CPD, also known as shell and auger drilling, uses a large tripod rig and winch to lift and drop a cutting tool inside a steel casing tube. This case maintains stability and prevents the borehole collapsing from any insecure soil. The cutting tool used is dependent on the type of ground substrate.
[pdf] DTH is short for “down-the-hole”. Since the DTH method was originally developed to drill large-diameter holes downwards in surface-drilling applications, its name originated from the fact that the percussion mechanism followed the bit down into the hole. Applications were later found for the DTH method underground, where the direction of drilling is generally upwards instead of downwards.
[pdf] Before starting casing, the drilling supervisor should hold a pre-job safety meeting and confirm the following with the crew: 1. Remove unnecessary tools. 2. Good Housekeeping before the job 3. Rig up Casing handling equipment: Using appropriate hand. .
A circulation sub, fitting the casing thread, equipped with a WECO connection, shall be readily available on the rig floor at all times during casing running.
[pdf] 
