Gas Well Deliquification Workshop Sheraton Hotel, Denver, Colorado February 19 – 22, 2012 Pseudo Steady-State Plunger Lift Model Kees Veeken Shell E&P Europe (NAM B.V.)
Gas Well Deliquification Workshop
Sheraton Hotel, Denver, Colorado
February 19 – 22, 2012
Pseudo Steady-State Plunger Lift Model
Kees Veeken
Shell E&P Europe (NAM B.V.)
Feb. 19 – 22, 2012 2012 Gas Well Deliquification Workshop
Denver, Colorado
2
Contents
• Reasons
• Assumptions and equations
• Observations
• Conclusions
Feb. 19 – 22, 2012 2012 Gas Well Deliquification Workshop
Denver, Colorado
3
Reasons
• Selection and justification of (high cost) deliquification
measures based on comparison of incremental
production and cost profiles
• Outflow models for production forecasting “easily”
constructed for steady-state techniques such as
velocity string, foam, gas lift and downhole pump
• More complicated for transient techniques such as
plunger lift and intermittent production (plunger-less
lift)
Feb. 19 – 22, 2012 2012 Gas Well Deliquification Workshop
Denver, Colorado
4
Production Forecast
• Need to calculate average capacity (Qcap) as function of
reservoir pressure (Pres), and minimum achievable
reservoir pressure (Pmin) to compare plunger lift
against alternatives
– Pmin dictates incremental reserves
– Qcap governs time to recover those reserves
– Combination determines discounted incremental reserves and
costs for economics
• To date plunger modeling has focused mostly on
understanding and optimizing plunger cycle, rather
than capturing associated production performance
Feb. 19 – 22, 2012 2012 Gas Well Deliquification Workshop
Denver, Colorado
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Production Performance – Prolific
Pmin dictates incremental reserves
Qcap governs time to recover reserves
Combi determines discounted reserves
Pmin
Compression
Pmin
Orginal
1 bara = 14.5 psia, 1e3 m3/d = 35.31 Mscf/d
Feb. 19 – 22, 2012 2012 Gas Well Deliquification Workshop
Denver, Colorado
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Production Performance – Poor
Production forecast follows
when combined with reservoir model
Pmin
Compression
Pmin
Orginal
1 bara = 14.5 psia, 1e3 m3/d = 35.31 Mscf/d
Feb. 19 – 22, 2012 2012 Gas Well Deliquification Workshop
Denver, Colorado
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Well Model – Three Curves
Inflow – Forcheimer Pres
2 – FBHP2 = A.Q + F.Q2
Back Pressure Curve (Pres
2 – FBHP2)n = Q/Cres Cres=1/A @ n=1
Outflow – Cullender & Smith FBHP2 = B.FTHP2 + C.Q2
Liquid Loading Rate – Turner Qmin = TC.FTHP0.5.ID2/[(FTHT+273).Z]
Qcap = {[A2+4(C+F).(Pres2-B.FTHP2)]0.5-A}/2(C+F)
Pmin2 = B.FTHP2 + A.Qmin+ (C+F).Qmin
2
1 bara = 14.5 psia, 1e3 m3/d = 35.31 Mscf/d
Feb. 19 – 22, 2012 2012 Gas Well Deliquification Workshop
Denver, Colorado
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Outflow Model – Approximation OK
LGR Bwet Cwet 20 1.37 0.0124 100 1.9 0.0144 500 4.5 0.026
Transition from “dry” gas well to “wet” gas well takes time
E.g. Q=100e3 m3/d, LGR=100 m3/e6m3, 4” ID 4 bar/hr
1 bara = 14.5 psia, 1e3 m3/d = 35.31 Mscf/d
Feb. 19 – 22, 2012 2012 Gas Well Deliquification Workshop
Denver, Colorado
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Compression: Qcap Benefit, Pmin Benefit
1 bara = 14.5 psia, 1e3 m3/d = 35.31 Mscf/d
Feb. 19 – 22, 2012 2012 Gas Well Deliquification Workshop
Denver, Colorado
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Velocity String: Qcap Penalty, Pmin Benefit
1 bara = 14.5 psia, 1e3 m3/d = 35.31 Mscf/d
Feb. 19 – 22, 2012 2012 Gas Well Deliquification Workshop
Denver, Colorado
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Nomenclature
• Pres = reservoir pressure
• Pmin = minimum achievable Pres
• Qcap = average well capacity
• Q = gas rate
• Qmin = minimum stable gas rate
• FTHP = flowing wellhead press.
• FBHP = flowing bottom hole pr.
• A = Darcy inflow resistance
• F = non-Darcy inflow resistance
• B = hydrostatic outflow
parameter
• C = friction outflow parameter
• TC = liquid loading parameter
• LGR = liquid to gas ratio
• Vup = average upward plunger
velocity
• Vdown = average downward
plunger velocity
• Toff = shut-in period
• DP = liquid load + plunger friction
• P = pressure buildup during
shut-in period
• Vt = tubing volume
• Va = annulus volume
• F = plunger frequency
Plunger Lift Cycle
Feb. 27 - Mar. 2, 2011 2011 Gas Well Deliquification Workshop Denver, Colorado
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• Cartoon depicts Fekete Virtuewell plunger model
Plunger moves up and down tubing at given velocities Vup and Vdown
Qmin ~ FTHP.ID2.Vup, Toff > Tdown
On
= U
p
Afte
r F
low
Off
=
Plu
ng
er
Do
wn
+ B
uild
up
Pe
rio
d
Picture
Fekete
James MacDonald
Plunger Lift Cycle
Feb. 27 - Mar. 2, 2011 2011 Gas Well Deliquification Workshop Denver, Colorado
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• ON (UP) – AFTER FLOW – OFF (BUILDUP)
Qmin is delivered by reservoir inflow Q plus blow down of annulus
volume if Q < Qmin
Up & Start Buildup
Q = {[A2+4.(C+F).(Pres2-(B0.5.THP+DP)2)]0.5-A}/2.(C+F)
After Flow
Q = {[A2+4.(C+F).(Pres2-(B0.5.THP+DP/2)2)]0.5-A}/2.(C+F)
Plunger Lift Cycle
Feb. 27 - Mar. 2, 2011 2011 Gas Well Deliquification Workshop Denver, Colorado
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• ON (UP) – AFTER FLOW – OFF (BUILDUP)
Pressure buildup ∆P during Off period is just sufficient to generate
required annulus decompression volume
Difference between Qcap and Qmin is delivered
by annulus decompression volume Va x ∆P
P = (Pres-B0.5.FTHP-DP).[1-EXP(-c*Toff-0.3*c2*Toff
2)]
where
c = 1e3*Q/[(Va+Vt).(Pres-B0.5.FTHP-DP)]
and
Q = {[A2+4.(C+F).(Pres2-(B0.5.THP+DP)2)]0.5-A}/2.(C+F)
Feb. 19 – 22, 2012 2012 Gas Well Deliquification Workshop
Denver, Colorado
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Plunger Lift – No Annulus Support
Qcap penalty due to DP and Toff
Pmin benefit
1 bara = 14.5 psia, 1e3 m3/d = 35.31 Mscf/d
Feb. 19 – 22, 2012 2012 Gas Well Deliquification Workshop
Denver, Colorado
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Plunger Lift – Annulus Support
Qcap penalty Pmin benefit
1 bara = 14.5 psia, 1e3 m3/d = 35.31 Mscf/d
Feb. 19 – 22, 2012 2012 Gas Well Deliquification Workshop
Denver, Colorado
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Plunger Modeling
• Liquid load x plunger frequency F equals produced
liquid volume LGR x Qcap
• Calculate maximum Qcap, F, Toff and ∆P by varying DP
• Calculate maximum Qcap, F, ∆P and DP as function of
reservoir pressure Pres
• Show impact of inflow performance, annulus volume,
liquid production, inflow performance and wellhead
pressure
• Ignore complexity and transient nature of plunger
cycle, including plunger friction, plunger by-pass,
annulus friction and varying plunger velocity !
Feb. 27 - Mar. 2, 2011 2011 Gas Well Deliquification Workshop Denver, Colorado
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0.00
0.02
0.04
0.06
0.08
0.10
0.12
0.14
0.16
0.18
0
5
10
15
20
0 5 10 15 20 25
T off
(d)
Q (e
3 m
3 /d
),
P (b
ara)
, F (
1/d
)
Liquid Load - DP (bara)
Gas Rate Frequency Buildup Toff
Vary Liquid Load DP to Maximize Qcap
1 bara = 14.5 psia, 1e3 m3/d = 35.31 Mscf/d
Small Annulus Volume – Va=4 m3
Feb. 27 - Mar. 2, 2011 2011 Gas Well Deliquification Workshop Denver, Colorado
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1 bara = 14.5 psia, 1e3 m3/d = 35.31 Mscf/d
Large Annulus Volume – Va=100 m3
Feb. 27 - Mar. 2, 2011 2011 Gas Well Deliquification Workshop Denver, Colorado
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1 bara = 14.5 psia, 1e3 m3/d = 35.31 Mscf/d
Medium Annulus Volume – Va=20 m3
Feb. 27 - Mar. 2, 2011 2011 Gas Well Deliquification Workshop Denver, Colorado
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1 bara = 14.5 psia, 1e3 m3/d = 35.31 Mscf/d
Vary LGR @ Pres=62 bara
Feb. 27 - Mar. 2, 2011 2011 Gas Well Deliquification Workshop Denver, Colorado
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Frequency, liquid load and
associated capacity loss
increase as LGR increases
1 bara = 14.5 psia, 1e3 m3/d = 35.31 Mscf/d
Vary LGR @ Pres=40 bara
Feb. 27 - Mar. 2, 2011 2011 Gas Well Deliquification Workshop Denver, Colorado
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Pmin increases as LGR increases
1 bara = 14.5 psia, 1e3 m3/d = 35.31 Mscf/d
Vary A @ FTHP=25 bara
Feb. 27 - Mar. 2, 2011 2011 Gas Well Deliquification Workshop Denver, Colorado
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Before Qmin = 46.9 e3m3/d
After Qmin = 31.7 e3m3/d (68%)
Plunger causes
deferment in
prolific wells
1 bara = 14.5 psia, 1e3 m3/d = 35.31 Mscf/d
Vary A @ FTHP=5 bara
Feb. 27 - Mar. 2, 2011 2011 Gas Well Deliquification Workshop Denver, Colorado
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Before Qmin = 19.2 e3m3/d
After Qmin = 6.3 e3m3/d (33%)
Plunger
most effective
at low FTHP
1 bara = 14.5 psia, 1e3 m3/d = 35.31 Mscf/d
Feb. 19 – 22, 2012 2012 Gas Well Deliquification Workshop
Denver, Colorado
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Observations
• Gas rate shows broad maximum Vs liquid load
• Suggests that plunger settings are quite forgiving
Parameter Pmin Benefit Qcap Penalty
Annulus Volume Increases (Decreases)
LGR Decreases Increases
Inflow Resistance Increases Decreases
FTHP Decreases (Increases)
Vup Decreases @ low Va
Vdown Decreases
Feb. 19 – 22, 2012 2012 Gas Well Deliquification Workshop
Denver, Colorado
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Conclusions
• Need pseudo steady-state plunger model to rank
plunger against alternative techniques
• Capture plunger performance by using simplest of
inflow and outflow models
• Make crude assumptions in the process
• Need to validate model against field results
• Plunger best suited for poor inflow and low liquid-gas
ratio
• Plunger performance benefits from significant annulus
volume and low wellhead pressure
Feb. 19 – 22, 2012 2012 Gas Well Deliquification Workshop
Denver, Colorado
28
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Feb. 19 – 22, 2012 2012 Gas Well Deliquification Workshop
Denver, Colorado
29
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