Multivariable Threshold-Processing Workflow Provides Comprehensive Cement Evaluation for Effective Well-Barrier Assessment in Plug and Abandonment Applications

Abstract

This paper presents a cement-evaluation workflow that encompasses the use of multiple measurement thresholds, proving that data processing with the use of logical discriminators can determine true cement-bond conditions with the use of conventional diagnostic tools.The algorithm filters raw and derivative acoustic data through various predetermined thresholds to discriminate well intervals that possess proper cement bond and vertical coverage. Should data associated with a well interval pass through all the chosen logical filters, the interval is flagged as having the necessary cement presence and bond to be considered an isolating annular barrier. The logical thresholds are operator-defined, enabling a customizable assessment of any cement type, regardless of operator standards, legal codes, or environmental regulations.The service was recently implemented in various wells where the customer required a decisive assessment to determine if a cement bond was minimally present prior to proceeding with abandonment. Their previous experiences with well-integrity diagnostics had resulted in contradictory information, requiring additional intervention work to help ensure zonal isolation. The interpretation workflow was able to indicate the presence of a minimum 11 ft of continuous cement and 100 ft of total cement behind the 7 5/8-in. OD production casing, which was one of the customer's well-integrity standards. The processed acoustic response, acquired with a cement-bond log tool and ultrasonic scanner, is presented in binary form, which clearly distinguished several intervals where annular cement complied with the various technical and legal variables that the client adopted.By eliminating the inconclusive nature inherent to cement evaluation, the new interpretation solution can rapidly serve operators with a simplified result, enabling faster decision making to determine whether or not remedial work is required. This routine can be especially valuable to asset decommissioning and new well drilling, where more assertive decisions regarding well-barrier integrity can result in operational efficiencies.