Page 258 - Introduction to Petroleum Engineering

GAS WELL DELIVERABILITY 245

Answer
The AOF is the rate when p = 0 psia so that
wf
.
.
.
q sc Cp 2 r p 2 wf n C p 2 r n 58910 2 1815 1815 0 3477 10 9 MMSSCFG/day
12.4.2 The LIT Method
Any gas well deliverability test can be analyzed using the LIT method. Deliverability
test data are fit to the LIT equation

m p r m p wf m aq sc bq sc 2 (12.34)
where q is the gas flow rate at standard conditions (MMSCFD), m(p ) is the real gas
sc
r
pseudopressure corresponding to p (psia /cp), and m(p ) is the real gas pseudopres-
2
wf
r
sure corresponding to p (psia /cp). The term aq represents uniform laminar flow.
2
wf
sc
2
More chaotic inertial and turbulent flow is represented by the term bq . Equation
sc
12.34 can be rearranged to give
m i bq a (12.35)
q sci sci
for each measurement i. This is a straight line with slope b and intercept a when
we plot Δm /q versus q . Least squares analysis of deliverability test data yields
sci
i
sci
values of a and b. The quadratic formula is used to rearrange Equation 12.34 to
express flow rate q as
sc
a a 2 4 bm
q (12.36)
sc 2 b
in terms of real gas pseudopressure and empirical parameters a, b. The condition for
determining AOF using the LIT method is m p( ) 0.
wf
Example 12.8 LIT Method
Application of the LIT method to data from a gas well deliverability test gives
a = 3.19 × 10 psia /cp/MMSCFD and b = 1.64 × 10 psia /cp/(MMSCFD ).
2
−6
2
2
−6
Estimate the AOF for the well at p = 1948 psia with pseudopressure m(p ) =
r
r
3.13 × 10 psia /cp. The deliverability test uses well rates in MMSCFG/day.
2
8
Answer
The AOF is the rate when m(p ) = 0 psia /cp so that
2
wf
a a 2 4 bm p
.
q r 12 9 MMSCFG/day
sc
2 b