Characteristics and Exploration Direction of Cambrian-Ordovician Carbonate Rocks in Tarim Basin

There are three depositional and structural cycles of the Cambrian-Ordovician carbonate rocks in Tarim basin, which form stable structural framework with uplifts and depressions reconstructed by four-stage tectonic movements and three types of reservoirs like reef flat, unconformity and dolomite. Followed by three-stage hydrocarbon chargings such as Caledonian, Late Hercynian and Himalayan orogenies, they become petroleum reservoirs. These carbonate rocks feature old ages and low matrix porosity, and secondary solution pores and vugs are the main reservoir pore spaces. The unconformable reservoirs and reef flat reservoirs are controlled by sedimentary facies and zones of steep hill and ramp. The unconventional carbonate reservoirs with large area, medium-low abundance and layer control are wide distributed. The low porosity and low permeability reservoir features and multistage hydrocarbon charging result in the differences of oil-gas-water distribution and production. The oil-gas distribution is controlled by the space-time configuration between paleo-uplifts and source rocks. The carbonate reservoir and late gas charging constitute the major controlling factors for hydrocarbon accumulation. It is concluded that the Paleozoic paleo-uplift slope areas are the main targets for petroleum exploration; Tazhong paleo-uplift, Lunnan and surrounding Ordovician systems are the realistic domains for exploration; Yi Maili-Yaha and Maigeti slope are strategically major explorative areas for replacement of resources; Gucheng, Tadong, deep Lunnan, deep Tazhong-Bachu dolomite of Cambrian are the favorable areas for exploratory researches.