critical velocity/ nodal stability gas well predictions...nodal analysis (slb) liquid friction...
TRANSCRIPT
-
Gas Well De-Liquification WorkshopAdams Mark Hotel, Denver, Colorado
March 5 - 7, 2007
Critical Velocity/ Nodal Stability Gas Well PredictionsBy J F Lea, PLTech LLCLynn Rowlan, Echometer Co.Charlie Reed, Devon
-
Gas Well De-Liquification WorkshopAdams Mark Hotel, Denver, Colorado
March 5 - 7, 2007
Liquid Loading
-
Mar. 5 - 7, 2007 2007 Gas Well De-Liquification Workshop Denver, Colorado
3
GAS WELL GRADIENT COMPOSED OF FRICTION AND GRAVITY
(dp/dl) = (dp/dl)el + (dp/dl)f + (dp/dl)acc
HOLDUP (LIQUID) BUILDS WITH TIME AND LOWER PRODUCTION
-
Mar. 5 - 7, 2007 2007 Gas Well De-Liquification Workshop Denver, Colorado
4
Recognize and Predict Loading by using
“Critical Rate” &
“Nodal Analysis Concepts”
-
Mar. 5 - 7, 2007 2007 Gas Well De-Liquification Workshop Denver, Colorado
5
-
Mar. 5 - 7, 2007 2007 Gas Well De-Liquification Workshop Denver, Colorado
6
( )6
3dggF GLC
Gravityπρρ ×−=
2, )(2
1dGdDG
CUPDrag VVACg
F −= ρWhereg = gravitational constant = 32.17 ft/s2gC = 32.17 lbm-ft/lbf-s2d = droplet diameterrL = liquid densityrG = gas densityCD = drag coefficientAd = droplet projected cross-sectional areaVG = gas velocityVd = droplet velocity
-
Mar. 5 - 7, 2007 2007 Gas Well De-Liquification Workshop Denver, Colorado
7
DG FF =
or( ) 2
3
21
6 CdDGCGL
C
VACg
dgg ρπρρ =−
Substituting Ad = πd2/4 and solving for VC gives,
( )DG
GLC C
dgVρρρ −
=3
4
-
Mar. 5 - 7, 2007 2007 Gas Well De-Liquification Workshop Denver, Colorado
8
Hinze, AICHE Journal Sept 1955, shows that droplet diameter dependence can be expressed in terms of the dimensionless Weber number
302
==C
GCWE g
dVNσρ
Solving for the droplet diameter gives
230CG
C
Vgd
ρσ
=
and substituting into Equation A-1 gives
( )2303
4
CG
C
DG
GLC V
gCgV
ρσ
ρρρ −
=
or
4/1
2
4/140
−
= σ
ρρρ
G
GL
D
CC C
ggV
-
Mar. 5 - 7, 2007 2007 Gas Well De-Liquification Workshop Denver, Colorado
9
Turner assumed a drag coefficient of CD = .44 that is valid for fully turbulent conditions. Substituting the turbulent drag coefficient and values for g and gC gives:
sftVG
GLC /514.17
4/1
2
−= σ
ρρρ
WhererL = liquid density, lbm/ft3rG = gas density, lbm/ft3S = surface tension, lbf/ftEquation A-2 can be written for surface tension in dyne/cm units using the conversionlbf/ft = .00006852 dyne/cm to give:
sftVG
GLC /593.1
4/1
2
−= σ
ρρρ
WhererL=liquid density, lbm/ft3rG=gas density, lbm/ft3s=surface tension, dyne/cm
-
Mar. 5 - 7, 2007 2007 Gas Well De-Liquification Workshop Denver, Colorado
10
Evaluating Equation A-4 for typical values ofGas gravity γG = 0.6Temperature T = 120 FGas deviation factor Z = 0.9gives:
3/0031.9.)120460(
6.715.2 ftlbmPPG =×+×=ρ
Typical values for density and surface tension areWater density = 67 lbm/ft3Condensate density = 45 lbm/ft3Water surface tension = 60 dyne/cmCondensate surface tension = 20 dyne/cm
-
Mar. 5 - 7, 2007 2007 Gas Well De-Liquification Workshop Denver, Colorado
11
( )( )( )
sftPP
PPV waterC /0031.
0031.67434.4600031.
0031.67593.1 2/14/14/1
2,−
=
−=
( )( )( )
sftPP
PPV condC /0031.
0031.45369.3200031.
0031.45593.1 2/14/14/1
2,−
=
−=
( )( )
sftPPV waterC /0031.
0031.67321.5 2/14/1
,−
=
( )( )
sftPPV condC /0031.
0031.45043.4 2/14/1
,−
=
Coleman, et al., (Exxon)
Turner et al., (with 20% adjustment)
-
Mar. 5 - 7, 2007 2007 Gas Well De-Liquification Workshop Denver, Colorado
12
( )( )
sftPPV waterC /0031.
0031.67321.5 2/14/1
,−
=
( )( )
sftPPV condC /0031.
0031.45043.4 2/14/1
,−
=
Turner et al., (with 20% adjustment)
2/1
4/12
, )0031(.)0031.45(
)460(0676.
)/(PP
ZTdP
DMMscfq ticondensatet−
+=
2/1
4/12
, )0031(.)0031.67(
)460(0890.
)/(PP
ZTdP
DMMscfq tiwatert−
+=
-
Mar. 5 - 7, 2007 2007 Gas Well De-Liquification Workshop Denver, Colorado
13
Turner
Coleman
Well Data
-
Mar. 5 - 7, 2007 2007 Gas Well De-Liquification Workshop Denver, Colorado
14
Example: Using Turner, 2 3/8’s, 100 psi, read~320 Mscf/D
Turner Unloading Rate for Well Producing Water
0
500
1000
1500
2000
2500
3000
0 50 100 150 200 250 300 350 400 450 500
Flowing Pressure (psi)
Rat
e (M
cfd)
4-1/2 OD 3.958 ID
3-1/2 2.9922-7/8 2.441
2-3/8 1.995
2-1/16 1.751
-
Mar. 5 - 7, 2007 2007 Gas Well De-Liquification Workshop Denver, Colorado
15
Other References Related to Critical Velocity or Rate
1. Lea, J.F., Nickens, H.V., and Wells, M.: Gas Well De-Liquification, first edition, Elsevier Press, Cambridge, MA (2003).
2. Turner, R.G., Hubbard, M.G., and Dukler, A.E.: “Analysis and Prediction of Minimum Flow Rate for the Continuous Removal of Liquids from Gas Wells,” J. Pet. Tech. (Nov.1969) 1475-1482.
3. Coleman, S.B., Clay, H.B., McCurdy, D.G., and Lee Norris, H. III: “A New Look at Predicting Gas-Well Load Up,” J. Pet. Tech. (March 1991) 329-333.
4. Veeken, K., Bakker, E., and Verbeek, P.: “Evaluating Liquid Loading Field Data and Remedial Measures,” presented at the 2003 Gas Well De-Watering Forum, Denver, CO, March 3-4.
5. Li, M., Li, S.L., and Sun, L.T.: “New View on Continuous-Removal Liquids from Gas Wells,” paper SPE 75455 presented at the 2001 SPE Permian Basin Oil and Gas Recovery Conference, Midland, TX, May 15-16.
6. Nosseir, M.A., Darwich, T.A., Sayyouh, M.H., and El Sallaly, M.: “A New Approach for Accurate Prediction of Loading in Gas Wells Under Different Flowing Conditions,” paper SPE 37408 presented at the 1997 SPE Production Operations Symposium, Oklahoma City, OK, March 9-11.
7. Duggan, J.O.: “Estimating Flow Rates Required to Keep Gas Wells Unloaded,” J. Pet. Tech.(December 1961) 1173-1176.
8. Yamamoto, H. and Christiansen, R.L.: “Enhancing Liquid Lift from Low Pressure Gas Reservoirs,” paper SPE 55625 prepared for presentation at the 1999 SPE Rocky Mountain Regional Meeting, Gillette, WY, May 15-18.
9. Bizanti, M.S. and Moonesan, A.: “How to Determine Minimum Flowrate for Liquids Removal,”World Oil, (Sept. 1989) 71-73.
10. Ilobi, M.I. and Ikoku, C.U.: “Minimum Gas Flow Rate for Continuous Liquid Removal in Gas Wells,” paper SPE 10170 presented at the 1981 SPE of AIME Annual Fall Technical Conference and Exhibition, San Antonio, TX, Oct. 5-7.
11. Guo, B., Ghalambor, A., Xu, C., “ A Systemic Approach to Predicting Liquid Loading in Gas Wells”, SPE 94081, Presented at the 2005 SPE Production and Operations Symposium, OK City, USA, 17-19, April, 2005.
-
Mar. 5 - 7, 2007 2007 Gas Well De-Liquification Workshop Denver, Colorado
16
Critical vs BWPD
-
Mar. 5 - 7, 2007 2007 Gas Well De-Liquification Workshop Denver, Colorado
17
Critical Rate: Summary• Turner, Coleman and other models do not agree• Most except Guo et al. are in dependent of liquid
rate• It is theoretically better to use at pressure
downhole but seldom done• Most critical models are fairly simplistic models• Must be considered approximate but widely used
with fair success• New model with critical as fn of bwpd seems
logical but untested by industry as far as is known
-
Gas Well De-Liquification WorkshopAdams Mark Hotel, Denver, Colorado
March 5 - 7, 2007
Nodal Analysis
-
Mar. 5 - 7, 2007 2007 Gas Well De-Liquification Workshop Denver, Colorado
19
Nodal Analysis ™ :
A Model of the Well
-
Mar. 5 - 7, 2007 2007 Gas Well De-Liquification Workshop Denver, Colorado
20
Nodal Analysis ™ (SLB)
Rate
Pres
sure
InflowOutflow
Inflow to the node
PR – ∆P (upstream components press drop’s) = Pnode
Outflow from the node
Psep + ∆ P (downstream components press drop’s) = Pnode
-
Gas Well De-Liquification WorkshopAdams Mark Hotel, Denver, Colorado
March 5 - 7, 2007
Inflow Curves
-
Mar. 5 - 7, 2007 2007 Gas Well De-Liquification Workshop Denver, Colorado
22
Inflow or Reservoir Curve
Rate
Pres
sure
Inflow
Reservoir Inflow curve often represented by:
Q = C ( Pr2 – Pwf2)n …. (back pressure equation)
-
Gas Well De-Liquification WorkshopAdams Mark Hotel, Denver, Colorado
March 5 - 7, 2007
Outflow Curves
-
Mar. 5 - 7, 2007 2007 Gas Well De-Liquification Workshop Denver, Colorado
24
Nodal Analysis ™ (SLB)
FrictionLiquidBuildup
Rate
Dow
n-ho
le p
ress
ure Tubing J-Curve
At low rates, liquid builds up in the tubing and requires more pressure to flow
(Use various correlations, Gray, etc. )
-
Mar. 5 - 7, 2007 2007 Gas Well De-Liquification Workshop Denver, Colorado
25
Liquid LoadingJ-Curve with Tubing to Perfs
0 200 400 600 800 1000 1200 1400 1600 1800 2000340380420460500540580620660700740780820860900
Flowing BHP (psig)Flowing BHP (psig)Flowing BHP (psig)
Gas Rate (mscf/d)Gas Rate (mscf/d)Gas Rate (mscf/d)
Liquid Loading J-Curve with GrayLiquid Loading J-Curve with GrayLiquid Loading J-Curve with GrayTbg - Critical Rate (Min BHP) = 547 mscf/dPfwh 125 psigCond .0 bbl/MMscfWater 15.0 bbl/MMscf2.375" at 10000 ft
Stable flowHigh frictionMay have some liquid buildup
Unstable flowHigh liquid buildup
Liquid loading occurs when gas rate is too low to efficiently remove the produced liquidsThis results in unstable flow behavior and potential logging off of the well
Optimal Operation
-
Mar. 5 - 7, 2007 2007 Gas Well De-Liquification Workshop Denver, Colorado
26
Flowpoint: Greene, SWPSC
-
Mar. 5 - 7, 2007 2007 Gas Well De-Liquification Workshop Denver, Colorado
27
Liquid Loading
• Liquid loading occurs when gas rate is too low to efficiently remove the produced liquids
• This results in unstable flow behavior and potential logging off of the well
0 800 1600 2400 3200 4000 4800 5600 6400 7200 80000
80
160
240
320
400
480
560
640
720
800
880PSIAPSIAPSIA
Gas Rate (mscf/d)Gas Rate (mscf/d)Gas Rate (mscf/d)
Tubing CurvesTubing CurvesTubing Curves
ISABEL A1ISABEL A1ISABEL A1
S1 - Tubing Flow - Ptbg = 250 psigS2 - Tubing Flow - Ptbg = 250 psigS3 - Tubing Flow - Ptbg = 250 psig
Cond .0 bbl/MMscfWater 29.6 bbl/MMscf
S1 - 2.875" at 3220 ftS2 - 3.5" at 3220 ftS3 - 4.5" at 3220 ftGray Correlation
S1
S2S3
S1 S2 S3
-
Mar. 5 - 7, 2007 2007 Gas Well De-Liquification Workshop Denver, Colorado
28
Liquid LoadingEffect of Tubing String
0 100 200 300 400 500 600 700 800 900 1000 1100 1200 13000
200
400
600
800
1000
1200
1400
1600
1800PSIAPSIAPSIA
Gas Rate (mscf/d)Gas Rate (mscf/d)Gas Rate (mscf/d)
Nodal PlotNodal PlotNodal PlotS1 - Tubing Flow - Ptbg = 500 psig S2 - Tubing Flow - Ptbg = 500 psigS3 - Tubing Flow - Ptbg = 500 psig Pbar = 1450 psiaPbar = 1250 psia Pbar = 1050 psiaStable Flow
Cond .0 bbl/MMscfWater 15.0 bbl/MMscfS1 - 2.375" at 10000 ft S2 - 1.9" at 10000 ft S3 - 1.66" at 10000 ft Gray Correlation
-
Mar. 5 - 7, 2007 2007 Gas Well De-Liquification Workshop Denver, Colorado
29
Nodal Analysis : Effects such as Size of the Tubing Diameter vs. Flow Rate can be
studied
-
Mar. 5 - 7, 2007 2007 Gas Well De-Liquification Workshop Denver, Colorado
30
Nodal “Turn-Up” Point is BIGGEST ERROR in Multiphase Flow Predictions
-
Gas Well De-Liquification WorkshopAdams Mark Hotel, Denver, Colorado
March 5 - 7, 2007
Nodal Stability
-
Mar. 5 - 7, 2007 2007 Gas Well De-Liquification Workshop Denver, Colorado
32BPD>
Psi o
n pe
rfs
Inflow or rsvr curve
Tubing crv, no flow
Tubing crv, more flow
Tubing crv, flow
Tubing crv, flow but unstable
Intersections are flow pts
Nodal Analysis Well Situations
-
Mar. 5 - 7, 2007 2007 Gas Well De-Liquification Workshop Denver, Colorado
33
Nodal Analysis : Stability
Stability
Rate
Dow
n-ho
le p
ress
ure
B
D
C
A
Flow around A & B is unstable
Flow around C and D is stable
-
Mar. 5 - 7, 2007 2007 Gas Well De-Liquification Workshop Denver, Colorado
34
What About Flow Below the Critical???
•Exxon said on average with their data, production was 40% less•Sutton, et al., Marathon, SPE 80887 modeled flow with gas bubbling through static liquid column.
-
Gas Well De-Liquification WorkshopAdams Mark Hotel, Denver, Colorado
March 5 - 7, 2007
Model Gas Well
-
Mar. 5 - 7, 2007 2007 Gas Well De-Liquification Workshop Denver, Colorado
36
Example Gas Well• Data:• Reservoir:• C = .0001414 Mscf/D• n = 1.0• Pr =1500 psi• Tubing: 2 3/8’s to 10,000’• Liquids: 50 bbl/MMscf
• Pressures/Temps/Fluid Properties• Pwh: 100 psi• Twh: 100 F• BHT: 200 F• GG: .7• WG: 1.03• WOR: 1.
SNAP: Ryder Scott
-
Gas Well De-Liquification WorkshopAdams Mark Hotel, Denver, Colorado
March 5 - 7, 2007
Example Output
-
Mar. 5 - 7, 2007 2007 Gas Well De-Liquification Workshop Denver, Colorado
38
Well Unstable and Also Flowing Below Critical for Water
This well unstable according to shape of outflow curve at point of intersection with IPR
-
Gas Well De-Liquification WorkshopAdams Mark Hotel, Denver, Colorado
March 5 - 7, 2007
Effects of Tubing Size
-
Mar. 5 - 7, 2007 2007 Gas Well De-Liquification Workshop Denver, Colorado
40
Smaller tubing such as 1.61 or 1.38 (or smaller) ID stabilizes flow.
Critical rate for 1.61 is 245 mscfd
Critical rate for 1.38 is 152 mscfd
So 1.61” or smaller stabilizes and flows above critical rate
-
Gas Well De-Liquification WorkshopAdams Mark Hotel, Denver, Colorado
March 5 - 7, 2007
Effects of Surface Pressure
-
Mar. 5 - 7, 2007 2007 Gas Well De-Liquification Workshop Denver, Colorado
42
Adding constant surface pressure such as higher separator pressure does not stabilize or tend to flow above critical rate
-
Mar. 5 - 7, 2007 2007 Gas Well De-Liquification Workshop Denver, Colorado
43
Lower Surface Pressure:
Flowing at 12 psig stabilizes and flows above critical of 157 mscfd
Flowing at 50 psig flows above critical rate of 241 mscfd but is “just stable” ?
-
Gas Well De-Liquification WorkshopAdams Mark Hotel, Denver, Colorado
March 5 - 7, 2007
Effects of Restrictions at Bottom of Tubing
-
Mar. 5 - 7, 2007 2007 Gas Well De-Liquification Workshop Denver, Colorado
45
Adding a choke restriction at bottom hole of .15” diameter or .14”diameter stabilizes flow. It is still below critical flow however
-
Gas Well De-Liquification WorkshopAdams Mark Hotel, Denver, Colorado
March 5 - 7, 2007
Effects of Restrictions at Surface
-
Mar. 5 - 7, 2007 2007 Gas Well De-Liquification Workshop Denver, Colorado
47
Adding a choke of .21” diameter or .18”diameter at surface stabilizes flow. It is still below critical rate however
-
Gas Well De-Liquification WorkshopAdams Mark Hotel, Denver, Colorado
March 5 - 7, 2007
Effects of Flowline
-
Mar. 5 - 7, 2007 2007 Gas Well De-Liquification Workshop Denver, Colorado
49
A flowline of more and more pressure drop has a stabilizing effect but flow is still below critical rate
-
Gas Well De-Liquification WorkshopAdams Mark Hotel, Denver, Colorado
March 5 - 7, 2007
Summary & Conclusions
-
Mar. 5 - 7, 2007 2007 Gas Well De-Liquification Workshop Denver, Colorado
51
Summary & Conclusions• Smaller tubing has stabilizing effect but if too
small will add too much friction (well known)• Adding constant pressure to the surface of the
well reduces rate and does not stabilize the well or tend to flow below critical
• Adding lower constant pressure to the surface of the well stabilizes the well and tends to flow above critical rate (compression)
• Adding a rate dependent pressure drop (choke) to bottom or top of well has stabilizing effect but flow remains below critical rate if below critical to begin with
-
Mar. 5 - 7, 2007 2007 Gas Well De-Liquification Workshop Denver, Colorado
52
Summary & Conclusions Continued
• The effects of a flowline (rate dependent pressure drop) has a stabilizing effect on the flow but flow continues below critical if below to start with as FL pressure drop is added.
• Never add rate dependent pressure drop (choke) to a well that is flowing above critical rate.. It will only reduce flowrate
• Adding too much of a rate dependent pressure drop (choke) will/can reduce flowrate to zero
-
Mar. 5 - 7, 2007 2007 Gas Well De-Liquification Workshop Denver, Colorado
53
Summary & Conclusions Continued
• In general never add a rate dependent pressure drop to plunger lift, or pumping wells or gaslift wells. There are some exceptions where back pressure may help beam handle gas better and choking gaslift well can sometimes reduce heading and cycling.
-
Mar. 5 - 7, 2007 2007 Gas Well De-Liquification Workshop Denver, Colorado
54
Questions Remaining• Since Nodal Analysis shows a stabilizing effect
on a loaded gas well only, (but still flows below critical rate), does this explain the anecdotal cases where adding chokes to wells in the field gets them to flow continuously where they would not before?
• Cases are reported where wells that require stop clocking will flow continuously if a choke is added to the surface. It may serve as intermediate solution to loading before AL is needed.
• Is critical rate alone good enough to evaluate loading wells or is Nodal Analysis also to evaluate stability?
-
Mar. 5 - 7, 2007 2007 Gas Well De-Liquification Workshop Denver, Colorado
55
Problems
• Multiphase correlations have poor agreement to evaluate stability in loaded/unloaded gas wells
• Critical velocity correlations also disagree and have problems previously discussed
-
Mar. 5 - 7, 2007 2007 Gas Well De-Liquification Workshop Denver, Colorado
56
November 2006 SPE Production & Operations
Better?
-
Mar. 5 - 7, 2007 2007 Gas Well De-Liquification Workshop Denver, Colorado
57
Possible Uses of Analysis• If a well is loaded and it must be intermitted to
continue production, consider using a choke to get the well to flow continuously once again. The cost is low to try this.
• DO NOT add chokes across the field indiscriminately or you will have problems.
• Thanks to Mohan Kelkar, Tulsa University, for pointing out the stabilizing effects of adding chokes to loaded gas wells. At least stabilizing as far as Nodal Analysis predictions are concerned. He also has reported success stories with this technique.
-
Mar. 5 - 7, 2007 2007 Gas Well De-Liquification Workshop Denver, Colorado
58
Disclaimer
The following disclaimer may be included as the last page of a Technical Presentation or Continuing Education Course. A similar disclaimer is included on the front page of the Gas Well Deliquification Web Site.
The Gas Well Deliquification Steering Committee Members, the Supporting Organizations and their companies, the author(s) of this Technical Presentation or Continuing Education Course, and their company(ies), provide this presentation and/or training at the Gas Well Deliquification Workshop "as is" without any warranty of any kind, express or implied, as to the accuracy of the information or the products or services referred to by any presenter (in so far as such warranties may be excluded under any relevant law) and these members and their companies will not be liable for unlawful actions and any losses or damage that may result from use of any presentation as a consequence of any inaccuracies in, or any omission from, the information which therein may be contained.