Diagenesis of Middle and Upper Cambrian Loushanguan Group reservoirs in Nanchuan area, Sichuan Basin

The Middle and Upper Cambrian Loushanguan Group reservoirs in the Nanchuan area of the Sichuan Basin mainly consist of platform margin shoal sediments. The main lithology is dolomite. The main diagenesis effects include dolomitization, solution, structural disruption, consolidated fill, compaction and pressure solution, among which, the first three of these work as the key effects for reservoir formation. According to dolomite types, order degree and C, O isotope analyses, the dolomites in the study area developed from three diagenesis effects, including penecontemporaneous dolomitization, mixing water dolomitization and burial dolomitization, among which the penecontemporaneous dolomitization is dominant. The Loushanguan reservoirs have experienced three periods of dissolution, including the corrosion action of atmospheric fresh water, the deep burial solution and the hypergene dissolution, among which the hypergene dissolution is the main controlling factor. Dolomitization and hypergene dissolution contribute to high-quality reservoir formation in the Middle and Upper Cambrian Loushanguan Group. Cementation and filling effects destroy a large number of primary and secondary pores, which is unfavorable for reservoir formation.