Abstract: Shale gas reservoirs in the Longmaxi Formation of the Weiyuan Area show significant single-well productivity differences,and the main controlling factors affecting gas content remain unclear,constraining effective exploration and development of shale gas in this area.Therefore,organic-riched shale reservoirs of the Long 1-1 submember in the Longmaxi Formation of the Weiyuan Area were investigated.By integrating X-ray diffraction(XRD) mineral analysis,organic geochemical tests,SEM observations,and rock petrophysical tests,the basic characteristics of shale gas reservoirs were systematically analyzed,and their controlling effects on gas content were discussed.The results show that shale reservoirs of the Long 1-1 submember have relatively high quartz content,total organic carbon(TOC) content and thermal maturity.The storage space is dominated by organic-matter pores,and both porosity and gas content are relatively high,indicating good resource potential.Shale gas-bearing properties are jointly controlled by material basis,storage space and preservation conditions.High TOC content,large effective reservoir thickness,high brittle-mineral content and a well-developed pore system provide favorable conditions for shale gas generation and storage,whereas strong sealing capacity of roof and floor and a high formation pressure coefficient are key to shale gas enrichment and preservation.Hydrocarbon expulsion in the study area is relatively weak,leading to high present-day residual gas content;moreover,shale gas wells in synclinal structural zones generally have higher production than those in anticlinal structural zones.The results provide a geological basis for favorable area selection and efficient development of shale gas reservoirs in the Longmaxi Formation.

Key words: organic-rich shale, reservoir characteristics, gas content, Longmaxi Formation, Weiyuan Area