Subsurface Data Integration, Novel Technology Improves Well Abandonment
Authors: Carpenter Chris 
Published: January 2025

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This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper IPTC 23330, “Reinventing Well Integrity and Zonal Isolation in Well Abandonment Through Prudent Subsurface Data Integration and Novel Dual-Casing Cement-Bond-Assessment Technology,” by Siti Najmi Farhan Zulkipli, SPE, M. Zahin Abd Razak, and Dzulfadly Johare, Petronas. The paper has not been peer reviewed. Copyright 2024 International Petroleum Technology Conference.

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The complete paper highlights well-abandonment case studies offshore Malaysia involving gas migration and the application of emerging technology to diagnose the root cause and source of the unwanted gas. A novel technology combining fiber-optic, acoustic, and ultrasonic measurement principles was deployed to evaluate cement-bond quality and zonal isolation simultaneously in both single- and dual-casing layers.

Introduction
Data analysis and interpretation during well abandonment play a key role in the assessment of well integrity and zonal isolation, particularly if the candidate well has been charged historically with gas migration and sustained annulus-pressure issues. The choice of logging-tool components, the principles of measurement, data-quality control, the processing and validation runs required, and specific data deliverables are critical, especially if the necessity of remedial cementing jobs needs to be evaluated in real time.
The presence of shallow gas accumulation near the well path also is a challenge and becomes a risk when no barrier or cement isolation exists across the well interval near such a shallow gas pool. Because the well has been put into production, stream-pressure depletion will occur and the presence of laterally continuous shallow gas, still at the virgin reservoir pressure, will induce gas migration toward the well based on the concept of pressure sink. Similarly, when the well is put in injection mode, high injection pressure will erode and degrade the cement barrier over time, creating a path for gas migration into the wellbore. Identifying and mitigating shallow gas risk is best approached holistically using multiple dimensions, multiphysics of measurement, and scale of investigation. Categorizing measurements into near-field and far-field acquisition could be an effective initial approach. Table 1 of the complete paper lists some of the measurements involved related to gas monitoring and cement-integrity evaluation in the near-field and far-field regions and the advantages and disadvantages of each.

Principles of Well-Abandonment Campaigns
Most well-abandonment campaigns will involve many types of well profiles in which some wells may not have the legacy cement-bond-log (CBL) information to determine the actual top-of-cement depth. This may create uncertainties in determining the casing cut and pull depth, particularly for a remedial cementing job. This procedure may involve a minimum of 3–4 days of rig time if the tubular cutting goes smoothly and may take up to 7 days if the first attempt of casing retrieval is not successful. In addition, rig-pulling capacity also must be sufficient to pull out all tubulars to the surface, a very energy-intensive activity with considerable fuel consumption and carbon emission. One of the solutions for this challenge is to conduct a reliable cement-integrity assessment behind multiple casings without cutting and pulling any tubulars to the surface. The complete paper highlights three case studies covering shallow gas challenges and poor zonal isolation behind multiple casing strings and recommends best practices for each. This synopsis details two of those case studies.