In situ measurements of mud cake properties and filtration rate are difficult to implement with conventional drilling and logging equipment. The wimline formation tester (WFI) can be used to measure the filtrate flowrate before performing a test Once the WFT is set at a given formation depth, the flowline of the WFT is isolated from the borehole mud. The flowline pressure is usually higher than the sandface pressure. The flowline pressure can actually be made equal to the mud pressure through the equalizing valve. A filtrate flow occurs through the mud cake trapped inside the WFT pad and results in a pressure decrease inside the flowline. This pressure decrease can be converted into a filtrate flowrate through the mud cake.