Search

The Muli permafrost area is the only midlatitude permafrost area where natural gas hydrates (NGHs) have been drilled. Although a series of achievements has been made in studies on NGH accumulation conditions in the permafrost area, related studies on gas hydrate stability zones, gas sources and groundwater are still controversial and need further work. Based on geophysical, geological and geochemical data, this paper systematically elaborates the main NGH accumulation conditions in the Muli area in terms of the pressure‒temperature stability conditions, fault structure, gas composition, gas source, reservoir characteristics, groundwater distribution and topographic characteristics. The results show that the thicknesses of the NGH stability zone range from 491.0 to 962.7 m. The fault structure can provide a pathway for hydrocarbon gas migration from deep to NGH stability zones, in which thrust faults can prevent the upwards migration of gas by sealing it below the hanging wall block. Rock fractures in the NGH stability zone can not only be gas migration channels, but also serve as a reservoir space for NGH accumulation. The hydrocarbon gas of NGHs shows multiple origins and is mainly composed of oil-associated gas. The formation of frost mounds related to the overpressured gas ejection caused by NGH decomposition may imply the existence of NGHs. Synthetically, similarities and differences in NGH accumulation conditions between the Muli permafrost area and other high-latitude permafrost areas are proposed, and the 'regression' NGH accumulation pattern in the Muli area is constructed. The study results can enrich theoretical knowledge of terrestrial NGH accumulation, and provide scientific guidance for NGH exploration in midlatitude permafrost areas. [ABSTRACT FROM AUTHOR]

The survey area is located in the planning area of Longquan national urban park, with frequent human activities, numerous water conservancy, transportation projects, and frequent geological disasters such as landslides. The Red Mudstone has low strength and easy to soften in the case of water, and it is very prone to landslide in rainy season. At present, there are many studies on Red Mudstone Landslides, but most of them are analyzed by geological means, and the monitoring process is also dominated by surface deformation and settlement; there is less analysis with hydrogeological that is caused by rainfall and human activities. For Red Mudstone Landslides, to effectively reveal and analyze the process of the Slip Mechanism, we need to carry out the characteristics of hydrogeological structure and underground physical structure, and compare with surface monitoring and point geological structure. In this study, a one-year field survey and hydrogeophysical survey were carried out. Combined with the characteristics of environmental geology, the geophysical forward modeling problem based on finite element method was used to verify the influence of rainfall on the electrical characteristics of underground media. The smoothness constrained least square method and three-dimensional unstructured grid method are used to interpret the ERT data, analyze the abnormal patterns of electrical structure of landslide in different seasons, and correspond well with the GPR data. According to the characteristics of surface vegetation and weathering, as well as the displacement and settlement monitoring after landslide, the spatial characteristics of red bed landslide are revealed, and the relationship between landslide, rainfall, and human activities is clarified. [ABSTRACT FROM AUTHOR]

Improving the resolution of the magnetotelluric (MT) method and reducing the non-uniqueness of MT inversion for abnormal bodies of different depth and different scale is a significant problem, and thus research on this issue is important. First, based on the classical optimal inversion theory of the MT method, we introduced the concept of multi-scale MT interpretation strategy (MSMIS). Then, typical geo-electric models were constructed, and numerical simulations were carried out; the results of these simulations illustrated the advantages of MSMIS, which can effectively identify not only the overall structural framework of deep bodies but also the spatial distribution characteristics of shallow local inhomogeneous abnormal bodies with small scale. Finally, by targeting the slurry leakage caused by underground karst in shale gas drilling, we used MSMIS to reprocess the existing audio magnetotelluric (AMT) data, which accurately identified the spatial location and distribution characteristics of the shallow underground karst and provided a reliable reference for the re-selection of the appropriate location of the borehole. Subsequent drilling data verified the correctness of MSMIS. The research results show that MSMIS can effectively improve the exploration effect of the MT method for deep and shallow anomalies, which effectively promotes and improves the practical application of the MT method. [ABSTRACT FROM AUTHOR]

Potassium‐rich brine in the Sichuan Basin has been much studied in recent years, but few studies have focused on the distribution and migration of salt basin and the differences of potassium formation mechanisms. This work examined the salt‐gathering and potassium formation of potassium‐rich brine during the Triassic in the Sichuan Basin using lithofacies palaeogeographic depiction and geochemical analyses. (1) The favorable sedimentary facies controlling the formation of potassium‐rich brine during the Triassic in the Sichuan Basin are evaporation platform and restricted platform, whereas the salt basin is one of the main factors controlling the poly‐salt center. (2) The distribution and migration of this salt basin were affected by certain factors. The salt basin of the Jialingjiang Formation was mainly distributed in the east and central Sichuan Basin, whereas that of the Leikoupo Formation was mainly distributed in the central and west Sichuan Basin. The sedimentary centers have gradually moved westward and become smaller. (3) Three main formation mechanisms were identified for the potassium‐rich brine during the Triassic in the Sichuan Basin, i.e., evaporation and concentration of seawater, surface fresh water leaching, and deep water‐rock reaction. Fresh water leaching was characterized by low anomaly δ18O and δ13C values. Water‐rock reaction was mainly related to temperature, and high temperature environment (caused by burial depth, overthrust and deep hydrothermal fluids) was beneficial to water‐rock reaction. The characteristics of water‐rock reaction do not correspond to the increase ratio of K•103/Cl and Br•103/Cl in brine, and the Rb+ content of the brine was high. (4) The formation mechanisms of potassium‐rich brine differed between different areas of the Sichuan Basin. In east Sichuan, the evaporation and concentration of seawater, together with meteoric fresh water leaching, was the main formation factor, whereas the evaporation and concentration of seawater and water–rock reaction predominated in west Sichuan. This study of the sedimentary environment and formation mechanisms is of significance to the exploration and exploitation of potassium‐rich brine in the Sichuan Basin. [ABSTRACT FROM AUTHOR]

The Longmenshan (LMS) southern section is the front of the eastwards material migration from the Qinghai–Tibet Plateau. To understand whether the 2022 Ms6.1 Lushan earthquake was a strong aftershock of the 2013 Ms7.0 Lushan earthquake and why the aftershocks of the two earthquakes were concentrated relative to the 2008 Wenchuan earthquake, a three-dimensional electrical structural model of the Lushan earthquake region is established based on magnetotelluric (MT) array data. The model shows high-conductor layers (HCL) in the Songpan–Ganzi terrane (SGT) middle crust, Sichuan Basin (SCB) shallow surface, western Sichuan foreland depression (WSCFD) and LMS Moho. The analysis suggests that the HCL in the study area at a depth of 10 km is caused by saline fluids in the fracture zone or porous sedimentary rock voids, while the high-conductor body in the middle and lower crust and upper mantle is caused by partial melting of rocks. The Lushan earthquake area is subject to compressional deformation horizontally as the eastwards migration of Qinghai–Tibet Plateau material is blocked by the SCB and vertically by the upwards extension of high-conductor plastic material at depth. The aftershocks of the Lushan earthquake area are mainly confined within the Baoxing–Zhonglin–Daxing–Lushan high-conductor region, which has noticeable electrical structural differences compared to the overall high-resistivity structure of the LMS southern section; these differences explain why the aftershocks of the two earthquakes did not expand in the northeast and southwest directions of LMS. Because the 2022 and 2013 Lushan earthquakes both occurred in the same high-conductor region in the deep part of the Dachuan–ShuangShi fault to the Danyi blind fault, the 2022 Lushan earthquake was a strong aftershock of the 2013 Lushan earthquake in terms of electrical structural characteristics. • A 3D crust–mantle electrical model at south section of Longmenshan was established. • Aftershocks of Lushan earthquake mainly distributed in the high-conductor region. • 2022 Lushan earthquake was a strong aftershock of the 2013 Lushan earthquake. [ABSTRACT FROM AUTHOR]

The mid-high mountain area in Western China is an important area for an aeromagnetic survey in China. To solve the problem that a ground survey cannot be carried out in the research area of Heizhugou (Sichuan, China), an unmanned aerial vehicle (UAV) aeromagnetic survey system based on a three-axis fluxgate sensor was developed. It can solve the large-scale magnetic survey problem in special areas (mountains, canyons, lakes, etc.). The noise level test, conformance test, and sensor correction methods used in the development of the UAV aeromagnetic system are discussed. When performing sensor calibration, the error generation mechanism was analyzed according to the basic principle of the sensor. Then, the component output model was established, and the zero offset factor was calibrated, as well as the scale factor. After the nine-element iteration method calibration, the steering error was reduced from hundreds to less than 20 nT, better than the least squares method. The aeromagnetic results were compared with ground magnetic measurements, and the results were good. • The feasibility of a UAV aeromagnetic survey system in a complex environment was studied and verified. • A script for route planning was developed to generate the flight line automatically. • The nine-element iteration method is better than the least squares method when correcting the steering error. • For the first time, a flight test and survey were carried out in the Heizhugou area, and the results were good. [ABSTRACT FROM AUTHOR]

Natural gas hydrate (NGH) is considered one of the most promising alternative energy sources in the 21st century. The exploitation and decomposition of NGHs could cause geological disasters and eco-environmental problems related to climate warming, seawater blue tides, submarine landslides, drilling platform collapses, slope instability, etc. Thus, an investigation of the eco-environmental effects of NGH exploitation and decomposition has scientific and practical significance. In this paper, the electrical characteristics of NGH reservoirs before and after NGH trial production in the Muli permafrost area of the Qilian Mountains are comparatively examined for the first time. The electrical structure models before and after NGH trial production are obtained through two-dimensional and three-dimensional inversion of the NE audio-magnetotelluric (AMT) sounding profile around production test well SK2. Notably, the electrical structure of the NGH reservoir changes greatly. The research indicates that (1) after NGH trial production, the formation resistivity increases remarkably within 200 m and burial depths in the range of 120– 340 m around the production test well; (2) the main reason for the increasing resistivity after trial production is the Joule-Thomson effect caused by depressurization production and the endothermic effect of NGH decomposition, which lead to the formation of ice-bearing strata; afterwards, we explain the formation process of ice-bearing strata after NGH trial production; and (3) we speculate that the formation stability is not adversely affected after NGH trial production. These findings and research results can provide guidance for subsequent geoenvironmental safety risk assessments of NGH development in permafrost areas. • Two AMT profiles are comparatively studied before and after NGH trial production. • The resistivity of NHG reservoir increases significantly after trial production. • Joule-Thomson effect and depressurization endothermic action is the main reason for ice-bearing strata formation. • The formation stability is not adversely affected after NGH trial production. [ABSTRACT FROM AUTHOR]