Zhijie Yang

The ultrafast photoionization dynamics of N₂ molecules by x-ray/XUV laser pulses is investigated. The molecular frame photoelectron momentum distributions (MF-PMDs) and the molecular frame photoelectron angular distributions (MF-PADs) are obtained by numerically solving 2D time-dependent Schrödinger equations within the single-electron approximation (SEA) frame. The results show that the molecular photoionization diffraction appears in 5 nm laser fields. However, when the laser wavelength is 30 nm, the molecular photoionization diffraction disappears and the MF-PMDs show four-lobe pattern. The ultrafast photoionization model can be employed to describe the MF-PMDs and MF-PADs of N₂ molecules.

CO2 geological storage (CGS) proved to be an enormously significant mid-to-long-term solution for mitigating and even nullifying the net greenhouse gas emissions, and CO2-enhanced water recovery (CO2-EWR) technology may improve the efficiency of CO2 injection and saline water production with potential economic value as a means of storing CO2 and supplying cooling water to power plants. The strata with dip-angle are common in nature, because of the effects of geological structure and diagenesis. It is of great significance to study the influence of the dip-angle on the efficiency and safety of CO2-EWR. Based upon the typical formation parameters of the China Geological Survey CO2-EWR test site in the eastern Junggar Basin, a series of three-dimensional (3D) injection-extraction models with fully coupled wellbores and reservoirs were established to evaluate the effect of dip-angle on the enhanced efficiency of CO2 storage and saline production, considering geochemical reactions. Numerical simulation results show that the dip-angle has a regular influence on the formation pressure field, the CO2 transport distance in the reservoir and the CO2 sealing capacity, and the influence of dip-angle strata on the total storage amount of CO2 changed in a non-monotone mode compared with the CO2 geological storage in horizontal strata at the same injection condition. The effect of water chemical characteristics on the migration of CO2 in different phases and the transformations of major sequestered carbon minerals were determined from the resulting mechanism. Because non-horizontal strata are predominant in deep saline aquifers in nature, regardless of the influence of formation dip, CO2 leakage risks in geological storage will be greatly underestimated, and the stratum dip angle must be considered in research related to CO2 geological storage. Overall, the results of analysis provide a guide and reference for the CO2-EWR site selection.

CO₂ geological storage in deep saline aquifers is an effective way to reduce CO₂ emissions. The injection of CO₂ inevitably causes a significant pressure increase in reservoirs. When there exist faults which cut through a deep reservoir and shallow aquifer system, there is a risk of the shallow aquifer being impacted by the changes in reservoir hydrodynamic fields. In this paper, a radial model and a 3D model are established by TOUGH2-ECO2N for the reservoir system in the CO₂ geological storage demonstration site in the Junggar Basin to analyze the impact of the CO₂ injection on the deep reservoir pressure field and the possible influence on the surrounding shallow groundwater sources. According to the results, the influence of CO₂ injection on the reservoir pressure field in different periods and different numbers of well is analyzed. The result shows that the number of injection wells has a significant impact on the reservoir pressure field changes. The greater the number of injection wells is, the greater the pressure field changes. However, after the cessation of CO₂ injection, the number of injection wells has little impact on the reservoir pressure recovery time. Under the geological conditions of the site and the constant injection pressure, although the CO₂ injection has a significant influence on the pressure field in the deep reservoir, the impact on the shallow groundwater source area is minimal and can be neglected and the existing shallow groundwater sources are safe in the given project scenarios.

CO₂ geological storage (CGS) proved to be an effective way to mitigate greenhouse gas emissions, and CO₂-enhanced water recovery (CO₂-EWR) technology may improve the efficiency of CO₂ injection and saline water production with potential economic value as a means of storing CO₂ and supplying cooling water to power plants. Moreover, the continuous injection of CO₂ may cause a sharp increase for pressure in the reservoir system, so it is important to determine reasonable reservoir pressure control strategies to ensure the safety of the CGS project. Based upon the typical formation parameters of the China Geological Survey CO₂-EWR test site in the eastern Junggar Basin, a series of three-dimensional (3D) injection-extraction models with fully coupled wellbores and reservoirs were established to evaluate the effect of the number of production wells and the well spacing on the enhanced efficiency of CO₂ storage and saline production. The optimal key parameters that control reservoir pressure evolution over time are determined. The numerical results show that a smaller spacing between injection and production wells and a larger number of production wells can enhance not only the CO₂ injection capacity but also the saline water production capacity. The effect of the number of production wells on the injection capacity and production capacity is more significant than that of well spacing, and the simulation scenario with 2 production wells, one injection well, and a well spacing of 2 km is more reasonable in the demonstration project of Junggar Basin. CO₂-EWR technology can effectively control the evolution of the reservoir pressure and offset the sharp increase in reservoir pressure caused by CO₂ injection and the sharp decrease of reservoir pressure caused by saline production. The main controlling factors of pressure evolution at a certain spatial point in a reservoir change with time. The monitoring pressure drops at the beginning and is controlled by the extraction of water. Subsequently, the injection of CO₂ plays a dominant role in the increase of reservoir pressure. Overall, the results of analysis provide a guide and reference for the CO₂-EWR site selection, as well as the practical placement of wells.

Faults in CO₂ storage reservoirs affect the migration and spatial distribution of injected CO₂ in reservoir formations. Based on geological data from the Ordos CO₂ geological storage demonstration project site, A 2D numerical model of the CO₂ storage reservoir was constructed to study the influence of high‐porosity and high‐permeability faults within a low‐porosity and low‐permeability reservoir. The results show that the faults had a significant effect on CO₂ migration and storage. If the permeability of the fault zone increased by 2–3 orders of magnitude (a common range of variation in fault zone) and porosity increased correspondingly compared to the base case (no fault in strata), the CO₂ migration distance in the reservoir after 100 years was approximately 1.18 times larger than that of the base case without faults, and the total CO₂ storage amount in the entire reservoir increased by 1.40–1.61 times. The faults weakened the sealing ability of the local interlayer caprocks (mudstone), which resulted in CO₂ migrating through mudstone and entering in the neighboring interlayer storage stratum. When highly permeable faults existed, the CO₂ migration distance and storage amount in the neighboring interlayer storage stratum were approximately two times and 19.41 times (maximum value) higher, respectively, compared with the case without a fault. Therefore, the faults distributed in strata should be given sufficient attention when selecting a CO₂ sequestration site.