Polymer flooding was selected as the preferred enhanced recovery process for a high permeability (2-5 Darcy) heavy oil (250 – 500 cP) reservoir with a strong bottom aquifer in South Oman. Several key uncertainties were identified through simulation modelling which would have a crucial impact on the process efficiency. These uncertainties formed the basis of a field trial design, and a detailed surveillance programme aimed at reducing these key uncertainties.
The presence of a strong bottom aquifer in this field resulted in near original reservoir pressure, which could provide a challenge to injectivity. The close proximity of injectors to the oil water contact reduces the efficiency of the polymer flood through water fingering, and polymer loss to the aquifer. Additional uncertainties include: reservoir heterogeneity, Kv/Kh, permeability distribution, baffles, natural fractures, remaining oil saturation, injectivity, induced fracturing and inflow profile along the horizontal well (producers and injectors). Hence, extensive data gathering was carried out in order to reduce these uncertainties through updating the static and dynamic models and allowing for a better understanding of the field behavior prior to polymer injection.
This paper details a fully integrated evaluation of the gathered data through a multi-disciplinary team during the drilling of the trial wells. The data includes: open hole logs, borehole images, core analysis, fluid sampling, dielectric measurements, vertical interference testing, production logging and existing dynamic production data. Also, single well water and polymer injectivity test and extended leak-off test were carried out to understand the injectivity and fracture behavior. The wealth of well data coupled with geological and dynamic data reduced the overall reservoir properties and fluid distribution uncertainties. Furthermore, the data were crucial to design the optimum injection and data gathering requirements during the field trial. Finally, the paper provides an overview of the surveillance aspects of the field trial.