Lined casing inspection method

Abstract

A log analysis method can be used to determine a relative condition of a lined casing within a geothermal well from logged instrument data. Uncertain conditions, such as an unknown scale layer thickness, may perturb the indicators of a casing condition within the logged signals. The method can be used to detect the perturbed signals, discern a perturbed reference interfacial indicator in the data, searches for an adjacent interfacial indicator within a window, and axially aligns the adjacent indicator by shifting the data signal towards the reference indicator. The baseline indicator may be an arbitrarily selected signal indicator or a prior (non-scaled/non-eroded) condition indicator. A prior condition indicator can also be used to determine a second window for detecting an adjacent surface signal indicators. The computations used in the present invention are based upon a theoretical model of signal(s) traversing first outward then back across the conducted fluid, scale (if present), liner, casing structure (pipe), cement (or borehole fluid, subsequent casing and cement), and subsurface formation/fluids. The arbitrary or prior condition baseline avoids the need to 'know' the actual properties of intervening materials currently required for analysis of casing conditions and some of the extrapolation limitations inherent in current analysis methods. The method can also achieve accurate results by iterating on the baseline indicator.