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## -5800 -5900 -5800 -5800

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## -5900CWR6G31931Shell Offshore Inc.WR7G31932Shell Offshore Inc.WR8G33958Shell Offshore Inc.WR50G31937Shell Offshore Inc.WR94G31942Marathon Oil CompanyRepsol E&P USA Inc.WR95G31943Shell Offshore Inc.WR96G25234Shell Offshore Inc.WR51G31938ConocoPhillips CompanyWR52G25232ConocoPhillips CompanyCD

13,000 ft Radius 1,000 ft Buffer

5,000 ft RadiusAnchor Chart CPrepared for:Anadarko Petroleum CorporationGeodetic InformationLocation MapINTERPRETATION: B. Monsalve, Z. ZhangGIS/CAD: B. DillardDATE: 3/4/2011REPORT NO: 4026-ANA-GOMFILE: 4064_Anchor_Chart_WR51_C_12.dwgSPHEROID:Clarke 1866INVERSE FLATTENING:1/294.978698SEMIMAJOR AXIS:6,378,206.40 ftSCALE FACTOR:0.9996PROJECTION:Transverse MercatorCENTRAL MERIDIAN::DATUM:NAD27LATITUDE OF ORIGIN:ZONE:UTM Zone 15 NorthFALSE EASTING:1,640,416.666667 ftLINEAR UNITS:Survey FeetFALSE NORTHING:0 ft 

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1: : : : : : : : : : : :: : : : : : : : : : : :111111111111111Amery TerraceEast BreaksGarden BanksGreen CanyonAtwater ValleyDestin DomeMississippi CanyonDe Soto CanyonLloyd RidgeHendersonFlorida PlainLundLund SouthWalker RidgeKeathley CanyonAlaminos CanyonSigsbee EscarpmentTexasLouisianaMississippiAlabamaFloridaBrownsvilleCorpus ChristiPort LavacaFreeportGalvestonHoustonThe WoodlandsPort ArthurLake CharlesLafayetteMorgan CityNew OrleansBiloxiPascagulaMobilePensacolaHouma0 25 50 100Nautical MilesWestCameronWestCameronWestWestCameronSouthWestDeltaGrandIsleEugeneIsland TR 3130

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TR 3520 TR 3100 TR 3070 TR 3040 TR 3010 TR 2980LN 31000LN 31100LN 31200LN 31300LN 31400LN 31500LN 31600LN 31700LN 31800LN 31900LN 32000LN 32100LN 32200



### E 2,100,000

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E 2,115,000 E 2,100,000

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E 2,115,000N 9,760,000N 9,765,000N 9,770,000N 9,760,000N 9,765,000N 9,770,000 

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TR 3520 TR 3100 TR 3070 TR 3040 TR 3010 TR 2980 TR 2950 TR 2920 TR 2890 TR 2860LN 31000LN 31100LN 31200LN 31300LN 31400LN 31500LN 31600LN 31700LN 31800LN 31900LN 32000LN 32100LN 32200LN 32300LN 32400N 9,775,000N 9,775,000



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

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1:12,000FeetWater Depth & Seafloor FeaturesShowing Potential Anchor TouchdownArea for Proposed WR51 Well C0 500 1000 2000 3000 4000 5000LN 32500LN 32600LN 32700LN 32500LN 32600LN 32700N 9,780,000N 9,780,000Southern WR7, Southern WR8,North-Central WR51, North-Central WR52Walker Ridge (WR)Gulf of MexicoInterpretive InformationBasemap InformationWR51CProposed Well Surface Location and DesignationLN 31555TR 33003D Seismic Survey Line, Trace, and Designation(LN=Line) (TR=Trace)Lease Block Boundary: Block Number, Lease Numberwith Operator and Primary Lease Holder shownWR511RWHV/LQHVKDYHDQD]LPXWKRI7UDFHVKDYHDQD]LPXWKRI'DWD6SDFLQJfor 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 Traceare shown2. Infrastructure information primarily from BOEMRE database, these data, andAOA database updated as of February 2011.Lowest Contour of Local DepressionFault with seafloor expression. Symbol showsdownthrown side and direction of fault dip -6000Water Depth Contours, 20 ft interval:Intermediate ContourWater Depth Contours:Index ContourFracture zone with valleys, ridges, andsteep slopesFaulted zones with grabensInterpreted fluid expusion structure, possiblehydrocarbon seep and deepwater benthiccommunitiesApproximate Maximum Anchor Radius - 13,000 ftApproximate Touchdown Point - 5,000 ft1,000 ft buffer beyond approximate maximum anchor radiusA 2,000 ft radius circle around well surface location isshown as required by Notice to Lessees 2009-G40Existing Well Location and Designation001LN 30900LN 30800LN 30700LN 30900LN 30800LN 30700 TR 2830 TR 2800 TR 2770

TR 2830 TR 2800 TR 2770



### E 2,090,000 E 2,090,000N 9,755,000N 9,755,000Grid North2500 Tanglewilde, Suite 120Houston, TX 77063(713) 532-2624WR51 Proposed Location D 1 AOA Geophysics Inc. Marine Geoscience Division 2500 Tanglewilde, Suite 120 Houston, TX 77063 713

- 532

- 2624

Letter Report No. 40 64

- ANA

- GOM

- WR 51 D 08 March 2011
Anadarko Petroleum Corporation 1201 Lake Robbins The Woodlands, Texas 77380

Attention: M r. Rick Kincaid

Site Clearance Letter Location D Block 51 , Walker Ridge Protraction Area

UTM Zone 15, NAD 1927 X = 2,103,17 9 ft Y = 9,767,04 1 ft Longitude: 91.579593 ° W Latitude: 26.909174 ° N Nearest I nline 31695 Nearest Crossline 3149 3
, 541 ft FE L 6,239 ft F N L

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 Protract ion Area. This letter report describes well site specific conditions but often refers to conditions and findings described in the main block

- wide shallow hazards report s for Walker Ridge blocks Southern WR7, Southern WR8, North

central WR51, and North

- cent ral 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 in line 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 Ge ophysics 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. FrequencyWR51 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 vertica l 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)

. Inl ines are spaced 41.01 04 ft (12.5 m) and crosslines are spaced 65.616 6 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 conte nt ( 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 ±1 6.8 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 WR 0 8#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, 83 7 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 b y 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

.
The re 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 locat ed in WR269 ( 26°41.07'
, 91°40.28' ) about 16.5 miles SW from proposed well WR51 D.

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 60WR51 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 mini

basin 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 nort h- 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 r equired for high

- density epi

- benthic coldwater coral communities, the only sites interpreted to have potential for high

- density biomass are the f our seep locations with potential for chemosynthetic activity ( Anchor Chart D ). These four sites, which are po ssible 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 at tached 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 sh ow cha otic feature s 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 trans port 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 T op of S alt

. Unit 3 composed of salt. The top of salt is at 733 ft BML. The slope at the top of s alt 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

.