Detailed sedimentary facies of a sandstone reservoir in the eastern zone of the Sulige gas field, Ordos Basin

Abstract

Given sustaining exploration, the eastern zone of the Sulige gas field may soon become a key area of exploitation. In order to explore its genesis, types and distribution of the reservoir sandstones in the eastern zone of this gas field, we focused in our study on the provenance and detailed sedimentary facies of sandstone of the He8 (the eighth part of the Shihezi formation, Permian system) and Shanxi1 (the first part of the Shanxi formation, Permian system) members, based on core observations, analyses in petrography, granularity and logging. The results show that: 1) the sandstone provenance of Shanxi1 and He8 in the eastern zone of the Sulige gas field is from the north of the Ordos Basin, characterized by dual directions from the north and northeast. 2) The He8 and Shanxi1 members were deposited in a fluvial-delta sedimentary system. The He8 was mainly deposited in braided rivers, including braided channels, channel bars, levee and floodplain sub-environments, whereas the Shanxi1 Member was deposited in braided rivers and deltas, including braided channels, channel bars, floodplains, tributaries and inter-tributary sub-environments. 3) Sedimentary facies bands migrated in drastic fashion towards the basin from the Shanxi1 to the He8 Member. Base levels of sedimentation generally present a trend of small increases in-amplitude, large decreasing amplitudes and slow and gradual Increases. 4) The continuity of the reservoir sandbodies along the source direction is better than that perpendicular to the direction. Compared with Shanxi1, both dimensions and continuity of the sandbodies in He8 are better from which we conclude that it is the most favorable part of the reservoir.