Geochemical Characteristics of Bentonite and its Influence on Shale Reservoir Quality in Wufeng-Longmaxi Formation, South Sichuan Basin, China

Based on XRD analysis, trace element test, rare earth element test, TOC analysis, total gas content and porosity test, the characteristics of bentonite and its influence on shale reservoir quality in Wufeng-Longmaxi Formation were studied in the South Sichuan Basin. The results show that (1) bentonite is K-bentonite, mainly composed of clay mineral (illite-montmorillonite mixed layer and illite) and amorphous body, containing a certain content of quartz, feldspar, pyrite and carbonate minerals in Wufeng-Longmaxi Formation. (2) Bentonite is rhyodacite dacite-andesite and its protomagma is basic-neutral. (3) Bentonite is rich in Th, U, Cs and Co but loss of Cr, Ni and Ta. Its partition diagram of rare earth elements leans to the right, rich in LREE but loss of HREE, presenting slight Eu negative anomaly. (4) Primordial magma eruption of bentonite occurred in volcanic arc environment, speculated to be related to the volcanic eruptions on the edge of the continent after post-collision proliferation between Ca...