Proposal
Before the start of an enhanced oil recovery project it is important to adequately describe the architecture of sand bodies, preferential flow directions and permeability barriers.
As a consequence of project implementation operating costs tend to increase so in order to guarantee the economic success of the venture, reservoir surveillance plays a major role. This is mandatory in highly heterogeneous reservoirs where it becomes strictly necessary to identify and adjust any deviation from the anticipated response to injection.
This paper presents the results of the use of chemical and radioactive tracers in Grupo Neuquen reservoir, Loma Alta Sur field, Argentina. The objectives have been to improve the dynamic description of the reservoir previous to the injection of costly polymers and surfactants and to optimise the secondary flood by increasing volumetric sweep efficiency.
This field has been in production since 1990. Water injection started in 1993 and due to field observations of poor reservoir connectivity an intensive programme of tracers was recommended. Three injectors were inoculated, one of them with ammonium thiocyanate and the rest with tritiated water. Fifteen producers were monitored throughout twelve months.
Field data is presented in this report. It shows that hydraulic connectivity is higher than expected although fluid migration among wells is highly variable depending on reservoir transmissibility and channel orientation. For wells separated only 300 feet arrival times of few hours were reported. From these observations it was concluded that many sand bodies still produce under primary recovery. Sands with better transmissibility and continuity are constantly recycling injected water contributing little to reduce oil saturation. As a consequence a full field reservoir description in a sand by sand basis was initiated before the implementation of an EOR process.
