Methods to enhance recovery and retention rates through variable-stage CO2 injection and reverse pressure drive

Abstract

This application provides a method for improving the recovery and burial rate of experimental cores via variable-stage CO2 injection and reverse hydraulic displacement. The method includes: scanning an experimental core containing injected crude oil to obtain a first nuclear magnetic resonance (NMR) curve; injecting a predetermined volume of fracturing fluid into the experimental core through a predetermined first port; wherein the experimental core is located in a predetermined container, and the predetermined container has predetermined first and second ports; performing well-shutting treatment on the experimental core in the predetermined container based on predetermined environmental conditions; injecting CO2 into the experimental core through a predetermined second port based on predetermined CO2 injection stage configuration information to obtain a second NMR curve; determining the recovery rate of the experimental core based on the area under the first and second NMR curves, and determining the burial rate of the experimental core based on the injected CO2 volume. By using the predetermined CO2 injection stage configuration information and injecting CO2 through the second port, the burial rate and recovery rate are improved.

Description

Technical Field

[0001] This application relates to the field of shale / tight oil reservoir development technology, and in particular to a method for improving recovery and burial rates through variable-stage CO2 injection and reverse pressure drive. Background Technology

[0002] Shale / tight oil reservoirs have complex pore structures, characterized by low porosity and low permeability, resulting in poor oil and gas flow within the reservoirs.

[0003] Traditional volumetric fracturing and conventional water injection development methods often fail to achieve ideal development results. While fracturing technology can effectively increase the conductivity of reservoirs, the poor connectivity between pores in shale / tight oil reservoirs limits its exploitation potential. Therefore, there is an urgent need to develop a method to improve the recovery rate of shale / tight oil reservoirs. Summary of the Invention

[0004] This application provides a method for improving the recovery and burial rate of variable-stage CO2 injection and reverse pressure drive, in order to solve the technical problem of low recovery rate in shale / tight oil reservoirs.

[0005] In a first aspect, this application provides a method for improving the recovery and burial rates of variable-stage CO2 injection and reverse pressure drive, comprising:

[0006] The experimental core containing crude oil is scanned to obtain a first nuclear magnetic resonance curve, and a predetermined volume of fracturing fluid is injected into the experimental core from a predetermined first port. The experimental core is located in a predetermined container, which is provided with a predetermined first port and a predetermined second port. The first nuclear magnetic resonance curve characterizes the relationship between relaxation time and signal intensity detected from the radio frequency signal of the experimental core.

[0007] Based on preset environmental conditions, the experimental core in the preset container was subjected to a well-steaming treatment.

[0008] Based on the preset CO2 injection stage configuration information, CO2 is injected into the experimental core from the preset second port to obtain the second nuclear magnetic resonance curve; wherein, the second nuclear magnetic resonance curve characterizes the relationship between relaxation time and signal intensity detected from the radio frequency signal of the experimental core;

[0009] The recovery rate of the experimental core was determined based on the area under the first nuclear magnetic resonance curve and the area under the second nuclear magnetic resonance curve, and the burial rate of the experimental core was determined based on the volume of injected CO2. The recovery rate represents the proportion of oil extracted from the experimental core relative to the total oil volume of the experimental core, and the burial rate represents the proportion of the core sealed by CO2.

[0010] In this application, the preset CO2 injection stage configuration information includes the initial velocity and velocity change rate of the injected CO2. Based on the preset CO2 injection stage configuration information, CO2 is injected into the experimental core from a preset second port to obtain a second nuclear magnetic resonance curve, including:

[0011] Based on the initial velocity and the rate of velocity change, CO2 was injected into the experimental core from a pre-set second port to obtain the saturation of the experimental core; whereby the saturation characterizes the distribution of CO2 in the experimental core.

[0012] If the saturation of the experimental core does not change within the preset time period, then the second nuclear magnetic resonance curve at the current moment is obtained.

[0013] In this application, the rate of change of velocity characterizes the increase in the rate of CO2 injection; based on the initial velocity and the rate of change of velocity, CO2 is injected into the experimental core from a preset second port to obtain the saturation of the experimental core, including:

[0014] Based on the initial velocity, CO2 is injected into the experimental core from the preset second port;

[0015] If the injection time reaches the preset time threshold, CO2 is injected into the experimental core from the preset second port according to the rate of change of velocity, and the saturation of the experimental core is obtained in real time.

[0016] In this application, the recovery rate of the experimental core is determined based on the area under the first nuclear magnetic resonance curve and the area under the second nuclear magnetic resonance curve, including:

[0017] Determine the area difference between the area of ​​the first NMR curve and the area of ​​the second NMR curve;

[0018] The first recovery rate of the experimental core was obtained based on the area difference and the area of ​​the second nuclear magnetic resonance curve; where the first recovery rate characterizes the recovery rate of the experimental core after CO2 injection.

[0019] This application also includes:

[0020] The permeation distance, core length, initial water saturation of the core, and water saturation of the preset second port of the experimental core were obtained after the well was shut-in treatment; among them, the permeation distance represents the distance that the fracturing fluid permeates into the experimental core.

[0021] The secondary recovery rate of the experimental core was determined based on the seepage distance, core length, initial water saturation of the core, and water saturation at the second port; the secondary recovery rate characterizes the recovery rate of the experimental core after fracturing fluid injection.

[0022] In this application, the burial rate of the experimental core is determined based on the injected CO2 volume, including:

[0023] Determine the volume of CO2 released from the preset first port;

[0024] The burial rate of the experimental core was determined based on the volume of injected CO2 and the volume of released CO2.

[0025] This application also includes:

[0026] Obtain initial oil-bearing information of the experimental core and oil-bearing information of the experimental core before CO2 injection; the oil-bearing information characterizes the oil saturation of the experimental core;

[0027] Based on the initial oil-bearing information of the experimental core and the oil-bearing information of the experimental core before CO2 injection, the tertiary recovery rate of the experimental core was obtained; among which, the tertiary recovery rate characterizes the recovery rate of the experimental core before the CO2 injection process.

[0028] Secondly, this application provides an apparatus for enhancing the recovery and burial rates of variable-stage CO2 injection and reverse pressure drive, comprising:

[0029] The first obtaining unit is used to scan the experimental core containing crude oil to obtain a first nuclear magnetic resonance curve, and inject a preset volume of fracturing fluid into the experimental core from a preset first port; wherein, the experimental core is located in a preset container, and the preset container is provided with a preset first port and a preset second port, and the first nuclear magnetic resonance curve characterizes the relationship between relaxation time and signal intensity detected from the radio frequency signal of the experimental core.

[0030] The processing unit is used to perform well-sealing treatment on the experimental core in the preset container based on preset environmental conditions;

[0031] The second obtaining unit is used to inject CO2 into the experimental core from a preset second port based on preset CO2 injection stage configuration information to obtain a second nuclear magnetic resonance curve; wherein, the second nuclear magnetic resonance curve characterizes the relationship between relaxation time and signal intensity detected from the radio frequency signal of the experimental core;

[0032] The determination unit is used to determine the recovery rate of the experimental core based on the area under the first nuclear magnetic resonance curve and the area under the second nuclear magnetic resonance curve, and to determine the burial rate of the experimental core based on the injected CO2 volume; wherein, the recovery rate represents the proportion of oil obtained from the experimental core relative to the total oil volume of the experimental core, and the burial rate represents the proportion of the core sealed by CO2.

[0033] Thirdly, this application provides an electronic device, including: a processor, and a memory communicatively connected to the processor;

[0034] The memory stores the instructions that the computer executes;

[0035] The processor executes computer execution instructions stored in memory to implement the method in this application.

[0036] Fourthly, this application provides a computer-readable storage medium storing computer-executable instructions, which, when executed by a processor, are used to implement the method of this application.

[0037] Fifthly, this application provides a computer program product, comprising: a computer program that, when executed by a processor, implements the first aspect and / or various possible implementations of the first aspect.

[0038] This application provides a method for improving oil recovery and burial rate through variable-stage CO2 injection and reverse hydraulic displacement. The method involves scanning an experimental core containing injected crude oil to obtain a first nuclear magnetic resonance (NMR) curve, and then injecting a predetermined volume of fracturing fluid into the experimental core through a predetermined first port. The experimental core is located in a predetermined container with predetermined first and second ports. The first NMR curve represents the relationship between relaxation time and signal intensity detected from the radio frequency signal of the experimental core. Based on predetermined environmental conditions, the experimental core in the predetermined container is subjected to a well-cooling process. Based on predetermined CO2 injection stage configuration information, CO2 is injected into the experimental core through a predetermined second port, resulting in a second NMR curve. This second NMR curve represents the relationship between relaxation time and signal intensity detected from the radio frequency signal of the experimental core. By injecting CO2 and fracturing fluid from different predetermined ports, the method better matches the characteristics of the experimental core, thereby improving the oil recovery rate. The recovery rate of the experimental core is determined based on the area under the first and second nuclear magnetic resonance curves, and the burial rate of the experimental core is determined based on the volume of injected CO2. The recovery rate represents the proportion of oil obtained from the experimental core relative to the total oil volume of the experimental core, and the burial rate represents the proportion of the core sealed by CO2. Based on the preset CO2 injection stage configuration information, CO2 injection is more suitable for the characteristics of the experimental core, thereby improving the recovery rate and burial rate. Attached Figure Description

[0039] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this application and, together with the description, serve to explain the principles of this application.

[0040] Figure 1 A schematic flowchart illustrating a method for improving recovery and burial rate using variable-stage CO2 injection and reverse pressure drive, provided in an embodiment of this application.

[0041] Figure 2A schematic diagram of a preset container provided in an embodiment of this application;

[0042] Figure 3 A schematic flowchart illustrating another method for improving recovery and burial rate using variable-stage CO2 injection and reverse pressure drive, provided in an embodiment of this application.

[0043] Figure 4 This is a schematic diagram of the experimental apparatus provided in the embodiments of this application;

[0044] Figure 5 A schematic diagram illustrating the evolution of the infiltration distance and saturation as provided in an embodiment of this application;

[0045] Figure 6 A schematic diagram illustrating the recovery rate and porosity utilization law of CO2 reverse pressure drive in a variable-stage manner, provided for an embodiment of this application;

[0046] Figure 7 A schematic diagram of the structure of the device for improving recovery and burial rate by variable-stage CO2 injection and reverse pressure drive provided in the embodiments of this application;

[0047] Figure 8 A schematic diagram of the structure of the device for improving the recovery and burial rate of variable-stage CO2 injection and reverse pressure drive provided in the embodiments of this application;

[0048] Figure 9 This is a schematic diagram of the electronic device structure provided in an embodiment of this application.

[0049] The accompanying drawings illustrate specific embodiments of this application, which will be described in more detail below. These drawings and descriptions are not intended to limit the scope of the concept in any way, but rather to illustrate the concept of this application to those skilled in the art through reference to particular embodiments. Detailed Implementation

[0050] Exemplary embodiments will now be described in detail, examples of which are illustrated in the accompanying drawings. When the following description relates to the drawings, unless otherwise indicated, the same numbers in different drawings denote the same or similar elements. The embodiments described in the following exemplary embodiments do not represent all embodiments consistent with this application. Rather, they are merely examples of apparatuses and methods consistent with some aspects of this application as detailed in the appended claims.

[0051] Currently, in shale / tight oil reservoirs, the poor connectivity of pores between fractures limits the extent of oil recovery. Water injection development, due to the low sweep efficiency of fluids in micropores, cannot displace residual oil in the reservoir. Furthermore, the application of conventional reverse pressure flooding (RPF) technology in shale and tight reservoirs faces several challenges. Due to the ultra-low permeability of the reservoir, the injected fluid during RPF struggles to penetrate deep into the reservoir, resulting in a limited sweep volume, reduced oil displacement efficiency, and impact on ultimate recovery. While conventional CO2 displacement technology offers advantages such as reducing interfacial tension, promoting miscibility, lowering viscosity, and altering wettability, CO2 has poor fluidity in shale / tight oil reservoirs. Injected CO2 tends to rapidly penetrate high-permeability channels, resulting in an effective sweep range but failing to effectively displace residual oil in the reservoir, leading to poor development outcomes in shale / tight oil reservoirs. Moreover, quantitative characterization of the burial rate of CO2 injection-enhanced RPF in shale / tight oil reservoirs at different stages has not yet been conducted. In summary, conventional reverse pressure flooding and CO2 flooding technologies have limited effectiveness in shale / tight oil reservoirs and cannot fully realize their potential recovery rate.

[0052] This application provides a method for improving the recovery and burial rate of a variable-stage CO2 injection and reverse hydraulic displacement system. The method involves scanning an experimental core containing injected crude oil to obtain a first nuclear magnetic resonance (NMR) curve, and then injecting a predetermined volume of fracturing fluid into the experimental core through a predetermined first port. The experimental core is located in a predetermined container with predetermined first and second ports. The first NMR curve represents the relationship between relaxation time and signal intensity detected from the radio frequency signal of the experimental core. Based on predetermined environmental conditions, the experimental core in the predetermined container is subjected to a well-cooling process. Based on predetermined CO2 injection stage configuration information, CO2 is injected into the experimental core through a predetermined second port to obtain a second NMR curve. This second NMR curve represents the relationship between relaxation time and signal intensity detected from the radio frequency signal of the experimental core. By injecting CO2 and fracturing fluid from different predetermined ports, the method better matches the characteristics of the experimental core, thereby improving the recovery rate. The recovery rate of the experimental core is determined based on the area under the first and second nuclear magnetic resonance curves, and the burial rate of the experimental core is determined based on the volume of injected CO2. The recovery rate represents the proportion of oil obtained from the experimental core relative to the total oil volume of the experimental core, and the burial rate represents the proportion of the core sealed by CO2. Based on the preset CO2 injection stage configuration information, CO2 injection is more suitable for the characteristics of the experimental core, thereby improving the recovery rate and burial rate.

[0053] In magnetic resonance imaging (MRI), relaxation time refers to the time required for an atomic nucleus to recover from an excited state to an equilibrium state. This process involves two main relaxation times: T1 (longitudinal relaxation time) and T2 (lateral relaxation time). T1 (longitudinal relaxation time) refers to the time required for the magnetization vector of an atomic nucleus to recover from a direction perpendicular to the magnetic field to a direction parallel to the magnetic field in a magnetic field. T1 relaxation time describes how quickly a spin system recovers from an excited state to thermal equilibrium. In MRI, T1-weighted imaging primarily reflects the differences in T1 values ​​between tissues; for example, fat, melanin, and proteins show bright high signals, while cerebrospinal fluid (CSF) shows low signals. T2 (lateral relaxation time) refers to the decay and disappearance time of the magnetization vector of an atomic nucleus in a plane perpendicular to the magnetic field in a magnetic field. T2 relaxation time reflects the decay rate of the lateral magnetization component, which is caused by the mutual interference between atomic nuclei and the inhomogeneity of the magnetic field. In T2-weighted imaging, cerebrospinal fluid (CSF) has a long relaxation time and appears as a bright high signal.

[0054] Oil recovery rate refers to the ratio between the actual amount of oil extracted from an oil reservoir and the original geological reserves (total crude oil) in the reservoir.

[0055] In petroleum engineering, saturation typically refers to the volume fraction of a certain fluid (such as water, oil, or gas) within the pores of an oil reservoir. For example, oil saturation refers to the proportion of oil in the pore space. Saturation is an important parameter for assessing reservoir properties and predicting oil recovery.

[0056] Storage efficiency refers to the efficiency of capturing carbon dioxide in the long-term safe storage of geological reservoirs. This concept has become particularly important in the context of addressing climate change and reducing greenhouse gas emissions.

[0057] Figure 1 This is a schematic flowchart illustrating a method for improving oil recovery and burial rate using variable-stage CO2 injection and reverse pressure drive, as provided in an embodiment of this application. Figure 1 As shown, the execution subject of this method can be a server or other servers; this embodiment does not impose any special restrictions here. Figure 1 As shown, the method includes:

[0058] S101. The experimental core containing crude oil is scanned to obtain a first nuclear magnetic resonance curve, and a preset volume of fracturing fluid is injected into the experimental core from a preset first port; wherein, the experimental core is located in a preset container, and the preset container is provided with a preset first port and a preset second port, and the first nuclear magnetic resonance curve characterizes the relationship between relaxation time and signal intensity detected from the radio frequency signal of the experimental core.

[0059] In this context, "experimental core" refers to a core with porosity and permeability consistent with the actual reservoir, but smaller in size, such as any type of shale core or tight oil reservoir core. The terms "first," "second," and "third" in this application do not indicate the order of execution but are only used to distinguish different technical features. Crude oil can be injected into the experimental core through either the first or second port; in most cases, it is injected through the second port. The entire experimental process involves online CT and offline nuclear magnetic resonance (NMR). Therefore, NMR curves are only available at the beginning (after crude oil injection) and the end (after CO2 injection); they are not available at other times.

[0060] Figure 2 This is a schematic diagram of a preset container provided in an embodiment of this application. Figure 2 In this embodiment, a core sample is placed inside a pre-set container 12. The pre-set container is a core holder with two ports: a first port 11 and a second port 16, both of which can be used for injecting materials. In this embodiment, the first port is the outlet for injecting fracturing fluid. During fracturing fluid injection, the outlet pressure is the same as the formation pressure. At the end of CO2 injection, the outlet pressure is connected to atmospheric pressure, at which point the outlet temperature is 25°C and 0 MPa. The second port is the inlet for injecting CO2. The inlet temperature and formation pressure are measured at the inlet; the specific values ​​need to be determined based on the actual formation block.

[0061] By setting up a first port and a second port for reverse pressure drive operation, reverse pressure drive means: injecting CO2 through the inlet end and injecting fracturing fluid through the outlet end.

[0062] The nuclear magnetic resonance curve is a curve obtained through a nuclear magnetic resonance device, with the horizontal axis representing relaxation time and the vertical axis representing signal intensity.

[0063] Crude oil refers to experimental crude oil, which is crude oil prepared in the laboratory under experimental conditions based on actual geological formations.

[0064] Pre-injection of crude oil into experimental cores refers to the following steps: cutting and washing the experimental core, drying it, weighing it, measuring its porosity and permeability, determining whether the experimental core is a shale core or a tight oil reservoir core, then using a vacuum testing device to evacuate the experimental core, and finally injecting crude oil into the experimental core through the inlet end so that the outlet end can stably output liquid.

[0065] The preset volume of fracturing fluid satisfies:

[0066]

[0067] Among them, v lab This refers to converting the on-site fracturing fluid displacement into the indoor experimental displacement, generally referring to the indoor experimental fracturing fluid injection displacement, Q.field For on-site construction displacement, B p N represents the area of ​​a single orifice in the reverse pressure drive system. p This refers to the number of firing ports on site.

[0068] The experimental core was placed in a pre-set container (i.e., a core holder), and crude oil was injected into the core from the inlet end until oil flowed steadily from the outlet end. Then, the injection of crude oil was stopped, and the core containing the injected crude oil was scanned to obtain the first nuclear magnetic resonance curve. V was then injected from the outlet end... lab Volume of fracturing fluid.

[0069] S102. Based on preset environmental conditions, the experimental core in the preset container is subjected to well-sealing treatment;

[0070] The preset environmental conditions refer to the formation temperature and pressure, and the well simmering time meets the preset values. The specific values ​​of formation temperature and pressure need to be determined based on the actual formation block.

[0071] Well-sealing treatment refers to a technology that uses multiple mechanisms, such as fracturing fluid and percolation, to increase shale oil production.

[0072] The well-sealing time is satisfied:

[0073]

[0074] Among them, t lab The term refers to the well-soaking time, where C is the core property parameter, specifically the Young's modulus of the experimental rock sample, μ. m The viscosity of the fluid used in the experimental core, i.e., the viscosity of the fracturing fluid, where r is the core radius and Q is the core radius. lab The experimental core flow rate is the velocity of the fluid (fracturing fluid) passing through a certain cross section of the core. cosθ is the contact angle after the experiment, i.e., the contact angle between the experimental crude oil and the surface of the experimental core. t field This refers to the time required for the well to be sealed on-site.

[0075] The temperature in the preset container (i.e., the core holder) is adjusted to the formation temperature and pressure, and t is performed. lab Prolonged well simmering treatment.

[0076] S103. Based on the preset CO2 injection stage configuration information, CO2 is injected into the experimental core from the preset second port to obtain the second nuclear magnetic resonance curve; wherein, the second nuclear magnetic resonance curve characterizes the relationship between relaxation time and signal intensity detected from the radio frequency signal of the experimental core.

[0077] The preset CO2 injection stage configuration information includes the initial CO2 injection rate and the rate of change of injected CO2. The conventional CO2 injection rate, obtained from the oilfield, is used as the initial injection rate. This conventional rate is then reduced to serve as the initial CO2 injection rate. For example, if the conventional injection rate is 0.1 mL / min, the initial CO2 injection rate would be 0.05 mL / min. The rate of change of injected CO2 can refer to gradually increasing the injection rate over time, or gradually increasing the injection rate based on changes in the recovery rate. Alternatively, it can refer to gradually increasing the injection rate while comprehensively considering both changes in the recovery rate and changes over time.

[0078] Inject CO2 through the inlet at the initial velocity, and gradually increase the CO2 injection rate until the core saturation no longer changes, then stop injecting CO2. 2， Obtain the second nuclear magnetic resonance curve.

[0079] In this embodiment, the preset CO2 injection stage configuration information includes the initial velocity and rate of change of injected CO2. Based on the preset CO2 injection stage configuration information, CO2 is injected into the experimental core from a preset second port to obtain a second nuclear magnetic resonance curve, including:

[0080] Based on the initial velocity and the rate of velocity change, CO2 was injected into the experimental core from a pre-set second port to obtain the saturation of the experimental core; whereby the saturation characterizes the distribution of CO2 in the experimental core.

[0081] If the saturation of the experimental core does not change within the preset time period, then the second nuclear magnetic resonance curve at the current moment is obtained.

[0082] The standard injection rate of CO2 at the oilfield site is defined as the conventional injection rate. This conventional rate is then reduced to become the initial CO2 injection rate. For example, if the conventional injection rate is 0.1 mL / min, the initial CO2 injection rate would be 0.05 mL / min.

[0083] The rate of change of injection rate of CO2 can refer to adjusting the injection rate of CO2 based on the rate of change of recovery rate (i.e., the increase in recovery rate). For example, if the recovery rate is obtained at various times when CO2 is injected, and the recovery rate does not change significantly when CO2 is injected at the initial injection rate, then the injection rate of CO2 needs to be increased. Alternatively, the rate of change of injection rate of CO2 can refer to gradually increasing the injection rate of CO2 over time.

[0084] In the initial stage of CO2 injection, CO2 is injected at an initial injection rate to ensure more uniform CO2 distribution throughout the reservoir, promoting miscibility between CO2 and crude oil (meaning a single phase formed by both). In the middle stage of CO2 injection, the injection rate is gradually increased. Once CO2 distribution becomes more uniform, the injection rate is appropriately increased to push more experimental crude oil towards the production end and prevent CO2 stagnation. In the later stage, the injection rate is further increased. In the later stage of CO2 injection, residual oil is often distributed in low-permeability areas, requiring a higher driving force to push this residual oil towards the production end. When the saturation of each section of the experimental core remains constant, CO2 injection is stopped, and the second NMR curve for that moment is obtained. The initial CO2 injection rate can be 0.05 mL / min, the middle stage can be 0.1 mL / min, and the later stage can be 0.15 mL / min.

[0085] The advantage of this setup is that by combining nuclear magnetic resonance curves and variable-speed CO2 injection, precise management of the CO2 flooding process is achieved, which can significantly improve the recovery rate and CO2 storage rate of the experimental core.

[0086] In this embodiment, the rate of change of velocity characterizes the increase in the rate of CO2 injection; based on the initial velocity and the rate of change of velocity, CO2 is injected into the experimental core from a preset second port to obtain the saturation of the experimental core, including:

[0087] Based on the initial velocity, CO2 is injected into the experimental core from the preset second port;

[0088] If the injection time reaches the preset time threshold, CO2 is injected into the experimental core from the preset second port according to the rate of change of velocity, and the saturation of the experimental core is obtained in real time.

[0089] The preset time threshold refers to the moment when the CO2 injection rate changes. Specifically, it includes the moment when the CO2 injection rate changes from the initial stage to the middle stage, and the moment when the CO2 injection rate changes from the middle stage to the late stage.

[0090] The saturation of the experimental core is acquired in real time, and the decision to continue injecting CO2 is made based on the saturation of the experimental core. When the saturation of each section of the experimental core changes, CO2 injection needs to continue. When the saturation of each section of the experimental core remains unchanged, CO2 injection is stopped.

[0091] The initial injection rate can be 0.05 mL / min. During the initial CO2 injection phase, this initial rate ensures more uniform CO2 distribution throughout the reservoir, promoting miscibility between CO2 and crude oil (meaning a single phase formed by both). In the middle stage of CO2 injection, the injection rate is gradually increased. Once CO2 distribution becomes more uniform, the injection rate is appropriately increased to push more experimental crude oil towards the production end and prevent CO2 stagnation. In the later stage, the injection rate is further increased. In the later stages of CO2 injection, residual oil is often distributed in low-permeability areas, requiring a higher driving force to push this residual oil towards the production end. CO2 injection is stopped when the saturation of each section of the experimental core remains constant.

[0092] The advantage of this setup is that by combining the control of time thresholds and rate of change, as well as real-time saturation monitoring, it enables refined management of the CO2 injection process, which can significantly improve the recovery rate and CO2 storage rate.

[0093] S104. Determine the recovery rate of the experimental core based on the area under the first nuclear magnetic resonance curve and the area under the second nuclear magnetic resonance curve, and determine the burial rate of the experimental core based on the volume of injected CO2; wherein, the recovery rate represents the proportion of oil obtained from the experimental core relative to the total oil volume of the experimental core, and the burial rate represents the proportion of the core sealed by CO2.

[0094] The recovery rate of the experimental core is obtained by substituting the areas of the first and second NMR curves into a pre-defined formula for calculating the recovery rate. Similarly, the CO2 burial rate in the experimental core is obtained by substituting the injected CO2 volume into another pre-defined formula for calculating the burial rate.

[0095] In this embodiment of the application, the recovery rate of the experimental core is determined based on the area under the first nuclear magnetic resonance curve and the area under the second nuclear magnetic resonance curve, including:

[0096] Determine the area difference between the area of ​​the first NMR curve and the area of ​​the second NMR curve;

[0097] The first recovery rate of the experimental core was obtained based on the area difference and the area of ​​the second nuclear magnetic resonance curve; where the first recovery rate characterizes the recovery rate of the experimental core after CO2 injection.

[0098] The recovery rate of injected CO2 can be obtained based on the change in the signal values ​​of the nuclear magnetic resonance curves before and after CO2 injection (i.e., the area difference between the area of ​​the first nuclear magnetic resonance curve and the area of ​​the second nuclear magnetic resonance curve).

[0099] The method for obtaining the first recovery rate is as follows:

[0100]

[0101] Where R1 is the first recovery rate, A1 is the area under the curve of the first nuclear magnetic resonance curve, A2 is the area under the curve of the second nuclear magnetic resonance curve, and A1-A2 represents the area difference.

[0102] The advantage of this setup is that, based on the changes in NMR curve signal values ​​before and after CO2 injection, and through the analysis of the NMR curve area, it is possible to accurately assess and optimize the oil recovery rate after CO2 flooding, thereby improving the technical effectiveness and economic benefits in experimental and practical applications.

[0103] In this embodiment of the application, it also includes:

[0104] The permeation distance, core length, initial water saturation of the core, and water saturation of the preset second port of the experimental core were obtained after the well was shut-in treatment; among them, the permeation distance represents the distance that the fracturing fluid permeates into the experimental core.

[0105] The secondary recovery rate of the experimental core was determined based on the seepage distance, core length, initial water saturation of the core, and water saturation at the second port; the secondary recovery rate characterizes the recovery rate of the experimental core after fracturing fluid injection.

[0106] The permeation distance is the distance of the fracturing fluid's reverse permeation, which can be obtained from the experimental core saturation change curve over time. That is, the change in saturation over a predetermined time is the distance of the fracturing fluid's reverse permeation.

[0107] By substituting the permeation distance, core length, initial water saturation of the core, and water saturation of the second port into the second recovery rate formula, the recovery rate of the experimental core after fracturing fluid injection and before well shut-in treatment can be obtained.

[0108] The formula for obtaining the secondary recovery rate is:

[0109]

[0110] Among them, R o To disregard the recovery rate of well-sealing treatment, X f S represents the distance of reverse absorption of fracturing fluid. winj x represents the water saturation at the inlet (i.e., the second port). max This represents the core length.

[0111] The advantage of this setup is that by calculating and analyzing the secondary recovery rate (i.e., the recovery rate after well shut-in treatment and before CO2 injection), it provides important opportunities for evaluation and optimization of well shut-in treatment. This method not only improves the accuracy and reliability of the experiment and enhances the recovery rate, but also provides valuable guidance for actual oilfield development.

[0112] In this embodiment of the application, the burial rate of the experimental core is determined based on the injected CO2 volume, including:

[0113] Determine the volume of CO2 released from the preset first port;

[0114] The burial rate of the experimental core was determined based on the volume of injected CO2 and the volume of released CO2.

[0115] Specifically, the volume of CO2 released from the outlet (i.e., the first port) and the volume of CO2 injected from the inlet (i.e., the second port) are obtained. Substituting the volume of CO2 released from the outlet and the volume of CO2 injected from the inlet into the preset formula for obtaining the burial rate of the experimental core, the burial rate of CO2 in the experimental core can be obtained.

[0116] The preset formula for the burial rate of experimental rock cores is:

[0117]

[0118] Among them, V IE The volume of CO2 injected under the given conditions is expressed in cm. 3 P refers to the volume of CO2 injected through the injection port under formation temperature and pressure conditions; E The injection pressure is measured in MPa, which is the formation pressure; Z E This refers to the CO2 deviation factor under injected temperature and pressure, i.e., the CO2 deviation factor under formation temperature and pressure; Z O This refers to the CO2 deviation factor at outlet temperature and pressure, specifically the CO2 deviation factor at atmospheric pressure and normal temperature (25℃); P O The outlet pressure is atmospheric pressure, expressed in MPa; V R The volume of CO2 released under outlet conditions, in cm3, is the volume of CO2 released at the outlet under atmospheric pressure and normal temperature.

[0119] The advantage of this setup is that by determining the volume of injected and released CO2 to calculate the sequestration rate, it provides important technical support and optimization opportunities for CO2 geological sequestration and oil displacement processes. This method not only improves the accuracy and reliability of the experiment but also provides valuable guidance for practical applications.

[0120] In this embodiment of the application, it also includes:

[0121] Obtain initial oil-bearing information of the experimental core and oil-bearing information of the experimental core before CO2 injection; the oil-bearing information characterizes the oil saturation of the experimental core;

[0122] Based on the initial oil-bearing information of the experimental core and the oil-bearing information of the experimental core before CO2 injection, the tertiary recovery rate of the experimental core was obtained; among which, the tertiary recovery rate characterizes the recovery rate of the experimental core before the CO2 injection process.

[0123] Among them, the initial oil-bearing information of the experimental core refers to the initial oil saturation of the experimental core.

[0124] The oil content information of the experimental core before CO2 injection refers to the oil saturation of the experimental core before CO2 injection.

[0125] Substituting the initial oil-bearing information and the oil-bearing information of the experimental core before CO2 injection into the formula for obtaining the tertiary recovery rate, the tertiary recovery rate of the experimental core before the CO2 injection process can be obtained. Substituting the initial oil-bearing information and the oil-bearing information of the experimental core after CO2 injection into the formula for obtaining the tertiary recovery rate, the secondary recovery rate of the experimental core after the CO2 injection process can be obtained.

[0126] The formula for obtaining the third recovery rate is:

[0127]

[0128] Where: R on V represents the recovery rate after CO2 injection and the recovery rate before CO2 injection. im V is the volume of oil displacement. o S represents the initial oil-bearing volume. oi To obtain the initial oil-bearing information of the experimental core, x max The length of the core sample.

[0129] S o (x) is the oil saturation distribution function, which includes the oil saturation of the experimental core before CO2 injection and the oil saturation of the experimental core before CO2 injection.

[0130] The advantage of this setup is that, in CO2-assisted oil recovery experiments, by acquiring and analyzing the initial oil-bearing information of the experimental core and the oil-bearing information before CO2 injection, the tertiary recovery rate can be calculated. This process helps to comprehensively assess the reservoir's recovery status and provides a basis for optimizing oil recovery strategies.

[0131] This application provides a method for improving the recovery and storage rate of a variable-stage CO2 injection and reverse pressure drive. By injecting fracturing fluid into the outlet end and accelerating the injection of CO2 into the inlet end, the fracturing fluid and CO2 are injected from different ends, which better suits the characteristics of low porosity and low permeability of the experimental core, thereby improving the recovery and storage rate.

[0132] Figure 3This is a schematic flowchart illustrating another method for improving oil recovery and burial rate using variable-stage CO2 injection and reverse pressure drive, provided in an embodiment of this application. Figure 3 As shown, the execution subject of this method can be a server or other servers; this embodiment does not impose any special restrictions here. Figure 3 As shown, the method includes:

[0133] S301. Obtain experimental materials on reservoir characteristics of the target block, including shale / tight oil reservoir cores, simulated formation water, fracturing fluid, experimental crude oil, and simulated formation water configured according to reservoir fluid characteristic parameters.

[0134] The target area reservoir is the reservoir of the study block.

[0135] The experimental material method for obtaining reservoir characteristics of the target block is as follows:

[0136] (1) Obtain the core, cut and wash the core, dry it, weigh it, and determine the core porosity and permeability. Based on the porosity and permeability, determine that the core is a shale / tight oil reservoir core.

[0137] (2) Based on the reservoir fluid characteristic parameters of the study block, configure formation water and fracturing fluid.

[0138] (3) Vacuuming test device was used to vacuum the experimental core to obtain a dry core.

[0139] S302. The CT values ​​of dry core, experimental crude oil, saturated oil core, and formation water were measured, and the signal value of the initial saturated oil in the core was obtained using a nuclear magnetic resonance experimental device.

[0140] The method for obtaining CT values ​​from saturated oil cores is as follows:

[0141] The saturated shale / tight core was displaced using experimental crude oil. After the liquid flow at the outlet end stabilized, the saturation process ended. The CT value of the core saturation section was obtained as the CT value of the saturated oil core. The signal value of the initial saturated oil in the core was obtained using a nuclear magnetic resonance experimental device.

[0142] The method for measuring the CT values ​​of dry core, experimental crude oil, saturated oil core, and formation water, and obtaining the initial saturated oil signal value from the core using a nuclear magnetic resonance experimental setup is as follows:

[0143] (1) Connect the CT scanning experimental apparatus instruments and pipelines according to the experimental apparatus diagram, and check the airtightness of the experimental apparatus. Figure 4 A schematic diagram of the experimental apparatus provided in the embodiments of this application. Figure 4As shown: 1 is a constant speed and constant pressure pump, 5 is a CO2 intermediate container, 6 is a fracturing fluid intermediate container control valve, 7 is a crude oil intermediate container, 12 is a core holder for placing cores, 13 is a confining pressure pump, 14 is a back pressure liquid, 15 is a back pressure pump, 17 is a CT information acquisition instrument, 18 is a back pressure valve, 19 is a gas-liquid separator, 20 is a gas flow meter, and 2, 3, 4, 5, 8, 9, 10, 11, and 16 are experimental device instrument control valves.

[0144] (2) Place the core into the core holder of the CT scanning device and measure the CT value of crude oil, the CT value of the simulated formation, the CT value of formation water and the CT value of fracturing fluid under the experimental temperature and pressure. The fracturing fluid is prepared according to the formation water. The experimental temperature refers to the temperature of the reservoir in the study block and the experimental pressure refers to the pressure of the reservoir in the study block.

[0145] (3) Based on the formation pressure of the study block, the CT value of the saturated oil core was obtained by saturating the experimental core using the displacement method.

[0146] (4) Turn on the nuclear magnetic resonance experimental device, set the relevant parameters, scan the saturated core, and obtain the initial nuclear magnetic resonance curve of the saturated oil core.

[0147] S303. Based on the on-site pressure drive construction parameters of shale / tight oil reservoirs, set experimental conditions to simulate the reverse pressure drive (fracturing fluid) injection process. After the experimental conditions are met, conduct experimental well-drainage permeation simulation under reservoir temperature and pressure in the study block according to the well-drainage time, and measure the CT value of the core after well-drainage permeation.

[0148] The experimental conditions refer to the temperature and pressure required to reach the reservoir in the study block.

[0149] Experimental conditions were set based on the on-site hydraulic displacement construction parameters of shale / tight oil reservoirs to simulate the reverse hydraulic displacement (fracturing fluid) injection process. After the experimental conditions were met, high-temperature and high-pressure well stagnation and seepage simulation was conducted. The method for measuring the CT value after well stagnation and seepage in the core was as follows:

[0150] (1) Place the core sample after nuclear magnetic resonance scanning into the CT scanning experimental device, open valve 13, and adjust the pressure to the experimental pressure.

[0151] (2) Place the prepared fracturing fluid into the intermediate container 2, and use a constant speed and constant pressure pump to inject the fracturing fluid into the core production end to simulate the reverse pressure drive process.

[0152] (3) Based on the principle of similarity criterion, determine the discharge rate of the fracturing fluid injected in reverse pressure at the outlet end:

[0153]

[0154] Among them, v labThis refers to converting the on-site fracturing fluid displacement into the indoor experimental displacement, generally referring to the indoor experimental fracturing fluid injection displacement, Q. field For on-site construction displacement, B p N represents the area of ​​a single orifice in the reverse pressure drive system. p This refers to the number of firing ports on site.

[0155] (4) Determine the simmering time tlab for the indoor experimental core.

[0156]

[0157] Among them, t lab The term refers to the simmering time of the experimental core sample, where C is a core property parameter, specifically the Young's modulus of the experimental sample, μ. m The viscosity of the fluid used in the experimental core, i.e., the viscosity of the fracturing fluid, where r is the core radius and Q is the core radius. lab The experimental core flow rate is the velocity of the fluid (fracturing fluid) passing through a certain cross section of the core. cosθ is the contact angle after the experiment, i.e., the contact angle between the experimental crude oil and the surface of the experimental core. t field This refers to the time required for the well to be sealed on-site.

[0158] (5) The core sample after pressure driving at the production end was scanned using an online CT scanning experimental device to obtain the reverse seepage distance of the fracturing fluid under pressure driving, the CT value of the core sample after well stagnation and seepage, and the recovery rate.

[0159] S304. Based on the conventional CO2 flooding injection parameters of the shale / tight oil reservoir in the field, design the variable-stage CO2 injection volume and injection rate to simulate the variable-stage CO2 flooding process. When the saturation of each section of the core remains unchanged, the CO2 displacement experiment is terminated, and the CT value and nuclear magnetic resonance signal value of the core after the variable-stage CO2 displacement are measured.

[0160] Based on the conventional CO2 flooding injection parameters of shale / tight oil reservoirs in the field, a variable-stage CO2 injection rate and volume were designed to simulate the variable-stage CO2 flooding process. The CO2 displacement experiment was terminated when the saturation of each section of the core remained constant. The method for measuring the CT values ​​and nuclear magnetic resonance signal values ​​of the core after variable-stage CO2 displacement was as follows:

[0161] (1) Determine the displacement rate and total injection volume of the indoor core. Based on the field CO2 injection volume parameters, combined with the field control range, oilfield porosity, experimental core radius, experimental core length, and experimental core porosity, determine the injection volume of variable-stage CO2 injection reverse pressure drive.

[0162] (2) Based on the principle of linear velocity, the on-site CO2 injection rate is converted into the indoor core injection rate. Combining the CO2 flooding mechanism with the heterogeneity of the reservoir, the injection rate is reduced in the early stage, so that CO2 can enter the reservoir more evenly and promote the miscibility of CO2 and crude oil.

[0163] (3) Gradually increase the injection rate in the medium term. After CO2 begins to be distributed more evenly, appropriately increase the injection rate to drive more crude oil to the production end and prevent CO2 from being trapped.

[0164] (4) Increase the injection rate in the later stage of pressure drive. In the later stage, the remaining oil is often distributed in the low-permeability area, and a higher driving force is required to push this part of the remaining oil to the production end.

[0165] (5) After the pressure drive at the production end is completed, close valves 3, 8, and 9, and open valves 2 and 10 to conduct a variable-stage CO2 injection experiment. During the experiment, the recovery rate, pressure, and fluid production characteristics are comprehensively considered to determine the recovery rate at different injection rates.

[0166] (6) After the CO2 flooding experiment, turn on the 17 information acquisition instrument and use online CT scanning to obtain the core section saturation under different PV (Pore Volume) during the CO2 flooding process, and determine the evolution law of the permeation distance and saturation. Figure 5 A schematic diagram illustrating the evolution of the infiltration distance and saturation provided in this application, as shown below. Figure 5 As shown, the horizontal axis represents the seepage distance, the vertical axis represents the water saturation, and the times in the upper right corner (1h, 3h, etc.) represent the seepage time (i.e., the well-sinking time of the experimental core). The well-sinking time of the experimental core here is based on the on-site well-sinking time t. field Obtain the simmering time t at different sites field For different experimental core simmering times, the 1.25 cm arrow represents the reverse seepage distance of fracturing fluid under pressure drive.

[0167] (7) Turn off the confining pressure pump, reduce the pressure of the constant pressure and constant speed pump to atmospheric pressure, take out the experimental core and perform nuclear magnetic resonance scanning to obtain the nuclear magnetic resonance curve of the core after CO2 injection, and determine the recovery rate and pore utilization law. Among them, the pore utilization law refers to the process and law of the gradual utilization and replacement of pore space in the reservoir by fluids such as oil, gas and water during the development of oil and gas fields.

[0168] S305. Based on experimental data, combined with nuclear magnetic resonance and CT scanning experimental devices, quantitatively characterize the recovery rate of fracturing fluid wells before and after variable-stage CO2 injection-enhanced reverse pressure drive, the reverse seepage distance and saturation distribution of fracturing fluid wells, CO2 oil displacement efficiency, and recovery rate before and after variable-stage CO2 injection-enhanced pressure drive.

[0169] The CT values ​​of different sections were measured at different injection rates during the CO2 flooding experiment using a CT experimental device to determine the saturation variation law and recovery rate of each section at different injection rates.

[0170] (1) Based on the CT values ​​before and after the experiment, calculate the water saturation at the extraction end, and obtain the evolution law diagram of the seepage distance and saturation based on the water saturation (see the evolution law diagram of the seepage distance and saturation as follows). Figure 5 As shown), thus obtaining the reverse permeation distance of the reverse-drive fracturing fluid (as shown). Figure 5 The 1.25cm indicated by the arrow in the diagram represents the reverse absorption distance of the fracturing fluid during reverse hydraulic displacement. The calculation formula is as follows:

[0171]

[0172] Among them, CT dry CT values ​​of dry cores, CT rock CT values ​​for rock particles, CT imbibition The CT value is the core sample after well simmering and seepage. air The CT value of air, specifically the CT value of carbon dioxide. oil The CT value of the experimental crude oil, CT water .

[0173] CT saturated =(1-φ)CT rock +φCT oil ,

[0174] Among them, CT rock CT values ​​for rock particles, CT saturated Here, φ represents the core porosity.

[0175] CT oil The CT value is the saturated oil core value after reverse hydraulic displacement (fracturing fluid).

[0176] (2) Based on the changes in nuclear magnetic resonance curve signal values ​​before and after CO2 injection and the recovery rate after CO2 injection, the recovery rate and porosity utilization law of CO2 reverse pressure drive in variable stage are calculated.

[0177]

[0178] Where R1 is the recovery rate after CO2 injection and pressure drive in the variable stage, A1 is the area of ​​the initial nuclear magnetic resonance curve of the core (that is, the nuclear magnetic resonance curve area obtained after the experimental crude oil displaces saturated shale / tight core), and A2 is the area of ​​the nuclear magnetic resonance curve after CO2 injection and pressure drive in the variable stage.

[0179] Figure 6 This application provides a schematic diagram illustrating the recovery rate and porosity utilization law of CO2 reverse pressure drive in a variable-stage manner, as shown in the embodiments. Figure 6 As shown, the horizontal axis represents relaxation time, the vertical axis represents signal intensity, and different curves represent CO2 injected into different PV (Pore volume).

[0180] (3) Calculate the recovery rate of CO2 oil recovery at different stages based on the changes in CT value during the CO2 injection process.

[0181]

[0182] Where: R on V represents the oil recovery rate after the variable-stage CO2 injection process and the oil recovery rate before the variable-stage CO2 injection process. im V is the volume of oil displacement. o S represents the initial oil-bearing volume. oi x represents the initial oil-bearing volume of the experimental core. max S is the core length. o (x) is the oil saturation distribution function, including the oil saturation of the core before CO2 injection at the variable stage and the oil saturation of the experimental core before CO2 injection. If S o (x) represents the oil saturation of the core before CO2 injection, then R on Characterizes the recovery rate before the CO2 injection process. If S o (x) represents the oil saturation after CO2 injection during the core transition stage, then R on Characterizes the recovery rate after CO2 injection during the variable phase.

[0183] (4) Calculate the oil recovery rate based on the changes in the volume and saturation of the infiltration before and after reverse pressure drive at the outlet end.

[0184]

[0185] Among them, R o X represents the recovery rate of the core sample before seepage absorption. f S represents the distance of reverse absorption of fracturing fluid. winj x represents the water saturation at the inlet end. max This represents the core length.

[0186] S206. Based on the variable-stage CO2 injection enhanced reverse pressure drive experiment, the CO2 burial rate after variable-stage CO2 injection reverse pressure drive is determined by measuring the injection volume under the same temperature and pressure conditions.

[0187] By experimentally measuring the CO2 injection rate under injection end temperature and pressure conditions, and the CO2 recovery rate (VR) under outlet temperature and pressure conditions, a CO2 burial rate calculation formula considering the influence of gas deviation factor is obtained by combining the gas state equation and the CO2 burial rate calculation formula.

[0188]

[0189] Among them, V IE The volume of CO2 injected under the given conditions is expressed in cm.3 P refers to the volume of CO2 injected through the injection port under formation temperature and pressure conditions; E The injection pressure is measured in MPa, which is the formation pressure; Z E This refers to the CO2 deviation factor under injected temperature and pressure, i.e., the CO2 deviation factor under formation temperature and pressure; Z O This refers to the CO2 deviation factor at outlet temperature and pressure, specifically the CO2 deviation factor at atmospheric pressure and normal temperature (25℃); P O The outlet pressure is atmospheric pressure, expressed in MPa; V R The volume of CO2 released under export conditions, in cm. 3 This refers to the volume of CO2 released at the outlet under atmospheric pressure and normal temperature.

[0190] The embodiments of this application provide another method for improving the recovery and burial rate of variable-stage CO2 injection and reverse pressure drive, which can fully utilize the crude oil in shale / tight oil reservoirs and combine variable-stage CO2 injection with enhanced reverse pressure drive to improve burial rate and recovery rate.

[0191] Figure 7 This is a structural example diagram of the device for enhancing oil recovery and burial rates through variable-stage CO2 injection and reverse pressure drive, provided in an embodiment of this application. Figure 7 As shown, the recovery and storage enhancement device 70 for variable-stage CO2 injection and reverse pressure drive includes: a first obtaining unit 701, a processing unit 702, a second obtaining unit 703, and a determining unit 704. Wherein:

[0192] The first obtaining unit 701 is used to scan the experimental core containing crude oil to obtain a first nuclear magnetic resonance curve, and inject a preset volume of fracturing fluid into the experimental core from a preset first port; wherein, the experimental core is located in a preset container, and the preset container is provided with a preset first port and a preset second port, and the first nuclear magnetic resonance curve characterizes the relationship between relaxation time and signal intensity detected from the radio frequency signal of the experimental core.

[0193] Processing unit 702 is used to perform well-steaming treatment on experimental cores in a preset container based on preset environmental conditions;

[0194] The second obtaining unit 703 is used to inject CO2 into the experimental core from a preset second port based on preset CO2 injection stage configuration information to obtain a second nuclear magnetic resonance curve; wherein, the second nuclear magnetic resonance curve characterizes the relationship between relaxation time and signal intensity detected from the radio frequency signal of the experimental core.

[0195] The determination unit 704 is used to determine the recovery rate of the experimental core based on the area under the curve of the first nuclear magnetic resonance curve and the area under the curve of the second nuclear magnetic resonance curve, and to determine the burial rate of the experimental core based on the volume of injected CO2; wherein, the recovery rate represents the proportion of oil obtained from the experimental core relative to the total oil volume of the experimental core, and the burial rate represents the proportion of the core sealed by CO2.

[0196] Figure 8 This is a structural example diagram of the device for enhancing oil recovery and burial rates through variable-stage CO2 injection and reverse pressure drive, provided in an embodiment of this application. Figure 8 As shown, the enhanced oil recovery and storage capacity device 80 for variable-stage CO2 injection and reverse pressure drive includes: a first obtaining unit 801, a processing unit 802, a second obtaining unit 803, and a determining unit 804. The second obtaining unit 803 includes a first obtaining module 8031 ​​and an acquisition module 8032, and the determining unit 804 includes a determining module 8041 and a second obtaining module 8042, wherein:

[0197] In one example, the second receiving unit 803 includes:

[0198] The first module 8031 ​​is used to inject CO2 into the experimental core from a preset second port based on the initial velocity and the rate of change of velocity, and to obtain the saturation of the experimental core; wherein, the saturation characterizes the distribution of CO2 in the experimental core.

[0199] The acquisition module 8032 is used to acquire the second nuclear magnetic resonance curve at the current moment if the saturation of the experimental core does not change within a preset time period.

[0200] In one possible implementation, the first module 8031 ​​is specifically used for:

[0201] Based on the initial velocity, CO2 is injected into the experimental core from the preset second port;

[0202] If the injection time reaches the preset time threshold, CO2 is injected into the experimental core from the preset second port according to the rate of change of velocity, and the saturation of the experimental core is obtained in real time.

[0203] In one example, unit 804 is defined as including:

[0204] The first determining module 8041 is used to determine the area difference between the area of ​​the first nuclear magnetic resonance curve and the area of ​​the second nuclear magnetic resonance curve.

[0205] Module 8042 is obtained to obtain the first recovery rate of the experimental core based on the area difference and the area of ​​the second nuclear magnetic resonance curve; wherein, the first recovery rate characterizes the recovery rate of the experimental core after CO2 injection.

[0206] In one instance, unit 804 is also used for:

[0207] The permeation distance, core length, initial water saturation of the core, and water saturation of the preset second port of the experimental core were obtained after the well was shut-in treatment; among them, the permeation distance represents the distance that the fracturing fluid permeates into the experimental core.

[0208] The secondary recovery rate of the experimental core was determined based on the seepage distance, core length, initial water saturation of the core, and water saturation at the second port; the secondary recovery rate characterizes the recovery rate of the experimental core after fracturing fluid injection.

[0209] In one instance, unit 804 is also used for:

[0210] Determine the volume of CO2 released from the preset first port;

[0211] The burial rate of the experimental core was determined based on the volume of injected CO2 and the volume of released CO2.

[0212] In one instance, unit 804 is also used for:

[0213] Obtain initial oil-bearing information of the experimental core and oil-bearing information of the experimental core before CO2 injection; the oil-bearing information characterizes the oil saturation of the experimental core;

[0214] Based on the initial oil-bearing information of the experimental core and the oil-bearing information of the experimental core before CO2 injection, the tertiary recovery rate of the experimental core was obtained; among which, the tertiary recovery rate characterizes the recovery rate of the experimental core before the CO2 injection process.

[0215] Figure 9 This is a schematic diagram of the structure of an electronic device provided in an embodiment of this application. Figure 9 As shown, the electronic device 90 includes:

[0216] The electronic device 90 may include a processor 901 with one or more processing cores, a memory 902 with one or more computer-readable storage media, a communication component 903, and other components. The processor 901, memory 902, and communication component 903 are connected via a bus 904.

[0217] In the specific implementation process, at least one processor 901 executes computer execution instructions stored in memory 902, causing at least one processor 901 to execute the above-mentioned method for improving the recovery and storage rate of CO2 injection and reverse pressure drive.

[0218] The specific implementation process of processor 901 can be found in the above method embodiments, and its implementation principle and technical effect are similar. It will not be repeated here.

[0219] In the above Figure 9 In the illustrated embodiments, it should be understood that the processor can be a Central Processing Unit (CPU), or other general-purpose processors, digital signal processors (DSPs), application-specific integrated circuits (ASICs), etc. The general-purpose processor can be a microprocessor or any conventional processor. The steps of the method disclosed in this invention can be directly implemented by a hardware processor, or implemented by a combination of hardware and software modules within the processor.

[0220] The memory may include random access memory (RAM) and may also include non-volatile memory (NVM), such as at least one disk storage device.

[0221] The bus can be an Industry Standard Architecture (ISA) bus, a Peripheral Component Interconnect (PCI) bus, or an Extended Industry Standard Architecture (EISA) bus, etc. Buses can be categorized as address buses, data buses, control buses, etc. For ease of illustration, the buses shown in the accompanying drawings are not limited to a single bus or a single type of bus.

[0222] In some embodiments, a computer program product is also provided, comprising a computer program or instructions that, when executed by a processor, implement the steps in any of the above-described methods for improving the recovery and storage rates of variable-stage CO2 injection and reverse pressure drive.

[0223] For details on the implementation of each of the above operations, please refer to the previous examples, which will not be repeated here.

[0224] Those skilled in the art will understand that all or part of the steps in the various methods of the above embodiments can be performed by instructions, or by instructions controlling related hardware. These instructions can be stored in a computer-readable storage medium and loaded and executed by a processor.

[0225] Therefore, embodiments of this application provide a computer-readable storage medium storing a plurality of instructions that can be loaded by a processor to execute steps in any of the methods for improving recovery and burial rates of variable-stage CO2 injection and reverse pressure drive provided in embodiments of this application.

[0226] The storage medium may include: read-only memory (ROM), random access memory (RAM), disk or optical disk, etc.

[0227] According to one aspect of this application, a computer program product or computer program is provided, the computer program product or computer program including computer instructions stored in a computer-readable storage medium.

[0228] Since the instructions stored in the storage medium can execute the steps in any of the methods for improving the recovery and storage rates of variable-stage CO2 injection and reverse pressure drive provided in the embodiments of this application, the beneficial effects that any of the methods for improving the recovery and storage rates of variable-stage CO2 injection and reverse pressure drive provided in the embodiments of this application can achieve can be realized. For details, please refer to the previous embodiments, which will not be repeated here.

[0229] Other embodiments of this application will readily occur to those skilled in the art upon consideration of the specification and practice of the invention disclosed herein. This application is intended to cover any variations, uses, or adaptations of this application that follow the general principles of this application and include common knowledge or customary techniques in the art not disclosed herein. The specification and examples are to be considered exemplary only, and the true scope and spirit of this application are indicated by the following claims.

[0230] It should be noted that, for the sake of simplicity, the foregoing method embodiments are all described as a series of actions. However, those skilled in the art should understand that this application is not limited to the described order of actions, as some steps may be performed in other orders or simultaneously according to this application. Furthermore, those skilled in the art should also understand that the embodiments described in the specification are all optional embodiments, and the actions and modules involved are not necessarily essential to this application.

[0231] It should be further noted that although the steps in the flowchart are shown sequentially according to the arrows, these steps are not necessarily executed in the order indicated by the arrows. Unless explicitly stated herein, there is no strict order restriction on the execution of these steps, and they can be executed in other orders. Moreover, at least some steps in the flowchart may include multiple sub-steps or multiple stages. These sub-steps or stages are not necessarily completed at the same time, but can be executed at different times. The execution order of these sub-steps or stages is not necessarily sequential, but can be performed alternately or in turn with other steps or at least some of the sub-steps or stages of other steps.

[0232] It should be understood that this application is not limited to the precise structure described above and shown in the accompanying drawings, and various modifications and changes can be made without departing from its scope. The scope of this application is limited only by the appended claims.

Claims

1. A method for improving the recovery and burial rate of variable-stage CO2 injection and reverse pressure drive, characterized in that, The method includes: The experimental core containing crude oil is scanned to obtain a first nuclear magnetic resonance curve, and a predetermined volume of fracturing fluid is injected into the experimental core from a predetermined first port; wherein, the experimental core is located in a predetermined container, and the predetermined container is provided with a predetermined first port and a predetermined second port, and the first nuclear magnetic resonance curve characterizes the relationship between relaxation time and signal intensity detected from the radio frequency signal of the experimental core. Based on preset environmental conditions, the experimental core in the preset container is subjected to a well-steaming treatment. Based on the preset CO2 injection stage configuration information, CO2 is injected into the experimental core from the preset second port to obtain a second nuclear magnetic resonance curve; wherein, the second nuclear magnetic resonance curve characterizes the relationship between relaxation time and signal intensity detected from the radio frequency signal of the experimental core; The recovery rate of the experimental core is determined based on the area under the curve of the first nuclear magnetic resonance curve and the area under the curve of the second nuclear magnetic resonance curve, and the burial rate of the experimental core is determined based on the volume of injected CO2; wherein, the recovery rate represents the proportion of oil obtained from the experimental core relative to the total oil volume of the experimental core, and the burial rate represents the proportion of the core sealed by CO2. Determining the recovery rate of the experimental core based on the area under the first nuclear magnetic resonance curve and the area under the second nuclear magnetic resonance curve includes: Determine the area difference between the area of ​​the first nuclear magnetic resonance curve and the area of ​​the second nuclear magnetic resonance curve; The first recovery rate of the experimental core is obtained based on the area difference and the area of ​​the second nuclear magnetic resonance curve; wherein, the first recovery rate characterizes the recovery rate of the experimental core after CO2 injection. The method further includes: The permeation distance, core length, initial water saturation of the core, and water saturation of the preset second port of the experimental core were obtained after the well was shut-in treatment; wherein, the permeation distance represents the distance that the fracturing fluid permeates into the experimental core. The second recovery rate of the experimental core is determined based on the seepage distance, the core length, the initial water saturation of the core, and the water saturation of the second port; wherein, the second recovery rate characterizes the recovery rate of the experimental core after fracturing fluid injection; The method further includes: The initial oil-bearing information of the experimental core and the oil-bearing information of the experimental core before CO2 injection are obtained; the oil-bearing information characterizes the oil saturation of the experimental core. Based on the initial oil-bearing information of the experimental core and the oil-bearing information of the experimental core before CO2 injection, the third recovery rate of the experimental core is obtained; wherein, the third recovery rate represents the recovery rate of the experimental core before the CO2 injection process.

2. The method according to claim 1, characterized in that, The preset CO2 injection stage configuration information includes the initial velocity and rate of change of injected CO2. Based on this preset CO2 injection stage configuration information, CO2 is injected into the experimental core from a preset second port to obtain a second nuclear magnetic resonance curve, including: Based on the initial velocity and the rate of change of velocity, CO2 is injected into the experimental core from a preset second port to obtain the saturation of the experimental core; wherein, the saturation of the experimental core characterizes the distribution of CO2 in the experimental core; If the saturation of the experimental core does not change within a preset time period, then the second nuclear magnetic resonance curve at the current moment is obtained.

3. The method according to claim 2, characterized in that, The rate of change of velocity characterizes the increase in the rate of CO2 injection; the step of injecting CO2 into the experimental core from a preset second port based on the initial velocity and the rate of change of velocity, and obtaining the saturation of the experimental core, includes: Based on the initial velocity, CO2 is injected into the experimental core from a preset second port; If the injection time reaches a preset time threshold, CO2 is injected into the experimental core from a preset second port according to the rate of change of velocity, and the saturation of the experimental core is obtained in real time.

4. The method according to claim 1, characterized in that, Determining the burial rate of the experimental core based on the injected CO2 volume includes: Determine the volume of CO2 released from the preset first port; The burial rate of the experimental core is determined based on the injected CO2 volume and the released CO2 volume.

5. A device for improving oil recovery and burial rate through variable-stage CO2 injection and reverse pressure drive, characterized in that, include: The first obtaining unit is used to scan and process the experimental core containing crude oil to obtain a first nuclear magnetic resonance curve, and inject a preset volume of fracturing fluid into the experimental core from a preset first port; wherein, the experimental core is located in a preset container, and the preset container is provided with a preset first port and a preset second port, and the first nuclear magnetic resonance curve characterizes the relationship between relaxation time and signal intensity detected from the radio frequency signal of the experimental core. The processing unit is used to perform well-steaming treatment on the experimental core in the preset container based on preset environmental conditions; The second obtaining unit is used to inject CO2 into the experimental core from a preset second port based on preset CO2 injection stage configuration information to obtain a second nuclear magnetic resonance curve; wherein, the second nuclear magnetic resonance curve characterizes the relationship between relaxation time and signal intensity detected from the radio frequency signal of the experimental core; The determining unit is used to determine the recovery rate of the experimental core based on the area under the curve of the first nuclear magnetic resonance curve and the area under the curve of the second nuclear magnetic resonance curve, and to determine the burial rate of the experimental core based on the volume of injected CO2; wherein, the recovery rate represents the proportion of oil obtained from the experimental core relative to the total oil volume of the experimental core, and the burial rate represents the proportion of the core sealed by CO2. The determining unit includes: The first determining module is used to determine the area difference between the area of ​​the first nuclear magnetic resonance curve and the area of ​​the second nuclear magnetic resonance curve. The module is used to obtain the first recovery rate of the experimental core based on the area difference and the area of ​​the second nuclear magnetic resonance curve; wherein, the first recovery rate characterizes the recovery rate of the experimental core after CO2 injection; The determining unit is also used to obtain the seepage distance, core length, initial water saturation of the core, and water saturation of the preset second port of the experimental core after the well-clogging treatment; wherein, the seepage distance characterizes the distance that the fracturing fluid seeps into the experimental core; The second recovery rate of the experimental core is determined based on the seepage distance, the core length, the initial water saturation of the core, and the water saturation of the second port; wherein, the second recovery rate characterizes the recovery rate of the experimental core after fracturing fluid injection; The determining unit is also used to acquire the initial oil-bearing information of the experimental core and the oil-bearing information of the experimental core before CO2 injection; the oil-bearing information characterizes the oil saturation of the experimental core; Based on the initial oil-bearing information of the experimental core and the oil-bearing information of the experimental core before CO2 injection, the third recovery rate of the experimental core is obtained; wherein, the third recovery rate represents the recovery rate of the experimental core before the CO2 injection process.

6. An electronic device, characterized in that, include: A processor, and a memory communicatively connected to the processor; The memory stores computer-executed instructions; The processor executes computer execution instructions stored in the memory to implement the method as described in any one of claims 1 to 4.

7. A computer-readable storage medium, characterized in that, The computer-readable storage medium stores computer-executable instructions, which, when executed by a processor, are used to implement the method as described in any one of claims 1 to 4.

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