Wellbore integrity is of paramount importance to subsurface resource extraction, energy storage 1
and waste disposal. After installation,
well casing and cement are subject to mechanical stress due to near-well pressure changes and fluid induced corrosion. This is
exacerbated for geothermal wells where produced fluid is at high temperature and corrosive. The current state-of-the-art technologies
for wellbore integrity assessments are an array of cased hole logging tools. Wireline deployed acoustic, electromagnetic and mechanical
tools are all available to inspect steel casing corrosion and casing-cement bond and these tools can provide high-resolution assessment
of borehole conditions. They are intrusive, however, in terms of borehole preparation and interruption to the normal operation of the
wells, and not suitable for high temperature or highly deviated well deployments. In addition, these measurements are performed
infrequently due to high cost, and are therefore incapable of providing frequent data to better predict borehole degradation trajectory,
which can help provide early warning of potential borehole failures.
For this project we are developing a suite of novel, non-invasive, casing based tools for wellbore integrity assessment, combining
fast/low cost screening with higher-precision investigation. Our approach is based on monitoring the response of the casing when
energized at the wellhead, thereby interrogating the casing without well intervention. Lab, field and numerical approaches are used in
our study. During the early stage of the research, we focus on numerical simulations, which have shown the sensitivity of the low
frequency electromagnetic (EM) signals to changes in borehole depths and have successfully tested the concept at a field site with
different length well casings. Initial seismic modeling efforts have also demonstrated our capability to simulate seismic tube wave and
seismic field alterations due to borehole breakage and associated fluid leakage. Further numerical, laboratory and field experiments are
underway for additional technology sensitivity analysis, particularly the transient EM/Seismic reflectometry methods, data acquisition
optimization, and numerical simulation improvements.
