Successful Polymer Flood Pilot Application in Lower Permeability Heterogeneous Sandstone Reservoir in the South of the Sultanate of Oman

Abstract

This paper summarizes the performance of a polymer flood pilot conducted in an unconsolidated sandstone reservoir in the South of the Sultanate of Oman with the objective of extending the envelope of polymer flood applications to lower permeability (average 100mD) and highly heterogeneous reservoirs. The water flood baseline phase performance was presented previously in paper SPE-188408 where the connectivity of the patterns together with injectivity were established prior to polymer injection. The main objectives of the pilot were to test ability to sustain injectivity of polymer into this particular reservoir, achieve sufficient water-cut reversal (10% or more), monitor polymer efficiency and evaluate operational impact on facilities due to sand production which was expected to increase with polymer flood. Several lab tests along with a previous polymer injectivity trial data were fed into the selection of the appropriate polymer and injection design for this reservoir type. The pilot pattern layout consisted of an inverted five spot with injector-producer spacing of 75m. The injector was equipped with fiber optics for data acquisition and real time surveillance. Polymer injection commenced in December 2017 using relatively low molecular weight HPAM3430. The plan was to inject polymer for a year and evaluate the performance for a potential field scale development. The fiber optics data acquisition has demonstrated clearly the injection conformance improvement during the switch from water injection to polymer. In addition, around 10% of incremental oil recovery was obtained with an average water cut reversal of 12% across the pattern where the total pattern recovery was over 30% (including the waterflood). In terms of sand production, no noticeable impact was found on the facilities from sand production due to the polymer. The pilot performance exceeded the pilot success criteria that were set prior to commencing the polymer injection in terms of water-cut reversal and incremental recovery over the waterflood and fall in line with the modeled high-end scenario.