Dynamics for multistage pool formation of Lunnan low uplift in Tarim Basin

Abstract

Lunnan area in the Tarim Basin has become an important onshore oil production base in China. Formation of the oil and gas pools in the low uplift of Lunnan has experienced a comparatively complex process of dynamics. Based on the hydrocarbon generation period of source rocks, the formation period of cap rocks and traps, the analysis of organic inclusion and the analysis of bitumen in the reservoir, this paper draws the conclusion that the low uplift area of Lunnan has experienced three pool formation periods: the Permian period, the Cretaceous-Early Tertiary period and the Late Tertiary-Quaternary period and two oil and gas reservoir adjustment periods: the Late Permian period and the Late Tertiary-Quaternary period. The comprehensive study indicates that the largescale Ordovician buried hill, formed in Early Hercynian, became the reservoir during the Permian period, because the Cambrian-Lower Ordovician oil was discharged laterally into the reservoir along the top of the Ordovician weathering crust from south to north. The reservoir experienced a complicated process—reconstruction in the end of Permian, adjustment in Cretaceous-Early Tertiary and redischarging process in Late Tertiary-Quaternary, leading to the early original heavy oil reservoir of marine facies and the late original light oil reservoir and gas pool. Carboniferous, Triassic and Jurassic oil and gas reservoirs result from upward adjustment and redistribution of Ordovician oil and gas reservoirs. Of those results, the formation of Triassic-Jurassic oil and gas pools came under the influence of the northwardtilting structure. The oil and gas sourcing from the different hydrocarbon source rock intervals vertically migrated into the base unconformity of Triassic system. Then the oil and gas migrated laterally from north to south and accumulated into the reservoir.