Acta Geologica Sinica ‐ English Edition最新文献

CO₂ capture and storage (CCS) has the risk of CO₂ leakage, and this leakage always increases soil CO₂ concentration, and the long-term CO₂ stress damages crop production in farmland. Using maize, the growth characteristics, such as plant height and yield, and physiological indexes (osmoregulation substances and antioxidant enzymes) were explored under different simulative CO₂ leakage conditions. Further, the relationship between maize physiological indexes and soil CO₂ concentration was analyzed, showing that soil CO₂ stress inhibited maize growth to a certain extent, resulting in shorter plants, thinner stems and lower kernel yield. With an increase in soil CO₂ concentration, the contents of malondialdehyde, soluble sugar and soluble protein in maize leaves increased; with continuing stress, the increase rate of malondialdehyde was greatly augmented, whereas the increase rates of soluble sugar and soluble protein decreased. With extended CO₂ stress, the activity of the enzyme superoxide dismutase (SOD) increased continuously, while the activities of catalase and peroxidase first increased and then decreased. Superoxide dismutase activity was closely correlated with soil CO₂ concentration (r = 0.762), and responded quickly to the change of soil CO₂ concentration (R² = 0.9951). Therefore, SOD plays an important role in maize resistance to soil CO₂ stress. This study will help further understanding of the mechanism of maize tolerance to soil CO₂ stress, providing a theoretical basis for agricultural production in CCS project areas.

Thermo-hydro-mechanical-chemical (THMC) interactions are prevalent during CO₂ geological sequestration (CGS). In this study, a sequential coupling THMC numerical simulation program was constructed, which can be used to explore the following issues of CGS: fluid and heat flow, solute transport; stresses, displacements and rock failures related to geo-mechanical effects; equilibrium and kinetic chemical reactions; chemical damage to mechanical properties of the rock. Then, the coupling program was applied to the Ordos CGS Project to study the formation response under the multi-field interaction caused by CO₂ injection. The simulation results show that the mechanical process dominates the short CO₂ injection period. Specifically, the formation's permeability near the injection well increases by 43%, due to the reduction of effective stress, which significantly promotes the lateral migration of CO₂. When the injection rate exceeds 0.15 million tons per year, the cohesion of the reservoir rock is not enough to resist the shear force inside the rock and rock failure may occur. During the subsequent long-term sequestration period (200 years), the influence of mineral reactions gradually increases. Due to calcite dissolution, the shear modulus of caprock is predicted to decrease by 7.6%, which will to some extent increase the risk of rock failure.

Supercritical carbon dioxide (ScCO₂) fracturing has great advantages and prospects in both shale gas exploitation and CO₂ storage. This paper reviews current laboratory experimental methods and results for sedimentary rocks fractured by ScCO₂. The breakdown pressure, fracture parameters, mineral composition, bedding plane angle and permeability are discussed. We also compare the differences between sedimentary rock and granite fractured by ScCO₂, ultimately noting problems and suggesting solutions and strategies for the future. The analysis found that the breakdown pressure of ScCO₂ was reduced 6.52%–52.31% compared with that of using water. ScCO₂ tends to produce a complex fracture morphology with significantly higher permeability. When compared with water, the fracture aperture of ScCO₂ was decreased by 4.10%–72.33%, the tortuosity of ScCO₂ was increased by 5.41%–70.98% and the fractal dimension of ScCO₂ was increased by 4.55%–8.41%. The breakdown pressure of sandstone is more sensitive to the nature of the fracturing fluid, but fracture aperture is less sensitive to fracturing fluid than for shale and coal. Compared with granite, the tortuosity of sedimentary rock is more sensitive to the fracturing fluid and the fracture fractal dimension is less sensitive to the fracturing fluid. Existing research shows that ScCO₂ has the advantages of low breakdown pressure, good fracture creation and environmental protection. It is recommended that research be conducted in terms of sample terms, experimental conditions, effectiveness evaluation and theoretical derivation in order to promote the application of ScCO₂ reformed reservoirs in the future.

Southeastern China (SE China) is located in the Pacific tectonic domain and has experienced a series of tectonomagmatic events induced by the subduction of the Paleo-Pacific Plate since the late Mesozoic. The subduction formed a series of NE-NNE oriented faults under a NW–SE regional stress field, along which a number of thermal springs occur. Previous studies have focused on the genesis mechanism of specific geothermal fields in SE China, but the general characteristics of hydrothermal systems in SE China remains unclear. In this study, we investigate the correlation between geothermal activity, hydrochemical type and regional faults by studying the distribution of hydrothermal activity and geochemical properties of typical hydrothermal systems in SE China. The hydrothermal systems in SE China have a crustal thermally-dominated structural origin unique to the specific geological and tectonic conditions of the Eurasian Plate margin. The upwelling of the asthenosphere and the widespread granitoids with high radiogenic heat production in SE China provide major heat sources for regional geothermal anomalies. The NE-oriented crustal thermally-dominated faults are critical for the formation of geothermal anomalies and NW-oriented extensional faults have created favorable conditions for meteoric water infiltration, transportation and the formation of thermal springs.

The Late Devonian–early Carboniferous deposits of the Anarak section in northeastern Isfahan, Central Iran, evaluated based on conodont biostratigraphy, sedimentary environment and sequence stratigraphy. According to the field observations, five lithological units were identified. Investigating the conodont fauna of the Late Devonian–Carboniferous (Mississippian–Pennsylvanian) deposits of Bahram, Shishtu, and Qaleh (Sardar 1) formations in Anarak section led to the identification of 67 species of 18 conodont genera, and accordingly 22 conodont biozones were differentiated. The correlation of sea-level change curves, regarding to the conodont biofacies with the global sea-level curve, demonstrates the relative correlation in the mentioned times due to the shallow condition of the central Iran basin compared to the European and American basins. The microfacies analysis led to the identification of 12 microfacies related to the open sea, bioclastic barrier, lagoon and tidal flat sub-sedimentary environments in a homoclinal carbonate ramp environment. Based on sequence stratigraphy studies, three 3^rd order sequences were identified. The first sequence, which is of the Late Devonian (upper part of the Bahram Formation, 32.5 m), the second sequence (12.5 m) is the Late Devonian (uppermost part of the Bahram Formation), and the third sequence (68 m) is the early Carboniferous (the Shishtu I Formation).