| The geological conditions of shale gas accumulation, gas-bearing characteristics and shale gas preservational
conditions of Doushantuo Formation in western Hubei Province was studied based on comprehensive analysis of drilling,
outcrops, and testing data. The Doushantuo Formation in the study area can be divided into four members, and the black
carbonaceous dolomite developed in the second Member of Doushantuo Formation (Z1d2) is the main shale gas reservoir.
From west to east, the shallow shelf, basin and platform facies are developed in turn, and two isolated platform are
developed among the basin. On the plane, the depocenter is mainly developed in Zigui-Wufeng region, with the thickness
of organic-rich strata more than 100 m; the areas with the TOC values greater than 1.0% are distributed in the
Shengnongjialinqu-Zigui-Wufeng area. Overall, the TOC values are at the range of 0.5%-2.0% belonging to low to medium
level, and Ro is mainly high maturity of 2.0%-3.5%. The Z1d2 is characterized by the dominated dolomite mineral, the
calcareous shale, the ultralow-low porosity, and ultra-low permeability reservoir. The dolomite intergranular pores and clay
mineral stratified pores are the most important pore types, and pyrite intercrystalline pores and organic matter pores are much
more developed in the samples with high TOC value. The areas with the high gas content are limited only to the north of the
Tianyangping fault and southern of the Huangling anticline with the gas content over 1.0 m3/t. It is believed that the shale
gas accumulation in Doushantuo Formation is mainly influenced by the superposition of sedimentary facies and structural
types. Basin and platform basin facies, stable structural belt, the footwall of reverse fault, and the area far away from
regional normal faults with a buried depth of more than 2,000 m are conducive for shale gas accumulation. This paper also
provide a scientific basis for further shale gas exploration and development of the Doushantuo Formation in western Hubei
Province. It is proposed that favorable areas are mainly distributed in the Yangye-1 well block and Yiye-1 to Yidi-3 well
block in the southeast margin of Huangling anticline. |
