Geological Risk Evaluation and Mapping in Nanpu Sag of Bohai Bay Basin, China

Suyun Hu¹, Qiulin Guo¹, Shiyun Mi¹, Zhuoheng Chen², and Hongbin Xie^1
1Research Institute of Petroleum Exploration and Development, PetroChina, Beijing, China
²Geological Survey of Canada, Natural Resources Canada, Calgary, AB, Canada

The Nanpu Sag is one of the many small oil rich Tertiary depressions developed on a complex Paleozoic-Mesozoic basement in the Bohai Bay Basin, China. The northern half of this sag is onshore, where active exploration and drilling have led to the discovery of four large oil fields and several small oil-bearing structures. The southern half extends offshore, where high exploration cost and unknown geological risk have hindered large-scale exploration. Up to 2004 only four offshore wells had been drilled with two oil discoveries and two dry wells. Rapid increase in demand for oil in China has sparked recent interest in the search for hydrocarbons in the offshore part. To understand better the essential elements of the petroleum system and reduce exploration risk, a study aimed at regional geological risk evaluation and resource assessment was undertaken by PetroChina in late 2004. The study was based on available data collected by the end of 2004 and results include a probability map of petroleum occurrence, showing the geological risk of the Oligocene Dongying structural play. In 2005, seventeen exploration wells were drilled in the offshore area and sixteen penetrated the Dongying Formation. The high potential and low risk areas predicted by this study in southeastern Nanpu Sag were confirmed by these exploratory wells that led to discovery of the largest oil field found in the last 30 years in China. This paper discusses the geological risk evaluation and compares the predicted probability map of petroleum occurrence with the exploratory drilling results, with an emphasis on the oil bearing structural play of the Oligocene Dongying Formation.

AAPG Search and Discovery Article #90078©2008 AAPG Annual Convention, San Antonio, Texas