Drill- off Test"- Selection of Weight on Bit and

Rotary Speed

When to carry out Drill- Bit Test:

• Drill-bit test needs to be done at the start of bit run

• On encountering a new formation• If there is a reduction in ROP

Step 1

Maintaining a constant RPM, WOB (near maximum available)

Step 2

Record the time required to drill a weight increment for example: 2000 kg

Step 3

Length of pipe drilled during step 2 is needs to be recorded

Step 4

From step 2 & 3, the drilling rate in meter per hour has to be calculated.

Step 5

Step 2 & 3 are repeated at least four times. The last test should be at the

same value as first.

Step 6

Penetration rate versus bit weight is plotted.

Step 7

The bit weight which produced the fastest ROP is selected.

Step 8

ROP versus RPM is plotted and the RPM which resulted in the fastest ROP is

selected. This is the optimum rotary speed.

Step 9

These values for RPM and WOB obtained will result in optimum ROP for

the particular formation and bit type.