- email@example.com (revised on 2 Aug 2010)
Would a better bathymetry chart have made the difference in averting a disaster? Bathymetry charts provide more than just depth information. The morphological features of the seafloor can be a useful guide to the nature of the sub-seabed. Figure 1 shows a section of the Gulf seafloor (with superimposed regional bathymetric contour extracted from NOAA) showing the domes and canyon topography. Figure 2 shows the visible deformation “cracks” around Whiting Dome due to down slope movement.
Figures 3, 4 & 5 show the typical high resolution 3m binning MBES (Multi Beam Echo Sounder) images that are normally produced for site surveys (data acquired in 2006 - 2008). Compare the details of these seafloor images with the bathymetry chart submitted by BP to MMS in the application to drill Macondo A and B wells in figure 6. The locations of the two relief wells (C & D) drilled after the blowout on 20 April 2010 are also plotted in figure 6.
Figure 7 & 8 shows BP’s bathymetry chart superimposed with the satellite image extracted from Google Earth. Satellite images are quick reconnaissance counter-checks and have been found to be useful in highlighting regional trends which are sometimes missed out from detailed survey charts. The superimposition reveals that Macondo wells A and B were sitting at the edge of a massive structure. As a general rule, wells and platforms are normally located away from the edge of any escarpment for a variety of geological reasons and obvious shallow sub-seabed problems. See the probable geological model for the blowout.
The AUV (autonomous underwater vehicle) is similar to ROV (remotely operated vehicle) and DTS (deep tow system), except that the vehicle is remotely controlled and programmed to run the survey lines without the use of cables. By mounting a MBES system onto one of these deep-underwater vehicles, high resolution data can be acquired at about 50m above the seafloor. This reduces noise, shortens the distance from the transducer to the seabed and enhances overall clarity, sampling intervals and resolution. Seafloor details such as tensional cracks, mega ripples, slumps, gullies etc, can be useful indications of the shallow sub-seabed condition and structure.
For example in figure 3 the seafloor image reveals a “U-shaped valley” of a regional lateral fault zone. Although not visible directly, there is another NE-SW trending fault which had been leaking gas from deeper reservoirs. The two mud-mounds on the upthrown side of the fault, are actually mud volcanoes spewing out 80m gas columns and mud debris. The original site survey report missed out on the high drilling risk posed by the massive shallow gas accumulation spanning more than 3 km in extent. This vital bathymetric information had been instrumental in pushing for a complete review of the initial geohazards assessment which completely missed out the risk of gas blowout. The extended survey confirmed that the severity of the gas hazards risks.
Figure 4 reveals a steeply sloping seafloor that was already developing signs of an ellipsoid bulge. Tensional crevices, longitudinal undulations and snaking gullies are some of the superficial seabed features, warning of an impending giant submarine landslide (2 to 2.5 km in diameter). Yet the 2008 geohazards site survey totally missed out on the impending geotechnical disaster; preferring instead to blindly copy a previous 2000 survey report on the same site inferring the presence of a fictitious Bottom Simulating Reflector (BSR). Strata of gas hydrates were therefore suspected, due to the presence of this fictitious BSR. The gas hydrates were (in turn) the suspected basis of sporadic gas thrusts causing undulations at the lower half of the slope. At the same time, both the 2000 and 2008 surveys reported the surficial sediment layer to be wholly composed of homogenous Very Soft Clay.
This is a classic case where the high resolution seafloor image had been useful in alerting a fundamentally flawed geohazard interpretation that had been blindly accepted as the industry’s standard in deep water site interpretation. More of this interesting story later in another posting, but essentially the seafloor image served as a red flag in stopping the cascading flow of blunders which would ultimately lead to some future disaster downstream. If the surficial sediment were to be Very Soft Clay, there would be insufficient soil strength to remain on the steep slope let alone develop gullies, tensional crevices and undulations on the seafloor notwithstanding the enormous hydrostatic pressure of 700 to 900 m of water column.
Gas hydrates were reported to be responsible for the localised vaporisation of gas which then forced upwards resulting in undulations on the seafloor. This inconsistency could not be more telling. Gas hydrates are regional deposits. If the deposits were to vaporize (due to a rise in temperature or decrease in pressure or both), the process would not have been so localised as to cause seabed undulation of only 10 to 50 m wavelengths in the very soft clay sediment. Vaporisation would also start from higher up the slopes. How would gas vaporized higher up the slope cause undulations found at the lower half of the slopes? Soft Clay would easily disintegrate at the slightest pressure. If there was any gas seepage, the seafloor would have been filled with pockmarks. Therefore the surficial sediment cannot be Soft Clay as erroneously interpreted. The BSR interpretation was found to be fictitious in 2008; 8 years after it was first mis-interpreted. Re-examination of the supposedly BSR reflectors confirmed them to be data artifacts generated by noise interferences due to limitations of the equipment used.
There are many more cases where the initial inconsistencies in the high resolution bathymetric information led to the discovery of erroneous presumptions and significant mistakes which would otherwise be buried under the thick layers of documentation and gigabytes of data. The seafloor images often provide the last minute check before the hectic submission of project details for approval.
In the light of the BP’s Macondo well blowout, some pertinent questions should be asked:
- Why the satellite image which had been acquired at considerably much larger imaging distances from the seafloor and at much lower resolution, is able to pick up vital seabed features missed out by BP’s site survey?
- Would the ill-fated wells (A & B), still be located where they are, had BP’s bathymetry chart been able to show more details of the escarpment, deformation and seabed unstable features? In the examples shown in figures 3 to 5, the oil company had been able to move their respective locations out of harm’s way. Could BP have done that with a better seabed bathymetry instead of an obviously “smoothened” seafloor?
- With so many stages (acquisition, data processing, quality control, site hazards evaluations, well location finalization etc) before the well location was submitted for approval, why did this apparent discrepancy on the escarpment not surface earlier?
- If the MBES data acquisition had not been acquired to the stated contract specifications or required resolution, it would also reveal a serious inadequacy in compliance with industry standards. From previous experiences, this appears to be an industry wide problem, not only confined to the US.
- It also reflects the general lack of importance attributed to seabed morphology by most exploration and geohazards experts, despite its usefulness in alerting numerous past mistakes, either in geohazards assessment or imprudence in exploration management.
Sometimes in an industry as big and sophisticated as the oil industry, it is difficult to know the true health of the industry. Bogged down by the sheer volume of paperwork, technical confidentialities, mazes of red tapes and test procedures, abuses and shoddy work are often carried along unnoticed by the torrential flow of offshore exploration programmes. It is worse when non-quantitative work is involved. How does one judge whether a geohazards map had been compiled diligently to the highest standard? A rush job with a colorful finish or dazzling display would look just as good as one which had been meticulously compiled from every piece of data and information available. Similarly how does one judge the geohazards or survey contractor before a serious problem surfaces or a disaster strikes?
QC consultants need to actively identify delinquents and improprieties in survey work instead of letting things pass. After all, who would know if the deep-towed equipment had malfunctioned for the last 10 km? Retrieving the equipment to check and towing in the 3 km long tow-cable would take at least half a day. If the critical and fail-safe fire detection and alarm system can be expediently switched off on the ill-fated Deepwater Horizon, such transgressions may be more common than we care to admit.
While it may be shocking to the general public to read news of deliberate misinformation, photoshop adulteration of scenes of the clean up effort, recycled video footage of the gushing well and the widely believed capping of the wrong well, such “irresponsible adulteration” had been going on for a long time in some segments of the industry; hidden under the guise of maintaining technical confidentiality and public confidence in the industry. The disaster has exposed the malaise and complacency that had set in with vested international business interest; what many in the industry had long feared and held in silence.
Could BP’s Oil Spill disaster have been averted?
As a normal safety precaution, wells are not located on seabed escarpments as these are surface manifestation of many geohazardous conditions such as the Gas-saturated Weak Sub-Formation (GWSF) hazards, deeper beneath the seafloor. See previous warning on GWSF hazards.
Any geohazards specialist worth his salt would have strongly advised moving location to a more stable ground. Could BP’s oil spill disaster have been averted if this fundamental mistake had been discovered in time, prior to drilling? Once the rig is on location, it is just a disaster waiting to happen on the slightest mistake to trigger an already explosive situation.
A year before the BP’s oil spill disaster, my colleagues and I at RPS had already felt the need for post-survey independent QC’s in view of the number of fundamental mistakes made during and after the geohazards site investigations. A paper was presented by Dr. Fiona Fittzpatrick on our behalf at the Geohazards Geophysics Seminar at Perth, Australia on 25th March 2010, less than a month before the fateful Deepwater Horizon Blowout. On 11 June 2010, another paper stressing the need for independent post survey QC to check the failures of geohazards predictions was presented by me at the National GeoScience Conference at Shah Alam, Malaysia. Clearly there is a need to check on these fundamental mistakes if another disaster is to be averted in the near future.
If the lowest denomination of the exploration work at the most basic work level, uncomplicated by any advanced mathematical formulae or analysis that requires projection to the highest unknown degree can be screwed up, then we should be really worried about the health of our oil industry. Clearly, the industry had failed on the lowly bathymetric litmus test.