Abstract

Under the strategic goal of “carbon peak, carbon neutral”, CCUS technology has become an important means of reducing CO2 emissions and sustainable energy development in China. The replacement of CH4/CO2 hydrate has the advantages of being environmentally friendly and maintaining the stability of geological reservoirs. At present, the laboratory has done quite a lot of experiments and simulations on the research of natural gas replacement and recovery, but it mainly focuses on the research in coarse sand such as glass sand, however, there is little research on the real marine environment. Some studies show that porous media has a great impact on the replacement effect. This study simulates the geological conditions of the South China Sea with real natural marine sediments of the South China Sea as porous media, systematically studies various factors affecting the replacement process, and explains the change of the replacement rate and CO2 storage rate through the analysis of the driving force of the replacement process. Under different pressure (1.9-5.6MPa), temperatures (-1.82-3.87℃), and hydrate saturation (10% – 20%), the CO2/N2 mixture is used to replace natural gas hydrate in argillaceous silt. The results show that higher displacement temperature and lower displacement pressure have a positive effect on the recovery of CH4, and lower displacement pressure and higher hydrate saturation are conducive to improving the storage capacity of CO2. In marine soil sediments with low permeability, the pore size of the hydrate reservoir is small, and the contact area between N2/CO2 and methane hydrate is small, which leads to the inconspicuous replacement effect and low efficiency. According to the experimental results, we should optimize the pressure and temperature conditions, further enhance the heat and mass transfer effect, improve the permeability of the reservoir, and then improve the storage rate and replacement efficiency.

Abstract

CO2 geological storage is the primary means of achieving large-scale, low-cost emission reductions. Compared with onshore basins, storage in offshore basins has the advantages of larger storage volume and less impact on people and the environment. At the same time, there are also challenges such as high cost and technical difficulty for storage. At present, there are many researches on the selection and suitability evaluation of CCS in China, and there are also very successful demonstration applications, while the research on CO2 geological storage in sea areas is relatively few. Taking Zhuyi Depression of Pearl River mouth Basin in the South China Sea as an example in this paper, with the goal of meeting the storage capacity of one million tons per year. Making statistics on the factors affecting the suitability of CO2 storage of oil and gas-bearing structures in the depression from three aspects: geological characteristics, storage economy and storage safety, and constructs a screening index system of CO2 geological storage field, which includes 3 levels and 18 evaluation factors. The index weight of each evaluation factor is calculated by AHP. The suitability of CO2 sealing of selected oil and gas-bearing structures is quantitatively evaluated by multi-source information overlap analysis. The results show that the Xijiang 23 and other oil-bearing structures in the west of Huizhou Sag have priority as the storage field. The results of this study can provide reference for the implementation and management decision of CO2 saline aquifers storage in this area.

Abstract

CO2-EOR (Enhanced Oil Recovery) is a vital method to increase oil recovery while significantly lower greenhouse gas emissions. The near-miscible conditions are useful to improve displacement efficiency and oil recovery by CO2 injection. In this study, at the near-miscible condition of 8MPa, 40°C, using X-ray micro-tomography (micro-CT), pore-scale interfacial characteristics can be obtained in the CO2-oil-glass beads system, such as wettability, which represents the tendency of fluids in the solid. A displacement of oil by CO2 was performed to examine the two-phase interfacial characteristics in the gas-oil-solid system. With the multi-phase identification approach and in-situ spatial distribution of contact angle (\theta), the \theta at 5.5PV was nearly 66.99° at near-miscible conditions, which indicates an intermediate-wet system. With increasing injection pore volumes (PV) from 5.5PV to 16.4PV, the contact angle increases from 66.99° to 70.42°, indicating a decrease in the water-wet property. Although oil resides in pores of all sizes (big, medium, and small), gas often fills the larger pores. The interfacial curvature examination revealed that in-situ capillary pressure provides a distribution with an average value near zero. The rock performed a wettability reversal from a water-wet to an intermediate-wet condition. The knowledge of near-miscible two-phase flow is helpful to enhance oil recovery and storage efficiency.

Abstract

Water-alternating-gas injection of CO2 flooding has received attention as a proven gas channeling controlling method for enhancing oil recovery. However, the application of this method led to the coexistence of corrosion and scaling, affecting well productivity. Current single agent has slight anti-corrosion effect, which mainly concentrates on scale prevention. Meanwhile, the treatment means of agent compounding has poor compatibility. Therefore, developing a single agent with both anti-scale and anti-corrosion properties is beneficial to production. In this study, the dehydrated product of cyclization of amine and acid were condensed with aldehydes and ketones under acidic conditions to prepare mannich base imidazoline groups, that could play the corrosion inhibition effect. The imidazoline – phosphate copolymer was synthesized by introducing the scale inhibition of phosphate esters into imidazoline, followed by a grafting reaction. Corrosion and scale inhibition properties of the synthesized agent were evaluated by rotary hanging weight loss method, and the biodegradable performance was analyzed. The results of infrared spectrum characterization illustrated the successful binding between the effective functional groups of imidazoline groups and phosphate groups. The scale inhibition rate of 30 mg/L of the synthesized agent to calcium carbonate (CaCO3) was 92.41%. The corrosion rate of CO2 on steel was 0.061 mm/a when the synthesized agent was added, indicating that the corrosion resistance of the imidazoline – phosphate copolymer was superior than that of most of the reported single agent used for corrosion inhibition and scale inhibition. The chemical oxygen demand of the synthesized agent decreased significantly when aging in the soil where plants grew, and the biodegradation rate of the synthesized agent at 28 days was 70.93%. The single agent of imidazoline – phosphate copolymer exhibited superior performance in solving the problems of corrosion and scaling in the wellbore, which could facilitate the application of captured and buried CO2 in oil displacement, so that meeting the requirements of environmental protection and efficient reservoir development.

Abstract

CO2 injection into shale and coalbed reservoirs to enhance methane (CH4) production is treated as a better way to promote gas recovery efficiency as well as easing carbon emission by CO2 sequestration. Most CH4 is adsorbed inside the organic micropores and mesopores (≤ 50 nm), enjoying large surface areas and serving abundant adsorption sites. And another key structure factor is the slit, which is usually treated as a sequestration medium. To better understand the microscopic mechanism of enhanced CH4 recovery by CO2 in nanopores and slit becomes necessary. Thus, Molecular Dynamics (MD) supports a solid foundation for constructing the nanosized kerogen frameworks to investigate the gas adsorption behavior on the kerogen-accessible surface. This study innovatively introduced a new method of constructing kerogen slit nanopores, making the model more practical and approaching real underground environments. The grand canonical Monte Carlo (GCMC) method is employed to uncover the gas adsorption and sequestration practices within the kerogen nanopores and slit at various subsurface conditions. According to our results, the previously overlooked slit particularly impacts gas adsorption and recovery efficiency. This study also examines the widespread water encroachments, including various pure water and saline environments. Pure moisture has an overall negative on gas adsorption and sequestration, promoting the recovery efficiency of CH4 by CO2 injection. Moreover, saline has a further enhanced negative influence on gas adsorption, whereas it advantages the displacement process. Ethane (C2H6) influences the CH4 adsorption negatively but favors the recovery process. This work shows significant importance in underlining the kerogen slit nanopores structure and develops the knowledge of the comprehensive underground conditions work on gas adsorption and recovery mechanisms at a thorough level to enhance CH4 extraction and CO2 utilization and sequestration.

Abstract

The idea of implementing CO2 injection for reservoir development is shifting from the traditional scheme of injecting small amounts of gas to prevent gas breakthrough, to a large pore volume (PV) injection approach based on expanding the swept volume gradually. To investigate the law and mechanism of EOR and gas sequestration by large PV injection during the CO2 drainage method, a series of large PV CO2 injection experiments were carried out. The cores’ permeability and porosity at different stages of injection were measured, and then the microscopic characteristics and mineral types were analyzed, full-diameter cores were used for large PV CO2 injection experiments to analyze the dynamic characteristics of CO2 injection under the influence of factors such as the degree of miscibility, heterogeneity, and core dip angle. Results showed that with the progress of CO2 injection, the porosity and permeability of the core followed a dynamic law of decreasing first and then increasing. The reaction of calcite, potassium feldspar, and other minerals with acid solutions to form precipitation and segregation, and the loss of fines leading to partial blockage of the throat, both are the main causes of early changes in the physical properties. However, migration and decomposition of the blockage and the development of micro-fractures caused by large PV CO2 injection can further improve the physical properties. Furthermore, it is found that heterogeneity can easily cause premature CO2 gas channeling and reduce the degree of recovery before the gas breakthrough. However, the high degree of miscibility is favorable for improving this situation. The amount of CO2 storage per unit of crude oil produced shows a pattern of rapid decrease followed by a gradual increase throughout the whole drainage stage, and the gas injection volume remains essentially unchanged when it exceeds 2 PV. Therefore, achieving high recovery efficiency and CO2 utilization rate is the fundamental reason for implementing large volume CO2 injection.

Abstract

Carbon Capture and Storage (CCS) is intended to capture CO2 created during the combustion of fossil fuels used in the production of thermal energy, chemical plants, and natural gas decarbonization process. Typically, pipeline transportation is often used to transport and store CO2 underground. Over the following ten years, there will be an increase in demand for carbon capture technology, CO2 pipeline transportation, and CO2 underground storage. In terms of pipeline transportation efficiency and safety, dense phase or supercritical phase are typically chosen. This paper uses KBC Multiflash 7.3 to compare the physical characteristics of fluids with various components under various equations of state. It is discovered that utilizing EOS-CG as the equation of state to describe fluid properties is a more conservative approach. This paper also analyzes transportation conditions of CO2 with a small amount of impurity under different injection rates, compares the differences in pressure and temperature, liquid hold up, hydrate and CO2 corrosion using the multiphase flow transient simulator OLGA as the primary simulation tool, along with its special pressure-enthalpy (PH) flash algorithm.

Abstract

In the field of carbon capture, utilization and storage (CCUS), geophysical exploration technology can make great contributions and has wide applications. Injecting high-pressure liquid or gaseous CO2 into the existing underground oil and gas field can drive oil and gas moving in the reservoir to improve the output of oil and gas production wells and increase the recovery rate of oil and gas fields. At the same time, most of the CO2 can also be sequestrated inside the reservoir formation. Sequestration of CO2 underground is one of the important means and measures to achieve the goal of “Carbon Reduction”. Integrated geophysical exploration technologies have a wide application prospect in the CO2 storage site selection, onsite monitoring of CO2 injection process, and long-term real-time dynamic monitoring of the CO2 storage site safety. The high-density and high-resolution 3-D seismic, gravity and electromagnetic surveys can accurately evaluate the stability and sealing conditions of the underground geological structure for CO2 sequestration, and identify all faults and fracture zones within the CO2 sequestration site. Borehole seismic and borehole electromagnetic surveys can monitor and evaluate the CO2 injection process in real time to avoid any safety risks such as CO2 leakage from the injection well. In the underground area where a large number of CO2 is stored, the time-lapse borehole seismic and electromagnetic surveys can be used to map the migration and storage status of CO2 plume underground. Using the downhole armored optical cables outside the casing can conduct long-term real-time dynamic monitoring of the safety state of underground CO2 to prevent and avoid catastrophic events where underground sealed CO2 migration leaks to the surface. Over the past 60 years, gravity, magnetic, electromagnetic and geochemical survey methods have been widely used in the field of geophysical exploration. Therefore, they are becoming more and more popular in the oilfield technical service market. Nowadays, the state has put forward the requirements of “carbon reduction” for companies specializing in oil and gas exploration and development. BGP has focused on expanding its applications in CCUS during last three years. It has not only made contributions in the stability, reliability and tightness of CCUS storage site selection, but also made use of the advantages of optical fiber sensing technology for the real-time engineering monitoring of the CO2 injection operation. At the same time, it has carried out research on the long-term safety monitoring of CO2 sequestration sites aimed at preventing surface leakage. When applied to the field, it can provide real-time evaluation of CO2 driving the oil and gas moving, which is of great reference significance for reservoir evaluation and enhanced oil recovery. This paper analyzes the applications of the above-mentioned geophysical technologies on CCUS and makes a prospect from four aspects. It hopes to provide help to many oil companies make scientific decisions and accurately find oil and gas under the background of improving quality and efficiency and achieving the requirements of the national green energy strategy.

Abstract

Injected acidic gas of CO2 and produced acidic fluid under high temperature and high pressure are the main factors that cause corrosion of downhole tubular column in Carbon capture, utilization and storage (CCUS) application. The traditional methods, such as corrosion inhibitor mixing and regular injection are not effective method to prevent corrosion of tubular column. In this paper, as a main component, novel organic polysiliconazane polymer (OPSZ) was added to the coating formulation to form a ceramic-like layer with Si-N-Si and Si-O-Si structures on the steel surface. After coating, the non-polar surface energy of the steel decreased to 14.7 mJ/m2. The hardness, thickness, friction strength, corrosion resistance and other related properties of the coating layer were evaluated in laboratory, showing its good tolerance to high temperature in corrosion resistance in the long term, which provided effective protection against corrosion and aging in the application. The novel coating material can be coated on the surface of the downhole tubular column and forming a super hydrophobic surface, which can effectively prevent the contact of acid corrosion medium and metal surface by greatly reducing surface energy, and greatly improving protection efficiency of steel due to carbon dioxide corrosion, indicating good potential in CCUS application.

Abstract

This study established a one-dimensional dynamic simulation model for a supercritical carbon dioxide pipeline containing impurities. By using C++ programming and numerical solution technology, the hydraulic and thermal properties of the pipeline during slow transient operating conditions can be calculated, enabling dynamic monitoring of the hydraulic and thermal properties along the pipeline during the transportation of impurities in supercritical carbon dioxide. The comparison and verification between the current authoritative engineering simulation software OLGA and this model indicate that the model has certain engineering application value and has reference significance for the development of domestic simulation software.