SAG Foam Flooding in Carbonate Rocks
C.S. Boeije (TU Delft - Reservoir Engineering)
W. Rossen (TU Delft - Reservoir Engineering)
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Abstract
Foam is
used in gas-injection EOR processes to reduce the mobility of gas, resulting in
greater volumetric sweep. SAG (Surfactant Alternating Gas) is a preferred
method of injection as it results in greater injectivity in the field, but
designing a successful process requires knowledge of foaming performance at
very high foam qualities (gas fractional flows). Here the use of foam in
low-permeability (~1 mD) Indiana Limestone cores for SAG foam applications is studied.
Coreflood experiments were performed for a range of foam qualities at high
pressure (100 bar), elevated temperature (55°C), high salinity (200,000 ppm)
and in the presence of crude oil. The effectiveness of the foam was studied by
differential pressure measurements along the core. Foam was still able to form
under these stringent conditions, but it was a relatively weak foam (i.e. its
ability to reduce gas mobility is modest). For one surfactant formulation,
further analysis of the experimental results show that the foam would be able
to maintain mobility control over the displaced phase, thus providing a stable
displacement front, and that it can be used in a SAG foam process in these
formations. For a second formulation the non-monotonic nature of the fractionalflow
data require further investigation before scale-up to the field. In addition,
further coreflood experiments were carried out using heterogeneous, vuggy Edwards
White cores with even lower permeability (~0.5 mD). These experiments were
performed to determine whether foaming is possible in heterogeneous media and
especially to investigate the effects of disconnected vugs on the foaming performance.
CT scans were taken during the period of foam injection to determine saturation
profiles within the core. Foam was able to form inside these cores, but inside
the vugs foam segregation was observed with liquid pockets visible in the
bottom of the vugs and gas in the remainder. This segregation was only a local
effect though, confined to the vug itself, and foam was able to persist in the
rest of the core.