Structural Analysis And Reservoir Character In Baiyinchagan Depression

Baiyinchagan depression is part of downwarping faulted rift basin developed on XingmengHercynian multicycle and collision fold basement in late Mesozoic.It is early faulting and laterifting, together with structural reverse and wrenching strike slipping,especially its well developedsub-fractures.Geological structural characteristics in the depression is very complicated because ofstacking of multi structural movement. So study on relationship between structural faulting andreservoir is of great importance for further exploration in this depression.Regarding multicycle structure and basin evolution,taking basis on 2D and 3D seismic datawith comprehensive analysis, focusing on historical occurrence, characteristics, strata depositionand development evolution of the depression, combining recent drilling and exploration anddevelopment data, this article has comprehensively analyzed this depression consisting of its type,fault and structural evolution,grasped its reservoir formation and distribution, built the evolutionmodel and consequently found its exploration target and potential.Study shows fractures of Baiyinchagan depression mainly trend NEE and NNE, and NNW,NWW and nearly EW as well. NEE and NNE striking fractures have long distance andpredominate early basement fracturing. On the plane, the fractures appear parallel, lateral, "X" andso on. While on the section the factures are like faulted steps, broom, flowers, "Y" and so on.Early tension fracture, middle shear strike slipping or normal overturning occurred during themovement.Present structure was developed in a complicated and various stress field environment. Thedepression was faulted to be a basin caused by early NW-SE stress, while in the late periodNNW-SSE compression happened to cause wrenching strike slipping and reverseg. 3D seismicdata shows most of the structures in the depression are of expanding style, consisting of reversefault block, accordant fault block, listric slipping fault block, horst and grabon expanding faultblock, vertical and lateral faulted nose or fold and so on, but overturning and shearing strike slipstructures are also developed in local area. Daerqi area in the south slope and north Guer area arebig nose structure developed on basal uplift, which is an important adjustment belt for EW strikingstructures. Both of their sides deposited very thick sandy mudstone formation.Development evolution provides the depression good geologic condition for reservoirformation. South of the depression is the most important area for petroleum migration andaccumulation. While north structural trap is mainly developed when rifting and reverse happened.It is a very favorable belt for petroleum accumulation.Reverse after Saihantala can both destroyearly preserved reservoir to escape and accumulate hydrocarbon in new traps. Current discoveredreservoir is controlled by structure for the most time. Reservoir formation is greatly relative tofracture and structural movement. Various structures and structural-lithologic trap are favorableplaces for hydrocarbon accumulation.Analysis suggests faulted belt and structural adjustment beltare advantageous to find oil and gas accumulation. Depression belt has weak structural movementwith good preservation so it is an important area to seek subtle reservoir and new types ofreservoir even production increasement as well.