Petroleum Exploration Prospect of the Chengbei Sag, Bohai Bay Basin, Offshore China

Located in the sea area of the Bohai Bay Basin, offshore China, Chengbei Sag is a NW-trending Cenozoic half graben, with faulting in the northeast direction and overlapping in the southwest direction. The differential evolution of the NW-trending sag-controlling fault in the northeastern part results in two sub-sags in the northern and southern parts, with respective proven reserves of 10 million tons and 300 million tons. Comprehensive analysis combining the seismic and well data reveals that the two sub-sags share similar fault system characteristics, major fault properties, formation development, and unconformity distribution. Meanwhile, there are also differences in formation thickness and source rock burial depth though source rocks in both sub-sags have reached the hydrocarbon generation threshold and thus can provide sufficient oil and gas. The northern sub-sag is of great exploration prospect, and the exploration and development of it can refer to that of the southern sub-sag. To be specific, we should highlight the areas under the unconformity in the gentle slope belt, in the shallow faulting zone in the steep slope belt, and inside the uplifted buried hill.