Experimental device and method for describing CO2 on-way miscible phase boundary quantitative characterization

Abstract

The embodiment of the invention provides an experimental device and method for describing CO2 on-way miscible phase boundary quantitative characterization, and relates to the field of oil displacement experimental equipment. Comprising a heat shrink tube, an upper clamping piece, a lower clamping piece and a pressure measuring point, the upper clamping piece and the lower clamping piece are symmetrically arranged relative to the heat shrink tube, a cavity can be formed after the upper clamping piece and the lower clamping piece are combined, and the shape of the cavity can accommodate the heat shrink tube; and the four pressure measuring points are respectively arranged on the upper clamping piece at equal intervals. A rock core can be clamped through the rock core clamping device, so that the stability during an experiment is ensured; the pressure of each part of the core holder can be detected through the pressure sensor; besides, in the experiment process, the core holder can be detected in real time through a nuclear magnetic resonance detection system, and the crude oil use amount of each position is judged by analyzing nuclear magnetic signals at different positions of the core, so that the miscible phase position of the crude oil under the condition of the purity CO2 and the crude oil physical property is judged.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of oil displacement experiment equipment, in particular to an experimental device and method for quantitatively characterizing the CO2 along-path miscibility limit. BACKGROUND

[0002] Compared with conventional oil reservoirs, low-permeability oil reservoirs have high development cost and relatively low productivity, and the development economy is poor. CO2 flooding technology is an important technical means for improving the oil recovery of low-permeability oil reservoirs. CO2 gas has high solubility in oil and water. When a large amount of CO2 gas is dissolved in the oil, the volume of the oil will expand, and the viscosity will also decrease. The interfacial tension between oil and water will decrease with the increase of CO2 concentration.

[0003] Among various enhanced oil recovery (EOR) methods, gas miscible flooding is a widely used and effective method. In the design of gas miscible flooding, the minimum miscibility pressure is one of the key parameters. At the minimum miscibility pressure, the theoretical oil recovery can reach 100%. At the same time, the interfacial tension (IFT) between the injected gas and the oil becomes 0. The miscibility capacity of the reservoir is highly dependent on the pressure. If the injection pressure is lower than the minimum miscibility pressure, the gas flooding cannot completely reach miscibility, which reduces the oil recovery. At high injection pressure, the injected gas and the oil are more likely to miscible, but the high injection pressure will increase the operating cost of the gas miscible flooding project and also make the project face great safety risks. Therefore, the determination of the minimum miscibility pressure under different oil-gas conditions has been the research direction of researchers. Therefore, when conducting research experiments, a related device is needed to quantitatively characterize the CO2 along-path miscibility limit.

[0004] Based on this, the present application is proposed. SUMMARY

[0005] According to the embodiments of the present application, an experimental device and method for quantitatively characterizing the CO2 along-path miscibility limit are provided to solve the existing background problems.

[0006] In the first aspect of the present application, a core holder is provided.

[0007] The core holder comprises a heat shrink tube, an upper clamping piece, a lower clamping piece and a pressure measurement point. The upper clamping piece and the lower clamping piece are symmetrically arranged relative to the heat shrink tube, and the upper clamping piece and the lower clamping piece can form a cavity after being combined, and the cavity shape can accommodate the heat shrink tube; the pressure measurement point has four, which are equally installed on the upper clamping piece.

[0008] Preferably, two first connecting members are symmetrically arranged at two ends of the upper clamping member; and two second connecting members are symmetrically arranged at two ends of the lower clamping member.

[0009] Preferably, a clamping block is arranged on the lower surface of the upper clamping member; and a clamping groove is arranged on the upper surface of the lower clamping member, and the clamping block is inserted into the clamping groove.

[0010] Preferably, a locking member is screwed on the first connecting member and the second connecting member, and the first connecting member and the second connecting member are fixedly connected through the locking member.

[0011] Preferably, a limiting tube member is arranged at one end of the locking member away from the heat shrink tube, and the diameter of the limiting tube member is smaller than that of the locking member.

[0012] Preferably, two flow guide tubes are respectively inserted into two ends of the space formed by combining the upper clamping member and the lower clamping member; and an extension tube is arranged at one end of the two flow guide tubes away from each other, and the extension tube extends into the inner cavity of the limiting tube member.

[0013] Preferably, a mesh is arranged at one end of the flow guide tube close to the heat shrink tube.

[0014] In the second aspect of the present application, an experimental device for quantitatively characterizing the CO2 along-path miscibility boundary is provided.

[0015] The device comprises the core holder according to any one of the claims, and further comprises a constant-pressure constant-speed displacement pump, an intermediate container, a six-way valve, a pressure sensor, a back pressure valve, a gas distribution bottle, a gas dosimeter, a hand pump and a pressure gauge. One of the constant-pressure constant-speed displacement pumps is connected with the core holder. The pressure sensor has four, and the four pressure sensors are respectively connected with four pressure measuring points; the gas distribution bottle and the gas dosimeter are connected with the core holder; the back pressure valve is arranged between the core holder and the gas distribution bottle; the hand pump is connected with the back pressure valve; and the pressure gauge is arranged between the hand pump and the back pressure valve. The core holder is connected with another constant-pressure constant-speed displacement pump, and the two are connected with the six-way valve and a plurality of intermediate containers in sequence.

[0016] In the third aspect of the present application, a method for quantitatively characterizing the CO2 along-path miscibility boundary is provided.

[0017] The method comprises the following steps. Step one: Before starting the experiment, the experimental core is first treated with oil and dried to a constant weight, and the dry weight of the core is measured. Step two: using a vacuum pump to saturate the experimental core with formation water, measure the wet weight of the core and measure the core pore volume; Step three: install the experimental equipment, and preheat the experimental equipment using the constant temperature oven; Step four: inject 10 MPa of N2 into the experimental system through the constant pressure constant speed displacement pump and perform a gas tightness check, observe for 1 hour, and if the pressure drop is less than 0.2 MPa, the sealing property is qualified; Step five: place the experimental core into the core holder, and use the tracking ring pressure system to control the constant pressure constant speed displacement pump to set the confining pressure, so that the confining pressure of each part of the core holder is always greater than the displacement pressure; Step six: slowly inject formation water into the core holder at a constant speed through the hand pump, and inject until the outlet flow is stable; Step seven: slowly inject crude oil into the core holder at a constant speed through the hand pump, and the formation water is discharged, and when the outlet is not water, it indicates that the crude oil is fully saturated, and the oil saturation is calculated according to the output water volume; Step eight: inject the experimental gas sample at a speed of 0.05-0.2 mL / min through the hand pump, and monitor through the back pressure valve, keep the difference between the injection pressure and the back pressure not more than 0.05 MPa, collect and measure the output oil sample and gas sample using the gas separation bottle and the gas flow meter, and stop the experiment after 1.2 PV of the experimental gas sample is accumulated.

[0018] Preferably, in step five, the tracking ring pressure system is used to control the constant pressure constant speed displacement pump (200) to set the confining pressure, so that the confining pressure of each part of the core holder is always greater than the displacement pressure by 5 MPa.

[0019] The one or more technical solutions provided in the application have at least the following technical effects or advantages: The experimental device for quantitatively characterizing the CO2 along-path miscibility limit provided by the application can clamp the core through the core holder, guarantee the stability during the experiment, detect the pressure at each part of the core holder through the pressure sensor, and detect the core holder in real time through the nuclear magnetic resonance detection system during the experiment, analyze the nuclear magnetic signals at different positions of the core to determine the oil production amount at each position, and thus determine the miscibility position of the pure CO2 and the oil under the physical condition of the oil.

[0020] It should be understood that the content described in the summary section is not intended to limit the key or important features of the embodiments of the application, nor is it intended to limit the scope of the application. Other features of the application will become apparent through the following description. BRIEF DESCRIPTION OF DRAWINGS

[0021] The above and other features, advantages, and aspects of embodiments of the present application will become more apparent by describing in detail the following embodiments thereof with reference to the accompanying drawings. In the drawings: Figure 1 A structural diagram of an experimental device for quantitatively characterizing a CO2 miscibility boundary is shown according to an embodiment of the present application; Figure 2 A perspective view of a core holder is shown according to an embodiment of the present application; Figure 3 An exploded structural schematic diagram of a core holder is shown according to an embodiment of the present application; Figure 4 A right-side sectional view of a core holder is shown according to an embodiment of the present application; Figure 5 A front sectional view of a core holder is shown according to an embodiment of the present application; Figure 6 A structural schematic diagram of a flow guide tube of a core holder is shown according to an embodiment of the present application.

[0022] Reference signs are as follows: 1, heat shrink tube; 2, upper clamping member; 3, lower clamping member; 4, pressure measurement point; 5, clamping block; 6, clamping groove; 7, first connecting member; 8, second connecting member; 9, locking member; 10, flow guide tube; 11, extension tube; 12, limiting tube member; 13, mesh; 100, core holder; 200, constant pressure and constant speed displacement pump; 300, intermediate container; 400, six-way valve; 500, pressure sensor; 600, back pressure valve; 700, gas cylinder; 800, gas dosimeter; 900, hand pump; 1000, pressure gauge; 1100, tracking ring pressure system; 1200, nuclear magnetic resonance detection system. DETAILED DESCRIPTION

[0023] In order to make the objects, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be described clearly and completely below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are some but not all of the embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by a person of ordinary skill in the art without creative work fall within the protection scope of the present application.

[0024] In addition, the term "and / or" herein merely describes an association relationship of associated objects, and indicates that there can be three relationships, for example, A and / or B can represent three cases of A alone, A and B together, and B alone. In addition, the character " / " herein generally represents an "or" relationship between the front and rear associated objects.

[0025] As Figure 1 shown, the experimental device for quantitatively characterizing the CO2 along the miscibility boundary, which is used to test different sampling crude oil, different purity of CO2 in the long core in the case of miscibility point and miscibility pressure. The device includes: core holder 100, constant pressure constant speed displacement pump 200, intermediate container 300, six-way valve 400, pressure sensor 500, back pressure valve 600, gas cylinder 700, gas dosimeter 800, hand pump 900, pressure gauge 1000, tracking ring pressure system 1100 and nuclear magnetic resonance detection system 1200.

[0026] Reference Figures 2 to 6The core holder 100 comprises a heat shrink tube 1, an upper clamping piece 2, a lower clamping piece 3, a pressure measuring point 4, a clamping block 5, a clamping groove 6, a first connecting piece 7, a second connecting piece 8, a locking piece 9, a flow guide pipe 10, an extension pipe 11, a limiting pipe 12 and a mesh 13. The heat shrink tube 1 is a special polyolefin material heat shrink sleeve, which is an existing device. The upper clamping piece 2 and the lower clamping piece 3 are symmetrically arranged relative to the heat shrink tube 1. The upper clamping piece 2 and the lower clamping piece 3 can form a cavity after being combined, and the cavity shape can accommodate the heat shrink tube 1. When the upper clamping piece 2 and the lower clamping piece 3 are combined, the heat shrink tube 1 is located in the space between the upper clamping piece 2 and the lower clamping piece 3. The pressure measuring point 4 has four, respectively equidistantly installed on the upper clamping piece 2. The lower surface of the upper clamping piece 2 is provided with the clamping block 5, and the upper surface of the lower clamping piece 3 is provided with the clamping groove 6. The clamping block 5 is inserted into the clamping groove 6. The shapes of the clamping block 5 and the clamping groove 6 are the shape of a back word, and they form a mortise and tenon structure. When the upper clamping piece 2 and the lower clamping piece 3 are combined, the mortise and tenon structure can realize the stable mutual limiting of the upper clamping piece 2 and the lower clamping piece 3, and ensure that dislocation does not occur. Two first connecting pieces 7 are symmetrically arranged at both ends of the upper clamping piece 2, and two second connecting pieces 8 are symmetrically arranged at both ends of the lower clamping piece 3. The first connecting piece 7 and the second connecting piece 8 are half ring structures with the same shape, and the outer walls are provided with threads. The threads of the upper and lower coaxial first connecting pieces 7 and second connecting pieces 8 are combined to form a complete spiral thread. The first connecting piece 7 and the second connecting piece 8 are screwed with the locking piece 9, and the first connecting piece 7 and the second connecting piece 8 are fixedly connected through the locking piece 9. The locking piece 9 is a hollow cylindrical structure, and the inner wall is provided with a threaded groove, which can form a screw connection relationship with the threads outside the first connecting piece 7 and the second connecting piece 8, thereby completing the fixed connection of the first connecting piece 7 and the second connecting piece 8. The locking piece 9 is provided with a limiting pipe 12 at the end away from the heat shrink tube 1. The diameter of the limiting pipe 12 is smaller than that of the locking piece 9, and the limiting pipe 12 is a hollow tubular structure. Two flow guide pipes 10 are inserted into the two ends of the space formed after the upper clamping piece 2 and the lower clamping piece 3 are combined. The two flow guide pipes 10 are provided with an extension pipe 11 at the ends away from each other. The extension pipe 11 extends into the inner cavity of the limiting pipe 12. The connecting end faces of the flow guide pipe 10 and the extension pipe 11 are in contact with the inner walls of the connecting end faces of the locking piece 9 and the limiting pipe 12, forming a limiting relationship, which avoids the whole flow guide pipe 10 and the extension pipe 11 from separating from the internal space formed after the upper clamping piece 2 and the lower clamping piece 3 are combined. The mesh 13 is arranged at the end of the flow guide pipe 10 close to the heat shrink tube 1. The mesh 13 can ensure that the fluid passes through and can block larger impurities. The whole core holder 100 is made of metal copper material, which can ensure that it can normally transmit the nuclear magnetic resonance signal. The core in the embodiment is placed in the heat shrink tube 1.

[0027] REFERENCE Figure 1There are several core holders 100 connected in series via pipes. There are four pressure sensors 500, each connected to a pressure measurement point 4 in one of the core holders 100, for real-time measurement of pressure changes at each point.

[0028] The gas separator 700 and gas dosimeter 800 constitute a gas-liquid separator, which is connected to the core holder 100 to measure the gas and oil output at the outlet of the gas-liquid separator. A back pressure valve 600 is installed between the core holder 100 and the gas separator 700. The back pressure valve 600 is an existing device and is an important device in fluid systems for controlling pressure and preventing backflow of the medium. A hand pump 900 is connected to the back pressure valve 600 via a pipeline, and a pressure gauge 1000 is installed on the pipeline between the hand pump 900 and the back pressure valve 600.

[0029] A constant-pressure, constant-speed displacement pump 200 is connected to the core holder 100 and is controlled by a tracking annular pressure system 1100. The tracking annular pressure system 1100 is a pre-programmed system that can control the confining pressure according to different core displacement pressures, ensuring that the confining pressure is always greater than the displacement pressure. In this embodiment, specifically, it controls the confining pressure of the core holder 100 to be always greater than the displacement pressure by 5 MPa in real time.

[0030] The nuclear magnetic resonance core detection system consists of a nuclear magnetic resonance monitor installed outside the core holder 100 to monitor the gas-liquid dynamics within the core in real time. Specifically, the nuclear magnetic resonance signal is transmitted through the core holder 100, and the gas-liquid dynamics at different locations are obtained based on the changes in the nuclear magnetic resonance signal.

[0031] The core holder 100 is connected to another constant pressure and constant speed displacement pump 200, and a six-way valve 400 and several intermediate containers 300 are connected in sequence between the two. The intermediate containers 300 are respectively connected to different channels of the six-way valve 400. Another pressure sensor 500 is also installed on the six-way valve 400.

[0032] Furthermore, embodiments of the present invention also provide a method for quantitatively characterizing the flow path miscibility boundary of CO2, comprising the following steps: Step 1: Before the experiment begins, the experimental core is washed with oil and dried to constant weight, and the dry weight of the core is measured. Step 2: Use a vacuum pump to perform negative pressure water suction treatment on the saturated formation water in the experimental core, measure the wet weight of the core and measure the core pore volume; Step 3: Install the experimental equipment and preheat it using a constant temperature chamber; Step 4: Inject 10 MPa of N2 into the experimental system using a constant pressure and constant speed displacement pump 200 and check for air tightness. Observe for 1 hour. If the pressure drop is less than 0.2 MPa, the sealing performance is qualified. Step five: Put the experimental core into the core holder 100, use the tracking ring pressure system 1100 to control the constant pressure and constant speed displacement pump 200 to set the ring pressure, so that the ring pressure of each part of the core holder 100 is always greater than the displacement pressure by 5 MPa; Step six: Slowly inject formation water into the core holder 100 at a constant speed by the hand pump 900 until the outlet flow is stable; Step seven: Slowly inject crude oil into the core holder 100 at a constant speed by the hand pump 900, and the formation water is discharged. When the outlet does not discharge water, it means that the crude oil is fully saturated. The oil saturation is calculated according to the volume of the output water; Step eight: Inject the experimental gas sample at a speed of 0.05-0.2 mL / min by the hand pump 900, and monitor it by the back pressure valve 600. The difference between the injection pressure and the back pressure is not greater than 0.05 MPa. The output oil sample and the gas sample are collected and measured by the gas separation bottle 700 and the gas flow meter 800. The experiment is stopped after 1.2 PV of the experimental gas sample is injected. Step nine: In the above injection process, the pressure sensor 500 is used to measure the pressure of each point of the core, and the nuclear magnetic resonance detection system 1200 is used to detect the whole experimental system. The oil displacement amount of each position is determined by analyzing the nuclear magnetic signal at different positions of the core, so as to determine the miscible phase position of the crude oil under the condition of the purity CO2 and the crude oil physical property.

[0033] The above specific embodiments do not constitute a limitation on the protection scope of the present application. It should be understood by those skilled in the art that various modifications, combinations, sub-combinations and substitutions can be made according to design requirements and other factors. Any modification, equivalent replacement and improvement within the spirit and principles of the present application should be included in the protection scope of the present application.

Claims

1. A core holder characterized by, It comprises a heat shrink tube (1), an upper clamping piece (2), a lower clamping piece (3) and a pressure measuring point (4). The upper clamping piece (2) and the lower clamping piece (3) are symmetrically arranged relative to the heat shrink tube (1), and the upper clamping piece (2) and the lower clamping piece (3) can form a cavity after being combined, and the cavity shape can accommodate the heat shrink tube (1); the pressure measuring point (4) has four, respectively equidistantly installed on the upper clamping piece (2). Two first connecting pieces (7) are symmetrically installed at the two ends of the upper clamping piece (2); two second connecting pieces (8) are symmetrically installed at the two ends of the lower clamping piece (3).

2. The core holder of claim 1, wherein, A clamping block (5) is installed on the lower surface of the upper clamping piece (2); a clamping groove (6) is formed on the upper surface of the lower clamping piece (3), and the clamping block (5) is inserted into the clamping groove (6).

3. The core holder of claim 1, wherein, A locking piece (9) is screwed on the first connecting piece (7) and the second connecting piece (8), and the first connecting piece (7) and the second connecting piece (8) are fixedly connected through the locking piece (9).

4. The core holder of claim 2 or 3, wherein A limiting tube (12) is installed at one end of the locking piece (9) away from the heat shrink tube (1), and the diameter of the limiting tube (12) is smaller than that of the locking piece (9).

5. The core holder of claim 4, wherein, Two extension tubes (11) are installed at the ends of the two flow guide tubes (10) away from each other, and the extension tube (11) extends into the inner cavity of the limiting tube (12).

6. The core holder of claim 5, wherein, A mesh (13) is installed at one end of the flow guide tube (10) close to the heat shrink tube (1).

7. The core holder of claim 6, wherein, The core holder comprises the core holder of any one of claims 1-7, and further comprises a constant pressure constant speed displacement pump (200), an intermediate container (300), a six-way valve (400), a pressure sensor (500), a back pressure valve (600), a gas cylinder (700), a gas dosimeter (800), a hand pump (900) and a pressure gauge (1000).

8. An experimental device for quantitatively characterizing the CO2 miscibility transition, characterized in that, One constant pressure constant speed displacement pump (200) is connected with the core holder (100). The pressure sensor (500) has four, and the four pressure sensors (500) are connected with the four pressure measuring points (4); the gas cylinder (700) and the gas dosimeter (800) are connected with the core holder (100); the back pressure valve (600) is installed between the core holder (100) and the gas cylinder (700); the hand pump (900) is connected with the back pressure valve (600); the pressure gauge (1000) is installed between the hand pump (900) and the back pressure valve (600). The core holder (100) is connected with another constant pressure constant speed displacement pump (200), and the two are connected with the six-way valve (400) and a plurality of intermediate containers (300) in sequence. The method comprises the following steps:

9. A method for quantitatively characterizing the CO2 miscibility transition, the implementation of which relies on the experimental device for quantitatively characterizing the CO2 miscibility transition according to claim 8, characterized in that, Step one: before the experiment, the experimental core is first treated with oil and dried to constant weight, and the dry weight of the core is measured. ​ Step two: use vacuum pump to saturate the experimental core with formation water, measure the wet weight of the core and calculate the pore volume of the core; Step three: install the experimental equipment and preheat the experimental equipment using the thermostat; Step four: inject 10 MPa of N2 into the experimental system through the constant pressure and constant speed displacement pump (200) and perform a gas tightness check, observe for 1 h, and if the pressure drop is less than 0.2 MPa, the sealing is qualified; Step five: place the experimental core into the core holder (100), use the tracking ring pressure system (1100) to control the constant pressure and constant speed displacement pump (200) to set the confining pressure, so that the confining pressure of each part of the core holder (100) is always greater than the displacement pressure; Step six: slowly inject formation water into the core holder (100) at a constant speed through the hand pump (900) until the outlet flow is stable; Step seven: slowly inject crude oil into the core holder (100) at a constant speed through the hand pump (900), and the formation water is discharged, and when the outlet is not water, it means that the crude oil is fully saturated, and the oil saturation is calculated according to the volume of the produced water; Step eight: inject the experimental gas sample at a speed of 0.05-0.2 mL / min through the hand pump (900) and monitor through the back pressure valve (600), keep the difference between the injection pressure and the back pressure not more than 0.05 MPa, use the gas separation bottle (700) and the gas flow meter (800) to collect and measure the produced oil sample and the gas sample, stop the experiment after 1.2 PV of experimental gas sample is injected.

10. The method of claim 9, wherein the method further comprises: In step five, use the tracking ring pressure system (1100) to control the constant pressure and constant speed displacement pump (200) to set the confining pressure, so that the confining pressure of each part of the core holder (100) is always greater than the displacement pressure by 5 MPa.

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