Case Studies In Evaluation of Cement With Wireline Logs In a Deep Water Environment

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.