Architecture-based Geological Modeling And Remaining Oil Distribution Of The Heavy Oil Reservoir In Venezuela

Braided river is a wandering river type.Its channel is subject to frequent migration and oscillation,and the multi-period sediments in geological time scale often interact with each other,resulting in rapid facies change on plane and complex superimposition of the inner sand bodies.Its reservoir is highly heterogeneous.These characteristics lead to an unclear estimate of the size and distribution of sand bodies in the reservoir.Traditional modeling methods based on vertical well data and planar facies control can not accurately characterize the reservoir.It can not meet the precision requirements of modeling and remaining oil prediction at development stage.This thesis takes the lower Oficina formation in the Orinoco heavy oil belt,Venezuela as an example to study the architectural characteristics of braided river reservoir.On the basis of this,a 3D geological model controlled by genetic evolution is established.The influencing factors of remaining oil controlled by the architectural model are analyzed.Remaining oil distribution rules are summarized,which will provide the basis for the further development of the reservoir in this area.The Orinoco heavy oil belt in Venezuela is the largest heavy oil accumulation area in the world.A large area of fluvial-deltaic strata is developed in the study area.The Upper Yabo and Jobo member of the strata have the sedimentary characteristics of braided river delta front.The Lower Morichal formation is a sedimentary type dominated by the braided river delta plain and characterized by braided river deposits.In this paper,the stratigraphic division and correlation of the whole area are carried out by means of well-seismic combination,and 11 stratigraphic framework sections with isochronous significance are established.Target formation of Oficina is located in the lower part of Morichal and consists of O-11,O-12S,O-12I and O-13 sand formations.On this basis,the architecture study of the reservoir was carried out.Based on the core observation of 2 coring wells in the area,10 different lithofacies types are identified.According to the characteristics and formation environment of different lithofacies,4 lithofacies associations in braided reservoir are summarized,and their genesis is analyzed.A knowledge base of lithofacies and lithofacies associations is constructed.Combining vertical well with horizontal well data,the interface identification of braided reservoir architecture is carried out by using seismic sedimentology assistant means.Under the control of the architecture interface,the architecture of reservoir is identified and the classification scheme is established.Based on the statistics of lithofacies association types corresponding to each architecture unit,and combining with logging and seismic responses,the identification and classification characteristics of each genetic unit are summarized.There are 4 main types of sedimentary architectural units such as compound channel bar,braided channel,abandoned channel and residual floodplain mudstone.A braided architectural sedimentary model is established for this area.The sandy sediment is mainly composed of compound bar with flat top and convex bottom and braided channel with the characteristics of erosion and filling.Both of them show the overlapping relation of splice-like interlock horizontally,which indicates that they have cut each other for many times.The distribution of the abandoned channel in the argillaceous part is more limited,and only some drilling paths are found in the traces of individual wells.The floodplain mudstone,which is widely distributed in the area,overlies the other sedimentary units and is often eroded by later water flow.The floodplain mudstone is not completely preserved,but mainly exists in residual state.In view of the strong heterogeneity and rapid evolution of braided river,it is necessary to focus on the study of genetic evolution process analysis and architectural constraints in geological modeling.The purpose is to restore the sedimentary evolution history of braided river reservoir and to reconstruct the reservoir process.To control the process of 3D geological modeling of braided reservoir,the information of sedimentary evolution is transformed into the constraint parameters,which can effectively reduce the uncertainty of modeling results.The information of sedimentary evolution is analyzed by using stratal slice of seismic sedimentology.The local azimuth angle data and probability volume data of sand and mudstone are obtained,which can be used to assist the geological modeling process.By restoring the temporal and spatial configuration of the unit,a 3D geological model that ultimately reflects the reality of the reservoir can be better established.In addition,the multi-point geostatistical modeling method based on the architectural model can reproduce the sedimentary pattern contained in the 3D training image.The simulation results reflect some details of the braided river reservoir in this area.The relationship between the architectural unit of sand bodies can be revealed,and the multi-stage superimposed development pattern of sand bodies has been well restored.The braided river geological model is controlled by genetic evolution information and architectural pattern.Apply the model to the drilling prediction of the newly built platform in the study area.It can improve drilling rate of horizontal wells to more than 95%and it has achieved good application effect.The remaining oil simulation results of the architectural model are analyzed based on the typical platform.The architectural prediction model based on actual data is studied.The controlling factors of remaining oil are discussed under different architectural interface and unit level of 6,5,4 and below.The residual floodplain mudstone and interlayer formed between the sand formation have a strong barrier to the gravity drainage path.So,it has a great influence on the distribution of remaining oil and later development of horizontal wells in cold production.The distribution patterns of remaining oil under the control of different architecture combinations are summarized.The interface combination pattern and the overlap area of architectures affect not only the complexity of residual oil distribution,but also the recoverable reserves of remaining oil.With larger superimposed area and more complex interface,higher the remaining oil reserves get formed by shielding.It is an advantage for further development.According to theoretical calculation,the remaining oil reserves developed with over 0.5km~2overlapping area can reach the value of industrial cold production.