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Paleogene lacustrine dolomicrite of Unit II of the lower Xingouzui Formation in the southern part of the Qianjiang Depression, China forms “tight carbonate” hydrocarbon reservoirs that can be divided into the following four dolomicrite types: dolomicrite, muddy dolomicrite, sandy dolomicrite, and gypsiferous dolomicrite. These four dolomicrite types occur in the following three distinct combinations, which are referred to as subfacies: (1) interbedded dolomicrite (or sandy dolomicrite) and dark-gray siliciclastic mudstone, interpreted as open lacustrine deposits, (2) grayish-dark siliciclastic mudstone with thinly-bedded muddy dolomicrite or gypsiferous dolomicrite, interpreted as restricted lacustrine deposits, and (3) grayish-green mudstone with thinlybedded brown-yellow siltstone, interpreted as lacustrine shoreline deposits. The spatial distribution of these subfacies was controlled by the paleo-provenance system, paleo-microgeomorphology, and lake level fluctuations. In the open lacustrine subfacies, dolomicrite or sandy dolomicrite are often vertically interbedded with dark argillite rocks, forming a suitable petroleum source rockreservoir association. The dolomicrite and sandy dolomicrite reservoirs possess many secondary crystalline pores and few dissolution pores, with mesopore porosities in the range of 15%–25%. The dark mud shale interval has total organic carbon (TOC) values exceeding 4% (averaging 1.29%). The organic matter is mainly type II2, with vitrinite reflectance values averaging 0.57, which indicates potential for the generation of immature oil. The oil-source correlation results indicated that the n-alkanes of the crude oil and source rock samples from Unit II of the lower Xingouzui Formation exhibit single peak values, with a main peak (post-peak) in C22 and a Pr/Ph ratio $#x003C; 1 in a C2920R $#x003E; C2720R $#x003E; C2820R distribution. These features indicate that source-reservoir interbedding is characteristic of selfsourced reservoirs. The interbedded dolomicrite (or sandy dolomicrite) and dark-gray siliciclastic mudstone, i.e., subfacies (1), is a favorable target for hydrocarbons in the study area.

The alternating stress caused by periodic high-pressure injection and extraction in gas storage can potentially induce fault slippage, compromising the sealing integrity of faults within these storages sites. Understanding the mechanical behavior of faults under alternating stress is crucial for ensuring the long-term stability and safety of gas storage operations. To explore the impact of fault dip angle and fault gouge strength on fault slip characteristics, fault samples were prepared with uniaxial compressive strengths of 20.1, 30.2, 42.4, and 51.4 MPa at two distinct dip angles. Triaxial compression experiments were conducted under alternating stress conditions corresponding to operational pressures at a specific gas storage site in China. The results indicate that faults with dip angles of 30° and 45° tend to fail at their weakest points. The increasing strength of fault gouges shifts failure mechanisms from interfacial failure between gouges and the surrounding rock towards internal gouge failure, often accompanied by shear failure across sections, resulting in characteristic "X"-shaped conjugate shear failures. The decrease in the ratio of bedrock strength to fault gouge strength elucidates the observed phenomena of an initial reduction followed by increased fault deformation. Transition points for faults with 30° and 45° dips occur around the strength ratios of 1.7/1 and 1.2/1, respectively. Fault damage exhibits a negative correlation with fault gouge strength and a positive correlation with fault dip angle. Samples with a higher-strength fault gouge at a 30° dip angle generally incur less damage compared to those with a lower-strength fault gouge at a 45° dip angle. Moreover, higher maximum static friction coefficients denote greater fault resistance to slipping, with 30° faults consistently demonstrating superior resistance compared to 45° faults. Additionally, a higher-strength fault gouge consistently enhances slip resistance under identical dip angles. [ABSTRACT FROM AUTHOR]

Depleted gas reservoirs are important natural gas storage media, thus research on the mechanical properties and damage evolution of reservoir rocks under alternating load conditions has significant practical implications for seal integrity studies. This paper conducted multi-level cyclic loading triaxial compression experiments on medium-porosity medium-permeability sandstone under different confining pressures and used acoustic emission (AE) instruments to detect the AE characteristics during the experiment, analyzing the mechanical characteristics, AE, and damage evolution characteristics. The experimental results show that after cyclic loading, the peak strength of sandstone increased by 14–17%. With the increase in the upper limit stress of cyclic loading, the elastic modulus showed a trend of first increasing and then gradually decreasing. The damage variable of rock samples rose with a rise in the upper limit stress of cyclic loading and confining pressure, and the rock damage was mostly localized at the peak stress. The AE b-value increased generally as confining pressure increased, showing that fractures occurred quicker and more unevenly at lower confining pressures. The distribution of RA-AF values shows that a sudden increase in stress causes the initiation and expansion of cracks in medium-permeability sandstone, and that tensile and shear cracks form continuously during the cyclic loading process, with shear cracks developing more pronounced. This research can provide some theoretical guidance for the long-term stable operation and pressure enhancement expansion of depleted gas reservoir storage facilities. [ABSTRACT FROM AUTHOR]

Compared with organic–inorganic hybrid perovskite solar cells (PSCs), carbon-based all-inorganic PSCs have the advantages of low preparation cost, simple process, and good thermal stability. Here, three polar materials of 4-tert-Butylpyridine halides (tBPX: X = Cl, Br, I) are modified between the perovskite absorbent layer and the carbon electrode. On the one hand, the introduction of tBPX effectively improves the dielectric constant of perovskite nanocrystals and reduces the carrier trapping ability of defects. On the other hand, the structural–functional groups act on the perovskite interface, effectively passivate the surface defects of the perovskite nanoscale thick film, and reduce the nonradiative recombination loss of carriers. In addition, the interface modification of tBPX forms a hydrophobic protective barrier, which significantly improves the moisture resistance of the device. As a result, the carbon-based CsPbI2Br PSCs achieve a power conversion efficiency (PCE) of 14.39%, which is higher than 12.79% of the pristine device. The optimized device can maintain more than 80% of the original efficiency after 800 h of aging under a 20 ± 5% relative humidity in the atmospheric environment. Therefore, it provides an idea for the preparation of efficient and stable carbon-based all-inorganic PSCs. [ABSTRACT FROM AUTHOR]

The structure of caprocks is often greatly altered by different scales of faults or fissures in long-term geological tectonic evolution, and the sealing performance may be deteriorated. In this paper, a simplified geological model characterized as multilayered sandstone and fault-bearing caprocks extracted from the Shuang 6 underground gas storage located in the Liaohe oilfield was established. Different fault geometry (e.g., fault length, fault dip angle, and fault type) and seepage attributes (porosity and permeability) were considered to illustrate their impacts on natural gas migration during the cyclic high rate of injection and production of natural gas. The results showed that the seepage anisotropy and the natural gas front are strongly affected by the formation properties and, especially, are hindered by the low permeability sandstone layers. The difference in the lateral migration distance of natural gas in different layers can reach 110 m at the end of the injection period, with an annual injection volume of 108 m3. The migration of natural gas along the fault zone is mainly controlled by the permeability of faults, followed by fault scale, fault dip angle, and fault type. The sealing failure of caprocks in the fault zone does not occur based on the simulated gas migration distribution, showing that a very limited amount of natural gas migrates into the caprocks. [ABSTRACT FROM AUTHOR]

In recent years, carbon-based CsPbI 2 Br perovskite solar cells (PSCs) have attracted more attention due to their low cost and good stability. However, the power conversion efficiency (PCE) of carbon-based CsPbI 2 Br PSCs is still no more than 16%, because of the defects in CsPbI 2 Br or at the interface with the electron transport layer (ETL), as well as the energy level mismatch, which lead to the loss of energy, thus limiting PCE values. Herein, a series of cadmium halides are introduced, including CdCl 2 , CdBr 2 and CdI 2 for dual direction thermal diffusion treatment. Some Cd 2+ ions thermally diffuse downward to passivate the defects inside or on the surface of SnO 2 ETL. Meanwhile, the energy level structure of SnO 2 ETL is adjusted, which is in favor of the transfer of electron carriers and blocking holes. On the other hand, part of Cd 2+ and Cl - ions thermally diffuse upward into the CsPbI 2 Br lattice to passivate crystal defects. Through dual direction thermal diffusion treatment by CdCl 2 , CdI 2 and CdBr 2 , the performance of devices has been significantly improved, and their PCE has been increased from 13.01% of the original device to 14.47%, 14.31%, and 13.46%, respectively. According to existing reports, 14.47% is one of the highest PCE of carbon-based CsPbI 2 Br PSCs with SnO 2 ETLs., (© 2022 Wiley-VCH GmbH.)