Apparatus and method for well logging utilizing associate particle imaging

Abstract

An apparatus for performing an operation in a borehole penetrating the earth includes a borehole tool and a neutron source within the borehole tool that emits neutron-alpha particles pairs as the result of a nuclear reaction. The apparatus also includes an alpha particle detector within the borehole tool arranged to detect when an alpha particle emitted by the neutron source strikes it and a gamma ray detector to detect gamma rays produced as a result of interactions between neutrons produced by the neutron source and at least one material in an area of interest outside of the borehole. The apparatus also includes a processing system that determines a characteristic of the area of interest based on a time difference between when the alpha particle strikes the alpha particle detector and a time when one or more gamma rays strikes the gamma ray detector.

What is claimed is: 
     
         1 . An apparatus for performing an operation in a borehole penetrating the earth, the apparatus comprising:
 a borehole tool having a neutron source that emits neutron-alpha particles pairs as the result of a nuclear reaction;   a plurality of alpha particle detectors associated with the borehole tool, each arranged to detect alpha particles emitted by the neutron source;   a gamma ray detector to detect gamma rays produced as a result of interactions between neutrons produced by the neutron source and an element in a formation outside of the borehole; and   a processing system that determines a vertical component of the element in the formation based on a relationship between alpha particles detected by different ones of the plurality of alpha particle detectors.   
     
     
         2 . The apparatus of  claim 1 , wherein the plurality of alpha particle detectors are formed by circular rings. 
     
     
         3 . The apparatus of  claim 2 , wherein the plurality of alpha particle detectors are concentric. 
     
     
         4 . The apparatus of  claim 1 , wherein plurality of alpha particle detectors are formed as azimuthal sections. 
     
     
         5 . The apparatus of  claim 1 , wherein the plurality of alpha particle detectors are formed by one or more flat plates. 
     
     
         6 . The apparatus of  claim 1 , wherein the plurality of alpha particle detectors and the neutron source are axially disposed within the borehole tool. 
     
     
         7 . The apparatus of  claim 1 , wherein the plurality of alpha particle detectors and the neutron source are non-axially disposed within the borehole tool. 
     
     
         8 . The apparatus of  claim 1 , further comprising:
 a mud channel disposed within the borehole tool.   
     
     
         9 . The apparatus of  claim 1 , further comprising:
 a plurality of mud channels disposed within the borehole tool and about central axis of the borehole tool.   
     
     
         10 . The apparatus of  claim 9 , wherein the plurality of alpha particle detectors are arranged to detect alpha particles related to neutrons that do not traverse any of the plurality of mud channels. 
     
     
         11 . The apparatus of  claim 1 , in combination with a drill bit configured to drill into the borehole. 
     
     
         12 . The apparatus of  claim 11 , wherein the gamma ray detector is located within the drill bit. 
     
     
         13 . The apparatus of  claim 1 , wherein the plurality of alpha particle are disposed within the borehole tool. 
     
     
         14 . The apparatus of  claim 1 , wherein the gamma ray detector is disposed within the borehole tool.