Interpretation of World First Polymer Injectivity Test in a HTHS Carbonate Reservoir Using SW Radial Model

Summary New polymer based EOR schemes are proposed to increase sweep efficiency and oil recovery from high temperature and high salinity carbonate reservoirs in Abu Dhabi. These reservoirs generally consists of two main geological zones, i.e., an Upper zone and a Lower zone with permeability contrast of up two orders of magnitude. The new EOR concepts rely on keeping the upper zone pressurized by continuous polymer injection and simultaneously injecting miscible gas or water into the lower zone. A lateral pressure gradient is maintained in the upper zone, providing gas or water confinement in the lower zone and improving sweep efficiency. Accordingly, a comprehensive de-risking program for the new polymer based EOR schemes was initiated which includes an extensive laboratory experimental program and field injectivity test to ensure that the identified polymer can be injected in the target formation below fracture pressure. The comprehensive experimental program and results were described in an earlier publication ( Masalmeh et. al., 2019 ) and the field injectivity test was also described by Rachapudi et. al., 2020 . The polymer injectivity test (PIT) consists of three main phases: water injection baseline, polymer injection with different rates and different polymer concentrations and chase water injection. The objective of this paper is to present the interpretation of the polymer injectivity test using a single well radial model. This PIT is the world first polymer injectivity test in carbonate under such harsh conditions and the polymer used in this test has never been field tested before. The model was built to integrate and assess the dynamic data collected during the PIT, incorporating laboratory experiments, and evaluating the impact of different parameters on the near-wellbore injectivity behavior. Interpretation of the PIT using a radial simulation model allowed to confirm that the qualified polymer can be injected and propagated in the extremely harsh conditions carbonate reservoirs, below fracture pressure and without well plugging. Despite the uncertainties and operational complexities presented during the PIT, a representative history match was obtained. More than 20 thousand sensitivity simulation runs were performed through a robust iterative optimization history match method. This workflow helped to address multiple uncertainties and captured many possible scenarios and validated laboratory parameters such as polymer bulk viscosity, in-situ rheology, RRF, adsorption, etc. The results of the PIT interpretation will be further utilized in the sector model and full field simulation models to investigate and design multi-well EOR pilots and full field development plans.