Geomechanics Assessment of Stability Eliminates Second Casing String to Save USD 200,000

Published: 12/19/2013

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Tension in excess of 10,000 lbf

While the 12 1/4-in section of a deepwater well in the Eastern Mediterranean well was being deepened, the drillstring got stuck. When the operator resorted to a 35° sidetrack, revision of the logging tension simulation predicted that tension would exceed 10,000 lbf. Schedule constraints and the remote location of the well prevented mobilizing a capstan in time to evaluate the 8 1/2-in section to total depth. The high probability of tool sticking occurring favored the alternative approach of drillpipe deployment to convey the wireline tools for a complete petrophysical evaluation, including pressure measurement, fluid sampling, and obtaining sidewall cores. However, this approach would require an additional 7 days of deepwater rig time to conduct.

Efficient cable deployment that also reduces risk

Schlumberger suggested short-notice deployment of TuffLINE 18000 torque-balanced composite wireline cable by airlifting a cable drum from a UK base in time for the 8½-in section. TuffLINE 18000 composite cable integrates the breakthrough technologies of polymerlocked armors and crush-free electrical cable cores to effectively overcome the fundamental limitations of current armored cables. The resulting torque-balanced condition maintains a consistent state of low torque to prevent birdcaging and premature cable breakage. Multiple high-tension operations can be conducted without compromising cable integrity while eliminating the requirement for seasoning of new cable and cable swapping for extended logging operations.

Because the polymer locking of the armors prevents rotation, TuffLINE 18000 cable is effectively in a permanent ends-fixed state, which raises the ends-free breaking strength to 27,000 lbf. That is only 1,000 lbf below the ends-fixed breaking strength and delivers a breaking-strength safety margin of 9,000 lbf above the safe working load. At these values, the risk of cable breakage occurring because of accidental overpull above the safe working load is significantly reduced to greatly improve performance while reducing operational risk compared with deployment on a capstan.

Graphic: Geomechanics Assessment of Stability Eliminates Second Casing String to Save USD 200,000

The bidirectional TuffTRAC cased hole services tractor incorporates sensors for monitoring the application of active traction control and tracking the progress of downhole operations

Graph: Geomechanics Assessment of Stability Eliminates Second Casing String to Save USD 200,000
Logging data from the Sonic Scanner acoustic scanning platform and ECS elemental capture spectroscopy sonde were the basis for mechanical earth modeling that identified a potential zone of wellbore instability. EXL Petroleum used this insight to mitigate drilling risk in a new lateral, which saved USD 200,000 per well by eliminating a casing string.
Delaware Basin, United States, North America, Onshore

Challenge: Construct a petrophysical and geomechnical model that determines horizontal wellbore stability while reducing drilling costs.

Solution: Use the TuffTRAC cased hole services tractor to convey a triple-combo toolstring, ECS elemental capture spectroscopy sonde, and Sonic Scanner acoustic scanning platform to collect the petrophysical and geomechanical data necessary for constructing a mechanical earth model (MEM).

Results: Used the MEM incorporating the high-resolution 3D geomechanical measurements by the Sonic Scanner platform to identify intervals with potential hole instability that enabled the EXL Petroleum to mitigate drilling risk by employing an appropriate mud weight, repositioning the casing shoe point, and installing a short liner string instead of running an intermediate casing, saving approximately USD 200,000.

Products Used