Research On Sedimentary Facies And Reservoir Features Of The Middle And Lower Member Of Oficina Formation In MPE-3 Block, Venezuela Basin

The Orinoco Heavy Oil Belt in the south-east of the Venezuelan basin is an oil abundance zone with the highest reserves and lowest development level in the world.The MPE-3 block is in the east of the oil belt.Besides,the complexity of the internal structure and uncertainty of sedimentary facies types,evolution pattern,distribution rules and reservoir characteristics significantly restrained the further exploration and development in the block.To deal with these problems,a series of reservoir geology researches focusing on the sedimentary facies and reservoir characteristics of the middle and lower member of Oficina Formation in MPE-3 Block is carried out this paper.Based on an integrated analysis on existing schemes of stratigraphic division and new well data,three sets of maker bed are selected via methods including maker bed control,base level cycle constrain as well as stepping division and contrast.An integrated and reasonable layer division and contrast strategy is then obtained with consideration of sedimentation genesis and development block.Multiple framework sections are established and correlation of formations is achieved.The result indicates that the MPE-3 block and extended area possess Oficina stratigraphic distribution with a gradual thickening from the south to the north and a thinning tendency from the west to the east.Besides,based on analysis of river-delta sedimentary background of the research area,the sedimentary environment is determined to be transitional facies according to characteristics of core lithology,sedimentary tectonics,palaeobios and particle size.It basically developed a river-controlled shallow gentle slope braided delta influenced by tide.By digging into the logging data,the sedimentary environment is further classified into braid delta plain and front subfacies.The former developed microfacies types including composite diara dam,braided channel,floodplain,crevasse splay and overbank,while the latter developed distributary channel,distributary bay,mouth bar/tidal sand bar and sheet sand.After that,the quantitative research on key parameters of development scale of channels in the area is done via methods including well logging and seismic data,modern sedimentary measuring and analogy,and experience formula method.A detailed description of the range and form of channel distribution is obtained,and the sedimentary facies model of the research is established by further analysis of the evolution pattern and distribution rule of the sedimentation in the reservoir during each sedimentary period.Finally,researches including an in-depth study on reservoir characteristics such as lithology and physical properties as well as analysis on porosity and permeability are done to draw the conclusion that the reservoir with high porosity and permeability possesses remarkable physical properties and the high porosity and permeability area distributes in braided channel with high thickness.The capability of reservoir depends on the influence of sand body sedimentary genesis,pore structure and diagenesis.After analyzing the relationship between the four characteristics of reservoir,the sub-layers are classified into????? layers with consideration of multiple indexes.Then the oil-bearing characteristics of the reservoir are analyzed from the longitudinal and the plane.And the favorable zones are predicted.The result shall provide theoretical and geological basis for further development of MPE-3 block.