Epilogue - Dual-string barrier evaluation

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Evaluate the A-and B-annulus without removing the inner pipe during well decommissioning operations

Page last modified
October 31 2023

The well decommissioning phase can be complex and costly because of the unknown status of the barrier (often cement) in the B-annulus that may have changed during the life of the well.

Part of Epilogue* efficient P&A services, Epilogue dual-string barrier evaluation enables you to avoid costly and unnecessary steps in the well decommissioning phase. It uses the most advanced method for imaging the B-annulus—all without inner-pipe (tubing or casing) removal, significantly reducing the time required for operations.

Epilogue dual-string barrier evaluation leverages a combination of deep-array multimode sonic measurement (0.5–20 kHz) and multimodality ultrasonic measurement (100–500 kHz). These advanced measurements produce phase and amplitude attributes that yield a combined image of the A- and B- annuli conditions. Ultrasonic measurements provide crucial pipe-to-pipe standoff information and enable you to charaterize liquid conditions in the A-annulus, as well as corrosionrelated gross deformations of the tubing or outer casing. The low-frequency, deeparray sonic measurement provides the B-annulus evaluation. Together, these two measurements provide a more reliable B-annulus evaluation with radial coverage and azimuthal mapping.


Combination of deep-array multimode sonic measurement (0.5–20 kHz) and multimodality ultrasonic measurement (100–500 kHz) to enable single trip in the well saving days of rig time and reducing respective scope 1 CO2e emissions
Evaluates the B-annulus through tubing to avoid inner-pipe removal during P&A well decommissioning operations, saving time and costs
Provides multiple deliverables depending on your operational objectives: corrected bond index, segmented bond log, 360° azimuthal maps
Commercially deployed in 2022, case studies under evaluation


Pressure rating, psi [kPa] 20,000 [137,895]
Temperature rating, degF [DegC] 350 [177]
Min. ID and restrictions, in[mm] 4 [101.6]
Min. inner tubing or casing OD, in[mm] 5-1/2 [139.7]
Max. outer casing OD, in[mm] 13-3/8 [339.7]

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Development Technology demonstration Mature / Proven
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SLB is a global technology company. New identity focuses on energy innovation and decarbonization to address the world’s energy needs today and to forge the road ahead for the energy transition.
SLB (NYSE: SLB) is a global technology company that drives energy innovation for a balanced planet. With a global footprint in more than 100 countries and employees representing almost twice as many nationalities, we work each day to decarbonize oil and gas and develop scalable new energy technologies to accelerate the energy transition. Find out more at slb.com.

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