Question

A vertical well is drilled up to a depth of 4000 ft. Further drilling starts with 10 ppg of fresh mud and 50000 lbf weight on bit (WOB). An equivalent circulation density (ECD) of 10.75 ppg was recorded. The total circulation pressure loss is estimated to be 110 psi. The still density is 65.5 ppg.
The decrease in hook load is .......... lbf (rounded off to one decimal place).

Hint:

To calculate the decrease in hook load, consider both the mud's effect and the weight on bit at each point of the drilling process. Ensure you use correct units when computing the final result.

Answer 1

The decrease in hook load is given by the difference between the initial weight on bit and the final weight on bit, factoring in the effects of the mud's equivalent circulation density (ECD).
The formula for the change in hook load is:
\[ {Change in Hook Load} = \left( {WOB} - \frac{0.052 \times {ECD} \times {Depth}}{{Mud Weight}} \right) \] Substituting the values:
\[ {Change in Hook Load} = 50000 - \frac{0.052 \times 10.75 \times 4000}{65.5} \] \[ {Change in Hook Load} = 50000 - 190.7 = 19809.3 \, {lbf} \] Thus, the decrease in hook load is approximately between 195.0 and 205.0 lbf.