Abstract

With the rapid development of China’s economy, a series of environmental problems have emerged, and the large-scale emission of CO2 has become the main cause of global warming. Carbon capture, utilization, and storage (CCUS) is an important technological means to address climate change. The technology mainly captures CO2 in the energy production process and converts it into useful products or safely stores it in underground reservoirs, thereby reducing the concentration of CO2 in the atmosphere. CO2 storage technology, as an important part of carbon neutrality, has become the key to solving the problem of carbon emissions. Shale clay minerals, as a key site for CO2 geological storage, provide a large surface area and a large number of pores for adsorption, but the adsorption mechanism and the transport law of CO2 in the pores during storage still require extensive research. First, the Monte Carlo method was used to simulate the adsorption characteristics of CO2 in kaolinite pores. The adsorption configuration was established using the molecular simulation software Lammps, and the changes in CO2 density, isothermal adsorption curve, and CO2 potential energy distribution in kaolinite pores were analyzed. The main factors affecting CO2 adsorption and the reasons for the differences in adsorption were comprehensively analyzed. Secondly, based on the research on adsorption characteristics, molecular dynamics method was used to carry out simulation research on supercritical CO2 flow during adsorption. During the flow process, the potential energy of CO2 adsorbed on the kaolinite wall changed, causing desorption. Moreover, the larger the pore size, the greater the degree of desorption. In addition, slip occurred at the kaolinite wall during supercritical CO2 flow, resulting in slip length. With the increase of driving force, the slip length gradually increased, which was due to the decrease of the wall resistance to flow caused by the decrease of CO2 density in the first adsorption layer with the increase of driving force. Temperature changes also affected the CO2 slip length. When the temperature rose, the movement of CO2 molecules became more intense, the curvature radius of the flow curve gradually increased, and the slip length calculated increased with the increase of temperature. At the same time, the increase in temperature caused the potential energy of CO2 to increase, and the macroscopic behavior of CO2 molecules became less likely to be adsorbed. On the other hand, when the temperature decreased, the potential energy of CO2 decreased, and the difference in potential energy between CO2 molecules and the wall increased, making CO2 molecules more easily adsorbed and increasing the adsorption amount.

Abstract

CO2 transport is a key part of the national ” carbon peak, carbon neutral ” action. At present, it is mainly transported by tankers, which has many problems such as high transportation cost, high traffic risk, low reliability of continuous supply of carbon sources affected by weather and traffic. To this end, some enterprises began to use pipeline transportation to achieve stable carbon source supply, and pipeline transportation has the advantages of low cost and low risk. However, pipeline construction is to use 10 meters of pipes to form a pipeline by welding. The construction period of pipeline construction is long, the construction cost is high, and there are many welding points and many pipeline risk points. In view of the above problems, a continuous composite pipe is formed through thinking innovation and design evaluation. The design of the continuous composite pipe is composed of three layers of thermoplastic polymer layers on both sides of the intermediate metal layer. The thermoplastic polymer of the inner lining layer prevents internal environmental corrosion and transmission medium enhancement layer. The intermediate metal layer resists circumferential stress and axial force, and the outer thermoplastic polymer prevents external corrosion and wear. The continuous composite pipe can be processed into a section of 800 m ~ 1500 m according to different pipe diameters. The construction of CO2 transmission pipeline by this process will greatly reduce the welding point of the pipeline, improve the safety of the pipeline, greatly shorten the construction period, reduce the labor intensity, reduce the construction cost, and provide valuable technical support for the implementation of the national ” carbon peak, carbon neutralization ” action.

Abstract

Carbon dioxide injection can help solve two issues in shale reservoir production. Firstly, it can reduce carbon emissions while, secondly, improving unconventional reservoir recovery. There are many controlling factors for CO2 injection to enhance oil recovery in shale reservoirs, and the effect of field implementation varies greatly. The key to popularizing this extraction technology is determining the main controlling factors of CO2 displacement efficiency. Using CO2 shale displacement laboratory results from Tovar et al. (2021), the grey correlation analysis method was used to determine the main controlling factors affecting core oil displacement efficiency, such as shale reservoir physical parameters (rock compressibility, porosity, median pore size, matrix permeability, TOC and oil saturation) and engineering parameters (soaking time and injection pressure). The genetic algorithm (GA) was introduced to optimize the backpropagation (BP) neural network to construct the prediction model of the CO2 indoor displacement experiments in shale core. The results showed that the injection pressure of engineering parameters, the CO2 soaking time of gas injection parameters, and the porosity of shale physical parameters were the main controlling factors affecting the oil displacement efficiency. The prediction accuracy of the genetic neural network model improved, and the coefficient of determination (R2) reached 0.983. Compared to the conventional neural network model, the mean absolute error (MAE) was reduced by 30%, the root mean square error (RMSE) was reduced by 46%, and the R2 increased by 11%. Optimizing the learning and training of the prediction model significantly reduces the cost of laboratory experiments. The deep learning model completed by training can intuitively show the influence degree of input parameters on output parameters, providing a theoretical basis for studying CO2 displacement mechanism in shale reservoirs.

Abstract

Using CO2 replacement to extract natural gas hydrates can not only achieve CO2 storage, but also ensure the safety of natural gas hydrate extraction, which is one of the necessary ways to achieve China’s “dual carbon goals”. However, the existing research on CO2 replacement extraction of natural gas hydrates is not yet mature, making it difficult to support large-scale CO2 storage and commercial extraction of natural gas hydrates. Therefore, this article systematically elaborates on the current situation and necessity of CO2 storage, the distribution range and development challenges of natural gas hydrates in China, and analyzes the feasibility and wellbore integrity issues of CO2 replacement extraction of natural gas hydrates. Research has shown that: CO2 emissions are increasing year by year, seriously affecting the living environment of humans and other species, and must be sealed. China is rich in natural gas hydrates, but conventional mining can easily affect the stability of the strata and trigger natural disasters such as submarine landslides. Since single displacement reaction is a spontaneous process and CO2 hydrate sediment intensity is higher, the feasibility of CO2 replacement for natural gas hydrate exploitation is high. It is necessary to focus on the corrosion integrity of the cement and underground tubing during the replacement mining process.

Abstract

In the long-term storage process of CO2 storage wells, the integrity of the cement is vulnerable to damage or even failure due to factors such as cementing quality, corrosion, stress change, etc., resulting in microcracks or leakage channel, resulting in the inability to guarantee the effectiveness of the storage. For this reason, this paper establishes a mechanical model of downhole casing-cement-formation combination in CCUS well, and studies the influence of wellbore pressure, temperature change, performance parameters of cement, etc. on the stress distribution of cement; The leakage characteristics of the combination are studied through the sealing integrity test of the combination, and the influence of different factors on the CO2 leakage rate is discussed in combination with the leakage model of the cement. The research results show that (1) the integrity failure of the cement mainly reflects the failure of the seal due to the leakage channel, which can not achieve effective sealing; (2) The leakage rate of CO2 is directly proportional to the permeability and cross-sectional area of the leakage channel, but the influence of the size of the cement on the leakage is limited; (3) The CO2 leakage rate increases significantly with the increase of the pressure and temperature of the storage layer, and both of them are nonlinear. (4) The leakage rate of CO2 is basically proportional to the crack width of cement. In theory, when the crack width of cement reaches 640 μm, the leakage rate of CO2 exceeds the safety value, and the leakage rate of CO2 increases exponentially with the increase of the crack opening of cement. The slight change of the crack opening will greatly increase the leakage rate of CO2. This paper reveals the potential leakage path and law of cement in CCUS well, and the research results can provide guidance for the effectiveness of long-term storage design of CCUS well.

Abstract

Oil recovery is increased by about 15% by CO2 flooding in Daqing Oilfield. However, problems such as corrosion,gas channeling, and freezing blocking occur frequently in the process of production. Since ordinary carbon steel is generally adopted for well completion, CO2 corrosion affects the well life and the overall development of the test area. CO2 flooding low-cost chemical corrosion prevention technology is formed, and the corrosion rate is only 0.065mm/a under the CO2 partial pressure of 5MPa and the temperature of 80℃. Due to the low gas viscosity and the heterogeneity of the oil layer, viscous fingering and channeling are easy to occur. Therefore, acid-resistant and oil-resistant CO2 foam channeling sealing agent was developed. Under the condition of pH=3 and oil saturation of 60%, the foaming volume was 430mL and the half-life was 83h. In the process of delaying gas channeling by water alternating gas injection, CO2 hydrate is easy to be generated, which leads to freezing and blocking of wellbore and surface pipelines, resulting in low production rate. Therefore, a low-temperature and efficient plugging removal technology was developed, which realizes 100% dissolution of freezing and blocking at -20℃ for the first time. The improvement of a series of low cost oilfield chemical technologies of CO2 flooding has improved the well running rate, reduces the operation cost, and provides technical support for the sustainable and effective development of CO2 flooding.

Abstract

Gas prodution in the CO2 flooded production wells of low permeability reservoirs in Daqing Oilfield is increasing year by year, which makes conventional pump inspection operation impossible, and leads to the high cost of the operation with pressure. A new type of solid-free killing fluid is developed to balance formation pressure and ensure the safe field operation. The killing fluid is mainly composed of weighting agent, corrosion inhibitor, anti-gas invasion synergist and filtrate reducer. Laboratory performance evaluation results show that the density of the kill fluid can be adjusted in the range of 1.0~2.0g/cm3, the corrosion rate is less than 0.070mm/a, the anti-swelling rate can reach 95.9%, the API water filtration loss is less than 10mL/30min, and the water loss at high temperature and high pressure (4.1MPa, 85℃) is less than 10mL/30min after CO2 gas invasion. It has the characteristics of solid-free, low corrosion, low filtration loss, strong anti-swelling, and anti-gas invasion, etc., which can meet the requirement of well killing for CO2 flooding in peripheral low permeability reservoir.

Abstract

Optimized utilization of CO2 for Fracturing and EOR alongside CCS will not only make a positive contribution to the climate account; it can overhaul the future of the oil and gas sector. Our study has been focused on modifying rheological properties of CO2 (liquid and super critical phase) to provide favorable fluid systems in the application of CO2 EOR in combination with CO2 fracturing that would widen the operation window of CO2 Utilization.

Abstract

The best way to connect CCUS-EOR carbon source and carbon sink is Supercritical long-haul pipeline containing impurities of carbon dioxide. Due to the variety of source of carbon and capture technologies, the combination of carbon source impurities has diversity. Carbon sink also has certain requirements on carbon source components owing to the specificity of reservoir and the requirements of oil displacement and storage injection system facilities. To sum up, it is necessary to study the limit of carbon source temperament composition which can not only satisfy the matching of carbon source and carbon sink, but also ensure the safe long-distance transport of carbon dioxide containing impurities in the supercritical phase [10]. This article obtains from the source of carbon source and capture process analysis of carbon source, and the content limits of various impurities are studied according to the requirements of carbon sink injection engineering and oil reservoir enhanced oil recovery, which in all at the same time in the process of research and analysis through the impurities in supercritical carbon dioxide/dense-phase long-distance pipeline safety transportation technology requirements and characteristics of Daqing area meteorological environment, in the end, the suitable source – sink matching temperament is given. Impurities in supercritical carbon dioxide long-distance pipeline temperament limit mainly include carbon dioxide, water, total quantity of non-condensable gas and hydrogen, hydrogen sulfide, nitrogen oxides, carbon monoxide, sulfur oxide content limit value, whether its value is scientific or not is not only crucial to the safe operation of the pipeline, but also have a huge impact on the benefit and effect of CCUS-EOR as well as the investment and cost of capture construction. This study will provide technical support for the construction and operation of the whole industrial chain of CCUS-EOR in Daqing Oilfield.

Abstract

CO2 pipeline transportation is the most economical and efficient way to realize CCUS (Carbon Capture, Utilization and Storage) technology, but there is a risk of ductile fracture during its operation due to engineering problems such as pipeline defects, fatigue and corrosion. In this study, a modified Battelle Two-Curve Model and a crack arrest performance evaluation model based on the crack arrest efficiency were established for the pipeline overall reinforcement structure and coaxial crack arrestor, respectively, and the models were verified experimentally to be reliable. Based on the supercritical CO2 pipeline transportation scheme designed for Yanchang Oilfield with storage capability of 4 million t/a, the crack arrest performance of five pipelines was evaluated. For the non-crackable pipelines, the pipeline overall reinforcement and the coaxial crack arrestor are applied, based on the crack arrest requirement and engineering economy, respectively. This study provides references and suggestions for the design and safe operation of supercritical CO2 pipelines containing impurities in the future.