Focused sampling of reservoir fluids achieves undetectable levels of contamination

A new generation of sampling technology is introduced which allows a Wireline Formation Tester to sample reservoir fluids in open-hole with levels of filtrate contamination that are below measurable limits, in many cases. Furthermore, the time required on station to cleanup before sampling is significantly reduced compared to conventional sampling methods. Formation fluid sampling has always been adversely affected by mud filtrate contamination, which introduces errors into the laboratory analysis and requires analytical methods to back-calculate the measured properties to the uncontaminated reservoir fluid. The ability to secure a totally clean sample of formation fluid at reservoir conditions is a significant advance, that replaces the need for sampling during Drill Stem Tests and provides accurate fluid information for characterization of the reservoir, flow assurance, facility design, production strategies, and defining reserves. The application of this new focused sampling technology is presented using four case studies from wells drilled on the Norwegian Continental Shelf. A wide range of formation fluids and permeabilities are examined, in both oil-based and water-based drilling fluids. Results from focused sampling are compared directly with conventional sampling in the same reservoir zones. This study also gives insight into the cleanup dynamics of invaded filtrate, and explores the different factors that affect performance of the focused sampling technique. An important consequence of negligible contamination is the ability to accurately measure fluid properties in-situ. And reduced cleanup time allows for multiple zones to be scanned efficiently. Downhole Fluid Analysis (DFA) can thus be utilized to reveal reservoir architecture that is unable to be determined by traditional wireline logs.