Microbial carbonates dominate the 2

nd

and 4

th

members of the Dengying Formation in the Upper Sinian

Sichuan Basin.The 2nd member contains mainly thrombolites and grapestones with botryoidalis pores

microbe visceral pores

microbe framework pores

inter-clot dissolved pores as reservoir space.Vertically

there are three reservoir intervals with bi-tumen concentrated 117 m below the unconformity of the first stage of the Tongwan movement.The 4th member contains largely laminites and stromatolites

with fenestral pores and karst pores as the main reservoir spaces and inter-clot dissolved pores and microbe visceral pores as the minor reservoir spaces.Three reservoir intervals occur in the member with bitumen concentrated 134.2 m below the unconformity of the second stage of the Tongwan movement.The development and distribution of microbial carbonate reservoirs in the members are suggested to be controlled mainly by shallow water tidal microbial mat

microbial structures

dolomitization and Mianyang-Changning intracratonic sag. The widespread mat might be the foundation of high-quality reservoirs

the microbial structures be the cause of the original reservoir diffe-rences

the dolomitization be the key to the formation of the reservoirs

and the weathering karst and burial dissolution controlled by the Mianyang-Changning intracratonic sag be the determinative factor for the modification and distribution of the reservoirs.And it is predicted that high-quality reservoirs in the Formation be along both sides of the margin area of Mianyang-Changning intracratonic sag.