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