Fluid inclusion characteristics of the Jurassic reservoir and hydrocarbon accumulation process in the eastern Kuqa Depression, Tarim Basin

Abstract

AbstractThere has been significant progress in hydrocarbon exploration of the eastern Kuqa Depression, Tarim Basin, whose Jurassic reservoir is a key area for abundant hydrocarbon with poorly understood accumulation mechanism. This study conducts an integrated investigation comprising petrographic observations, microthermometry measurements, and fluorescence spectroscopy analyses on fluid inclusions to reconstruct hydrocarbon accumulation history in the Jurassic reservoir. These conclusions are combined with biomarker characteristics to reveal the burial history and thermal evolution of the study area. The results show that (1) there were two episodes of oil charging that occurred at 6~4 Ma and 4~2 Ma, respectively. The QGF experiment response and yellow fluorescent oil inclusions indicated that low-maturity medium crude oil from the Triassic source rocks was expelled into the upper Ahe Formation. In the second charging stage, some mature oil generated from Jurassic source rocks was charged into the reservoir of the Kezilenuer and Yangxia formations, while the condensate from the Triassic source rocks was migrated upward to the Jurassic reservoir, consistent with smaller QGF-E intensity values and blue-white fluorescent petroleum inclusions. (2) There were two kinds of hydrocarbon accumulation models including the lower-generation and upper-storage and the self-generated and self-stored models. (3) It was noted that active faults were developed under the compression stress to provide channels for hydrocarbon vertical migration. Moreover, the early reservoir was destroyed resulting from the strata denudation and a large amount of crude oil was escaped to the surface. The findings of this study can help for better understanding of hydrocarbon accumulation mechanism in the eastern Kuqa Depression and provide theoretical guidance for further oil and gas exploration.