Ritts, Bradley D.1
(1) Utah State University, Logan, UT
ABSTRACT: Paleozoic Reservoirs and Petroleum Systems of the Onshore Ordos Basin, China
The Ordos basin is one of the large Mesozoic nonmarine basins common to China. However, it has a Paleozoic history of passive craton sedimentation that is unique to the North China Block, and similar to the Bohai basin to the east. The Ordos basin is also a proven petroleum province. Although Mesozoic and Paleozoic petroleum systems are presently exploited, exploration efforts are relatively immature, particularly with respect to Paleozoic reservoirs.
The Paleozoic stratigraphy of Ordos consists of a Cambrian-Ordovician section that is dominantly marine limestone and dolomite, and a Carboniferous-Permian section that passes from shallow marine limestone, sandstone and shale low in the section to mostly deltaic and fluvial sandstone and mudstone higher in the section. The upper Paleozoic and lower Paleozoic sections are separated by a Late Ordovician-Early Carboniferous unconformity. Potential reservoirs in the lower Paleozoic consist of fractured and paleokarst carbonates, which are developed best directly beneath the base Carboniferous unconformity. Potential reservoirs in the upper Paleozoic section are primarily fluvial sandstone. In both upper and lower Paleozoic reservoirs, the distribution and quality of reservoir facies is heterogeneous because of the lenticular complexly-stacked fluvial sandstone facies and nonuniform paleokarst, respectively. Quality of the upper Paleozoic sandstone reservoirs is dependent on framework composition and diagenesis, which is in turn related to sandstone provenance. Quality of lower Paleozoic reservoirs is influenced by the type or paleokarst, density and orientations of fractures, diagenesis, and matrix infilling. Excellent exposures of each reservoir type on the margins of the basin allow the geometry, quality, and heterogeneity of each reservoir to be described explicitly.
AAPG Search and Discovery Article #90026©2004 AAPG Annual Meeting, Dallas, Texas, April 18-21, 2004.