Developmental Characteristics And Distribution Predicting Of Shanxi Formation Shaly Fractures In Yanchang Oil-gas Field,Ordos Basin

It contains a large amount of shale gas resources in the southeast area of Ordos Basin,a set of dark shale of marine-continental transitional facies developped Shanxi formation of Permian,that has good condition of source rocks for shale gas.The shale gas is self-generation and self-accumulation,shale layer not only could be source rocks but also reservoirs.Fractures provide migration conditions and accumulation spaces for shale gas.,will contribute to artificial modification and production.Therefore,evaluating and researching cracks in organic-rich shales is significance to accumulation and preservation of shale gas,but also has important significance to the exploration.The paper based on abundant geological materials,logging data,experiment test,core observation,etc.Using the denudation recovery,logging identification and numerical simulation methods and techniques,etc,to study ancient tectonic background,fracture development characteristics,the distribution on the single well and on the surface.Aanalysis factors that influenced the fracture development,predict favorable areas of fractures in the study area.Today the overall structure of Shanxi Formation was east is high,meanwhile the west is low,north-south trending west-dipping monoclinic-relief.From Triassic to the Cretaceous experienced subsidence uplifting movement,that assist the fracture developped.The shale of Shanxi Formation developped several major types of fractures,Such as structural fractures and bedding fractures,diagenetic shrinkage fractures,and organic matter evolution abnormal pressure fractures,etc.aboveall,the main type was structural fractures and bedding fractures.Mainly length at 6.5 cm to 13 cm,mainly angle with low angle fractures and oblique fractures,the high angle was the leaset.Micro cracks are mainly composed of organic matter banding fractures,then the intragranular flange grain fractures,dissolution fractures,etc,The major was open fracture,filling fractures was the minority,fillings with organic matter.Using stress field numerical simulation to predict the structural fracture distribution in the study area.Structural fracture mainly distributed in northeast Xiasiwan-southwest transition zone and northern YunYan,trending was North west-south east on the whole.The fracture mainly distribution was at the top and bottom section on the single well.Factors influencing fractures were tectonic stress,lithology,layer thickness,etc.High tectonic stress assisted tectonic fractures developed.The quartz and high brittleness mineral content assisted natural fractures.Rich organic matter in thick layers of shale,a large number of lamellation seam developped between the layers,the higher the organic matter,organic matter fractures developped.Considering the influence factors,evaluating and predicting favorable areas for fracture development was,besides southwestern transition zone and southwestern YunYan,the other areas fractures developped.