Meet at Audley Clevedon Speaker Mike Marray on RISK

Mike said that he was originally from Liverpool. He spent 31 years in the oil drilling industry working for Shell Plc. His initial job was as an offshore driller, then he became a drill tool pusher who is the supervisor responsible for managing day-to-day drilling operations on a rig. He then moved onshore managing various drilling operations. He also spent 4 years involved in health and safety risk management. His final job was as the manager for Shell’s North Sea operations.

He then showed a 5 minute video from YouTube that gave the basics of drilling offshore for oil and gas: -
https://www.youtube.com/watch?v=VWQnuPOuO0c 

He said that there are 2 main controls to stop unwanted fluid coming back up the drill tube. The primary control is mud. The seawater creates a pressure of approximately 0.5psi for every foot depth. To overcome this a mud mixture is pumped into the tube which creates a downward pressure of 0.52psi per foot. The secondary control is the Blow Out Protector (BOP).

There are various types of drilling rig used.

• A Semi-submersible rig floats in the sea so that in bad weather the rig doesn't tilt much but goes up and down with the waves by up to 30 feet. Some of this type are tied by wire to the seabed whilst others have propellers to steady them.
• Jack up rigs have legs which can elevate them completely out of the water. The legs jack down onto the seabed lifting the rig clear of the water for drilling which avoids rough seas. The legs are jacked up to move the rig to a different location. These rigs are limited to 400 feet water depth.
• A Drill Ship is a 65,000-ton vessel which can go to remote areas with all equipment needed and can drill an entire well without being replenished. These rigs are good in that they can be moved into location much faster than the other 2 rigs which have to be towed by tugs. But they can't operate in bad weather

Where there is the risk of a hurricanes or typhoon rigs have an hydraulic release which allows them to be disconnected from the well head. The well head being sealed off by automatic shut of valves.

Other interesting facts about drilling rigs that Mike gave were: -

• A Big deep sea rig costs about £1 million a day to operate.
• There are different types of drilling bits: -
  • Milled Tooth bits with steel teeth for soft materials.
  • Tungsten carbide bits for harder formations.
  • Polycrystalline diamond bits which last much longer than the other 2 but cost over £30,000 per bit.
• To Determine the porosity and permeability of the rock formation being drilled various methods are used such as core analysis and well testing methods. More recently well logging tools can be lowered down the drill shaft to take sonic and magnetic resonance readings on a continuous basis.
• A BOP can withstand pressures of 10,000 to 20,000 psi.

Risk Management
One of the main things that can go wrong is that the drilling mud mixture is too thin which causes an overbalance and water goes up the drill tube instead of the outer tube. Also human error can cause equipment to be wrongly deployed. He gave an example of a blow back in Brunei where somebody was testing the BOP but opened a valve below the BOP allowing oil and gas to escape. The blowback caught fire and subsequently burnt for 2 week completely destroying the well. The well was explorative and had started to go horizontal which meant that the bore didn't fill completely with cement. Also, various wells were being drilled off the main bore each of which had different pressures. Trying to meet 2 objectives meant that the planners in the office had set the drillers up to fail.

Mike listed the key risk components that a planner should always check: -

• What can go wrong.
• How bad can it be.
• How can we prevent it.
• What is the probability.
• What are the consequences.