Spill Containment

A LETTER TO THE FEDERAL GOVERNMENT
05/25/2010

The Offshore Industry Is Big and We can Clean Up Big Mistakes - If We Think Big and Use Experience

I am a moderately well-respected Naval Architect/Civil Engineer/Professional in the Offshore industry.  I have been designing dynamically sensitive structures in the ocean for over three decades.  While I have knowledge of most aspects of offshore drilling and production operations, I do not purport to have the knowledge needed to STOP the BP Oil Spill.  I do have the knowledge to help MITIGATE the spill effects and to COLLECT the spilling oil EFFICIENTLY and close to the source, in the open ocean.  My solution(s) are not cheap, but they are effective.

I first started with designing oil spill collection systems in the open ocean with a study for the MMS back in 1986 when I was VP for DNV in the Americas.  We realized that commercially available booms at that time were generally too small for effectively corralling the oil in the open ocean as a consequence of inadequate freeboards and drafts.

Most of what is described below is oil-field thinking in terms of big ocean environments, big volumes of oil, big collection and separation requirements with completely new boom designs that are built and designed for Offshore, not harbor conditions.  To protect the marshes, that now appears to be rather difficult, a smaller variation of the big theme is possible.  Production of robust booms would need to be on a larger scale in length/week.

OrcaFlex Simulation of Offhore Boom System

My main objective is to collect unweathered oil as close to the source as soon as possible, with secondary intelligent collection where we can see the oil being driven by currents.  The currents in the Gulf of Mexico are complicated, but we have some excellent commercial professionals who produce tremendous mathematical models, calibrated and constantly tuned with both satellite and field data.  The US Government does not always use the obvious resources.

In what I am proposing for this new system I am aiming at a freeboard of about 4 feet and a draft of about six feet, with each Offshore Boom system being about one mile long, as illustrated in the attached pdf file.  The main boom is a 63" OD HDPE water supply pipe.  Lengths of about 50 feet can be extruded in the factory, with a wall thickness of around 2".  They would be transported by road or rail to a port on the Gulf Coast, loaded onto work barges with suitable handling equipment and taken offshore for assembly into the boom system.  For rapid assembly they would be welded together offshore, on a construction barge, using standard HDPE pipe welding equipment.  Alternatively they would be fitted with blank end flanges before delivery and bolted together offshore on a construction barge. 

A one-half inch thick, 5' deep neoprene skirt would be fitted.  At the bottom of the skirt another 12" HDPE pipe would act as a carrier for a 1" (or larger) steel wire rope.  This rope would be used in controlling the skirt behavior in boom towing operations.  Some attention to feasible details has been given in the attached sketches, but detailed drawings have not been developed.

One or more weirs are incorporated in the central part of each boom system, with most all materials being purpose fabricated by an HDPE pipe fittings fabricator, using standard designs where feasible.

The largest two facilities that can extrude 63"OD 2" wall thickness HDPE pipe in the US can produce a combined output of about 4.5 miles per month.  About 20 miles per month of 54" OD HDPE might be produced in the US and maybe 50 miles per month of 48" could be produced.  With governmental pressure these amounts might be significantly increased.

In the engineering estimates of quantities provided below, generally feasible and sensible numbers are provided.  However, many estimates must be regarded as having a variability of plus/minus one order of magnitude.

Assuming an average oil film thickness of only about one half of one thousandth of an inch before entering a boom capture area, and an oil slick drift speed into the boom (or a boom rate of travel into the oil) of one knot, the total oil volume collected with a perfect system would be around 4,000 bbl/day.   Even though the boom system would concentrate the oil film thickness towards the weirs, the maximum thickness at the weirs would be unlikely to exceed one quarter inch.  With a weir width of about one foot and an assumption that only 3% of liquid passing over the weir is oil and 97% is sea water, the total liquid flow rate over the weirs would be about 133,000 bbl/day.

One third of the total liquid flow would be taken by each of three barge separation systems, each operating at around 45,000 bbl/day.

It is not certain that the efficiencies of the oil collection system would be improved with dispersants being mixed with the oil prior to collection and separation. It seems likely that oil close to the source that has been in the ocean for less than 36 hours would be more efficiently collected by this system without dispersants added at the subsea source.

A schematic arrangement of the barge separation system is indicated on Sheet 3 of the attached pdf file.  Power sources and heat, as well as advanced separation equipment are needed on each barge.  The intent would be to finally polish the water to an oil content of less than 20 ppm oil in water.  However, for initial start-up of the system, this polishing may be of no interest and returning water with a maximum of 0.05% oil in water (starting with 3% oil and water and discharging 0.05% oil in the water going out would equate to only a 60% collection rate).

On Sheet 6 of the attached pdf drawing set, some calculations are provided and a map of the spill is overlaid on currents and water temperatures.  This map data is provided by ROFF, who are referenced on the sheet.  Potentially good locations for two sets of Offshore Booms are indicated, one set being 23 miles long and another 14 miles long.  Additional Offshore Booms could be located around the source.

Sheet 6 also has some volume estimates of the amount of oil that is presently thought to be on the surface.  These data are not very reliable as thicknesses are unlikely to be uniform.  However, taking an average thickness of only one half of one thousandth of one inch (0.5 mils, or about one tenth of the thickness of a coat of house paint) for the thickest part of the slick (not the stuff that has reached the shore) and only a tenth of this again for the thinnest identified parts of the slick, indicates a volume of oil on the ocean surface of about 1.8 million barrels, or 74 million US gallons.  If only this volume had been spilled (and no account is made for evaporation or, oil collected, or oil that has reached the shore, or oil that has sunk beneath the surface) the average spill rate would be around 54,000 barrels per day.  This rate, as pointed out by one of my engineering friends, is higher than the average 15,000 bbl/day production well in this area of the GoM, but production wells are usually choked (meaning they could generally flow faster if not choked.  Additionally it should be noted that some information reported on 60 Minutes offered that BP anticipated the planned 16 wells would produce a combined 800,000 bbl/day, or 50,000 bbl/day/well).

It can also be seen from Sheet 6 that there are obvious ways for unpredictable amounts of this oil to enter into the section of the Gulf Stream that leaves the Gulf of Mexico.  It could, on the way, present oil on the reefs and beaches of the keys and Cuba.  Then it (because it is always pretty close to the east coast of Florida, put some unwanted stuff on their beaches and poison their fish.  In passing by the Bahamas, it could leave some unwanted stuff on their beaches and reefs.  All up the East Coast of America and parts of Canada the Gulf stream has potential to take the oil from the Horizon spill.  Then some could go north to the Arctic, and some could swing down south and east to the UK, Ireland, France, Spain, Portugal, and others.

Dynamic simulations of the Offshore Boom behavior in seas in excess of 10 feet maximum wave height (7 ft significant wave height with a JONSWAP spectrum)using OrcaFlex show virtually no over topping in a 1-knot current (or tow speed).  One audio-visual presentation is attached.  Stresses in the boom structure appear to be well within allowable in 10-ft seas.

The barges selected for the operation are not special, but each would need modifications.  Hundreds of reasonably suitable barges are available in the Gulf Coast Region. They would each need a special mooring system to keep them in place behind the boom and to prevent them riding up over the sumps.  They would need permanent manning, 3 person minimum, requiring a container with hotel facilities.

Each one mile Offshore Boom System requires two 4000 bhp towing vessels.  The complete system needs a Sea Traffic Control System. 

In my previous estimates, sent several weeks ago to the Horizon Response Team (including BP, MMS, Transocean) I have suggested a little less than a one billion dollar capital expenditure and about a $50 million per day operational expenditure for a total of one hundred Offshore Boom Collection and Separation Systems.  As time has gone by and the magnitude of the disaster has increased I find it frustrating that I see no really big efforts to contain and collect the oil that may be spilling at ten times the rate of 5,000 bbl per day suggested at the outset of the disaster.  In view of the dramatically increased scale of the event, I believe my previous estimates may be several times too small.

This is the Offshore Oil Industry.  Costs are very large.  A replacement for the Horizon may cost $700 million.  The cost for the eleven lives is not calculable.  The cost per day for the drilling program was probably about $1 million when all factors are accounted for, about 50% being the rig contract.

In the Offshore Industry we build big things in big water depths.  A few hundred miles of polyethylene pipes and a few hundred steel barges and a few hundred pretty cheap separator/hotel/power systems should not be a deterrent to cleaning up the largest oil slick in the world that is still spewing at maybe 50,000 bbl/day.

I need to make it clear that I am not a manufacturer and cannot supply the equipment needed.  I can help in making the collection effective. I care for the world and for all civilized persons and countries.  I care for our environment.  We need energy in our world and in our efforts to help all those less fortunate than us.

I see our Offshore Industry and our US Government fighting and not cooperating, largely in my view, because our government is bureaucratic and will not easily admit that it does not possess the necessary technology to cap and clean this enormous spill.  Partly there also seems to be an inevitable desire on the part of the companies involved to minimize their own liabilities.

Again, I emphasize there are two separate solutions to the mitigation of this disaster; you kill the well and you contain the spill.  You cannot bring back the dead, but you can minimize the loss of marine life and businesses dependent on the coasts and oceans.

Kind regards, Bil Stewart.

See Also: Offhore Boom Drawings, sent with above letter    (PDF)

Animations of Currents in and around the Gulf of Mexico