Sedimentary Filling Evolution And Tectonic Control On Deposition Of The Lower Cretaceous In Wunan Depression

Hailaer basin is in the Inner Mongolia and it is one of the biggest oil-rich basins outside the Songliao basin. Wunan depression is one of the most potential prospecting area and plays an important role in exploration strategies.Based on the new theory and methods sequence strategy, tectonic strategy and basin analysis, there are 6 regional unconformities and 3 local unconformities, thus we can divide 9 third-order sequences, 5 second-order sequences and 1 first-order sequences.There are 5 kinds of sedimentary systems in Wunan depression, for example fan delta, bride river delta, sublacustrine, meandering river delta and lacustrine. Drawing the sedimentary facies map in third-order sequence can illustrate the type of sedimentary facies in different sequence and their evolution in three dimensions very well.Through the analysis of tectonic subsidence in single well, the evolution of the basin can be divided into different evolution stages. We find that the syndepositional faults have a major control over the evolution of the basin. The Tongbomiao formation is formed in synrift extension stage when the north-northeast faults is very active. The Nantun formation is formed in half-graben stage when the NS faults are very active. The Damoguaihe formation is formed in faulted-depressed stage.Analyzed the control of syndepositional fault over the center of deposition and subsidence, and their control over the sedimentary systems.The fan delta in HST, the frontier of braid delta, braid river delta in LST and sublacustrine fan in different sequences are the best place for reservoirs. And their distributions are along the syndepositional fault.