A study of paleo-ocean redox environments is important for understanding the deposition of black shale and has practical implications for shale gas exploration. Here, we selected a total of 52 shale samples from JY1 Well, the first shale gas well of commercial exploitation in China, to analyze the redox conditions of Upper Ordovician Wufeng (O₃w) and the first member in lower Silurian Longmaxi shale (S₁l¹) in the Jiaoshiba area. Abundant pyrite framboids are observed in these units, with average framboid diameters ranging from 3.1 to 4.7 μm and maximum diameter about 10 μm. Analyses of redox-sensitive trace elements suggest the redox environment has evolved from an anoxic condition in the bottom of Member A to a dysoxic condition in the top of Member A, and to a dysoxic–oxic environment in Members B and C. Graptolite and radiolarian are discovered in these shale samples, indicating an oxygenated seafloor, which seems to be contradictory to the results from pyrite framboids and redox-sensitive trace elements. This contradiction is explained as follows: when the shale was deposited, the sedimentation was dominated by euxinic conditions; however, some oxygen may also occasionally migrate to the bottom water due to oxygen-deficient environment, deglaciation, and (or) strong upwelling of nutrient-enriched seawater, while the limited oxygen and anoxic environment is favorable for the preservation and accumulation of organic matter. Combined with the geological characteristics and redox conditions, Member A, especially the shales at the bottom of Member A, is expected to be the most favorable shale gas reservoir in the Jiaoshiba area.

This paper evaluated the oil and gas potential of the Cretaceous Yageliemu clastic reservoir within the Yakela condensed gas field lying in the Kuqa Depression, Tarim Basin, China. The petrophysical properties of the interest zones in the Kuqa area were characterized using geophysical logs from five wells. The results reveal that the gas-bearing zones are characterized by high resistivity, good permeability (K) and effective porosity (Φeff), low water saturation (Sw), and low shale concentration (Vsh), reflecting clean sand. The shale distribution model showed that these shales have no major influence on porosity and fluid saturation. The average shale volume, average effective porosity, and hydrocarbon saturation indicate that the Cretaceous Yageliemu Formation in the studied area contains prospective reservoir properties. The spatial distribution of petrophysical parameters, reservoir rock typing (RRT), and lithofacies were analyzed using the cross plots of litho saturation (volumetric analysis), iso-parametric representations of the petrophysical characteristics, cluster analysis, and self-organizing feature maps, respectively. The southeastern and northeastern regions of the research area should be ignored because of their high water and shale concentrations. The sediments in the southwest and northwest include the most potential reservoir intervals that should be considered for the future exploration and development of oil and gas fields in the study area.