A Convective Segregation Model for Predicting Reservoir Fluid Compositional Distribution

Convective rolls resulting from a geothermal gradient coupled with thermodiffusion and gravity effects may induce large spatial changes of fluid composition in hydrocarbon reservoirs. This paper presents a theoretical modelling of these phenomena based on the equations of natural convection in porous media and of mass transfer. The numerical model aims at predicting the fluid property distribution from a single representative sample. The therniodynamical properties of the fluid are computed by the PENG-ROBINSON equation of state. Viscosity, diffusion and ther modiffusion coefficients of the various components are functions of temperature, pressure and total fluid composition. The porous medium can be anisotropic and heterogeneous. The equations are solved by a control volume method and the numerical integration scheme is discussed. An example is given for a typical reservoir. The distributions of the components and of the corresponding fluid properties are computed in different cases. A simple criterion is proposed to define the application range of the model.