Abstract
Eastern Ordos Basin is an important region for the development of Carboniferous-Permian coalbed methane in China; however, there are significant differences of the coalbed methane exploration and development prospects among different regions within eastern Ordos Basin due to the multiple tectonic movements. In this study, the No. 5 coal of the Shanxi Formation of the Lower Permian in the Daning-Jixian region was selected for analysis. The influences of structures on coalbed methane content and permeability of coalbed methane reservoirs in the Daning-Jixian region were discussed and the favorable target areas for coalbed methane development were determined based on the analysis of tectonic characteristics and evolution. The results indicate that the main structures in this region extend in the NE–NNE direction with distinct E-W-trending zoning, which can be specifically divided into, from the east to the west, the fault depression zone in basin margins, the gentle fold zone in basin slopes, and the gentle slope zone. The formation and evolution of the structures in this area are primarily formed during the Indosinian, the Yanshanian, and the Himalayan movement, and the tectonic movement during the Middle Yanshan Period is critical for the formation of the structural frameworks. The coalbed methane contents in the No. 5 coal increase from the east to the west; therefore, low gas contents are found in the eastern margin zone, while the Yaoqu-Wucheng zone of middle slope belt displays high coalbed methane contents. The permeability is relatively high in the eastern margin zone and in the Mingti-Yangjiahe region of the middle slope zone, where there exist relatively strong structural deformations. The Guyi and Mingzhu blocks are selected as the favorable target areas for coalbed methane exploitation by a comprehensive analysis of burial depth, coalbed methane content, and the permeability.
Highlights
The Ordos Basin is a large coal industry base with many large natural gas fields, high oil reserves, and productions
The Ordos Basin is one of the hot spots in the exploration and development of coalbed methane (CBM) in China, and the Carboniferous-Permian CBM development is mainly concentrated within the eastern margin
The CBM formation process was influenced by tectonic deformations (Jiang et al, 2010)
Summary
The Ordos Basin is a large coal industry base with many large natural gas fields, high oil reserves, and productions. The Daning-Jixian block, located in the south part of eastern Ordos Basin, is an important CBM development area in China, which is bounded by the Zijingshan Fault (the south part of Zijingshan Fault) to the east (Liao et al, 2007) and the Yellow River to the west. It is part of the south of the Jinxi fold belt, which lies in eastern Ordos Basin. The structural deformation intensity decreases from the east to the west, suggesting that tectonic stress decreases from the east to the west and generates the distinct E-W zoning characteristics for the folds and faults in the Daning-Jixian block. Faults observed within the basin are relatively weak, and wide and gentle folds and bends are relatively well-developed, indicating that deformation intensity decreases from the basin margins to the interiors
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