Abstract

A polymer flood pilot has been ongoing since September 2008 in Suriname in the heavy oil Tambaredjo field operated by Staatsolie. Initially, the pilot consisted of one injection well and four producers and was later expanded to three injection wells and nine direct offset production wells (all vertical).

The Tambaredjo oil field is the largest oil field in Suriname and has been producing since 1982. The field contains approximately 525 MMSTB STOOIP of 16° API oil with an initial viscosity of 300 - 600 cP at reservoir conditions. Primary recovery (± 30% OOIP) is relatively high given the oil viscosity; this is believed to be due to a combination of compaction drive, edge water drive in the northern part of the field and limited bottom water influx in other areas, and perhaps foamy oil behavior. In spite of this high primary recovery, large quantities of oil remain in the reservoir, making it an attractive target for EOR.

Due to the relatively thin pay, thermal methods have not been considered for the reservoir but on the other hand polymer flood was judged suitable. The oil viscosity is high but still lower than in other successful projects for instance in Canada while other reservoir characteristics are also suitable: low reservoir temperature and low water salinity allow the use of standard HPAM polymer, and high permeability is beneficial for injectivity. Moreover, the reservoir is highly heterogeneous, which has presented some challenges to the process.

Initially, a polymer viscosity of 45 cP was injected which was later increased, first to 85 cP and then to 125 cP in order to improve the sweep efficiency. The overall response to polymer injection has been positive even if some wells have not responded positively to the injection, and incremental recovery (over primary) to date is estimated at on average 11% STOOIP. Due to the unconfined nature of the pattern some wells adjacent to the pilot have also shown response to injection.

Given the success of the project, work is currently under way for an expansion of the polymer flood to encompass 33 additional injection wells.

The paper presents the results of the pilot and describes the operations and challenges encountered during the project, in particular during the injection of the higher viscosity polymer. The combination of high reservoir heterogeneity, use of hydraulically fractured vertical wells and high polymer viscosity injected contribute to make this pilot an interesting field case.

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