Sediemntary facies and reservoir characteristics in the Permian Maokou Formation in the Ganzhai section, Pingtang, southern Guizhou

Sediemntary facies and reservoir characteristics in the Permian Maokou Formation in the Ganzhai section, Pingtang, southern Guizhou are dealt with on the basis of cast section, SEM and physical properties. The Permian Maokou Formation is dominantly made up of biosparite, biogenic limestone, micritic limestone, intrasparite, siliceous rocks, nodular and/or chert-bearing limestone. The organic fossils in the Formation contain ostracods, gastropods, brachiopods, trilobites, algae, echinoderms, fusulinids, corals and crinoids. All these evidences indicate an open carbonate platform environment of the Middle Permian Maokou Formation including the intraplatform shoals and intershoal subfacies. The reservoir spaces in the Maokou Formation are dominated by intercrystal solution openings and intercrystal pores, with low porosity and low permeability. The relatively developed dissolution pores and structural fissures may contribute a lot to the modification of the porosity and permeability of the hydrocarbon reservoirs. The types of the hydrocarbon reservoirs in the study area are represented by the fissure-porosity type carbonate reservoirs. The reservoir quality and position tend to be governed by sedimentary facies, diagenesis and tectonism.