CO2-enhanced shale gas recovery technology (CO2-ESGR) is one of the most potential carbon capture, storage and utilization (CCUS) technologies to mitigate the greenhouse effect and achieve the goal of carbon neutrality. The adsorption characteristics of CO2 and CH4 in shale are the key factors for CO2-ESGR, and fast and accurate prediction of adsorption capacity is still challenging, especially for the mixture of CO2 and CH4. This paper conducted a prediction study of CO2 and CH4 adsorption in shale in a large range of temperatures, pressures and total organic carbon (TOC) by employing the Langmuir model and the back propagation artificial neural network (BP-ANN) method. The key parameters of Langmuir model, saturation adsorption capacity Q0 and Langmuir pressure PL, were optimized for improving the prediction accuracy of CO2 and CH4 adsorption capacity in shale, and the determination coefficient of the improved model was R2=0.9691. In addition, the activation function, number of hidden layer neurons, learning efficiency and other key parameters of the BP-ANN were optimized by using data normalization method. The determination coefficients R2 of the BP-ANN prediction to experimental data for pure CH4 and pure CO2 were 0.9921, 0.9867 , respectively, a little better than the improved Langmuir model. The improved Langmuir model and BP-ANN method proposed in this study can accurately predict the adsorption characteristics of CO2 and CH4 in shale, which can provide theoretical support for CO2-ESGR.
Carbon capture, use and storage (CCUS) has been widely developed worldwide as a technology with great potential for large-scale emission reduction. The petroleum industry is a “three high” industry with high energy consumption, high pollution and high carbon emission. Under the social development of carbon peaking and carbon neutrality, in order to achieve the goal of carbon peaking and carbon neutrality, promoting the coordinated and sustainable development of the petroleum industry and ecological environment has become a hot issue facing today. On the basis of the new demands brought by carbon capture, utilization and sequestration in current development and the concrete measures and results taken by our country for achieving carbon peak and carbon neutralization goals, this paper analyzed the current development status of carbon neutralization goals, and investigated and analyzed the development path for the future green development in the petroleum field under carbon peak and carbon neutralization goals. The carbon peaking contribution value of the petroleum industry and the estimated amount of carbon peaking contribution were obtained through the emission prediction. The assisting ways of the petroleum industry in carbon neutralization were analyzed, and the contributions to carbon neutralization through underground storage and enhanced oil recovery by carbon dioxide capture were also analyzed.
CCUS is widely seen as a practical solution to the challenge of rising global temperatures. Enhanced oil recovery (EOR) using CO2 flooding, as part of CCUS, can achieve both long-term geological sequestration of greenhouse gases and improved crude oil recovery, bringing significant economic benefits. In a low-permeability field, long-term water flooding is no longer able to achieve good oil recovery results, and CO2 flooding methods are then adopted. Previous studies on CO2 storage in reservoirs have often used qualitative and static characterization methods for CO2 storage mechanisms. In this paper, based on the CO2 storage mechanisms in depleted reservoirs, a method for characterizing the CO2 storage mechanisms in low-permeability reservoirs is developed through quantitative characterization and dynamic analysis of the key parameters of the four storage mechanisms. A low permeability reservoir mechanism model is established, and the various characteristics of the four storage mechanisms with time and space as well as the distribution law are analyzed. Through this study, it can be concluded that structural and stratigraphic trapping and residual gas trapping are the main CO2 storage methods in low permeability reservoirs, while non fluid gas in the reservoir is the main contributor to residual gas trapping. In the later stage of storage, some CO2 is converted into residual gas in the reservoir. The effect of dissolution trapping is poor, and the influence of mineralization reaction on reservoir porosity in low permeability reservoirs is relatively small.
The CCUS/CCS process is an important means to achieve carbon neutrality goals. From the current scale of the industry, a complete industry chain covering carbon capture, transportation, utilisation, and storage has been established, led by state-owned enterprises. However, the development of the industry chain faces high barriers to cross-industry cooperation among upstream, midstream, and downstream enterprises as well as difficulties in matching cross-regional sources and sinks, making the coordination of the entire industry chain more difficult. In addition, there is a lack of large-scale industrial demonstration of the process in China; at the same time, the business model is not mature. This paper proposes policy-making suggestions to promote the construction of the CCUS industry chain from four aspects: ①providing special incentive policies for high-cost links such as carbon capture and carbon storage; ②creating marketing and benefit-sharing mechanisms among upstream, midstream, and downstream enterprises in the industry chain; ③ formulating special laws, regulations, and standard system for each link of CCUS/CCS project construction and operation; ④setting up programs for leading enterprises to integrate various links of the industry chain. To systematically organize the development characteristics of China’s CCUS industry, this paper recommends three policies to promote the construction of the CCUS industry chain: ①strengthening the construction of basic databases and collaborative sharing platforms, and accelerating the construction of CCUS infrastructure; ②accelerating the construction of industrial clusters by utilizing mechanisms such as division of labor and collaboration between upstream, midstream, and downstream enterprises in the industrial chain, and using business models that create mutual benefit, complementarity, and synergy; ③ issuing special incentive policies for carbon capture and sequestration, formulating marketization and benefit distribution mechanisms for upstream, midstream, and downstream enterprises in the industrial chain, and formulating special laws, regulations, and standards for CCUS/CCS systems.
Injection of CO2 into hydrocarbon reservoirs is an attractive method to enhance hydrocarbon recovery and CO2 storage. However, the non-homogeneity of hydrocarbon reservoirs can lead to low sweep efficiency during CO2 flooding and leakage during CO2 storage. This inhomogeneity can be caused by highly permeable matrices and microfractures, which provide channels for CO2. Gel plugging technology is an effective technique to prevent gas escape and plays an important role in CO2 flooding and storage. Polymer gel system has good injection ability and can achieve in-depth plugging. Particle gel system has high strength, acid and temperature resistance, and can realize long-term sealing. Foam gel has good injectability and cost advantages, and less damage to the formation. Inorganic gel has good injectability and strong chemical stability. This paper reviewed the research progress and existing problems of four kinds of hydrogels and looked forward to the future development of the CO2 consistency control gel systems.
CO2 sequestration which is one of the important means to avoid global warming today provides an economically viable technical means to reduce greenhouse gas emissions. To maximize the sequestration efficiency while evaluating the effect of formation uncertainty, a numerical simulator of multiphase flow is required to simulate high-dimensional nonlinear multiphase flow within a non-homogeneous porous medium. Due to the inherent inhomogeneity of the formation of porous media and the nonlinear coupling of multiple complex physical processes, a significant amount of repetitive numerical simulation processes impose considerable computational costs and require prolonged computational time to obtain simulation results. In this paper, we propose an efficient and fast flow surrogate modeling process for deep learning, proposing that the extended hyperparameter optimization process will incorporate the neural network architecture and the loss function as relevant parameters into the optimization process. Subsequently, we conducted experiments based on the workflow proposed in this study for the case of CO2 storage in a homogeneous deep saltwater layer and achieved accurate predictions at 120-time steps with mean MSE of 5E-5 and 2E-5 for gas saturation and pressure, and MSSIMs of 0.9989 and 0.9998, respectively, under different production parameters and well placement settings.
CO2 transportation is an indispensable intermediate link in the CCUS industry chain. When transporting large capacity and long-distance CO2 with impurities, pipeline transportation is more safe and more efficient. In the event of accidental CO2 pipeline leakage or engineering venting process, the sudden phase change and expansion of CO2 in the pipeline will lead to a sudden drop in the temperature of the pipeline, which will increase the risk of pipeline rupture. The research on the change of temperature on the wall of the pipeline during the venting process and the heat transfer properties of phase change has essential significance in avoiding the cracking of cracks and reducing the risk of crack expansion. In order to conduct small-scale pipeline safety research, a 16m long, 100mm inner diameter pipeline test device is set up. The distribution of temperature in the pipeline, the temperature on the pipe wall and the change of pressure in the pipeline in the process of slow valve opening and instantaneous full-diameter venting of nitrogen-containing supercritical phase CO2 were measured by venting experiment with inner diameter of 25mm. The influence of different venting modes on the depressurization of the pipeline, the temperature change inside and outside the pipeline, and the influence of phase change on the heat transfer in the pipeline were analyzed. The pressure, temperature and wall temperature values at the front, middle and rear sections of the pipeline were measured. It can be seen from the results that at the same elevation, the wall temperature drop at the vent end is smaller than that at the medium injection end, and the trend is the same as that of the temperature change in the pipeline. On the same section, the wall temperature drop at the bottom of the pipeline is the largest, and it is much larger than the wall temperature drop at the top and middle of the pipeline. At the injection end of the pipeline, the wall temperature is lower than the bottom temperature of the pipeline due to the continuous phase change and heat absorption of the medium. Compared with instantaneous full-diameter venting, valve opening venting has a longer phase change heat transfer time, larger wall temperature drop, and greater brittle fracture risk.
Aiming at the problems of sealing and tearing failure of packer rubber cylinder during CO2 downhole injection.Using Comsol multi-physical field simulation software, the packer rubber cylinder model in SC-CO2 environment is established. Based on the thermal analogy method to simulate the gas invasion swelling process, analyze the deformation and stress of the rubber cylinder caused by temperature, pressure and CO2 gas invasion swelling.The results show that under the SC-CO2 environment, with the influence of gas invasion and swelling, the packer rubber cylinder body is prone to large deformation, and the maximum shear stress is significantly increased, leading to shear failure of the rubber cylinder.Reducing the initial setting pressure can alleviate the impact of deformation, but the reduction of the maximum contact pressure can easily cause the rubber cylinder to lose its seal.Analyze the change rule between various factors and the maximum contact pressure of the rubber cylinder, which provides a certain theoretical basis and technical support for improving the sealing performance of the packer rubber cylinder in the SC-CO2 environment.
CO2 flooding is one of the main methods to enhance oil recovery under the background of carbon neutralization and carbon peak. In some fields, however, injected gas is mainly produced gas that contains a lot of acid gas. The EOR effect of acid gas flooding is rarely mentioned in the literature. Therefore, it is necessary to study the displacement process of acid gas flooding. In this paper, acid gas composed of H2S and CO2 is studied. Oil samples from typical blocks of T reservoir are selected to study the EOR effect of acid gas. Under different displacement pressure, different proportions of acid gas were used to carry out slim tube experiments. The percentages of H2S and CO2 in acidic gases are 0%, 20%, 40%, 50%, 60%, 80% and 1, respectively. The experimental process is to fill the tube with crude oil and then flood the oil with acid gas with different proportions of H2S and CO2 content at a constant temperature. The ultimate recovery factor is the displacement efficiency, obtained at 1.2 pore volume gas injection or without oil production. Displacement experiments under different pressures were also carried out. The results show that the displacement efficiency increases with the increase of displacement pressure at the same temperature, oil composition and gas composition. The experimental results also show that, at the same temperature, oil composition and displacement pressure, displacement efficiency increases with the increase of the proportion of acid gas in the injected gas. The production gas of high sulfur gas field is injected back into the formation theoretically, and the effect of acid gas mixed displacement composed of H2S and CO2 is studied, which provides a new direction for the application of H2S and CO2.
For the coupled reaction-extraction-alcohol precipitation process, it is necessary to investigate the effect of ethanol on MgCO3·3H2O at the molecular level. In this study, DFT calculations of the nesquehonite growth models were performed to analyze the growth unit adsorption mechanism in the presence of solvent molecules. Furthermore, molecular dynamics simulations of solid-liquid interface models and Mg(HCO3)2 solution boxes were conducted. The calculated results showed that with the ethanol eﬀects, the adsorption rate of GU was increased by weakening competition of water molecules and the transformation rate of Mg(HCO3)2 to nesquehonite was raised by reducing the coordination number of magnesium ions.