Petroleum System and Exploration Implication of the Deepwater Qiongdongnan Basin, Northwestern South China Sea: Learning from the New Wells(PPT)

摘要

The deepwater Qiongdongnan Basin, northwestern South China Sea was the frontier in China in last five years. There were 3D seismic data of 11000 square kilometers. Five deepwater wildcat wells were drilled with only one discovery. The petroleum system was analyzed and favorable prospects were evaluated. The Qiongdongnan Basin underwent the Paleogene syn-rift episode and the Neogene post-rift episode. Most deepwater wells penetrated the lower Oligocene to Quaternary and indicated the early bathyal environment in Late Oligocene. Integrated with the regional 3D seismic interpretation, drilling results, and geological studies, petroleum system developed in the deepwater Basin. The primary elements of petroleum system were source rocks, reservoirs, and hydrocarbon migration. The source rocks were coastal plain mudstones of the lower Oligocene, which were coaly, rich in TOC and gas-prone. Upper Miocene turbidite sandstones developed generally in the Central Canyon with thick sandstones and good porosity and permeability. The lower Miocene and Upper Oligocene submarine fans developed in several subbasins. Due to the absence of areal distribution of sandstones carrier, the hydrocarbon migration distance was relatively short. Major faults or fissure zones were the vertical migration pathways. The proven play by the gas well Lingshui A-1 was the structural-lithological trap of Upper Miocene in the Central Canyon , with high quality turbidite sandbodies. This well confirmed the vertical gas migration from deeper Oligocene into the shallower Upper Miocene trap. The reasons for failures of other wells were mainly the absence of quality sandstone reservoirs , or difficulties of lateral migration with long distance. The most favorable prospects are the similar traps in the Central Canyon in Lingshui Subbasin, belonging to the same play of Lingshui A gas reservoir. The secondarily favorable prospects would be several faulted anticlines in southern Baodao Subbasin. Conclusively, large exploration potentials remain in the deepwater and further wells would be drilled soon.