Device and method for analyzing tortuosity of porous medium rock seepage channel

Abstract

The invention discloses a device and method for analyzing the tortuosity of a porous medium rock seepage channel, and belongs to the field of rock tortuosity. The tracking constant-pressure module is used for monitoring and controlling the pressure in the liquid tank; the automatic liquid supplementing module is used for monitoring the liquid level in the liquid tank and automatically supplementing liquid to the liquid tank; the image acquisition module is used for acquiring an image of a tortuous channel on the rock core casting body slice and performing calculation processing; the automatic liquid supplementing module comprises an intermediate container assembly and a valve assembly, the tracking constant-pressure module comprises a constant-pressure constant-speed displacement pump, and the constant-pressure constant-speed displacement pump is connected with the liquid tank through the intermediate container assembly and the valve assembly. By adopting the device and the method for analyzing the tortuosity of the porous medium rock seepage channel, the tortuosity of the porous medium seepage channel can be accurately analyzed, so that the problem of calculating permeability and flow efficiency parameters of a low-permeability reservoir is solved.

Description

Technical Field

[0001] The invention relates to the technical field of rock tortuosity, and in particular to a device and method for analyzing the tortuosity of a seepage channel of a porous medium rock. Background Art

[0002] During the oil extraction process, oil is mainly stored in the pores of underground rocks. As a typical porous medium, rock has a complex and diverse pore structure. Rocks of different lithologies, such as sandstone, limestone, shale and conglomerate, have significant differences in pore size, shape, connectivity and distribution. These pore structure characteristics directly affect the storage and seepage capacity of oil in rocks.

[0003] Tortuosity is a key parameter that describes the complexity of the seepage channel in porous media. It represents the ratio of the actual flow path length of the fluid in the porous medium to the straight-line distance between the two ends of the porous medium. In an ideal uniform medium, the tortuosity is close to 1, while in actual rock porous media, due to the complex pore structure, the tortuosity is often greater than 1.

[0004] The tortuosity of rocks of different lithologies can also result in differences in permeability, for example: Sandstone has relatively large pores and good connectivity, but its tortuosity and permeability vary due to the different arrangement and cementation of mineral particles. Generally speaking, sandstone with neatly arranged particles and moderate cementation has relatively low tortuosity. Low tortuosity is conducive to fluid flow, and correspondingly, such sandstone has high permeability, and oil can flow relatively easily through it. However, if the sandstone particles are mixed in size and unevenly cemented, the tortuosity will increase, the fluid flow path will become complicated, and the permeability will decrease, which will hinder the oil flow.

[0005] The pore structure of limestone is mainly composed of dissolved pores and cracks. Its tortuosity depends on the development degree of the caves and cracks and their interconnection. In limestone with well-developed and interconnected caves, the tortuosity may be relatively low, which helps the fluid to pass more smoothly, making the permeability at a high level, which is conducive to oil seepage. However, if the caves and cracks exist in isolation, the tortuosity will increase significantly, causing the fluid to bypass a long distance, the permeability will drop sharply, and the flow of oil in it will become very difficult.

[0006] Shale is a rock with extremely small pores and high anisotropy. Most of its internal pores are flat and poorly connected, which makes the shale very tortuous. High tortuosity leads to an extremely long actual flow path of fluid in shale, which greatly limits the ability of fluid to pass through, that is, extremely low permeability, which is one of the main technical difficulties faced by shale oil extraction.

[0007] Conglomerate is composed of gravel-sized rock fragments cemented together. Due to the varying sizes and shapes of the gravel components, its pore structure is highly heterogeneous. In well-sorted, well-cemented conglomerates, tortuosity may be moderate, and permeability can be relatively good due to the presence of relatively direct fluid flow paths between the larger gravel particles. However, in poorly sorted conglomerates with irregular gravel shapes and inconsistent cementation, tortuosity can be very high. The complex arrangement of gravels creates tortuous fluid paths, resulting in low permeability and making it difficult for oil to flow.

[0008] Moreover, tortuosity also affects other parameters of reservoir rocks, such as: Changes in tortuosity can affect the porosity of reservoir rocks. In rocks with high tortuosity, although pores may exist, the actual pore space that can be effectively occupied by oil may be reduced due to the complexity of the fluid flow path. For example, in shale, high tortuosity makes it difficult for many tiny pores to be completely filled with oil, resulting in a relatively low effective porosity. On the contrary, in sandstone with low tortuosity, if the particles are neatly arranged and well cemented, the porosity is not only higher in value, but also a larger proportion of pores that can be effectively utilized by oil.

[0009] Tortuosity also has a significant effect on capillary pressure. In rocks with high tortuosity, the capillary channels are more tortuous, which increases capillary pressure. For example, in shale, its high tortuosity leads to very high capillary pressure, which requires greater resistance to migrate oil in it. For lithologies such as sandstone and conglomerate, when the tortuosity increases, the capillary pressure will also increase accordingly, affecting the distribution and flow of oil in the pores.

[0010] There is a certain relationship between the tortuosity of rock and its elastic modulus. Generally speaking, high-tortuosity rocks (such as shale) tend to have more complex microstructures, which will show different mechanical responses from low-tortuosity rocks when subjected to external pressure. The elastic modulus of high-tortuosity rocks may change due to the complexity of pore structure and fluid flow path, which in turn affects the stress-strain state of the reservoir during the production process, and has an impact on the stability of the oil well and the choice of production process.

[0011] At present, the research methods of rock porous media tortuosity in the oil industry are limited. Traditional methods are often based on theoretical models or indirect measurement methods, which make it difficult to accurately measure the tortuosity of rocks of different lithologies under actual reservoir conditions. Since tortuosity is closely related to permeability, it is difficult to accurately evaluate the permeability of rocks if the tortuosity cannot be accurately measured. In reservoir development practice, the lack of accurate tortuosity and permeability data will cause great uncertainty for petroleum engineers when conducting reservoir numerical simulations, designing development plans, and formulating measures to improve oil recovery. For example, in the process of water injection development, if the tortuosity and permeability of the rock are not accurately understood, the flow direction and sweep efficiency of the injected water cannot be accurately predicted, which will affect the oil production efficiency and the final recovery rate.

[0012] In summary, the development of a device and method that can accurately analyze the tortuosity of seepage channels in porous media is of vital importance for in-depth understanding of the seepage characteristics of rocks of different lithologies, accurate evaluation of other rock parameters such as permeability, optimization of oil extraction plans, and improvement of oil recovery. Summary of the invention

[0013] The purpose of the present invention is to provide a device and method for analyzing the tortuosity of seepage channels in porous media rocks, which can accurately analyze the tortuosity of seepage channels in porous media to solve the problem of calculating permeability and flow efficiency parameters of low permeability reservoirs.

[0014] To achieve the above object, the present invention provides a device for analyzing the tortuosity of seepage channels in porous media rocks, comprising a liquid box on which a core casting thin slice is arranged; Tracking constant pressure module, used to monitor and control the pressure in the liquid tank; Automatic liquid filling module, used for monitoring the liquid level in the liquid tank and automatically filling the liquid tank; An image acquisition module is used to acquire images of tortuous channels on the core casting thin slice and perform computational processing; The automatic liquid replenishment module includes an intermediate container component and a valve component, and the tracking constant pressure module includes a constant pressure constant speed displacement pump, which is connected to the liquid tank through the intermediate container component and the valve component.

[0015] Preferably, the intermediate container assembly includes an intermediate container 1 and an intermediate container 2, wherein the intermediate container 1 is used to contain distilled water, and the intermediate container 2 is used to contain the thermochromic agent.

[0016] Preferably, the valve assembly includes a six-way valve and a three-way valve, and the constant pressure and constant speed displacement pump is connected to the intermediate container assembly and then connected to the six-way valve, the three-way valve and the liquid tank in sequence.

[0017] Preferably, the tracking constant pressure module also includes a pressure sensor and a computer 1. The pressure sensor is arranged at the six-way valve to monitor the pressure of the liquid tank. The computer 1 is connected to the pressure sensor and controls the pressure in the liquid tank.

[0018] Preferably, the image acquisition module includes a second computer and a microscope, the microscope is used to observe the self-absorption changes of the tortuous channels on the core casting thin slice, and the second computer is used to collect images observed by the microscope and perform computational processing.

[0019] Preferably, the automatic liquid replenishment module also includes an optical sensor, which is arranged on the liquid tank for monitoring the liquid level in the liquid tank. The optical sensor is connected to computer 2, and computer 2 controls a constant pressure and constant speed displacement pump to replenish liquid into the liquid tank.

[0020] Preferably, photolithography glass is provided in the core casting sheet.

[0021] The present invention also provides a method for analyzing the tortuosity of a seepage channel in a porous medium rock, using the above-mentioned device for analyzing the tortuosity of a seepage channel in a porous medium rock, comprising the following steps: Step 1: Prepare core casting slices: Before the experiment, representative samples were selected from the core, cleaned, oil washed, resin cured, ground to a suitable thickness, and bonded with photolithographic glass to prepare the core casting thin slices; Step 2: fix the prepared casting thin slice on the liquid tank, and turn on the microscope, computer 1, computer 2, constant pressure and constant speed displacement pump, six-way valve, and three-way valve, inject the distilled water and dye respectively contained in the intermediate container 1 and the intermediate container 2 into the liquid tank through the constant pressure and constant speed displacement pump, and check the air tightness of the device, observe the pressure change in the liquid tank through the pressure sensor, and maintain a constant pressure environment in the liquid tank; Step 3, closing the three-way valve, allowing the lower end of the core casting slice to absorb liquid through self-imbibition, observing the self-imbibition changes of the tortuous channels on the core casting slice through a microscope, and calculating the displacement and distance changes of the tortuous channels of the core casting slice absorbing water with the help of a computer 2; Step 4: Record the displacement and distance changes at different times, approximately fit a function, obtain the functional relationship between tortuosity, distance and displacement, introduce the time and pressure dependence of distance and displacement, and analyze the tortuosity of the core casting thin section.

[0022] Preferably, in step three, if the liquid volume in the liquid tank is insufficient, the light sensor on the liquid tank will provide feedback to computer two, and liquid will be injected into the liquid tank through a constant pressure and constant speed displacement pump.

[0023] Preferably, in step 4, the functional relationship among tortuosity, distance and displacement is: ; in, It indicates tortuosity, which describes the curvature of the curve; Represents the straight-line distance between the two ends of the porous medium; It represents the actual flow path length of the fluid in the porous medium; Introduction and The expression after the time and pressure dependence is: ; in, represents the initial flow path length; Indicates pressure The influence coefficient on the flow length; Indicates time The influence coefficient on the flow length; Substituting into the tortuosity formula: .

[0024] Therefore, the present invention adopts the above-mentioned device and method for analyzing the tortuosity of seepage channels in porous media rocks, which has the following beneficial effects: The present invention can monitor and control the pressure in the liquid tank through a tracking constant pressure module, can monitor the liquid level in the liquid tank and the automatic liquid replenishment of the liquid tank through an automatic liquid replenishment module, can observe the self-absorption change of the tortuous channel on the core casting thin slice through an image acquisition module, and calculate the displacement and distance change of the tortuous channel of the core casting thin slice absorbing water, introduce the time and pressure dependence of the distance and displacement, and accurately analyze the tortuosity of the core casting thin slice, which is of vital importance for in-depth understanding of the seepage characteristics of rocks of different lithologies, accurate evaluation of other rock parameters such as permeability, optimization of oil extraction plans, and improvement of oil recovery rate, and can solve the problem of calculating relevant parameters such as permeability and flow efficiency of low-permeability reservoirs.

[0025] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 Schematic diagram of the overall structure of the device according to an embodiment of the present invention.

[0027] Reference numerals 1. Constant pressure and constant speed displacement pump; 2. Intermediate container 1; 3. Intermediate container 2; 4. Six-way valve; 5. Pressure sensor; 6. Three-way valve; 7. Liquid tank; 8. Core casting slice; 9. Optical sensor; 10. Computer 1; 11. Microscope; 12. Computer 2; 13. Tracking constant pressure module; 14. Automatic liquid replenishment module; 15. Image acquisition module. DETAILED DESCRIPTION

[0028] In order to make the purpose, technical scheme and advantages disclosed in the embodiments of the present invention clearer, the embodiments of the present invention are further described in detail in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the embodiments of the present invention and are not intended to limit the embodiments of the present invention. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of this application. Examples of the embodiments are shown in the accompanying drawings, where the same or similar reference numerals throughout represent the same or similar elements or elements with the same or similar functions.

[0029] It should be noted that the terms "including" and "having" and any variations thereof are intended to cover non-exclusive inclusions. For example, a process, method, system, product or server that includes a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units that are not explicitly listed or inherent to these processes, methods, products or devices.

[0030] Like reference numerals and letters denote similar items in the following drawings, and thus, once an item is defined in one drawing, further definition and explanation thereof is not required in subsequent drawings.

[0031] In the description of the present invention, it should be noted that the terms "upper", "lower", "inside", "outside", etc. indicate directions or positional relationships based on the directions or positional relationships shown in the accompanying drawings, or are directions or positional relationships in which the product of the invention is usually placed when in use. They are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific direction, be constructed and operated in a specific direction, and therefore should not be understood as a limitation on the present invention.

[0032] In the description of the present invention, it is also necessary to explain that, unless otherwise clearly specified and limited, the terms "setting", "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 mechanical connection or an electrical connection; it can be a direct connection, or it can be an indirect connection through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0033] Example like Figure 1 As shown, a device for analyzing the tortuosity of seepage channels in porous media rocks according to the present invention comprises a liquid tank 7, a tracking constant pressure module 13, an automatic liquid replenishment module 14 and an image acquisition module 15. A core casting thin slice 8 with a built-in photolithography glass is provided on the liquid tank 7. The core casting thin slice 8 is cast with epoxy resin all around and a photolithography glass is provided on the side, so that the core seepage channel can be better observed. The tracking constant pressure module 13 is used to monitor and control the pressure in the liquid tank 7. The automatic liquid replenishment module 14 is used to monitor the liquid level in the liquid tank 7 and the automatic liquid replenishment of the liquid tank 7. The image acquisition module 15 is used to collect images of the tortuous channels on the core casting thin slice 8 and perform calculation processing.

[0034] The tracking constant pressure module 13 includes a constant pressure constant speed displacement pump 1, a pressure sensor 5 and a computer 10. The automatic liquid replenishment module 14 includes an intermediate container assembly, a valve assembly, and an optical sensor 9. The constant pressure constant speed displacement pump 1 is connected to the liquid tank 7 through the intermediate container assembly and the valve assembly. The intermediate container assembly includes an intermediate container 1 2 and an intermediate container 2 3. The intermediate container 1 2 is used to contain distilled water, and the intermediate container 2 3 is used to contain thermochromic agent. The valve assembly includes a six-way valve 4 and a three-way valve 6. After the constant pressure constant speed displacement pump 1 is connected to the intermediate container assembly, it is connected to the six-way valve 4, the three-way valve 6, and the liquid tank 7 in sequence.

[0035] When the pressure in the liquid tank 7 is too high or too low, it can be detected by the pressure sensor 5 and the signal is transmitted to the computer 10. The computer 10 changes the pressure in the liquid tank 7 by controlling the flow rate of the constant pressure and constant speed displacement pump 1.

[0036] The intermediate container assembly is located outside the liquid tank 7 and is controlled by the constant pressure constant speed displacement pump 1. The optical sensor 9 is installed on the top of the liquid tank 7 and can monitor the liquid level in real time. When the liquid level is insufficient, the optical sensor 9 transmits a signal to the computer, and the computer system controls the constant pressure constant speed displacement pump 1 to inject dyeing liquid into the liquid tank 7 to maintain the normal operation of the system.

[0037] The image acquisition module 15 includes a second computer 12 and a microscope 11, and the microscope 11 is arranged in front of the photolithography glass. The microscope 11 is connected to the second computer 12, and the complex graphics obtained by the microscope 11 are processed by existing graphics processing software.

[0038] A method for analyzing the tortuosity of a seepage channel in a porous medium rock according to the present invention comprises the following steps: Step 1: Prepare core casting slice 8: Before the experiment begins, representative samples are selected from the cores, which are usually cleaned and oil-washed to remove impurities and dirt on the surface of the cores and residual oil inside. They are then resin-cured, ground to a suitable thickness and bonded to photolithographic glass.

[0039] Step 2: Fix the prepared casting thin slice on the liquid box 7, and turn on the microscope 11, computer 1 10, computer 2 12, constant pressure and constant speed displacement pump 1 and other equipment.

[0040] The distilled water and dye respectively contained in the intermediate container are injected into the liquid tank 7 through the constant pressure and constant speed displacement pump 1 and the air tightness of the device is checked. The pressure change in the liquid tank 7 is observed through the pressure sensor 5 to maintain a constant pressure environment in the liquid tank 7.

[0041] Step 3: Close the three-way valve 6. At this time, the lower end of the core casting slice 8 begins to absorb water due to self-priming. If the liquid volume in the liquid tank 7 is insufficient, the optical sensor 9 above the liquid tank 7 will feed back to the computer 2 12, and water will be injected into the liquid tank 7 through the constant pressure and constant speed displacement pump 1, thereby realizing the effect of automatic liquid replenishment.

[0042] Step 4: Observe the self-absorption change of the tortuous channel on the core casting thin slice 8 through the microscope 11, and then calculate the displacement and distance change of the tortuous channel of the core casting thin slice 8 absorbing water with the help of the computer image processing system, which are recorded as and .

[0043] Record different times The displacement and distance changes under the condition are approximately fitted with a function to obtain the tortuosity ,distance and displacement The functional relationship is: ; in, : Tortuosity, describing the curvature of the curve; : represents the straight-line distance between the two ends of the porous medium, cm; : represents the actual flow path length of the fluid in the porous medium, cm; when When =1, it means that the flow path of the fluid is equal to the straight-line distance, indicating that the medium is uniform.

[0044] when When >1, it means that the flow path of the fluid is longer than the straight-line distance, indicating that the pore structure of the medium is more complex and the flow path is curved or circuitous.

[0045] To take time and pressure into account, and The time and pressure dependence of , forms a more complex expression.

[0046] ; in, : initial flow path length, cm; : The influence coefficient of pressure on flow length; : The influence coefficient of time on flow length; The flow length Substituting into the tortuosity formula: .

[0047] Therefore, the present invention adopts the above-mentioned device and method for analyzing the tortuosity of seepage channels in porous media rocks, which can accurately analyze the tortuosity of seepage channels in porous media to solve the problem of calculating permeability and flow efficiency parameters of low permeability reservoirs.

[0048] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that they can still modify or replace the technical solution of the present invention with equivalents, and these modifications or equivalent replacements cannot cause the modified technical solution to deviate from the spirit and scope of the technical solution of the present invention.

Claims

1. A device for analyzing the tortuosity of seepage channels in porous rock media, characterized in that: It includes a liquid box, on which a core casting sheet is arranged; Tracking constant pressure module, used to monitor and control the pressure in the liquid tank; Automatic liquid filling module, used for monitoring the liquid level in the liquid tank and automatically filling the liquid tank; An image acquisition module is used to acquire images of tortuous channels on the core casting thin slice and perform computational processing; The automatic liquid replenishment module includes an intermediate container component and a valve component, and the tracking constant pressure module includes a constant pressure constant speed displacement pump, and the constant pressure constant speed displacement pump is connected to the liquid tank through the intermediate container component and the valve component; The tracking constant pressure module also includes a pressure sensor and a computer 1, the pressure sensor is arranged at the six-way valve to monitor the pressure of the liquid tank, and the computer 1 is connected to the pressure sensor and controls the pressure in the liquid tank; The image acquisition module includes a second computer and a microscope, wherein the microscope is used to observe the self-absorption changes of the tortuous channels on the core casting thin slice, and the second computer is used to collect images observed by the microscope and perform calculation processing; The automatic liquid replenishment module also includes an optical sensor, which is arranged on the liquid tank to monitor the liquid level in the liquid tank. The optical sensor is connected to the second computer, and the second computer controls the constant pressure and constant speed displacement pump to replenish the liquid in the liquid tank. Photolithography glass is set inside the core casting slice.

2. The device for analyzing the tortuosity of seepage channels in porous media rocks according to claim 1, characterized in that: The intermediate container assembly comprises an intermediate container 1 and an intermediate container 2. The intermediate container 1 is used for containing distilled water, and the intermediate container 2 is used for containing thermal colorant.

3. The device for analyzing the tortuosity of seepage channels in porous media rocks according to claim 2, characterized in that: The valve assembly comprises a six-way valve and a three-way valve. The constant pressure and constant speed displacement pump is connected to the intermediate container assembly and then connected to the six-way valve, the three-way valve and the liquid tank in sequence.

4. A method for analyzing the tortuosity of seepage channels in porous media rocks, characterized in that: The device for analyzing the tortuosity of seepage channels in porous media rocks according to any one of claims 1 to 3 comprises the following steps: Step 1: Prepare core casting slices: Before the experiment, representative samples were selected from the core, cleaned, oil washed, resin cured, ground to a suitable thickness, and bonded with photolithographic glass to prepare the core casting thin slices; Step 2: fix the prepared casting thin slice on the liquid tank, and turn on the microscope, computer 1, computer 2, constant pressure and constant speed displacement pump, six-way valve, and three-way valve, inject the distilled water and dye respectively contained in the intermediate container 1 and the intermediate container 2 into the liquid tank through the constant pressure and constant speed displacement pump, and check the air tightness of the device, observe the pressure change in the liquid tank through the pressure sensor, and maintain a constant pressure environment in the liquid tank; Step 3, closing the three-way valve, allowing the lower end of the core casting slice to absorb liquid through self-imbibition, observing the self-imbibition changes of the tortuous channels on the core casting slice through a microscope, and calculating the displacement and distance changes of the tortuous channels of the core casting slice absorbing water with the help of a computer 2; Step 4: Record the displacement and distance changes at different times, approximately fit a function, obtain the functional relationship between tortuosity, distance and displacement, introduce the time and pressure dependence of distance and displacement, and analyze the tortuosity of the core casting thin section.

5. The method for analyzing the tortuosity of seepage channels in porous media rocks according to claim 4, characterized in that: In step three, if the liquid level in the liquid tank is insufficient, the light sensor on the liquid tank will provide feedback to computer two, and the liquid tank will be filled with liquid through a constant pressure and constant speed displacement pump.

6. The method for analyzing the tortuosity of seepage channels in porous media rocks according to claim 5, characterized in that: In step 4, the functional relationship between tortuosity, distance and displacement is: ； in, It indicates tortuosity, which describes the curvature of the curve; Represents the straight-line distance between the two ends of the porous medium; It represents the actual flow path length of the fluid in the porous medium; Introduction and The expression after the time and pressure dependence is: ； in, represents the initial flow path length; Indicates pressure The influence coefficient on the flow length; Indicates time The influence coefficient on the flow length; Substituting into the tortuosity formula: 。

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