Improved Casing Integrity Evaluation Enables Multiple Strings Metal-Loss Profilling in Aging Wells

Abstract

BNX field is a mature oil field with complex wells targeting multiple reservoirs across the field. The introduction of an Enhanced Oil Recovery (EOR) project has set a new challenge on determining the integrity of aging wells. In the past, comprehensive downhole casing integrity testing was rarely done with the exception of conventional pressure integrity checks. Such methods may have limited effectiveness in analyzing wells with multiple strings and complex completion configuration, and cannot precisely locate or quantify the magnitude of metal loss. Convention is to run a Multi-fingered caliper inspection tool to evaluate the single tubing inner metal loss, but again this has limited value as it could not measure tubing thickness or more importantly the condition of the casing behind the tubing. A solution was needed that could allow the evaluation of tubing and casing to be done offline and simutaniously. An innovative approach with a combination of slim-hole ultrasonic borehole imaging tool and electromagnetic imaging tool is deployed to provide a new insight in the casing integrity evaluation in the field of study. The idea being that the borehole imager would accurately describe the tubing string while the electromagnetic tool would describe the total metal, both tubing and casing, subtracting the tubing thickness from the total metal measured would then leave an accurate measurement of the casing thickness. Three well candidates were identified, each well was planned for a sidetrack, but before moving a rig onto these old wells the team wanted to know if the 9 5/8? casing was in good enough condition to use. And for the first time, the thickness of multiples strings up to 13.375 inch casing was evaluated simultaneously utilizing a low frequency electromagnetic and a high resolution ultrasonic measurement. The ultrasonic tool provides comprehensive metal loss evaluation for inner most string while the electromagnetic tool provided the total metal thickness of both strings. The combined interpretation of these two through-tubing evaluation outputs provides a viable technique to evaluate metal loss profile for first two strings under study without the need to pull the inner most string. The overall casing evaluation operation is further optimized by the maiden deployment of an e-line light weight unit. The successful application of this newly integrated casing integrity evaluation technology has greatly reduced the intervention related risks, costs and time. The case study presented will serve as the critical pilot to extend the same workflow to other wells across the field. In addition it paves the way for the next generaltion of EM and slim ultrasonic tools discussed at the end of the paper.