An optimization method and system for the partition spacing of carbon dioxide injection into compartments in a shale oil reservoir

Abstract

The present invention belongs to the technical field of shale reservoir development, and particularly relates to a method and system for optimizing the partition spacing of carbon dioxide injection in compartments for shale reservoirs; it solves the problems of carbon dioxide gas channeling and low oil displacement efficiency caused by unreasonable partition spacing in the current carbon dioxide injection in compartments for shale reservoirs; the technical solution is: building a physical model for carbon dioxide injection in compartments for oil recovery, establishing the initial state of the physical model for carbon dioxide injection in compartments for oil recovery, conducting an oil displacement experiment with carbon dioxide injection in compartments, continuously increasing the number of partitions, obtaining the carbon dioxide oil displacement efficiency at different partition spacings, establishing a relationship chart between different partition spacings and the carbon dioxide oil displacement efficiency and the gas breakthrough time, and obtaining the optimal partition spacing of the physical model for carbon dioxide injection in compartments for oil recovery according to the chart. Through similarity criteria, the optimal partition spacing of carbon dioxide injection in compartments for the shale reservoir in actual field production can be determined; the new method in the present invention can optimize the shale reservoir development plan and improve the overall economic benefits.

Description

Technical Field

[0001] The present invention belongs to the technical field of shale reservoir development, and particularly relates to a method and system for optimizing the partition spacing of carbon dioxide injection in compartments of a shale reservoir. Background Art

[0002] Shale reservoirs are unconventional oil and gas resources with great development difficulty. The traditional water injection development method has limited effects. In recent years, carbon dioxide flooding technology has gradually been applied in shale reservoir development. By injecting carbon dioxide, the reservoir pressure is increased, the oil fluidity is improved, and thus the recovery rate is increased.

[0003] Through extensive research, the patent "A method for evaluating the effective displacement distance of carbon dioxide injection in low-permeability and tight reservoirs" with the patent number CN202310774476.X analyzes the starting pressure gradient of cores with different permeabilities, establishes the mathematical relationship between it and permeability, and calculates the effective displacement distance of the reservoir under different conditions, so as to determine the actual effective displacement distance of carbon dioxide flooding in the oilfield to optimize the oil production efficiency; the patent "A method and system for optimizing carbon dioxide injection development based on non-complete miscible characteristics" with the patent number CN202410342868.3 constructs a three-dimensional reservoir model including fluid and reservoir characteristics, and analyzes the non-complete miscible characteristics of carbon dioxide injection development based on this model to realize the optimized development of the entire life cycle of carbon dioxide injection.

[0004] Generally speaking, there are many methods for carbon dioxide injection in reservoirs. However, in the actual process of carbon dioxide injection, due to the heterogeneity of shale reservoirs, carbon dioxide gas channeling is likely to occur, affecting the oil displacement effect. These methods have their own limitations. Therefore, it is crucial to study a scientific method and system for optimizing the partition spacing of carbon dioxide injection in compartments of a shale reservoir to solve the problem of carbon dioxide gas channeling in the existing technology, improve the recovery rate of shale reservoirs, and enhance the overall economic benefits of oilfield development. Summary of the Invention

[0005] The purpose of the present invention is to solve the problem that the unreasonable partition spacing of carbon dioxide injection in compartments of current shale reservoirs leads to carbon dioxide gas channeling and low oil displacement efficiency. The present invention combines experiments and theories, builds a physical model for carbon dioxide injection in compartments for exploitation, establishes the initial state of the physical model for carbon dioxide injection in compartments for exploitation, conducts carbon dioxide flooding experiments in compartments, continuously increases the number of partitions, obtains the carbon dioxide oil displacement efficiency at different partition spacings, establishes the relationship charts of different partition spacings with carbon dioxide oil displacement efficiency and gas breakthrough time, and according to the charts, the optimal partition spacing of the physical model for carbon dioxide injection in compartments for exploitation can be obtained. Through similarity criteria, the optimal partition spacing of carbon dioxide injection in compartments of the actual on-site production shale reservoir can be determined, with convenient calculation and strong reliability.

[0006] To achieve the above objectives, the present invention provides a method and system for optimizing the spacing between partitions for carbon dioxide injection in compartments of shale oil reservoirs. The method comprises the following steps:

[0007] The first step is to collect reservoir characteristic parameters of shale oil reservoirs, design and build a physical model for sub-compartmental CO2 injection production;

[0008] The second step is to set the temperature of the CO2 injection physical model to 90°C and the pressure to 50 MPa, measure the total porosity of the CO2 injection physical model, and establish the initial oil saturation of the CO2 injection physical model. The total porosity and initial oil saturation of the CO2 injection physical model are obtained.

[0009] The third step is to start with no baffles and add one baffle at a time to obtain the CO2 recovery efficiency at different baffle spacings, and calculate the CO2 recovery efficiency at different baffle spacings.

[0010] The fourth step is to inject carbon dioxide for oil recovery without baffles. After carbon dioxide is injected, it will quickly advance along the area with good physical properties. After adding baffles, carbon dioxide cannot break through the baffles and advances evenly along the compartments between the baffles. A relationship chart of different baffle spacing and carbon dioxide oil recovery efficiency and gasification time is established. As the number of baffles increases, the baffle spacing shortens, and the carbon dioxide oil recovery efficiency and gasification time gradually increase. When the baffle spacing is ≤l m When the CO2 flooding efficiency increases by less than 2%, the baffle spacing l can be determined. m Optimal bulkhead spacing for carbon dioxide injection into physical model compartments;

[0011] The fifth step is to obtain the optimal baffle spacing of the physical model of sub-compartment CO2 injection under experimental conditions. Through the similarity criterion, the optimal baffle spacing of sub-compartment CO2 injection in shale oil reservoirs in actual field production can be determined.

[0012] ,

[0013] Among them, l z is the optimal partition spacing for on-site production, in m; l m is the optimal partition spacing of the physical model of carbon dioxide injection for sub-compartmental production, in m; L is the length of the physical model of carbon dioxide injection for sub-compartmental production, in m; L z is the length of the on-site production horizontal well, in meters.

[0014] In the above-mentioned method and system for optimizing the spacing between partitions for compartmentalized carbon dioxide injection in shale oil reservoirs, the steps of building a physical model for compartmentalized carbon dioxide injection production are as follows:

[0015] First step: In a pressure-resistant cuboid container, horizontal wells with the same length are arranged in parallel along the longest side, and vertical partitions are arranged at equal intervals perpendicular to the axis of the horizontal wells. The compartments between the partitions are independent of each other.

[0016] Second step: Quartz sand is filled around the horizontal wells and solidified after adding an adhesive. By changing the amount of the adhesive, the physical model for compartmentalized CO₂ injection for oil recovery is made to be consistent with the reservoir characteristics of the actual shale oil reservoir.

[0017] In the above method and system for optimizing the partition spacing in a shale oil reservoir for compartmentalized CO₂ injection, the steps for obtaining the total porosity and initial oil saturation of the physical model for compartmentalized CO₂ injection for oil recovery are as follows:

[0018] First step: The physical model for compartmentalized CO₂ injection for oil recovery in the pressure-resistant container is dried and weighed. Formation water is pressurized and injected into the pressure-resistant container so that the formation water fully enters the pore volume of the physical model. Then, the physical model for compartmentalized CO₂ injection for oil recovery is weighed again. Using the weight difference between the two times, the total porosity of the physical model for compartmentalized CO₂ injection for oil recovery is measured.

[0019] Second step: For the physical model for compartmentalized CO₂ injection for oil recovery saturated with formation water, oil is displaced at a constant rate. When no more water flows out of the physical model for compartmentalized CO₂ injection for oil recovery, the displacement process is stopped. At this time, the oil saturation is the initial oil saturation.

[0020] In the above method and system for optimizing the partition spacing in a shale oil reservoir for compartmentalized CO₂ injection, the steps for calculating different partition spacings and CO₂ oil displacement efficiency are as follows:

[0021] First step: The number of partitions is continuously increased, and the partitions are arranged at equal intervals in the physical model for compartmentalized CO₂ injection for oil recovery. The calculation model for different partition spacings can be established as:

[0022] ,

[0023] where l i is the different partition spacing, with the unit of m; L is the length of the physical model for compartmentalized CO₂ injection for oil recovery, with the unit of m; i is the number of partitions, with the unit of piece.

[0024] Second step: Through the physical model for compartmentalized CO₂ injection for oil recovery, a compartmentalized CO₂ oil displacement experiment is carried out. The cumulative oil displacement amount and gas breakthrough time at different partition spacings are recorded. At the same time, the CO₂ oil displacement efficiency is calculated, and the calculation model for the CO₂ oil displacement efficiency is established.

[0025] ,

[0026] where R o is the CO₂ oil displacement efficiency, with the unit of %; V oiis the cumulative oil displacement volume of the i-th baffle, with the unit of m³; B o is the coefficient of formation volume factor of crude oil, with the unit of dimensionless; L is the length of the physical model for CO₂ injection in compartments of shale oil reservoir, with the unit of m; D is the width of the physical model for CO₂ injection in compartments of shale oil reservoir, with the unit of m; H is the height of the physical model for CO₂ injection in compartments of shale oil reservoir, with the unit of m; P is the total porosity of the physical model for CO₂ injection in compartments of shale oil reservoir, with the unit of %; S oi is the initial oil saturation, with the unit of %.

[0027] Compared with the prior art, the present invention has the following beneficial effects: (1) enhanced flexibility and customization; (2) the method is convenient and effective, with high working efficiency; (3) high reliability and stability. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] In the drawings:

[0029] Figure 1 is the overall technical roadmap of the method;

[0030] Figure 2 is the relationship chart of different baffle spacings and gas breakthrough time;

[0031] Figure 3 is the relationship chart of different baffle spacings and CO₂ oil displacement efficiency. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0032] The present invention will be further described below in combination with the embodiments and the drawings;

[0033] The present invention provides a method and system for optimizing the baffle spacing of CO₂ injection in compartments of shale oil reservoir, Figure 1 is the overall technical roadmap of the method. The method includes the following steps:

[0034] First step, collect the reservoir characteristic parameters of the shale oil reservoir, design the physical model for CO₂ injection in compartments of shale oil reservoir, and build the physical model for CO₂ injection in compartments of shale oil reservoir;

[0035] Second step, set the temperature of the physical model for CO₂ injection in compartments of shale oil reservoir to 90 °C and the pressure to 50 MPa, measure the total porosity of the physical model for CO₂ injection in compartments of shale oil reservoir, and simultaneously establish the initial oil saturation of the physical model for CO₂ injection in compartments of shale oil reservoir, so as to obtain the total porosity and the initial oil saturation of the physical model for CO₂ injection in compartments of shale oil reservoir;

[0036] Third step, starting from no baffle, add 1 baffle each time, obtain the CO₂ oil displacement efficiency at different baffle spacings, and calculate the different baffle spacings and the CO₂ oil displacement efficiency;

[0037] Step 4: Inject carbon dioxide for oil displacement without baffles. After the injection of carbon dioxide, it quickly advances along the area with good physical properties. After adding the baffles, the carbon dioxide cannot break through the baffles and uniformly advances along the compartments between the baffles. Establish a relationship chart between different baffle spacings and carbon dioxide oil displacement efficiency and gas breakthrough time. As the number of baffles increases and the baffle spacing shortens, the carbon dioxide oil displacement efficiency and gas breakthrough time gradually increase. When the baffle spacing ≤ l m , the growth rate of the carbon dioxide oil displacement efficiency is less than 2%. The baffle spacing l m can be determined as the optimal baffle spacing for injecting carbon dioxide into compartments in the physical model;

[0038] Step 5: Under experimental conditions, obtain the optimal baffle spacing of the physical model for injecting carbon dioxide into compartments. Through similarity criteria, the optimal baffle spacing for injecting carbon dioxide into compartments in the actual on-site shale oil reservoir can be determined.

[0039] ,

[0040] wherein, l z is the optimal baffle spacing for on-site production, with the unit of m; l m is the optimal baffle spacing of the physical model for injecting carbon dioxide into compartments, with the unit of m; L is the length of the physical model for injecting carbon dioxide into compartments, with the unit of m; L z is the length of the horizontal well in on-site production, with the unit of m.

[0041] Furthermore, the steps for building the physical model for injecting carbon dioxide into compartments are as follows:

[0042] Step 1: In a pressure-resistant container in the shape of a cuboid, horizontally arranged horizontal wells with the same length are arranged parallel to the longest side, and vertical baffles are arranged at equal intervals perpendicular to the axis of the horizontal wells. The compartments between the baffles are independent of each other;

[0043] Step 2: Fill quartz sand around the horizontal wells and consolidate them after adding an adhesive. By changing the amount of the adhesive, make the physical model for injecting carbon dioxide into compartments consistent with the reservoir characteristics of the real shale oil reservoir.

[0044] Furthermore, the steps for obtaining the total porosity and initial oil saturation of the physical model for injecting carbon dioxide into compartments are as follows:

[0045] Step 1: Dry the physical model for injecting carbon dioxide into compartments in the pressure-resistant container and weigh its dry weight. Inject formation water into the pressure-resistant container under pressure so that the formation water fully enters the pore volume of the physical model. Weigh the physical model for injecting carbon dioxide into compartments again. Using the weight difference between the two times before and after, measure the total porosity of the physical model for injecting carbon dioxide into compartments;

[0046] In the second step, the physical model of CO₂ injection into separate compartments for the exploitation of saturated formation water is subjected to constant-rate displacement of crude oil. When no more water flows out of the physical model of CO₂ injection into separate compartments, the displacement process is stopped, and the oil saturation at this time is the initial oil saturation.

[0047] Furthermore, the steps for calculating different baffle spacings and CO₂ oil displacement efficiencies are as follows:

[0048] In the first step, the number of baffles is continuously increased, and the baffles are arranged at equal intervals in the physical model of CO₂ injection into separate compartments. The calculation model for different baffle spacings can be established as:

[0049] ,

[0050] where l i is the different baffle spacing, with the unit of m; L is the length of the physical model of CO₂ injection into separate compartments, with the unit of m; i is the number of baffles, with the unit of piece;

[0051] In the second step, through the physical model of CO₂ injection into separate compartments, a CO₂ injection and oil displacement experiment is carried out. The cumulative oil displacement volume and gas breakthrough time at different baffle spacings are recorded. At the same time, the CO₂ oil displacement efficiency is calculated, and a calculation model for the CO₂ oil displacement efficiency is established.

[0052] ,

[0053] where R o is the CO₂ oil displacement efficiency, with the unit of %; V oi is the cumulative oil displacement volume of i baffles, with the unit of m³; B o is the crude oil volume factor, with the unit of dimensionless quantity; L is the length of the physical model of CO₂ injection into separate compartments, with the unit of m; D is the width of the physical model of CO₂ injection into separate compartments, with the unit of m; H is the height of the physical model of CO₂ injection into separate compartments, with the unit of m; P is the total porosity of the physical model of CO₂ injection into separate compartments, with the unit of %; S oi is the initial oil saturation, with the unit of %.

[0054] Taking a certain shale oil reservoir as an example, the burial depth of the reservoir of this oil reservoir reaches 4250 m, the original reservoir pressure is 50 MPa, the formation temperature is maintained at 90 °C, the crude oil volume factor is 1.21, the designed length of the horizontal well section is 1200 m. After obtaining the reservoir characteristic parameters of the shale oil reservoir, a physical model of CO₂ injection into separate compartments is built, and its length, width and height are 2×0.5×0.5 m. The basic parameters of the physical model of CO₂ injection into separate compartments are shown in Table 1. Through the CO₂ injection and oil displacement experiment, the CO₂ oil displacement efficiency and gas breakthrough time at different baffle spacings are obtained, as shown in Table 2.

[0055] Establish a relationship chart of different baffle spacings with carbon dioxide flooding efficiency and gas breakthrough time. As the number of baffles increases, the baffle spacing shortens, and the gas breakthrough time gradually increases. As shown in Figure 2 , the carbon dioxide flooding efficiency gradually increases and then slows down. As shown in Figure 3 , when the baffle spacing ≤ 0.33 m, the growth rate of carbon dioxide flooding efficiency is less than 2%. It can be determined that the optimal baffle spacing for compartmentalized carbon dioxide injection in the physical model is 0.33 m. Through similarity criteria, the optimal baffle spacing for compartmentalized carbon dioxide injection in the actual shale oil reservoir in field production can be determined to be 198 m.

[0056] Table 1 Basic parameters of the physical model for compartmentalized carbon dioxide flooding

[0057]

[0058] Table 2 Carbon dioxide flooding efficiency and gas breakthrough time at different baffle spacings

[0059]

[0060] Compared with the prior art, the present invention has the following beneficial effects: (1) enhanced flexibility and customization; (2) the method is convenient and effective, with high working efficiency; (3) high reliability and stability.

[0061] Finally, it should be noted that the above embodiments are only used to illustrate rather than limit the technical solutions of the present invention. Although the present invention has been described in detail with reference to the above embodiments, those of ordinary skill in the art should understand that the present invention can still be modified or equivalently replaced. Any modification or partial replacement without departing from the spirit and scope of the present invention shall be covered by the scope of the claims of the present invention.

Claims

1. A method for optimizing the spacing of partitions for injecting carbon dioxide into compartments in a shale oil reservoir, characterized in that, The method includes the following steps: S100. Collect the reservoir characteristic parameters of the shale oil reservoir and design a physical model for CO₂ injection into separate compartments. The steps for building the physical model for CO₂ injection into separate compartments are as follows. S101. In a pressure-resistant cuboid container, horizontally arranged wells with the same length are parallel to the longest side, and vertical partitions are arranged at equal intervals perpendicular to the axis of the horizontal wells. The compartments between the partitions are independent of each other. S102. Quartz sand is filled around the horizontal wells and consolidated after adding an adhesive. By changing the amount of the adhesive, the physical model for CO₂ injection into separate compartments is made to be consistent with the characteristics of the actual shale oil reservoir. S200. Set the temperature of the physical model for CO₂ injection into separate compartments to 90 °C and the pressure to 50 MPa, measure the total porosity of the physical model for CO₂ injection into separate compartments, and simultaneously establish the initial oil saturation of the physical model for CO₂ injection into separate compartments. The steps for obtaining the total porosity and the initial oil saturation of the physical model for CO₂ injection into separate compartments are as follows. S201. Dry the physical model for CO₂ injection into separate compartments in the pressure-resistant container and weigh it dry. Inject formation water into the pressure-resistant container under pressure so that the formation water fully enters the pore volume of the physical model. Weigh the physical model for CO₂ injection into separate compartments again. Using the weight difference between the two times before and after, measure the total porosity of the physical model for CO₂ injection into separate compartments. S202. Use constant-rate displacement of crude oil for the physical model for CO₂ injection into separate compartments saturated with formation water. When no more water flows out of the physical model for CO₂ injection into separate compartments, stop the displacement process. At this time, the oil saturation is the initial oil saturation. S300. Starting from no partition, add 1 partition each time to obtain the CO₂ oil displacement efficiency at different partition spacings. The steps for calculating different partition spacings and the CO₂ oil displacement efficiency are as follows. S301. Continuously increase the number of partitions. The partitions are arranged at equal intervals in the physical model for CO₂ injection into separate compartments. The calculation model for different partition spacings is established as follows. ， Among them, li is the different baffle spacings, with the unit of m; L is the length of the physical model for CO₂ injection in separate compartments for exploitation, with the unit of m; i is the number of baffles, with the unit of piece; S302. Through the physical model for CO₂ injection into separate compartments, conduct an experiment on CO₂ injection into separate compartments for oil displacement, record the cumulative oil displacement volume and the gas breakthrough time at different partition spacings, and simultaneously calculate the CO₂ oil displacement efficiency and establish a calculation model for the CO₂ oil displacement efficiency. ， Among them, R o is the carbon dioxide oil displacement efficiency, in %; V o i is i the cumulative oil displacement volume of the partition boards, in m 3 ; B o is the formation volume factor of crude oil, dimensionless; L is the length of the physical model for compartmentalized carbon dioxide injection for oil recovery, in m; D is the width of the physical model for compartmentalized carbon dioxide injection for oil recovery, in m; H is the height of the physical model for compartmentalized carbon dioxide injection for oil recovery, in m; P is the total porosity of the physical model for compartmentalized carbon dioxide injection for oil recovery, in %; S o i is the initial oil saturation, in %; In the S400, carbon dioxide flooding is carried out without baffles. After the injection of carbon dioxide, it quickly breaks through along the area with good physical properties. After adding baffles, carbon dioxide cannot break through the baffles and uniformly advances along the compartments between the baffles. A relationship chart of different baffle spacings with carbon dioxide flooding efficiency and gas breakthrough time is established. As the number of baffles increases and the baffle spacing shortens, the carbon dioxide flooding efficiency and gas breakthrough time gradually increase. When the baffle spacing ≤ lm , the growth rate of carbon dioxide flooding efficiency is less than 2%. Determine the baffle spacing lm as the optimal baffle spacing for compartmentalized carbon dioxide injection in the physical model; S500. Under experimental conditions, obtain the optimal partition spacing of the physical model for CO₂ injection into separate compartments. Through the similarity criterion, the optimal partition spacing for CO₂ injection into separate compartments of the shale oil reservoir in actual field production can be determined. ， Among them, lz is the optimal baffle spacing for on-site production, with the unit of m; lm is the optimal baffle spacing for the physical model of CO₂ injection in compartments for exploitation, with the unit of m; L is the length of the physical model of CO₂ injection in compartments for exploitation, with the unit of m; Lz is the length of the horizontal well for on-site production, with the unit of m.

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