Page 336 - Standard Handbook Petroleum Natural Gas Engineering VOLUME2

Estimation of Waterflood Residual Oil Saturation 303

to the flowing fluids. This important information can be obtained from the
transient well tests.
Transient Tests

Whereas the producing well production data can only provide a relative
permeability ratio, transient well testing can provide estimates of reservoir
permeabilities to both oil and water (and free gas, if present):

(5-242)

(5-243)

where k, q, B, and p are as previously defined and have units of millidarcies,
barrels per day, reservoir barrels per stock tank barrel, and centipoise, respectively.
The thickness of the interval, h, is in ft and m is the appropriate slope from
the Miller-Dyes-Hutchinson (MDH) plot or the Horner plot.
Multiple well or single well tests can be used to estimate the effective
permeability to oil by using typecurve matching:

(5-244)

where (pJM is the dimensionless pressure at the match point for type-curve
matching, ApM is the pressure change from transient test data at the match point
for typecurve matching, and the previously defined terms are in field units.
Laboratory relative permeability curves are then used to find the saturations
that correspond to the relative permeabilities obtained from the transient tests.
Multiple well testing can also be used to estimate oil saturation by using the
total compressibility from the match point data and
c, = CwSw + coso + CESS + cy (5-64)

where cr is system total compressibility; C, is 'the formation or pore volume
compressibility; c+ cot and cg are compressibilities of water, oil and gas, all with
units of psi-'; and S is the corresponding saturation [321]. Since the gas term
is assumed to be zero for the waterflooded case and since Sw = (1 - So,,),

c, = cw(l - So) + coso + Cf (5-245)
By rearranging,

C,-C, -cf
so = (5-246)
(c, - c, 1
With a knowledge of oil, water, and formation pore volume compressibilities,
and the total compressibility determined from the typecurve matching, reservoir
oil saturation can be estimated [319]. Oil saturation based on compressibility