sheen source tec’s subsea acoustical, water column, and ... · platform deck area, and area...
TRANSCRIPT
Sheen Source TEC’s Subsea Acoustical, Water
Column, and Soils Analysis
Taylor Energy Mississippi Canyon Block 20 A
Dr. Richard Camilli
Navistry Corp.
58 Dec 18, 2015
“a plume sample collected during an ROV survey in April 2005 indicated that fresh water was issuing from fissures in the ground. Flow of this type strongly suggests that excess pressures exist at depth below the seafloor. The fresh-water character of the flow indicates that fissures/cracks likely emanate from a large sand body somewhere below the well bay area. This pressure and flow could cause serious seafloor stability problems for the bottom of the excavation at the well bay area.”
(from 2007 Report No. 0201-6235-1, p 2.1-2.2)
59 Dec 18, 2015
“Hurricane Katrina apparently triggered a relatively small but measurable mudflow at the site. Comparison of post-Ivan and post-Katrina water depths clearly shows significant, non-uniform, differences in water depth across the area. Because Katrina was the largest storm to occur between the two survey dates, we infer that the water depth changes resulted from a Katrina-triggered mudflow. Most of the survey area gained 10 ft or less of new mudflow sediment. However, areas some 1500 ft to several thousand feet across to the northwest and northeast of MC 20-A well site gained about 10 to 20 ft of sediment. A third area, to the southeast of well MC20 A in a low, re-entrant area between mudflow lobes, gained from 10 to more than 40 ft of new sediment. Other scattered areas had a net loss of as much as 20 ft of sediment.”
(from 2007 Report No. 0201-6235-1, p 1.1)
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2006 sidescan survey showing plume near well bay area and near platform jacket
plume
plume
well bay
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2006 map showing location of conductors between the well bay and platform jacket
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2006 map showing depth of conductors between the well bay and platform jacket
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RESULTS FROM 2007 SOIL BORINGS
• Free oil at depths down to 78 ft below the seafloor
• Wood and organic debris at 135 ft below the seafloor
• Pockets of gas collected at depths down to 300 ft below the seafloor
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2007 sub-bottom profile survey showing two plumes near well bay and platform jacket
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2006 sidescan survey of water column plumes
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2007 Mass spectrometer survey of water column hydrocarbon plumes
Plume A
Plume B
Plume C
extent of excavation
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2010 side scan sonar survey of MC-20 area indicating absence of plumes
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2011 sector scanning sonar (Mesotech) survey of MC-20 area using 66 sonar circles, no evidence of plumes
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2012 R/V Okeanos Explorer multibeam sonar (EM302) survey of MC-20 area indicating a plume originating above the platform jacket, near the oil-gas collector separator.
extent of excavation
containment dome “A”
containment dome “C”
well bay
oil-gas separator
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2012 Okeanos Explorer multibeam sonar data perspective view
extent of excavation
containment dome “A”
containment dome “C”
well bay
oil-gas separator
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2012 side scan sonar mosaic with Okeanos Plume data and sub-bottom profile data (17 lines)
extent of excavation
containment dome “A”
containment dome “C”
well bay
oil-gas separator
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Correspondence of SBP water column anomaly and Okeanos plume data
extent of excavation
containment dome “A”
containment dome “C”
well bay
oil-gas separator
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Comparison of 2007 and 2012 sub bottom profile data
2007
SB
P lin
e 12
3 20
12 S
BP
line
503
2012
SB
P lin
e 20
2B
containment dome “A” containment dome “C”
oil-gas separator
containment dome “A” containment dome “C”
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2012 water column view from East: Okeanos plume and SBP water column anomaly origins correspond to oil-gas separator
containment dome “A”
containment dome “C”
well bay oil-gas separator
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Water column view from North: 2007 Mass spectrometer survey of surface sediment contamination, showing contamination generally contained within excavated area.
(geo coordinates in UTM, NAD27 datum, US survey feet)
extent of excavation
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DC1
DC2
DC3
DC4
DC5
DC6
DC7
DC8 DC9
DC10
DC11
DC12
extent of excavation
containment dome “A”
containment dome “C”
well bay
oil-gas separator
PC
2007 Mass spectrometer survey of sediment contamination shown with 2012 SBP (lines 202A, 505), 2012 drop core (DC#), and 2013 diver push core (PC) locations
(red cores = hydrocarbon contamination, green cores = baseline)
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2012 subsurface view from East: diffuse high-contrast acoustic anomaly in shallow subsurface below well bay and containment dome A, with deeper acoustic blanking.
containment dome “A”
containment dome “C”
well bay
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DC1
DC2
DC3
DC4
DC5
DC6
DC7
DC8 DC9
DC10
DC11
DC12
extent of excavation
containment dome “A”
containment dome “C”
oil-gas separator
PC
2012 Side scan map shown with 2012 SBP (lines 202A, 505), 2012 drop core, and 2013 push core locations (red cores = hydrocarbon contamination, green cores = baseline)
well bay
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Summary points from analysis of geotechnical and acoustic data 2005 -2013
• 2005 physical samples collected by ROV indicate fresh water plumes issuing from the seafloor in the vicinity of the well bay area
• 2006 sidescan sonar survey identifies two water column plumes, one near the well bay and the other near the base of the platform jacket.
• 2006 buried well conductors are located from a depth of approximately 150 ft below the mud line at the well bay, sloping upward up to 70 ft below the mud line at the platform jacket.
• 2007 multibeam sonar survey comparison with 2004 multibeam survey indicates sediment erosion areas of up to 10 ft and deposition areas of up to 40ft.
• 2007 air gun survey identifies shallow gas accumulations within mudflow and sand layers.
• 2007 sub bottom profiler survey confirms two water column plumes, one near the well bay and the other near the base of the platform jacket.
• 2007 mass spectrometer confirms two closely-spaced water column plumes near well bay area (Plumes A & B) , and one near the base of the platform jacket (Plume C).
• 2007 mass spectrometer survey identifies sediment contamination predominantly within the excavated area, with highest hydrocarbon concentrations located near well bay area (Plumes A & B).
• 2008 follow up mass spectrometer survey reconfirms plume locations for containment dome placement.
• 2008 intervention commences (including pipeline decommissioning, containment dome placement, intervention well drilling, debris removal).
• 2010 side scan sonar survey of MC-20 area does not find evidence of water column plumes.
• 2011 scanning sonar survey of MC-20 area does not find evidence of water column acoustic anomalies plumes.
• 2012 R/V Okeanos Explorer ship multibeam sonar identifies water column acoustic anomaly (presumably gas plume) originating near the oil-gas separator.
• 2012 sub bottom profiler survey confirms water column acoustic anomaly (presumably gas plume) source originating near oil-gas separator.
• 2012 sub bottom profiler survey reveals diffuse high-contrast acoustic anomaly in shallow subsurface below well bay and containment dome A, with deeper acoustic blanking.
• 2012 drop core and box core survey confirms sediment hydrocarbon contamination in surface sediments near well bay.
• 2013 push core data confirms sediment hydrocarbon contamination in surface sediments adjacent to containment dome C.
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A
B
C
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2015 Kongsberg EM-2040 multibeam sonar survey of MC20 downed platform area (bathymetric map 1m gridding) showing 3 depression areas
Dec 18, 2015
Difference map of 2012 and 2015 multibeam bathymetry, indicating areas of deposition (blue), and erosion (red).
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2015 multibeam survey reveals presence of numerous scour marks despite recent sediment erosion/deposition
Dec 18, 2015
At right: example of extinct 45,000 yr old seafloor pock marks imaged with multibeam sonar off the coast of California (sedimentation rate ~1cm/100yrs).
(from :Paull, Ussler, et al. Marine Geology, 2002)
“In addition to indicating areas of the seabed that are ‘hydraulically active’, pockmarks are known to occur on continental slopes with gas hydrates and in association with slides and slumps. However, possibly their potentially greatest significance is as an indicator of deep fluid pressure build-up…”
(from: Hovland, Gardner, and Judd. Geofluids, 2002)
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(from: Hill et al., Journal of Geophysical Research, 2004)
Subsurface gas accumulation triggered slumping of shelf slope sediments
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2015 multibeam survey reveals extensive pock mark fields that have developed since the MC20 platform toppled
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2015 multibeam map of backscatter intensity
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Yellow circles indicate areas of high backscatter, potentially associated with active fluid flow
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Magenta icons indicate water column acoustic anomalies
Hose suspended between Dome “A” and separator
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Yellow circles show two areas where the platform deck was removed exhibiting increased seafloor acoustical backscatter and water column anomalies
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White and black icons indicate multiple origination points of surface sheens
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• Multi-year survey operations provide no evidence of sediment hydrocarbon recharge or new areas of sediment contamination.
• Sonar survey results indicate a highly dynamic seafloor with significant deposition and erosion occurring within the MC20 block. Evidence of sediment deposition is seen in the well bay area, platform deck area, and area around dome C.
• 2015 multibeam sonar data indicate pockmarks associated with diffuse fluid seepage throughout the M20 block. These pockmarks have developed at MC20 since the platform toppled, and persist despite high continuing rates of sediment erosion and deposition.
• Previously identified hydrocarbon point sources have been undetectable since 2010. Repeated subsea surveys since 2010 have not detected any point source of oil leaking from the seafloor.
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Subsea Acoustical, Water Column, and Soils Analysis
Dec 18, 2015