Stabilizer Selection Based on Physics and Lessons Learned

Pastusek, Paul E. (ExxonMobil Development Co.)



The objective of this paper is to share lessons on stabilizer selection with the industry that minimize drilling and tripping problems. Ideally the stabilizers and BHA will drill a round, ledge free hole, without patterns, with minimum vibration, minimum unplanned dog legs, that reach all directional targets in one run per section. They should not constrain ROP, be able to trip in and out on elevators past ledges and hole irregularities without the need for rotation.

These lessons were based on a number of forensics observations while drilling and tripping and a physical understanding of the BHA and its effects on vibrations, trajectory, and tripping in high angle holes.

A draft of these lessons were presented at a SPE Gulf Coast section meeting in 2015 and were sent to all that requested them as well as suppliers used by this operator for comments and suggestions. It is hoped that this publication and the reasoning behind the lessons will help improve this often neglected tool.

A few significant events initiated this work. The first was a mechanical sticking event in 17 ½ inch hole where the BHA could be rotated and moved downward, but hung up trying to trip out. The formation being drilled at high angle was a vuggy limestone. Inspection of the BHA and stabilizer design found that there was a sharp, 75 degree, transition taper on one of the rotary steerable system stabilizers. This coupled with a formation ledge made it impossible to ream or trip, resulting in a lost BHA and sidetrack.

The second key event was a 6 ¾ BHA that required control drilling to avoid plugging the near bit stabilizer. This showed up as an increase in standpipe pressure and a decrease in an annular pressure gauge located above this stabilizer. The root cause was low bypass area on the near bit stabilizer.

The third event was in 12 ¼ inch high angle hole in soft rock. This required circulation on the trip out of the hole on some wells and not others. The wells requiring circulation on the trip out had high spiral stabilizers that packed off rather than passing the cuttings bed.

A practical set of lessons have been developed that may be used as a starting point for developing industry best practices. The physics behind these lessons are given so that they can be improved over time. One improvement expected is the requirement for low coefficient of friction on the stabilizer OD to minimize whirl and on the end tapers to reduce tripping hang up.