DYNAMIC UNDERBALANCE PERFORATIONS
BRING HIGHER PRODUCTIVITIES THAN
CONVENTIONAL PERFORATIONS
A large scale comparative review from the Tunu Gas Field
(Indonesia)
Sebastien Perrier, Tomi Sugiarto, TOTAL E&P INDONESIE
European and West African Perforating Symposium 2012
•
What is the TUNU field (Indonesia, PSC Mahakam)?
Tubingless completions
WNW
ESE
mss
0
MFA
Very
Shallow
MFA
1000
MF0
MF1
Beta
2000
MF6
MF1.5
MF2
Fresh
Water
Sand
Tunu
Shallow
MFB
Multilayer
thin sandstone
Reservoirs
Gas + condensate
Intra-beta
3000
SU1
SU2
Deltaic channels
and mouth bars
SU3
4000
High Pressure
Belly
>=1.20sg
5000
Fluviatil channel
Distributary channel
Mouth bar
Gas
SU4
Tunu
Main
Zone
Perforations
are added
10-20% Porosity
by light intervention
1-500md Permeability
barges (electric lines)
• Annually: more than 2500 ms of perforations, 600 intervals
SU5
SU6
• Large activities and workload continue to increase as field become mature
• Sufficient data for developing comprehensive perforation analysis
EWAPS 2012
WHAT IS “DYNAMIC UNDERBALANCE” (DUB)?
Dynamic Underbalance (DUB) Technology
• Generate a large dynamic under balance from modest static under
balanced or over balanced pressure.
• DUB system needs set of charges and additional void space inside the gun
(blank section, implosive chamber).
• DUB system required liquid (water / oil / mud) around the gun when shot.
• Fast gauge is run in tandem with the gun to measure actual dynamic
underbalance (optional, record up to 100,000 samples/second)
Unload using coiled tubing and nitrogen
Fired
0.05 seconds
Result: pressure drop within perforation intervals by 1500 to 2500 psi during a
few milliseconds
Objective: optimized clean up of the perforation cavity
EWAPS 2012
DOES IT WORK?
Legend in this presentation:
Conventional perforations, without DUB
Perforations with Dynamic UnderBalance
Data from TUNU gas field (2005-2011), operated by TOTAL EP INDONESIE
Perforation results, by classes of gain
(mmscfd per job)
Productivity by meter of perforation
(mmscfd / m)
Perforation initial production rates 2005-2011
( one reservoir only per job)
50%
45%
40%
35%
30%
25%
20%
15%
10%
5%
0%
Conv.Perfos
%
Dynamic UB
Reservoir productivity
Virgin pressure reservoirs only
40%
35%
30%
25%
20%
15%
10%
5%
0%
Conv.Perfos (100 res.)
Dynamic UB (23 res.)
<1
No/Weak
flow
2-5
5-10
10-15
15-20
Perforation gains (mmscfd)
20+
1-3
3-5
5-8
8 - 10
> 10
Perforation Gain per Meter of Net Pay
(mmscfd/m)
EWAPS 2012
ARE WE SURE THERE IS NO BIAS?
There are always some classical bias
•
•
Choice/selection of best reservoirs for application of DUB? “Quality bias”?
~30 DUB perforations only: “luck” effect ?
Example of petrophysical
indicator : Porosity
Porosity
Dynamic Underbalance perforations
Full Sample Conventionnal Perfos
25%
20%
15%
It is a fact that reservoirs
perforated
with DUB in Tunu tend to
have better petrophysical
properties on average
10%
5%
0%
<9% 9-10%
1011%
1112%
1213%
1314%
1415%
1516%
1617%
17%+
Porosity classes
The question becomes:
“once we remove quality bias and adjust for the sample size,
will DUB still make a difference?”
EWAPS 2012
FIRST METHOD: A POLL (13 INNOCENT PAIRS OF EYES)!
Poll with 13 engineers/Geologists familiar with the Field:
• Random sets of 50 reservoirs , with all the data used by “Tunu field”
practitioners
• 15 random reservoirs perforated with DUB dissimulated in each set
1 question: “for each reservoir, which perfo. gain (in mmscfd) do you expect?”
Gain
<2
2-5
5-10
10-15
15-20
>20
Mark
1
2
3
4
5
6
(MMscfd)
Participants’ guess
(average)
Real result
Conv. perfos
2,0 / 6
2,1 / 6
Dynamic UB
2,4 / 6
2,8 / 6
EWAPS 2012
SECOND METHOD: USING EPIDEMIOLOGICAL METHODS
Epidemiological methods = classically used to test new drugs or health
issues
1.Which steps?
• Validation of data quality is essential
• Perforations without a clear outcome are not considered
 No perforation job with multi reservoirs
Reservoirs diagnosed with technical problems or water problems are excluded
Need to have reliable pressure data (cf infill wells)
– Degree of dependence between parameters
– Influence of porosity, res. pressure, etc…
– gun size, static underbalance, brand, etc…
(cf. SPE paper 158083 for extensive details)
Prob. of flow
• The statistical influence of each parameter on differences between results
using the same perforation technique must be understood before any
comparison
Increasing porosity
EWAPS 2012
SECOND METHOD: USING EPIDEMIOLOGICAL METHODS
Epidemiological methods = classically used to test new drugs or health
issues
• The challenge: Build “comparable samples”, free of size and quality bias
• More than 200 eligible conventional perforations
• 29 flowing DUB perforations
• Two possible approachs:
• Our original approach 
–
–
Our group of 29 DUB perfo is the reference sample
Let’s downscale the 200 conv. perforations into random draws of 29 representatives,
respecting same res. characteristics as DUB samples
To get an apple to apple comparison, let’ s try a comparison
between
“Basket filled with 29 apples” and “baskets with 29 apples ”!
EWAPS 2012
RANDOM GENERATION OF 150 COMBINATIONS OF 27-30 CONV.PERFOS, WITH
SAME RESERVOIR PROPERTIES AS DUB SAMPLE
Percentiles of sub-samples distribution
Porosity
Pressure (deq)
DUB
Only MDT data valid (less than 1 yr)
35%
90%
P90 to P100
P50 to P90
P10 to P50
P0 to P10
""
Dynamic UB
Full Sample Conv. Perfos
30%
25%
20%
15%
80%
70%
60%
50%
40%
30%
10%
20%
5%
10%
NA
0,9+
0.7-0.9
Mobility
Net Pay Thickness
60%
70%
50%
60%
40%
0.5-0.7
9-10% 10-11% 11-12% 12-13% 13-14% 14-15% 15-16% 16-18% 18%+
0.3-0.5
<9%
<0.3
0%
0%
50%
40%
30%
20%
30%
20%
10%
10%
0%
0%
Sub-samples randomly created, but “matching” DUB sample
distributions of porosity, pressure, mobility, and thickness
EWAPS 2012
RESULT: AN EXPLICIT INSIGHT IN THE PERFORATION RESULTS
Distribution of Results (in mmscfd/m) of the 150 randomly created sub-samples of
conventional perforations
3.4 MODE
3.0
P10
3.7
P90
Confidence interval at 90%
for DUB estimator:
3,7 – 4,3
Dynamic UB
Sample : 4mmscfd/m
At 90% confidence level:
Dynamic UB does bring better productivity results than conv. perfos
Explicit evaluation of benefit = +10 to +25% initial productivity
(3.7-4.3 vs 3.4)
EWAPS 2012
CONCLUSIONS
In Tunu gas sandstones, Dynamic UnderBalance makes a difference
+10 to +25% initial productivity per meter of perforation
after removing all possible statistical bias (reservoir quality & sample sizes)
10 additionnal jobs performed post-study reinforce the quantitative results
They still give 4.0mmscfd/d, with similar quality
Applicability?
–
–
In gas wells, DUB is limited to wells with a liquid column (provider)
Unlikely adapted for tighest reservoirs (operator’s observation)
• Why not having worked with evaluations of “skin” ?
– Too little data to be analysed (see paper)
– Skin data validity and quality are a major variable, with little control, as
associated to well testing procedures
• Independent analysis, and more in SPE158083
EWAPS 2012
Slide 12
Acknowledgements
Total E&P Indonesie
INPEX
BPMigas - MIGAS
Thank You / Questions
Paper # • Paper Title • Presenter Name
EWAPS 2012
DYNAMIC UNDERBALANCE SUCCESS
Reservoir Data
 Porosity: 12.95%
 Pore Pressure: 5211 psi
 Mobility: 31.6
 Interval 3620.5-3623.5m (3m reservoir P131)
Technique
 Design gun to get optimum dynamic underbalance
 Design 100psi static UB and estimate the reservoir pressure is enough to lift up the
fluid column
 Clean up the well right after perforation, CT ready to start up in case well unable to flow
 RIH fast gauge tandem with gun to measure the dynamic underbalance
Completion Data
 Casing Size: 3.5” (9.2ppf)
 Min restriction: 2.81”
 Brine in borehole (1.03 sg)
 BHP=5120 psi
Gun Type
 2.5” PJO 2506
 estimated DUB at bottom gauge: 1560 psi
 real DUB at bottom gauge was 1620 psi
Result
 Real DUB at bottom gauge: 1620psi (fast gauge data)
 Well flow 15.9 MMscfd without unloading job
EWAPS 2012