Unconventional Natural Gas Accumulations in Stacked Deposits: A Discussion of Upper Paleozoic Coal‐Bearing Strata in the East Margin of the Ordos Basin, China

Abstract

The Upper Paleozoic (Carboniferous to Permian) succession in the east margin of the Ordos Basin in the North China Craton has a potential to contain significant hydrocarbon resources, though attention have been mainly attracted for its successful development of coalbed methane (CBM). To improve the previous resource estimates and evaluate the hydrocarbon play possibilities, this study incorporated new discoveries of hydrocarbon units and their stratigraphic relation with source rocks, hydrocarbon migration and trapping configurations. Continuous hydrocarbon accumulation units were identified within the Upper Paleozoic, including the Taiyuan, Shanxi and Xiashihezi formations with great tight gas potential, and the Taiyuan and Shanxi formations also containing shale gas and CBM. Different strata combinations are identified with coal deposition and favour for continuous gas accumulations, including the tidal flat, deltaic and fluvial systems distributed in most of the study areas. Methane was not only generated from the thick coal seams in the Taiyuan and Shanxi formations, but also from shale and dark mudstones. The coal, shale and tight sandstones are proved of remarkable gas content and hydrocarbon indications, and the gas saturation of tight sandstones decreases upward. The stacked deposit combinations vary isochronally in different areas, while the coal seams were developed stably showing good gas sources. Two key stages control the hydrocarbon enrichment, the continuous subsidence from coal forming to Late Triassic and the anomalous paleo‐geothermal event happened in Early Cretaceous, as indicated by the fluid inclusions evidence. Extensive areas show good hydrocarbon development potential presently, and more works should be focused on the evaluation and selection of good reservoir combinations.

Controlling Effects of Tight Reservoir Micropore Structures on Seepage Ability: A Case Study of the Upper Paleozoic of the Eastern Ordos Basin, China

“…These gas fields include the Sulige, Wushenqi, Daniudi, Shenmu, and Yulin gas fields, which account for 84% of the total natural gas reserves found in the basin. Among them, Sulige gas field is the first integrated tight sandstone gas field with reserves of more than one trillion cubic meters discovered in China , showing its rich and tight sandstone gas resources (Fu et al, 2004;Ma, 2004;Li et al, 2019). The study area is located in the eastern part of the basin with an area of 45000 km 2 (Fig.…”

Characteristics of in situ stress and its influence on coalbed methane development: A case study in the eastern part of the southern Junggar Basin, NW China

“…24,56,57 Among them, the G value tends to increase with the increase in the R o and P o , whereas the T em , moisture content, and ash yield are not beneficial to gas absorption of coal reservoirs. 24,56,57 Among them, the G value tends to increase with the increase in the R o and P o , whereas the T em , moisture content, and ash yield are not beneficial to gas absorption of coal reservoirs.…”

“…The gas content (G) of coal reservoirs is influenced by complex geological factors, for example, coal rank (R o ), T em , P o , and coal macerals. 24,56,57 Among them, the G value tends to increase with the increase in the R o and P o , whereas the T em , moisture content, and ash yield are not beneficial to gas absorption of coal reservoirs. 58,59 When the R o , T em , and coal macerals are relatively stable, as discussed above, the current in situ stress regime controls the P o and affects the G and saturation of coal reservoirs.…”

Study on the Fractal Characteristics of Coal Body Fissure Development and the Law of Coalbed Methane Migration of around the Stope

“…Therefore, effectively improving the CBM drainage rate and reducing its pressure have become the key to preventing coal and gas outburst disasters and securing the environment for coal and CBM coexploitation. China has a potential to contain significant hydrocarbon resources [8]. But due to the complicated CBM occurrence and most reservoirs are close-knit with high-gas pressure and low gas permeability, CBM exploitation is prone to trigger disasters, such as rock burst and coal and gas outbursts.…”