What is it about?

The evaluation of subsurface well integrity is an important business for the oil and gas industry. It is driven primarily by the need to optimize production while maintaining a safe environment despite the inexorable corrosion of downhole metal pipes (casings) and other harsh downhole conditions. Many technologies have been developed to address the challenges of evaluating casing and cement integrity under varied downhole conditions. These technologies are necessarily growing increasingly more sophisticated to meet the requirements of evaluating multiple cemented casing strings. In particular, wireline cased-hole logging techniques based on electromagnetic (EM) and acoustic techniques have been applied to casing corrosion and cement integrity evaluation. Here, we consider some of the well-established logging techniques for downhole well integrity evaluation by deploying tools to characterize casing corrosion and cement quality from within the casings.

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Why is it important?

The combination of tubing, casing(s), and cement provide the required barrier to operate the well safely. The system is expected to provide hydraulic isolation across different reservoir layers and a seal that prevents uncontrolled fluid flow toward the surface that could contaminate groundwater layers or result in an accidental surface spill. The harsh conditions encountered in downhole environments inevitably degrade the integrity of the well construction, for instance through corrosion or deformation of the steel pipes and mechanical or chemical deterioration of the annular cement sheath. The importance of evaluating well integrity has been amplified by aging wells in mature oil and gas fields, stricter regulatory requirements, more complex well construction designs, increases in hydraulic fracturing in shale basins, harsh production or injection fluids, high-pressure/high-temperature conditions, optimization of well plug and abandonment or slot recovery operations, and increasing needs for long-term downhole gas storage. As a result, well integrity management strategies encompass disciplines and expertise in wide-ranging fields of downhole operations, corrosion engineering, maintenance, and production. The evaluation of well integrity is based on downhole logs, laboratory measurements, theoretical models, statistics, and risk analyses.

Perspectives

There is a growing need for thorough and repeated assessment of casing corrosion and cement integrity in multiple barrier completions over a well’s life cycle until plug and abandonment and/or slot recovery to ensure that the barriers continue to provide zonal isolation and maintain safe operations. The nature of EM wave propagation has led to the development of multispacing sensor arrangements, multifrequency, and, more recently, transient PFEC modes of operation coupled with advanced inversion schemes to provide corrosion evaluation across multiple casings. Machine learning or artificial intelligence frameworks are emerging for predictive purposes or as solutions for the multidimensional complexity of interpreting EM or acoustic logging measurements for well integrity evaluation in multistring completions.

Dr. Thilo M Brill
Schlumberger Ltd

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This page is a summary of: Well integrity evaluation using acoustic and electromagnetic measurements, The Leading Edge, February 2022, Society of Exploration Geophysicists,
DOI: 10.1190/tle41020122.1.
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