Characteristics and main controlling factors of the Cambrian pre-salt dolomite reservoirs in Tazhong Block, Tarim Basin

Studies on the Cambrian pre-salt dolomite reservoirs is still rare in eastern Tarim Basin, although the exploration there has made great discovery. Research on reservoir types and characteristics, main controlling factors and distributions of the Cambrian pre-salt dolomite reservoirs were presented on the basis of drilling data, cores, thin section SEPM, logging and 3-D seismic data. The results show that grain dolomite reservoir of beach facies and gypsodolomite reservoir of tidal flat facies are two main reservoirs in the pre-salt dolomite of Cambrian in Tazhong Block, Tarim Basin. The former exists in the Lower Cambrian Xiaoerbulake Formation and the Middle Cambrain Upper Shayilike Formation. Lithologies include algae granular dolomite from shoals in platform proximate, algae dolomite and silty crystalline dolomite, and were mainly controlled by facies. The reservoir quality are mostly inherited from deposition and the porosity was improved by the later interlayer Karst processes. The latter mainly exists in the Middle Cambrian Awatage Formation and Middle Cambrain Lower Shayilike Formation. Lithology include gypsiferous dolostone, silty crystalline dolomite, gypsodolomite breccia and they were controlled by both petrography and later fracturing. For its microporous reservoir, the matrix formed during deposition while micropores formed due to later organic acid dissolution. Nowadays, the favorable objectives are most likely to be grain dolomite reservoirs of beach facies in Lower Cambrian Xiaoerbulake Formation. © 2017, Editorial Office of Oil and Gas Geology. All right reserved.