Reef Development Distribution and its Controlling Factor in Xisha Offshore

Taotao, Yang; Fuliang, Lu; Bin, Wang

Reef reservoirs are important exploration targets for oil&gas. Currently there are 13 oil&gas fields accumulated in the reefs, and each EUR(Estimated Ultimate Reserves) is as high as 80 million tones. In the worldwide, 8 wells each has daily production as high as 10 thousand tones, half of which accumulated in the reef. Reef plays an important role in oil&gas exploration in South China Sea. More than 90 oil&gas fields accumulated in reef, and accounts for 12% in all the fields discovered in South China Sea while their reserves accounts for 33%. The biggest gas filed in South China Sea and the biggest oil field in northern South China Sea both accumulated in reef. It's extremely meaningful for oil&gas exploration and economic analysis to study reef distribution. Geophysical data is important for reef comprehensive research. In the worldwide reef discovered through geophysical data accounts for more than 70%. 200 reefs were discovered, and a series of oil&gas reservoirs were discovered through geophysical data in South China Sea. Geophysical data should be attached great importance for the development and distribution study on reef.

Xisha offshore lies in northern South China Sea, with water depth 0~3000m, and wholly there are a central uplift and depressions around. At present, there is no well targeting oil&gas in this area. The study suggested that reef forming condition should be proper. There was a carbonate platform, which developed abundant reef from Miocene to Holocene, and now it is developing to an island. Based on the 2-D & 3-D seismic data in recent years, the seismic reflection feature of typical reef was discussed. The seismic identification standards of reef were set up. And the reef recognition study was extended to the entire study area. Based on the reef distribution feature, taking the structure and sedimentary evaluation into account, and revolving around the ancient sea level changing, the reef distribution feature was studied. Vertically the reef appeared retrogradation characteristics, which was mainly controlled by the level change of South China Sea. In the plane, reef was controlled by the north to east trend structural framework and influenced by sedimentary source, while developed on a wide range along the uplift. Study on the reef distribution and controlling factor made sure the reef distribution, provided direct basis for oil&gas exploration, and greatly promoted the geology research in this area.

AAPG Search and Discovery Article #90163©2013AAPG 2013 Annual Convention and Exhibition, Pittsburgh, Pennsylvania, May 19-22, 2013