TITLE:
Distribution and Geochemical Characteristics of Source Rocks in Chang 7 Member of Qilicun Oilfield in Ordos Basin
AUTHORS:
Wuernisahan Maimaitimin, Chenhang Xu, Shanshan Chen
KEYWORDS:
Qilicun Oilfield, Hydrocarbon Source Rock, Evaluation of Tight Oil Reservoir Forming Conditions, Chang 7
JOURNAL NAME:
Open Access Library Journal,
Vol.10 No.3,
March
30,
2023
ABSTRACT: In the past, the research on tight oil accumulation in the eastern part of Shanbei slope of Ordos basin is relatively weak, mainly because the effective source rock is not developed in this area, and the crude oil is migrated from Chang 7 source rock in the center of the lake basin. Taking Qilicun Oilfield in Yan’an area as an example, this paper studies the reservoir-forming conditions of Chang 7 tight oil according to the methods and means of well logging, thin section identification, reservoir physical properties and core description, source rock geochemistry and so on. the results show that the hydrocarbon source rocks of Chang 7 member in the study area can be divided into black shale and dark mudstone with a wide distribution range, and the thickness of hydrocarbon source rocks is thinned from southwest to northeast as a whole. Organic geochemical indexes of source rocks reveal that Chang 7 black shale is a high quality source rock. The sand bodies of each subformation of Chang 7 are distributed, but the thickness of the single layer is thin and the physical property of the reservoir is poor, so it is a typical tight reservoir. The comprehensive analysis of the reservoir forming conditions of Chang 7 shows that the study area has a good source rock foundation, poor reservoir conditions and superior reservoir assemblage, but due to the development of vertical macroscopic microfractures, the oil generated by vertical Chang 7 source rocks is mainly overpass Chang 7 reservoir, and the probability of accumulation is small, which indicates that the exploration potential of Chang 7 reservoir in this area is poor as a whole.