A Shell-contracted deepwater drilling rig accidently spilled 319 barrels of oily mud into the sea yesterday while operating in in the Gulf of Mexico’s Mississippi Canyon. This news is not as terrible as it may sound however…
Sources tell gCaptain that the leak happened at a water depth of around 5,000 feet and was due to a failed seal on the drilling riser mud boost line that went undetected. The mud losses were indicated in the drill shack, however indications at the time pointed to downhole mud losses. These sort of mud “losses” happen quite frequently while drilling and in fact, many thousands of gallons of drilling mud can, and sometimes do get absorbed into the “formation” while drilling. The formation is the earth through which the drill bit passes and is made up of many different layers of material including sand, shale, or thousands of feet of pure salt.
To further explain the use of mud while drilling…
While drilling a well, a blend of synthetic and biodegradable oil, and a dense material called Barite, (plus other chemicals/materials depending on the downhole conditions) are mixed together and pumped down the drill string. It’s a critical element of the drilling process as this weighted mud lubricates and cools the drill bit, provides a medium for the drill cuttings to be removed from the well, actually helps turn the drill bit via the downhole “mud motor”, and also provides the hydrostatic pressure needed to keep the well from collapsing in on itself (most important).
The mud is pumped down the drill string using high pressure pumps, then circulates out the drill bit and up the annulus of the well until it reaches the blow out preventer (BOP). It then travels through the BOP and up the riser where it is then reprocessed on board the rig.
The problem yesterday occurred within the riser system.
On the outside of the riser, are 4 pipes attached to it that are used for various well control and drilling operations. They are the Choke and Kill lines (used for well control operations), the accumulator line (used for supplying fluid to help operate the BOP), and the Boost line (used to increase the flow velocity of the mud and cuttings returning up the riser).
One of the connections of the boost line failed, and the mud leaked out of the line until the source of the leak was discovered.
Due to the biodegradeable nature of this oil, and the depth at which it was released, it’s unlikely that there will be any sort of environmental impact.