Determination of the In-situ Polymer Viscosity from Fall-off Tests (SPE 154832)

Laboratory experiments and simulations showed that for an Austrian oil reservoir, oil recovery can be significantly increased using polymers. One of the key design parameters for optimizing displacement efficiency while minimizing costs is the in-situ viscosity of the polymer solutions. Whereas the viscosity of polymer solutions can be measured at surface, the viscosity in the reservoir is difficult to estimate owing to the degradation of the polymers during the injection process. In addition, polymers exhibit Non-Newtonian behaviour resulting in different viscosities of the polymer solutions dependent on the shear rate in the reservoir. For the Austrian reservoir, water injection fall-off tests have been performed. With these tests, a simulation model was calibrated. The calibrated model was used to simulate injection of polymer solutions for some time followed by fall-off tests. The results show that conducting a base-line fall-off test prior to polymer injection and a set of fall-off tests during polymer injection can be used to determine the in-situ viscosity of polymer solutions and the distance of the polymer front from the injection well. Even for Non-Newtonian shear-thinning behaviour, the results show that the average polymer solution viscosity prior to shut-in of the well and location of the front can be determined with reasonable accuracy. Due to the costs of polymers, knowing the in-situ viscosity of polymer solutions is of paramount importance. The injection process can be modified (e.g. changing pumps, modifying perforations) if the degradation of the polymer viscosity is significant. Also, knowing the in-situ viscosity rather than estimating can be applied to tailor the polymer concentration to achieve stability of the displacement process and improve the displacement efficiency.