Abstract:

Based on outcrop investigation,thin-section observation and SEM analysis,a detail division scheme of sedimentary facies was proposed for the Lower Cambrian in southern Anhui combining with geology and wellbore data.The most favorable facie belt for shale gas accumulation is deep-water deduction environment in the basin,while the carbonate ramp is unfavorable for shale gas exploration.Fractures make the greatest contribution to the storage of shale gas reservoir,followed by the secondary dissolution micro-pores.In contrast,intercrystalline pores contribute the least due to their relatively poor development.This paper comprehensively studied the geological characteristics of the Lower Cambrian shale gas play in southern Anhui in such aspects as spatial distribution of organic-rich shale,geochemical behaviors and preservation conditions.The study was focused on quantitative evaluation of shale thickness,TOC content,R_o and brittleness.The Lower Cambrian shale in southern Anhui is more than 50 meters on average,with the maximum thickness in the range from 200 to 600 meters occurring in Shitai and Nanling counties.The shale gas play has an average TOC content of 2.37%.The average Ro is more than 2%,indicating that the shale is at mature-high mature stage.The average brittle mineral content is 46.89%,being favorable for the creation of fracture networks through hydraulic fracturing.Based on comparison with the geochemical parameters of the main large shale gas plays in America,it is indicated that the Lower Cambrian shale in southern Anhui has favorable accumulation conditions for shale gas,thus can be selected as one of the play fairways in China.

Key words: sedimentary facies, thermal evolution, tectonic movement, shale gas, southern Anhui, province