Reservoir fluid sampling is important for reservoir characterization and management. When sampling formation water or hydrocarbons with wireline formation testers in wells drilled with WBM and SBM respectively, it is important to track mud filtrate contamination by distinguishing between formation fluid and mud filtrate. Current techniques for water sampling are mainly qualitative, either readings by stations or require coloring the mud and could be affected by temperature. While for hydrocarbon sampling a wider set of downhole fluid analyzers exist to address the more complex nature of the reservoir hydrocarbons. We present a solution that allows continuous monitoring of the formation fluid sampling cleanup process using a fluorescent tracer added to the mud systems while drilling the zone of interest by means of a downhole fluorescence sensor of a wireline formation test string. Prejob calibrations allowed us to interpret the fluorescence sensor’s reading, considering that the formation water is free of fluorescence response and any response will indicate the presence of filtrate in the flowing fluid. For the hydrocarbons sampling, since the formation hydrocarbons have components with natural fluorescence, the tracer solution is applicable but the tracer needs to have a clearly different fluorescence response compared to the formation fluids to indicate the presence of filtrate or by using the fluorescence of the reservoir hydrocarbon when it is well distinguished from the SBM filtrate fluorescence response. The fluorescent tracers identified for these processes were found appropriate for this task because they are detectable at very low concentrations during qualification tests. Additionally, no tracer absorption issues were detected in the reservoir or pressure and temperature limitations on the cases studied. Field examples compared with laboratory results that confirm the success of this real-time monitoring solution are presented for heterogeneous offshore conditions. Complimentary, best practices for selection of sampling stations and formation testers were improved.

Technical Paper presented at Rio Oil & Gas Expo and Conference 2012, held between September 17-20, 2012, in Rio de Janeiro.