The development wells in South China Sea today are mostly extended reach wells with a measured depth of about 4000m and a high deviated or horizontal displacement of over 3000m. The accurate assessment of cement bond is given even more attention because of the cementing challenges in such environment: the uncertainty of cement distribution in highly deviated intervals due to uneven mud removal, the difficulty in evaluating two-stage cement job with both light and heavy slurries pumped in one section. Furthermore, rising cost concern of offshore operations requires an efficient manner to acquire comprehensive integrity evaluation data without extending rig time.
The combination of ultrasonic and flexural attenuation measurements was adopted in this project for cement integrity evaluation, conveyed with a wireline tractor. Analysis from the combined measurements discriminates the materials behind casing circumferentially regardless of cement density, and identifies liquid or gas filled channeling in cement sheath. The flexural wave imager reveals the "Third-Interface" information that illustrates annulus shape and casing centralization, from which a three-dimensional cement sheath image can be generated. We conducted the operation rigless by tractoring the tool-string down for over 3300 meters to the target depth, to acquire good quality data in a single run.
In this paper field examples are presented to explain the workflow of getting a more definitive cement integrity answer. We will also discuss how the new method aids to understand why the integrity losses occur in certain sections by analyzing the Third-Interface information uniquely provided by flexural waves, hence to suggest improvement actions in future cementing jobs.
This method gained more explicit cement integrity evaluation result with detailed graphical annulus information comparing with limited outputs from conventional acoustic measurements. Furthermore, this solution was launched for the first time in South China Sea and great efficiency was demonstrated with a new tractoring distance record in China offshore operation, which saved 2 days rig time in comparison with previous jobs conveyed by drill pipe.