Seismic Sedimentology And Its Application In Sandbody Prediction Of Continental Fault-depressed Lacustrine Basin

With the development of geophysical technology,deep study of reservoir sedimentology and the improvement of computation power,seismic sedimentology,as an innovative crossing discipline,is undergoing a continuous developing and improving in its theoretical method and application.Seismic sedimentary has been successfully used in foreign marine reservoirs.But for continental reservoirs,especially for continental fault-depressed lacustrine basin,the sedimentary system has such characteristics as many sedimentary types,fast phase changing and fault complexity,current method and technology of seismic sedimentary can not solve the problem of complex lithology and changeable sedimentary facies.This dissertation takes turbidite fan body and complex sand reservoir in beach bar in continental fault-depressed lacustrine basin of east China as a study case.Turbidite fan bodies and sandy body in beach bar of different stages has characteristics of thin sedimentary body and weak seismic response.By using technology of seismic sedimentology,this dissertation innovatively studies the calibration of thin interbed,judges the isochronism of stratigraphic interface,and makes the identification of thin bed.In the frame of isochronic stratigraphy,this work realizes correct identification and description of thin beds,proposes a set of method for identification of turbidite fans of different stages,and a set of method for identification of thin beds of beach bars.A proprietary method is proposed for fine calibration of thin beds.The thickness of single stage fans of turbidite fan facies is usually thin.Beach bar sands of beach bar facies are usually thin beds or interbed.Their seismic responses are usually weak reflection or complex reflection,so it is difficult to determine seismic profiles by geological horizons.To solve the proceeding problems,principle of recalibration is proposed,in which correct polarity judgment of seismic profile is a foundation,and various wavelets are analyzed and used in combination effectively.From apparent seismic events to small wavelet group,from strong to weak stages,thin beds are precisely calibrated by principle of secondary calibration.A set of method is concluded to determine isochronism of seismic reflection interfaces.To study turbidite fan sand and beach bar sands interbeds of different stages by seismic sedimentology,it should be used in the frame of isochronic horizons.But seismic reflection interfaces has a problem of“diachronism",thus,it is important to determine isochronism of seismic reflection events.To solve the proceeding problem,isochronic interfaces of different stages are identified and determined by analyzing from limitation to interface,and finally to minimum isochronic interface.Research scales covers sub-member,sand member and subzone,so that isochronic interfaces are precisely identified.As for identification of thin beds,a proprietary method is proposed for identification and predication of thin reservoirs.The thickness of single stage fans of turbidite fan facies is usually thin.Beach bar sands of beach bar facies are usually thin beds or interbed.Not only their sedimentary thickness and horizontal spreading range has serious imbalance,but also the resolutions of single fan and beach bar sandbody are smaller than the resolution of seismic data.So that,it is diff-icult to identify thin beds by seismic data.To solve the problem,a modified slicing method is used to identify and describe sedimentary body.By using slicing method and horizons' geophysical information in combination,the disadvantage of slicing method that "only a slice is seen" is overcomed,and the range for retrieving geophysical information from interpreted horizons is shrinked.Thus it is realized to precisely identify and fine describe thin beds.A set of method is proposed for identification of turbidite fans.Turbidite fans without channels and turbidite fans with channels are taken as study examples.The turbidite fans without channels of Dongying depression has thin sedimentary thickness,single fan is difficult to be identified in vertical,and spreading range is difficult to be determined in horizon.Turbidite fans with channels of Chezhen depression is seriously disturbed by faults,turbidite channels and spreading range of fans are difficult to identify.Under the direction of sedimentary patterns,conventional sedimentary method and modified methods are used in combination,a set of method for identification of turbidite fans are formed in the frame of isochronic horizons.This method determines stages by single well facies,identifies seismic characteristics of turbidite fans,then identify turbidite fans' seismic plane facies of different stages,and finally reveal the spreading principle of turbidite fans.The proposed method is successfully used in identification and description of distal turbidite fans body and slump turbidite fans body.In the study of identification of beach bar sand,a method is proposed for identification of beach bar facie.Beach bar sand of Bingdong is taken as a research case.Beach bar sand has thin sedimentary thickness in vertical,small spreading range in horizon and weak seismic response.Under the direction of sedimentary patterns,conventional sedimentary method and modified methods are used in combination,a set of method for identification of beach bar fans are formed in the frame of isochronic horizons.This method identifies beach bar sand at wells,retrieves seismic characteristics of beach bar sand,identifies seismic horizontal facies of beach bar sand,and finally reveal the spreading principle of beach bar sands.The proposed method is successfully used in identification and description of beach bar sands.