Lessons Learned from In-well Fiber-optic DAS/DTS Deployment

Abstract

Abstract Fiber-optic sensing technology has gradually become one of the pervasive tools in the monitoring and surveillance toolkit for reservoir and production engineers. Traditionally, sensing with fiber optic technology in the form of distributed temperature sensing (DTS) or distributed acoustic sensing (DAS), and most recently distributed strain sensing (DSS) and distributed chemical sensing (DCS), were done with the fiber being permanently clamped either behind the casing or production tubing. Clamping the fiber behind tubing or casing is sometimes beleaguered with operational challenges that often lead to rendering the fiber partially damaged or inoperable. The emergence of the composite carbon-rod (CR) system that can be easily deployed in and out of a well, similarly to wireline logging, has made it possible to sense any well without prior fiber-optic installation. In this paper, we present the lessons learned from the first well where we deployed in-well fiber-optic DAS/DTS. The DAS/DTS sensing was done in a few vertical oil producer wells and water injector wells without prior fiber-optic installation. The key objectives of the tests were to (1) investigate any well integrity across the entire length of each well, (2) assess production and injection flow profile across the perforations and behind casing, which hitherto was not possible with conventional production logging tool (PLT) tool, and (3) investigate the possibility of using the combination of distributed acoustic survey and distributed temperature survey for quantitative production flow analysis. This paper reviews the complete design and implementation of the in-well fiber-optic deployment, field operational issues, analyses, and interpretation of the sensing results. The combination of DAS/DTS data showed no well integrity related issues. The sensing data surprisingly pinpointed a few geological features such as cooling shallow aquifers that hitherto had not been noticed. The combination of different pulse widths during shut-in and production/injection cycles helped to refine the resolution of the flow profile from the production and injection zones.