Multi-scale characterization method of CO2-WAG oil displacement interface wrinkles

Abstract

The present application belongs to the technical field of oil and gas exploitation, and relates to a CO2-WAG oil displacement interface fold multi-scale characterization method. The present application aims at the technical bottleneck that the CO2-WAG oil displacement field lacks a dynamic and quantitative interface fold characterization method suitable for actual reservoir conditions, and constructs a multi-scale collaborative characterization system of cores, microfluidic chips and molecular dynamics simulation. The key parameters of the fold are quantified at the core scale, the interface evolution is dynamically tracked and the fold characteristics are quantified at the microfluidic chip scale, and the fold formation and evolution mechanism is revealed from the molecular level at the molecular dynamics simulation scale. The three are mutually verified and progressively advanced, realizing full-dimensional characterization from the macroscopic to the molecular level, providing core technical support for elucidating the regulation mechanism of the interface fold on the CO2-WAG oil displacement efficiency. The method has a standardized process, controllable operation, unified and clear indicators, is suitable for different reservoirs and is convenient for result reuse, and has important significance for promoting the research and development and industrial application of low-carbon and efficient oil displacement technology.

Description

Technical Field

[0001] This invention belongs to the field of oil and gas extraction technology and relates to a multi-scale characterization method for CO2-WAG oil displacement interface folds. Background Technology

[0002] CO2-WAG enhanced oil recovery (EOR) technology, a low-carbon and efficient technology in the oil and gas extraction field that combines enhanced oil recovery (EOR) with CO2 sequestration, has been widely adopted globally since ExxonMobil completed the world's first field trial in the North Pabina oilfield in Canada in 1957. Field trials in domestic oilfields such as Daqing and Changqing have shown that this technology can improve EOR by approximately 10% compared to single CO2 or water-driven EOR. After optimizing injection parameters such as the water-gas ratio and injection timing, the EOR can be further improved by 25%–35%. In the Middle East and North America, relying on carbonate reservoirs with simple structures and excellent physical properties, the application of this technology has improved EOR by an average of 15%–25%. Specific studies on the Bakken and BuHasa oilfields further show that when the water-gas ratio is optimized to 1:1, the EOR increases by 35.6% and 18% respectively, fully demonstrating the significant effectiveness and optimization potential of this technology.

[0003] In CO2-WAG enhanced oil recovery, interfacial folding is a key microscopic factor regulating oil recovery. Core displacement CT scans and microfluidic chip experiments show that under different displacement velocities, the residual oil and displaced phase exhibit three states: no folding, moderate folding, and excessive folding. Related studies indicate that moderate interfacial folding can increase the pressure gradient of the displaced phase, expand the displacement sweep volume, and enhance the stripping efficiency of residual oil, thereby improving recovery. However, excessive interfacial folding can block reservoir flow channels, trigger the Jamin effect, increase oil flow resistance, and disrupt the continuity of the displaced phase, ultimately leading to a decrease in oil displacement efficiency and recovery. This finding provides important microscopic theoretical basis for subsequent optimization of displacement parameters to control the morphology and quantity of interfacial folds and improve oil recovery.

[0004] Interface wrinkles are a core microscopic controlling factor for precise regulation of CO2-WAG enhanced oil recovery, and they are of great significance for optimizing oil displacement processes and improving development efficiency. However, the lack of dynamic and quantitative characterization methods that are suitable for actual reservoir conditions has become a core obstacle restricting in-depth exploration of mechanisms and technological upgrading in this field. Summary of the Invention

[0005] To address the aforementioned technical problems, this invention proposes a multi-scale characterization method for CO2-WAG oil displacement interface wrinkles.

[0006] The technical solution of the present invention to solve the above-mentioned technical problems is as follows: a multi-scale characterization method for CO2-WAG oil displacement interface wrinkles, including the following contents.

[0007] Characterizing CO2-WAG oil displacement interface folds at the core scale includes the following steps; Step 1: Core Pretreatment. Select representative core samples from the reservoir, clean and dry them, and measure basic parameters such as porosity. Saturate the samples with simulated formation water and crude oil at the original oil saturation level. Step 2: Set up and debug the system. Load the core into the high-temperature and high-pressure CT displacement system, seal it, set the formation temperature and pressure conditions, and debug the CO2 and formation water injection, flow control system and CT scanning equipment to ensure accuracy and clarity; Step 3: Displacement and Data Acquisition. Initiate the CO2-WAG displacement experiment and acquire in-situ real-time CT images of fluid distribution within the core. Step 4: Construct a 3D model. Denoise the CT images, extract pore structure information, and construct a 3D network model of the core pores; Step 5: Quantification of Fold Parameters. Use ImageJ software to extract the oil-displacement phase interface and quantify the size and distribution of folds.

[0008] Characterizing CO2-WAG oil displacement interface wrinkles at the mesoscale using a microfluidic chip experimental system includes the following steps; Step 1: Core pore feature acquisition. After preprocessing the core, high-precision CT scanning and 3D reconstruction are used to extract pore slices and morphology, pore size, and connectivity features, which serve as the basis for chip etching prototypes. Step 2: Chip fabrication. Microchannels are designed to replicate the pore structure of the rock core. Chips are fabricated using high-temperature and high-pressure resistant materials. After cleaning and drying, the channel surface is modified as needed to simulate the pore characteristics of the oil reservoir. Step 3: System Setup and Debugging. Install the chip into the experimental platform, connect the micro-injection pump, high-speed microscope, and temperature and pressure controller to build the system, debug the airtightness, calibrate the equipment parameters, and set the temperature and pressure. Step 4: Displacement and Image Acquisition. Initiate the CO2-WAG displacement experiment, dynamically photograph the fluid morphology within the chip using a high-speed microscope, record the interface evolution, and save the image sequence; Step 5: Quantification of fold parameters. ImageJ software is used to process the image, extract the oil-displacement phase interface, quantify parameters such as fold wavelength and amplitude, and statistically analyze the distribution patterns of different displacement stages.

[0009] Characterizing CO2-WAG oil displacement interface wrinkles at the microscale using molecular dynamics simulations includes the following steps; Step 1: Sample Testing and Data Acquisition. Preprocess core samples and crude oil, determine rock mineral composition and analyze crude oil composition and molecular structure using XRD, simultaneously test rock contact angles, and obtain basic simulation data; Step 2: Molecular Model Construction. Based on measured data, a four-phase molecular model of CO2-oil-water-rock was constructed using MS software (replicating mineral crystals and crude oil characteristics), and geometric optimization was performed after assembly. Step 3: Simulation Parameter Settings. Set the reservoir matching temperature and pressure, suitable force field, and periodic boundary conditions. Optimize parameters such as simulation step size and number of iterations to ensure stable convergence of the simulation. Step 4: Simulation and Data Acquisition. Start the simulation, collect data on the interface molecular density distribution, contact angle, adsorption characteristics, and CO2 diffusion coefficient, and record the dynamic evolution of the interface morphology; Step 5: Data Processing and Mechanism Analysis. Simulated data is processed and combined with experimental verification to quantify the interface wrinkling characteristics and reveal the wrinkle formation and evolution mechanisms.

[0010] The beneficial effects of this invention are as follows: Addressing the current technical shortcomings of lacking dynamic and quantitative characterization methods for CO2-WAG oil displacement interface folds adapted to actual reservoir conditions, a multi-scale collaborative characterization system has been constructed. For the first time, it achieves full-dimensional characterization of interface folds from macroscopic reservoir response and microscopic pore evolution to molecular interaction mechanisms, completely breaking the limitations of traditional single-scale characterization and clearing key obstacles for in-depth mechanism exploration and technological upgrading in this field. Specifically, at the core scale, in-situ, real-time monitoring of the displacement process is achieved through a high-temperature, high-pressure CT scanning system. Combined with three-dimensional reconstruction and ImageJ quantitative analysis, the wavelength, amplitude, and distribution patterns of folds are accurately obtained. At the microfluidic chip scale, the pore structure of the real core is replicated, and the instantaneous morphological changes of the fluid are captured by a high-speed microscope, enabling visualized tracking of the dynamic evolution of folds. At the molecular dynamics simulation scale, a model is constructed based on experimental data, revealing the essence of fold formation at the molecular level. These three scales mutually verify and progressively advance each other, providing comprehensive data support for mechanism analysis. Meanwhile, the characterization method of this invention is standardized and controllable. The experimental equipment and simulation tools used are all standardized equipment commonly used in the industry. The characterization indicators are unified and clear, which facilitates horizontal comparison and reuse of results by different research teams. Moreover, it can be adapted to CO2-WAG oil displacement research of different types of reservoirs by adjusting core samples, temperature and pressure parameters, etc., which has important practical significance for promoting the research and development and industrial application of low-carbon and high-efficiency oil displacement technology. Attached Figure Description

[0011] Figure 1 Figures are attached to the abstract; Figure 2 A high-temperature, high-pressure core displacement CT scanning system for monitoring dynamic oil displacement processes; Figure 3 This represents the core framework and cross-sectional fluid and interface fold distribution during the oil displacement process. Figure 4 To establish a microfluidic chip experimental system; Figure 5The distribution of residual oil wrinkles at different times in water-driven oil recovery; Figure 6 A CO2-oil-water-rock molecular dynamics model; Figure 7 This is a method for calculating contact angle; Figure 8 Models for oil-water-rock with different wettability; Figure 9 This describes the distribution characteristics of oil and water in micro- and nano-pores. Detailed Implementation

[0012] This invention provides a multi-scale characterization method for CO2-WAG oil displacement interface wrinkles, including: Core-scale characterization of CO2-WAG oil displacement interface folds includes the following steps; Representative core samples from the Mahu reservoir were selected and processed into standard core columns that meet the specifications of a high-temperature and high-pressure core displacement system. The cores were then cleaned, dried to constant weight, and their basic parameters (porosity, permeability, density, etc.) were measured. Subsequently, the cores were saturated with simulated formation water and crude oil according to the original oil saturation requirements of the reservoir. The pretreated core was loaded into a high-temperature, high-pressure core displacement CT scanning system (such as...). Figure 2 As shown, the core holder was sealed, and the experimental temperature and pressure parameters were set to simulate the actual formation conditions of the reservoir. The CO2 and formation water injection modules and flow control system were debugged to ensure injection accuracy and stability. At the same time, the CT scanning equipment was calibrated to ensure the clarity of image acquisition. The displacement system was started, and a CO2-WAG water-gas alternating displacement experiment was carried out according to the preset plan. During the displacement process, continuous scanning images of fluid distribution inside the core were acquired in situ and in real time through the CT scanning system, and pressure change data throughout the displacement process were recorded simultaneously to capture the dynamic migration characteristics of fluid in the pores at different displacement stages. Based on a series of image data obtained from CT scans, professional 3D reconstruction software was used for image post-processing to remove noise interference, extract core pore structure information, construct a 3D network model of core pores, and accurately restore the spatial morphology of pores and the location of fluid occurrence. ImageJ image processing software was used to process CT scan images and cross-sectional images exported from 3D models to extract the interface region between residual oil and displaced phase. Software measurement tools were used to quantify and calculate key parameters of interface wrinkles, and to statistically analyze the distribution density and development range of wrinkles at different displacement stages. Figure 3 (As shown).

[0013] The microfluidic chip experimental system characterizes the wrinkles at the CO2-WAG oil displacement interface, including the following steps; Core samples were selected, and surface cleaning and drying pretreatment were performed first. Then, a full-size high-precision CT scan was used to scan the core to acquire images of the internal pore structure. The scanned images were denoised, segmented and reconstructed using 3D reconstruction software to generate a 3D pore network model of the core. Key pore slice images were extracted, and the pore morphology, pore size distribution and connectivity characteristics were analyzed to provide a prototype basis for chip etching. Based on the real structural characteristics of the core pore network slices, a chip microchannel pattern was designed (replicating the pore morphology, connectivity, and size ratio); quartz, which is resistant to high temperature and pressure and has strong chemical stability, was selected as the chip substrate, and a micro-nano etching process was used to prepare the micro-etched chip; after the chip was prepared, it was subjected to ultrasonic cleaning and drying treatment in sequence, and if necessary, the channel surface was modified to be hydrophilic or hydrophobic to simulate the surface characteristics of reservoir pores, for later use. The prepared micro-etched chip was installed on the experimental platform, and the components were connected according to the procedure, such as... Figure 4 As shown. A micro-injection pump is connected to the chip's fluid inlet (for delivering CO2, simulated formation water, and crude oil), a high-speed microscope is aligned with the chip's observation area (ensuring clear capture of the fluid morphology within the pores), and a temperature and pressure controller is connected to the chip cavity, constructing a complete high-temperature, high-pressure microfluidic chip experimental system. The system's airtightness is tested, the flow accuracy of the micro-injection pump is calibrated, and the high-speed microscope's imaging parameters (frame rate, resolution) are set. Temperature and pressure parameters are set to match the actual formation conditions of the oil reservoir, and the system is allowed to operate stably. The CO2 water-gas alternating displacement experiment was started by a micro-injection pump according to the preset scheme. During the displacement process, a high-speed microscope was activated to dynamically capture the instantaneous morphological changes of the fluid in the chip pores, record the interface evolution process between crude oil and the displacement phase in real time, and save the continuous image sequence simultaneously to ensure complete capture of the formation, development and change characteristics of interface wrinkles. Image sequences acquired by a high-speed microscope were imported into ImageJ image processing software. Preprocessing included image denoising and contrast enhancement to accurately extract the interface region between crude oil and the displaced phase within the pores. Key parameters (wavelength, amplitude) of the interface folds were quantified using software measurement tools, and the distribution density, development range, and evolutionary patterns of folds at different displacement stages were statistically analyzed (e.g.,...). Figure 5 (As shown).

[0014] Molecular dynamics simulations characterize the wrinkles at the CO2-WAG oil displacement interface, including the following steps; Representative core samples and crude oil samples from the reservoir were selected, and X-ray diffraction (XRD) was used to test the mineral composition and content of each component in the rocks, clarifying the main composition of the rock surface. After dehydration and degassing, crude oil samples were analyzed using mass spectrometry-chromatography (MS / GC) to determine the component distribution, main molecular structure, and relative content, thus establishing the prototype of the characteristic molecular model for crude oil. Simultaneously, a Krüss DSA100 droplet shape analyzer with a seated drop method module was used to test the rock contact angle, obtaining basic interfacial characteristic data to provide experimental reference for simulation. Based on the above experimental data, molecular-scale models were built using Materials Studio software, such as... Figure 6 As shown in the diagram, firstly, a rock surface model was constructed based on XRD results (replicating the crystal structure and surface properties of major minerals); a crude oil molecular model was built by selecting representative molecules, and an oil phase system was constructed according to the component ratios; CO2 molecular models and water molecular models were constructed separately to form gas and water phase systems. Subsequently, the oil phase, water phase, and CO2 phase were arranged in an orderly manner on top of the rock surface model according to the actual displacement scenario, assembling a complete CO2-oil-water-rock four-phase system. The model was then subjected to preliminary geometric optimization to eliminate unreasonable interatomic forces. Temperature, pressure, and boundary conditions are set for the completed multiphase model to simulate the actual formation temperature and pressure range of the reservoir. A suitable force field is used to describe the interactions between molecules and between molecules and the rock surface. Periodic boundary conditions are set (to meet the needs of multiphase interface simulation), simulation step size, number of iterations, and trajectory output frequency are set, and energy minimization algorithm and molecular dynamics simulation parameters are optimized to ensure stable convergence of the simulation process and to accurately capture the molecular behavior of the interface. Molecular dynamics simulations were performed, running the simulation system under set temperature and pressure conditions, and simultaneously acquiring simulation trajectory data. During the simulation, the density distribution of CO2, oil, and water molecules at the oil-water and oil-rock interfaces was calculated and recorded. The interface contact angle (e.g., ...) was calculated using the MS software analysis module. Figure 7 As shown), characterizing changes in interfacial wettability (e.g. Figure 8 As shown); simultaneously, the adsorption amount, adsorption sites, and adsorption strength of molecules on the rock surface are analyzed to obtain interfacial adsorption characteristics (such as...). Figure 9 (As shown). In addition, separate simulation groups were set up for different temperature and pressure conditions to calculate the diffusion coefficient of CO2 molecules in the oil phase and record the dynamic evolution of the interface morphology under each condition.

[0015] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A multi-scale characterization method for CO2-WAG oil displacement interface wrinkles, characterized in that, The representation methods include the following three scales: (1) Core-scale characterization Core samples representing the reservoir characteristics were selected, cleaned, dried, and their basic parameters, such as porosity, were measured. Simulated formation water and crude oil were saturated at the original oil saturation level. The samples were then loaded into a high-temperature, high-pressure (CT) displacement system. Formation temperature and pressure conditions were set under sealed conditions, and CO2, formation water injection and flow control, and CT scanning equipment were adjusted to ensure accuracy. A CO2-WAG displacement experiment was initiated, and in-situ real-time CT images of fluid distribution within the core samples were acquired. Pore structure information was extracted, and a three-dimensional network model was constructed. Finally, ImageJ software was used to extract and quantify the size and distribution of fold waves, and the distribution patterns at different displacement stages were statistically analyzed. (2) Microfluidic chip scale characterization After pretreatment of the core sample, pore sections, morphology, pore size, and connectivity characteristics were extracted using high-precision CT scanning and 3D reconstruction, serving as the basis for chip etching prototypes. Microchannels were designed to replicate this pore structure, and chips were fabricated using high-temperature and high-pressure resistant materials through micro-nano etching. After cleaning and drying, the channel surface was modified as needed to simulate reservoir porosity characteristics. The chips were then mounted on an experimental platform, connected to a micro-injection pump, a high-speed microscope, and a temperature and pressure controller to construct the system. Air tightness was adjusted, equipment parameters were calibrated, and formation temperature and pressure conditions were set. A CO2-WAG displacement experiment was initiated, and the fluid morphology within the chip was dynamically captured using a high-speed microscope. Interface evolution was recorded, and image sequences were saved. Images were processed using ImageJ software to statistically analyze the distribution patterns of different displacement stages. (3) Microscale characterization of molecular dynamics simulation After preprocessing core and crude oil samples, rock mineral composition and crude oil composition and molecular structure were tested by XRD, and rock contact angle was measured simultaneously to obtain basic simulation data. Based on the measured data, a molecular model replicating the characteristics of mineral crystals and crude oil was constructed using Materials Studio software, and geometric optimization was performed after assembly. Subsequently, temperature and pressure conditions, suitable force fields and periodic boundary conditions matching the reservoir were set, and parameters such as simulation step size and number of iterations were optimized to ensure stable convergence of the simulation. Finally, molecular dynamics simulation was started to collect the molecular density distribution, contact angle and adsorption characteristics of the interface, and the dynamic evolution of the interface morphology was recorded simultaneously.

2. The multi-scale characterization method for CO2-WAG oil displacement interface wrinkles according to claim 1, characterized in that, The image processing software is ImageJ.

3. The multi-scale characterization method for CO2-WAG oil displacement interface wrinkles according to claim 1, characterized in that, The microfluidic experimental model was fabricated using temperature- and pressure-resistant quartz material.

4. The multi-scale characterization method for CO2-WAG oil displacement interface wrinkles according to claim 1, characterized in that, In the molecular dynamics simulation, the rock composition was silica (with quartz being the most abundant mineral). The dynamics simulation used the COMPASS force field, with the Berendsen method for pressure control and the Andersen method for temperature control.

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