Development and reservoir significance of mud mounds in Sinian Dengying Formation, Sichuan Basin

Based on core and outcrop profile observation, the characteristics and reservoir significance in oil and gas accumulation of mud mounds in the Sinian Dengying Formation of the Sichuan Basin were studied. Small-scale mud mounds in platform are widespread in the Sinian Dengying Formation, Sichuan Basin, mostly less than 2 m thick per cycle, but high in occurrence frequency, especially in Member 2 and Member 4 of the Sinian Dengying Formation. Particles constituting the mud mounds are thrombolite, algal stromatolite, oncolite and bindstone, related to cyanobacteria biocoenosis buildup, which bind and capture lime mud for the mud mound construction, and the relevant rock types include algal bound clotted dolomitite, algal bound frame-dolomitite, and undulating-cylindrical algal stromatolite associated with clotted dolomitite. Multiphase mud mounds with positive relief have abundant frame structures, zebra structures and stromatactis. Two kinds of depositional models are mound base-core-flat and mound base-core-cap, the former is more common. The mud mounds are closely related to reservoirs. Different sizes of pores developed in the mud mound core provide space for oil and gas accumulation, so the mound-shoal complex is the main exploration target of the Sinian Dengying Formation.