Evaluation of a Pilot Polymer Flood in the Marmul Field, Oman

Abstract

ABSTRACT In view of the high permeability, fairly high oil viscosity, moderate reservoir temperature, low salinity formation water and availability of low salinity injection water, the Marmul A1 Khlata formation was considered a good candidate for polymer flooding. A pilot consisting of an unconfined 5-spot on a 200 m spacing was initiated in May 1986. After the injection of a water preflush of 0. 23 PV, a polymer slug of 0. 63 PV and a water postflush of 0.34 PV, the total oil production was 59% of STOIIP. The injection of polymer resulted in a sharp increase in oilcut in all four wells. From the viscosity/concentration relationship of the produced polymer and from a detailed rheological characterisation it was shown that no significant degradation of the polymer has occurred. A satisfactory history match of the oilcut response and of the polymer production was obtained with a numerical simulator. From the simulation results and from analytical calculations it was deduced that the reduction of oil in place in the pilot area since the beginning of the preflush was some 50% of STOIIP. This indicates that a pattern polymer flood in the pilot region offers scope for an increase in ultimate recovery of some 25% to 35% of STOIIP compared to primary production with aquifer support. The corresponding amount of polymer is about 2.3 to 3.2 kg of active matter per additional m3 of oil (0.81–1.1 lb/bbl). In a forthcoming pilot extension project polymer flooding will be carried out in an unconfined 5-spot on the original 600 m Marmul well-spacing.