Accumulation Conditions of Upper Palaeozoic Coal-Derived Gas in Eastern Linqing Depression. Issue 1 (March 2013)

• Record Type: Journal Article
• Authors: Wang, Mingjian; Zhang, Xunhua; Zhang, Yunbo; Li, Wentao; He, Dengfa; Sun, Yanpeng
• Is Part Of: Energy exploration & exploitation. Volume 31:Issue 1(2013)
• Page Start: 31
• Page End: 56
• Publication Date: 2013-03
• Subjects: Eastern Linqing Depression -- Upper palaeozoic -- Coal-measure source rocks -- Accumulation; Power resources -- Periodicals; 333.79
• DOI: 10.1260/0144-5987.31.1.31
• Languages: English
• ISSNs: 0144-5987

Abstract

The hydrocarbon exploration is presently going on well in the Bohai Bay Basin, where several coal-derived gas fields have been found in the Upper Palaeozoic. However, no significant breakthrough has been made in the exploration of Eastern Linqing Depression, which is located in the southwest of the Bohai Bay Basin. To improve the gas exploration efficiency, this study employed the petroleum system theory to analyze the accumulation elements and processes of coal-derived gas of Upper Palaeozoic in this area, and further summarized the natural gas accumulation model. Results showed that the source rocks of Upper Palaeozoic in Eastern Linqing Depression mainly consist of coal-measure strata of Benxi-Taiyuan Formations of Carboniferous, as well as Shanxi Formation and the Lower Shihezi Formation of Permian. Reservoirs are widely distributed from the bottom to the top, mainly consisting of carbonate rocks and sandstones. The carbonate rock reservoirs include the weathering crust of Ordovician and the dolomite within Ordovician, while sandstone reservoirs include the distributary channel sand bodies of delta plain and the meandering river channel sand bodies in Upper Palaeozoic, as well as sandstones of river and lacustrine in Mesozoic and Cenozoic. The whole region is covered by the semideep-deep lacustrine mudstone of Sha 3 member (Es3 ) of Palaeogene, which constitutes the regional cap rock in presence of many other localized cap rocks. There are four source-reservoir-cap assemblages including Upper Palaeozoic-generating and Mesozoic-preserving assemblage, Upper Palaeozoic-generating and Cenozoic-preserving assemblage, Upper Palaeozoic-generating and Upper Palaeozoic-preserving assemblage and Upper Palaeozoic-generating and Lower Palaeozoic-preserving assemblage. The source rock, reservoir and cap rocks match well in time and space. Tectonic evolution controlled the thermal evolution of the Upper Palaeozoic coal-measure source rocks, which experienced five hydrocarbon generation stages. Hydrocarbon generated from the coal strata of Upper Palaeozoic migrated to the surrounding traps through migration pathways consisting primarily of faults, cracks and unconformities, among which faults and unconformities played a major role. Multiple types of traps, mainly structural traps, were formed by the intense tectonic movements that historically occurred in this area. The trap formation stages match well with the hydrocarbon generation stages. By analyzing the accumulation conditions of coal-derived gas of Upper Palaeozoic, we identified four accumulation models and further predicted the favorable hydrocarbon accumulation zone in the study area.