Lower Paleozoic Stratigraphy and Reservoir Architecture of the Western North China Block

Benjamin J. Kessel
Department of Geology, Utah State University
Logan, UT
bjkessel@cc.usu.edu

The Ordos Basin is located in north-central China covering approximately 250,000 km2. This basin encompasses one of the largest gas fields in China (the Central Gas Field), reservoired in paleokarst in Lower Paleozoic carbonates. River and road cuts expose Lower Paleozoic reservoir analogs that are only constrained by subsurface data in the productive central plateau area of the basin. Lower Paleozoic rocks of the Ordos Basin consist of a thick package of Lower Cambrian to Middle Ordovician limestones, dolomites and minor siliciclastics. Although previous studies have documented aspects of the sequence stratigraphy of the Lower Paleozoic section, the position and characteristics of paleokarst within that framework has not been addressed.

Documenting the distribution and nature of sub-aerial paleokarst surfaces as reservoir analogs is crucial to gain a more thorough understanding of hydrocarbon systems within the Ordos Basin. The dominant gas reservoir of Ordos Basin is located within the Ordovician Majiagou Formation, therefore outcrop analogs allow the geometry, style, and heterogeneity of paleokarst intervals to be described. I propose to achieve this by measuring 4-6 complete, stratigraphic sections within the Lower Paleozoic carbonates of the Ordos Basin, emphasizing the stratigraphic location and character of paleokarst horizons with additional, analytical work including petrography and basin modeling. The geometry and character of paleokarst intervals will be mapped on photomosaics at the outcrop scale to better document the reservoir heterogeneity. The results of this study are expected to contribute to future hydrocarbon reservoir prediction within the Ordos Basin, as well as similar provinces elsewhere.