A Massive 3D VSP in Milne Point, Alaska
Claire Sullivan, Allan Ross, James Lemaux, Dennis Urban, Brian Hornby, Chris West, and John Garing,
BP Exploration Alaska
Bjorn Paulsson, Martin Karrenbach, and Paul Milligan, Paulsson Geophysical Services, Inc.
What we did:
Why we did it:
Acquired a 3 million trace 3D VSP with 4 wells, each instrumented with 80 3-component receivers recording simultaneously.
High resolution data set for field development.High resolution data set for field development.Determine variation in permafrost velocities.
Outline
• Introduction
• Planning the VSP
• Acquisition
• The Data
• Conclusions
TA
PS
ANWR
Prudhoe
Bay
Miles
0 5 10
Badami
SDI
West
Dock
Not to scale
Pt. Thomson
Prudhoe Bay
Pt. McIntyre
NiakukEndicott
Kuparuk
Milne PointNorthstar
B e a u f o r t S e a
Lisburne
PS1
Tarn
Sourdough
Milne Point Location 2
3
4
5
6
7
8
9
10
11
12
1
ARCTIC OCEAN BEAUFORT SEAPRUDHOE BAY
CAPE SIMPSON
CHUCKCHI SEA
Arctic National Wildlife Refuge
BARROW
CO
OK
INLE
T
PR. WILLIAM SOUND
National Petroleum Reserve Alaska
0 200
SCALE IN MILES
United S
tates
ALASKA
S-pad
Schrader Bluff S-pad Highlights
• 53 mmbo recoverable• Reservoir depth = 4000 ft.• Viscous Oil – API 14-24, biodegraded, low temperature
• Economic breakthrough with multi-lateral drilling design.
• Success depends on accurate placement of laterals in the reservoir and elimination of drilling sidetracks.
Multiple, stacked sands
Main reservoirs are O & N at Milne Point
Schrader Bluff Geology
Motivation for the 3D VSP
• Current seismic data was low fold (4-6).
• Thin sands (20-30 ft) with sub-seismic faulting.
• Need a high resolution data set to steer development drilling and avoid sidetracks.
MPH-08A SIDETRACK BORE HOLE PROFILE CROSS-SECTION
-4,200
-4,175
-4,150
-4,125
-4,100
-4,075
-4,050
-4,025
-4,000
-3,975
-3,950
-3,925
-3,900
-3,875
-3,850
6,500 6,750 7,000 7,250 7,500 7,750 8,000 8,250 8,500 8,750 9,000 9,250 9,500 9,750 10,000
ESE SSE
First hole
vertical exaggeration =10x
Second hole
'OA' Sands
Dep
th
Feet from surface location
Planning the Survey
P/GSI Illumination modeling.
Various scenarios were simulated:
•single well and combined deviated wells
•different shot spacing and coverage
•varied placement of geophone arrays in borehole
•designed trajectory of borehole
Complete 3D volume of hit counts computed.
Image coverage modeling
Contour interval = 200 hits
Modeled illumination at 4000 feet with 320 receivers placed in 4 wells.
One mile
1000-8000
10,000-30,000
30,000- 60,000
# of hits
Receiverlocations
Placement of geophone arrays4 geophone arrays
Each array has80 levels spaced50 ft apart.
Length of array is 4000 ft.
Total of 320 multi-componentgeophones
Receivers in deviatedwells are placed below permafrost.
Permafrost
1000
ft
2000 ft
Acquisition of the Survey
Source point interval 250 ft
8 second sweeps, 1 vib, 5 - 205 Hz, 6 sec listening, 0.1 - 0.2 sec tapers, 2 vib, 5 - 160 Hz, “ “
VP coverage and active receiver wells map
3232 VPs into 4 wells, 80 three-component geophone levels, 960 channels, 3 million traces.
4 walk-above lines at 50 ft source interval to aid in 3C geophone orientation.
1 mile
A Look at the Data
Raw records: near offset (500 - 670 ft)
MPS-09 MPS-15 MPS-31
Direct P wave
Direct S wave
Upgoing reflections
Tim
e
Receivers or Depth down the wellbore (ft)
0
500
1000
Raw records: far offsets (5000 - 6200 ft)
MPS-09 MPS-15 MPS-31
Direct S wave
Upgoing reflectionsDirect P wave
Tim
e
0
500
1000
Receivers or Depth down the wellbore (ft)
Direct wave spectral analysis Near offset – 376 ft 10-170Hz
bandpassF
requ
ency (H
z)
200
0
50
100
150
Wavenumber (cycles/ft)
+0.01-0.01 0
sig
nal
Raw axial data
Data rotated towards source.
Data rotated towards reflectors
Data after wavefield separation – upgoing P wave
Depth1787 3219Depth1787 3219Depth1787 3219Depth1787 3219T
ime
(us)
1000
500
100
Offset from well head (ft)365 3806
Source point is 2400 ftSW of lowest receiver
Common Source Gather
North – South example line through center of S-pad
-4350
-4150
-4050
Depth
-3950
¼ mile
1/4 mile1/4 mile
Reprocessed Surface Seismic
Preliminary VSP
Massive 3D VSP / W-E Profile
Reprocessed Surface Seismic
Preliminary 3D VSP
Hz
-dB
10 – 70 Hz
25 – 125 Hz
Hz
-dB
Well Planning Impact
S-Pad
MPS-13
OA
Original OA
•The MPS13 injection well was moved 400 ft to the SW avoiding a faulted zone.
Coherency plot of VSP data
Velocity issues
Correlation between sonic data, offset VSP’s and 1D migration velocity
Shallow permafrost velocity variationsDepth (ft)
Vel
ocity
(ft
/s)
First Break Tomography
• Direct arrivals from surface to deviated wellbores are used to determine local shallow velocity variations
surface
wellbore
Permafrost boundary
source
receivers
North – South example line through center of S-pad
-4350
-4150
-4050
Depth
-3950
¼ mile
Original 1D velocity model
2000
0
100014,000
11,000
8000
Velocity (ft/s)
6400
Dep
th (
ft)
W E
Permafrost boundary
11,000 – 15,000 ft/s 6000 – 9000 ft/s 7500 ft/s
What does the permafrost really look like?
0
2000
1000
Depth (ft)
Thaw bulb
3D velocity model from FB tomographyW E
14,000
11,000
8000
Velocity (ft/s)
6400
2000
0
1000
Dep
th (
ft)
Permafrost boundary
Conclusions
VSP data supported first phase of field development.
No sidetracks were required.
Production started Sept. 1, 2002 with 8000 bopd.
VSP data provides twice the frequency of surface seismic.
First break tomography identifies permafrost velocity variations.
Processing is ongoing and survey will be used for reservoir management and identification of deeper Kuparak targets.
Acknowledgements
Thanks to the S-pad development team, BP Exploration Alaska, for the opportunity to work on and present this project.
Thanks to Grunde Ronholt, READ Well Services, Sue Raikes, BP Sunbury, and Jonathon Woolley, a summer intern from the Colorado School of Mines.Trace Geophysical recorded the data.
Equipment used for this survey was funded under a DOE grant,# DE-FC26-01NT41234.
Back-up slides
Data processing sequence (1):
Determine 3C orientation
Pick first break times
Rotate towards source
Invert for zero offset 1D velocity model
Tomographic inversion for 3D model
Convert to zero phaseand band pass filter
Assign & check source-receiver geometry,pass only valid records on for processing.
Initial QC, 3C orientationand Velocity Model building
Raw VSP data
Survey data
Invert for source statics
Data processing sequence (2):Create source wavelet inversion filters
Rotate towards source
Convert to zero phaseand band pass filter
Align on first breaks & mix
wavelet inversion
200 ms window
Common SourceGathers (CSGs)
Source wave filters
Data processing sequence (3):3C upgoing wavefield separation
Rotate to true x,y,z
Rotate H1 towards source
Common SourceGathers (CSGs)
Sum: H1 - V
ConvolveSource wave filters
AGC
Convert to zero phaseand band pass filter
Gapped decon
Band pass
Radon filterUpgoing P-waves
Top mute FBs
Data processing sequence (4):Prestack Depth Migration & Stacking
Upgoing P-waves
PSDM
3D Velocity model
Trim Statics
Stack
3D reflectivity image in depth
Time shift
Source statics
Multi component summing:
V
H1+
+
1) Rotate H1 (azimuth only) towards source
2) Reverse V polarity
V
H1+
-
-
-
+
-
3) Sum: -V + H1
Results:Downgoing p-waves are attenuated with a dipole response in the Q1 quadrant.Downgoing s-waves are amplified with an isotropic response in the Q1 quadrant.Upgoing p-waves are amplified with an isotropic response in the Q2 quadrant.Upgoing s-waves are attenuated with a dipole response in the Q2 quadrant.
Q1
Q2Q3
Q4
sv
p
source
p
reflection
sv
source
Reprocessed Surface Seismic Preliminary VSP
N S
N-S line from MPS15 volume: preliminary 3D velocity model
2000 ft
North – South example line through center of S-pad
VSP20-125 Hz (-20dB)
Surface Seismic10-65 Hz (-20dB)
Frequency spectrum
11,000 ft/s
6500 ft/s
7500 ft/s
9500 ft/s
Velocity modelD
epth
(ft
)
Distance (ft)
-4300 -4000 -3700
Schrader Bluff Structure Map
The central well in the VSP program is located in a narrow graben. It is the only well in the area with log data.
The velocities are anomalous at this well.
Original 1D velocity model was based on zero offset VSP at this well.
1 mile