In heavy oil reservoirs, water flooding leaves behind unswept hydrocarbon volumes due to unfavourable mobility ratios resulting in low ultimate recoveries. Increasing the viscosity of the injected water using polymer improves the water-oil mobility ratio resulting in improved recovery factors. This paper discusses for a large field in South Oman the successful implementation of a polymer flood project, the early results of Phase I and the planned expansions to Phase II and Phase III. Following a number of field trials and a series of laboratory studies, a full-field polymer project was implemented in the field in 2010. One of the key risks identified prior to starting the project was poor polymer injectivity. However, initial field results showed better injectivity than expected. Surveillance efforts are in progress to understand the better injectivity. The data analysis so far indicate that wellbore clean up due to polymer injection, improved as a result of improved mobility ratio and small scale induced fractures in some injectors are contributing to the improved injectivity. These factors enabled injection of more volumes of polymer than planned resulting in improved volumetric sweep efficiency and producer response. Results to date are encouraging, as after over a year of polymer injection, the oil gain due to the polymer flood is higher than expectation. Based on the initial results of Phase I, expansion phases II and III are being planned. Phase II is based on utilizing the available ullage in the system to accelerate the oil gain from polymer; it requires a relatively small upgrade of the existing infrastructure and surface facilities. Phase III is a full-field polymer flooding expansion combined with an intense infill drilling. Currently, a study is in progress to optimize the development concept for the infill wells and polymer flooding of Phase III.

A comprehensive integrated study was performed in the Study Centre of Petroleum Development Oman (PDO) on an ultra-mature field located in South Oman. The field has 30 years of production history and more than 300 penetrations with a current recovery factor of 48%. The study aimed to develop robust subsurface (static and dynamic) models to identify the remaining and by-passed oil opportunities. Furthermore, the subsurface models are planned to be used for a potential future Enhanced Oil Recovery development (Alkaline Surfactant Polymer). SPE 138202recovery factor can be improved up to 53% by conventional infill drilling. In summary, a profound understanding of reservoir performance behavior is a key driver to produce the limit of an ultra-mature field.