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

Post combustion capture using chemical absorption is one of the most mature technologies, which can effectively reduce CO2 emissions from plants. But it usually comes with the cost of high energy consumption. Aiming to reduce the regeneration energy consumption of post combustion CO2 capture technology, a novel ammonia based CO2 capture process with bipolar membrane electrodialysis(BMED) and CO2 regeneration reactor is designed. In the CO2 regeneration reactor, the CO2 loaded by rich solvent is completely released and collected due to the reactions between the rich solvent and strong acid. After that, energy consumption of the BMED unit is effectively reduced because there is no bubble formation in the cell during the electrodialysis process. The performance of conventional amine based process and the novel process is evaluated by simulation and calculation. Result shows that the CO2 regeneration energy consumption of the novel process is as low as 1.80MJ/kgCO2, which is much lower than that of the conventional process(3.91MJ/kgCO2). Given the volatilization of the NH3, the treatments of escaped NH3 in the novel process is discussed. When the value-added products is considered, sent the escaped NH3 washing solution to the desulfurization part as absorbent may be a better choice than recovering NH3 with heating. With the development of the membrane technology, the energy consumption of the novel process will be further reduced. If combined with renewable energy technology, it is expected to be a new CO2 capture technology.

Abstract

In view of the common problems of CCUS injection wells, such as casing pressure, difficulty in maintenance and high cost, in order to improve the wellbore integrity of injection wells and reduce comprehensive costs, the research and test of coiled tubing gas injection completion technology were carried out. By optimizing the stainless steel coiled tubing for well completion, the string can resist the corrosion of downhole long-term acidic environment, the leakage point is minimized, and the whole well completion under pressure can be conducted. A special gastight packer has been developed, which adopts a double rubber cylinder sealing structure. The gastight pressure bearing is 50MPa, and the unsealing tonnage is controlled below 8.0t, providing a means to solve the tripping problem caused by the low tensile strength of coiled tubing. Large diameter coiled tubing hanger, metal auxiliary sealing device, dual function safety release and gas seal connector are designed to meet the comprehensive requirements of the overall sealing performance of the gas injection string and the later operation under pressure. On this basis, a new process test was carried out for the first well of coiled tubing gas injection in Changqing Oilfield. It only takes 2.5 hours to lower the tubing string to the design depth. The testing of the large diameter coiled tubing hanger and metal auxiliary sealing device at the wellhead was normal, and the setting and verification of the gas seal packer were successful once. The success of this test provides a new solution for the completion of CCUS injection wells, which is of great significance in improving the integrity of injection wells, realizing safe gas injection throughout the life cycle of injection wells, and building Changqing Oilfield into the largest CCUS industrial base in China. It has a very broad application prospect.