Abstract: Upper Carboniferous Dolomite Gas Reservoirs in High-Steep Structural Belt, Eastern Sichuan, China

YANG, BAOXING

Upper Carboniferous gas pools of Eastern Sichuan are the important gas producing units in China. Seven rows of high-steep anticlines developed in en echelon pattern with NE trend in the study area. The commercial gas has been found to accumulate in the fault-anticlinal traps corresponding mostly with the anticlinal crests.

The reservoir rocks which are the salinized lagoon carbonate series of Middle Huanglon Formation (C₂h) include desiccation-cracked dolomite breccia and zebra-stretching porous dolomite grainstones. Dolomite reservoirs buried at the depth of 3000-4500m with average porosity of 1.8%-4.2% and low-matrix permeability of 0.25 X10^-3 micrometers². The main reservoir pore space includes synsedimentary and early diagenetic dissolution pores,vugs and fissures. Epigenetic leaching, interbreccia vugs,caverns and fractures improved the reservoir qualities. The high porosity zones are usually found in structural highs and along anticlinal axes because the structures developed successively on the paleotopographical highs. Open fractures serve as the infiltration way of natural gas and the key contributor for the high producing wells.

Folding and fracturing occurred mainly in Xishan movement during Tertiary time. Undoubtedly, the fracture characteristics and distribution will be the key point to commercial gas exploration.

AAPG Search and Discovery Article #90942©1997 AAPG International Conference and Exhibition, Vienna, Austria