Page 181 - Formulas and Calculations for Petroleum Engineering

174 Formulas and calculations for petroleum engineering

3.56 Time to pseudo-steady state (single well-circular 3.58 True wellbore storage coefficient (pressure
reservoir) 200 build-up test) 201
3.57 Time to reach the semi-steady state for a gas well 3.59 Well flow efficiency (geothermal well) 202
in a circular or square drainage area 201 3.60 Well shut-in pressure during buildup (Horner plot) 202

3.1 Analysis of a flow test with smoothly varying rates

Input(s)
t 1 : Time at P wf1 from Given Values or Trendline (h)
t 2 : Time at P wf2 from Given Values or Trendline (h)
q 1 : Flow Rate at P wf1 (STB/day)
q 2 : Flow Rate at P wf2 (STB/day)
p i : Initial Pressure (psi)
p wf2 : Wellflow Pressure at Point 2 from Given Values or Trendline (psi)
p wf1 : Wellflow Pressure at Point 1 from Given Values or Trendline (psi)
p wf : 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)

m: Slope of Line (dimensionless)
k: Permeability (mD)
s: Skin Factor (dimensionless)

Formula(s)

p p wf2 p p wf1
i
i

q 2 q 1
m ¼
log t ðÞ log tðÞ
2
1
m
k ¼ 162:6 B
m h
0 1

1 k
B C
s ¼ 1:151 B log +3:23 C
@ p p wf Ø m c r 2 w A
t
i
m
q
Reference: Lee, J., Rollins, J. B., & Spivey, J. P. (2003). Pressure Transient Testing (Vol. 9). Richardson, Texas: Society of
Petroleum Engineers, Page: 31.
3.2 Analysis of a post-fracture—Constant-rate flow test with boundary effects
Input(s)
q g : Gas Flow Rate (MSCF/day)
B g : Gas formation Volume Factor (RB/MSCF)