WR51 Proposed Location D 4 

Gas Hazards. No amplitude anomalies suggestive of gassy sediments are penetrated at the 

proposed well site. There is a negligible risk for gas hazards at the proposed well location D. The nearest 

interpreted gassy sediments are about 1,360 ft NE in Unit 2. 

Shallow-Water-Flow (SWF). A negligible risk for severe SWF is assessed. There is a possible 

contribution of salt movement to overpressure pore fluids. However, it is not a strong driver of 

overpressure in thin shallow sediments that overlie the salt. 

Suitability for Temporary Occupation for Drilling. Proposed WR51 Location D is suitable for 

temporary occupation for drilling provided that the conditions and constraints that have been identified are 

considered and planned for in the final well design.
WR51 Proposed Location D 5 

We appreciate the opportunity to work with you on this project and look forward to continuing as 

your geohazards and marine geoscience consultants. Please call us at 713-532-2624 if you have any 

questions or if we can offer further assistance.

Sincerely,

AOA GEOPHYSICS INC.

Brenda I. Monsalve

Geophysicist- Marine Geohazards Specialist

Dan McConnell, P.G.

Manager- Marine Geohazards

Attachments:

• Description of 3-D Seismic Data including Amplitude and Power Spectrum Figure and Wavelet 

Figure

• Figure Appendix C-51D-1: Tophole Prognosis Chart Location D, Block 51, Walker Ridge Area

• Figure Appendix C- 51D-2: 3-D Seismic Record, Line 31695, Location D, Block 51, Walker Ridge 

Area

• Figure Appendix C- 51D-3: 3-D Seismic Record, Crossline 3149, Location D, Block 51, Walker 

Ridge Area

• Water Depth & Seafloor Features Showing Potential Anchor Touchdown for Proposed Well D, 

Walker Ridge (WR) 51, and Vicinity, Gulf of Mexico, Anchor Chart D (1:12,000)
WR51 Proposed Location D Description of 3-D Seismic Data

Description of 3-D Seismic Data Sets:

The 3-D seismic surveys that have been provided to AOA Geophysics Inc., by Anadarko, are of good 

quality to interpret the shallow section. The 3-D seismic data volume called VTS Walker Ridge I

(wrph1_3d) are interpreted around the proposed well sites and are used for most of the surface and all 

of the subsurface interpretation. These data are thirty-two-bit format. The 3-D seismic data parameters 

for VTS Walker Ridge I are described in the table below:

3-D Seismic Data VTS Walker Ridge I (wrph1_3d)

Spacing, Increment, and 

Orientation 

Spacing Increment Orientation

Inlines 41.0143 ft (12.5 m) 5 EW

Traces 65.6161 ft (20 m) 1 NS

Frequency Content in Tophole 

Section

Spectral analysis shows significant (0.45 to 0.65 on a normalized scale of 0 to 1) 

50 Hz frequency content in the data at each of the proposed well locations. 

Reprocessed for Shallow 

Section?

Yes, spectral whitening 

Processed sample interval Acquired at 2 ms- Processed at 4 ms

Acquisition Parameters • Acquisition Contractor CGG Veritas

• Vessel Polar Princess/Polar Search

• Date Available 1998

• Source Airgun 

• Streamer length 7,200 meters

• Shotpoint Interval 37.5 meters 

• CMP Xline 40 m

• Record Length 12.5 seconds

• Nominal Fold 48

Processing Parameters • Reformat 

• Anti-alias filter (Minimum Phase, Out – 90 Hz) 

• Resample to 4 ms 

• Adjustment for differences in recording systems 

• Trace edits 

• Merge navigation with seismic 

• Spherical divergence correction (V2T) 

• Mute - First break suppression 

• Gap deconvolution based on waterbottom

- Operator Length: 240 ms

- Predictive Gap: 24 ms

- 15 trace average 

• Mutiple attenuation, Radon transform algorithm 

• DMO velocity analysis (2 km grid) 

• Bin offset regularization (Utilizing 2 km grid) 

• 3D dip moveout correction on common offsets, (V(Z)) 

• Bin fold normalization 

• Interpolation to 12.5 x 20 m bins on each common offset 

• One pass phase shift migration of each offset (V(Z)) 

• Migration velocity analysis (Moves Velocity Analysis) 0.5 km grid 

• 3D normal moveout correction (Moves Velocity Field) 

• Offset weighting - based on waterbottom 

• Mute - based on waterbottom 

• Common mid-point stack 12.5 x 20 m bins 

• Inverse migration of MOVES stack, (V(Z)) 

• One pass migration with velocity model generated from inversion of moves 

velocities (GLINVEL) 

• Datum correction to sea level +10 ms

Quality of Primary 3-D Data with 

respect to NTL Guidelines and 

Comments

• The 32 bit data were loaded as 16 bit format for interpretation and these 

data show good quality.

• The data show significant energy in the 50 Hz range.
WR51 Proposed Location D Description of 3-D Seismic Data

• Assuming a shallow section velocity of ~5500 ft/sec at 50 Hz the limit of 

separability between reflectors is approximately 27.5 ft. 

• There are no indications of over migration artifacts in the shallow section.

• The seabed reflector is continuous at faults and is characterized by a 

wavelet of stable form.

• The data are good at imaging gas.

• Faults are well imaged in the data.
0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

0 10 20 30 40 50 60 70 80 90 100 110 120 130 140

A

m

p

l

i

t

u

d

e

Frequency (Hz)

Reprocessed Amplitude Spectrum Well WR51_D

WR51_D

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

0 10 20 30 40 50 60 70 80 90 100 110 120 130 140

P

o

w

e

r

Frequency (Hz)

Reprocessed Power Spectrum Well WR51_D

WR51_D

Report No. 4064-ANA-GOM WR52D Amp and Power Spectra
Wavelet Report No. 4064-ANA-GOM

-0.6 -0.4 -0.20

0.2

0.4

0.6

0.81

-0.05-0.04-0.03-0.02-0.010 0.01 0.02 0.03 0.04 0.05

Original: 33 ft

Reprocessed:27.5ft

0.024 sec

0.021 sec

Wavelet

NormalizedAmplitude

Time (sec)
Trace: 3100.0 3200.0

WR51_D WR51_C

1027 ft

2.400

2.500

2.600

2.700

2.800

WR51_A WR51_A Inferred Lithology

and Comments

W E

Event and

Unit

Designations

Depths

BML

(ft)

BSS

(ft)

TOPHOLE PROGNOSIS CHART

LOCATION D

BLOCK 51, WALKER RIDGE AREA

Thickness

(ft)

TWT 

BSS

(s)

thole51D.cdr

Hazardous

Shallow Gas

Risk

Shallow

Water Flow

Risk

TWT: Two-Way Travel Time

BML: Below Mudline

BSS: Below Sea Surface

3-D Seismic Record at

Proposed Location D

Walker Ridge Block 51

X = 2,103,179 FT, Y = 9,767,041 FT

LINE 31695 ~1000 ft

0 5837 2.401

280 6117 2.475

389 6226 2.504

733 6570 2.595

2264 8101 3.000

SEAFLOOR

1

280 NEGLIGIBLE NEGLIGIBLE

HOR. 1

2

109 NEGLIGIBLE NEGLIGIBLE

Topsalt

3

344 NEGLIGIBLE NEGLIGIBLE

salt

1531 NEGLIGIBLE NEGLIGIBLE

453

Seafloor slopes less than 1 degree to 

the east

Marine clays with mass transport 

deposits

Mostly clay-prone sediments with 

possible mass transport deposits

Most clay-prone deposits with possible 

sand

Reflectors show a chaotic feature in the 

unit due to the vertical and lateral salt 

movement. Faults may cross the wellbore 

in the unit, but do not have clear seismic 

expression. 

Report No. 4064-ANA-GOM-WR51D Figure Appendix C-51D-1

Slope at top of salt is 2.8o to the 

southwest

All depths and thicknesses are 

approximate and are based on 

drilling report of WR08#1 provided 

by Anadarko

WR 08#1 is located 6,448 ft NE from 

A possible salt stringer was found 140 ft 

above top of salt in WR08#1 well.

Possible inclusions and rafted sediments
31695.0

2700.0

31695.0

2800.0

31695.0

2900.0

31695.0

3000.0

31695.0

3100.0

31695.0

3200.0

31695.0

3300.0

31695.0

3400.0

31695.0

3500.0

Line:

Trace:

Offset: 10000 15000 20000 25000 30000 35000 40000

WR51_D WR51_C

2.400

2.500

2.600

2.700

2.800

2.900

3.000

Report No. 4064-ANA-GOM-WR51D Figure Appendix C-51D-2

3-D Seismic Record, Line 31695, Location D, Block 51, Walker Ridge Area

Two-Way Travel Time (s)

Unit 1

Unit 2

Seafloor

H1

Topsalt

5000 ft

WR51 WR52

W E

Salt

Possible 

gassy 

sediments

Pos

R

e

l

a

t

i

v

e

A

m

p

l

i

t

u

d

e

Neg
30800.0

3149.0

31300.0

3149.0

31800.0

3149.0

32300.0

3149.0

32800.0

3149.0

Line:

Trace:

Offset: 10000 15000 20000 25000 30000 35000 40000

WR51_D

2.300

2.400

2.500

2.600

2.700

2.800

2.900

Report No. 4064-ANA-GOM-WR51D Figure Appendix C-51D-3

3-D Seismic Record, Crossline 3149, Location D, Block 51, Walker Ridge Area

Unit 1

Unit 2

Seafloor

H1

Topsalt

Salt

WR51 WR07

S N

Pos

R

e

l

a

t

i

v

e

A

m

p

l

i

t

u

d

e

Neg