De-risking Polymer Flooding of High Viscosity Oil Clastic Reservoirs - A Polymer Trial in Oman

Abstract

A long term polymer injectivity trial has been conducted in a medium-high oil viscosity field in Oman, with a suite of objectives to assess the feasibility of the high viscosity polymer concept, evaluate alternative polymers and de-risk the low-salinity polymer hybrid for field implementation. An integrated analysis of this injectivity trial is presented. Performance in the field during injection of low and high molecular weight (MW) polymer in hybrid with low salinity water is analysed along with interpretations of the intermediate water injection, shut-ins, pressure fall-off and step rate test at the end. The analysis is based on simulation models to history match the pressure response in the injector during the polymer trial. Key realizations focusing on two aspects – polymer rheology and wellbore/reservoir fluid propagation mechanism – are presented that were used to history match baseline water injection, low and high MW polymer injection, low salinity water injection and polymer low salinity water hybrid. Other sources of information – step rate test and pressure fall-off tests conducted during the trial – were interpreted to validate the conclusions from the HM model. The study highlighted the risks of either inducing fractures or reactivating an existing fracture network in the reservoir during the polymer injection. Different sources of data indicated fracture pressure lower than anticipated. The dynamic characterization of the fractures – propagation and shrinkage – depending on the injection rate, injection fluid type and viscosity are found critical to explain the entire polymer trial response. The study also highlighted that capturing the polymer rheology adequately in the model, based on laboratory data, helps to explain the trial response. Changing well conformance has been found another important parameter in explaining the trial response. Finally, using the baseline water injection to ensure the permeability field is adequately modelled constitutes another step in understanding the polymer trial.