15070.0

13800.0

35000 40000

1.700

1.800

1.900

2.000

2.100

2.200

2.300

2.400

2.500

2.600

2.700

2.800

2.900

3.000

3.100

3.200

3.300

3.400

Line:

Trace:

WATER

FLOW AND

GAS

POTENTIAL

Shallow Water Flow and Gas Potential

HIGH

0 1 2 3

0 = NEGLIGIBLE

1 = LOW

2 = MODERATE

3 = HIGH

NEGLIGIBLE

Horizon Lithology/Stratigraphy

Illustration MC555-A-2. Tophole Prognosis Chart, Proposed Wellsite MC555-A, Mississippi Canyon, Block 555

Potential Drilling

Constraints

Project No. 0712-2117b Filename: 122117b_ill_MC555-A-2.cdr

Water 

Flow

Gas

3-D Seismic Section Through

Proposed Wellsite MC555-A

X = 1,109,157 FT; Y = 10,320,035 FT

 Inline 15070 at Crossline 13840 

NW SE

Horizon

TWT

(sec, bsl)

Depth

(ft, bml)

Depth

(ft, bsl)

INLINE 15070

TWO-WAY TIME TRAVEL (SEC)

SEAFLOOR

HORIZON 10

HORIZON 30

HORIZON 40

0.084

1.609

0.467

0.925

200

4,812

1,234

2,620

-4,651

-4,851

-9,463

-5,885

-7,270

Proposed 

Wellsite MC555-A

INTERFACE 2

 FAULT 0.821 -6,948 2,297

Distance (ft):

Horizontal

Negligible potential for encountering overpressured sands

and shallow gas.

Silt- to sand-prone turbidites. Mud-dominated rotated

slide blocks possible. 

Muddy- to sandy turbidites. Mass-transport deposits and

thick continuous sands possible. 

Moderate potential for encountering overpressured sands

and low potential for minor shallow gas.

Horizon

TWT

(sec, bml)

1.891

1.975

3.500

2.358

2.816

2.712

Sand-prone slope fan system. Mud-dominated rotated

slide blocks possible. 

Mass-transport deposits underlain by muddy- to sandy

turbidites. Sand-prone erosional remnants possible

within the MTD. 

 LIMIT OF

INVESTIGATION

HORIZON 20 2.149 0.258 -5,300 649

Mass-transport deposits (MTD) interlayered by siltyto silty-clay turbidites.

Moderate potential for encountering overpressured sands

and low potential for minor shallow gas.

Low potential for encountering overpressured sands

and minor shallow gas.

The Seafloor slopes less than 2° to the SE. There is no

potential for benthic communities within 2,000 ft of the

wellsite. The closest well lies 1.3 miles southeast of the

proposed location. No shallow water flow conditions

were reported at this location.

INTERFACE 1 2.519 0.628 -6,360 1,709

Mud-dominated turbidites. Sand pockets possible. Low potential for encountering overpressured sands

and minor shallow gas.

MC 554 MC 555

UNIT 1

UNIT 2

UNIT 3

UNIT 4

UNIT 5

Hemipelagic clay- to silt-rich sediments. 
Project No. 0712-2117b

Green circle repreradius and outer 

(A)

Expulsion 

features

Faults

Grid

North

Buried rafted 

blocks

MC 554 MC 555

BACKSCATTER

Buried slump

Buried 

slump

Buried rafted 

blocks

(C) Faults

SEAFLOOR REND

Grid

North

MC 554 MC 555

MC555-A 

Filen

Potential for Benthic Communities

radius and outer circle represents 11anchor radius.1,000 ft buffer beanchor radius

(A) 1,000 ft

Faults

MC555-A

Illustration MC555-A-3. 

(B)

Expulsion 

features

Faults

1,000 ft

Buried rafted 

blocks

Grid

North

SIDE-SCAN SONAR MOSAIC

MC 554 MC 555

Buried slump

MC555-A

High reflectivity on backscatter data irregular rocky topography on sonar dof carbonate hard grounds at expulsiomultibeam bathymetry (C), show sofeatures (mounds and depressions) radius. The presence of hard grounds growth and support of potential benthic The mound-like features associated wilack hard returns. This validates that hydrocarbon related.
10615 Shadow Wood Drive, Suite 200 

 Houston, Texas 77043

713.468.1410[o] 713.468.1438 [f] 

www.gemsinc.com 

February 20, 2013 Project No. 0712-2117b 

Apache Deepwater LLC 

2000 W. Sam Houston Parkway South 

Suite 1600 

Houston, TX 77042 

Attention: Mr. John Worthen 

Site Clearance Letter 

Proposed Wellsite MC554-A 

Block 554 (OCS-G-34444) 

Mississippi Canyon Area 

Gulf of Mexico 

Apache Deepwater LLC (Apache) contracted Geoscience Earth & Marine Services, Inc.®, (GEMS) to 

prepare a Site Clearance Letter for the proposed well location in Block 554 (OCS G-34444), Mississippi 

Canyon (MC) Area. This letter addresses specific seafloor and subsurface geologic conditions around 

the proposed location (2,000 ft radius) to the limit of investigation, 4,819 ft below the mudline (bml). 

Apache will drill the proposed MC554-A with a semi-submersible or dynamically positioned (DP) 

semi-submersible. The seabed conditions within an 11,500 ft mooring radius plus an additional 1,000 ft 

buffer zone are discussed to satisfy seabed disturbance guidelines. 

Surface conditions are clear at the proposed wellsite; however, moorings or other seabed disturbance 

activities need to avoid a potential shipwreck, possible unexploded ordnance sites, and potential sites for 

benthic communities. Sandy units with potential for shallow water flow occur at 714 ft bml (546 ft thick) 

and 1,456 ft bml (492 ft thick). 

This letter provides the following details specific to the well location: available data, attachments 

(accompanying the letter), Notice to Lessees (NTL) requirements, man-made features and archaeological 

assessment, wellsite conditions, anchoring considerations, and the conclusions and recommendations. 

Proposed Well Location and Available Data 

The proposed MC554-A surface location lies in the eastern portion of MC 554 (Figure MC554-A-1). 

Apache provided the following coordinates: 

Proposed Wellsite MC554-A 

Spheroid & Datum: Clarke 1866, NAD27 

Projection: UTM Zone 16 North Line Reference Block Calls 

MC 554 

X: 1,108,169 ft Latitude: 28o 25’ 35.9228” N Inline 15055 631 ft FEL 

Y: 10,319,561 ft Longitude: 88o 39’ 22.9797” W Crossline 13849 7,721 ft FSL 

The details provided in this letter are based on the findings from a geohazard assessment performed by 

GEMS (GEMS, 2012). The report which was submitted to Apache in December, 2012 described the 

geologic and archaeological conditions within the Guadalupe Prospect (in Blocks 554 and 555) and 

vicinity. Apache provided two sets of geophysical data for this assessment: a conventional, 

3-D exploration seismic volume and a high-resolution Autonomous Underwater Vehicle (AUV) data. 

The detailed data specifications are provided in the main report (GEMS, 2012). Well logs and drilling 

reports from the closest existing well (ExxonMobil #1 in MC 555) to the proposed location were also 
Proposed Wellsite MC554-A Clearance Letter 

Apache Deepwater LLC // February 20, 2013

Geoscience Earth & Marine Services, Inc. ® // 2 

FORUM ENERGY TECHNOLOGIES, INC. 

provided by Apache. Integrating these data allowed a thorough analysis of potential drilling hazards 

within the suprasalt stratigraphy at the proposed wellsite. 

Attachments 

The page-size maps and accompanying illustrations were extracted from the available data provided by 

Apache. A maximum anchor radius of 11,500 ft and an additional 1,000 ft buffer zone are included on the 

maps should Apache use a moored rig to drill. The figures embedded within the body text are also 

provided below. 

Map No. MC554-A-1: Bathymetry Map 

 Map No. MC554-A-2: Seafloor Features Map 

Map No. MC554-A-3: Side-Scan Sonar Mosaic 

Map No. MC554-A-4: Geologic Features Map 

Illustration MC554-A-1: Portions of Inline 15055 and Crossline 13849 Showing Conditions Beneath 

Proposed Wellsite MC554-A 

Illustration MC554-A-2: Tophole Prognosis Chart, Proposed Wellsite MC554-A, Mississippi Canyon, 

Block 554 

Illustration MC554-A-3: Potential for Benthic Communities 

Figure MC554-A-1: Regional Rendering of Mississippi Canyon Area, Gulf of Mexico 

Figure MC554-A-2: Power Spectrum Analysis Curve, Proposed Wellsite MC554-A 

Figure MC554-A-3: Seafloor Conditions at the Proposed Wellsite 

Figure MC554-A-4: Suprasalt Stratigraphy between the Proposed Wellsite and ExxonMobil #1 

Figure MC554-A-1. Regional Rendering of Mississippi Canyon Area, Gulf of Mexico 

MC554-A

MC555-A

MC555-B

Grid

North

MISSISSIPPI CANYON

AREA

3 miles

Survey Area

AUV Survey Area

High-potential 

Archaeological Area

Chemosynthetic Area

Shallow Water flow Area

Ordnance Disposal Area

Existing Platform

Existing Well 

Proposed Well Location

Existing Pipeline/

Umbilical

MENSA

Mass-wasting Pathway

Erosional Remnants
Proposed Wellsite MC554-A Clearance Letter 

Apache Deepwater LLC // February 20, 2013

Geoscience Earth & Marine Services, Inc. ® // 3 

FORUM ENERGY TECHNOLOGIES, INC. 

NTL Requirements

The following letter complies with the Bureau of Ocean Energy Management (BOEM) Notice to Lessees 

(NTL’s) 2008-G04, 2008-G05, and 2009-G40, (MMS, 2008a, b and 2010). The requirements set forth in 

NTL 2005-G07 are applicable because the Federal lease block MC 554 is considered to be a high 

probability archaeological block (MMS, 2005 and BOEM, 2011). In compliance with NTL 2005-G07, the 

required archaeological assessment was performed by GEMS and included as an appendix in the main 

report (GEMS, 2012). 

According to NTL 2008-G05 (MMS, 2008b), 3-D seismic reflection data may be used for shallow hazard 

assessments with approval from the BOEM, Gulf of Mexico Region. A power spectrum analysis was 

conducted from the 3-D seismic data cube provided by Apache to illustrate the data parameters 

(Figure MC554-A-2). The power spectrum curve was generated within a 500 ft radius of the intersection 

of the inline and crossline at the proposed wellsite. We converted the amplitude vs. frequency spectrum, 

generated by the SMT software, to power vs. frequency by squaring the amplitude values as described by 

J. A. Coffeen, 1978. 

Figure MC554-A-2. Power Spectrum Analysis Curve, Proposed Wellsite MC554-A 

Man-Made Features and Archaeological Assessment

The surface location is clear of any wells, pipelines, or platforms within a 2,000 ft radius from the 

proposed wellsite. The closest existing well (ExxonMobil #1) is located approximately 1.4 miles southeast 

of the proposed wellsite location in MC 555 (Map MC554-A-1). The well was an exploratory well and is 

currently temporarily abandoned. 

GEMS delineated 27 unidentified side-scan sonar contacts in the digital data within 12,500 ft (11,500 ft 

maximum anchor radius plus 1,000 ft buffer) of the proposed MC554-A (Maps MC554-A-2 and 554-A-3). 

Side-Scan Sonar Contact Number 54 appears to represent a potential shipwreck. The contact is located 

approximately 2.3 miles southeast of the proposed wellsite and a 1,000 ft archaeological avoidance is 

recommended around the contact. No known shipwrecks or objects exist within the area of potential 

effect for the proposed well location. 

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

Power (Amp

2

)

Frequency (Hz)

POWER SPECTRUM
Proposed Wellsite MC554-A Clearance Letter 

Apache Deepwater LLC // February 20, 2013

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FORUM ENERGY TECHNOLOGIES, INC. 

None of the other 26 contacts appear to represent cultural resources. Several of the unidentified sonar 

contacts form part of a northeast-southwest trending debris trail in MC Blocks 554 and 598. The debris 

likely represents unexploded ordnance because the designated historic ordnance disposal area lies west 

of the Guadalupe prospect (Figure MC554-A-1). The side-scan sonar contacts within 12,500 ft of the 

proposed wellsite forming part of the debris trail are Side-Scan Sonar Contact Numbers 43, 45-46, 48, 

and 73-78. None of these unidentified side-scan sonar contacts are recommended for archeological 

avoidance or investigation, but Apache should use caution when working near the debris trail because of 

the risk for contact with unexploded ordnance. Other similar contacts along the path of the debris trail 

were identified in the side-scan sonar data, but were not retained in the final contact list. Since these 

contacts were not visible in two or more overlapping swaths of data, it was not possible to verify if the 

contacts represented actual debris or noise in the sonar record. A 100 ft shallow hazard avoidance is 

recommended for the remaining 26 side-scan sonar contacts. 

Table 1. Sonar Contacts Located Within 12,500 ft of MC554-A. 

No. Area Block Length 

(ft) 

Width 

(ft) 

Height 

(ft) Shape 

X 

NAD27 

(ft) 

Y 

NAD27 

(ft) 

Avoidance

Radius (ft) 

19 MC 511 5.44 1.86 0.00 Linear 1112591.97 10329220.90 100 

20 MC 511 14.68 7.23 1.75 Irregular 1112902.20 10329423.85 100 

21 MC 511 35.69 13.33 1.24 Irregular 1112951.32 10329320.37 100 

42 MC 554 12.42 6.58 0.00 Linear 1100325.29 10313357.68 100 

43 MC 554 10.12 2.37 0.00 Linear 1101971.94 10312550.76 100 

44 MC 554 16.49 7.46 0.00 Irregular 1102351.14 10324394.30 100 

45 MC 554 26.64 9.48 0.00 Irregular 1102457.87 10313328.31 100 

46 MC 554 16.93 3.61 0.00 Linear 1102620.96 10313548.00 100 

47 MC 554 13.22 2.94 0.00 Linear 1102642.15 10327125.63 100 

48 MC 554 12.65 4.52 0.00 Linear 1103307.63 10315340.61 100 

49 MC 554 11.29 3.64 0.00 Linear 1104028.27 10311991.31 100 

50 MC 555 11.52 4.74 0.00 Irregular 1112644.89 10312564.17 100 

51 MC 555 10.50 8.70 0.00 Linear 1113273.53 10315889.23 100 

52 MC 555 11.52 2.48 0.00 Linear 1116727.29 10314034.61 100 

53 MC 555 20.24 5.06 0.00 Linear 1118118.76 10326028.12 100 

54 MC 555 42.49 24.57 0.00 Irregular 1119186.80 10314174.41 1,000 

73 MC 598 15.67 5.79 0.00 Linear 1100286.61 10310357.55 100 

74 MC 598 9.26 3.17 0.00 Linear 1100695.83 10310457.55 100 

75 MC 598 7.48 2.30 0.00 Linear 1100794.98 10310635.80 100 

76 MC 598 15.20 3.37 0.00 Linear 1101123.39 10311196.89 100 

77 MC 598 10.12 2.17 0.00 Linear 1101235.39 10311328.45 100 

78 MC 598 9.00 2.18 0.00 Linear 1101247.04 10311266.08 100 

82 MC 598 10.86 2.08 0.00 Linear 1105782.24 10308511.16 100 

83 MC 598 10.86 2.65 0.00 Linear 1106972.13 10311235.93 100 

86 MC 599 17.16 18.29 0.00 Irregular 1110651.55 10309177.14 100 

87 MC 599 14.68 5.20 0.00 Linear 1111038.82 10307413.92 100 

89 MC 599 15.74 5.94 0.00 Linear 1113261.85 10308889.05 100 

*Blue indicates a recommended archaeological avoidance. 

Wellsite Conditions

The proposed surface location is clear of any constraining seafloor geologic conditions as defined by the 

available geophysical data. MC554-A is not expected to intersect faults (seabed or buried) and the 

potential for encountering significant amounts of shallow gas is low. However, there is a moderate potential 

for encountering shallow water flow within possible overpressured sands. 

 
Proposed Wellsite MC554-A Clearance Letter 

Apache Deepwater LLC // February 20, 2013

Geoscience Earth & Marine Services, Inc. ® // 5 

FORUM ENERGY TECHNOLOGIES, INC. 

Water Depth and Seafloor Conditions

The water depth at the proposed surface location is approximately -4,647 ft and the seafloor slopes 

southeast at less than 1° (Map MC554-A-1). Side-scan sonar data show that the seabed in the vicinity of 

the proposed wellsite is primarily characterized by uniform low reflectivity (Map MC554-A-3). The low 

reflectivity is likely associated with very soft clays. 

The proposed wellsite MC554-A is located along a relatively shallow mass-wasting pathway trending 

northwest-southeast across the Survey Area (Figure MC554-A-1 and Map MC554-A-2). The hummocky 

topography within the vicinity of the proposed location represents the seafloor expression of buried slumps. 

The slumps are buried by more than 100 ft of strata (Figure MC554-A-3, GEMS, 2012). Mound-like 

features in the same area are associated with rafted blocks within the mass-transport deposits (MTD) matrix 

and are not hydrocarbon related (GEMS, 2012). A drainage feature (gully) located approximately 950 ft to 

the northwest suggests low-level sediment transport activities in the recent geologic past (> 10,000 yrs), 

Figure MC554-A-1. 

Figure MC554-A-3. Seafloor Conditions at the Proposed Wellsite 

Deepwater Benthic Communities 

BOEM and BSEE did not designate Federal lease Block MC 554 as having high-density deepwater 

benthic communities (MMS, 2010). There are no apparent geophysical indicators at the seafloor or at 

depth that would suggest conditions capable of supporting significant deepwater benthic communities 

within 2,000 ft of the proposed wellsite (Maps MC554-A-2 and 554-A-3). 

Stratigraphy 

Stratigraphic conditions are shown on Illustrations MC554-A-1 and 554-A-2. The lithology at the 

proposed wellsite was inferred by integrating the seismic facies with the well log response at the existing 

well, ExxonMobil #1. Generally, the suprasalt seismic facies were correlated across both locations; 

however, only remnants of the sand-prone channel system observed within Unit 4 at ExxonMobil #1 is 

present at the proposed location (Figure MC554-A-4). The sediments below the seafloor to the limit of 

Portion of AUV Line 130

Seafloor expression of 

rafted blocks

500 ft

Assumed velocity: 5,000 ft/sec

W E

Two-way travel time (secs)

Horizontal

Distance (ft)

Proposed Wellsite MC554-A

138 ft north of AUV Line 130

Weakly stratified 

INDEX MAP

AUV Line 130

Seafloor expression of 

rafted blocks

Grid

North

MC 554

1,000 ft

MC554-A 

Circle represents

2,000 ft radius around

proposed wellsite

Gully

10 ft

Seafloor Rendering

Buried slump

Mound-like features at the seabed

represent the seafloor expression of

rafted blocks within buried slumps.

The slumps are buried by more than

100 ft of strata.

The lack of direct hydrocarbon

indicators (DHI) at these sites confirm

that the features are not hydrocarbon

related. See the main report for more

details (GEMS, 2012).

Shallow strata comprises of

hemipelagic clay- to silt-rich

sediments.

Well-layered 

unit
Proposed Wellsite MC554-A Clearance Letter 

Apache Deepwater LLC // February 20, 2013

Geoscience Earth & Marine Services, Inc. ® // 6 

FORUM ENERGY TECHNOLOGIES, INC. 

investigation (4,819 ft bml or -9,466 ft bsl) consist primarily of hemipelagic clays, muddy- to sand-prone 

turbidites, slope fan deposits, and mass-transport deposits. 

The shallow stratigraphy (Seafloor to Horizon 10, Unit 1) is interpreted to be hemipelagic clay- to silt-rich 

sediments down to approximately 205 ft bml. The sediment units between Horizon 10 and Horizon 30 

(Units 2 and 3) are dominated by mass-transport deposits (MTD) with intermittent silty- to sandy turbidites 

to approximately 1,260 ft bml. Sand-prone erosional remnants from older strata are possible within the 

MTD matrix. Unit 3 is associated with a regional basin-floor fan system known as the “Blue Unit” (GEMS, 

2012). The low gamma ray log response (inferring sand) at ExxonMobil #1 suggests that there is a high 

potential for sandy turbidites within the Blue Unit between 714 ft bml and 1,260 ft bml 

(Figure MC554-A-4). 

Remnants of a sand-prone channel system occur in the upper portion of Unit 4 (Horizon 30 to 

Horizon 40). A vertical borehole at the proposed location will intersect the channel system from 

approximately 1,456 ft bml to 1,948 ft bml. The lower portion of the strata to approximately 2,732 ft bml 

comprises of mud-dominated rotated slide blocks and silt- to sand-prone turbidites. The underlying 

strata, Unit 5 (Horizon 40 to the limit of investigation) comprises of muddy- to sandy turbidites and 

possibly MTDs. Thick, continuous sand layers are possible within this sediment unit (between 2,732 ft 

bml and 4,819 ft bml), Figure MC554-A-4. 

Figure MC554-A-4. Suprasalt Stratigraphy between the Proposed Wellsite and ExxonMobil #1 

Faults 

A vertical wellbore at the proposed location will not penetrate seafloor or buried faults between the 

seafloor and the limit of investigation (Illustrations MC554-A-1 and 554-A-2). The top of the nearest 

buried fault occurs at approximately 1,400 ft northwest of the proposed wellsite MC554-A. The fault is 

downthrown southeast towards the wellbore and is buried by up to 2,700 ft of sediments.

INDEX MAP

Seafloor Rendering

Grid

North

MC 554

2,000 ft

MC554-A 

Circle represents 2,000 ft 

radius around proposed 

wellsite

ExxonMobil #1

MC 555

MC 599

Two-way travel time (secs)

Horizontal

Distance (ft)

Proposed Wellsite 

MC554-A ExxonMobil #1

MC 554 MC 555 MC 599

Arbitrary Line A-A`

5,000 ft NW SE

Seafloor

Horizon 10

Horizon 20

Horizon 30

Horizon 40

Limit of 

Investigation

GR R

GR - Gamma Ray

R - Resistivity

UNIT 1

UNIT 2

UNIT 3

UNIT 4

UNIT 5

Channel

Generally, the suprasalt stratigraphy at the

existing well location (ExxonMobil #1) and

the proposed wellsite MC554-A is similar. The

main difference observed is within Unit 4

where only remnants of the channel system

exist at the proposed location.

The 22” casing got stuck and was later jarred

free at ExxonMobil #1. The casing was stuck

in possibly clay-prone sediments within the

channel system in Unit 4.

Relative Amplitude

Low High

Blue 

Unit

22” casing stuck
Proposed Wellsite MC554-A Clearance Letter 

Apache Deepwater LLC // February 20, 2013

Geoscience Earth & Marine Services, Inc. ® // 7 

FORUM ENERGY TECHNOLOGIES, INC. 

Shallow Gas and Shallow Water Flow 

The scout tickets from ExxonMobil # 1 did not report any shallow geohazard conditions related to shallow 

water flow and/or shallow gas. As a result, significant shallow gas is not expected at the proposed 

wellsite; however, a moderate potential for shallow water flow is possible within the identified sand prone 

sequences (Illustration MC554-A-2). 

Shallow Gas. There are no apparent subsurface high-amplitude anomalies directly below the proposed 

location (Map MC554-A-4). The potential for encountering shallow gas is considered negligible in the 

clay-prone unit between the Seafloor and 714 ft bml. There is a low potential for encountering significant 

accumulations of shallow gas in underlying sand-prone layers above the limit of investigation 

(4,819 ft bml). 

Shallow Water Flow. There is a moderate potential for encountering overpressured sands within the 

Blue Unit, Unit 3 (714 ft bml to 1,260 ft bml) and the underlying sand-prone channel remnants (1,456 ft 

bml to 1,948 ft bml), Illustration MC554-A-2. Although, numerous wells in the Mississippi Canyon Area 

have experienced water flow within the Blue Unit, no such occurrence was reported at ExxonMobil #1. 

Potential overpressures may have been mitigated while drilling the well, and hence not reported. 

A low potential for shallow water flow is interpreted between 1,260 ft bml to 1,456 ft bml and beneath 

1,948 ft bml. The shallow, clay-rich sediments (Seafloor to 714 ft bml) are considered to have a negligible 

potential for shallow water flow. 

Anchoring Considerations

The 11,500 ft radius outlined on the accompanying maps represents the area of potential effect for 

anchoring. An additional 1,000 ft buffer zone is also included. The following discussions address the 

seafloor conditions related to anchoring considerations within the total 12,500 ft radius. 

Water Depth and Seafloor Conditions

Water depths within the potential mooring area range from about -4,440 ft to -4,830 ft (Map MC554-A-1). 

The seafloor slopes southeast with shallow water depths in the western portion of the mooring radius. 

Seafloor gradients within the mooring radius range from nearly flat to approximately 42° (GEMS, 2012). 

Most of the seafloor has low gradients (less than 3°). 

Irregular seafloor morphology within the potential mooring area is associated with erosion-related features 

(e.g. gullies and erosional scarps) and seep-related features (e.g. mounds and pockmarks), 

Map MC554-A-2. The hummocky seafloor across most of the remaining area represents shallow buried 

slumps and the mound-like features within the slumps represent buried rafted blocks (Figure MC554-A-3). 

Seafloor slopes associated with the erosion-related and seep-related features range from 5° to 13° 

(GEMS, 2012).

Seafloor faulting is located in the northeastern portion of the radius in central MC 555. The faults trend 

northeast-southwest, are downthrown mainly to the northeast, and bound the expulsion features. 

Seafloor offsets associated with the faults are up 50 ft with associated slopes reaching 42°. 

Deepwater Benthic Communities 

The expulsion features that exhibit high backscatter reflectivity and “rocky” topography on sonar data are 

likely associated with carbonate hard grounds (conditions conducive for benthic communities), 

Map MC554-A-3 and Illustration MC554-A-3. These expulsion features have a high potential for 

supporting densely populated benthic communities and are shown as orange polygons on 

Map MC554-A-2. The features lacking irregular topography but still exhibit high backscatter and sonar 

reflectivity represent limited hard ground areas. These sites have a lower potential for supporting seep 

communities and are shown as green polygons on Map MC554-A-2. 

BOEM requires at least a 250 ft buffer around potential benthic community sites for all proposed seafloor 

disturbances (including those caused by anchors and anchor chains), MMS, 2010. However, if seafloor 

disturbances occur within 500 ft of these sites, Apache is required to submit an as-placed anchor plat to 
Proposed Wellsite MC554-A Clearance Letter 

Apache Deepwater LLC // February 20, 2013

Geoscience Earth & Marine Services, Inc. ® // 8 

FORUM ENERGY TECHNOLOGIES, INC. 

BOEM. We recommend conducting an ROV investigation to confirm or deny the existence of deepwater 

benthic communities at the potential hard grounds if these areas occur near the proposed anchors or 

anchor chains. 

Conclusions and Recommendations

We appreciate the opportunity to be of service to Apache and look forward to working with Apache on 

future projects. The conclusions and recommendations from this assessment are as follows: 

Wellsite Conditions 

No major seafloor hazards or constraints are defined by the available data within 2,000 ft radius of the 

proposed location. Caution and possible mitigation is recommended when encountering potential 

overpressured sands between 714 ft bml to 1,260 ft bml, and 1,456 ft bml to 1,948 ft bml. 

Anchor Maximum Radius Conditions 

The potential seafloor constraints within the mooring radius include possible hard grounds that could 

support benthic communities, a potential shipwreck, and possible unexploded ordnance sites. 

A minimum of a 250 ft radius is recommended around the potential benthic communities’ sites. Other 

recommendations include, a 1,000 ft archaeological avoidance around Side-Scan Sonar Contact Number 

54, and a 100 ft shallow hazard avoidance for the remaining 26 side-scan sonar contacts. Care should 

be taken near the debris trail of potential unexploded ordnance in MC 554 and 598. All operations must 

cease and BOEM notified within 48 hours should any potentially historic materials such as textiles, wood, 

ceramics, or other items be uncovered during operations in the area. 

Sincerely, 

GEOSCIENCE EARTH & MARINE 

SERVICES, INC.®

Oluwayomi Oyedele Daniel Lanier 

Geoscientist Vice President-Geosciences 

Erin Williams Janes 

Project Manager/Senior Geoscientist 

Attachments (4 Maps and 3 Illustrations) 

Distribution: 

Mr. John Worthen, Apache Deepwater LLC (3 copies) 

REFERENCES 

Bureau of Ocean Energy Management, 2013, ASCII Data Files, published on the BOEM Gulf of Mexico Region 

Homepage, <http://www.gomr.boem.gov/homepg/pubinfo/freeasci/freedesc.html>, accessed January, 2013. 

Bureau of Ocean Energy Management, 2012, Seismic Water Bottom Anomalies Map Gallery, published on the 

BOEM Homepage, <http://www.boem.gov/Oil-and-Gas-Energy-Program/Mapping-and-Data/Map-Gallery/SeismicWater-Bottom-Anomalies-Map-Gallery.aspx>, accessed November, 2012. 
Proposed Wellsite MC554-A Clearance Letter 

Apache Deepwater LLC // February 20, 2013

Geoscience Earth & Marine Services, Inc. ® // 9 

FORUM ENERGY TECHNOLOGIES, INC. 

Bureau of Ocean Energy Management, 2011, Notice to lessees and operators (NTL) of federal oil and gas leases 

and pipeline right-of-way (ROW) holders on the outer continental shelf (OCS), Revisions to the list of OCS lease 

blocks requiring archaeological resource surveys and reports: U. S. Department of the Interior, Bureau of Ocean 

Energy Management, Bureau of Safety and Environmental Enforcement Gulf of Mexico Region (GOMR), NTL 2011-

JOINT-G01. Effective Date December 29, 2011. 

Coffeen, J. A., 1978, Seismic Exploration Fundamentals: Tulsa, the Petroleum Publishing Co., p. 125. 

Geoscience Earth & Marine Services, Inc.®

 (GEMS), 2012, Geohazard assessment, Guadalupe Prospect, blocks 554 

and 555, Mississippi Canyon Area, Gulf of Mexico, Project No. 0712-2117b. 

Minerals Management Service, 2005, Notice to lessees and operators of federal oil, gas, and sulphur leases and 

pipeline right-of-way holders in the outer continental shelf, Gulf of Mexico OCS region, Archaeological resource 

surveys and reports: U. S. Department of the Interior, Minerals Management Service, Gulf of Mexico, NTL 2005-G07. 

Minerals Management Service, 2008a, Notice to lessees and operators of federal oil, gas, and sulphur leases and 

pipeline right-of-way holders in the outer continental shelf, Gulf of Mexico OCS region, information requirements for 

exploration plans and development operations coordination documents: U. S. Department of the Interior, Minerals 

Management Service, Gulf of Mexico, NTL 2008-G04. 

Minerals Management Service, 2008b, Notice to lessees and operators of federal oil, gas, and sulphur leases and 

pipeline right-of-way holders in the outer continental shelf, Gulf of Mexico OCS region, shallow hazards requirements: 

U. S. Department of the Interior, Minerals Management Service, Gulf of Mexico, NTL 2008-G05. 

Minerals Management Service, 2010, Notice to lessees and operators of federal oil and gas leases in the outer 

continental shelf, Gulf of Mexico OCS region, deepwater benthic communities: U. S. Department of the Interior, 

Minerals Management Service, Gulf of Mexico, NTL 2009-G40. Effective Date January 27, 2010.