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
EWAPS 2012
0
1000
2000
3000
4000
5000
High Pressure Belly
>=1.20sg
Fluviatil channelDistributary channelMouth bar
Gas
SU1
Tunu
Mai
n
Zone
Tunu
Sha
llow
SU2
SU3
SU4
SU5
SU6
Fresh Water Sand
MFA
MFB
MF0
MF1
MF1.5MF2
Intra-beta
ESEWNW
Very Shallow
mssTubingless completions
Perforations are added
by light intervention barges (electric lines)
Multilayer thin sandstone Reservoirs
Gas + condensate
Deltaic channelsand mouth bars
10-20% Porosity1-500md Permeability
• What is the TUNU field (Indonesia, PSC Mahakam)?
• Annually: more than 2500 ms of perforations, 600 intervals
• 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) TechnologyDynamic 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
FiredFired
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 DUBPerforations with Dynamic UnderBalance
Data from TUNU gas field (2005-2011), operated by TOTAL EP INDONESIE
Perforation results, by classes of gain(mmscfd per job)
0%5%
10%15%20%25%30%35%40%45%50%
No/Weak flow
2-5 5-10 10-15 15-20 20+Perforation gains (mmscfd)
Perforation initial production rates 2005-2011( one reservoir only per job)
Conv.Perfos
Dynamic UB
Productivity by meter of perforation(mmscfd / m)
0%5%
10%15%20%25%30%35%40%
< 1 1 - 3 3 - 5 5 - 8 8 - 10 > 10
%
Perforation Gain per Meter of Net Pay(mmscfd/m)
Reservoir productivityVirgin pressure reservoirs only
Conv.Perfos (100 res.)Dynamic UB (23 res.)
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 ?
The question becomes: “once we remove quality bias and adjust for the sample size,
will DUB still make a difference?”
0%
5%
10%
15%
20%
25%
<9% 9-10% 10-11%
11-12%
12-13%
13-14%
14-15%
15-16%
16-17%
17%+
PorosityDynamic Underbalance perforationsFull Sample Conventionnal Perfos
It is a fact that reservoirs perforated with DUB in Tunu tend to have better petrophysical properties on average
Porosity classes
Example of petrophysical indicator : Porosity
EWAPS 2012
Participants’ guess(average)
Real result
Conv. perfos 2,0 / 6 2,1 / 6
Dynamic UB 2,4 / 6 2,8 / 6
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)
EWAPS 2012
SECOND METHOD: USING EPIDEMIOLOGICAL METHODSEpidemiological 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 reservoirsReservoirs diagnosed with technical problems or water problems are excludedNeed to have reliable pressure data (cf infill wells)
• The statistical influence of each parameter on differences between results using the same perforation technique must be understood before any comparison– Degree of dependence between parameters– Influence of porosity, res. pressure, etc…– gun size, static underbalance, brand, etc…
(cf. SPE paper 158083 for extensive details)
Increasing porosity
Pro
b. o
f flo
w
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
0%
5%
10%
15%
20%
25%
30%
35%
<9% 9-10% 10-11% 11-12% 12-13% 13-14% 14-15% 15-16% 16-18% 18%+
Porosity
P90 to P100P50 to P90P10 to P50P0 to P10""Dynamic UBFull Sample Conv. Perfos
0%
10%
20%
30%
40%
50%
60%
70%
Mobility
0%
10%
20%
30%
40%
50%
60%
Net Pay Thickness
0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
<0
.3
0.3
-0.5
0.5
-0.7
0.7
-0.9
0,9
+
NA
Pressure (deq)Only MDT data valid (less than 1 yr)DUB
Percentiles of sub-samples distribution
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
At 90% confidence level: Dynamic UB does bring better productivity results than conv. perfos
3.0P10
3.7P90
3.4 MODE
Dynamic UBSample : 4mmscfd/m
Confidence interval at 90%for DUB estimator:
3,7 – 4,3
Explicit evaluation of benefit = +10 to +25% initial productivity (3.7-4.3 vs 3.4)
EWAPS 2012
CONCLUSIONSIn 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 resultsThey 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
AcknowledgementsTotal E&P Indonesie
INPEX
BPMigas - MIGAS
Thank You / QuestionsPaper # • Paper Title • Presenter Name
Slide 12
EWAPS 2012
DYNAMIC UNDERBALANCE SUCCESS
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
Gun Type 2.5” PJO 2506 estimated DUB at bottom gauge: 1560 psi real DUB at bottom gauge was 1620 psi
Completion Data Casing Size: 3.5” (9.2ppf) Min restriction: 2.81” Brine in borehole (1.03 sg) BHP=5120 psi
Reservoir Data Porosity: 12.95% Pore Pressure: 5211 psi Mobility: 31.6 Interval 3620.5-3623.5m (3m reservoir P131)
Result Real DUB at bottom gauge: 1620psi (fast gauge data) Well flow 15.9 MMscfd without unloading job
