6. Routine Exploratory Drilling and Support Operations

Weight on the bit is accomplished by running in the hole, between the bit and the drill pipe, several lengths of extremely heavy thick-walled pipe, called “drill collars”. Drill pipe may weigh up to 30 kg/m. Drill collars, of larger diameter than drill pipe and of constant diameter throughout, can weigh up to IS0 kg/m. The full hanging weight of the whole assembly in the blocks in the derrick (bit, drill collars and drill pipe), which is continually monitored by the driller at the rig floor, is gradually paid off by lowering the whole string until the bit rests on the bottom of the hole with the precise desired weight applied to it.