Study On The Sedimentary Characteristics And Distribution Of Sandbodies Of The Second Member Of The Shahejie Formation In Chezhen Area

The sedimentary period of the 2nd member of the Shahejie formation is placed in faulted-depression period with the flat terrain and gentle gradient, and large shore-shallow lacustrine sandbodies were developed. It is the main increasing potential production purpose layer in Chezhen sag. By the comprehensive utilization of drilling core data, logging data, seismic data etc. , and based on the fundamental principles of sequence stratigraphy , sedimentology and reservoir geology, the framework of sequence stratigraphy, under the control of seismic the sequence framework was established, the sedimentary characteristic, genetic types, controlling factors and space evolution law of the shore-shallow sandbody was discussed. The results and conclusions are obtained as follow:Controled by the 3-D seismic, several levels of sequence boundary identification methods are used to do the work of stratigraphic correlation in the region. As the results show, the Es2 strata of study area are divided into 3 sub-paragraphs, 3 fourth level sequences and 12 sand layers. Chexi has the most complete stratigraphic, with much thinning in the east, and Dawangbei and Guojuzi areas miss the formation of the lower part of Es2.In the period of the 2nd member of the Shahejie formation, Chezhen Sag was characterized by shallow water and flat basin; North of Chengzikou salient and south Yihezhuang salient supplied the sedimentary source recharge. So the sedimentary system of shallow water delta (fan delta) -beach and bar commensalisms was developed. And then, work area's sedimentary facies model was established. Belong a transitional type, the sandbody was sheeted the distributary channel sandbody reformed by wave or box bar sand with sedimentary structure of channel.From the plane and space during the depositon development characteristic and distribution rule of sandbody in narrow lake shallow basin was discussed. Summarized: Succession development of sedimentary systems, structure controlling deposition centre, deposition space migration significantly, frequent changes of water depth. The distribution was controlled by three factors. The different activities of episodic fault and basement subsidence is the main controlling factor about shore-shallow sandbody development. Hydrodynamic controls the genetic types, and source of sediments controls the sandbody scale. The nearly north-south faults controlled the stratigraphic unit formation and distribution of lower Sha-2 member. The nearly north-east faults located south slope controlled the stratigraphic unit formation and distribution of medium Sha-2 member. Basement subsidence controlled the stratigraphic unit formation and distribution of upper Sha-2 member. The reformation of wave was stronger and the effection of coastal flow was weak, so reformed type beach and bar was developed. The distance from study area to provenance was short, so by the control of source system the sandbody was coarse grained and low maturity.