Origin, characteristics and significance of collapsed-paleocave systems in Sinian to Permian carbonate strata in Central Sichuan Basin, SW China

Abstract

The origin, characteristics and geological significance of the collapsed-paleocave systems in the Sinian to Permian carbonate strata in Central Sichuan Basin are studied based on 3D seismic interpretation and attributes analysis, as well as imaging logging and cores. Collapsed-paleocave systems are distributed in the Sinian to Permian carbonate strata vertically and along the ends, releasing offsets and intersections of faults horizontally. On profile, they occur as seismic events push-down. The collapsed-paleocave systems mainly originated from fault movements at three main structural phases, the first stage of Tongwan, the second and third stages of Tongwan and the Early Caledonian, and eventually got into shape at the end of the Permian. The collapsed-paleocave systems are featured by multi-layers, wide distribution and good reservoir quality, in which reservoir space is made up of pre-existing pores, structure genetic fractures and collapsed genetic fractures. According to seismic response characteristics, three types of collapsed-paleocave systems are identified in this area, including multi-layer cave system collapsed complex, multi-layer cave passage collapsed system and intra-bed cave collapsed system. The multi-layer cave system collapsed complex and multi-layer cave passage collapsed system in the overlying deformed layers where fractures are widely distributed may be the favorable targets for future exploration. Key words: collapsed-paleocave systems, collapse mechanism, concentric circular faults, Sinian to Permian, Central Sichuan Basin