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Well test analysis formulas and calculations Chapter 3 199

3.52 Skin during infinite-acting pseudoradial flow for vertical wells

Input(s)
p i : Initial Pressure (psi)
p 1hr : Pressure After 1 Hour (psi)
m: Slope (psi/h)
k: Permeability (mD)
ø: Porosity (fraction)
m Total : Viscosity (cP)
c t : Total Compressibility (1/psi)
r w : Wellbore Radius (ft)

Output(s)

S: Skin (dimensionless)

Formula(s)

p p 1hr k

i
S ¼ 1:151 log +3:23
m ø m Total c r 2 w
t
Reference: Ahmed, T., McKinney, P.D. 2005. Advanced Reservoir Engineering, Gulf Publishing of Elsevier, Chapter: 1,
Page: 99.

3.53 Skin estimation type-1 (pressure buildup test)

Input(s)
P hr : Pressure After One Hour of Well Shut-in (psi)
P wf : Well Flowing Pressure (psi)
m: Slope of Horner Plot (psi/cycle)
k: Permeability (mD)
ø: Porosity (fraction)
c t : Total Compressibility (1/psi)
r w : Wellbore Radius (ft)
m o : Oil Viscosity (cP)

Output(s)
s: Skin Factor (dimensionless)

Formula(s)

ð P Þ P wf k
hr
s ¼ 1:151 log +3:23
m ø m c r 2
o t w
Notes: Skin Estimation from Horner Plot (Semi Log Plot).
Reference: Lee, J., Rollins, J. B., & Spivey, J. P. (2003). Pressure Transient Testing (Vol. 9). Richardson, Texas: Society of
Petroleum Engineers, Page: 104.