Trough Structure And Its Control On Reservoir Forming In Middle Rift Zone Of Hailer-Tamtsag Basin

Trough is a secondary sag unit in continental basin. Single or multiple troughs candevelop in a sag. Most troughs are asymmetric. In general, its boundary is fault systems onone side and formation slope or secondary fault system on the other side.On the basis of Hailer-Tamtsag Basin tectonic evolution analysis, with middle rift zoneof Hailer-Tamtsag Basin as target, major faults distribution rule and activity was analyzed.Then troughs structure and their combination style were analyzed. Then a qualitative andquantitative recognition model, which is a relationship between fault throw-distance profile,fault throw backstripping method, seismic reflection characteristics and syn-tectonicsedimentation thickness, was established. With this technology, palo-trough was restored andtheir evolution process was analyzed in middle rift zone of Hailer-Tamtsag Basin. Duringactive rifting, Hailer-Tamtsag Basin was cut into multiple small troughs. There are fivestructure styles in section, which are troughs with single fault type, asymmetrical double faulttype, ramp-flat fault type, double fault with central uplift type and fault-steps type. Multipletroughs combined into a complex spatial pattern. There are five combination styles, which areindependent half-graben, parallel half-graben combination, tandem half-graben combination,‘back to back’ half-graben combination and echelon half-graben combination.On the basis of growth characteristics of boundary faults, fault growth associatedstructures, sedimentary model and stratigraphic sequence, four kinds of fault displacementpropagation manners and seven trough-growth manners were summarized. While inHailer-Tamtsag Basin, five trough growth manners were recognized. They are multipletroughs growth at same time which are controlled by segmented growth fault, isolate troughgrowth with constant length which is controlled by isolate fault, isolate trough growth withunidirectional lateral propagation which is controlled by isolate fault, multiple troughsdifferent growth controlled by reactive fault and troughs with one period developed.Palo-through and its evolution controlled distribution of hydrocarbon source rocks. Center ofsource rocks thickness is consistent with depocenter of troughs. While source rocks ontransverse anticline is thin.System analysis of troughs structure and palo-troughs restoration plays an importantrole in guiding source rocks prediction and submitting new high-quality reserves in oil fields.Further more, it will have very good practicability and popularization in deep exploration of aseries of basins in central Asian tectonic domain eastern Mongolia. It has importanttheoretical significance in improvement of ‘trough control hydrocarbon’ theory andenrichment ‘fault control oil reservoir theory in rift basin.