## Drill Bit Selection Criteria

A common criterion for drill bit selection is 'BALANCED WEAR . Balanced wear is the method of bit selection in which the teeth, bearings, and gauge, wear-out at exactly the same time. It is easy, but does not necessarily give minimum cost. Some of the problems in selecting drill bits with the 'MINIMUM COST' method are 1. bit selection can only be based on drilling experience 2. lowest cost is usually interpreted as lowest cost per foot which is not necessarily true 3. cost comparisons between...

## Ellipse Of Uncertainty

The concept of an ellipse at any point in a drill hole to quantify the possible locations of the point is illustrated with the following example. Suppose the measured depth is 2500 feet as shown in the sketch and that systematic errors errors which regularly re-occur and are not compensating at any survey station are 1 in azimuth, 0.5 in inclination, and 1 part in 500 for measured depth. Further, suppose the inclination and azimuth are thought to be 30 and 90 , respectively. The expected...

## Example Maximum Available

The maximum available weight on bit WOB for a tangential horizontal well is planned with the drill bit and BHA in the horizontal section, which is the important case. Let the horizontal plan which has been solved in a previous example be as shown in the sketch. Let the drillpipe be composed of 8,000 feet of 5 0D by 4.276 ID drillpipe with an average weight of 21.6 ppf and the BHA be 90 feet with average diameters of 7 by 2.5 114 lb ft . Mud weight is 11.0 ppg. The gravity weight of the...