Page 233 - Fundamentals of Enhanced Oil and Gas Recovery

Waterflooding 221

S w 2 S wir
RF 5
1 2 S wir
From the chart below, the linear system showed an average saturation S w 5 0.52
and that for the radial system was S w 5 0.63. Inputs of the extrapolated values into
the expression above, it was observed that the recovery factor was much higher for
the radial displacement system with a recovery of about 53% and that of the linear
system was calculated to be about 40%. This has shown that radial displacing mecha-
nism is much more practicable in terms of performance for radial waterflooding
scenarios.
The pilot-scale analysis showcased the importance of water cut for reservoir per-
formance analysis. This can give engineers an understanding of their unique flooding
design with forecasted reports on the location of invading water with respect to pro-
duction while preventing negative impacts on economic benefits. A major drawback
for this work is how best capillary pressure can be estimated. Linear displacement
assumes negligible capillary pressure. However, the inclusion of capillary pressure for
the radial system contributed to lower water cut as observed in Fig. 7.6. If higher
water cuts are observed, there is a tendency for early water breakthrough at the pro-
duction well which isn’t the best scenario in terms of economics. However, this can
be resolved by increasing the viscosity of water during flooding with additives.

7.5 APPLICATION OF BUCKLEY LEVERETT THEORY
AND FRACTIONAL FLOW CONCEPT

The performance analysis of waterflooding is often based on reservoir flow sys-
tems. The two geometries of a system widely used are the linear displacement system
and the radial displacement system [6]. The oil recovery factor for both systems would
be estimated using the average saturation of both systems. At water breakthrough, the
average water saturation would be determined and used to estimate the recovery fac-
tor for comparison of both systems. The Buckley Leverett theory estimates the rate
at which an injected water moves through a porous medium [6]. The approach applies
fractional flow theory and assumes that
• Flow is linear and horizontal
• Water is injected into an oil reservoir
• Oil and water are both incompressible
• Oil and water are immiscible
• Gravity and capillary-pressure effects are negligible