| Chang6 reservior belongs to sandstone reservior which has extremely low permeability (permeability mostly less than 0.3md ), low pressure and low productivity in Yanhewan area in Ansai oilfield.Lithology is more tight and rock brittleness is bigger for low permeable sandstone, Reservior commomly develops tectonic fracture after an extent of tectonic movement.In low permeable reservior, fracture not only controls distribution of hydrocarbon reservoir,but also is the key of exploitation plan study for hydrocarbon reservoir.In unconventional reservior by low permeability,development of natural fracture will alter our attitude of evaluation for the type of reservior to a certain extent. Oil flow, reserve or production scale commonly gets the control of fracture system,clarifying development and distribution law of fracture is the key of successful oil exploration and rational development in low permeable reservior. Therefore, To make clear distribution law study of fracture for low permeable reservior certainly has a guidance sense for exploration and development in Yanhewan area.The main conclusion is as follows:1, Make certain the dominant direction of development for tectonic fracture system. In yanhewan area, Chang six reservoir fracture mainly develops NEE-EW snd SN direction of fracture system,which mostly is high angle tectonic fracture . Transformational fracture is less saw. fracture is mostly filled up and a large number of fracture is invalid fracture . fracture mostly develops in siltstone and fine sandstone.In addition,bed thickness and fracture density has a negative exponential relation.2, Make certain triaxial stress state of tectonic movement in primary deformation period-Yanshan period in yanhewan area. Major principal stress direction is NW in Yanshan period, the dominant direction of Major principal stress is 129°∠10°and the dominant direction of minor principal stress is 129°∠10°. 3,Make certain that Major principal stress is about 80-98Mpa in primary formation period of fracture- Yanshan Middle-Late period; Major principal stress is about 20.3-44.1MPa form Rock record in different depth.Major principal stress and depth has a relation (δ1=0.0149H+22.858(MPa),R2=0.907). Major principal stress direction is about NE68-76°for Chang six reservior in Yanhewan area.4, tectonic fracture primarily comes into being evening in middle Jurassic for Chang six reservior,migration time is evening of Late Crataceous. Analyse that tectonic fracture has an action in oil accumulation.5, Have an estimation of what is the range of fluid pressure for tectonic fracture reopenning and the induced fracture's formation in Yanhewan area. The fluid pressure for high angle tectonic fracture reopenning is about 15-19MPa and intrabed fracture reopenning is about 21-24Mpa. While the formation of induced fracture is about 21-24Mpa for Chang six reservior in Yanhewan area .6, Have a study of principal stress and direction for Chang six reservoir and an establishment of mathematical predication model for tectonic fracture in primary formation time of fracture in Yanhewan area and have a preliminary predication and estimationof favorable place for exploration inYanhewan area.. The predication of distribution law for fracture density of target and developmet direction of extension and shear fracture,and the application of the theory methods that tectonic stress drive the migration and accumulation of oil, supplies the scientifical reference for petroleum exploration in low permeability reservior.
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