Research of Types and Causes about None-beaded Fracture-cave Reservoirs in the Ordovician Carbonate of Tarim Basin

Strong beaded reflection are important exploration target for carbonate reservoirs of Tarim Oilfield. In contrast, the widely distributed weak reflection with none-beaded feature are has not taken seriously.

Recent exploration proves that the none-beaded reflection can still output hydrocarbon, so the paper will focus on it. We divide this kind of reservoir into three types according to the degree of fracture-cave development and considering the influence of weathering crust and fracture. First is fracture-cave reservoirs closer to weathering crust, second is small scaled inner fracture-cave reservoirs, third is mainly fracture reservoir which can be further divided into three sub types such as fractured reservoirs mainly caused by tectonic movement, collapse-fracture zone at the roof of cave and fracture zone formed by differential compaction above the ancient river. Through detailed analysis, we think that, besides tectonic fractured reservoirs, the fracture-cave reservoirs closer to weathering crust and collapse-fracture zone at the roof of big caves are most likely favorable targets, which is helpful for researchers in Tarim oilfield to jump out of the beads strong reflection. The fracture zone formed by differential compaction above the ancient river may be a potential exploration target and field in the future.