Study On The Structural Characteristics Of The Neogene ?-? Oil-bearing Group In The Footwall Of The No. 2 Fault In Gaskule Oilfield, Qaidam Basin

At present,the N1-N21 reservoir in the Gasikule Oilfiedld is currently in the late stage of exploration and development,with high comprehensive water cut and complicated oil-water distribution.In the early stage,many different researches have been carried out and many achievements have been made.However,for the deep well section of N1 reservoir ?-?reservoir group,strata with low drilling rate and unclear local structure have not been carefully studied by predecessors.Therefore,it is of great significance to carry out the research on fine structural characteristics to recognize the structural form,fracture characteristics and adjustment of development plan in this area.Under the theoretical guidance of the theories of logging geology,structural geology,seismic stratigraphy and other disciplines,this paper takes Neogene ?-? reservoir group in the north of footwall of fault ? in Gasikule Oilfield as the research objectives,comprehensively uses geological,3D seismic,drilling and logging data,and divides the target reservoir group by using seismic reflection standard layer method drilling and logging date maker layer method and sedimentary cycle method combined with previous research results.Well Y58 is selected as the standard section for the division and correlation of small layers of the target layer in the study area.The division and correlation of small layers of 17 survey lines and 194 wells in the whole area are completed by comprehensive application of marker layer method,slice method and cycle method,and a relatively fine sequence stratigraphic framework is finally established.Taking the synthetic seismic records of 40 wells as the standard,the top boundary of ?-1,the top boundary of ?-1 and the bottom boundary of ?-13(corresponding to K51,K61 and K7 respectively)are calibrated and compared by the method of well-earthquake combination,and the interface characteristics of each seismic reflection standard layer are summarized,and the horizon tracking of the whole region is carried out.On the basis of seismic reflection comparison of standard layers,equivalent t0 maps of the three reflection standard layers of ?-1 top boundary,?-1 top boundary and ?-13 bottom boundary are compiled.Using the time-depth relationship of synthetic seismic records from 40 wells,variable velocity fields of each standard layer are established,and finally the structural maps of the three reflection standard layers of ?-1 top boundary,?-1 top boundary and ?-13 bottom boundary are completed.Through the above research and the compilation of structural maps,the structural characteristics of the work area are clearly displayed:the research area is a fault nose structure cut by fault ?,the south of the fault nose structure is broken by several secondary faults,and fault ? is the main control factor.The extension direction of the structural axis is north south direction,rising to the north,plunging to the south,and gentle in the east and steep in the west.Longitudinal shallow structure is wider and slower than deep structure;There are 4 interpretation faults in the study area:fault ?,?,(15)and(17),of which faults ?,?,(15)are reverse faults and(17)are strike-slip faults.These faults all cut off the three reservoir groups of the target layer and strike NNE except Fault ?,which is near east-west direction.The dip angle of faults is about 60-70 degrees except for fault ?,which is about 45-55 degrees.On the basis of the above small layer division and macro structural background research,the top surface of the main oil layer is taken as the micro structure layer location,and the micro structure map of the top surface of the reservoir is drawn by using dense well pattern and small spacing interpolation(generally 2m),and the micro structure type,amplitude,area and cause of formation are deeply analyzed.Three common microstructural types of reservoir in the work area are summarized:small high point,small nose and small fault nose.The average range of micro structure is 3-8m and the average area is 800-3102m2.There are two main causes of micro structure:sedimentation and tectonics.