Eni uses dual-string barrier evaluation to assess well integrity and improve carbon footprint of its Hewett Field, saving 42 rig days

Published: 03/09/2023

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Eni used Epilogue dual-string barrier evaluation to accurately assess the cement barrier behind the 13 3/8-in casing (B-annulus) without inner-pipe removal. This plug and abandonment operation avoided complex casing pulling and section milling operations, saving Eni 42 rig days and 670 metric tons of CO2e.

The objective

Decommissioning offshore assets poses many challenges for operators due to the remote environment and high cost of operations. Inner casing or tubing is often retrieved from these old wells to assess well integrity and determine if remediation of the well barrier (B-annulus, which is often cement) is necessary. Removing the inner pipe is one of the main causes of operational delays if issues are encountered: A cutter must be deployed to a sufficient depth to cut the tubing, and after the cutter is retrieved, attempts to pull the tubulars may prove unsuccessful. In such cases, the process must be repeated until a successful pull is made. And if large amounts of tubular remain in the well, milling operations may be necessary before pulling can be resumed. This results in expensive rig NPT. In addition, well integrity evaluation of the B-annulus after pulling the inner casing or tubing may reveal a good barrier quality, in which case remediation is not necessary, and pulling the inner pipe could be avoided altogether.

Eni wanted to evaluate the B-annulus of two wells in its Hewett Field. Previously, Eni attempted pulling the inner tubing but was unsuccessful, leading to several days of rig NPT.

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Eni’s offshore platform in the Hewett Field.

The solution

During a field test, SLB deployed its Epilogue dual-string barrier evaluation, part of the Epilogue efficient P&A services family—an innovative approach for assessing well integrity without removal of the inner pipe (casing or tubing). The technology was used in Hewett Field to evaluate the 13 3/8-in B-annulus (cement behind the outer pipe) without removing the inner 9 5/8-in production casing. Combining deep-array multimode sonic and multimodality ultrasonic measurements, Epilogue dual-string barrier evaluation provides an accurate B-annulus interpretation, overcoming crucial well conditions such as pipe eccentering and A-annulus liquid type.

Using barrier information of the B-annulus from Epilogue dual-string barrier evaluation, Eni was able to determine that the quality of cement behind the 13 3/8-in casing of the first well was in good condition. This quick data interpretation provided confidence to Eni that it was not necessary to cut the 9 5/8-in inner casing at the original planned cut nor perform milling of the 13 3/8-in casing to regain a rock-to-rock seal. Instead, the 9 5/8-in casing was cut at a shallower section of the casing and successfully removed without issue. A verification pass confirmed the Epilogue dual-string barrier evaluation results. Then, the environmental cap was placed across the region of good bond in the 13 3/8-in casing, providing the same rock-to-rock barrier without the need for additional complex operations.

Similar data interpretations on the second well were used to plug and abandon the well without section milling operations.

The results

The quick data delivery within a few hours enabled Eni to make substantial changes to the planned work scope. By eliminating unnecessary operations using Epilogue dual-string barrier evaluation, Eni avoided associated HSE risks and saved 42 rig days and 670 metric tons of CO2e. This approach has also opened the possibility for rigless P&A in the Hewett Field.

North Sea, Offshore
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