Evaluation of perforating techniques and the use of cesium formate kill pills to optimise productivity in HPHT gas wells

1. An Evaluation of Perforating Techniques and
Use of Caesium Formate Kill Pills to Optimise
Productivity in HPHT Gas Wells
IQPC HPHT Summit
Ardoe House
20th November 2007
Alistair Roy (BP)

2. Presentation Outline
• Rhum Field Overview & Reservoir Parameters
• Appraisal Well 3/29A-4 DST Parameters
• Proposed Perforation Design for Development Wells
• Dynamic Underbalance Perforation
• Caesium Formate Kill Pill Design
• 3/29A-4 Perforation Operations & Well Clean-Up
• Comparison of Overbalance vs Underbalance Productivity
in 3/29a-4 well (in same well and interval)
• 3/29A-5 -On Balance E-line Perforation
– Gas Suppression during operations
– Well Clean-Up and Productivity
• Summary & Overall Comparison

3. Rhum Field Overview &
Reservoir Parameters

4. Rhum Field Partners
Partners
50% owned by BP
50% owned by The National Iranian Oil Company (NIOC)
This presentation relates to the Rhum Field, 50% of which is owned by an entity of
the Government of Iran, and therefore US sanctions (specifically the Iranian
Transaction Regulations) apply. If you fall into any of the categories of persons noted
below, you may use this presentation for your own purposes, but please do not
contact any member of the Rhum Field project team or attempt to provide any
assistance to the Rhum Field project. This restriction applies to: US citizens and US
Green Card holders, any person physically present in the US regardless of
nationality, and any company or entity incorporated or established in the US and
such entities' foreign branches.
Employees, regardless of their own nationality, of any such US company or entity
located anywhere in the world are also deemed to be included in the definition of "US
Persons" under the Iranian Transaction Regulations as their actions would be
attributed to the US company that employs them. This includes, by way of example,
BP's offices in locations such as Trinidad, Egypt and Sharjah which are branch
offices of Delaware corporations.

5. Rhum Field Overview
Environmental Conditions
Water Depth : 108m
Field Concept: 3 Subsea Wells with 40km Tieback
Reservoir Type High UCS Sandstone
Reservoir Depth 4745m TVDss (Datum)

6. Reservoir Conditions
• H2S : 10ppm
• CO2 : 4.5%
• Permeability : Range 0.01 – 530md (ave. 45)
• Porosity : Range 6-12% (ave. 9%)
• Gross Interval :130 – 150m
• Dry Gas :CGR of 4-6bbl/mmscf
• Flowing Conditions : 136 deg C @
150MMscf/day
• Downhole conditions: 150 deg C &12418psi
@ 4745m TVDss
• Downhole conditions: 155 deg C &13600psi
(Transition zone)

7. Appraisal Well DST Parameters &
Perforation design for
Development Wells

8. 3/29a-4 Appraisal Well Perforation
UCS (psi) TWC (psi)
Shale 12,985 - 30,685 8,640
Cemented Sandstone 32,520 – 34,425 20,000+
Stained Sandstone 8,145 – 16,040 16,000 -17,580
• Rock Strength V. high
– Absolutely No sanding predicted
• Perforating in UCS of 25,000psi typically
reduces penetration by 75%
• Productivity
– Mechanical skin: 4.21
– Reservoir Pressure : 12350psi @ 4647.28m
MDbrt
– Non-Darcy Skin : 0.00041 per ‘000scf/day
– KH : 6,788 md.ft.
– Perforated Interval : 4,692 – 4,735m (43m)
– Permeability : 48.1md based on H of
141ft (Perforated Interval)
– Rate and Drawdown : 43MMSCFD on 575psi
drawdown
– THP : 7,960psi
– AOF Potential : 245MMSCFD
• Note – Difficult to match rate dependant skin without
major changes to either perforated interval or
perforation performance
• Perforation Parameters
– 3-3/8” JM HTX 21 gram
Charges
– 6 shots per foot
– 60 degree Phasing
– 1000psi Under-balance
Rhum 3/29a-4
10-3
10-2
10-1
100
101
10
-5
10
-4
10
-3
Delta-T (hr)
DP
+
DERIVATIVE
(MPSI2/CP/MSCF/D)
PD=1/2
2001/01/30-1200 : GAS (PSEUDO-PRESSURE)

9. Development Well Perforation Design
Mechanical
Skin
1 4.21
(Actual)
12
Production
Potential
175
MMscfd
171
MMscfd
165
MMscfd
Non Darcy
Skin
0.00041 /
MMscfd
0.00011 /
MMscfd
Production
Potential
171 MMscfd 243 MMscfd
• Deployment Techniques
– TCP on completion
• HT Explosives reduce penetration,
• Sump not desirable due to slow drilling, presence
of HP water zone
– CT Conveyed thru completion
• Significant Rig mods required for deployment of
coil (erection of temporary platform)
• Insufficient riser for single run deployment
• Coil cycling at high WHP
– Wireline Conveyed Perforating
• Up to 15 runs required with 3-3/8” guns
• Only 1st run is underbalance
– Stackable Gun systems
• 15 runs to deploy / retrieve
• Drilling Sump not desirable
• Reservoir access required
– Shoot & Pull & Isolate
• V0 barrier required for running upper completion
• HMX charges on TCP
• Larger Guns deployable on DP
• Single Trip
• Maintain hydrostatic
Kh Product 6788md.ft
(Actual)
5973md.ft
Production
Potential
171 MMscfd 164 MMscfd
• Perforation Requirements
– Maximum Interval 150m
– Desire to minimise Rate dependant
skin (Penetration, hole size)
– Mechanical skin Not crucial
– Reservoir Access Required
– Minimise gas to rig

10. Development Well Perforation Design
• Selected Perforation technique
– Inability to satisfactorily model non-darcy
effects indicated go with largest guns
available.
– Increasing penetration and EH diameter seen
as best way of reducing the rate dependent
skin component (this was demonstrated by
vendors modeling even if absolute match
wasn’t)
– 4.72” guns drove choice of 7” 41# liner (also
seen as mitigation against compaction) but
lose mono-bore concept
– The Dynamic Under-balance solution
deployed on drillpipe was selected on the
following basis;
• Perforating the well in drilling mode was seen as
the simplest and most cost effective solution
• Modelling indicated same productivity achieved
as underbalance perforating
• Flow restrictors placed at top of liner
– Appropriate Perforation fluid to be selected
5-1/2” DP to surface
7” Liner Top
9-5/8” Casing Shoe
Flow Restrictors
3.5” Drillpipe to space-
out
4.72" PerfoXtreme
Guns - PJ4505 HMX - 5
SPF -72deg Phasing

11. Theoretical PURE Response
• PURE Response for 4.72” Guns
and 600psi Static O/B
– Graph shows first 100ms of
predicted pressure response
– The predicted underbalance
duration is not currently
calculated by the Schlumberger
software and is dependant on
the well conditions,
– The Rhum configuration (120m
of 4.72” guns with flow
restrictors at the liner top was
estimated to be 2-3seconds.
– BHP goes from 13,100psi to
between 3-5,000psi across the
perforations.
– No high resolution gauges run
to confirm pressure response

12. Caesium Formate Kill Pill Design

13. Well Control strategy – fluid barrier
• Needed a minimum of one mechanical and one fluid barrier
• Required density of fluid barrier: SG 1.9-2.2
• Only two clear fluid options at this density range : caesium formate brine
or zinc bromide brine
• HSE risks of zinc bromide were unacceptable
• Question : Could caesium formate brine be used both for maintaining
well control while running the completion and as a perforating kill fluid ?

14. Perforating kill pill – requirements
• Stable and predictable properties for at least 72 hours under HPHT
conditions (BHST : 149oC)
• Minimise loss of overbalanced fluids to the formation
• Allows hydrocarbons to flow back freely under low drawdown pressure
• Basically it must cause tractable and superficial formation damage
(purely by physical pore blocking) that is removable by low pressure
backflow or washing with dilute organic acid
• It is essential that the brine phase (filtrate) itself is not damaging in way

15. Formation damage test with brine phase only
• SG 1.85 caesium formate brine
previously tested on Marnock
core gave 100% return
permeability
• Tests at reservoir conditions on
Rhum core with SG 1.87
caesium formate brine gave
84% return permeability to gas
• Brine phase (filtrate) causes
little damage
Reservoir core Rhum
Temperature 149oC
Initial gas
permeability
148 mD
Brine volume
injected
10 PV
Pressure to
initiate gas flow
5 psi
Return gas
permeability
125 mD
Permeability
loss
16%

16. Kill pill formulation
• Based on standard formate
drilling mud formulation for
HPHT wells– used since 1996
• High yield point : 65-80
• Median diameter of the sized
calcium carbonate : 9 micron
• Not hot-rolled before testing
• Designed to provide fluid loss
control for at least 72 hours at
149oC
Caesium
formate brine
SG 1.94
Xanthan 1 ppb
Modified starch
FL7plus
6 ppb
ULV PAC 6 ppb
Potassium
carbonate
5 ppb
Calcium
carbonate solids
30 ppb

17. Fluid testing on BP’s Mud Cake Clean-up
(MCC) Rig
Determine Initial Permeability
to Kerosene or gas
Generate Filter Cake By Placing Mud
at Overbalance Under Both Dynamic and
Static Conditions
Produce Core with Mud Cake to Kerosene or gas
Determine Extra Pressure to Initiate Production
and Residual Damage
Used in static mode at 1,350 psi confining pressure with humidified nitrogen gas

18. Formation damage test on MCC with kill pill
• Core face exposed to kill pill
fluid under static conditions for
72 hours @ 500 psi
overbalance
• Return permeability measured
at room temperature with
humidified nitrogen gas
• 38% reduction in return
permeability was considered
acceptable for a kill pill
Core material Berea
sandstone
Temperature 149oC
Initial gas
permeability
84 mD
Fluid loss 6.6 g
Pressure to
initiate gas flow
18 psi
Return gas
permeability
52 mD
Permeability
loss
38%

19. 3/29a-4 Perforation Operation and
Productivity

20. 3/29a-4 Productivity
• Welltest data matched with IPR curve from DST analysis
– Indicates Dynamic Underbalance has at least matched Underbalance Well
Performance (close analysis suggests the higher rate data lies above the
original IPR)
– Slope on the IPR is due to the non-darcy skin which has essentially
remained the same
• No downhole gauge
ran in 3/39a-4 well
• Surface Parameters
only available for
analysis
• BHPs calculated using
same Tubing
correlation used on
3/29a-5 and DST
(which did have
gauges)

21. 3/29a-4 well Clean-Up
• Clean-up data shows that low lift off pressures observed in lab were not uniformly achieved across the
reservoir interval.
• Well came on production relatively smoothly but there is a 1,000psi increase in WHP while remaining on
the fixed choke setting. The assumption is that this is a high permeability zone at the base of the well
coming on-line.
• Operational problems meant the kill pill was on bottom for several weeks longer than the laboratory
testing period;
– high permeability zone was more susceptible to solids ingress and perfs were plugged during the initial perforation
program
– Significant Sag occurred (not predicted from the laboratory testing) blocking production from the higher perms at the
base of the well. It should be noted that there was only 1.4m of sump in this well.
– The mud properties degraded over the extended period downhole
Rhum 3/29a-4 Welltest Data
7500
7700
7900
8100
8300
8500
8700
8900
9100
4/12/2006
11:45
4/12/2006
16:33
4/12/2006
21:21
4/13/2006
2:09
4/13/2006
6:57
4/13/2006
11:45
WHP
(Psia)
0
10
20
30
40
50
60
70
80
90
Choke
(/64")
WHT
(degC)
GasQ
(MMscfd)
Q
WHP [psiA]
CHOKE [/64"]
WHT [degC]
GASQ [MMscf/d]
High Perm Zone
Cleans-up
• Laboratory testing
indicated Caesium
Formate slow to
clean-up once gas
flow was initiated
• Wells observed to
clean-up efficiently but
gradual improvement
seen over weeks

22. E-line Perforation

23. Perforation of 3/29a-5
• Operational issues with middle completion
assembly led to TCP operation being ruled
out for 3/29a-5
– Required to perforate in alternate fashion
– Well logged, liner installed and well
suspended
• 106m Gross 88.4m Net Perforation Interval
– Much improved reservoir quality found
(25,000md.ft versus 7,000md.ft in Appraisal
well
• Deep Sea Bergen Coil Rig Up 7 – 10 days
– Erection of fixed platform online due to
requirement for hot work
• 10 E-line perforation runs planned instead
• Productivity target okay with skin of 80+ (0.4MMscf/d at 150MMscf/d= 60)
– Friction drop in 5-1/2” Tubing is main production constraint above 100MMscf/day
– Decide to shoot all runs over-balance,
– Non damaging Caesium Formate in Liner
– Poor perforation clean-up a risk, Accept potential for formation damage

24. Gas Suppression during Multiple
E-line Perforation Runs (1)
• All runs planned to be shot over-balance,
– With open perfs require to pump while shooting
– Calculated required over-balance 200 – 350psi to give sufficient fluid compressibility to
fill void from firing guns and newly created perforation tunnels
• First 3 runs brought no gas back to surface
– Gauge data from DHPG showed stayed over-balance throughout operation
• Gun run 4 only generated 100psi over-balance
– Clearly go under-balance on perforation
– Riser full of gas at surface (17bbls at 6,000psi)
• Subsequent gun runs shot over-balance with no gas to surface
Perforation Run 2
10900
11000
11100
11200
11300
26/08/2005 17:02:24 26/08/2005 17:16:48 26/08/2005 17:31:12
Pressure
(Psi)
128.12
128.16
128.2
128.24
128.28
Temperature
(DegC)
Pressure Psia
Temperature
degC
Perforation Gun fired
250psi Overbalance
Perforation Run 4B
11500
11550
11600
11650
11700
11750
8/28/2005
11:26
8/28/2005
11:26
8/28/2005
11:26
8/28/2005
11:26
8/28/2005
11:26
8/28/2005
11:26
Pressure
(Psi)
127.98
128.01
128.04
128.07
BHT
(DegC)
Pressure Psia
Temperature degC
120psi Overbalance
Perforation gun fired (Well
Goes underbalance)

25. Gas Suppression during Multiple
E-line Perforation Runs (2)
• Gas Suppression worked well
– Pump out of hole with
glycol/water or methanol
ensuring cable volume
replaced
– 200psi above equalisation
pressure when opening
Valves
– Perforate while pumping to
ensure over-balance
– Riser filled with base oil for
each run to give a cushion to
absorb any gas which either
percolated to surface or was
brought to surface in the
guns.
Rhum 3/29a-5 (NF-1) Perforating Program - Pressure Data
4000
6000
8000
10000
12000
25/08/2005 00:00 27/08/2005 00:00 29/08/2005 00:00 31/08/2005 00:00 02/09/2005 00:00
DHPG
(Psia)
&
THP
(Psia)
DHPG Psia
WHP Psia
• WHP increased from 5100psi (run 1) to 9300psi (run 9)
– SIWHP 10,200psi with gas gradient to surface, clearly bulk of well displaced to gas
– Apart from run 4 no gas seen at surface
• Significantly reduced operational time
– No flushing of surface lines required

26. Perforation Sequence
• Perforation runs 1, 6, 7 and 9 (depth order) shot first to ensure delivery of initial rate
requirement of 150MMscf/day
• Optimised perforation sequence proved to be of significant value
– During operations the SCSSV control line was leaking (at BOP), Runs 9 and 10 abandoned.
– Shooting in depth order would have seen a reduction in predicted KH of 645md.ft and left the
UMR1 and UMR2 flow units un-perforated
– Shooting in value order the 2 unperforated LMR intervals were predicted to be drained by the
perforations already added on run number 6.
Rhum 3/29a-5 Perforation Selection
0
20
40
60
80
100
120
140
01 (1) 02 (6) 03 (7) 04 (9) 05 (10) 06 (3) 07 (8) 08 (2) 09 (4) 10 (5)
Run number
mmscf/d
or
Bcf
PSEUDO
Reserves
• Maximum Gun Length 9.6m
• 10 Gun runs were planned to
perforate 92.3% interval
– blank intervals between runs
to omit shales or weak sands.
• Significant possibility of not
fully completing required 10
electric gun on an HPHT well
from a semi-submersible
• Order of the gun runs altered
from a bottom up approach to
value order

27. 3/29a-5 Production Data
• Smooth Clean-up without any evidence of the large increases in THP
observed on 3/29a-4(no solids in liner?)
Rhum 3/29a-5 Flowing Parameters
8500
9000
9500
10000
10500
11000
11500
12000
12500
9/3/2005
4:48
9/3/2005
9:36
9/3/2005
14:24
9/3/2005
19:12
9/4/2005
0:00
9/4/2005
4:48
9/4/2005
9:36
9/4/2005
14:24
9/4/2005
19:12
9/5/2005
0:00
BHP
(Psia)
/
THP
(Psia)
0
50
100
150
200
250
BHP [psiA]
WHP [psiA]
BHT [degC]
WHT [degF]
GASQ [MMscf/d]
CHOKE [/64"]

28. 3/29a-5 Production Data
• Good Quality TA available from
clean-up to rig and 15months later
– Low mechanical skin achieved
– Low rate dependant skin observed
significantly higher KH (x2.5)
– Significantly improved KH with
increased rate / depletion
– KH from TA approx ½ that of core
– Significant clean-up observed over
initial weeks of production (THP
increasing gradually on fixed
choke setting)
– Doubling of rate also helps clean-
up effect
– Gauges 1750ft above reservoir,
need to remove frictional dP to get
accurate total skin
– Low mechanical skin achieved
04/09/05 15/01/07
KH (md.ft) 9,646 11,483
Total Skin (mechanical +
non-darcy + friction drop to
gauge)
+11.5 +10.8
Total Reservoir Skin
(mechanical + non-darcy)
+8 +3
Max Prod. Rate (MMscf/day) 73 150

29. Mis-runs with Swetech EFI
• First 2 e-line perforation runs resulted in
mis-runs
• Root cause identified as Swetech Firing
Initiator
• New Component to beat ITR embargo
• Not fully Qualified (known risk prior to
running)
– Component heated to 400degF
– Cooled to ambient temperature
– Initiated successfully
• Downhole the foil produced a “slow burn”
only and did not eject initiation pellet
• 4 successful runs with conventional firing
head (non-SAFE system)
• A further mis-run occurred with a parted
earth cable
• Further 4 successful runs completed after
implementing “tight wire” procedures

30. Conclusions

31. Conclusions
• In HPHT hard rock formations Dynamic Underbalance Perforating can achieve similar or
slightly improved productivity versus optimized underbalance perforating.
– Optimising the liner size & perforating on DP offers the opportunity to increase gun size and
penetration which is crucial for hard rock perforating
• Caesium Formate has been shown in laboratory testing to be a non-damaging fluid in the
Rhum HPHT gas field when deployed as either neat brine or as a viscosified kill pill.
– Field results confirm this with low mechanical skins being achieved.
• Dynamic Underbalance Perforating on DP can significantly reduce operational complexity
for completing large intervals when combined with robust isolation solutions to allow
displacement to under-balance fluids at the end of the Upper Completion Phase. This is
particularly true when comparing to CT and e-line operations from a semi-submersible.
• In subsea HPHT wells the combined use of Dynamic Underbalance Perforating & Caesium
Formate brine across the entire range of completion operations brings significant HSE
benefits by;
– Allowing the well to remain in an over-balance condition until the Tubing Hanger is landed
– Facilitating over-balance or dynamic underbalance perforating on DP in long reservoir intervals
– Eliminating the requirement to bring hydrocarbons to surface during perforating operations
• With careful planning multiple electric line perforations runs can be successfully shot in
HPHT wells without requiring underbalance conditions or working with gas to surface.
Keys to achieving this are the use of base oil to absorb gas and maintaining positive
hydrostatic on the formation throughout perforation operations
• The combination of non-damaging clear fluids and on-balance perforating can deliver wells
with low mechanical skins.