New-Generation, Circumferential Ultrasonic Cement-Evaluation Tool for Thick Casings: Case Study in Ultradeepwater Well

Abstract

Abstract This paper describes the deployment of a new circumferential ultrasonic tool for cement evaluation used in a thick-casing environment. The operation was performed in a deepwater well, where massive loads often require heavier linear-weight casings with thicknesses greater than 1.0 in. A new-generation, circumferential, ultrasonic cement-evaluation tool was run in combination with a cement bond-log (CBL) tool to evaluate a primary cementing operation and assure zonal isolation in an ultradeepwater well with 10 3/4-in. casing set in the 14 3/4-in. hole section. Casings with thicknesses greater than 1.0 in. are outside the operating range of current circumferential ultrasonic tools. The improvement features, main specifications, and measurement physics comparing the new tool with previous-generation technology are presented. The operation was performed in a well containing two sizes of 10 3/4-in. casing in the same casing string. Both 85.3 lbm/ft (0.8-in. thick) and 109.0 lbm/ft (1.0-in. thick) casing sections were present and evaluated in the same pass. The sonic/circumferential ultrasonic combination was able to effectively evaluate the quality of the primary cementing operation behind both casing weights, as well as positively detect the top of cement (TOC). The combination of the ultrasonic tool with traditional bond-log technology provides independent and complementary measurements of cement bond quality. This presented the operator with the ability to radially analyze the zonal isolation using an image map and to identify cement quality issues, such as channeling and the presence of microannuli. In addition, the casing integrity was evaluated in the same pass using the ultrasonic tool. The new ultrasonic tool makes it possible to achieve confirmation of well integrity in complex, deepwater environments, clearly identifying zones ranging from free pipe to fully cemented conditions, including radial mapping. Improvements in the measurement physics enables the analysis of the annulus in cases of heavy, thick-walled tubulars, as well as in the presence of heavier drilling fluids.