Drill bits

Question 0

2 categories of cutter

Answer 0

1. Roller cutters (steel tooth, insert tooth of tungsten carbide)
2. Fixed cutter (natural diamond, industrial diamond PDC)

Question 1

3 aims of drilling

Answer 1

1. Drill as fast / economical as possible
2. Run bits with a long life (can be $1mn to change a bit in deep well)
3. Use buts which drill full size hole

Question 2

Bit price range?

Answer 2

$4000 12.25”in mill tooth bit through to

$100k 17.5” PDC (industrial diamond)

Question 3

Would you use a longer or shorter tooth. To drill in soft rock?

Answer 3

A longer tooth and wider gauge bit will be used as it can basically gauge and scrape at the rock, called shearing. In harder rock with a fixed bit it cuts using compression method (basically a hammer)

Question 4

What is a disadvantage of too much WOB (weight on bit) on the drill bit?

Answer 4

The teeth should only have adequate weight to dig about 2/3rds of the teeth length into the rock. More weight can result in the bit becoming “balled up” meaning all the teeth are filled with rock (especially in softer rocks) which can require you to POH (pull out of hole) to clean /replace.

Question 5

Key determinant of bit choice?

Answer 5

Rock formation.

Question 6

What drill bit used to cut a core? What is the process? What type of wells are cored?

Answer 6

A core head is used, it us a hollow donut shaped bit that enables the core column to feed up the centre. It needs to have a core barrel inside of the tool work above the drill bit.
Inside the core barrel there is a rough core catcher which holds the core in place and cuts it at the bottom.
The core head has special channels in place for the mud to file through rather than through the core barrel.

Coring requires two round trips in and out which is costly, you need to be clear about the need / value.

An exploration and and appraisal wells will be cored all the way through the reservoir.