Schlumberger

Technical Paper: Case Studies in Evaluation of Cement with Wireline Logs in a Deep Water Environment

Society: SPWLA
Paper Number: SPWLA 52nd Annual Logging Symposium
Presentation Date: 2011
 

Abstract

The evaluation of cement placement and zonal isolation in deep water environments is increasingly challenging. Traditional wireline evaluation methods rely on contrasting attenuation rates of sonic or ultrasonic waves to discriminate between cement and fluid behind pipe. In today's deepwater environment, heavy synthetic based drilling fluids can have properties that render the evaluation of the typical lightweight cements extremely difficult. In addition, cement evaluation logs are often run within 48 hours of pumping the cement which results in lower acoustic impedance at the time of logging. This further reduces the contrast in acoustic impedance between the cement and heavy synthetic based muds that are used in this environment. As a result, traditional cement evaluation logs can be ambiguous and difficult to interpret which has led to industry suspicion regarding the application of these measurements. A recently developed ultrasonic measurement called flexural attenuation combined with traditional measurements addresses these uncertainties, and results in more accurate cement evaluation under these difficult conditions.

This paper focuses on the practical application and interpretation of this recently developed measurement and will detail case studies from Gulf of Mexico offshore wells comparing results from traditional CBL/VDL and ultrasonic measurements, with methods that include the utilization of flexural attenuation. The physics of measurement and limitations of each measurement are reviewed and a workflow is presented to integrate all of the data to provide quantitative cement evaluation. Examples are used to illustrate the reduction in uncertainty that can be achieved using this workflow and the combination of these measurements leading to a more definitive determination of zonal isolation.

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