A variety of methods to determine the accumulation period of tight gas reservoirs in the Upper Paleozoic of Ordos Basin

Abstract

There is no unified view on the formation period of Upper Paleozoic gas reservoirs in Ordos Basin, China. This study takes Yulin area located in Yishan slope of Ordos Basin as an example, and comprehensively determines the period of gas accumulation through various methods. The study process includes : Firstly, according to the geological background and accumulation model, the idea of accumulation period analysis is established. Secondly, the necessary key parameters for the accumulation period are put forward. Thirdly, the burial history of strata, the dynamic characteristics of hydrocarbon generation of source rocks and the dynamic change of hydrocarbon content in reservoirs are studied. The key necessary parameters required for the study are obtained through the above process. Finally, according to these parameters, each time node in the accumulation process is determined, and then each accumulation period is determined. The results show that the Upper Paleozoic in Yulin area is ' three periods of hydrocarbon generation and two periods of hydrocarbon accumulation '. The three periods of hydrocarbon generation occurred in the Triassic ( -229 Ma ~ -200 Ma ), Jurassic ( -188 Ma ~ -151 Ma ) and Early Cretaceous ( -138 Ma ~ -100 Ma ). The intensity of hydrocarbon generation in each period increases in turn. The two periods of hydrocarbon accumulation occurred in Late Jurassic ( -178.5 Ma ~ -151 Ma ) and Early Cretaceous ( -138 Ma ~ -100 Ma ). The late Early Cretaceous ( -126.7Ma ~ -100 Ma ) is the main accumulation period. In order to avoid the application defects of various methods in this area, the research work uses the determined parameters obtained by every single research method. According to each accurate parameter analysis, the start time of hydrocarbon generation, the start time and end time of gas reservoir, and the time of each period of accumulation are obtained. This research process eliminates possible errors in the research process and ensures the credibility and accuracy of the research results.