Chen, Y., Deng, B., Zhang, J., 2020. Shallow gas in the Holocene mud wedge along the inner East China Sea shelf. Marine and Petroleum Geology 114, 104233.

http://www.sciencedirect.com/science/article/pii/S0264817220300167 High-resolution seismic surveys were carried out in the inner shelf of the East China Sea to investigate the distribution of shallow gas in Holocene sediments. Shallow gas is distributed extensively in the Holocene strata of the shelf which is dominated by the Yangtze River. Organic-rich, fine-grain sediments deposited throughout the Holocene are essential for gas generation and accumulation. The thickness of the Holocene sediment is the main controlling factor determining the distribution of shallow gas. Gas seepages were found mostly at a water depth up to 20 m, where sediment erosion mainly occurs. Coincidence between shallow gas seepage and high methane concentration in the water column suggests that gas emission from these sediments is a potentially significant source of greenhouse gas. The interaction between shallow gas migration and coastal erosion would therefore potentially lead to increased greenhouse gas emission and accelerated sediment erosion. Such results can be applied to other costal locations around the world.

Cheng, B., Liu, H., Cao, Z., Wu, X., Chen, Z., 2020. Origin of deep oil accumulations in carbonate reservoirs within the north Tarim Basin: Insights from molecular and isotopic compositions. Organic Geochemistry 139, 103931.

http://www.sciencedirect.com/science/article/pii/S0146638019301688 Large amounts of light oil have been produced from carbonate reservoirs at depths below 7 km in the recently discovered Shunbei and Yuecan oil fields within the north Tarim Basin. Eighteen samples were investigated for molecular and isotopic compositions to help understand the origin of these deep oil accumulations. Several ratios based on C and C hydrocarbons suggest that they were not affected by evaporative fractionation. Linear 6 7 n relationships between the carbon number and log of the mole fraction of -alkanes support no fractionation alteration. The correlation between concentrations of methyldiamantanes and stigmastane indicates that these oils were not severely cracked and probably at the beginning or an early stage of intense oil cracking. C 29 sterane isomerization ratios 20S/(20S + 20R) and ββ/(ββ + αα) have reached their equilibrium points while a good linear relationship between the concentrations of terpanes and steranes suggests variations in maturity. Calculated vitrinite reflectance of source rocks based on phenanthrene and diamondoid hydrocarbons shows 13 different ranges, which may reflect multiple oil charges to these deep oil accumulations. A narrow range of δ C values of whole oil and oil fractions suggest a genetic correlation of these oils. Triangular plots based on C and 6 n C hydrocarbons and diamantanes also indicate a very similar source. In addition, several ratios based on - 7 alkanes, isoprenoids, tri-, tetra-, and pentacyclic saturated hydrocarbons support a common source. However, oil SB7 seems to differ from the others in terms of source rock depositional environment, indicated by its much higher pristane/phytane ratio and lower dibenzothiophene/phenanthrene ratio as well as a much lower dibenzothiophenes concentration.

Cheng, L., Wu, Y., Huang, S., Fang, S., Ma, M., Xue, Y., Jia, P., 2020. A comprehensive model for simulating gas flow in shale formation with complex fracture networks and multiple nonlinearities. Journal of Petroleum Science and Engineering 187, 106817.

http://www.sciencedirect.com/science/article/pii/S0920410519312367 Shale gas reservoirs are characterized by gas adsorption and multiple flow mechanisms in shale matrix and complex fracture networks after hydraulic fracturing stimulation. It is of significance to capture the dynamic pressure-dependent properties, including gas PVT properties, gas desorption, flow mechanisms, and stress- dependent fracture permeability. In this paper, this problem is handled by proposing a novel Green element method, which is a good extension of the traditional boundary element method. The domain is discretized into many Cartesian grids, and boundary element method is applied to each element. Discrete fractures are flexibly handled by embedding the fractures into the background grids for the domain, and finite difference method is applied to model flow within the fracture system. The flow between the fracture system and matrix system is coupled to obtain the eventual matrix equation, and Picard successive approximation method is applied to obtain the solution of the nonlinear system. The solution of the novel Green element method is validated by the