Shale core fluid direct saturation experiment device and method
By designing a direct saturation experimental device for shale core fluid and using temperature and pressure control, the problem of low saturation quality of shale core fluid is solved, and a single-phase and uniform direct saturation of the fluid in the core is achieved, providing technical support for shale oil and gas development.
Patent Information
- Application Number
- CN202311808914.6
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2023-12-26
- Publication Date
- 2025-06-27
AI Technical Summary
The existing core fluid saturation methods are not suitable for dense cores such as shale, resulting in low fluid saturation quality and the single-phase and uniform saturation of the fluid in the core cannot be achieved, affecting the experimental results.
A shale core fluid direct saturation experimental device is designed, including a core holder, a molecular vacuum pump, an venting collection container, an intermediate container, a first pressure metering pump and a temperature control unit. By controlling the ambient temperature and pressure, a single-phase and uniform direct saturation of the core fluid is achieved.
It achieves efficient, high-quality single-phase, uniform direct saturation of shale core fluid, providing a reliable foundation for subsequent experiments, supporting the study of phase state characteristics and flow laws of fluids in the core, and promoting the effective development of shale oil and gas.
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Figure CN120213767A_ABST
Abstract
Description
Technical Field
[0001] The present invention relates to the technical field of physical experiments of oil and gas reservoirs, and particularly, to a direct fluid saturation experimental device for shale cores and a direct fluid saturation experimental method for shale cores. Background Art
[0002] In the field of oil and gas development, the saturation of fluids in cores is the basis for conducting core fluid flow experiments (such as permeability tests, relative permeability tests, etc.) and fluid phase experiments in cores. The quality of fluid saturation in the core will have an important impact on the experimental results. Therefore, achieving uniform and sufficient saturation of fluids in the core is of great significance for understanding the fluid phase characteristics and flow laws in the core, and is one of the key technologies for laboratory experiments.
[0003] The original fluids in oil and gas reservoir formations contain multiple hydrocarbon components, and oil and gas two-phase separation will occur under ground conditions. Once two-phase separation occurs in the core, due to the different flow capacities of the oil and gas two phases, the two-phase migration leads to uneven distribution of oil and gas, greatly reducing the saturation quality, and even phenomena such as "liquid lock" and "gas lock" occur, resulting in fluid saturation failure. Therefore, maintaining the single-phase state of the target fluid during the core fluid saturation process is a key link, which is conducive to achieving uniform and sufficient saturation of fluids in the core.
[0004] For conventional cores, in order to ensure that the target fluid is always in a single-phase state during the saturation process, generally, a pre-filled gas or liquid is used to pre-fill and saturate and then maintain a high-pressure state. On this basis, the target fluid (oil or gas) is then displaced out of the core in a single-phase form under high pressure, so as to achieve single-phase saturation of the target fluid. Although this method can complete the core fluid saturation process, it still has the following deficiencies:
[0005] (1) First, the pore size in the matrix of shale cores reaches the nanometer level. Due to the compactness of the cores, using the conventional core fluid saturation method results in a very slow process of multiple fluid injections and displacements, and the experiment is time-consuming and laborious;
[0006] (2) Second, during the saturation process of shale cores, the pressure gradient is large, and higher requirements are placed on maintaining the overall pressure of the core. In actual experiments, oil and gas two-phase separation is likely to occur under local low pressure in the core;
[0007] (3) Third, the effect of using pre-set fluids to displace and saturate shale cores is not ideal. Due to small pores and poor connectivity, it is impossible to completely displace the pre-set fluids, and it is impossible to achieve single-phase and uniform saturation of the target fluid, affecting the final experimental results.
[0008] In summary, the current core fluid saturation method is only applicable to conventional cores (including medium-high permeability, low permeability, etc.). For tight cores such as shale, a new experimental device and method for directly saturating core fluids need to be established to achieve efficient and high-quality saturation of shale core fluids, providing technical support for studying the fluid phase characteristics and flow laws in the core and realizing the effective development of shale oil and gas. Summary of the Invention
[0009] Aiming at the technical problem that the core fluid saturation method in the prior art is only applicable to conventional cores and not suitable for tight cores such as shale, the present invention provides an experimental device and method for directly saturating shale core fluids. Using this device can achieve single-phase and uniform direct saturation of shale core fluids, establishing an experimental basis for subsequent shale core fluid flow experiments and fluid phase experiments in the core, and providing technical support for studying the fluid phase characteristics and flow laws in the core and realizing the effective development of shale oil and gas.
[0010] To achieve the above object, on the one hand, the present invention provides an experimental device for directly saturating shale core fluids, which includes: a core holder, a molecular vacuum pump, a vent collection container, an intermediate container, a first pressure metering pump, and a temperature control unit; the core holder is used to place the core, the outlet of the core holder is connected to the molecular vacuum pump, and the molecular vacuum pump is used to evacuate the core; the inlet of the core holder is connected to the outlet of the intermediate container, and the intermediate container is used to place the target fluid; the first pressure metering pump is connected to the inlet of the intermediate container and is used to inject the target fluid into the core; the temperature control unit is used to control the ambient temperature of the target fluid during the core fluid saturation process; the outlet of the core holder is also connected to the vent collection container, and the vent collection container is used to collect the target fluid discharged from the core.
[0011] In an exemplary embodiment of the present invention, the temperature control unit may be a constant temperature box, and the core holder and the intermediate container are placed in the constant temperature box.
[0012] In an exemplary embodiment of the present invention, the experimental device may further include: a second pressure metering pump connected to the core holder, and the second pressure metering pump is used to adjust the confining pressure of the core during the core fluid saturation process.
[0013] On the other hand, the present invention provides a method for directly saturating shale core fluid, which is realized by the above experimental device and includes the following steps: setting the ambient temperature of the core holder and the intermediate container to the saturation process control temperature through the temperature control unit, where the saturation process control temperature is greater than the critical condensation temperature of the target fluid; evacuating the core through a molecular vacuum pump until the pressure of the molecular vacuum pump remains unchanged; filling the intermediate container with the target fluid, and injecting the target fluid into the core at a predetermined flow rate through the first pressure metering pump; when the pressure of the first pressure metering pump reaches the set saturation experiment pressure and the volume value no longer changes, the core fluid saturation process is completed.
[0014] In an exemplary embodiment of the present invention, the saturation process control temperature can be set to the sum of the critical condensation temperature of the target fluid and a temperature constant, and the temperature constant is 20 - 30°C.
[0015] In an exemplary embodiment of the present invention, the critical condensation temperature of the target fluid can be determined through the PT phase diagram of the target fluid.
[0016] In an exemplary embodiment of the present invention, the PT phase diagram of the target fluid can be determined through fluid phase equilibrium calculation.
[0017] In an exemplary embodiment of the present invention, during the core fluid saturation process, the pressure of the second pressure metering pump can be adjusted in real time so that the pressure of the second pressure metering pump is always higher than the pressure of the first pressure metering pump.
[0018] In an exemplary embodiment of the present invention, the experimental method may further include: before injecting the target fluid into the core, recording the first volume value V1 of the first pressure metering pump; after completing the core fluid saturation process, recording the second volume value V2 of the first pressure metering pump; determining the pore volume of the core as the difference between the second volume value V2 and the first volume value V1.
[0019] In an exemplary embodiment of the present invention, the experimental method may further include: after completing the core fluid saturation process, reducing the ambient temperature of the core holder and the intermediate container from the saturation process control temperature to the core flow experiment temperature at a predetermined cooling rate through the temperature control unit, and at the same time canceling the flow rate limit of the target fluid, and maintaining the fluid in the core at the saturation experiment pressure through the first pressure metering pump to ensure that the fluid in the core is always in a single-phase state during the cooling process.
[0020] Through the technical solution provided by the present invention, the present invention has at least the following technical effects:
[0021] The shale core fluid direct saturation experimental device and method provided by the present invention can efficiently and qualitatively achieve single-phase and uniform direct saturation of shale core fluid by controlling the ambient temperature of the fluid during the fluid saturation process, can establish an experimental basis for subsequent shale core fluid flow experiments and in-core fluid phase experiments, and can provide technical support for studying the in-core fluid phase characteristics and flow laws and realizing the effective development of shale oil and gas.
[0022] Other features and advantages of the present invention will be described in detail in the subsequent specific implementation section. Brief Description of the Drawings
[0023] The drawings are used to provide a further understanding of the embodiments of the present invention, and constitute a part of the specification. Together with the following specific implementation, they are used to explain the embodiments of the present invention, but do not constitute a limitation to the embodiments of the present invention. In the drawings:
[0024] Figure 1 It is a typical multi-component fluid PT phase diagram provided by an embodiment of the present invention;
[0025] Figure 2 It is a schematic structural diagram of a shale core fluid direct saturation experimental device provided by an embodiment of the present invention;
[0026] Figure 3 It is a C1-C2-nC7 system fluid PT phase diagram provided by an embodiment of the present invention.
[0027] Description of the Reference Numerals in the Drawings
[0028] 1 - High-pressure metering pump A, 2 - Constant temperature box, 3 - High-pressure metering pump B, 4 - Intermediate container, 5 - Target fluid, 6 - Core, 7 - Core holder, 8 - Three-way valve, 9 - Venting and collecting container, 10 - Molecular vacuum pump. Specific Implementation
[0029] The following will describe in detail the specific implementation of the embodiments of the present invention with reference to the drawings. It should be understood that the specific implementation described herein is only used to illustrate and explain the embodiments of the present invention, and is not used to limit the embodiments of the present invention.
[0030] It should be noted that, without conflict, the embodiments in the present invention and the features in the embodiments can be combined with each other.
[0031] In the present invention, "first", "second", etc. are only for convenient description and easy distinction, and cannot be understood as indicating or implying relative importance.
[0032] In the description of the present invention, it should also be noted that, unless otherwise clearly defined and limited, terms such as "installation" and "connection" 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; it can be a wired connection or a wireless connection. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.
[0033] The present invention will be described in detail below with reference to the accompanying drawings and in conjunction with embodiments.
[0034] An embodiment of the present invention provides a shale core fluid direct saturation experimental device, which includes a core holder, a molecular vacuum pump, a venting and collecting container, an intermediate container, a first pressure metering pump, and a temperature control unit.
[0035] Specifically, the core holder is used to place the core. The outlet of the core holder is connected to the molecular vacuum pump, and the molecular vacuum pump is used to evacuate the core; the outlet of the core holder is also connected to the venting and collecting container, and the venting and collecting container is used to collect the target fluid discharged from the core. The inlet of the core holder is connected to the outlet of the intermediate container, and the intermediate container is used to place the target fluid. The first pressure metering pump is connected to the inlet of the intermediate container and is used to inject the target fluid into the core. The temperature control unit is used to control the ambient temperature of the target fluid during the core fluid saturation process.
[0036] Furthermore, in a possible implementation manner, the temperature control unit can be set as a constant temperature box. The core holder and the intermediate container are placed in the constant temperature box, and by setting the temperature inside the constant temperature box, the ambient temperature of the target fluid during the core fluid saturation process can be controlled, so that the target fluid remains in a single-phase state under any pressure, thereby realizing the single-phase and uniform direct saturation of the fluid in the shale core.
[0037] Furthermore, in a possible implementation manner, the experimental device further includes a second pressure metering pump, and the second pressure metering pump is connected to the core holder and is used to adjust the confining pressure of the core during the core fluid saturation process.
[0038] In the real underground reservoir environment, underground rocks are often subjected to confining pressure from the surrounding strata, which will affect the seepage properties of fluids and the physical properties of rocks. By setting the second pressure metering pump to control the confining pressure of the core in this application, the underground storage conditions can be accurately simulated, which will be beneficial to accurately measuring the liquid-phase permeability and fluid saturation in the subsequent core fluid saturation experiment, as well as studying the mechanical properties of rocks.
[0039] An embodiment of the present invention also provides a direct saturation experiment method for shale core fluid, which is realized by the above-mentioned direct saturation device for shale core fluid and may include the following steps:
[0040] Step S101: Set up the direct saturation device for shale core fluid and place the shale core in the core holder.
[0041] Step S102: Set the ambient temperature of the core holder and the intermediate container to the saturation process control temperature through the temperature control unit.
[0042] Here, it should be noted that the basic design principle of this application is: the ambient temperature during the core fluid saturation process is controlled to the saturation process control temperature through the temperature control unit. When the saturation process control temperature is greater than the critical condensate temperature of the target fluid, regardless of how the pressure of the target fluid changes, the target fluid always remains in a single-phase state. In this way, the single-phase and uniform direct saturation of the fluid in the shale core can be achieved.
[0043] Step S103: Vacuum the core through a molecular vacuum pump until the pressure of the molecular vacuum pump remains unchanged.
[0044] Step S104: Fill the intermediate container with the target fluid and inject the target fluid into the core at a predetermined flow rate through the first pressure metering pump.
[0045] Here, it should be noted that due to the tightness of the core, if the injection speed of the target fluid is too fast, the fluid may directly pass through the large pores and fail to penetrate into the micro-pores of the rock, which may cause the fluid in the core to be not fully saturated. In addition, if the injection speed of the target fluid is too large, it may also cause high-pressure impact inside the core, the expansion of micro-cracks on the rock surface, and even the rupture of the core. Therefore, it is necessary to control the target fluid to be injected into the core at a preset flow rate. For example, the flow rate of the target fluid can be set to no more than 0.1 ml / min through the first pressure metering pump.
[0046] Step S105: When the pressure of the first pressure metering pump reaches the set saturation experiment pressure and the volume value no longer changes, complete the core fluid saturation process.
[0047] Further, in a possible implementation manner, the saturation process control temperature is set to the sum of the critical condensate temperature of the target fluid and a temperature constant.
[0048] Further, in a possible implementation manner, before conducting the direct saturation experiment of shale core fluid, based on determining the composition of the target fluid, the PT phase diagram of the target fluid can be determined through fluid phase equilibrium calculation, and then the critical condensate temperature of the target fluid can be determined through the PT phase diagram of the target fluid.
[0049] For example, Figure 1 is a typical PT phase diagram of a multi-component fluid, Figure 1 where P represents pressure in MPa; T represents temperature in °C; T m represents the critical condensate temperature in °C; T s is the environmental temperature required to be controlled during the core fluid saturation process set by the present invention, in °C.
[0050] Such as Figure 1 shown, the critical condensate temperature T m can be further determined by determining the envelope of the fluid PT phase diagram. When the environmental temperature is higher than the critical condensate temperature, the target fluid is always in a single-phase state regardless of the pressure of the system.
[0051] The current theory of fluid phase states in porous media generally believes that the envelope of the fluid in micro-nano pores shrinks, that is, T m in the core decreases. However, considering the errors in experimental temperature control equipment, phase equilibrium calculation, etc., in order to ensure the single-phase state of the target fluid, a temperature constant can be added on the basis of the critical condensate temperature, that is, the saturation process control temperature is set to: T s = T m + ΔT. Here, in order to eliminate the temperature error generated by the experimental temperature control equipment and phase equilibrium calculation, ΔT can be determined to be 20 - 30 °C.
[0052] Furthermore, in a possible implementation, during the core fluid saturation process, the pressure of the second pressure metering pump can be adjusted in real time so that the pressure of the second pressure metering pump is always higher than the pressure of the first pressure metering pump.
[0053] For example, in order to ensure the core confining pressure, the pressure of the second pressure metering pump can be adjusted in real time during the core fluid saturation process so that it is always about 1 MPa higher than the actual pressure of the first pressure metering pump.
[0054] Furthermore, in a possible implementation, the experimental method further includes: before injecting the target fluid into the core, recording the first volume value V1 of the first pressure metering pump; after completing the core fluid saturation process, recording the second volume value V2 of the first pressure metering pump; and determining the pore volume of the core as the difference between the second volume value V2 and the first volume value V1.
[0055] Further, in a possible implementation manner, the experimental method further includes step S106: After completing the core fluid saturation process, the environmental temperature of the core holder and the intermediate container is reduced from the saturation process control temperature to the core flow experiment temperature at a predetermined cooling rate by the temperature control unit. At the same time, the flow rate limit of the target fluid is cancelled, and the first pressure metering pump is used to keep the fluid in the core at the saturation experiment pressure to ensure that the fluid in the core is always in a single-phase state during the cooling process.
[0056] To better understand the above exemplary embodiments of the present invention, the following further illustrates them with specific examples and drawings.
[0057] The structural schematic diagram of the shale core fluid direct saturation experimental device involved in the present invention is as Figure 1 shown. It can be seen that the shale core fluid direct saturation experimental device is composed of a high-pressure metering pump A1, a constant temperature box 2, a high-pressure metering pump B 3, an intermediate container 4, a core holder 7, a three-way valve 8, a vent collection container 9, and a molecular vacuum pump 10. Among them, the core 6 is placed in the core holder 7, the target fluid 5 is stored in the intermediate container 4, and the core holder 7 and the intermediate container 4 are placed in the constant temperature box 2. The outlet of the core holder 7 is connected to the molecular vacuum pump 10 through the connection port d of the three-way valve 8, the outlet of the core holder 7 is connected to the vent collection container 9 through the connection port e of the three-way valve 8, the inlet of the core holder 7 is connected to the intermediate container 4 through the valve c, the intermediate container 4 is connected to the high-pressure metering pump A1 through the valve a, and the high-pressure metering pump B 3 is connected to the core holder 7 through the valve b.
[0058] The specific process of the shale core fluid direct saturation experimental method involved in the present invention is as follows:
[0059] (1) According to the composition of the target fluid, determine the fluid PT phase diagram through fluid phase equilibrium calculation, and then determine the critical condensation temperature T m and determine the saturation process control temperature T s .
[0060] For example, the target fluid contains 3 components, namely methane (C1), ethane (C2), and n-heptane (nC7), and the molar percentages of each component are 50 mol%, 40 mol%, and 10 mol% respectively. Thus, according to the fluid phase equilibrium simulation calculation, the PT phase diagram of the target fluid is as Figure 3 shown.
[0061] According to the phase diagram, the critical condensation temperature T m of the target fluid is 136.23 °C. From this, the saturation process control temperature is calculated to be T s = T m + 20 = 156.23 °C.
[0062] (2) According to Figure 2 Set up the experimental device, and set the saturation process control temperature of the constant temperature box to 156.23 °C.
[0063] (3) Close valves a, b, c and the connection port e of the three-way valve, open the connection port d of the three-way valve, and evacuate the core through a molecular vacuum pump until the pressure of the vacuum pump remains unchanged, that is, the evacuation is completed, and then close the connection port d of the through valve and the molecular vacuum pump.
[0064] (4) Set the high-pressure metering pump A to a constant saturation test pressure (such as 20 MPa), open valve a, and after the pressure of the high-pressure metering pump A is stable, record the volume number of the high-pressure metering pump A as V1 = 30.226 ml, and set the maximum flow rate of the high-pressure metering pump A (such as 0.1 ml / min).
[0065] (5) Open valves b and c simultaneously to inject the target fluid into the core. Due to the restricted injection speed, the pressure inside the core will rise slowly; to ensure the confining pressure of the core, the pressure of the high-pressure metering pump B is adjusted in real time during the saturation process so that it is always about 1 MPa higher than the actual pressure of the high-pressure metering pump A.
[0066] (6) When the pressure of the high-pressure metering pump A reaches the set saturation test pressure and the volume value remains unchanged for a long time (the value does not change for 48 hours), record the current volume number as V2 = 31.936 ml to complete the core fluid saturation process. At this time, the pore volume of the core can be calculated as V2 - V1 = 1.71 ml.
[0067] (7) Adjust the set temperature of the constant temperature system to the subsequent core flow test temperature: 100 °C, set the cooling rate to 1 °C / hour, and always keep the high-pressure metering pump 1A at a constant pressure of 20 MPa during the cooling process. At the same time, cancel the restriction of its maximum flow rate to ensure that the fluid inside the core is always in a single-phase state during the cooling process. When the system temperature reaches 100 °C and the pressure and volume readings of the high-pressure metering pump 1A remain unchanged, the system temperature adjustment is completed. On this basis, subsequent core flow experiments can be carried out.
[0068] The preferred embodiments of the present invention have been described in detail above with reference to the accompanying drawings. However, the present invention is not limited to the specific details in the above embodiments. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solutions of the present invention, and these simple modifications all fall within the protection scope of the present invention.
[0069] In addition, it should be noted that, in the above specific embodiments, the various specific technical features described can be combined in any suitable manner without conflict. To avoid unnecessary repetition, the present invention will not separately describe various possible combination methods.
[0070] In addition, any combination can be made among various different embodiments of the present invention, as long as it does not violate the idea of the present invention, and it should equally be regarded as the content disclosed by the present invention.
Claims
1. A direct saturation experimental device for shale core fluid, characterized in that, The experimental device includes: a core holder, a molecular vacuum pump, a vent collection container, an intermediate container, a first pressure metering pump, and a temperature control unit; The core holder is used to place the core. The outlet of the core holder is connected to the molecular vacuum pump, and the molecular vacuum pump is used to evacuate the core; The inlet of the core holder is connected to the outlet of the intermediate container, and the intermediate container is used to place the target fluid; The first pressure metering pump is connected to the inlet of the intermediate container and is used to inject the target fluid into the core; The temperature control unit is used to control the ambient temperature during the core fluid saturation process; The outlet of the core holder is also connected to the vent collection container, and the vent collection container is used to collect the target fluid discharged from the core.
2. The shale core fluid direct saturation experimental device according to claim 1, characterized in that The temperature control unit is an incubator, and the core holder and the intermediate container are placed in the incubator.
3. The shale core fluid direct saturation experimental device according to claim 1, wherein The experimental device further includes: a second pressure metering pump connected to the core holder, and the second pressure metering pump is used to adjust the confining pressure of the core during the core fluid saturation process.
4. A direct saturation experimental method for shale core fluid, characterized in that, The experimental method is implemented by the experimental device according to any one of claims 1 to 3, and includes: Setting the ambient temperature of the core holder and the intermediate container to the saturation process control temperature through the temperature control unit, and the saturation process control temperature is greater than the critical condensate temperature of the target fluid; Evacuating the core through the molecular vacuum pump until the pressure of the molecular vacuum pump remains unchanged; Filling the intermediate container with the target fluid, and injecting the target fluid into the core at a predetermined flow rate through the first pressure metering pump; When the pressure of the first pressure metering pump reaches the set saturation experiment pressure and the volume value no longer changes, the core fluid saturation process is completed.
5. The direct saturation experiment method for shale core fluid according to claim 4, wherein The saturation process control temperature is set to the sum of the critical condensate temperature of the target fluid and a temperature constant, and the temperature constant is 20 - 30 °C.
6. The direct saturation experimental method for shale core fluid according to claim 4, wherein Determining the critical condensate temperature of the target fluid through the PT phase diagram of the target fluid.
7. The direct saturation experiment method for shale core fluid according to claim 6, wherein Determining the PT phase diagram of the target fluid through fluid phase equilibrium calculation.
8. The direct saturation experiment method for shale core fluid according to claim 4, wherein During the core fluid saturation process, adjusting the pressure of the second pressure metering pump in real time so that the pressure of the second pressure metering pump is always higher than the pressure of the first pressure metering pump.
9. The direct saturation experimental method for shale core fluid according to claim 4, wherein, The experimental method further includes: Before injecting the target fluid into the core, recording the first volume value V1 of the first pressure metering pump; After completing the core fluid saturation process, recording the second volume value V2 of the first pressure metering pump; Determining the pore volume of the core as the difference between the second volume value V2 and the first volume value V1.
10. The shale core fluid direct saturation experimental method according to claim 4, characterized in that The experimental method further includes: After completing the core fluid saturation process, reducing the ambient temperature of the core holder and the intermediate container from the saturation process control temperature to the core flow experiment temperature at a predetermined cooling rate through the temperature control unit, and at the same time canceling the flow rate limit of the target fluid, and keeping the fluid in the core at the saturation experiment pressure through the first pressure metering pump to ensure that the fluid in the core is always in a single-phase state during the cooling process.