Axially symmetric compositional simulation of formation tester measurements

This paper describes the development, testing, and successful application of a new compositional code for the numerical simulation of oil-based mud invasion and formation tester measurements that involve arbitrary miscibility between oil-based mud and native oil. The simulator assumes axially symmetric variations of petrophysical properties as well as axially symmetric flow-rate sources and boundary conditions. However, there are no restricting assumptions to the degree of miscibility between the fluids involved in the simulations. We solve the time–space evolution of component concentration with a time-marching implicit pressure explicit concentration (IMPEC) scheme. This method of solution considers the complete equations of state and implements flash calculations to describe the thermo-dynamical evolution of the various compositional phases due to space–time variations of pressure and concentration.Simulations described in this paper consider the process of oil-based mud–filtrate invasion into reservoirs containing mixtures of connate water and oil. Subsequently, we simulate formation tester measurements by enforcing fluid withdrawal through the dual-packer section of the tester. Measurements consist of fluid pressure, fractional flow rates, fluid density, and fluid viscosity. Examples of application include homogenous and multi-layer formations as well as a capillary transition zone. Comparison of simulation results against those obtained with a commercial code confirms the efficiency, accuracy, and reliability of our method of solution.Sensitivity analysis indicate that time evolution of fractional flow rates, fluid density, and fluid viscosity measured with the formation tester remain influenced by the petrophysical properties of the formation, volume of mud–filtrate invasion, and by saturation-dependent rock–fluid properties (relative permeability and capillary pressure). The simulations described in this paper provide suitable guidelines for the acquisition of clean samples of in-situ formation fluids in the presence of invasion and heterogeneous conditions of petrophysical and rock–fluid properties.