ula field miscible wag flood assessment - core & log experience from behind a maturing wag front...
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Ula Field Miscible WAG Flood Assessment
- Core & Log Experience from behind a Maturing WAG FrontSimon Thomas, Jon Duncan, Ula Subsurface Team, BP Norway
FORCE Mature Field Life Extension WorkshopRealising value from existing data, data acquisition planning and modelling
2nd October 2007
Ula Field Introduction
Discovered: 1976; First Oil: 1986
Water depth 67m
100m thick shallow marine reservoir
Moderately deep and hotDepth: 3350-3800mtvdss
Temperature: 150ºC
Volumes:In-place: ~1 billion barrels
Produced: ~ 420 million barrels
Late field-life initiatives:
Infill drilling Unit 1 horizontal wells
WAG Injection EOR
Living QDrilling
Production
ULA
Ula Field Reservoir
RetrogradationalShelf
ProgradationalShelf
ProgradationalShelf
Aggradational Shelf
ProgradationalShelf
Unit 1
Unit 2A1-2
Unit 2A3-6
Unit 2B
Unit 3A-B
DepositionalEnvironment
ReservoirLayering
UpperJurassicUla SstMember
(Farsund Fm)
Stratigraphy
Ula Sandstone Bioturbated fine-medium grained
sandstone withnodular calcite cement stringers
Depositional Setting:Storm dominated shallow marine
shelf
Ula Field Producing Wells
8 Crestal Oil Producers
3xUnit 2-3 WAG
5xUnit 1 horizontal
7 Flank Injectors
3xUnit2-3 water injectors
4xUnit 2-3 WAG injectors
Ula Field WAG Surveillence
Monthly well testing
Living QDrilling
Production
ULA
Wellhead P & T
Injection PLT’sGas & Water
Gas Injection TracersWater Injection Tracers
7/12-A-9A Logs & CorePilot well for planned horizontal injector
A15-A3A WAG Panel
87 88 89 90 91 92 93 94 95 96 97 98 99 00 01
0
4.00
8.00
12.0
16.0
20.0
24.0
28.0
32.0
36.0
(1)40.0
0
2.00
4.00
6.00
8.00
10.0
12.0
14.0
16.0
18.0
20.0(2)
0
5.00
10.0
15.0
20.0
25.0
30.0
35.0
40.0
45.0
(3)50.0
0
5000
10000
15000
20000
25000
30000
35000
40000
45000
50000(4)
(1)Oil Rate,MB/d (2)Gas Rate,MMCF/d (3)Water Rate,MB/d (4)OilCum_MB,MB VS Time
Name: 7/12-A-15 ID: A15:7/12-A-15 Type: OIL Format: ula_prod_group
A-3A WAG Inector
A-9A Observation Well
A-15 Oil Producer
2000A-15 WAG Oil ArrivalIncreased Oil rates & GOR (1-4kb/d)
500m
1500m
1994A-15 Water
Breakthrough
8kb/d
1998A-3A WAG
Start-up
1kb/d
1989/1990A15 & A3A
Start-up
20kb/d
28kb/d
Ula WAG Observation Well Objectives
Is current Ula Field WAG working?
Halted production decline & increasing GOR support pilot success
Where and how big is the ultimate WAG prize?
Recent SCAL data indicates high potential prize: Sorm 5% (Sorw 30%) & Sgt 35%
How efficient is the WAG process?
Which intervals of the reservoir are being contacted by the WAG injection?
Fundamentally: Sorw, Sorm, Sg, kh & kv
What do we do next?
How do we optimally design the future WAG injector/producer drilling program to access to remaining oil in Ula?
Data Acquisition Challenges
Core Data
3-phase fluid mobility system
Miscible gas injection process
Wireline Data
complicated logging environment
Sample InvasionCoring & Plugging
Sample LossesGas-expansion drive
Oil Propertiesdensity, formation factor
Water Propertiesdensity (salinity)
Deep Invasion3-phase mobility
Gas Presencegas injection
Mixed Watersformation & seawater
Reservoir Coolingwater injection
COST!!– Justified by the large size (>100mmbbl) but large uncertainty of the potential WAG prize
Ula A9A Wireline Logging Program
Baker Atlas Wireline Logging Contract
Gamma-ray, density, neutron, sonic & laterolog resistivity
57 Pressures & 7 fluid samples
Nuclear Magentic Resonance – Gas & Non-RT based saturation profiles
Openhole Pulsed Neutron – Gas saturation profiles
Carbon/Oxygen – Non RT based saturation profiles
Electrical resistivity images – Small-scale heterogeneities
Directional induction resistivity – fluid related anisotropy
Ula A9A Coring Program
Low invasion, high ROP coring system
Low invasion water-based (NaCOOH) mud with Deuterium tracer
Assumed that the dominant mobile fluid phase would be water
Slow, staged tripping to avoid gas driveAssumed that both free gas and high GOR oil would be present
Ula A9A Core Analysis & Program
Core plugged offshore under oil & brine and onshore under nitrogen
Multiple measurements including:Porosity, vertical, horizontal permeability & probe permeametry
Dean & Stark Water & oil saturations
Spun Water Resistivities - for calibrating Archie water saturation model
Gas Chromatography Analysis – for determining degree of WAG contact
Plug Sampling Program
30cm
Wrapped & waxed in laboratory
CT Scanned10 Samples selectedPlugged whilst frozen
1vertical & 1 horizontal
20cm
Dean-Stark SwD2O; Ø & k
Centifuged WaterD2O; Rw
Plugged under oilat well site
20cm
Dean & Stark SoØ & k
Centrifuged OilGas Chromatography
Plugged under brineat well site
15cm 15cm
Dean & Stark SwØ & k
Gas Chromatography
Plugged with N2gas in lab
Plugged with N2 gas in lab
Dean & Stark SwØ & k
Gas Chromatography
100m of core; 800plugs & >2000 petrophysical measurements
Reservoir Quality & Layering
Unit 1
Unit 2A
Unit 2B
Unit 3A
1
2
3
4
Reservoir Pressure
3 layer pressure system
2 key pressure barrier/bafflesUnit 1A shale barrier (1200psi)
Unit 2A6 baffle (40psi)
Producing from 1A & 2A with injection into Units 1A+2A+2B
Unit 1A Barrier
Unit 2A6 Baffle
Pressure
Depletion
1200psi
Calcite
Calcite
Calcite
Calcite
Calcite
Unit 1A Barrier
Oil & Water Saturation Profiles
Offshore & onshore samples
Oil, water & nitrogen cutting
Sw range between 40-60%
0-50% sample contamination
So range between 10-70%
1.36 FVF used to covert from stock-tank to reservoir conditions
Core So more robust than Sw
Mobile water may have been lost
Sw from from logs used to check
In-situ So
Gas or fluid loss?
No gas or fluid loss
Preserved Core SCAL Sample So after Bump-
flood
Minor Gas or fluid loss?
Log-based Water Saturation
Archie Model:
Rw profiles determined from: 100 spun-water samples from core
2 downhole fluid samples
wellhead produced water samples
historical water resistivity data
n-exponent determined from:20 oriented electrical plugs
We trust:Spun data with <15% contaminationMDT data with ~15% contaminationHigh permeability intervals have become contaminatedand comprise dominantly of mud filtrateResistivity values fall well below levels for A3A injected & A15 produced waterMDT and clean-up data are consistent and in agreement with production and injection values
3820.00
3840.00
3860.00
3880.00
3900.00
3920.00
0.000 0.050 0.100 0.150 0.200
Resistivity (@25C Ohmm)
Mea
sure
d D
epth
(m
)
Centrifuged Data (<15% Invasion)
Centrifuged Data (15-30% Invasion)
Centrifuged Data (>30% Invasion)
MDT Samples (~15% Invasion)
MDT Sample (>15% Invasion)
MDT Sample (60%+ Formate)
Rmf Core #1
Rmf Core #2
Rmf Core #3
Injection Water
A15 Produced Water
A9A
Clean-up W
ater
Rmf (Flowline)
ZeroInvasionBaseline
Adjust?
Adjust?
nm RtØ
RwaSw
.
.
0.0
1.0
2.0
3.0
4.0
5.0
6.0
7.0
8.0
9.0
10.0
0.0 10.0 20.0 30.0 40.0 50.0 60.0 70.0 80.0
1-Sw (%)
n e
xp
on
en
t
Native Horizontal
Native Vertical
Post Bump Horizontal
Post Bump Vertical
Gas Desaturation Horizontal
Gas Desaturation Vertical
At So >30% n exponents are typically ~2.3-2.6AT So<30% n expoents rise rapidly tow ards values ~4
Trend is similar for both vertical & horizontal plugs but exponenets are slightly higher w ithin vertical samples (see above)
Fluid Saturation Uncertainty Reduction
Gas
Gas
Gas
Log Sw reconciles well with core based CSo & CSw
Core-log comparison highlights:
Intervals of remaining gas
Intervals of lost core water
Core-log comparison does not illustrate WAG contact
An independent method was required to assess gas contact
Original Oil
Oil Composition Analysis
Compositional oil analysis key to understanding WAG performance
Toluene extracted oil samples
Gas chromatography analysis
C50/Cn ratio analysis
Identified compositional profiles
Reduction in lighter end components unambiguously identifies WAG contact
’Stripped’ Oil
Oil Composition Analysis Results
Raw GC Dataset prior to normalisation.Note the correspondence between the low remaining oil saturations combined with gas indications and the reduced low carbon components.
Normalised GC DatasetThe upper <1A3 & lower >3B intervals are compositionally unchangedThe 2A3-2A6 & 3A intervals appear to have minor compositional strippingThe 1B-2A2 & 2B1-2B3 intervals have undergone extreme stripping
CSw
CSo
1A1B
2A
2B
3A
3B
A-15OP
A-3AINJ
A-9AOBS
Reservoir LayeringPermeability Layering1987: Initial Oil Saturation1989: Water-flood1990: Water-flood1991: Water-flood1993: Water-flood1994: Water-flood1995: Water-flood1996: Water-flood1997: Water-flood1998: WAG Injection1999: WAG Injection2000: WAG Injection2001: WAG Injection2002: WAG Injection2003: WAG Injection2004: WAG Injection2005: WAG Injection2006: A-9A Observation Well
Sector Modelling
1A1B
2A
2B
3A
3B
A-15OP
A-3AINJ
A-9AOBS
Summary
Innovative integration of core & log data has been key to reducing saturation profile uncertainty
fluid property profiles (resistivity & composition) are key descriptors
Gas-flood has contacted only 40% of the reservoir within 2 layers
Sorm’s reach down to 10-20%, consistent with SCAL Sorm’s
Gas-flood by-passed intervals make up 60% of the reservoirWater-flood sweep has been variably effective
Target intervals for future WAG confirmed with Sorw’s of 30-75%
Acknowledgements
BP Exploration & Production Technical Group (Sunbury, UK)
ICCS (UK) & Reslab (Norway) Core Analysis Laboratories
Baker Hughes (Wireline & Coring Operations)
Andrew Spence (Independent Core Analysis Consultant)
Questions or Comments?