The design of wireline formation testers (WFT) features a flowline full of drilling fluid. The compressible drilling mud in the flowline results in a "flowline storage effect" (FLSE) similar in nature to the well bore storage effect.

This paper presents a 3-D analytical model that includes the FLSE. The model is used to investigate the importance of this effect and its impact on pressure response. It shows that the response of the WFT is a combination of fluid decompression in the flowline and flow from the formation. Due to decompression of drilling mud in the flowline, the sandface flow rate is not constant and gradually increases from zero to the piston displacement rate. Slow pressure buildup observed in some field tests is partially due to the FLSE.

A laboratory experimental setup is used to investigate the effect of different parameters on the WFT response. Type curves based on the FLSE model are constructed and result in permeability values that are in good agreement with measured values.

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