Types and main controlling factors of Ordovician reservoirs in Bozhong 21-2 Tectonic belt

The Ordovician carbonate reservoir spaces of the Bozhong 21-2 structural belt were analyzed comprehensively using drill core, rock section, cast section, cathodoluminescence data, fluid inclusion microthermometry, and imaging... [ view full abstract ]

The Ordovician carbonate reservoir spaces of the Bozhong 21-2 structural belt were analyzed comprehensively using drill core, rock section, cast section, cathodoluminescence data, fluid inclusion microthermometry, and imaging logging results. The Ordovician carbonate reservoir spaces in that belt are typically pores, caves, and fractures. Three types of reservoirs: cave, fracture, and composite cave-fracture existed. The formation of reservoirs in the studied area is controlled mainly by sedimentary facies, tectonism, karstification, and cementation. Sedimentary facies provide the material basis for reservoir formation and control the congenital causes underlying the types and properties of the rocks in these reservoirs. The reservoirs in the area are predominantly restricted platform and tidal flat limestone, calcite dolomite, and dolomite. Multiple tectonic movements have created conditions for the development of karstic reservoirs and governed strata elevation and denudation in the area, resulting eventually in different paleo-geomorphologies, in addition to playing a controlling role in karstic reservoir development. Karstification is the key decider in the development of reservoirs in the studied area. These reservoirs can be divided vertically in a set of weathering crust karstic reservoirs and a set of inner dissolution reservoirs, with the former consisting mainly of dissolution fractures and caves, and the latter comprising mainly caves. Cementation is an important diagenetic process for the reservoirs in the studied area because of its highly destructive effect on reservoir performance.