ACCIDENT
INVESTIGATION REPORT- SHELL OFFSHORE DRILLING – DISCHARGE OF DRILLING MUD IN
THE GULF OF MEXICO
INVESTIGATION FINDINGS
Incident occurred on 11 February 2014 at AC 857 operated by
Shell. Estimated spill was 144 BBLS. The
JSA dated February 12, 2014, titled Transferring mud from reserve pit to active
pits utilized for the mud transferring operation during the time of incident
occurring on February 11, 2014, does not make any mention for a procedure
assuring the proper alignment of all dump valves on the mud pits after they
were cleaned and before they were refilled.
Not all persons responsible for opening and closing the mud pit
valves had signed the JSA for the mud transferring operation.
The JSA was not properly completed or executed due to incorrect
date when the document was generated.
Date Generated indicates 2-12-2014; the incident occurred 2- 11-2014
during the JSA applicable operation.
The JSA was not properly completed or executed due to all
personnel performing the job tasks during the time of incident failed to review
the proper Lock Out/ Tag Out safety steps to be taken in order to properly
identify the #3 Dump Valve was still in the open position as also documented in
the H&P LO/TO/TRY Record Sheet.
The Lessee failed to properly gather a sample for the Static
Sheen Test at the correct sample location prior to releasing pit fluids to gulf
waters during the pit cleaning operation.
Samples were gathered from the #4 Auxiliary Tank and the Trip Tank, but not
the #3 Active Pit. The Dump Valve on the
#3 Active Pit was utilized to discharge the pit fluids into the gulf
waters. The #4 Auxiliary Tank was
utilized in order to pre-stage the washing fluid for cleaning purposes.
LIST THE PROBABLE
CAUSE(S) OF ACCIDENT:
Contractor did not follow JSA in place for opening and closing
overboard discharge valves.
LIST THE CONTRIBUTING
CAUSE(S) OF ACCIDENT:
Piping layout design did have an isolation valve which would
have provided another barrier against accidental discharge of mud into the Gulf
of Mexico. See Attachment for Diagram.
LIST THE ADDITIONAL
INFORMATION:
Witness statements detailing the events of the Synthetic Base
Mud spill are contradictory in the date of the incident given in the
reports. The Alleged Incident Report
given by the Toolpusher states the incident occurred on February 11, 2014. The Alleged Incident Report given by the Tank
Hand states the incident occurred on February 12, 2014. The Alleged Incident Report given by the
Floorman states the incident occurred on February 12, 2014. In the official Timeline given by the lessee,
the date of the incident is February 11, 2014.
The Driller's Report states the date of the incident occurred on
February 12, 2014.
Shell Offshore INC. has changed their operational procedures
taken by H&P personnel for moving fluids between the mud tanks along with
the planned installation of an additional valve downstream to eliminate the
possibility of the issue happening again.
Also Shell Offshore INC. has added procedures for reporting
incidents to BSEE to prevent the incident from happening again.
SPECIFY VIOLATIONS
DIRECTLY OR INDIRECTLY CONTRIBUTING. NARRATIVE:
G-110
AT THE TIME OF THE INVESTIGATION, THE LESSEE FAILED TO PERFORM
ALL OPERATIONS IN A SAFE AND WORKMANLIKE MANNER AND PROVIDE FOR THE
PRESERVATION AND CONSERVATION OF PROPERTY AND THE ENVIRONMENT.
E-841
AT THE TIME OF THE INVESTIGATION THE OPERATOR FAILED TO ORALLY
REPORT WITHOUT DELAY TO BSEE.
E-100
During the investigation it was discovered the operator failed
to prevent the unauthorized discharge of pollutants into offshore waters.
_______________________________________________
MUD STORAGE TANKS AND
RESERVE PIT
Mud is made up at the Rig location. Most Rigs have
several steel Mud Tanks. Muds and additives are mixed and held in the tanks.
Some land Rigs also have a Reserved Pit dug out of the ground. Mud tanks are
also called Mud Pits, a carry-over from the days of earthen pits. Mud Tank is
the preferred term. The Rig does not necessarily use all the Mud Tanks at once
although it does use several. The Active Tanks hold mud the pump actively
circulates. Often mud components come to the Rig in sacs.
Normally the crew stores the sacs in a special component called
the Mud House or Sac Room. The house or room keeps the sacs dry and allows them
to be stored with care. These silo like tanks are bulk tanks or P tanks. They
hold mud additive like Barite and Bentonite. Crew members use some additives in
such large quantities that suppliers load them into the bulk tanks to save time
and money. Bulk tanks usually have their own Hopper or Pneumatic system for
transferring the additives to the mud system. The pump takes the mud out of the
active mud tanks and circulates it through the system. Crew members connect the
mud tanks with the piping and manifolds.
The number of active mud tanks depends on the amount of mud
needed to keep the hole full. And the volume required on the surface to keep
the mud in good condition for circulating. The Sand Trap is the tank
directly below the Shale Shaker. The Shale Shaker removes most of the
cuttings from the mud. But some are so small the Shaker cannot trap them, these
fall into the Sand Trap. The Sand Trap is the first Settling Tank. Crew members
have to clean it regularly to remove the built-up solids. Some small or old
Rigs may have two or more Settling Tanks in the tank system. They allow solids
in the mud to settle out but settling tanks do not do a very good job as
compared with newer generation solids removal equipment so today most Rigs use
a de-sander and de-silter. Reserve Tanks are not a part of the active mud
tank system. Instead the crew uses them to hold excess mud. Or they may use
them to hold a different type of mud than the pump is currently
circulating. They may also store heavy mud for emergency well control
operations.
A Slug Tank is a relatively small separate tank or it may be
small separate part of a larger tank. The crew uses the Slug Tank to mix the
slug. A slug is a small amount of a heavy mud that is pumped down the String.
Crew members may also use a slug tank to mix a small amount of mud for a
special purpose. For example the driller may need place or spot a small
quantity of high viscosity mud also called a Pill at some point downhole. The
Suction Tank is where the mud pump picks up mud ready to circulate downhole.
Mud in the Suction Tank should be clean, free of solids and gas and be properly
formulated or conditioned. Crew members use the Chemical Tank to mix special
chemicals such as Caustic that they will put into the Active Mud Tank.
On some land Rigs, the Rig owner digs a large pit next to the
Rig. This pit is called the Reserve Pit. The crew puts waste mud and the
run-off from the work site in the Reserve Pit. In an emergency they can also
use it as a place to put more mud than the tanks can hold. Often the Rig operator
lines the Reserve Pit with a thick plastic sheet to prevent Liquids from
leaching into the soil. And if the Rig is on a migratory bird fly way the
operator covers it with netting to keep the water fowl from landing in it. Land
Rigs drilling in environmentally sensitive areas will not have a Reserve Pit.
Instead waste and run-off or hulled to an approved waste disposal area.
________________________________________________
MUD TANK CLEANING
The History
When oil based mud was first developed in the 1970s, the
supply vessels of the day were not fitted with purpose built tanks, and
initially the product was carried in converted fuel tanks. The result was that
little of the product actually reaching the oil rig, the majority being removed
by the tank cleaners. Tank cleaning took days and cost a fortune. Hence it was
not long before the tanks were improved.
Often the improvement consisted of plating in the internal
framing to present smooth sides and bottom, but even this process did not com pletely
cure the problem. If the mud was left in the ship for more than a couple of
days the baryte began to drift out of the oil and settle on the bottom where it
would remain until manually removed.
The oil industry is never at a loss for a knee-jerk response,
known by some as "opinioneering", and some ships were fitted with
jetting nozzles not unlike those fitted to the mud pits of oil rigs. They are
known on the rigs as "mud guns".
If mud guns were successful on oil rigs the success certainly
was not repeated on the support vessels. The mud was of course drawn from the
suctions in the bottom of the tanks, using the discharge pumps or possibly
specially installed circulating pumps, and then re-injected into the bottom of
the tanks through nozzles.
The baryte continued to drop out of suspension so that the
liquid at the bottom of the tanks became thicker and thicker. This was
circulated by the pumps until they finally gave up or the nozzles blocked up.
Even worse, the suctions from the tanks frequently blocked so that ships
returned to port with a full cargo and were faced with the problem of how to
discharge it. In the 1970s contractors in Lerwick were often employed to
transfer mud from one tank to another through the deck manholes using portable
pumps. So a further development
understandably was the multi-level suction. Many ships were fitted with a lower
and an upper suction and some even had three levels. The theory was that even
if you had to leave a couple of feet of
the product in there, it was nothing com pared with a full tank.
Of course tank cleaning became more frequent on the theory that
no sediment meant no blockages.
Eventually the circulating systems became more practical,
taking the liquid from the bottom of the tank and returning it to the top
although designers remained obsessed with small diameter nozzles. The nozzles
were usually removed by the ship's staff as soon as the vessel entered services
on the basis that the possibility of blockages would be reduced.
Improvements in formulation of the product and the provision of
agitators, together with the acceptance that frequent tank cleaning must take
place more or less removed the requirement for the upper suction. However the
main suctions were generally placed well above the tank bottoms and were of
large diameter, both factors which reduced the possibility of a com plete
discharge.
Alternatives were tried, and hopper suctions usually worked
though they were com plex to install. Suctions in hatboxes were generally less
successful due to the tendency for the mud residues to drop into the hatbox
after discharge had been com pleted, and then solidifying.
It appears to be purely an accident of design that many tanks
were, and probably still are, filled through the suctions and this ensures that
they will be kept clear.
Many early systems used conventional centrifugal pumps, and
indeed some are still so fitted where economy is considered to be of greater
importance than efficiency. Centrifugal pumps suffer from a tendency to lose
suction if the pump is higher than the suction or if the lines to them are at
any point higher than the pump. These inherent deficiencies may well result in
high levels of residues remaining in the tanks.
The increasing use of constant displacement pumps has
considerably reduced this problem, and hydraulically powered pumps which offer
variable pumping rates may well provide the means of reducing residues by
avoiding cavitation at the suctions.
Recent Developments
During the 1990s the major Norwegian designers addressed the
whole problem of the carriage of mud, and almost universally adopted
cylindrical tanks with hopper bottoms. The redesign of the tank on its own has
vastly improved the ability of the vessels to discharge com plete cargoes.
These cylindrical tanks are also now often fitted with a single
tank cleaning machine somewhere in the upper part and an agitator in the lower
part.
The agitator replaces the circulating system.
It is certain that the tank designs and coating has reduced the
level of residues remaining in the tanks and that the tanks may now be cleaned
to what ever standard is required using tank cleaning machines. Here there is a
difference in view as to the manner in which the tank cleaning should take place
between the British machine suppliers and the Scandinavian suppliers.
The British, represented by Marex and Dasic believe that the
tanks should be cleaned with the product during discharge, reducing and
maintaining the residues to a minimal level, and that very occasionally a water
wash should be undertaken. The Scandinavians represented by Gunclean Toftejorg
and Scanjet think that a water wash should be carried out every time.
The Brits are of the view that their continental rivals have
taken this stance because of limitations in the ability of their machine to
circulate mud. The Dasic manufactured
machine can successfully circulate mud with its attendant impurities which
gives it a number of advantages. On the other hand the continental
manufacturers are always looking to reduce throughput in order to limit the
amount of water which is required to be heated and the volume of residue
produced. In the tank cleaning business this aim can be counter productive. If
too little volume is applied to the surface to be cleaned then more cleaning
cycles have to be carried out. Result - same amount of contaminated water.
The British suppliers
also claim that their process of cleaning the tanks with the product is more
beneficial for retro-fitting to vessels constructed before the latest designs
ensured easy-to-clean tanks.
Even where there is substantial internal framing, the
installation of one or two machines can reduce residues to a minimal level when
the tanks are cleaned with the product and no heaters or chemical injectors are
required. The result will be a substantial reduction in or the removal
altogether of tank cleaning costs, and most importantly today, a vast reduction
in the volumes of contaminated water which have to be disposed of somewhere.
Tank Cleaning on Oil Rigs
Only a few oil rigs and platforms have been fitted with tank
cleaning systems. Tofjorg have supplied some platforms in the Norwegian sector
and Marex has supplied a full set of machines to the semi-submersible Stena Don,
and a number of individual machines to other rig owners.
Drilling fluids are as difficult to deal with on board rigs as
they are on support vessels. The solids still settle out even in pits which
have been provided with mud guns and agitators. This is probably because the
mud guns were never going to work anyway and the agitators are mainly too small
and of unscientific design.
Mariners who visit oil rigs are usually surprised that these
floating objects are provided with mud pits at all. Virtually none of the pit
systems are totally enclosed. The best are decked in but still have holes
through which pipes may pass. Some have manhole coamings but no hatches. The
worst are decked out only with gratings. They are therefore not tanks in any
sense of the word except in the way that an ordinary domestic bath is a tank.
In the past this was not much of a problem. When the pits were
empty some-one would open what is known as a "Dump Valve" or to
continue with the bath tub analogy – pull out the plug, and then some minions
would climb into the pit and wash it out with water. The result would then
drain out through the dump valve into the sea.
Traditionally the only place which held mud was the mud pit
area and the total quantity held was about 2000 barrels in oilfield figures or
about 300 tonnes.
Now with the great increase in the expected water depths at
which mobile rigs will operate, and the extra depth in the substrata to which
they are expected to drill, it has be com e impractical to hold all the mud in
the pits and so older rigs are modified so that some can be held in tanks in
the legs or pontoons. New rigs are provided with purpose built tanks. Of course
offshore oil industry, remaining oblivious to the technology available in the
marine industry, have also fitted these new tanks with agitators and mud guns
and the lack of effectiveness is only apparent when the rigs return to port for
maintenance and the tanks are found to be half full of solids. The solids can
cost a five figure sum to remove.
In addition to the unwanted costs to the rig owners, their
clients are now be com ing more interested in the environmental effects of the
drilling process. Today drill cuttings are being transported back to the shore
for processing solely because they are contaminated with drilling fluid.
However the residues within the mud pits and the mud tanks remain a problem.
Even knowing the extent of the problem does not seem to provide
the industry experts with a solution. The manifestation of their difficulty is
the depth of sediment in the bottom of the pit and so the approach up to today
has been to clean out the pits with water and then to send the resulting
contaminated fluid ashore in the tanks of supply vessels. This process transfers
both the sediment and the problem to the support vessel and still necessitates
the processing of the contaminated water. When the water is discharged, all the
sediment from the pits is left in the bottom of the supply vessel tanks which
then have to be cleaned. This produces even more contaminated water which has
to be sent for processing. It is a total lose, lose, situation.
In an effort to reduce the levels of residues some Operators in
the North Sea have employed contractors who use tank cleaning machines,
detergent and water, and then suck out the fluid for transport to the shore in
one way or another. This technique appears to have cut down the level of
residues, although claims of a maximum of 60 bbls (For those who deal in cubic
metres there are 6.3 bbls to a cubic metre) per tank seem to be a trifle
optimistic. Retired mariners may remember that Dasic and other tank cleaning
machine manufacturers actually provided experts who carried out exactly the
same task on oil tankers in the 1950s.
Attempts to install fixed nozzle mud cleaning machines in the
mud pits of rigs have been frustrated by the tendency for the mud spray all
over the pit room through holes in the top of the tank, and programmable single
nozzle machines so far have been unable to cycle the product. However Marex are
now marketing an ingeniously modified fixed nozzle machine which only jets
downwards, and which can therefore be installed in open mud pits. Hence the
operators of rigs can now enjoy the same advantage as the operators of ships.
They can clean the pits with the product, removing the sediment without
producing any residues for disposal.
Therefore – by cleaning the pits with the product every time
they are emptied there will be a minimum of sediment left, and by making a
special effort during the return of the mud to the supply ship there should be
no sediment left. Similarly if the supply vessels clean the tanks with the
product at every discharge the residues will also be minimised. Production of
contaminated water is negligible. Operators and ship-owners can conform to
their environmental policies and avoid needless expenditure. This is surely a
win, win situation.
Metropolitan
Engineering, Consulting & Forensics (MECF)
Providing
Competent, Expert and Objective Investigative Engineering and Consulting
Services
P.O.
Box 520
Tenafly,
NJ 07670-0520
Tel.:
(973) 897-8162
Fax:
(973) 810-0440
E-mail:
metroforensics@gmail.com
We are happy to
announce the launch of our twitter account. Please make sure to follow us at
@MetropForensics or @metroforensics
Metropolitan
appreciates your business.
Feel
free to recommend our services to your friends and colleagues.