Evaluation of cement bonding and zonal isolation is arnchallenge that the oil and gas industry continues to face asrnwells are drilled deeper within more hostile environments. Therncomplexity of this task has increased as these wellbores havernmore challenging trajectories and being drilled in formationsrnfor which there is little drilling and completions experience. Inrnaddition, cement slurries have become more complex with thernaddition of inert gases, micro-spheres, non-traditional liquids,rnand many other additives designed to improve the cementrnsheath quality. These slurries require non-traditionalrninterpretation methods to effectively evaluate the cementrnsheath because older methods do not yield accurate results inrnthese situations. This paper will present informationrnconcerning the existing cement evaluation logging tools, basicrninterpretation techniques, and an overview of the new,rnadvanced methods for existing tools available from a varietyrnof vendors in the industry.rnProgress is continuously being made in the development ofrnmore effective cement evaluation tools and evaluationrntechniques. Standard cement evaluation logging tools consistsrnof two major classes, sonic and ultrasonic. The standardrncement bond log, segmented bond log, and radial bond log arernall part of the sonic logging family. The ultrasonic familyrnconsists of tools with either a rotating transducer or arnstationary array of transducers. This paper, however, will notrnfocus on the hardware but will focus on the interpretation ofrnavailable measurements and on facilitating optimizedrndecisions using measurements from both families.rnAdvanced interpretation methods discussed in this paperrnbroaden and refine previously published methods in order torneffectively evaluate wellbore conditions with the commonlyrnavailable cement evaluation tools. The original processesrndeveloped in the early 1990s now incorporate a statisticalrnvariance mapping display for both the sonic and ultrasonic tools. The resulting variance image from the ultrasonic toolsrnallows detection of minor changes in cement or fluidrncomposition and aids in the interpretation of the pipe-to-cementrnbond. This technique provides a robust answer productrnhelpful in diagnosing zonal isolation and highlightingrnchanneling and quality of materials behind pipe for all cementrncompositions. It is also possible today to process and interpretrnnon-standard sonic data, such as refracted monopole andrnflexural dipole from logging tools not specifically designed forrncement evaluation.rnCorrect application of the newer interpretation techniquesrndescribed in this paper can lead to fully evaluated cementrnsheath quality and distribution behind pipe. Several examplesrnusing the new advanced interpretation methods will bernpresented including comparisons (1) between a scanningrnultrasonic tool and a radial bond tool (2) a sequence ofrnevaluations using a cement bond log combined with anrnultrasonic tool before and after several multiple remedialrnsqueeze operations, and (3) also a comparison between tworndifferent scanning ultrasonic tools and a segmented bond tool.rnThe final example shows a successful use of the newrntechnique in a completion using titanium casing.
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