Study On The Structure Characterization And Fine Geologic Modeling Of The Braided River Reservoirs In Fula Oilfield Of Sudan

Fula oilfield is located in the northeastern of Fula depression in Sudan Block 6 which is controlled by two NNW-SSE faults,the northern terrain is more gentle.Fula oilfield is a reservoir with high porosity and permeability.Bentiu strata is the purpose layer in the study with complex of formation structure and change quickly of sedimentary microfacies characteristics.With the complex of the reservoir property and the relationship between oil and water distribution,poor 3D seismic data and early reservoir model,there is not good to fine description of reservoir in the middle-late period of oil development.It's necessary to have a fine description of the braided river and having a refined reservoir geological model.According to the plenty of logging data and laboratory analysis of examples from cored wells,the main conclusions are as follows:(1)Establish a fine isochronous stratigraphic framework.There are two main division basis,one is the original small layers with the thick mudstone interlayer,the other is many sand body in different period with the same layers.We adopt the bridge-triangle network correlation method.Firstly we establish a backbone section with standard well and flatten the standard layer,then make a stratigraphic correlation by standard well in cross section.And then make all the cross sections by the firstly established backbone section.For the wells out of the backbone section,we make a small triangle network with the backbone section to make a stratigraphic correlation.(2)Braided river sedimentary microfacies and sand body distribution.Sandy braided river deposits with lots of rivers,big slope of riverbed,lateral migration quickly.The main reservoir sand of braided river zone is mid-channel bar and sandy braided river channel and the source direction is NE-SW.From the distribution of the thickness of the sand body,the zone with larger thickness sand body belong to mid-channel bar.From the period of B1 b to B1 a,the hydrodynamic stronger gradually and with less Argillaceous braided river channel and sandy-argillaceous braided river channel.(3)Reservoir geological modeling.We adopt the method with the combination of deterministic model and stochastic model.Deterministic modeling was used in the purpose layer and limited by sedimentary microfacies;stochastic modeling was used in other layer,limited by sand-mudstone.We use sequential gauss stimulation method to simulate the heterogeneity model in this study area.For the purpose layer B1 b and B1 a,we adjust the variogram of the facies alone to comply with the changes of the parameter of facies zone.(4)Geological model analysis.We established the tectonic model,stratigraphic model,facies model,Lithofacies model and Reservoir attribute model.The mid-channel bar and some sandy braided river channel showed the high value in porosity model and permeability model.It shows that B1b-3 and B1b-2 having the similar depositionalenvironment,B1b-1 ? B1a-3 and B1a-2 having the similar depositionalenvironment too,and B1a-1 having the different depositionalenvironment beyond them.Although the calculation of reserves by reservoir geological model constrained by facies with a slightly bigger,the geological model with scale up well logs and the simulation data are follow the original logging data,the result of the simulation truly reflect the changes of reservoir property underground.