The genetic classification and evaluation of the Lower Ordovician carbonate reservoirs in the Tahe Oil Field, Xinjiang

The oil and gas in the Tahe Oil Field, Xinjiang mostly occur in the Lower Ordovician carbonate (reservoirs). The study of the storage spaces and reservoir types is believed to be significant for the exploration and development of the oil field. The present paper deals with the genetic classification of the Lower Ordovician (carbonate) reservoirs in the Tahe Oil Field on the basis of the examination of boreholes, cast thin sections and well logs, and the evaluation of the reservoir quality has been made on the basis of the development of storage spaces, porosity and permeability, and other analytical data of the carbonate reservoirs. The results of research have disclosed that: (1) five types of storage spaces are recognized, i.e. solution pores, solution spaces, caves, weathered fissures and structural fissures; (2) five genetic types consist of shoal grainstone solution pores-type reservoirs, weathered (fissure)-type reservoirs, cavity-type reservoirs, surficial fissure- and pore space (pore)-type reservoirs and structural fissure-type reservoirs, and (3) the cavity-type reservoirs are interpreted as the main target due to their high quality and high production. In addition, the structural fissure-type and weathered (fissure)-type reservoirs have been found to be very significant in the Lower Ordovician carbonate reservoirs in the study area.