Diagenetic Facies and Reservoir Quality of Paleogene-Cretaceous in Northern Tarim Basin

The Paleogene-Cretaceous reservoirs with lithic sandstone and greywacke lithic sandstone in northern Tarim basin is mainly in stage of medium diagenesis, and have obvious differentces among them in different areas, different intervals, rock composition, diagenetic evolution, diagentic mineral assemblage and pore type. This paper presents the diagenesis classification in terms of authigenic mineral type, distribution and genetic order as well as the effect of pore type assemblage, pore characteristic and tectonic action on the reservoirs, including the intense cementation and compaction diagenetic facies, the medium cementation and dissolution diagenetic facies and weak cementation diagenetic facies, among which the reservoirs with analcite-dolomite cementation are the best ones. Also, the reservoir quality is divided into four types of reservoirs base on the lithologic and pethophysical parameters of Paleogene and Cretaceous in different areas and different structural belts. TypeⅠand Type II reservoirs could be as the main targets for oil and gas exploration, Type III low permeability reservoir is as the target for gas exploration, and Type IV reservoir with super low porosity-permeability and compaction even belongs to non-reservoir.