System and method for determining contribution rate of CO2 fracturing to shale oil core imbibition oil displacement
By designing a system including a nuclear magnetic unit and an injection unit, CO2 and fracturing fluid can be injected into the shale oil core, and the crude oil signal in the core is detected through the nuclear magnetic signal, which solves the problem of CO2 fracturing's impact on shale oil in the existing technology. The problem of the lack of evaluation methods for the core imbibition oil contribution rate has been achieved to improve the recovery rate of shale oil reservoirs and support CCUS technology.
Patent Information
- Application Number
- CN202310874622.6
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2023-07-17
- Publication Date
- 2025-01-17
AI Technical Summary
The existing technology lacks systematic and method research on the contribution rate of CO2 fracturing to shale oil core seepage and oil flooding, and it is difficult to accurately evaluate the oil flooding effect of CO2 fracturing on shale oil cores.
A system is designed, including a nuclear magnetic unit, core holder, fracturing fluid injection unit, CO2 injection stirring unit and pipeline. By injecting CO2 and fracturing fluid into the imbibition space at the front end of the core, the nuclear magnetic signal is used to detect the core crude oil. NMR signals are used to calculate the contribution rate of CO2 fracturing to shale oil core imbibition oil displacement.
It achieves an accurate evaluation of the contribution rate of CO2 fracturing to shale oil core imbibition oil displacement, which helps optimize reservoirs, improve shale oil reservoir recovery, and provide technical support for CCUS.
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Figure CN119322000A_ABST
Abstract
Description
Technical Field
[0001] The present invention relates to the technical field of oil and gas production enhancement and modification, and in particular to a system and method for determining the contribution rate of CO2 fracturing to shale oil core imbibition oil recovery. Background Art
[0002] Shale oil reservoirs have low porosity and low permeability, and strong capillary forces, so oil is difficult to be used in the pores. Under the spontaneous imbibition induced by high capillary forces, water can spontaneously displace oil, which is an important mechanism for shale oil production. Clarifying the contribution rate of spontaneous imbibition at specific locations of shale oil cores is helpful for optimizing reservoir sweet spots, improving shale oil reservoir recovery, and providing technical support for CCUS.
[0003] At present, the research on spontaneous imbibition recovery of shale oil reservoirs mainly focuses on the analysis of the mechanism and influencing factors of spontaneous imbibition recovery, as well as the design and development of experimental equipment and the establishment of experimental methods. Existing research does not involve the study of the system and methods of the contribution rate of CO2 fracturing to shale oil core imbibition recovery, and there is also a lack of corresponding evaluation methods. Summary of the invention
[0004] The present invention provides a system and method for determining the contribution rate of CO2 fracturing to shale oil core imbibition oil recovery, aiming at accurately evaluating the contribution rate of CO2 fracturing to shale oil core imbibition oil recovery.
[0005] The present invention is achieved through the following technical solution: a system for determining the contribution rate of CO2 fracturing to shale oil core imbibition oil recovery, comprising a nuclear magnetic unit (1), a core holder, a fracturing fluid injection unit (5), a CO2 injection stirring unit (6) and a pipeline, wherein the core holder comprises a core placement unit (3);
[0006] The nuclear magnetic unit (1) is used to detect the nuclear magnetic signal of the core crude oil before or after the injection of CO2 in real time;
[0007] The core placement unit (3) is used to place the shale oil core to be tested, and the space between the core and the core placement unit (3) is the core front end absorption space (2). The core front end absorption space (2) is connected to the CO2 injection stirring unit (6) and the fracturing fluid injection unit (5) through a pipeline, and is used to provide a space for the injected liquid and CO2 to interact with the shale oil core.
[0008] In the system for determining the contribution rate of CO2 fracturing to the imbibition oil recovery of shale oil cores in this scheme, the shale oil core can be placed on a core placement unit, and CO2 and fracturing fluid are respectively injected into the imbibition space at the front end of the core. The end of the core placed on the core placement unit can perform self-imbibition, and then the nuclear magnetic resonance signal of the core crude oil is detected by the nuclear magnetic resonance unit, thereby facilitating the calculation and determination of the contribution rate of CO2 fracturing to the imbibition oil recovery of the shale oil core.
[0009] This scheme provides a system device for determining the contribution rate of CO2 fracturing to shale oil core imbibition recovery, which can accurately obtain the contribution rate of CO2 fracturing to shale oil core imbibition recovery, thereby solving the technical problems raised by the background technology.
[0010] In this scheme, the core front end imbibition space in the core placement unit provides space for the injected liquid and CO2 to interact with the shale oil core, thereby facilitating the subsequent self-imbibition of the shale oil core, and further facilitating the subsequent real-time detection of the core crude oil nuclear magnetic signal before or after the injection of CO2 into the shale oil core.
[0011] Furthermore, it also includes a constant speed and constant pressure pump (4), which is connected to the fracturing fluid injection unit (5) and the CO2 injection and stirring unit (6) through pipelines. Such an arrangement can provide a stable displacement pressure for the core and the fracturing fluid or CO2.
[0012] Furthermore, the fracturing fluid injection unit (5) is used to inject the liquid to be tested, and the liquid is the fracturing fluid used for on-site fracturing. This arrangement can improve the accuracy of the detection.
[0013] Furthermore, the CO2 injection stirring unit includes a stirring tank and a stirring paddle, wherein the stirring paddle is located in the stirring tank, and a motor for driving the stirring paddle to rotate is provided on the stirring tank. Such a configuration can fully stir and mix the CO2.
[0014] The method for determining the contribution rate of CO2 fracturing to shale oil core imbibition oil recovery, using the above-mentioned system for determining the contribution rate of CO2 fracturing to shale oil core imbibition oil recovery, comprises the following steps:
[0015] S1. Carry out NMR T2 spectrum parameter debugging;
[0016] S2. Saturated oil layered T2 spectrum test: evacuate the shale oil core, pressurize and saturate the core, age the saturated core, and use a nuclear magnetic resonance unit to test the saturated oil T2 spectrum;
[0017] S3. Prepare a solution according to the fracturing fluid formula and inject it into the fracturing fluid injection unit, and evacuate the prepared solution for 2 to 4 hours; this can avoid interference from external factors and improve the accuracy of the test results;
[0018] S4. Spontaneous imbibition of the core: the core is placed on the core placement unit in the core holder, and then pressurized so that the solution enters the imbibition space at the front end of the core and contacts the end face of the core, so that the end face of the core spontaneously imbibes;
[0019] S5. After the core end face is fully spontaneously imbibed, the core T2 spectrum is tested to calculate the core imbibition oil displacement efficiency η1 under the action of the solution;
[0020] S6, injecting CO2 into the CO2 injection stirring unit, testing the T2 spectrum after the interaction between CO2 and the core, and obtaining the final imbibition oil recovery efficiency η2 of the core after the action of CO2;
[0021] S7. Obtain the contribution rate η of CO2 fracturing to the imbibition oil recovery efficiency of shale oil reservoirs.
[0022] Further, in S5, the core imbibition oil displacement efficiency η1 under the action of the solution is calculated using the following formula:
[0023]
[0024] The final imbibition oil recovery efficiency η2 of the core in S6 after the action of CO2 is calculated as follows:
[0025]
[0026] The contribution rate η of CO2 fracturing to the imbibition recovery efficiency of shale oil reservoirs in S7 is calculated as follows:
[0027]
[0028] Where t0 represents the initial time before spontaneous imbibition, t represents the imbibition time, represents the oil signal amplitude corresponding to the initial time t0, f t (x) represents the signal amplitude of the core at the imbibition time t.
[0029] The method of this scheme for determining the contribution rate of CO2 fracturing to shale oil core imbibition oil recovery is to conduct nuclear magnetic resonance T2 spectrum tests on the core before and after CO2 injection, and obtain the spontaneous imbibition oil recovery volume of the core and the imbibition oil recovery efficiency after CO2 injection through the nuclear magnetic resonance signal quantity, so as to determine the contribution rate of CO2 injection to the imbibition oil recovery efficiency of the shale oil reservoir, which is helpful to optimize the reservoir sweet spots, improve the recovery rate of shale oil reservoirs, and also provide technical support for CCUS, which is suitable for large-scale promotion and application.
[0030] Furthermore, the NMR T2 spectrum parameter debugging in S1 includes: center frequency calibration, setting TE time, TW time and number of superpositions.
[0031] Furthermore, the fracturing fluid is prepared with heavy water. In this way, the fracturing fluid is prepared with heavy water, which can avoid signal interference.
[0032] Furthermore, in step S4, during the spontaneous imbibition process of the core, the side surface of the core is wrapped. Such an arrangement can prevent spontaneous imbibition from occurring on the side surface of the core.
[0033] Furthermore, in step S5, after the spontaneous imbibition of the core is completed, the floating water on the surface of the core is wiped off. Such a setting can remove the interference of the floating water on the T2 spectrum signal.
[0034] Compared with the prior art, the present invention has the following advantages and beneficial effects:
[0035] The present invention provides a system and method for determining the contribution rate of CO2 fracturing to shale oil core imbibition oil recovery. After obtaining the shale oil reservoir core of the target well, the nuclear magnetic resonance T2 spectrum parameters are first debugged, and T2 spectrum tests are carried out before and after CO2 injection respectively. The spontaneous imbibition oil recovery amount of the core and the imbibition oil recovery efficiency after CO2 injection are obtained through the nuclear magnetic resonance signal quantity, so as to determine the contribution rate of CO2 injection to the imbibition oil recovery efficiency of the shale oil reservoir, which is helpful to optimize the reservoir sweet spot and improve the recovery rate of the shale oil reservoir, and also provides technical support for CCUS, which is suitable for large-scale promotion and application. BRIEF DESCRIPTION OF THE DRAWINGS
[0036] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for use in the embodiments. It should be understood that the following drawings only illustrate certain embodiments of the present invention and should not be regarded as limiting the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative work. In the drawings:
[0037] Figure 1 A schematic diagram of a system embodiment of the present invention for determining the contribution rate of CO2 fracturing to shale oil core imbibition oil recovery;
[0038] Figure 2 The present invention is a flow chart of an embodiment of a method for determining the contribution rate of CO2 fracturing to shale oil core imbibition oil recovery.
[0039] Marks and corresponding parts names in the attached drawings:
[0040] Nuclear magnetic unit 1, core front end imbibition space 2, core placement unit 3, constant speed and pressure pump 4, fracturing fluid injection units 5, 6, CO2 injection stirring unit 6, valve 7, pipeline 8. DETAILED DESCRIPTION
[0041] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Generally, the components of the embodiments of the present invention described and shown in the drawings here can be arranged and designed in various different configurations.
[0042] Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the invention claimed for protection, but merely represents selected embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.
[0043] It should be noted that similar reference numerals and letters denote similar items in the following drawings, and therefore, once an item is defined in one drawing, further definition and explanation thereof is not required in subsequent drawings.
[0044] In the description of the present invention, it is also necessary to explain that, unless otherwise clearly specified and limited, the terms "set", "install", "connect", and "connect" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a direct connection, or an indirect connection through an intermediate medium, or it can be the internal communication of two elements. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.
[0045] like Figure 1-Figure 2 As shown, this embodiment provides a system and method for determining the contribution rate of CO2 fracturing to shale oil core imbibition oil recovery, wherein the system for determining the contribution rate of CO2 fracturing to shale oil core imbibition oil recovery includes a nuclear magnetic unit 1, a core holder, a fracturing fluid injection unit 5, a CO2 injection stirring unit 6 and a pipeline 8, the core holder includes a shell and a core placement unit 3, and the core placement unit 3 is located inside the shell;
[0046] The nuclear magnetic unit 1 is used to detect the nuclear magnetic signal of the core crude oil before or after the injection of CO2 in real time. In this embodiment, the nuclear magnetic unit 1 is a low-field nuclear magnetic structure, and the core holder is placed in it as a whole, which is used to monitor the change of the oil content of the core in the core holder in real time;
[0047] The core placement unit 3 is used to place the shale oil core to be tested. The core placement unit 3 in this embodiment is a core rubber sleeve, and the core is wrapped inside it. The outer side of the core placement unit 3 and the outer shell of the core holder form an annular space, and the annular space is used to pressurize the rubber sleeve and the core;
[0048] In this embodiment, the core placement unit 3 is located inside the shell of the core holder. The core placement unit 3 has a cavity for placing the core. When the core is placed in the core placement unit 3, a gap will be left between the core and the core placement unit 3. The space between the core and the core placement unit 3 is the core front end infiltration space 2 ( Figure 1 The front end imbibition space 2 of the core is indicated by a section line for ease of description and identification, but in fact the front end imbibition space 2 of the core is a cavity structure, not a solid structure). The front end imbibition space 2 of the core is connected to the CO2 injection stirring unit 6 and the fracturing fluid injection unit 5 through a pipeline, which is used to provide a space for the injected liquid and CO2 to interact with the shale oil core.
[0049] The system for determining the contribution rate of CO2 fracturing to shale oil core imbibition oil recovery in this embodiment also includes a constant speed and constant pressure pump 4, which is connected to the fracturing fluid injection unit 5 and the CO2 injection and stirring unit 6 through a pipeline. The fracturing fluid injection unit 5 and the CO2 injection and stirring unit 6 are finally connected through a main pipe and inserted into the front end imbibition space 2 of the core. In this embodiment, a valve is installed on the pipeline between the constant speed and constant pressure pump and the fracturing fluid injection unit 5 and the CO2 injection and stirring unit 6, and a valve is also installed on the pipeline between the CO2 injection and stirring unit 6 and the fracturing fluid injection unit 5.
[0050] The fracturing fluid injection unit 5 is used to load the liquid to be tested, which is the fracturing fluid used for on-site fracturing. In this embodiment, the CO2 injection stirring unit includes a stirring tank and a stirring paddle, the stirring paddle is located in the stirring tank, and a motor for driving the stirring paddle to rotate is provided on the stirring tank. In this embodiment, the stirring tank is a sealed structure, the container is 15L, and the stirring paddle is a three-blade stirring paddle driven by a motor and suspended in the stirring tank for fully stirring and mixing the CO2.
[0051] The method for determining the contribution rate of CO2 fracturing to shale oil core imbibition oil recovery, using the above-mentioned system for determining the contribution rate of CO2 fracturing to shale oil core imbibition oil recovery, comprises the following steps:
[0052] S1. Carry out NMR T2 spectrum parameter debugging: including center frequency calibration and debugging of stacking times;
[0053] S2. Saturated oil layered T2 spectrum test: vacuum the shale oil core, pressurize and saturate the core (immerse the core in saturated oil to simulate the initial oil-bearing state of the core under original formation conditions), age the saturated core for 24-48 hours, and use a nuclear magnetic resonance unit to test the saturated oil T2 spectrum;
[0054] S3, preparing a solution according to the fracturing fluid formula and injecting it into the fracturing fluid injection unit. In this embodiment, the fracturing fluid is prepared with heavy water to avoid signal interference. The prepared solution is vacuumed for 2 to 4 hours to remove dissolved gas in the heavy water solution;
[0055] S4, spontaneous imbibition of the core: the core is placed in the core placement unit in the core holder, and then pressurized to allow the solution to enter the imbibition space at the front end of the core and contact the end face of the core, so that the end face of the core spontaneously imbibes; in the spontaneous imbibition process of the core in this embodiment, the side of the core needs to be wrapped to prevent spontaneous imbibition from occurring on the side of the core;
[0056] S5. After the core end face is fully and spontaneously imbibed, wipe off the floating water on the core surface to remove the interference of the floating water on the T2 spectrum signal, test the core T2 spectrum, and calculate the core imbibition oil displacement efficiency η1 under the action of the solution. The calculation formula is as follows:
[0057]
[0058] S6. Inject CO2 into the CO2 injection stirring unit, test the T2 spectrum after the interaction between CO2 and the core, and obtain the final imbibition oil recovery efficiency η2 of the core after the action of CO2. The calculation formula is as follows:
[0059]
[0060] S7. Obtain the contribution rate η of CO2 fracturing to the shale oil reservoir imbibition recovery efficiency, and the calculation formula is as follows:
[0061]
[0062] Where t0 represents the initial time before spontaneous imbibition, t represents the imbibition time, represents the oil signal amplitude corresponding to the initial time t0, f t (x) represents the signal amplitude of the core at the imbibition time t.
[0063] The specific implementation process is as follows: This method is used to evaluate the spontaneous imbibition contribution rate of shale oil reservoir cores in the central Sichuan Basin. The evaluation results are shown in Table 1.
[0064] Table 1 Evaluation results of the contribution of CO2 fracturing to shale oil core imbibition recovery
[0065]
[0066] It can be seen from the above embodiments that by adopting the method provided in the embodiments of the present invention, nuclear magnetic resonance T2 spectrum tests are carried out before and after CO2 injection, and the spontaneous imbibition oil recovery amount of the core and the imbibition oil recovery efficiency after CO2 injection are obtained through the nuclear magnetic resonance signal quantity, so as to determine the contribution rate of CO2 injection to the imbibition oil recovery efficiency of the shale oil reservoir, which is helpful to optimize the reservoir sweet spots, improve the recovery rate of shale oil reservoirs, and also provide technical support for CCUS, which is suitable for large-scale promotion and application.
[0067] The specific implementation methods described above further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above description is only a specific implementation method of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.
Claims
1. A system for determining the contribution of CO2 fracturing to shale oil core imbibition recovery, characterized in that: It comprises a nuclear magnetic unit (1), a core holder, a fracturing fluid injection unit (5), a CO2 injection stirring unit (6) and a pipeline, wherein the core holder comprises a core placement unit (3); The nuclear magnetic unit (1) is used to detect the nuclear magnetic signal of the core crude oil before or after the injection of CO2 in real time; The core placement unit (3) is used to place the shale oil core to be tested, and the space between the core and the core placement unit (3) is the core front end absorption space (2). The core front end absorption space (2) is connected to the CO2 injection stirring unit (6) and the fracturing fluid injection unit (5) through a pipeline, and is used to provide a space for the injected liquid and CO2 to interact with the shale oil core.
2. The system for determining the contribution rate of CO2 fracturing to shale oil core imbibition oil recovery according to claim 1, characterized in that: It also comprises a constant speed and constant pressure pump (4), which is connected to the fracturing fluid injection unit (5) and the CO2 injection and stirring unit (6) through pipelines.
3. The system for determining the contribution rate of CO2 fracturing to shale oil core imbibition oil recovery according to claim 1, characterized in that: The fracturing fluid injection unit (5) is used to load the liquid to be tested, and the liquid is the fracturing fluid used for on-site fracturing.
4. The system for determining the contribution rate of CO2 fracturing to shale oil core imbibition oil recovery according to claim 1, characterized in that: The CO2 injection stirring unit comprises a stirring tank and a stirring paddle, wherein the stirring paddle is located in the stirring tank and a motor for driving the stirring paddle to rotate is disposed on the stirring tank.
5. A method for determining the contribution rate of CO2 fracturing to shale oil core imbibition oil recovery, using the system for determining the contribution rate of CO2 fracturing to shale oil core imbibition oil recovery according to any one of claims 1 to 4, characterized in that: The following steps are involved: S1. Carry out NMR T2 spectrum parameter debugging; S2. Saturated oil layered T2 spectrum test: evacuate the shale oil core, pressurize and saturate the core, age the saturated core, and use a nuclear magnetic resonance unit to test the saturated oil T2 spectrum; S3, preparing a solution according to the fracturing fluid formula, injecting it into the fracturing fluid injection unit, and evacuating the prepared solution for 2 to 4 hours; S4. Spontaneous imbibition of the core: the core is placed in the core placement unit in the core holder, and then pressurized so that the solution enters the imbibition space at the front end of the core and contacts the end face of the core, so that the end face of the core spontaneously imbibes; S5. After the core end face is fully imbibed spontaneously, the core T2 spectrum is tested to calculate the core imbibition oil displacement efficiency η1 under the action of the solution; S6, injecting CO2 into the CO2 injection stirring unit, testing the T2 spectrum after the interaction between CO2 and the core, and obtaining the final imbibition oil recovery efficiency η2 of the core after the action of CO2; S7. Obtain the contribution rate η of CO2 fracturing to the imbibition oil recovery efficiency of shale oil reservoirs.
6. The method for determining the contribution rate of CO2 fracturing to shale oil core imbibition recovery according to claim 5, characterized in that: In S5, the core imbibition oil displacement efficiency η1 under the action of the solution is calculated using the following formula: The final imbibition oil recovery efficiency η2 of the core in S6 after the action of CO2 is calculated as follows: The contribution rate η of CO2 fracturing to the imbibition recovery efficiency of shale oil reservoirs in S7 is calculated as follows: Where t0 represents the initial time before spontaneous imbibition, t represents the imbibition time, and f t0 (x) represents the oil signal amplitude corresponding to the initial time t0, f t (x) represents the signal amplitude of the core at the imbibition time t.
7. The method for determining the contribution rate of CO2 fracturing to shale oil core imbibition recovery according to claim 5, characterized in that: The debugging of nuclear magnetic T2 spectrum parameters in S1 includes: center frequency calibration and debugging of the number of superposition times.
8. The method for determining the contribution rate of CO2 fracturing to shale oil core imbibition recovery according to claim 5, characterized in that: The fracturing fluid is prepared with heavy water.
9. The method for determining the contribution rate of CO2 fracturing to shale oil core imbibition recovery according to claim 5, characterized in that: In step S4, during the spontaneous imbibition process of the core, the side of the core is wrapped.
10. The method for determining the contribution rate of CO2 fracturing to shale oil core imbibition recovery according to claim 5, characterized in that: In step S5, after the spontaneous imbibition of the core is completed, the floating water on the surface of the core is wiped off.