pump to increase the injection pressure at a preset constant rate during the pressurization phase of the current injection cycle; and to control the injection pump to stop injecting pressure during the corresponding depressurization phase, and to control the data acquisition module to continuously acquire the bottom hole pressure during that phase. The generation unit is used to generate a logarithmic curve of pressure change over time during the pressurization stage, with time as the horizontal axis and the logarithm of the bottom hole pressure as the vertical axis. The determination unit is used to determine the current dynamic rupture pressure based on the logarithmic curve of the current logarithmic curve and the logarithmic curve of the previous injection cycle. The control unit is also used to control the injection pressure during the pressurization phase of the next injection cycle based on the current dynamic rupture pressure.

9. An electronic device, characterized in that, The electronic device includes a processor, a communication interface, a memory, and a communication bus, wherein the processor, the communication interface, and the memory communicate with each other through the communication bus; Memory, used to store computer programs; A processor, when executing a program stored in memory, implements the method of any one of claims 1-7.

10. A computer-readable storage medium, characterized in that, The computer-readable storage medium stores a computer program that, when executed by a processor, implements the method described in any one of claims 1-7.

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