Shiyou shiyan dizhi (Jul 2021)
Hydrocarbon generation characteristics and significance of accumulation of Upper Paleozoic source rocks in Dongpu Sag, Bohai Bay Basin
Abstract
In order to clarify the conditions and rules of hydrocarbon accumulation of the Upper Paleozoic in the Dongpu Sag of Bohai Bay Basin, source rock evaluation, pyrolysis experiment and basin modelling were carried out in this paper, the history of hydrocarbon generation and intensity of source rocks have been quantitatively studied, consequently, the significance of hydrocarbon accumulation in this area has also been discussed. The micro-composition of the Carboniferous-Permian source rocks in the Dongpu Sag is featured by high contents of hydrogen-rich exinite and matrix vitrinite (>10%), and the source rocks have a high oil-generating potential. The hydrocarbon generation process is characterized by multiple stages and wide gas generation band. During the Yanshanian period, the Carboniferous-Permian source rocks were shallowly buried, the Ro value ranged between 0.6%-0.8%, and only a little gas has been generated. In the Himalayan period, due to the differential thermal evolution of the Paleogene deposits, from the western part of the sag to the western slope, gas generation was significantly decreased, with an average of (1-20)×108 m3/km2. While in deep sag of the eastern part, source rocks were deeply buried with a high thermal degree, and a large amount of gas was generated with an intensity of (60-110)×108 m3/km2. Past exploration results have shown that the area with a gas generation intensity greater than 40×108 m3/km2 is favorable for natural gas accumulation. The gas generation intensity of the Qianliyuan sub-sag ranges (60-110)×108 m3/km2, which has favorable conditions for the formation of primary as well as paleogenetic and new-storage coal-derived gas reservoirs, and is a favorable exploration zone for the future exploration.
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