instrument measures the fluid motion in the pore space using nuclear magnetic resonance methods any type of instrument that can generate a pressure gradient is suitable including instruments that are remote from the nmr instrument magnetic field gradients can be used to localize the nmr signal to a specific region within the porous medium the magnetic field gradient also provides the method by which the fluid motion is encoded on to the nmr signal the permeability is calculated from the known pressure gradient present in the porous medium by virtue of the applied pressure gradient or pressure wave and the velocity of the fluid in the rock pore space as measured by nmr application_number US 87111504 A description the invention disclosed here describes methods that determine formation permeability by measuring nmr signals that respond to pressure gradients created by acoustic stimulation in the bore hole these pressure gradients create motion of fluids in the rock pore space of the rocks in the formation surrounding the bore hole in the case of hydraulic contact between the fluid in the borehole and the fluid in the formation rock the displacement of the fluid in the borehole creates the displacement of the fluid in the formation rock this is frequently referred to as the squirt boundary condition motion of the fluid in the formation rock can also be created when there is no direct hydraulic contact between the fluid in the borehole and the fluid.