Upper Paleozoic Coal Measures and Unconventional Natural Gas Systems in the Ordos Basin, China

Tang, Xuan ¹; Zhang, Jinchuan ¹
(1)School of Energy Resource, China University of Geosciences, Beijing, China.

The upper Paleozoic coal measures in the Ordos Basin are widespread important source rocks, consist of multi-layer dark mudstone and coal beds, have great potential of gas generation. Gas derived from coal measure strata forms various types of gas accumulations including coal bed methane (CBM), tight gas and conventional gas accumulations in different structural area in the Ordos Basin. CBM accumulations are mainly distributed in the marginal area of the Ordos Basin, estimated 3.5×10¹²m³ of resource in place. The tight gas accumulations exist in the middle part of Yishan Slope, used to be considered as the basin-centered gas system (2002), and then be thought as stratigraphic lithologic gas reservoirs. This paper reviews the tight gas accumulations characteristics: poor physical property (porosity<8%, permeability <0.85×10^-3µm²), abnormal pressure and no well-defined gas water contact, which accord with the tight gas accumulation model modified by new observations. The unconventional gas enrichment and concentration are mostly controlled by the source rock quality, thermal evolution of adjacent source rocks and sealing effectiveness.

AAPG Search and Discovery Article #90135©2011 AAPG International Conference and Exhibition, Milan, Italy, 23-26 October 2011.