Research On Depositional System And Forecast Of Source Rocks Of Shahezi Formation In Xujiaweizi Fault Depression

Deep Songliao Basin is a part of northeastern fault depression group of Late Jurassic - Early Crataceous, alternating with depressions and uplifts. Xujiaweizi Fault-depression is an important hydrocarbon bearing fault-depression, located in the middle-north of the fault-depression group of Deep Songliao Basin. In this thesis, the target formation is Shahezi Formation.The purpose of this thesis is to forecast the spacial distribution and reserve of the source rocks by the method of depositional system with rock data, well data, log data and seismic data. The thesis employs Sedimentology, Sequence Stratigraphy, Logging Geology, Seismic Stratigraphy and Seismic Sedimentology. The research includes defining sequence on wells and on seismic sections, defining deposit facies, correlating wells and seismic sections, summarizing the relation between seismic facies and deposit facies, drawing seismic-deposit well link and the spacial distribution of depositional system, and finally forecasting the source rocks distribution according to which deposit facies are favorable for source rocks.It is found in the research that Xujiaweizi is a large-scaled half fault depression beginning from Shahezi period. Due to compression and volcano eruption in the period of Yingcheng, the strata in the basin suffered from being folded, inversed and divided, so when interpreting the seismic facies, the impact from post reformation needs to be revised. In the thesis, the deposit system is build with well method and seismic method. Deep lake and shallow lake dominate in the project area, with fan delta on the steep slope and braid river delta on the gentle slope.There are eight seismic facies identified in the project area. Moundy progradation and moundy random dominate at the steep slope, reflecting fan delta; wedge diverge dominates at the gentle slope, reflecting braid river delta; sill-like parallel dominate in the middle, reflecting deep lake and shallow lake. The project area has several deposit centers; the thickest two are at SongZhan and Xingshan; there are also small center in the north and south; deposit centers are closely related to dark mudstone namely good source rocks. The dark mudstone, part of the good source rocks, is mainly distributed at deep lake, shallow lake and the delta front. In the end, the result of the assessment comes out that the gas generation potential of Shahezi Formation in Xujiaweizi is quite considerable.