Fine Characterization Of Single Sand Bodies And Division Of Reservoir Units In The Eastern Third Member Of The C71 Fault Block In The Chaheji Oilfield

The C71 fault block of the Chaheji Oilfield was put into production in 1986,and water injection development began in 2013.So far,it has entered the high water cut stage of oilfield development,the reservoir heterogeneity is strong,the inter-layer contradiction is prominent,and the water injection development effect is poor.Previous studies based on small layers as the basic research unit have been unable to meet current production development needs.At this time,the remaining oil exists in the reservoir in a highly dispersed state,which is difficult to mine.Therefore,it is necessary to carry out a detailed characterization study on the reservoir with a single sand body as the basic research unit to guide the potential tapping work of the remaining oil.In view of the thin sand body in the longitudinal direction of the C71 block and the fast change in the horizontal direction,the reservoir unit research is carried out to effectively identify the oil and water layers and to clarify the distribution characteristics of the remaining oil in the reservoir.Taking the eastern third member of the C71 fault block in the Chaheji oilfield as an example,this paper conducts a detailed characterization of the single sand body by establishing an isochronous stratigraphic framework and conducting sedimentary microfacies research.On this basis,combined with reservoir production data,production and absorption profiles,oil and water wells,and oil and water distribution characteristics and other dynamic data,finely describe the reservoir unit.Based on the theory of sequence stratigraphy,this paper establishes the sequence stratigraphic framework of the eastern third member of the C71 fault block with the principle of “revolution contrast,hierarchical control,well-seismic combination and skeleton closure”.The eastern section of the study area is divided into 4 oil groups,38 small layers and 82 single sand layers.In the sedimentary period of the third member of the Dongsan Formation,the source of the fault block of the C71 block was mainly in the northwest direction;four types of sedimentary microfacies of the underwater distributary channel,the underwater natural levee,the far sand dam and the underwater diversion bay were identified,and corresponding the shallow water delta sedimentary model.Based on the study of sedimentary microfacies,six vertical sandstone connectivity patterns and four single sandstone lateral connectivity patterns were identified.The single sand body in the study area is mainly thin interbedded with narrow strips on the plane.And forked dendritic spreads.Based on the identification of single sand body superimposed pattern in the study area,combined with the dynamic data of oilfield production and development,the six types of reservoir units are summarized,which are closely related to the type of single sand body.The main types of reservoir units are sand bodies.Longitudinal superposition,fault closed occlusion,physical property difference,lithologic extinction,structural height,oil-water relationship and other factors control.