地质科技通报 (May 2022)
Sealing model of tight gas reservoirs in the edge of Claraton Basin: A case study from the first Member of Lower Shihezi Formation in Hangjinqi area of the northern margin of the Ordos Basin
Abstract
Gas and water distribution of large-scaled tight sandstone gas reservoirs in the margin of typical craton basin is generally much more complicated than that in the center of the basin, and there are various types of traps, therefore, the updip sealing models of gas reservoirs is controversial.This study takes the Permian gas reservoirsof the first Member of Lower Shihezi Formation (He-1 member)in Hangjinqi area of the northern margin of the Ordos Basin as an example, and aims to investigate the differential distribution characteristics, including sandbody thickness, lithofacies association, sandbody superimposition, reservoir physical properties and transverse connectivity of typical channels in the He-1 memberat different locations. The results suggest three types of river depositional models, including shallow-water braided river model in the western gentle slope zone, alluvial fan-braided river model in the central steep slope zone, and deep-water braided river model in the eastern slope break zone. The three depositional models control the difference of channel updipsealing conditions. Based on the relationship between updip reservoir variation and trap types, three models of natural gas migration and accumulation are proposed aslithologic sealing model in the western gentle slope zone, strata coupled with lithologic sealing model in the central steep slope zone, and transitional model of lithologic sealing-trap accumulation in the eastern zone.It is concluded that the upward sealing conditions under these three migration and accumulation models constitute the boundary of the large-scaled continuous reservoir-forming area of He-1 memberin the northern margin of the Ordos Basin, and also control the distribution of different traps and gas enrichment in the Hangjinqi area.
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