A microfluidic chip-based gas-water-rock reaction and particle dissolution-migration in-situ visualization and quantitative determination method and device

Abstract

The present application belongs to the technical field of unconventional oil and gas development, and particularly relates to a gas-water-rock reaction and micro-particle dissolution-migration in-situ visualized quantitative determination method and device based on a micro-fluidic chip. The quantitative determination method designs a chip model containing a real core by simultaneously considering factors such as strong heterogeneity of a dense conglomerate reservoir, strong difference of pore throat structure and the like; then records the gas-water-rock reaction and micro-particle dissolution-migration process through an optical camera; finally, combines image processing software and a mathematical model to analyze the contribution degree of different minerals to the gas-water-rock reaction and to distinguish different dissolution modes of conglomerate. The method can quantitatively determine the gas-water-rock three-phase reaction, micro-particle dissolution and secondary migration process in a conglomerate reservoir under the conditions of reservoir temperature, pressure and fluid chemistry.

Description

Technical Field

[0001] This invention belongs to the technical field of unconventional oil and gas development, specifically relating to a method and device for in-situ visualization and quantitative determination of gas-water-rock reaction and particle dissolution-migration based on microfluidic chips. Background Technology

[0002] Tight conglomerate oil reservoirs typically have low porosity ( Tight conglomerate reservoirs are characterized by low permeability (k < 1mD), small pore-throat size (submicron to millimeter scale), complex mineral composition, strong heterogeneity, and complex oil-water relationships. Their production is mainly influenced by reservoir properties, crude oil quality, and fracturing techniques. Currently, horizontal wells combined with volumetric fracturing are commonly used for the development of tight conglomerate reservoirs. While this method can improve initial reservoir productivity, as development progresses, formation energy rapidly declines, leading to low single-well production. Therefore, there is an urgent need to explore an effective method for replenishing and enhancing the production of tight reservoirs in the mid-to-late stages. Research and extensive practical experience have demonstrated that CO2 injection after fracturing can significantly improve reservoir recovery.

[0003] Fracturing fluids and CO2 react with clay minerals and carbonates in tight conglomerate reservoirs. For example, dolomite and calcite in carbonates, and chlorite in clay minerals, react with CO2, causing dissolution and corrosion, forming solution pores and pits, thus increasing reservoir porosity. Conversely, montmorillonite, illite, and chlorite in clay minerals absorb water and swell, reducing reservoir permeability and causing damage. Therefore, it is crucial to study the gas-water-rock reaction to characterize the effects of CO2 and fracturing fluids on different minerals in tight conglomerate reservoirs.

[0004] Currently, experimental research methods for gas-water-rock reactions can be broadly divided into two types: static reaction experiments and dynamic displacement experiments. Static reaction experiments, based on scanning electron microscopy, compare and observe the pore-throat structure of rocks before and after the gas-water-rock reaction. Although this method can directly study the changes in the pore-throat structure of rocks before and after the gas-water-rock reaction, it has a long experimental cycle, high research costs, and cannot continuously monitor the dynamic process.

[0005] Dynamic displacement experiments involve displacing minerals with CO2 or fracturing fluid at the core scale and then inverting pore throat changes using macroscopic parameters such as permeability and nuclear magnetic resonance T2 spectra to characterize the dissolution of minerals and the changes in the size of different pore throats. Although this method is simple to operate, it is difficult to distinguish the dissolution-swelling contributions of different minerals and cannot capture the details of particle-level migration.

[0006] Therefore, there is an urgent need for a quantitative measurement method that can simultaneously consider factors such as the strong heterogeneity and significant differences in pore-throat structure of tight conglomerate reservoirs, analyze the contribution of different minerals to the gas-water-rock reaction and the microparticle dissolution-migration process, and identify different dissolution modes of conglomerate. Summary of the Invention

[0007] One of the objectives of this invention is to provide an in-situ visualized quantitative determination method for gas-water-rock reaction and particle dissolution-migration based on a microfluidic chip. This method can perform in-situ visualized quantitative determination of gas-water-rock three-phase reaction, particle dissolution and secondary migration processes in conglomerate reservoirs under reservoir temperature, pressure and fluid chemistry conditions.

[0008] The present invention describes an in-situ visualized quantitative measurement method for gas-water-rock reaction and particle dissolution-migration based on microfluidic chips. First, a chip model containing real rock cores is designed, taking into account factors such as the strong heterogeneity and strong differences in pore throat structure of tight conglomerate reservoirs. Then, the gas-water-rock reaction and particle dissolution-migration process are recorded using an optical camera. Finally, image processing software and mathematical models are used to analyze the contribution of different minerals to the gas-water-rock reaction and to identify different dissolution modes of conglomerate.

[0009] The specific technical solution is as follows:

[0010] A microfluidic chip-based in-situ visualized quantitative determination method for gas-water-rock reaction and particle dissolution-transport includes the following steps:

[0011] (1) Fabrication of microfluidic chips containing real rock cores:

[0012] The microfluidic chip includes a main fluid channel I, a main fluid channel II, a fluid guiding region, and a core matrix region.

[0013] The core matrix region consists of 25-35 μm thick real core sections mounted on a glass plate. These real core sections provide the reaction space for fluid flow and gas-water-rock reactions. The core matrix region uses real conglomerate core sections; the types, quantities, and distribution of rock minerals conform to actual field development, effectively simulating the reservoir modification by gas during CO2 injection after fracturing and effectively predicting dissolution modes.

[0014] The fluid guiding region is a Z-shaped crack with a depth of 20-30 μm and a width of 400-600 μm, formed by cutting on the actual core section; the Z-shaped crack penetrates the core matrix region.

[0015] The fluid diversion zone passes through the core matrix area and is connected to the main fluid channel I and main fluid channel II, forming a complete injection-production relationship.

[0016] The main fluid channel I and main fluid channel II are located on opposite sides of the core matrix region and communicate only with the fluid guiding region. The core matrix region only contacts the fluid guiding region, while its other edges remain closed, ensuring that the fluid only reacts with the rock within the fluid guiding region.

[0017] The other end of the main fluid channel I is the injection end, and the other end of the main fluid channel II is the extraction end.

[0018] Both fluid main channels I and II are twice the depth of the Z-shaped fracture. This allows for the storage of more fracturing fluid and CO2, ensuring the smooth progress of the gas-water-rock reaction.

[0019] (2) Simulation experiment of CO2 flooding after fracturing fluid displacement:

[0020] S1. The fracturing fluid prepared according to the on-site construction is injected into the microfluidic chip containing the real rock core prepared in step (1) at a rate of 0.0001-0.00015 mL / min to simulate the displacement of fracturing fluid; until the fluid guiding area inside the microfluidic chip is observed to be full of fracturing fluid in the camera, the particle dissolution-migration process of the rock wall is recorded.

[0021] S2. First, CO2 gas is used to purge the fracturing fluid. Then, CO2 is injected into the microfluidic chip at a rate of 0.0001-0.00015 mL / min to simulate CO2 displacement. After the fluid guiding area inside the microfluidic chip can be observed to be filled with CO2 in the camera, the particle dissolution-migration process of the rock wall is recorded.

[0022] S3. Change the injection rates of fracturing fluid and CO2, and repeat steps S1 and S2 to conduct gas-water-rock reaction experiments under different injection rate conditions. Quantitatively evaluate the dissolution mode using the Pe number.

[0023] S4. By observing the dissolution characteristics of the core matrix region in the microfluidic chip, the dissolution modes are divided into the following four types:

[0024] If the dissolution front is blunt, the dissolution zone is narrow, and the overall process is uniform, then it is considered compact dissolution; Figure 3 As shown.

[0025] If a concentrated and straight dissolution channel forms perpendicular to the fracture direction, it is called dominant channel dissolution; such as Figure 4 As shown.

[0026] If a single or several thin, elongated dominant channels are formed, it is called wormhole dissolution; such as Figure 5 As shown.

[0027] If the contact surface between the rock and the fluid is uniformly eroded, the dissolution zone is large, and there are no obvious dominant channels, then it is uniform dissolution; Figure 6 As shown.

[0028] (3) Quantitative characterization of gas-water-rock reaction and particle dissolution-migration:

[0029] First, from the video of the particle dissolution-transport process of the rock wall recorded by the camera in steps S1-S3 of step (2), one clear image of the microfluidic chip is captured every minute.

[0030] Then, using MATLAB software, the gas, water, and rock phases in the captured image were sequentially processed by grayscale conversion, median filtering for noise reduction, contrast enhancement, and binarization. The dissolution channels in the rock matrix region of the microfluidic chip were then extracted, and the characteristic parameters were calculated: the rock volume before and after the gas-water-rock reaction, the surface area of ​​the rock minerals and fluid reaction, the average width of the rock fissures, and the specific value of the initial porosity of the rock.

[0031] The mineral dissolution amount ΔV, mineral dissolution rate R, and porosity increment in the rock mineral gas-water-rock reaction within the core matrix region were calculated using the aforementioned characteristic parameters. Pe number (Péclet number / Peclet number).

[0032] Among them, the mineral dissolution amount ΔV refers to the total volume of minerals dissolved in a unit volume of rock before and after the gas-water-rock reaction in the core matrix region.

[0033] The mineral dissolution rate R refers to the volume of minerals dissolved per unit time and per unit reaction area within the core matrix region before and after the gas-water-rock reaction.

[0034] Porosity increment It refers to the difference in porosity of rock minerals before and after the gas-water-rock reaction within the core matrix region.

[0035] The Pe number is the ratio of convective mass transfer rate to diffusion mass transfer rate, used to predict dissolution modes.

[0036] The formula for calculating the mineral dissolution amount ΔV of rock minerals in the core matrix region due to gas-water-rock reaction is as follows:

[0037] ;

[0038] In the formula: V – Dissolution of rock minerals, in meters 3 ;

[0039] V(t) — Volume of rock minerals at the initial time t, in meters 3 ;

[0040] V(t+ t) — Rock minerals in gas-water-rock reaction Volume after time t, m 3 .

[0041] The formula for calculating the mineral dissolution rate R of rock minerals in the core matrix region due to gas-water-rock reaction is as follows:

[0042] ;

[0043] Where: R—mineral dissolution rate, m / s;

[0044] V —Mineral dissolution amount, m 3 ;

[0045] A avg —The average reaction area between the fluid and the rock / mineral, in m 2 ;

[0046] t —Reaction time of fluid with rock minerals, t.

[0047] Porosity increment of rock mineral gas-water-rock reaction in the core matrix region The calculation formula is as follows:

[0048] ;

[0049] In the formula: —Porosity increment, dimensionless;

[0050] —Porosity of the rock at the initial time t, dimensionless;

[0051] — Rocks in gas-water-rock reactions Porosity after time t, dimensionless.

[0052] The formula for calculating the Pe number (Péclet number / Peclet number) of rock mineral gas-water-rock reaction in the core matrix region is as follows:

[0053] ;

[0054] Where: Pe—Pe number, a characteristic parameter representing the dissolution mode;

[0055] Q —Darcy velocity during displacement, m / s;

[0056] l— Width of the crack, in meters;

[0057] —Initial porosity of the rock, dimensionless;

[0058] D —Diffusion coefficient of CO2 in fracturing fluid, m 2 / s.

[0059] Relative dissolution of minerals The calculation formula is as follows:

[0060] ;

[0061] In the formula, V —Measured mineral dissolution amount; V max —Maximum soluble amount under the same temperature and pressure conditions.

[0062] Relative porosity increment The calculation formula is as follows:

[0063] ;

[0064] In the formula, Δ —Porosity increment; 0 — Initial porosity.

[0065] The formula for calculating the mineral dissolution rate index Ri is as follows:

[0066] ;

[0067] In the formula, R —Measured dissolution rate; R 0 — Initial dissolution rate.

[0068] The calculated relative dissolution amount of minerals Mineral dissolution rate index Ri, relative porosity increment The Pe number and the relative dissolution amount of the mineral are plotted in the same dimensionless coordinate system, with the Pe number as the horizontal axis. The left vertical axis represents the relative porosity increment. With the right vertical axis as the coordinate and the mineral dissolution rate index Ri as the contour line, we obtain Pe- -Ri- Dissolution pattern diagram.

[0069] This dissolution pattern chart can be directly used for the Pe-mineral relative dissolution amount in experimental-field data normalization. -Mineral dissolution rate index Ri-Relative porosity increment The multi-factor dissolution model chart can quickly determine or predict the reservoir stimulation effect under different gas injection conditions (gas injection rate).

[0070] In Pe- -R- In the figure, the four types of dissolution modes (compact dissolution, dominant channel dissolution, "wormhole" dissolution, and uniform dissolution) are represented by different "Pe zones" and "relative mineral dissolution amount - relative porosity increment" envelopes.

[0071] Among them, based on the Pe number and the relative dissolution of minerals Relative porosity increment The ranges of four characteristic parameters—including the mineral dissolution rate index Ri—are used to quantitatively characterize four dissolution modes, as detailed below:

[0072] When the Pe number is ≤10, the relative dissolution of minerals The relative porosity increment is between 0.05 and 0.10. When the mineral dissolution rate index Ri ≤ -0.5 in the range of 0.05-0.10, the dissolution mode is compact dissolution.

[0073] When 10 < Pe number ≤ 30, the relative dissolution amount of minerals The relative porosity increment is between 0.15 and 0.25. When the mineral dissolution rate index is between 0.15 and 0.25, and -0.5 < Ri ≤ 0, the dissolution mode is wormhole dissolution.

[0074] When 30 < Pe number ≤ 80, the relative dissolution of minerals The relative porosity increment is between 0.25 and 0.35. When the mineral dissolution rate index is 0 < Ri < 0.5, the dissolution mode is dominant channel dissolution, which is between 0.25 and 0.35.

[0075] When the Pe number is ≥200, the relative dissolution of minerals The relative porosity increment is between 0.10 and 0.15. When the mineral dissolution rate index Ri ≥ 0.5 in the range of 0.10–0.15, the dissolution mode is uniform dissolution.

[0076] This invention utilizes a combination of high-temperature, high-pressure microscopic visualization experiments, image processing, and MATLAB software self-programming methods to quantitatively characterize the gas-water-rock reaction and microparticle dissolution-migration in tight conglomerate, resulting in a set of prediction charts for dissolution modes applicable to tight conglomerate under different CO2 injection rates.

[0077] In this invention, the in-situ visualized quantitative determination method for gas-water-rock reaction and particle dissolution-transport based on microfluidic chip has a depth of 40-60 μm and a width of 800-1200 μm for both fluid main channel I and fluid main channel II in the microfluidic chip.

[0078] In this invention, the in-situ visualized quantitative determination method for gas-water-rock reaction and particle dissolution-transport based on a microfluidic chip includes a microfluidic chip comprising glass slides with thicknesses of 1.5 mm and 2 mm. The main fluid channel I, main fluid channel II, fluid guiding region, and core matrix region are all etched or adhered to the 2 mm thick glass slide. The 1.5 mm thick glass slide is a smooth, unetched glass, serving as a cover plate for the microfluidic chip, and is bonded to the 2 mm thick glass slide to obtain a sealed microfluidic chip. High borosilicate glass can be used for the glass slides. The core matrix region is located at the center of the 2 mm thick glass slide.

[0079] Theoretically, this microfluidic chip can withstand a pressure of 10 MPa without confining pressure, withstand any high pressure under the condition that the internal and external pressure difference is no more than 2 MPa, and theoretically withstand a high temperature of 180℃. It has the ability to reduce the pressure and temperature conditions of oil reservoir formations.

[0080] In this invention, the method for in-situ visualized quantitative determination of gas-water-rock reaction and particle dissolution-transport based on microfluidic chip is described below:

[0081] (1) Prepare the real core thin sections as described:

[0082] Select representative core samples from the study area, cut them into rectangular pieces, and then grind and polish them into rectangular thin slices with a thickness of 25-35 μm. Cutting can be done using an STX-202A small diamond wire cutting machine. Grinding and polishing can be done using a UNIPOL-1202 automatic precision grinding and polishing machine.

[0083] Furthermore, the rectangular sheet has a length of 15-25mm and a width of 10-20mm.

[0084] (2) Fabrication of microfluidic chips:

[0085] First, select two glass plates with thicknesses of 1.5mm and 2mm respectively.

[0086] Then, a region matching the size of the real core sheet obtained in step (1) is cut out on a glass plate with a thickness of 2 mm; after the glass plate is polished and cleaned, the real core sheet is glued to this region.

[0087] Furthermore, a region matching the size of the real core sheet obtained in step (1) is formed by laser cutting at the center of a 2mm thick glass plate. After the glass plate is polished and cleaned, the obtained real core sheet is bonded to this region.

[0088] Z-shaped cracks with a depth of 20-30 μm and a width of 400-600 μm are cut into the bonded real core thin sections to form the fluid guiding region of the microfluidic chip;

[0089] Two main fluid channels, each 40-60 μm deep and 800-1200 μm wide, are formed on both sides of a 2 mm thick glass plate using laser cutting. A circular hole with a diameter of 800-1200 μm is drilled at one end of the main fluid channel I as the injection end; the other end of the main fluid channel I is connected to one end of the Z-shaped crack.

[0090] A circular hole with a diameter of 800-1200μm is drilled at one end of the main fluid channel II as the extraction end; the other end of the main fluid channel II is connected to the other end of the Z-shaped fracture.

[0091] The connection between the main fluid channel and the fluid diversion area is smoothed to ensure that the fluid can flow more easily into the core matrix area.

[0092] (3) Bond the two glass plates together to ensure that the fluid can only flow in from the injection end and out from the extraction end. The bonding can be done using an EVG-510 electric field-assisted bonding machine.

[0093] Another objective of this invention is to provide an apparatus, specifically a microscopic visualization experimental apparatus, for the aforementioned in-situ visualized quantitative determination method of gas-water-rock reaction and particle dissolution-migration based on microfluidic chips.

[0094] The specific technical solution is as follows:

[0095] A microscopic visualization experimental device is used for the above-mentioned in-situ visualized quantitative determination method of gas-water-rock reaction and particle dissolution-migration based on microfluidic chip. The device includes a gas intermediate container, a crude oil intermediate container and a deionized water intermediate container arranged in parallel; a visual vessel for placing the microfluidic chip and a camera located above the visual vessel; and a temperature control system connected to the gas intermediate container, the crude oil intermediate container, the deionized water intermediate container and the visual vessel.

[0096] The gas intermediate container, crude oil intermediate container, and deionized water intermediate container are connected to the visible reactor through their respective valves and pipelines.

[0097] Vent lines and vent valves are installed on the pipelines between the gas intermediate container, crude oil intermediate container, deionized water intermediate container and the visible reactor.

[0098] Temperature sensors are connected to the gas intermediate container, crude oil intermediate container, and deionized water intermediate container.

[0099] The gas cylinders are connected to the intermediate gas container via valves and pipelines, through an air compressor and a gas booster pump.

[0100] The displacement pump is connected to the gas intermediate container, crude oil intermediate container, and deionized water intermediate container via valves and pipelines.

[0101] The visual reactor is connected to a confining pressure tracking system and a back pressure tracking system via valves and pipelines; a venting pipeline and a venting valve are installed on the pipeline between the back pressure tracking system and the visual reactor.

[0102] The confining pressure tracking system is equipped with a venting pipeline and a venting valve on one side.

[0103] The back pressure tracking system is connected to a waste liquid bottle at its bottom.

[0104] The visible vessel is connected to a vacuum pump via valves and pipelines, and the vacuum pump is connected to a pressure sensor; the pressure sensor is also connected to the displacement pump.

[0105] The camera, temperature control system, confining pressure tracking system, and back pressure tracking system are all integrated into the computer.

[0106] The beneficial effects of this invention are as follows: The method described in this invention targets tight conglomerate reservoirs with low porosity and permeability and extremely strong pore throat heterogeneity. It utilizes a detachable, temperature- and pressure-resistant microfluidic chip to realistically reproduce the strongly heterogeneous pore throat structure of the conglomerate. CO2 flooding experiments are conducted after fracturing fluid flooding under reservoir temperature and pressure conditions. The entire process of particle dissolution, stripping, and migration caused by the three-phase reaction of CO2-fracturing fluid-rock is captured simultaneously, and the particle migration distance, migration velocity, dissolution rate, and dissolution mode are quantified. Through multimodal information fusion of "microscopic image-mathematical model", a particle dissolution-migration coupled model is established, providing key experimental basis and theoretical support for CO2 fracturing energy replenishment and subsequent displacement scheme optimization in tight conglomerate reservoirs.

[0107] This invention integrates a 25-35μm real core section with a Z-shaped laser etching channel that is 20-30μm deep and 400-600μm wide. For the first time, it achieves in-situ visualization of the entire process of gas-water-rock reaction, microparticle dissolution and migration at the pore throat scale in dense conglomerate under high temperature and high pressure conditions, completely eliminating the drawback of traditional homogeneous chips being disconnected from the pore structure in the field.

[0108] Using a high-temperature, high-pressure visualization experimental device and a MATLAB-programmed image processing system, the relative dissolution amount of minerals can be output simultaneously in one go. Mineral dissolution rate index Ri, relative porosity increment The four quantitative parameters, Pe and Pe number, were used to construct the Pe- -Ri- The multi-factor dissolution mode chart allows for second-level prediction of four dissolution modes (compact, "wormhole", dominant channel, and uniform) and their corresponding porosity increases simply by inputting the gas injection rate on-site.

[0109] The entire process, from core cutting, polishing, laser etching, EVG510 anodic bonding to high-temperature and high-pressure experiments, is standardized. The chip can be reused more than 50 times, and the cycle of a single experiment is reduced to 6 hours. The efficiency is 8-10 times higher than that of traditional core displacement, providing an efficient, accurate, and scalable experimental platform for optimizing CO2 flooding schemes for dense conglomerate. Attached Figure Description

[0110] Figure 1 This is a schematic diagram of the structure of the microscopic visualization chip of the present invention.

[0111] Figure 2 This is a schematic diagram of the structure of the chip after the gas-water-rock reaction, which is visualized at a microscopic level.

[0112] Figure 3 This is a schematic diagram of the compact dissolution mode after the gas-water-rock reaction of a microscopically visualized chip.

[0113] Figure 4 This is a schematic diagram of the dominant channel dissolution mode after the gas-water-rock reaction of a microscopically visualized chip.

[0114] Figure 5 This is a schematic diagram of the wormhole dissolution mode after the microscopic visualization of the gas-water-rock reaction of the chip.

[0115] Figure 6 This is a schematic diagram of the uniform dissolution mode after the gas-water-rock reaction of a microscopically visualized chip.

[0116] Figure 7 This is a schematic diagram of the structure of a microscopic visualization experimental device.

[0117] Figure 8 Pe- -Ri- A diagram of a multifactorial dissolution model.

[0118] In the figure, A is the injection end, B1 is the main fluid channel I, B2 is the main fluid channel II, C is the fluid guiding area, D is the core matrix area, and E is the extraction end.

[0119] 1 is a gas cylinder, 2 is an air compressor, 3 is a gas booster pump, 4 is a gas intermediate container, 5 is a crude oil intermediate container, 6 is a deionized water intermediate container, 7 is a displacement pump, 8 is a temperature control system, 9 is a confining pressure tracking system, 10 is a vacuum pump, 11 is a visual vessel, 12 is a microfluidic chip, 13 is a back pressure tracking system, 14 is a waste liquid bottle, 15 is a computer, 16 is a camera, 17 is a pressure sensor, 18 is a temperature sensor, 19 is a vent line, and 20 is a vent valve. Detailed Implementation

[0120] The present invention will be further described below with reference to the accompanying drawings. The scope of protection of the present invention is not limited to the following description:

[0121] Example 1

[0122] First, the microscopic visualization experimental device used in the above-mentioned in-situ visualization quantitative determination method of gas-water-rock reaction and particle dissolution-migration based on microfluidic chip includes a gas intermediate container 4, a crude oil intermediate container 5, and a deionized water intermediate container 6 arranged in parallel; a visual vessel 11 on which the microfluidic chip 12 is placed and a camera 16 located above the visual vessel 11; and a temperature control system 8 connected to the gas intermediate container 4, the crude oil intermediate container 5, the deionized water intermediate container 6, and the visual vessel 11.

[0123] Gas intermediate container 4, crude oil intermediate container 5 and deionized water intermediate container 6 are respectively connected to the visible vessel 11 through their respective valves and pipelines.

[0124] Venting lines 19 and venting valves 20 are installed on the pipelines between the gas intermediate container 4, the crude oil intermediate container 5, the deionized water intermediate container 6 and the visible vessel 11.

[0125] Temperature sensors 18 are connected to the gas intermediate container 4, crude oil intermediate container 5, and deionized water intermediate container 6.

[0126] Gas cylinder 1 is connected to intermediate gas container 4 via various valves and pipelines, through air compressor 2 and gas booster pump 3.

[0127] Displacement pump 7 is connected to gas intermediate container 4, crude oil intermediate container 5 and deionized water intermediate container 6 via valves and pipelines.

[0128] The visual vessel 11 is connected to the confining pressure tracking system 9 and the back pressure tracking system 13 via valves and pipelines; wherein, a venting pipeline 19 and a venting valve 20 are provided on the pipeline between the back pressure tracking system 13 and the visual vessel 11.

[0129] The confining pressure tracking system 9 is provided with a venting pipeline 19 and a venting valve 20 on one side.

[0130] The back pressure tracking system 13 is connected to a waste liquid bottle 14 at its bottom.

[0131] The visible vessel 11 is connected to a vacuum pump 10 via valves and pipelines. The vacuum pump 10 is connected to a pressure sensor 17. The pressure sensor 17 is also connected to the displacement pump 7.

[0132] The camera 16, temperature control system 8, confining pressure tracking system 9, and back pressure tracking system 13 are all integrated on the computer 15.

[0133] Then, the in-situ visualized quantitative determination method for gas-water-rock reaction and particle dissolution-transport based on microfluidic chip, using the micro-visualization chip and high-temperature and high-pressure micro-visualization experimental device as described above, is as follows:

[0134] (1) Fabrication of microfluidic chips containing real rock cores:

[0135] First, core samples from the Ma2 well area of ​​the Mahu Oilfield in Xinjiang were selected. The core samples were cut into rectangles with a length and width of 20mm × 15mm and a thickness of 500μm using an STX-202A small diamond wire cutting machine. Then, the cut core slices were polished into rectangles with a length and width of 20mm × 15mm and a thickness of 30μm using an UNIPOL-1202 automatic precision grinding and polishing machine.

[0136] Then, two pieces of high borosilicate glass with thicknesses of 1.5 mm and 2 mm were selected. A region with a length and width of 20 mm × 15 mm and a thickness of 30 μm was cut out on the 2 mm thick glass plate using a high-frequency high-power laser. The cut, polished core slices were then bonded to this region. A Z-shaped crack with a depth of 25 μm and a width of 500 μm was cut out on the bonded core slices using a high-frequency high-power laser as the fluid guiding region C.

[0137] Two main fluid channels, each 50 μm deep and 1000 μm wide, are formed on both sides of a 2 mm thick glass plate using laser cutting. A circular hole with a diameter of 1000 μm is drilled at one end of the main fluid channel I B1 as the injection end A. The other end of the main fluid channel I B1 is connected to one end of the Z-shaped crack.

[0138] A circular hole with a diameter of 1000μm is drilled at one end of the main fluid channel II B2 as the extraction end E; the other end of the main fluid channel II B1 is connected to the other end of the Z-shaped fracture.

[0139] Finally, the two prepared glass plates are polished and cleaned, and then bonded together using an EVG-510 electric field-assisted bonding machine to ensure that the fluid can only flow in from the injection end A and out from the extraction end E.

[0140] The specific structure of the fabricated microfluidic chip is as follows: Figure 1 As shown, it includes injection end A, main fluid channel I B1, main fluid channel II B2, fluid guiding area C, core matrix area D, and extraction end E.

[0141] (2) Simulation experiment of CO2 flooding after fracturing fluid displacement:

[0142] S1. Install the microfluidic chip 12 in a high-temperature and high-pressure visual vessel 11. During the installation process, ensure that the microfluidic chip 12 is placed flat and in the chip slot of the visual vessel 11.

[0143] All sealing rings are clean, dry, and intact. The cavity of the visible vessel 11 is evacuated by the vacuum pump 10 to ensure that there is no air in the cavity. Then, pure water is added and the temperature control system 8 of the visible vessel 11 is turned on to the formation temperature. In this embodiment, the formation temperature is 80°C.

[0144] The confining pressure tracking system 9 is activated to control the confining pressure, making it 2 MPa higher than the inlet pressure of the microfluidic chip 12.

[0145] Place the camera 16 (Leica high-speed camera) above the glass window of the viewing vessel 11, and simultaneously open the installed camera software on the computer 15. Adjust the focus position and magnification of the camera 16 until a clear image of the rock and minerals in contact with the core matrix region D and the fluid flow region C is displayed on the computer 15.

[0146] S2. Close the inlet valve of the microfluidic chip 12 and open the outlet valve to evacuate the microfluidic chip 12 to ensure that there are no air bubbles inside the chip.

[0147] S3. Prepare fracturing fluid (slippery water) for on-site construction by mixing 0.5% by mass of drag-reducing agent (Gemini surfactant YZS18-YZS18) and 99.5% by mass of pure water. After re-preparation, place it in the deionized water intermediate container 6. Open the vent valve 20 at the inlet of the microfluidic chip 12 and inject the fracturing fluid into the injection port through the high-precision displacement pump 7. When continuous fracturing fluid without bubbles appears in the vent line 19, close the inlet vent valve 20.

[0148] Open the inlet valve of the microfluidic chip 12 and inject fracturing fluid into the chip at an injection rate of 0.0001 mL / min until the fluid guiding area C inside the microfluidic chip 12 can be observed to be filled with fracturing fluid in the camera 16. Record the particle dissolution-migration process on the rock wall. After waiting for 1 hour of reaction, close the high-precision displacement pump 7, the inlet valve and the deionized water intermediate container 6.

[0149] S4. High-purity CO2 in gas cylinder 1 is injected into intermediate gas container 4 through gas booster pump 3. The vent valve 20 at the inlet of microfluidic chip 12 is opened, and CO2 is injected into the injection port through displacement pump 7.

[0150] When no more fracturing fluid appears in the venting line 19, close the inlet venting valve 20, open the inlet valve of the microfluidic chip 12, and inject CO2 into the microfluidic chip 12 at an injection rate of 0.0001 mL / min until the fluid guiding area C inside the microfluidic chip 12 can be observed to be full of CO2 in the camera. Record the particle dissolution-migration process on the rock wall, wait for the reaction for 1 hour, and then close the displacement pump 7, the inlet valve and the gas intermediate container 4.

[0151] S5. Change the injection rate of fracturing fluid and CO2, and repeat steps S3 and S4 sequentially at injection rates of 0.0005 mL / min, 0.001 mL / min and 0.005 mL / min to carry out gas-water-rock reaction experiments under different injection rates. The dissolution mode is quantitatively evaluated by Pe number.

[0152] S6. Add petroleum ether or toluene to the crude oil intermediate container 5, turn on the displacement pump 7, and pump the petroleum ether into the microfluidic chip 12 until there is no residual fluid inside the microfluidic chip 12. Remove the microfluidic chip 12, wipe it dry, and store it properly.

[0153] Taking the experimental results with a CO2 displacement flow rate of 0.0001 mL / min as an example, images meeting the experimental requirements were extracted from the video captured by the high-speed camera 16, such as... Figure 2 As shown.

[0154] Using MATLAB software, the gas, water, and rock phases in the image were processed through grayscale conversion, median filtering for noise reduction, contrast enhancement, and binarization. Then, the dissolution channels in the rock matrix region D were extracted. Using image processing techniques, a series of characteristic parameters were quantitatively calculated, including the rock volume before and after the gas-water-rock reaction, the average reaction area between the fluid and rock minerals, the rock porosity before and after the gas-water-rock reaction, the Darcy velocity during displacement, the average width of rock fractures, and the diffusion coefficient of CO2 in the fracturing fluid.

[0155] The values ​​of these parameters are shown in Table 1 below.

[0156] Table 1 Summary of parameter values

[0157]

[0158] The formula for calculating the mineral dissolution amount ΔV of rock minerals in the core matrix region due to gas-water-rock reaction is as follows:

[0159] =9×10 -9 -8.82×10 -9 =1.8×10 -10 m 3 .

[0160] The formula for calculating the mineral dissolution rate R of rock minerals in the core matrix region due to gas-water-rock reaction is as follows:

[0161] =2.4×10 -11 m / s.

[0162] Porosity increment of rock mineral gas-water-rock reaction in the core matrix region The calculation formula is as follows:

[0163] =0.085-0.08=0.005.

[0164] The formula for calculating the Pe number of the gas-water-rock reaction of rock minerals in the core matrix region is as follows:

[0165] = =4.2.

[0166] Relative dissolution of minerals in the gas-water-rock reaction of rock minerals within the core matrix region The calculation formula is as follows:

[0167] =1.8×10 -10 ÷2.65×10 -9 =0.0698.

[0168] The formula for calculating the mineral dissolution rate index Ri of the gas-water-rock reaction in the core matrix region is as follows:

[0169] =log 10 (2.4×10 -11 / 8.5×10 -11 = -0.549.

[0170] The relative porosity increment of rock mineral gas-water-rock reaction in the core matrix region The calculation formula is as follows:

[0171] =0.005 / 0.08=0.0625.

[0172] In Pe- -R- In the figure, the four types of dissolution modes (compact dissolution, dominant channel dissolution, "wormhole" dissolution, and uniform dissolution) are represented by different "Pe zones" and "mineral relative dissolution amount - relative porosity increment" envelopes. The numerical classification of the four dissolution modes and characteristic parameters (Pe number, mineral relative dissolution amount, relative porosity increment and mineral dissolution rate index) is shown in Table 2 below.

[0173] Table 2 Numerical partitioning of feature parameters

[0174]

[0175] Based on the numerical classification of the above dissolution modes and characteristic parameters, Table 2 shows that when the CO2 injection rate is 0.0001 mL / min, the conglomerate minerals undergo compact dissolution with CO2 during the gas-water-rock reaction of the dense conglomerate.

[0176] Experiments were conducted at different CO2 injection rates to obtain the corresponding mineral dissolution amount ΔV, mineral dissolution rate R, and porosity increment. The values ​​of the Pe number (Péclet number) are shown in Table 3 below.

[0177] Table 3 Feature parameter values

[0178]

[0179] Based on high-temperature and high-pressure microscopic visualization experiments, characteristic parameters of the above experiments with different CO2 injection rates were obtained. The relative dissolution rate of minerals was then calculated using a self-programmed method in MATLAB software. Mineral dissolution rate index Ri, relative porosity increment The Pe number is unified in a dimensionless coordinate system.

[0180] In this figure, the Pe number is used as the horizontal axis of the chart, representing the relative dissolution of minerals. As the left vertical axis of the chart, the relative porosity increment Using the right vertical axis of the chart and the mineral dissolution rate index Ri as the contour lines, a set of multi-factor dissolution model charts (referred to as Pe-) that can be directly used for experimental-field data normalization is obtained. These charts represent the "Pe-relative mineral dissolution amount-mineral dissolution rate index-relative porosity increment". -Ri- (Images), such as Figure 8 As shown, this facilitates the rapid determination or prediction of reservoir stimulation effects under different gas injection conditions (gas injection rate).

Claims

1. A microfluidic chip-based in-situ visualized and quantitative determination method for gas-water-rock reaction and particle dissolution-migration, characterized in that, The method comprises the following steps: (1) preparing a microfluidic chip containing real core: The microfluidic chip comprises a fluid main channel I, a fluid main channel II, a fluid guide area and a core matrix area; The core matrix area is a real core slice with a thickness of 25-35 μm loaded on a glass plate; The fluid guide area is a Z-shaped crack with a depth of 20-30 μm and a width of 400-600 μm cut on the real core slice; the Z-shaped crack penetrates the core matrix area; The fluid main channel I and the fluid main channel II are arranged on the two sides of the core matrix area and only communicate with the fluid guide area; The other end of the fluid main channel I is an injection end, and the other end of the fluid main channel II is a production end; The depth of the fluid main channel I and the fluid main channel II is twice the depth of the Z-shaped crack; (2) CO2 displacement simulation experiment after fracturing fluid displacement: S1, the fracturing fluid prepared according to the field construction is injected into the microfluidic chip containing real core prepared in step (1) at a speed of 0.0001-0.00015 mL / min to simulate fracturing fluid displacement; after observing that the fluid guide area inside the microfluidic chip is filled with fracturing fluid in the camera, record the particle dissolution-migration process of the rock wall surface; S2, first empty the fracturing fluid with CO2 gas, then inject CO2 into the microfluidic chip at a speed of 0.0001-0.00015 mL / min to simulate CO2 displacement; until the fluid guide area inside the microfluidic chip is filled with CO2, which can be observed in the camera, record the particle dissolution-migration process of the rock wall surface; S3, change the injection speed of fracturing fluid and CO2, repeat steps S1 and S2, and conduct gas-water-rock reaction experiment under different injection speed conditions; S4, by observing the dissolution characteristics of the core matrix area in the microfluidic chip, the dissolution mode is divided into the following four types: If the dissolution front is blunt, the dissolution area is small, and the whole is uniformly advanced, it is compact dissolution; If a concentrated and straight dissolution channel is formed perpendicular to the fracture direction, it is dominant channel dissolution; If a single or several fine and long dominant channels are formed, it is wormhole dissolution; If the contact surface of the rock and the fluid is uniformly eroded, the dissolution area is large, and there is no obvious dominant channel, it is uniform dissolution; (3) Quantitative characterization of gas-water-rock reaction and particle dissolution-migration: First, from the video of the particle dissolution-migration process of the rock wall surface recorded by the camera in steps S1-S3 of step (2), one frame of picture of the microfluidic chip is taken every minute; Then, using MATLAB software, the gas, water and rock in the intercepted picture are sequentially subjected to gray scale processing, median filter noise reduction, contrast enhancement and binary processing, and then the dissolution channel in the rock matrix area of the microfluidic chip is extracted, and the characteristic parameters are calculated: the specific values of the rock volume before and after the gas-water-rock reaction, the rock mineral and fluid reaction surface area, the average width of the rock fracture, and the initial porosity of the rock; The mineral dissolution amount AV, the mineral dissolution rate R, and the porosity increment of the rock mineral gas-water-rock reaction in the core matrix region are respectively calculated by the characteristic parameters Pe number; The calculation formula of the mineral dissolution amount ΔV of the rock mineral gas-water-rock reaction in the core matrix area is as follows: ； In the formula: V - rock mineral dissolution amount, m 3 ; V(t) - volume of rock minerals at initial t time, m 3 ; V(t + t) - volume of rock minerals after gas-water-rock reaction at time t, m t) - volume of rock minerals after gas-water-rock reaction at time t, m t) - volume of rock minerals after gas-water-rock reaction at time t, m 3 ; The calculation formula of mineral dissolution rate R of the rock mineral gas-water-rock reaction in the core matrix area is as follows: ； In the formula, R is the mineral dissolution rate, m / s; V - amount of mineral dissolution, m 3 ; A avg - average reaction surface area of the fluid with the rock minerals, m 2 ; t - the reaction time of the fluid with the rock minerals, t; Porosity increment of rock mineral gas-water-rock reaction in core matrix region The calculation formula is as follows: ； In the formula: — porosity increment, dimensionless; - the porosity of the rock at the initial time t, dimensionless; - rock in gas-water-rock reactions porosity after t time, dimensionless The calculation formula of Pe number of the rock mineral gas-water-rock reaction in the core matrix area is as follows: ； In the formula, Pe is the Pe number, which is a characteristic parameter of the dissolution mode; Q - Darcy velocity during displacement, m / s; l - average width of rock fractures, m; - initial porosity of the rock, dimensionless; D - Diffusion coefficient of CO2 in the fracturing fluid, m 2 / s; mineral phase relative dissolution amount The calculation formula is as follows: ； In the formula, V — measured mineral dissolution amount; V max — maximum dissolvable amount under the same temperature and pressure conditions; The relative porosity increment The formula for calculating the relative porosity increment is as follows: ； wherein Δ — porosity increment; 0 — initial porosity; The calculation formula of mineral dissolution rate index Ri is as follows: ； wherein R — measured erosion rate; R 0 — initial erosion rate; The calculated mineral relative dissolution amount , mineral dissolution rate index Ri, relative porosity increment and Pe number are plotted in the same dimensionless coordinate system, with Pe number as horizontal axis, mineral relative dissolution amount as left vertical axis, relative porosity increment as right vertical axis, and mineral dissolution rate index Ri as contour line, to obtain Pe- -Ri- dissolution pattern chart. Based on Pe number and relative mineral dissolution Relative porosity increment The ranges of four characteristic parameters—including the mineral dissolution rate index Ri—are used to quantitatively characterize four dissolution modes, as detailed below: When Pe number ≤ 10, the relative dissolution amount of minerals At 0.05-0.10, the relative porosity increment When the mineral dissolution rate index Ri is ≤-0.5 at 0.05-0.10, the dissolution mode is compact dissolution; When 10 < Pe number < 30, the relative amount of mineral dissolution At 0.15-0.25, the relative increment of porosity At 0.15-0.25, the mineral dissolution rate index -0.5 < Ri < 0, the dissolution mode is wormhole dissolution; When 30 < Pe number < 80, the relative amount of mineral dissolution At 0.25-0.35, the relative increment of porosity When 0 < Ri < 0.5, the dissolution mode is dominant channel dissolution. When Pe number ≥ 200, the relative dissolution amount of minerals At 0.10-0.15, the relative porosity increment When the mineral dissolution rate index Ri is ≥ 0.5, the dissolution mode is uniform dissolution.

2. The microfluidic chip-based gas-water-rock reaction and particle dissolution-migration in-situ visualized quantitative determination method according to claim 1, characterized in that, The depth of the fluid main channel I and the fluid main channel II in the microfluidic chip is 40-60 μm, and the width is 800-1200 μm. 3.The microfluidic chip-based gas-water-rock reaction and particle dissolution-migration in-situ visualized quantitative determination method according to claim 1, wherein, The microfluidic chip further comprises glass sheets with thicknesses of 1.5 mm and 2 mm, wherein the fluid main channel I, the fluid main channel II, the fluid conduction area and the core matrix area are etched or adhered to the glass sheet with a thickness of 2 mm; the glass sheet with a thickness of 1.5 mm is a smooth glass without etching, which is used as a cover plate of the microfluidic chip and is bonded with the glass sheet with a thickness of 2 mm to obtain a sealed microfluidic chip.

4. The microfluidic chip-based gas-water-rock reaction and particle dissolution-migration in-situ visualized quantitative determination method according to claim 1, characterized in that, The preparation method of the microfluidic chip is as follows: (1) manufacturing the real core slice: selecting a core with a representative block in a research area, cutting the core into a rectangle, and polishing to a rectangular slice with a thickness of 25-35 μm; (2) manufacturing the microfluidic chip: firstly, selecting two glass plates with thicknesses of 1.5 mm and 2 mm; then, cutting a region matching the size of the real core slice obtained in step (1) on the glass plate with a thickness of 2 mm; after polishing and cleaning the glass plate, the real core slice is adhered in the region; cutting a Z-shaped crack with a depth of 20-30 μm and a width of 400-600 μm on the adhered real core slice to form a fluid conduction area of the microfluidic chip; using laser cutting to form two fluid main channels with a depth of 40-60 μm and a width of 800-1200 μm on both sides of the glass plate with a thickness of 2 mm, one end of the fluid main channel I is drilled with a circular hole with a diameter of 800-1200 μm as an injection end; the other end of the fluid main channel I is communicated with one end of the Z-shaped crack; one end of the fluid main channel II is drilled with a circular hole with a diameter of 800-1200 μm as a production end; the other end of the fluid main channel II is communicated with the other end of the Z-shaped crack; (3) bonding the two glass plates together to ensure that the fluid only flows in from the injection end and flows out from the production end.

5. The microfluidic chip-based gas-water-rock reaction and particle dissolution-migration in-situ visualized quantitative determination method according to claim 4, characterized in that, The length of the rectangular slice in step (1) is 15-25 mm, and the width is 10-20 mm.

6. The microfluidic chip-based gas-water-rock reaction and particle dissolution-migration in-situ visualized quantitative determination method according to claim 4, characterized in that, The cutting in step (2) adopts laser cutting; a region matching the size of the real core slice obtained in step (1) is formed on the center position of the glass plate with a thickness of 2 mm by laser cutting.

7. A micro-visualization experimental apparatus, characterized by, The device is used for the gas-water-rock reaction and micro-particle dissolution-migration in-situ visualized quantitative determination method based on the micro-fluidic chip of claim 1, and comprises gas intermediate container, crude oil intermediate container and deionized water intermediate container arranged in parallel; visual reactor in which the micro-fluidic chip is placed and camera located above the visual reactor; temperature control system connected with the gas intermediate container, crude oil intermediate container, deionized water intermediate container and visual reactor; The gas intermediate container, crude oil intermediate container and deionized water intermediate container are respectively connected with the visual reactor through respective valves and pipelines; The pipelines between the gas intermediate container, crude oil intermediate container and deionized water intermediate container and the visual reactor are provided with venting pipelines and venting valves; The gas intermediate container, crude oil intermediate container and deionized water intermediate container are all connected with temperature sensors; The gas cylinder is connected with the gas intermediate container through respective valves and pipelines, air compressor and gas booster pump in sequence; The displacement pump is connected with the gas intermediate container, crude oil intermediate container and deionized water intermediate container through respective valves and pipelines; The visual reactor is connected with the confining pressure tracking system and back pressure tracking system through respective valves and pipelines; wherein, the pipeline between the back pressure tracking system and the visual reactor is provided with venting pipeline and venting valve; The confining pressure tracking system is provided with venting pipeline and venting valve on one side; The back pressure tracking system is connected with waste liquid bottle at the bottom end; The visual reactor is connected with the vacuum pump through respective valves and pipelines, and the vacuum pump is connected with pressure sensor; the pressure sensor is also connected with the displacement pump; The camera, temperature control system, confining pressure tracking system and back pressure tracking system are integrated on the computer.

Images