Synthetic Fractal Modelling of Heterogeneous and Anisotropic Reservoirs for use in Simulation Studies: Implications on their Hydrocarbon Recovery Prediction

Optimising production from heterogeneous and anisotropic reservoirs challenges the modern hydrocarbon industry because such reservoirs exhibit extreme inter-well variability making them very hard to model. Reasonable reservoir models can be obtained using modern statistical techniques, but all of them rely on significant variability in the reservoir only occurring at a scale at or larger than the inter-well spacing. In this paper we take a different, generic, approach. We have developed a method for constructing realistic synthetic heterogeneous and anisotropic reservoirs which can be made to represent the reservoir under test. The main physical properties of these synthetic reservoirs are distributed fractally. The models are fully controlled and reproducible and can be extended to model multiple facies reservoir types. This paper shows how the models can be constructed and how they have been tested. Varying the fractal dimension and anisotropy factor of each of these physical properties can tell us how sensitive the reservoir is to uncertainties in its heterogeneity and anisotropy as well as how poroperm cross-plot shapes are controlled. Initial reservoir simulation results of the tested models with this approach show that heterogeneity in the reservoir's physical parameters has a little effect on high and moderate porosity and permeability reservoirs. The effect is more pronounced in the models representing tight reservoirs. The production from more heterogeneous reservoirs lasts a little longer, but eventually declines faster. This may be attributed to the fact that water channelling is more significant as heterogeneity increases.