Enhanced CO2 Adsorption and Selectivity of CO2/N2 on Amine@ZIF-8 Materials

The ZIF-8 crystals were successfully postsynthetically modified using methylamine (MA), ethylenediamine (ED), and N, N′-dimethylethylenediamine (MMEN) to improve their adsorption performance toward CO2. Results showed that, compared with the original ZIF-8, the BET specific surface area of MA-ZIF-8, MMEN-ZIF-8, and ED-ZIF-8 has increased by 118.2%, 92.0%, and 29.8%, respectively. In addition, their total pore volume increased separately by 130.8%, 100%, and 48.7%. The adsorption capacities of CO2 on the amine-modified ZIF-8 samples followed the order MA−ZIF−8>MMEN−ZIF−8>ED−ZIF−8>ZIF−8. The CO2 adsorption capacities at 298 K on MA-ZIF-8, MMEN-ZIF-8, and ED-ZIF-8 were increased by 118.2%, 90.2%, and 29.8%, respectively. What is more, the CO2/N2 selectivities calculated using an IAST model of the amine@ZIF-8 samples at 0.01 bar and 298 K were also significantly improved and followed the order MA−ZIF−8 31.4>ED−ZIF−8 25.1>MMEN−ZIF−8 14.1>ZIF−8 11.5, which increased by 173.0%, 121.4%, and 22.6%, respectively. The isosteric heat of CO2 adsorption (Qst) on the MA-ZIF-8, MMEN-ZIF-8, and ED-ZIF-8 all becomes higher, while Qst of N2 on these samples was slightly lower in comparison with that on the ZIF-8. Furthermore, after six recycle runs of gravimetric CO2 adsorption-desorption on MA-ZIF-8, the adsorption performance of CO2 is still very good, indicating that the MA-ZIF-8 sample has good regeneration performance and can be applied into industrial CO2 adsorption and separation

Development characteristics of natural fractures in horizontal wells for deep shale gas and their implications for enhanced development: a case study of Wufeng-Longmaxi formations in Luzhou area, southern Sichuan Basin

The analysis of natural fracture development characteristics is crucial for evaluating deep shale gas exploration and development. It provides valuable insights for assessing reservoir quality comprehensively and designing fracturing strategies differentially. This study focused on the deep shale of the Wufeng-Longmaxi formations in Luzhou area of southern Sichuan Basin (hereinafter referred to as southern Sichuan). Using core analysis, horizontal well imaging logging and seismic data, this study systematically investigated aspects such as descriptions of core natural fractures, development characteristics of horizontal well imaging logging, and the correlation between natural fractures in horizontal wells and seismically predicted fracture zones. The results show that horizontal well imaging logging can accurately identify three types of natural fractures: high-conductivity fractures, high-resistance fractures, and micro-faults. The fracture orientations identified by horizontal wells align with the direction of the current maximum horizontal principal stress, with fracture dip distribution patterns similar to those observed in vertical evaluation wells in the same structural positions. Seismically predicted fracture zones control the development of core-scale natural fractures identified through imaging logging. The influence distances of medium-intensity curvature body fracture zones, low-intensity curvature body fracture zones, and ant-track fracture zones on core-scale fractures are 110, 80, and 30-50 m, respectively. The Luzhou area's core-scale natural fractures exhibit "double-high" characteristics (high dip angle and high degree of calcite filling). The revealed correlations between the deve-lopment characteristics of core-scale natural fractures in horizontal wells, vertical well sections and seismic fracture zones serve as valuable references for the fine characterization of natural fractures, reservoir classification evaluation and differential fracturing technology testing of marine shale in southern Sichuan

Evaluation of the remaining reserves of shale gas and countermeasures to increase the utilization of reserves: Case study of the Wufeng–Longmaxi formations in Changning area, southern Sichuan Basin, China

The evaluation of remaining reserves is crucial for assessing the developmental effect and further enhancing the recovery of a gas field. In this research, with the Changning shale gas field in the southern Sichuan Basin as the center of study, a comprehensive analysis was conducted on reservoir distribution, remaining reserves, and strategies to enhance recovery through the utilization of diverse methodologies, including organic geochemical testing, triaxial rock mechanics experiments, and numerical simulations. The results show that, in the study area, the recovery percentage of the well-controlled reserves ranges from 45% to 70%, with the average remaining reserves of wells falling within the (50–150) × 106 m3 range, alongside the potential for additional development in specific local areas. The Changning shale gas field exhibits three distinct types of undeveloped reserves, identified in areas where no wells have been drilled, inadequately fractured zones, and vertically undeveloped areas, respectively. In the areas where the average remaining reserves of wells are exceeding 100 × 106 m3, wells for repeated fracturing are selected depending on the coupling of geological, engineering, and development. In the case of well infilling, areas characterized by developed reticular fractures and existing well spacing >500 m are prioritized, taking into account the surface wellsite conditions. Through an extensive analysis, which include reservoir assessments, rock mechanics evaluations, and numerical modeling, sublayer⑤ is identified as the optimal target in the upper gas interval, with a vertical distance of more than 20 m from sublayer① in the lower gas interval. Zones with well-developed reticular natural fractures, a pressure coefficient >1.2, and a continuous thickness of Class I reservoirs in the upper gas interval >10 m, are selected for staggered tridimensional development with an expected increase in the platform-level recovery percent by 30%. These findings can provide valuable references and guidance for the deployment of well patterns in shale gas blocks