Sedimentary Characteristics And Sand Body Distribution Of The Xiagou Formation In The Changshaling Structure Belt,Yinger Sag

The Yinger sag is the major petroliferous sag in the Jiuquan Basin,the Changshaling structure belt is the major petroleum exploration area in the sag,where the Xiagou Formation is the main oil-bearing stratum.Based on the theory of sequence stratigraphy,logging geology and sedimentology,and using core,logging,mud logging,seismic and analysis assay data of the research area,this paper sets up the sequence stratigraphic framework,illustrates provenance and depositional system,and reveals expanding characteristics of sedimentary faces and sand body of the Xiagou Formation in the Changshaling structure belt in the Yinger sag.The main results as follow: The Xiagou Formation can be divided into three third-order sequence SQ1,SQ2 and SQ3,and correspond to Xia1 Segment,Xia2 Segment and Xia3 Segment;The sedimentary provenance of the Xiagou Formation in the research area is mainly derived from the Wenshushan uplift in the northwest of the Yinger sag,the sedimentation has good inheritance in the longitudinal direction and as the whole is braided delta-sublacustrine fan-lacustrine facies sediment system in the plane,the sedimentary environment changes from shallow lake to deep lake,which can identify the microfacies of underwater distributary channel,estuary bar,sheet sand,main channel,branch channel and turbidite sheet sand;The sand body of the main exploration sequences in the research area are generally distributed from northwest to southeast,with braided river delta front sand bodies and sublacustrine fan sand bodies widely developed,the development of the sand body is controlled by tectonic activities and palaeogeomorphology,fault transfer zone form entrance of provenances and control the development position of sand bodies,stage fault bench zone provide sedimentary space and dynamics,control the distribution direction,types and scale of sand bodies.These results provide theoretical basis for looking for favorable sands and further exploration and development in the research area.