Summary
Despite the widespread application of reservoir simulation to study
waterflood reservoirs, petroleum engineers still need simple predictive tools
to forecast production decline, estimate ultimate oil recovery, and diagnose
the production performance from the historical field data.
On the basis of the Buckley-Leverett equation and the assumption of a
semilog relationship between the oil-to-water relative permeability ratio and
water saturation, a consistent analytical solution can be derived as:
qoD (1 - qoD ) = (EV
/B)(1 / tD )
where qoD is the oil fractional flow, tD is
the fraction of cumulative liquid production to related formation volume,
B is the relative permeability ratio parameter, and EV
is the volumetric sweep efficiency. Two equivalent linear plots can be
developed: a log-log plot and a reciprocal time plot. The log-log plot has a
slope of -1 and intercept of EV /B. The reciprocal
time plot has a slope of EV /B and an intercept value
of 0. Both plots can be applied for the diagnostic analysis of waterflood
reservoirs.
Model and field case studies show the benefits of this technique as a
production-decline analysis tool in forecasting the waterflood production
decline and the ultimate oil recovery. This method can also be applied as a
diagnostic tool to evaluate various aspects of waterflood performance. Examples
include assessing waterflood maturity, calculating volumetric sweep efficiency,
distinguishing the normal waterflood breakthrough from the premature water
breakthrough through hydraulic fractures, and examining the consequences of
operational changes. The appropriate use of this analytical method will help to
optimize the field waterflood operation.
© 2009. Society of Petroleum Engineers
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History
- Original manuscript received:
21 January 2008
- Meeting paper published:
29 March 2008
- Revised manuscript received:
11 June 2008
- Manuscript approved:
14 July 2008
- Published online:
15 April 2009
- Version of record:
15 April 2009
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