Well logging interpretation of the carbonate karst strata in the Dengying Formation in central Sichuan

Affected by the episodes I and II of the Tongwan movement, the topmost parts of the 2nd and 4th members of the Dengying Formation were subjected to the weathering and denudation, which gave rise to the widespread dissolution of the carbonate rocks in the Sinian Dengying Formation in the Moxi-Gaoshi region, central Sichuan. The distribution of hydrocarbon reservoirs may be predicted on the basis of boreholes, well logging and FMI images. The karst sections in the study area may be divided, in a decending order, into surficial karst weathering zone, vertical infiltration karst zone, horizontal subsurface flow karst zone and deep sluggish flow karst zone. The surficial karst weathering zone accumulated by chaotic accumulation of the weathered residual materials and the horizontal subsurface flow karst zone with developed pore spaces are believed to be the best favourable horizons for the development of the reservoir rocks, followed by the vertical infiltration karst zone. Regionally, the karstification becomes progressively stronger from southwest to northeast in the study area in the palaeokarst slope zone.