© ChevronTexaco 2001
Use of Transient Simulators to Assess Gas Lift Viability for Offshore Angola
2002 North American Gas Lift WorkshopSHAUNA NOONAN / FRED BROWNLEE
2February 5, 2002
Produce 40,000 BWPD
from 23,000 ft MD (8800 ft TVD)
via Gas Lift
Fact or Fiction?
Actually a better title would be:
3February 5, 2002
Presentation Outline
Operating Parameters
Discussion on software (transient and static programs)
Work scope
Some of the results
What did we learn?
Questions
4February 5, 2002
Parameters
• 4500 psi injection pressure at wellhead
• Target production of 40,000 bwpd / well
• 0.68 gravity injection gas
• Up to 30 MMscfd source gas available / well
• 1.06 gravity water
• Wellhead pressure of 250 psi
• Reservoir Pressure of 3500 psi
• Dry Tree (offshore in 1200 ft water)
5February 5, 2002
0 2000 4000 6000 8000 10000 12000 14000 16000 18000 200000
1000
2000
3000
4000
5000
6000
7000
8000
9000
Offset (feet)
Tru
e V
ert
Dep
th (
feet
)
Deviation Profile ( Whd @ 20.00 feet )
Deviation Profile
6February 5, 2002
From previous nodal analysis...
The target rate may be reached via conventional gas lift for a flow area equivalent to 8 5/8” tubing.
This would require gas lift rates of approximately 20 MMscfd.
BUT…..
7February 5, 2002
• Strategic importance of this well for project development
• Static nodal program cannot predict whether the well could be unloaded.
• Transient program can predict unloading conditions, but uses flow correlations that are not valid for large tubing sizes (greater than 5.5”)
• Existing transient flow program is not capable of reverse flow completions analysis.
• At the high injection pressures required, is the gas actually in a gaseous state at the orifice?
We have the following concerns:
8February 5, 2002
OLGA 2000
“OLGA 2000 is the market-leading simulator for transient multiphase flow of oil, water and gas in well and pipelines with process equipment. “
→ Over 10,000 experiments were run in eight years on the SINTEF Two-Phase Flow Laboratory near Trondheim, Norway
→ The tests were run in both steady state and transient modes
→ The resultant data / correlations reside within OLGA 2000
→ ChevronTexaco has been using this program for many years to assess flow assurance issues in pipelines and risers. It has not been used for downhole analysis applications
→ Limited to single point gas lift configurations
9February 5, 2002
The Plan
• Evaluate various completion options for high rate water wells using three different flow analysis software packages:
– Well Evaluation Manager (WEM) using OLGAs
– Dynalift
– OLGA2000
• Evaluate Dynalift when used for large tubing completions
• Develop & validate the well unloading sequence
• Confirm importance of surface controlled downhole choke
10February 5, 2002
Scope of Study
The following scenarios were evaluated:
• Case WA1: Lift gas injection down 11¾” casing with 8⅝” tubing.
• Case WA2: Lift gas injection down 11¾” casing with IPC 7” tubing
• Case WA3: Lift gas injection down 11¾” casing with IPC 8⅝” tubing
• Case WB1: Lift gas injection down 3½” tubing with 9⅝” casing
• Case WB2: Lift gas injection down 2⅞” tubing, with 9⅝” casing
11February 5, 2002
Results
12February 5, 2002
Case WA1 - Steady State
Water Well (Case WA1: 8 5/8 tubing, gas injection down annulus)
0
5000
10000
15000
20000
25000
30000
35000
40000
45000
0 5000 10000 15000 20000 25000 30000
Injected Gas Rate (mscfd)
To
tal
Wa
ter
Pro
du
ce
d (
bw
pd
)
WEM (OLGAs) Dynalift (transient with Beggs Brill) Scandpower (OLGA2000)
13February 5, 2002
Case WA1 - Steady State
WA1: Comparison of Operating Pressures
0
500
1000
1500
2000
2500
3000
3500
0 5000 10000 15000 20000 25000 30000
Injected Gas Rate (mscfd)
Inje
ctio
n P
ress
ure
at
Wel
lhea
d (
psi
a) /
Dif
fere
nti
al P
ress
ure
ac
ross
Ori
fice
(p
si)
0
250
500
750
1000
1250
1500
1750
OLGA2000 Dynalift dP (OLGA2000) WEM (OLGAs) dP (WEM) dP (Dynalift)
14February 5, 2002
Case WA1
Notes:
• Separation between WEM & OLGA2000 not fully explained; (possibility - OLGA2000 starting with transient flow first)
• Dynalift example uses 0.5” orifice - significant at higher flow rates (problems with 1”)
• OLGA2000 & WEM assume a fixed pressure differential not a fixed choke
15February 5, 2002
Note the 180,000 bwpd slug OLGA predicted during the unloading cycle.
BBT Water Voidage Well - GLG Down Annulus - Std. Tubing
ACCUMULATED LIQUID VOLUME FLOW TUB_OUT_Q [bbl]
PRESSURE ANN_IN [ps ia]
PRESSURE ANN_OUT [ps ia]
PRESSURE TUB_IN [ps ia]
GAS MASS FLOW ANN_OUT_Q [kg/s]
TOTAL LIQUID VOLUME FLOW TUB_OUT_Q [bbl/d]
CONTROLLER SIGNAL CTL_GLV [-]
bb
l
2000
1500
1000
500
0
ps
ia
4500
4000
3500
3000
2500
2000
1500
1000
500
0
kg
/s
7
6
5
4
3
2
1
0
bb
l/d
200000
150000
100000
50000
0
-
1
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
Time [h]Benguela-Belize - Gas-Lift down Annulus
161050
16February 5, 2002
Case WA1 - Unloading
BBT Water Voidage Well - GLG Down Annulus - Std. Tubing
TubGIunload20: PRESSURE NAT_IN [ps ia]
TubGIunload20r: PRESSURE NAT_IN [ps ia]
TubGIunload20: TOTAL LIQUID VOLUME FLOW TUB_OUT_Q [bbl/d]
TubGIunload20r: TOTAL LIQUID VOLUME FLOW TUB_OUT_Q [bbl/d]
ps
ia
4500
4000
3500
3000
2500
2000
bb
l/d
200000
150000
100000
50000
0
Time [h]
16151050
17February 5, 2002
Case WA2
Water Well (Case WA2: 7" plastic lined tbg, gas injection down annulus)
0
5000
10000
15000
20000
25000
30000
35000
40000
45000
0 5000 10000 15000 20000 25000 30000
Injected Gas Rate (mscfd)
To
tal
Wat
er P
rod
uce
d (
bw
pd
)
WEM (OLGAs) Scandpower (OLGA2000) Dynalift (transient with Beggs Brill)
18February 5, 2002
Case WA1 versus Case WA3
WA1 versus WA3 (conventional versus plastic lined 8 5/8" tubing.
0
5000
10000
15000
20000
25000
30000
35000
40000
45000
50000
0 5000 10000 15000 20000 25000 30000 35000
Injected Gas Rate (mscfd)
To
tal W
ate
r P
rod
uce
d (
bw
pd
)
WA1 WEM (OLGAs) WA1 Dynalift WA1 Scandpower (OLGA2000)
WA3 WEM (OLGAs) WA3 Dynalift WA# Scandpower (OLGA 2000)
19February 5, 2002
WA1 versus WA3: Comparison of Operating Pressures
0
500
1000
1500
2000
2500
3000
0 5000 10000 15000 20000 25000 30000
Injected Gas Rate (mscfd)
Inje
ctio
n P
ress
ure
at
Wel
lhea
d (
psi
a) /
Dif
fere
nti
al P
ress
ure
acr
oss
O
rifi
ce (
psi
)
WEM (OLGAs) dP (WEM) WA3 WEM (OLGAs) WA3 dP (WEM)
Effect of IPC
Roughness Difference
Case WA1: 0.0018
Case WA3: 0.00006
20February 5, 2002
Water Well (Case WB1: Reverse flow gas lift.. 9 5/8" csg with 3.5" tbg .... equivalent flow area of 8 5/8"))
0
5000
10000
15000
20000
25000
30000
35000
40000
45000
0 5000 10000 15000 20000 25000 30000
Injected Gas Rate (mscfd)
To
tal
Wa
ter
Pro
du
ced
(b
wp
d)
WEM (OLGAs) Scandpower (OLGA2000) Dynalift (equiv. Flow area using Beggs Brill)
Case WB1
OLGA2000 & WEM include pressure loss from casing connections in annulus; Dynalift uses equivalent area
21February 5, 2002
WHAT DID WE LEARN?
• Have a higher degree of confidence that this well could be unloaded.
• Question of conventional versus reverse gas lift must include drilling feasibility and operational safety concerns
• WEM OLGAs works well for assessing well performance but does not answer unloading questions
• For higher rate / pressure single point gas lift systems, surface controlled downhole gas lift valves are mandatory to reduce upsets while unloading the well
22February 5, 2002
QUESTIONS?
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