Page 202 - Formulas and Calculations for Petroleum Engineering

Well test analysis formulas and calculations Chapter 3 195

c t : Compressibility (1/psi)
r w : Wellbore Radius (ft)

Output(s)

s: Skin Factor (dimensionless)

Formula(s)

pws pws
0 1
a b
0 1

tp + dt tp + dt
B b C
B log log a C
dt dt
B C
B C
B C
B b a C
s ¼ 1:151 B ð phr pwf Þ logB 2 C +3:23 C
Ø m c r
B C
B t w C
B C
@ A
@ A
Reference: Pressure Buildup and Flow Tests in Wells, Matthews & Russell, Page: 21.
3.44 Permeability and skin factor from a constant-rate flow test
Input(s)
t a : Time at Pwf1 from given values or trendline (h)
t b : Time at Pwf2 from given values or trendline (h)
p w : Well flowing Pressure at point 2 from given values or trend line (psi)
p wf : Well flowing Pressure at point 1 from given values or trendline (psi)
p i : Initial Pressure (psi)
p hr : Pressure Value at t ¼ 1 h (psi)
q: Flow Rate (STB/day)
B: Volume factor (RB/STB)
h: Thickness of reservoir (ft)
m: Viscosity of Oil (cP)
Ø: Porosity (fraction)
c t : Compressibility (1/psi)
r w : Wellbore Radius (ft)

Output(s)
s: Skin Factor (dimensionless)

Formula(s)

0 1
0 1
m
p p
162:6 q B
B wf w C
B h C
p phr B C
B C
B i B log tðÞ log tðÞ C C
a
b
s ¼ 1:151 B p p logB 2 C +3:23 C
B wf w B Ø m c r C C
t
B w C
@ A
@ log tðÞ log tðÞ A
b a
Reference: Pressure Buildup and Flow Tests in Wells, Matthews & Russell, Page: 57.