Abstract:

The Hala’alate Mountain (Hashan) area located in the northwestern margin of the Junggar Basin is associated with an ancient continental margin island arc, where the Carboniferous-Permian (C-P) volcanic rock reservoirs are the main target for oil and gas exploration. To further assess the exploration prospect of the volcanic rock reservoirs we carry out a systematic investigation into the mechanism of reservoir development in Hashan. Core log, thin section, scanning electron microscope, micro CT, fluid inclusion and other techniques are used for the characterization of reservoir rocks, in combination with major and trace element analysis. We find (1) the main pore types in the volcanic rock reservoirs are dissolution pores, intergranular pores and dissolution fractures with large pore-diameter and good connectivity but strong heterogeneity. (2) Volcanic rock facies, fractures, weathering leaching and deep hydrothermal fluid are key factors affecting reservoir quality, where overflow facies and explosive facies are favorable facies belts for reservoir development. Tectonic uplift and thrust napping improve reservoir quality at the front wing of nappes and fault intersections (“Triangle” area), and weathering/leaching contribute to further improvement. (3) Based on the combined analysis of reservoir rock property and lithofacies, the volcanic rock reservoirs are classified into three quality grades. High-quality reservoirs are mainly located in the “Triangle” area of the thrust nappe belt. We conclude that the C-P volcanic rocks in Hashan area has good prospect of forming large-scale, high-quality reservoirs with huge exploration and development potentials.

Key words: volcanic rock, reservoir porosity, reservoir physical property, formation mechanism, Hasan district