ANALYSIS OF DOWNHOLE FORMATION FLUID CONTAMINATED BY OIL-BASED MUD

摘要

A method and apparatus is provided for determining a quality of downhole fluid. A series of measurements are taken of at least one parameter of borehole fluid that is indicative of oil-based mud filtrate contamination. By curve-fitting, the series of the measured parameter values are used to create an asymptotic curve indicative of the quality of the downhole fluid. One embodiment determines oil-based mud filtrate fraction in a borehole fluid sample. Another is used when there is little or no difference between the coloration of formation fluid and the coloration of OBM filtrate. Another determines gas-oil ratio of formation fluid corrected for oil-based mud filtrate contamination. Another determines the optical density of formation fluid corrected for oil-based mud filtrate contamination. Another determines conditions that would render optical density measurements invalid and sample capture premature. Another predicts the reduction of filtrate fraction for a specific extended pumping time. Another initiates sample capture when computed contamination fraction exhibits stable asymptotic convergence.