The minimum testing time determination for wireline formation tester applying tolow porosity/low permeability formation

摘要

The wireline formation tester (WFT) is a very importanttool for formation evaluation, such as calculatingformation pressure and permeability, identifying fluidtype, and determining the interface between oil andwater. However, in low porosity /low permeabilityformation, the supercharge pressure effect exists as themudcake has poor sealing ability. The mudcake cannotisolate the hydrostatic pressure of the formation aroundthe borehole and the mud seeps into the formations,leading to inaccurate formation pressure measurement.At the same time, the tool can be easily stuck in the lowporosity/low permeability formation due to the longwaiting and testing time.We present a method for determining the minimumtesting time for the wireline formation tester. Thepressure distribution of the mudcake and the formationwere respectively calculated with the finite elementmethod (FEM). The radius of influence of the mudpressure was also computed, and the minimum testingtime in low porosity/low permeability formation wasdetermined with a range of values for differentformation permeabilities. The determination of theminimum testing time ensures accurate formationpressure measurement and avoids possible accident dueto long waiting and testing time.