Genesis and Distribution Prediction of High Calcareous and Low Permeability Sandstone

The Zhujiang Formation in A oilfield of Yangjiang Sag, Pearl River Mouth Basin has superior reservoir-cap assemblage and good oil accumulation conditions. However, due to the frequent drilling of high-calcareous and low-permeability sandstone, and the unclear understanding of the formation of high-calcareous and low-permeability sandstone and the distribution of sand bodies, the oil and gas exploration progress is restricted. In this paper, the formation and vertical distribution of high calcareous and low permeability sandstone are studied by using core, logging and analysis data combined with the sedimentary background in this area, and seismic inversion of reservoir is carried out by using seismic data combined with permeability, so as to realize the plane distribution prediction of high calcareous and low permeability sandstone. The results show that the Zhujiang Formation in the study area is mainly characterized by underwater river-bay microfacies, which provides abundant carbonate provenance conditions for high calcium content of sand bodies. And the sand bodies in the underwater distributary channel microfacies are closely interlaced with the calcare-rich mudstone at the top-bottom interface, moreover the migration of carbonate from mudstone to sandstone and related chemical reactions occur at the junction, which further increases the calcium content of sand bodies. Combined with the study of permeability inversion model, it is considered that the high-calcareous and low-permeability sandstones are mainly distributed in the underwater distributary channel near the provenance in the northern part of the study area.