Lost in hole event

K&M’s On-site Advisors were recently working for a client when a lost in hole event occurred. While reaming to bottom in the high angle portion of the well, the driller observed a significant loss in pump pressure and surface torque. The surface equipment was checked to rule out equipment failure then the drill string was pulled to surface to inspect the BHA. K&M was able to monitor the trip out of the hole and quickly determined the BHA parted at the shock-sub/agitator assembly, leaving ~1,994’ of BHA down hole through the use of the “Tripping Hookload Plot”. The plot displays theoretical hookloads versus actual measured hookload while tripping to surface. It was quickly determined what piece in the drill string failed so fishing services could be dispatched immediately with a realistic ideal of what would be fished out.

The lost-in hole BHA was 1,994’ long and laying on the low side in the high angle portion of the well (90° inclination). The first fishing run was able to latch onto the fish and circulate through the lost BHA then began to pull with maximum overpull of 4” drill string. It was determined that the lost in hole BHA was differentially stuck due operating in an overbalance environment within a sandstone layer though unrestricted flow was possible. The slick, un-stabilized BHA was left stationary for +30 hours which contributed to the exponential pinning forces enacted on the BHA.

The On-site Advisor was able to utilize K&M’s Proprietary Software, ERA, to design the fishing string for maximum overpull capacity and remove any weak points. ERA, takes into account Von Mises Equivalent (VME) or the total sum all of sources of stress such as axial, torsional, bending, radial and hoop to ensure all loads applied to the fishing string can be maximized though stay within limits. The second fishing string utilized an optimized 4½” x 4” tapered fishing string. Utilizing the VME plot, it was determined that a maximum of 24 k ft-lbs of torque along with 90 kips overpull would still be within the limits of the drill string. The Tripping Tension snapshot plot was utilized to observe all drill pipe tension loads at various depths to ensure not exceed any one portion of the fishing string. It was determined that when applying 440 kips hookload on surface, a total of 125 kips overpull would be applied to the top of fish. As it was determined the fish was differentially stuck, K&M modeled a 100 bbl diesel pill which would reduce the ECD from 13.8 ppg to 11.24 ppg EMW which was safely above pore pressure and collapse gradients. The lowest ECD was modeled to occur when the pill was in the annulus and nearing surface. For this unique scenario, the fish ultimately pulled free with 420 kips surface hookload and reducing the overbalance from 13.8 ppg EMW to 11.24 ppg to overcome the pinning forces enacted on the fish. The successful retrieval of the fish at 16,170’ in the high angle lateral resulted in a $1.7 million cost savings due to eliminating a sidetrack.

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