Advances in Cement Bond Logging Technology and Issues in Cement Job Quality Evaluation

Abstract

The Cement Bond Log (CBL) is currently the primary method used in domestic oilfields to evaluate cement job quality. However, its interpretation results are prone to ambiguity, leading to misjudgment and erroneous conclusions. This results in artificially high reported pass rates for cement jobs, which hinders the development of cementing technology. This paper systematically analyzes the limitations of CBL in evaluating cement job quality, discusses in detail ten influencing factors including tool eccentricity, fast formations, micro-annulus, cement sheath thickness, gas-cut drilling fluid, casing parameters, localized channeling, cement slurry properties, logging timing, and acoustic frequency. It also points out inherent shortcomings of CBL in evaluating the second interface, identifying thin beds, locating channels, and providing quantitative interpretation. Research indicates that the consistency rate of CBL in reflecting actual cement job quality is only about 33%. In contrast, the Sector Bond Tool (SBT) offers technical advantages through multi-parameter visual display and cement sheath imaging. It is recommended that SBT be used as a means for detailed evaluation of cement job quality in key or problematic wells.