Post-rifting structure characteristics and shallow hydrocarbon accumulations in Qikou sag
Qi Peng1,2, Ren Jian-ye1,3, Ai Neng-ping4, Shi Shuang-shuang1, Zhou Jiang-yu1, Zhang Jun-xia5
1. Key Laboratory of Tectonics and Petroleum Resources of Ministry of Education, China University of Geosciences(Wuhan), Wuhan, Hubei 430074, China;
2. Research Center of CNOOC, Beijing 100027, China;
3. Secondary Center of CUG, Structural Research Center of Oil & Gas Bearing Basin, Ministry of Education, Wuhan, Hubei 430074, China;
4. Zhanjiang Branch, CNOOC, Zhanjiang, Guangdong 300280, China;
5. Faculty of Economics and Management, China University of Geosciences(Wuhan), Wuhan, Hubei 430074, China
Abstract：The bottom surface of the Guantao Formation,in Qikou sag,is an important unconformity interface which can be traced in the region.This surface divides the basin evolution into the rifting stage in Paleogene and post-rifting stage in Neogene-Quaternary.The most post-rifting structure styles include faults,faulted-folds and the igneous structures in the Qikou sag.Through detailed interpretation on high quality 3D seismic data,we summarize the post-rifting structure characteristics and calculate fault active rate to determine the tectonic activity law in Qikou sag.Then we get the following observations:①The active faults includes continued growing main faults and numerous EW trended new faults,and these two kinds of faults intersects to each other with low angle which show as the broom shape on the plane,associated with the regional dextral tensile shearing stress field.②The fold structure includes drape anticline,reservoir drag fold and normal shaped negative flower structure which distributes orderly from west to east on the plane,but they coexist together in some place.③Igneous structures usually show as a long volcanic channel with several hat shape structures.The top of volcano characterizes as strong reflections because of the onlap of the overlaying strata,and several faults formed beside these volcano channels.④The main fault active rates show that the activity of the post-rifting faults can be divided into three types in Qikou sag:continuous decrease after continuous increase,continuous increase and mixed pattern.The first and second types of the faults are most beneficial to hydrocarbon accumulations and distributed in the oil fields.The most valuable shallow reservoirs in Qikou sag are the faulted-fold type and the buried-hill drape anticline type.Active igneous rocks are also very valuable to the generation and migration of the hydrocarbon.
