5.6 Multiphase Buildup Test Analysis

Basic buildup equations can be modified to model multiphase flow. For an infinite-acting reservoir, the buildup equation becomes

where

q _t = total flow rates of oil, gas, and water (bbl/day) and is given by

• q ₀ = oil flow rate (stb/day)

• ? ₀ = oil formation volume factor (rb/stb)

• q _g = gas flow rate (mscf/day)

• R _s = solution gas oil ratio (scf/stb)

• ? _g = gas formation volume factor (rb/mscf)

• q _w = water flow rate (stb/day)

• ? _w = water formation volume factor (rb/stb)

• ? _t = total mobility (mD/cP) and is given by

Total system compressibility c _t is estimated by using the equation:

It can be determined from the slope mofa buildup test run on a well that produces two or three phases simultaneously by the following equation:

Perrine has shown that it is also possible to estimate the permeability to each phase flowing from the same slope, m:

and

The skin factor s is estimated using the following equation:

where c ₀ is given by

Values of (dR _s/dp) and ( d ? ₀ / dp ) are obtained as the slopes of laboratory determined curves of R _s and ? ₀ versus p; the slope is drawn at the estimated average pressure:

Applications of these equations are illustrated by the following example. Average reservoir pressure, p, is...