AN ANALYSIS OF THE DISTRIBUTION OF SUBSURFACE FLUID PRESSURE AND ITS RELATION TO THE PETROLEUM MIGRATION AND ACCUMULATION IN YANCHANG GROUP, SHANXI-GANSU-NINGXIA BASIN
Chen Heli;Liu Yong;Song Guochu Northwest University Xian Petroleum College Changqing Oil Field
This study is concentrated on the distribution of fluid pressure in the Mesozoic strata in south of Shanxi-Gansu-Ningxia Basin by means of“equaldepth”technique based on the formation compaction curves. It has been discovered that abnormally high pressure is existed in all wells penetrating Chang-7 oil-group. The distribution of abnormally high pre-ssure in each subgroups of Yanchang Group shows a similar pattern areally. Such pressure is highest nearby Lingwu-Yanchi in the northwest part of the studied area, is moderate nearby Hulu Rever-Luo Rever in the southeast part; and is lowest in the northeast and the southwest parts. A contrast of the distribution of abnormally high pressure and known oil-bearing areas suggests that oil fields and commercially productive wells is located mainly in the regions having lower abnormal pressure in the corresponding oil-bearing formation group; and the oil-bearing formations mainly is located in the normal pressure section, veatically, and relative lower pressure zones within the abnormal pressure zones come to the next. Based on the above analysis, this paper emphatically discusses the migration and accumulation of oil and gas in Chang-7 oil-group, the main source rock in Yanchang Group. It is pointed out, that there are two belts in favour of accumulation of oil and gas; one is Jirigbian-Wuqi-Qingyang and a region sourthwest to it, i. e, an area located between the abnormally high pressure regions: Lingwu-Yanchi and Hulu River-Luo River, being the first, and Ansai-Fuxian and its eastern region being the second.