A review of shale pore structure evolution characteristics with increasing thermal maturities

   Pore structure has a significant effect on the occurrence state of shale hydrocarbons and the hydrocarbon storage capability of shale reservoirs. Consequently, it is quite meaningful to clarify the shale pore structure evolution characteristics for understanding the migration and enrichment mechanisms of hydrocarbons within shale reservoirs during different geological stages. The abundant existence of organic matter within shales complicates the shale pore structure evolution process by hydrocarbon generation, migration and cracking. Many studies have been conducted to reveal the shale pore structure evolution characteristics and the controlling factors. Basically, these studies could be divided into two categories based on the sample source: comparing the pore structure of natural shale samples with different thermal maturities; obtaining shale samples with different thermal maturities by conducting thermal simulation experiments on low-mature shale samples and comparing the pore structure of these simulated shale samples. However, no consistent viewpoint on shale pore structure evolution has been reached. This review presents the state of the art of shale pore structure evolution studies. It is widely recognized in the literature that both the inorganic and organic diagenesis control the shale pore structure evolution process. However, it is found that the shale pore structure evolution models proposed in the literature were largely dependent on the samples used. And it is recommended to conduct the two categories of studies simultaneously in order to obtain more reliable shale pore structure evolution characteristics in future investigations.Cited as: Gao, Z., Fan, Y., Xuan, Q., Zheng, G. A review of shale pore structure evolution characteristics with increasing thermal maturities. Advances in Geo-Energy Research, 2020, 4(3): 247-259, doi: 10.46690/ager.2020.03.0

DASES: a database of alternative splicing for esophageal squamous cell carcinoma

Esophageal carcinoma ranks as the sixth leading cause of cancer-related mortality globally, with esophageal squamous cell carcinoma (ESCC) being particularly prevalent among Asian populations. Alternative splicing (AS) plays a pivotal role in ESCC development and progression by generating diverse transcript isoforms. However, the current landscape lacks a specialized database focusing on alternative splicing events (ASEs) derived from a large number of ESCC cases. Additionally, most existing AS databases overlook the contribution of long non-coding RNAs (lncRNAs) in ESCC molecular mechanisms, predominantly focusing on mRNA-based ASE identification. To address these limitations, we deployed DASES (http://www.hxdsjzx.cn/DASES). Employing a combination of publicly available and in-house ESCC RNA-seq datasets, our extensive analysis of 346 samples, with 93% being paired tumor and adjacent non-tumor tissues, led to the identification of 257 novel lncRNAs in esophageal squamous cell carcinoma. Leveraging a paired comparison of tumor and adjacent normal tissues, DASES identified 59,094 ASEs that may be associated with ESCC. DASES fills a critical gap by providing comprehensive insights into ASEs in ESCC, encompassing lncRNAs and mRNA, thus facilitating a deeper understanding of ESCC molecular mechanisms and serving as a valuable resource for ESCC research communities

The Influence of Hydrothermal Activity on the Long-Distance Migration and Accumulation of Hydrocarbons: A Case Study from the Y8 Area in the Songnan-Baodao Sag of Qiongdongnan Basin

The Qiongdongnan (QDN) basin in the northwestern South China Sea has been shown to be rich in petroleum resources and has significant exploration potential for deepwater oil and gas resources. Therefore, it is of great significance to clarify the gas accumulation process in the deepwater area of the QDN basin, specifically the Y8 area. In this study, fluid inclusion analysis, including the identification and localization of fluid inclusions under a microscope, laser Raman spectrum analysis and homogenization temperature (Th) measurement, reconstruction of the thermal evolution burial history, geochemical analysis, and typical seismic section analysis were comprehensively used to interpret the gas accumulation process of the Y8 area. The laser Raman spectrum analysis results of fluid inclusions verified the existence of methane and confirmed the hydrocarbon charging event in this area. However, the Th of fluid inclusions in the reservoir, the mixed compositions of hydrothermal compositions (H2S + SO2) and hydrocarbons (methane) in the fluid inclusions, and the low Tmax values of some wells in the Y8 area comprehensively confirmed that the coincidence of hydrothermal activity with the accumulation process affected the long-distance gas accumulation of the Y8 area. The hydrothermal activity was also confirmed by the presence of fluid diapirs in seismic profiles of the Y8 area. Furthermore, the hydrocarbon accumulation process was reconstructed using the modified thermal evolution history considering the effect of hydrothermal activity. Overall, this study attributed the high Th of fluid inclusions in the reservoirs of the Y8 area to hydrothermal activity and proposed a long-distance migration model of hydrocarbon accumulation coinciding with hydrothermal activity, both of which are beneficial to understanding the accumulation process of the Y8 area

Performance investigation on DCSFCL considering different magnetic materials

In order to protect high voltage direct current (HVDC) system from destructive consequences caused by fault current, a novel concept of HVDC system fault current limiter (DCSFCL) was proposed previously. Since DCSFCL is based on saturable core reactor theory, iron core becomes the key to the final performance of it. Therefore, three typical kinds of soft magnetic materials were chosen to find out their impact on performances of DCSFCL. Different characteristics of materials were compared and their theoretical deductions were carried out, too. In the meanwhile, 3D models applying those three materials were built separately and finite element analysis simulations were performed to compare these results and further verify the assumptions. It turns out that materials with large saturation flux density value Bs like silicon steel and short demagnetization time like ferrite might be the best choice for DCSFCL, which can be a future research direction of magnetic materials

A novel concept of fault current limiter based on saturable core in high voltage DC transmission system

To develop mechanical circuit breaker in high voltage direct current (HVDC) system, a fault current limiter is required. Traditional method to limit DC fault current is to use superconducting technology or power electronic devices, which is quite difficult to be brought to practical use under high voltage circumstances. In this paper, a novel concept of high voltage DC transmission system fault current limiter (DCSFCL) based on saturable core was proposed. In the DCSFCL, the permanent magnets (PM) are added on both up and down side of the core to generate reverse magnetic flux that offset the magnetic flux generated by DC current and make the DC winding present a variable inductance to the DC system. In normal state, DCSFCL works as a smoothing reactor and its inductance is within the scope of the design requirements. When a fault occurs, the inductance of DCSFCL rises immediately and limits the steepness of the fault current. Magnetic field simulations were carried out, showing that compared with conventional smoothing reactor, DCSFCL can decrease the high steepness of DC fault current by 17% in less than 10ms, which verifies the feasibility and effectiveness of this method

Lateral Percolation and Its Effect on Shale Gas Accumulation on the Basis of Complex Tectonic Background

As a result of complex tectonic background, shale gas in China exhibits differential enrichment. Choosing a favorable exploration target accurately is a crucial problem to be solved. In this study, the tests show that there is a superior transportation pathway within shale layer. Gas in the shale layer percolates much more in the direction parallel to the plane. Therefore, the accumulation pattern of shale gas indicates a complex tectonic background. Gas in the lower part of the structure diffuses and percolates in the vertical direction into the surrounding rock. Most gas percolates towards the high part of the structure in the direction parallel to the plane. When the shale was exposed, gas percolated along the parallel direction into the air. In the case of fracture development, if there is a reverse fault, gas would be enriched in the footwall. However, if there is an unsealed fault, it would become a pathway for gas migration. The above accumulation pattern was proved in several Areas. Also, this research presented a basis of evaluation units division. According to the buried depth, fractures, and structural position, Xiuwu Basin was divided into five evaluation units and Unit A3 is the most favorable exploration target