What is a down-the-hole drill?

A down-the-hole drill, usually called DTH by most professionals, is basically a jackhammer screwed on the bottom of a drill string. The fast hammer action breaks hard rock into small cuttings and dust that are evacuated by a fluid (air, water or drilling mud). The DTH hammer is one of the fastest ways to drill hard rock.

How was a hole drilled?

This system could not guarantee a finished hole size and only pure vertical holes could be drilled as the system basically relied on gravity. Debris from the hole was baled out using a baling tube with a clack valve, which was periodically dropped on a winch to capture the slurry, which was then brought to the top of the hole to be discharged.

What can we learn from the Deepwater Horizon accident?

The lessons from this tragedy are potent reminders of the pitfalls that can plague complex programs and projects in any industry, even (perhaps especially) those with long track records of success. Prior to the accident, Deepwater Horizon was one of the best-performing deepwater rigs in BP’s fleet.

Who employed the driller in the incident?

Silver City Drilling (NSW) Pty Ltd employed the driller in the incident. The incident occurred within the surface boundary of Mining Lease 1533. Silver City Drilling was conducting a drilling operation under contract from Ashton Coal Operations Pty Ltd for the purpose of installing a dewatering pump to dewater the underground longwall operation.

What type of drilling technique was used at the incident site?

The drilling technique used at the time was air rotary hammer. Air rotary hammer drilling is primarily used in hard formations where penetration rates are superior to other rotary techniques such as rotary mud. The incident site was known as dewatering Borehole 4.

What happens when a well is drilled?

At that point, drilling stops, the well is cemented and capped, and the rig is removed. The well owner returns later (typically with a less expensive production rig) to collect the oil.