The Moxizhuang field is a small oil field in the central Junggar Basin containing several low-saturation, low-resistivity oil reservoirs, which display a complex correlation between oil saturation and porosity and permeability that is atypical of both the filled and drained reservoirs. Biomarker associations of crude oil and grains containing oil inclusions (GOIs) of both the present-day water-bearing zones (water zones) and the oil- and water-bearing zones (low-oil-saturation pay zones) were analyzed to investigate the mechanisms for the formation of the low-saturation, low-resistivity oil accumulations. The biomarker assemblage and hierarchical cluster analysis indicate that oil in the Moxizhuang field was mostly generated from Permian source rock deposited in brackish to hypersaline anoxic environments. The pay zones and several water zones display GOI values as much as 38%, greater than the generally accepted threshold GOI value for an oil column (5%). These GOI values are similar to those for high-saturation oil reservoirs in the Bohai Bay Basin and oil zone samples from Australian basins, suggesting that both pay zones and water zones were high-saturation oil reservoirs in the geologic past. Geologic history analysis shows that the Moxizhuang field was located on the north wing of a paleoanticline during oil charge in the Late Cretaceous to Paleogene. This anticline has gradually evolved into a south-dipping monocline since the Neogene, causing northward remigration of accumulated oil. Differential lateral leakage of accumulated oil in different sandstone layers during the remigration phase led to the formation of the water zones with high GOI values (completely drained reservoirs) and the low-saturation, low-resistivity pay zones (partially preserved reservoirs) and caused the complex correlation between oil saturation and porosity and permeability. Compared with other postaccumulation physicochemical alteration processes, lateral leakage has rarely been recognized. Recognizing differential lateral leakage of accumulated petroleum with the existence of high-quality unfaulted cap rocks has important implication for petroleum exploration in sedimentary basins having complex evolution histories.

The concentrations of polycyclic aromatic hydrocarbons (PAHs) in the leachate from the gangue and 20 groundwater samples, which were collected from the 12th Coal Mine around gangue piles in Henan Province, China, were determined by SPE-GC-MS. The characteristics of PAHs pollutants in groundwater were investigated, and compared with the concentrations of PAHs in the leachate from different weathered gangues to discuss the pollution effects of PAHs from coal gangue on groundwater. The results showed that total concentrations of the 16 EPA preferentially controlled PAHs ranged from 146.9 ng/L to 1220.6 ng/L.The components of PAHs such as chrysene, benzo[a]anthracene, benzo[b + k]fluoranthene, indeno[1,2,3-c,d]–pyrene, and dibenz[a,h]anthracene were fairly high. The 2–4 rings PAHs such as naphthalene, phenanthrene, fluorene and chrysene were dominant in groundwater, which was similar to those of the leachate from the different weathered gangues. Therefore, it should be paid much more attention on the transport of lower ring numbered PAHs leached by rains from the coal mines after landfilling and dumping. Based on the spatial distribution of PAHs and the high concentrations of PAHs with 2–4 rings in groundwater and leaching samples, there might be other pollution sources of PAHs except for penetration from coal gangue into groundwater in the Pingdingshan coal mine area.