--> Abstract: Subtle Surface Expressions Over a Gas Prospect in Ordos Basin, NW China, by Q. Fei; #91004 (1991)

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Subtle Surface Expressions Over a Gas Prospect in Ordos Basin, NW China

FEI QI, China University of Geosciences, Wuhan, People's Republic of China

The gas prospect studied is located in the center part of the Ordos basin, where oil and gas potential has long been overlooked. The strata are dominantly in a monocline, dipping southwest at an angle less than 4 degrees. The gas is trapped some 3000 m deep in the unconformity between the Ordovician carbonates and upper Palaeozoic coal formation. Being covered by eolian sands, the surface is very flat and barren, and no surface expressions and structural controls have been identified. However, the gas prospect is well expressed by the C(1)-C(5) concentrations in carbonate crystals attached on the transported quartz grains, which have been studied by optical observation, X-ray defraction, and scanning electronic microscope. The well-developed rhombus shape of less resistant carbonates n the rounded quartz substrate is indicative of the in situ origin of the mineral by evaporation of the ground water. The light hydrocarbons [C(1)-C(5)] incorporated in these crystals are believed to be representative to the concentrations of ascending gas plume. By contouring the C(1)-C(5) concentrations in carbonates, several drill sites are proposed. Three wells have been finished and all of them are commercial, which would lead to a sizable gas field in Palaeozoic carbonates.

 

AAPG Search and Discovery Article #91004 © 1991 AAPG Annual Convention Dallas, Texas, April 7-10, 1991 (2009)