One of the main applications of carbon capture, utilization, and storage (CCUS) technology in the industry is carbon-dioxide-enhanced oil recovery (CO₂-EOR). However, accurately and rapidly assessing their application potential remains a major challenge. In this study, a numerical model of the CO₂-WAG technique was developed using the reservoir numerical simulation software CMG (Version 2021), which is widely used in the field of reservoir engineering. Then, 10,000 different reservoir models were randomly generated using the Monte Carlo method for numerical simulations, with each having different formation physical parameters, fluid parameters, initial conditions, and injection and production parameters. Among them, 70% were used as the training set and 30% as the test set. A comprehensive analysis was conducted using eight different machine learning regression methods to train and evaluate the dataset. After evaluation, the XGBoost algorithm emerged as the top-performing method and was selected as the optimal approach for the prediction and optimization. By integrating the production prediction model with a particle swarm optimizer (PSO), a workflow for optimizing the CO₂-EOR parameters was developed. This process enables the rapid optimization of the CO₂-EOR parameters and the prediction of the production for each period based on cumulative production under different geological conditions. The proposed XGBoost-PSO proxy model accurately, reliably, and efficiently predicts production, thereby making it an important tool for optimizing CO₂-EOR design.

CCUS-EOR is a crucial technology for reducing carbon emissions and enhancing reservoir recovery. It enables the achievement of dual objectives: improving economic efficiency and protecting the environment. To explore a set of CCUS-EOR reservoir screening criteria suitable for continental reservoirs in China, this study investigated and compared the CCUS-EOR reservoir screening criteria outside and in China, sorted out the main reservoir parameters that affect CO₂ flooding, and optimized the indices and scope of CCUS-EOR reservoir screening criteria in China. The weights of parameters with respect to their influences on CCUS-EOR were determined through principal component analysis. The results show that there are 14 key parameters affecting CO₂ flooding, which can be categorized into four levels. For the first level, the crude oil-CO₂ miscibility index holds the greatest weight of 0.479. It encompasses seven parameters: initial formation pressure, current formation pressure, temperature, depth, C₂–C₁₅ molar content, residual oil saturation, and minimum miscibility pressure. The second level consists of the crude oil mobility index, which has a weight of 0.249. This index includes four parameters: porosity, permeability, density, and viscosity. The third level pertains to the index of reservoir tectonic characteristics, with a weight of 0.141. It comprises two parameters: permeability variation coefficient and average effective thickness. Lastly, the fourth level focuses on the index of reservoir property change, with a weight of 0.131, which solely considers the pressure maintenance level. Based on the CCUS-EOR reservoir screening criteria and index weights established in this study, comprehensive scores for CCUS-EOR were calculated for six blocks in China. Among these, five blocks are deemed suitable for CCUS-EOR. Based on the comprehensive scoring results, a planning for field application of CCUS-EOR is proposed. The study provides a rational method to evaluate the CCUS-EOR reservoir screening and field application in continental reservoirs in China.

Separate-layer CO₂ flooding has increasingly been used to improve the overall development of multi-layer heterogeneous reservoirs. Due to their field technical limitations, layer combinations have to be carried out to reduce the number of layer-groups required for the separate injection of CO₂. Currently there are few studies of the method of designing layer combinations. In field practice, the layer combinations are often made based on the permeability ratio of the layers to be developed, but it is not possible to accurately obtain the optimal scheme in many cases. Therefore, in this paper, a new design and optimization method based on the weighted standard deviation of permeability is proposed, which comprehensively considers the effects of multiple geological and fluid properties in different layers. The new method is applied to study the layer combination schemes in separate-layer CO₂ flooding in H block, Daqingzijing Oilfield, Jilin, China. The prioritization of all of the schemes is obtained via the method, and a related numerical model is also established to perform verification and quantitative analysis. The results show that designing layer combinations using the new proposed method can achieve better development effect than using the conventional permeability ratio based method. It can achieve a more uniform interlayer CO₂ displacement with an obvious improvement in the CO₂ swept volume in low permeability layers and a higher overall oil recovery. According to the numerical simulation results, using the optimal layer combination scheme designed via the new proposed method, the ten-year swept volume of CO₂ in the low permeability layer can be increased by 16.2%, and the ten-year overall oil recovery efficiency can be increased by 3.3%, with both measures showing a remarkable improvement. The work can provide a significant reference point for the field design of layer combinations in separate-layer CO₂ flooding.

Due to its economic benefits and the ability to reduce carbon emissions on a large scale, the CCUS-EOR project has been widely promoted and implemented globally. By using carbon dioxide flooding, oil water transition zone reservoirs that were once considered worthless may have new potential for development because of its rich geological reserves and high quality carbon sequestration conditions. Unlike water flooded layer, the oil in the TZ is unsaturated rather than residual oil after water flooding, which would lead to special oil-water seepage law of initial oil saturation. It is necessary to clarify special oil-water seepage law of oil-water transition zone to evaluate its production & storage potential. In this paper, we present a series of experiments to characterize the relationship between residual oil saturation and initial oil saturation. Cores in four different permeability and oil in four different viscosity are used to simulate different reservoir conditions, and that CO2 immiscible flooding experiments for each cores permeability and oil viscosity are performed with four different initial oil saturation. A total of 36 sets of CO2 flooding experiment data are used to draw the initial oil saturation & residual oil saturation chart. The results show that the residual oil saturation depends on the initial oil saturation rather than constant under certain conditions of core and oil. Under the condition of low permeability and high oil viscosity, the influence of initial oil saturation on residual oil saturation is relatively strong. The initial oil saturation & residual oil saturation chart can accurately calculate the residual oil saturation, initial water cut and final recovery based on the core permeability, oil viscosity and the initial oil saturation which is the first time to put forward this kind of chart and of the great significance to evaluate the recovery potential of the TZ.

Enhanced Oil Recovery (EOR) techniques, particularly CO2 injection, have garnered significant attention due to their potential to improve oil extraction efficiency while concurrently sequestering CO2. The impact of carbon dioxide on the properties of the hydrocarbon-water interface is currently not well established. The influence of CO2 on the interfacial characteristics of crude oil-water systems was examined using molecular dynamics (MD) simulations. Eight distinct interface models, varying in the ratio of polar to non-polar crude oil components, were constructed. The effect of CO2 was characterized by calculating IFT, molecular conformation and orientation, and oil-water-CO2 interaction energies. This study reveals three key findings: 1) As the concentration of CO2 increases, the IFT between polar and non-polar crude oils diminishes and ultimately plateaus. 2) Non-polar crude oil molecules exhibit ordered inter facial arrangements, while polar molecules are randomly distributed. Specifically, CO2 promotes perpendicular orientation of linear non-polar molecules and parallel alignment of cyclic non-polar molecules at the interface; 3) CO2 strengthens interactions between non-polar crude oil molecules, while initially weakening and then stabilizing interactions between polar molecules. These results provide crucial insights into hydrocarbon-water-CO2 IFT behavior and offer a theoretical basis for optimizing related industrial processes.