The control of Moho uplift over the distribution of the oil-gas-rich sag belt in the Beibu Gulf Basin
摘要
The Beibu Gulf Basin is an important oil- and gas-bearing basin offshore the China Sea, but the geological reserves of oil and gas are not very high, and there are significant differences between different sags. Previous studies have shown that the formation and accumulation of oil and gas are closely related to deep structures, especially the crustal thickness or the relative undulation characteristics between the Moho and basement, but there is a lack of specific evaluation and quantitative standards. In this paper, we first invert the depth of the Moho in the Beibu Gulf Basin using satellite gravity anomalies and calculate the crustal thickness value based on this. Then, we count and analyze the crustal thickness value as well as the stretching factor that characterizes the crustal extension and thinning degree, and find that the NWW-trending contour closure of the 28 km Moho depth or 26 km crustal thickness corresponds significantly to the Weixinan-Fushan sag belt, which has already been proven to have considerable oil and gas discoveries, with a typical feature of crustal thinning to 22 km and the stretching factor reaching 1.1. Finally, we propose a comprehensive evaluation scheme based on the entropy weight method to normalize and evaluate the statistical features of the crust, and take a comprehensive score of Si > 0.5 as an evaluation indicator for an oil-gas-rich sag. Based on this research, we believe that the Haizhong sag has considerable exploratory potential, followed by the Maichen sag, while the Leidong and Haitoubei sags have relatively smaller exploratory potential. The research results will help strategic decision-making of the oil and gas exploration in the Beibu Gulf Basin and provide new perspectives for studying the relationship between deep structures and the differential distribution of oil-gas-rich sags.