Sediment Fill and Hydrocarbon Reservoir Character of Xiagou Formation and Their Correlation with Tectonic Evolution Feature and Mechanism of Mesozoic and Cenozoic in Qingxi Sag, Jiuquan Basin, NW China

The sediment supply in depositional stage, sedimentary dynamic procedure, evolution in post-depositional processes, and the responses of geologic bodies on multiple factors should be studied in the processes of basin analysis. Under the constraint of comprehensive and elaborate isochronous sequence stratigraphic framework, sediment fill and hydrocarbon reservoir feature of Xiagou Formation reflects the total control of episodic dynamical tectonic evolution laws in Qingxi Sag. Changes in the post-depositional processes could cause stratigraphic variations of Xiagou Formation in vertical times and transverse spaces as the tectonic reactivates laterally.

The sediment fill of basin is inseparable with the multiple interdependent factors of tectonic activity, basin subsidence, palaeogeomorphology, sediment supply and depositional system. Tectonic evolution of Mesozoic and Cenozoic affects and controls the inner sediment fill and hydrocarbon reservoir of basin directly. Different from general rifted basin, the Jiuquan Basin experienced the evolutionary phases of fault basin, fault-depressed diversionary period and foreland basin because of the influence of extensional rift faulting in Early Crataceous and thrust nappe motion in Tertiary, which presents the characters of both extensional rift and compression convergence and formed some special tectonic combination patterns.

Based on this structural setting, the basin had experienced the processes of depositional stage and subsequent reconstructive stages. It was still in fault basin environment during the depositional stage of Xiagou Formation, and then it experienced an ephemeral strong longitudinal compressional movement, which made the Xiagou Formation strata fold modified. Afterwards, thrust nappe motion in Tertiary not only reformed the sediment of Xiagou Formation, but also made the hydrocarbon source rocks, which reached critical mature stage in Early Crataceous but didn’t generate oil largely, be deeply buried in short time and come to oil forming fastigium.

The structural evolution reformed reservoir character, and resulted in peculiarity of reservoir patterns. The lithosomic bodies, unconformity surfaces, and faults, which experienced sedimentary stage and was reworked during the subsequent reconstruction, provide migration pathway and favorable traps for hydrocarbon accumulation, which are favorable for the formation of reservoirs.

AAPG Search and Discovery Article #90142 © 2012 AAPG Annual Convention and Exhibition, April 22-25, 2012, Long Beach, California