In-well hydraulics of the electromagnetic borehole flowmeter

Previous studies have suggested that head losses associated with the application of the electromagnetic borehole flowmeter (EBF) can have important and detrimental effects on the use of the instrument for measurement of hydraulic conductivity (K) profiles. Head losses associated with now through the meter may cause bypass flow around the packer if the well is gravel packed. In any type of well, changing head losses with meter position can cause changes in flow into the well that are not related directly to the K distribution. Such flow changes, or redistribution, can cause errors in the calculation of the K profile. Numerical simulations, based on measured head losses, indicate that bypass now in gravel packed systems increases with increasing flow rate through the meter, increasing gravel pack conductivity, and increasing gravel pack thickness. Ideally, the EBF should not be used in gravel packed wells, due to the occurrence of bypass flow. Investigations into the flow redistribution phenomenon indicate that the top portion of the aquifer is where the greatest overestimation of K occurs. The portion of the well below the flowmeter is isolated from the observed drawdown as measured from the surface. In this region, the well experiences a reduced drawdown, which differs from the observed drawdown by an amount equal to the head loss at that meter position. Flow redistribution causes a more pronounced effect in more highly conductive mediums and may be almost negligible in mediums of low conductivity.