Structural Evolution Of Tangyuan Faulted Depression And Its Control For Reservoir In Yi-Shu Graben

The Tangyuan Fault Depression in Yi-Shu Graben is the object of this study.Based on the geology, seismic and drilling data, the structural evolution of TangyuanFault Depression and its impacts on basin formation, hydrocarbon formation and oilaccumulation are systemically studied by the study of geo-kinetics, tectonics,sedimentology, petroleum geology and other analysis.The structural evolution of Tangyuan Fault Depression shows that: its Mesozoicbasin is overridden by its Cenozoic basin;the Cenozoic fault controlled the boundaryof the depression and the depression is a passive rift basin. The structural andsedimentary evolution experienced 6 phases: Mesozoic fault depression phase,Cenozoic strong fault depression phase, continuing fault depression phase,fault-depression transformation phase, fault depression suppression phase and faultdepression subduction phase. The faults developed mainly in NE and NNW, secondlyin approximately NS and approximately EW. The NE faults controlled thetrend of thedepression and the sub-depressions;the NWW faults dependented on and cut the NEfaults, dividing the NE structural trends into North and south blocks. 3 main types offault exists: tensional/ tensional-shear faults, compression/ compression-shear faultsand strike slip faults. The bounary major faults controlled the distribution of sourcerocks;major faults controlled the formation and distribution of traps;the faults whichdisrupted or near the source rocks provided good passage forpetroleum migration;sealed faults acted as the favorable shelter to petroleum accumulations.The tectonic –kinetics study reveals that IV Block in the depressiopn has themaximal basement extension distance., while I Block has the maximal basementextension rate and factor, and the Wutonghe syncline and Jnjiaotun structure in VBlock have the minimal basement extension distance. Since the first member ofBaoquanling Group sedimented, the Pacific Plate diving direction changed from NWto approximately EW, causing the dextral strike slip faulting happened to the majorfaults in the depression, then some approximately NE slump faults appeared.The petroleum geology study shows the main petroleum accumulation patternsare stratigraphic overlapping, fault screening, sandstone updip pinchout and faultblocking. The 4 main types of hydrocarbon reservoirs in the depression arestructural-lithologic reservoir, lithologic reservoir, structral reservoir, stratigraphicoverlap reservoir and stratigraphic unconformity screening reservoir.Comprehensive analysis reveals that the central convex trends is most favorableexploration play, III Block is the most favorable exploration block.. The main zonesof interest are the deeper beds below the first member of Baoquanling Group.