Method and apparatus for measuring underground fluid flow characteristics

A method for determining the characteristics of flow of earth formation fluid, moving horizontally past a borehole, comprising the steps of:

• (a) irradiating the formation fluid with neutrons from a neutron source positioned within the borehole;
• (b) providing a gamma ray detector;
• (c) providing a shield at least partially enclosing said detector, said shield being equipped with a slot through which said detector may be exposed to radiation, and said shield being rotatable to vary the angle of orientation of rotation of said slot relative to said detector and providing a means for detecting the direction of the orientation of said shield with respect to a fixed reference direction;
• (d) exposing said detector, through said slot, to radiation from the neutron-irradiated formation fluid to acquire count rate data from said detector as said shield is being so rotated;
• and
• (e) comparing said count rate data from said detector with the instantaneous angles of orientation of said slot as said data was acquired to determine the direction of movement of said formation fluid.