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-5900 C 

WR7 G31932 Shell Offshore Inc. WR8 G33958 Shell Offshore Inc. 

WR95 G31943 Shell Offshore Inc. WR96 G25234 Shell Offshore Inc. WR51 G31938 ConocoPhillips Company WR52 G25232 ConocoPhillips Company C D 

adius

5,000 ft Radius Anchor Chart C Prepared for: Anadarko Petroleum Corporation Geodetic Information Location Map INTERPRETATION: B. Monsalve, Z. Zhang GIS/CAD: B. Dillard DATE: 3/4/2011 REPORT NO: 4026-ANA-GOM FILE: 4064_Anchor_Chart_WR51_C_12.dwg SPHEROID: Clarke 1866 INVERSE FLATTENING: 1/294.978698 SEMIMAJOR AXIS: 6,378,206.40 ft SCALE FACTOR: 0.9996 PROJECTION: Transverse Mercator CENTRAL MERIDIAN: : DATUM: NAD27 LATITUDE OF ORIGIN:  ZONE: UTM Zone 15 North FALSE EASTING: 1,640,416.666667 ft LINEAR UNITS: Survey Feet FALSE NORTHING: 0 ft

1
 1 : : : : : : : : : : : : : : : : : : : : : : : : 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 Amery Terrace East Breaks Garden Banks Green Canyon Atwater Valley Destin Dome Mississippi Canyon De Soto Canyon Lloyd Ridge Henderson Florida Plain Lund Lund South Keathley Canyon Walker Ridge Alaminos Canyon Sigsbee Escarpment Texas Louisiana Mississippi AlabamaFlorida Brownsville Corpus Christi Port Lavaca Freeport Galveston Houston The Woodlands Port Arthur Lake Charles Lafayette Morgan City New Orleans Biloxi Pascagula Mobile Pensacola Houma 0 25 50 100 Nautical Miles West Cameron West Cameron West West Cameron South West Delta Grand Isle Eugene Island

TR 2980

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TR 3190

TR 3220

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TR 3520 

E 2,100,000

E 2,105,000

E 2,110,000

E 2,115,000

E 2,100,000

E 2,105,000

E 2,110,000

E 2,115,000 

N 9,760,000 N 9,765,000 N 9,770,000

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TR 3520 LN 31000 LN 31100 LN 31200 LN 31300 LN 31400 LN 31500 LN 31600 LN 31700 LN 31800 LN 31900 LN 32000 LN 32100 LN 32200 LN 32300 LN 32400 

N 9,775,000

E 2,095,000 E 2,095,000

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:
 1:12,000 Feet Water Depth & Seafloor Features Showing Potential Anchor Touchdown Area for Proposed WR51 Well C 0 500 1000 2000 3000 4000 5000 LN 32500 LN 32600 LN 32700 

N 9,780,000 Southern WR7, Southern WR8, North-Central WR51, North-Central WR52 Walker Ridge (WR) Gulf of Mexico Interpretive Information Basemap Information WR51C Proposed Well Surface Location and Designation LN 31555 TR 3300 3D Seismic Survey Line, Trace, and Designation (LN=Line) (TR=Trace) Lease Block Boundary: Block Number, Lease Number with Operator and Primary Lease Holder shown WR51 1RWHV/LQHVKDYHDQD]LPXWKRI7UDFHVKDYHDQD]LPXWKRI'DWD6SDFLQJ for 3D seismic survey: Line 65.62 ft, Trace 41.01 ft. Line numbering increment is 5, Trace numbering increment is 1. Locations of every 20th Line and every 30th Trace are shown 2. Infrastructure information primarily from BOEMRE database, these data, and AOA database updated as of February 2011. Lowest Contour of Local Depression Fault with seafloor expression. Symbol shows downthrown side and direction of fault dip -6000 Water Depth Contours, 20 ft interval: Intermediate Contour Water Depth Contours: Index Contour Fracture zone with valleys, ridges, and steep slopes Faulted zones with grabens Interpreted fluid expusion structure, possible hydrocarbon seep and deepwater benthic communities Approximate Maximum Anchor Radius - 13,000 ft Approximate Touchdown Point - 5,000 ft 1,000 ft buffer beyond approximate maximum anchor radius A 2,000 ft radius circle around well surface location is shown as required by Notice to Lessees 2009-G40 Existing Well Location and Designation 001 

LN 30900 LN 30800 LN 30700

N 9,755,000 Grid North 2500 Tanglewilde, Suite 120 Houston, TX 77063 (713) 532-2624
WR51 Proposed Location D 1 

AOA Geophysics Inc.

Marine Geoscience Division

2500 Tanglewilde, Suite 120

Houston, TX 77063

713-532-2624

Letter Report No. 4064-ANA-GOM-WR51D 

08 March 2011

Anadarko Petroleum Corporation

1201 Lake Robbins 

The Woodlands, Texas 77380

Attention: Mr. Rick Kincaid

Site Clearance Letter

Location D 

Block 51, Walker Ridge Protraction Area

 

UTM Zone 15, NAD 1927

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

Longitude: 91.579593° W Latitude: 26.909174° N

Nearest Inline 31695 Nearest Crossline 3149

3,541 ft FEL 6,239 ft FNL

Introduction. AOA Geophysics Inc. (AOA) was contracted by Anadarko Petroleum Corporation 

to prepare a site clearance letter for Location D in Block 51, Walker Ridge Protraction Area. This letter 

report describes well site specific conditions but often refers to conditions and findings described in the 

main block-wide shallow hazards reports for Walker Ridge blocks Southern WR7, Southern WR8, Northcentral WR51, and North-central WR52 in the Walker Ridge Protraction Area, Gulf of Mexico, report 

number 4026-ANA-GOM dated 28 March 2008, prepared for Anadarko Petroleum Corporation by AOA 

Geophysics Inc. The principal scope of this site clearance letter is to assess seafloor disturbance from 

drilling with respect to possible deepwater benthic communities and to identify and assess potential 

drilling hazards in the tophole section to a limit of about 1.5 seconds below mudline (BML) or top of salt, 

whichever is shallower. If the well is drilled from a moored drilling rig, the anchor zone must be assessed 

in addition to the well site. We have specifically assessed conditions between 5,000 ft and 13,000 ft of the 

wellbore, as the grounded anchor chains should fall between those distances, with an assessment within 

an additional buffer zone of 1,000 ft beyond the maximum potential anchor spread. 

This site clearance letter is based on the interpretation of reprocessed 3-D exploration seismic

data integrated with offset well data. Annotated data examples of the nearest inline and crossline from the 

3-D survey are attached. A 1:12,000 water depth and seafloor features map shows the proposed location 

relative to seafloor features (Anchor Chart D). The proposed location with a 2,000 ft radius circle and a 

1,000-foot buffer area beyond the approximate maximum anchor radius are shown as per Bureau of 

Ocean Energy Management, Regulation and Enforcement (BOEMRE) Notice to Lessee's (NTL) No. 

2009-G40. The attached chart conforms to the digital structure requirements for drawings as per NTL No. 

2008-G05. The proposed wellsite is not in an area that requires an archeological assessment (NTLs 

2008-G20, 2006-G07, and 2005-G07). 

Data Set and Offset Well Information. The 3-D data were reprocessed by AOA Geophysics Inc

to enhance resolution in the tophole section. The data show significant energy above 50 Hz with good 

signal to noise ratio and are consistent with the guidelines for the use of 3-D seismic data for shallow 

hazards analysis. The 3-D data are centered on WR51 and WR52 and cover twelve blocks. Frequency 
WR51 Proposed Location D 2 

and power spectra show significant content at 50 Hz and higher in the tophole section at the well site. At 

50 Hz and assuming the average velocity of the tophole sediments to be approximately 5,500 ft/sec, the 

limit of separability (λ/4) is about 27.5 ft. Data were provided at a 4 ms vertical sampling rate, were loaded 

to 4 seconds two-way traveltime (TWT), and interpreted to approximately 3 seconds TWT (0.5 seconds 

BML because of shallow salt). Inlines are spaced 41.0104 ft (12.5 m) and crosslines are spaced 65.6166 

ft (20 m) apart. Inline increment is 5 and crossline increment is 1. These data meet or exceed the current 

NTL requirements including the requirements for the frequency and power content (Figure Amplitude and 

Power Spectrum). Tophole logs and drilling reports from WR08#1 (5,819 to 7,736 ft) were reviewed in the 

assessment of geological conditions and constraints for this proposed location.

Depth Conversion. The water depth at the well site was calculated using the velocity function 

published by Advocate and Hood (1993). This function is based on velocimeter profiles from the northern 

Gulf of Mexico and is expected to be accurate to about ±16.8 ft (~0.3% of water depth) at this location. 

The water depth was further calibrated by additional wide azimuth seismic data that ties the location 

WR08#1 well (water depth 5819 ft BSS, which was within 4 ft of the uncalibrated water depth calculation). 

Subsurface depths at the well site are based on depths derived from well WR08#1 (API: 608124003400). 

The following function was used for subsurface depth conversions in this report.

D = 3780.2 (T)

where D is depth (ft BML) and T is two-way-travel time (seconds BML). 

Water Depth and Seafloor Slope. The water depth at proposed Location D is predicted to be 

5,837 ft below sea surface (BSS). The local slope (gradient) of seafloor at the proposed well site is less 

than 1o dipping to the east. 

Seafloor Features. In general, WR51 is located within an area of irregular seafloor controlled by 

the interaction and migration of shallow salt. Although there are possible localized low-angle surficial 

mass movement deposits to the east and northeast, especially in WR52, and there is a steep scarp to the 

west in WR50, in general the block WR51 has no obvious evidence of seafloor instability. Furthermore 

the immediate region around the proposed well location D has no evidence for seafloor instability within 

2,000 ft of the well site. The nearest seafloor fault is northeast-southwest trending, dipping southeast, and 

is about 140 ft east of the proposed wellsite. 

There is no evidence for high-density benthic communities in the vicinity of the well location D. 

Within 2,000 ft of the proposed location, there are no interpreted seeps that would support a high-density 

chemosynthetic community, and there are no interpreted seafloor hardgrounds or stable bathymetric 

highs that might support a slow-growing filter-feeding coldwater coral community. The nearest reported 

deepwater benthic community is located in WR269 (26°41.07', 91°40.28') about 16.5 miles SW from 

proposed well WR51D. 

Man-Made Obstructions. The nearest existing well location is WR8#1, more than 6,448 ft NE

from the proposed well site. No other man-made features or other potentially hazardous seafloor 

conditions are identified in the vicinity of the proposed well site. However, there may be uncharted 

obstructions present that are not detectable within the resolution of the reprocessed 3-D data set, so it is 

recommended that an ROV be used to inspect the seafloor at the proposed well site immediately before 

spud-in to confirm that there are no seafloor obstructions.

Assessment of Touchdown Area for Notional Anchor Pattern. The BOEMRE NTL 2009-G40 

mandates that proposed seafloor disturbances (including those caused by anchors, anchor chains, wire 

ropes, seafloor template installation, and pipeline construction) be more than 500 ft from areas that could 

support high-density deepwater benthic communities. If design requires seafloor disturbances between 

250 ft and 500 ft of potential deepwater benthic communities a state-of-the-art positioning system (e.g., 

differential global positioning system) on anchor-handling vessel(s) must be used, and the BOEMRE must 

receive plats that depict the “as-placed” location of all anchors, anchor chains, and wire ropes within 60 
WR51 Proposed Location D 3 

days after completion of operations to demonstrate that the features or areas were not physically 

impacted by the anchoring activities. 

The notional anchor touchdown area is between 5,000 and 13,000 ft from the proposed well site. 

An additional 1,000-foot buffer area beyond the approximate maximum anchor radius is between 13,000 

ft and 14,000 ft from the proposed well site. The areas contain ridges and scarps associated with salt 

tectonics.

There are numerous faults within the anchor touchdown area, predominantly to the northeast and 

south (see Anchor Chart D). The immediate vicinity of the fault scarps should be avoided if possible but 

otherwise the faults should not significantly constrain the anchor placement. In the vicinity of the faults, 

there may be locally variable soil properties and steep slopes. The steep slopes associated with minibasin formation and salt tectonics are located west and southwest of the well location at slightly greater 

than 14,000 ft. Some small channels and gullies are present in the touchdown area.

There are four sites, one in the notional touchdown area and three in the additional 1,000-foot 

buffer area, that are interpreted to have potential for seepage of hydrocarbons and/or brines (Anchor 

Chart D). These sites may host high-density chemosynthetic communities. None of the bathymetric highs

or steep margins, where nutrient-rich bottom water is necessary to support a high-density epi-benthic 

community of filter feeders, was interpreted to be stable over the length of time necessary to establish a 

slow-growing coldwater coral community (typically around 1 meter of growth per 100 years). The three 

regions likely to have the required exposure to nutrient-rich bottom waters that were examined most 

closely in the data were: the scalloped head scarp in the northeast of WR8, the steep scarp running 

north-south through WR6, WR50, WR94; and the irregular seafloor resulting from mass movement 

predominantly in WR52, WR96, and WR53. There were no obvious seafloor hardgrounds interpreted 

from the seafloor amplitude data that may form a suitable substrate for a high-density coldwater coral

community in the provided data and especially in these regions. Because the exposure to nutrient-rich 

bottom water, a hard substrate on which to anchor, and greater than centuries-scale stability in the 

geomorphology are all required for high-density epi-benthic coldwater coral communities, the only sites 

interpreted to have potential for high-density biomass are the four seep locations with potential for 

chemosynthetic activity (Anchor Chart D). These four sites, which are possible high-density deepwater 

benthic communities, should be avoided by more than 500 ft during anchor placement as per NTL

requirements.

Tophole Stratigraphy. The seafloor and two subsurface horizons, H1 and Top of Salt, were 

mapped. Depths below sea surface and below mudline to each of these intervals are included on the 

attached Tophole Prognosis Chart.

Unit 1 is about 280 ft thick and is composed of flat-lying and laterally continuous reflectors 

possibly representing recent mud-rich sediments. 

Unit 2 is about 453 ft thick. The reflectors show chaotic features in the unit due to the vertical and 

lateral movement of the salt. The unit is subdivided into an upper and lower section. The upper section is 

interpreted to be composed of mostly clay-prone sediment interbedded with thin mass transport 

complexes (109 ft thick). The lower section is interpreted to be composed of mostly clay-prone sediment 

with possible sands (344 ft thick). Salt stringers may be present near base of the unit. The base of this 

unit is the Top of Salt. 

Unit 3 composed of salt. The top of salt is at 733 ft BML. The slope at the top of salt is 2.8o to the 

southwest. Possible inclusions and rafted sediments in the uppermost salt.

Fault Penetrations. Although the area is faulted to the east and northeast of the wellsite, no 

obvious fault planes are interpreted to crosscut the wellbore path at proposed well location D. The closest 

prominent seafloor fault is located 140 ft to the east of the well location.