Characteristic Of Transverse Faults And Its Significance In Hydrocarbon Accumulation In Northwestern Margin Of Junggar Basin

Northwestern margin of Junggar Basin is the richest re gion of oil and gas in the whole basin.There are several NW tending transverse faults being perpendicular or oblique to the NE-directed Ke—Wu fault.From southwest to northeast,they are east side of Hongshanzui fault,Dazhuluogou fault,Huangyangquan fault,Fengcheng fault and Hebukehe fault respectively.These transverse faults have serious geological significance,and be an important component of the tectonic framework of the northwestern margin of Junggar basin.Transverse faults also have significance of structural segmentation,cutting the thrust belt into several parts and transforming the difference of movement directions,of deformation rates,of strike orientation,and of structural styles between the two adjacent structural segmentation.On the basis of analyzing of regional geology background,by analysing and interpreting the data of topographic image,regional bouguer gravity anomalies and seismic data,the transverse faults are identified and their characteristics are also analysed.Finally according to the results of the structure modeling experiments,the formation of the transverse faults are investigated.Researches show that firstly,these transverse faults in northwestern margin of Junggar Basin are the associate structure of the Ke—Wu thrust nappe belt,trending northwest,distributing in Ke Wu fault approximately equal distance,with the properties of strike slip and being flower shaped structure in cross section;secondly,the structure modeling experiments shows that these transverse faults may be from the X-type conjugate shear faults formed under the tectonic condition of oblique compression or the accommodating faults caused by the difference activities of the main thrust fault.Based on the structure and the distribution of oil and gas reservoirs in the Northwestern margin of the basin,close relations can be found that: firstly,oil and gas reservoirs distribute along the Ke-wu fault,especially more rich at the intersection of the transverse faults and Ke-Wu fault;secondly,in the direction of the transverse faults extending into the slope of the basin,there are some different scales reservoirs appear on the transverse faults zone or on its both sides.By analyzing the relationship between the transverse fault and the elements of the hydrocarbon accumulation,it can be found that firstly,transverse faults usually are the channel of mountain stream into the basin,controlling the distribution of the sedimentary fan;secondly,the transverse faults penetrate into the source centre,and being the important source faults;thirdily,various traps formed during the active of the transverse faults,such as fault-block traps,fault nose traps,faultblock-lithlolgic traps and so on.These traps were on the dominant path of hydrocarbon migration,and were the oil and gas migration and accumulation direction area.O n this basis,the hydrocarbon enrichment area related to the transverse faults are predicted.This will provide some new thought for the next petroleum exploration in northwestern margin of Junggar Basin.