Thanks to Dave Smith, the ESO Operations Superintendent on-board for this look at drilling……..
Drilling and coring on a floating platform riding up and down on the swell of the sea and tides is a complex process involving winches, cables, hydraulics, compressed air and a lot of control systems. A full explanation would be too long for a blog, so I won’t cover heave compensation, suffice to say the drill string stays stationary and the drilling derrick and ship ride up and down around it!
Our hardworking drilling team from Fugro are split into two 12 hour shifts, each shift comprises of a Driller, 2 Assistant Drillers, 2 Coring Specialists, and 2 Roughnecks. These teams are supported by a Back Deck Supervisor, Technical Drilling expert and Party Chief.
Our Fugro team, from top left: Ronnie; Piet; Max (driller); Geoff (driller); Jay, Tom and Zander; Marvin, Tom and Jesse; Matt R and Marlon; Gilbert, Roland and Matt C.
The drill string has reached the seabed a core barrel is lowered inside the drill string and lands in a special pipe at the base called a BHA (Bottom Hole Assembly). The type of coring tool used depends on the type of geology we expect to encounter underneath the seabed.
The subsurface geology comes in many forms, soft muds, sands, to hard rock and everything in between. At the location of our first hole, there are soft clays at the seabed. To core this type of material, a hollow tube with a clear plastic liner inside is pushed into the ground ahead of the main drill bit using water pressure pumped from the surface. When the core barrel has been extended as far as it will go, up to 3m, it is then pulled out of the ground and back up the drill string with a wire to where the scientists are eager to get their hands on it. This method is called Piston Coring. The Driller then drills the main drill string to the depth that the core barrel had been pushed into the ground and the whole process starts again, that’s a lot of 3m core runs to get to 750m below the seabed!
From top left: The push corer tool; sending the push corer down the hole; Main drill bit; two images of work on the drill floor, and extracting a core liner from the core barrel.
However, as we progress down the hole the sediments can get much harder, either due to a change in rock type or due to compression by the weight of the 860m of sea and several hundred metres of clay above it. If it gets too hard to piston core, we use a different coring method. Rotary coring is where a complete triple wall coring assembly is lowered and locked into the BHA at the bottom of the drill string. The main drill string is then rotated and the ground beneath is cut with a diamond drill bit. The core travels up the core barrel as the bit cuts downwards.
On the left we have Martin “Bat” Barnett (Back Deck Supervisor) and Tony Halliday (Technical Lead) – yes they do go to sea!!
The drill teams have to be experts in many different operations to make what sounds like a simple operation work safely, smoothly and efficiently. These skills include operating the drilling derrick, semi-automated pipe crane and handler that feeds the drill pipe to the and from the drill derrick, the Iron roughneck that tightens and loosens the drill pipe at each 9m connection, maintaining hydraulic and mechanical and control systems, welding, working at height in the rooster box, (the platform that sits on top of the drill pipe). Consuming copious amounts of coffee and biscuits are also a pre-requisite!
This image shows bringing the coring tool up to the rooster box on the drilling derrick. The main image at the top of the page shows a rotary coring bit with core catcher.
All images courtesy of DSmith@ECORD_IODP