Mineralogical Characteristics and Petroleum Geological Significance of Wufeng-Longmaxi Formation Shale in the Tianba Area, Northeast of Chongqing

Key words: 
• shale gas /
• Wufeng-Longmaxi Formation /
• mineralogy /
• sedimentology /
• Northeast of Chongqing /
• Tianba area /

Abstract: Shale samples are from Wufeng-Longmaxi Formation of Tianba area in northeast of Chongqing. The results showed that major components of the Wufeng-Longmaxi Formation mud shale were composed of quartz, clay minerals and feldspar. In addition, other mineral components include Sulfide mineral like pyrite, gypsum and few carbonate. The mineral assemblage revealed that the Wufeng-Longmaxi Formation was composed of neritic shelf deposits that was in favor of the preservation and enrichment of organic matter and provided a good depositional condition for the shale gas reservoirs. Shale reservoir contained much quartz, and brittleness index was high that were conductive to form crack. Comparing adjacent Fuling area and Tianba area, we would find they were similar and the quartz and brittleness mineral content of Tianba shale was greater that of than the Fuling area, however, the clay minerals content and carbonate mineral content of Tianba shale was less than that of the Fuling area. Clay mineral compositions characterization reflected that Wufeng-Longmaxi Formation had already been in a phyllomorphic stage and that was corresponding to a highly mature or postmature evolutionary stage of hydrocarbons and provided with a suitable maturity condition for shale gas formation. Moreover, the Wufeng Formation and Longmaxi Formation were highly poriferous and which provided a better place for the shale gas reservoirs.