Method and apparatus for measuring underground fluid flow characteristics
 An underground logging tool is equipped with a gamma ray detector encircled by a rotatable shield featuring a collimator slot. After the fluid in a formation is activated by a neutron source, the detector is used to obtain radiation count information as a function of horizontal direction as the shield is rotated. Comparison of count rate data as a function of the shield slot orientation gives information concerning the direction of the formation fluid flow. Measurements at different time intervals following the activation of the fluid, made with the shield retracted from the detector, may also be interpreted in terms of speed of horizontal fluid flow past the tool. 
Texaco Inc.
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Albert P. Hans J. Dan M. Harold E. Hubert D.
Richter, Jr. Paap Arnold Peelman Scott