Characteristics of Shale Reservoirs in the Upper Paleozoic Shanxi Formation,Central Ordos Basin

Key words: 
• Shanxi Formation /
• shale /
• pore /
• fracture /
• reservoir characteristics /
• Ordos Basin

Abstract: Shanxi Formation shale is a stratum of marine-continental transitional facies with potential for shale gas exploration in the Ordos Basin. The petrology, mineralogy,reservoir space,pore structure and reservoir quality of the shale show that Shanxi Formation shale comprises black mud shale,grey-black mudstone and dark grey silty mudstone. It mainly consists of 59.6% clay minerals and 36.9% quartz,on average. Fractures are classified into macroand microfractures;the latter mainly occur in the shale and organic macerals, with an average surface density of 116.6/m. In addition to mineral and diagenetic pores,organic pores occur in organic macerals,formed by hydrocarbon generation as a result of the high degree of thermal evolution. Shanxi Formation mud shale has an average porosity of 0.77% and an average permeability of 0.06×10^-3 μm².A positive correlation was found between total organic carbon (TOC), vitrinite reflectance(R_o) and clay mineral content;quartz content and shale porosity are negatively correlated. The general development of fractures increases the permeability of shale,favorable to the accumulation of shale gas. Comprehensive analysis shows that the geological conditions of the shale gas reservoir in the Shanxi Formation are general and difficult to develop. However,there are good prospects for shale gas in the layers and regions with fractures and associated properties.