Borhole correction of formation photoelectric factors

A logging tool comprising:

• a logging tool body;
• a gamma ray source in the logging tool body;
• at least one gamma ray detector spaced apart from the gamma ray source in the logging tool body;
• and
• a processor configured to:
• cause the at least one gamma ray detector to detect gamma rays corresponding to gamma rays emitted by the gamma ray source while the logging tool rotates in a borehole;
• process the detected gamma rays to compute a photoelectric factor image including a photoelectric factor measurement in each of at least first and second azimuthal sectors in the borehole;
• and
• process a system of equations that relates the photoelectric factor image to a photoelectric factor of a formation through which the borehole penetrates and a photoelectric factor of drilling fluid in the borehole to compute the photoelectric factor of the formation and the photoelectric factor of the drilling fluid.

A method for making borehole corrected photoelectric logging measurements, the method comprising:

• rotating a logging tool in a deviated borehole such that the logging tool is eccentered in the deviated borehole, the logging tool including a gamma ray source and at least one gamma ray detector, the borehole including drilling fluid therein and penetrating a formation;
• emitting gamma rays into the deviated borehole using the gamma ray source while the logging tool rotates in the deviated borehole;
• causing the at least one gamma ray detector to detect gamma rays corresponding to the emitted gamma rays;
• processing the detected gamma rays to compute a photoelectric factor image including a photoelectric factor measurement in at least first and second azimuthal sectors in the borehole;
• repeating the causing the at least one gamma ray detector to detect gamma rays and the processing the detected gamma rays at a plurality of depths in the borehole to generate a log including a photoelectric factor image at each of the plurality of depths;
• depth shifting the photoelectric factor measurements in at least one of the first and second azimuthal sectors in the log to generate a depth shifted log;
• and
• processing a system of equations that relates the depth shifted log at each of the plurality of depths to a photoelectric factor of the formation and a photoelectric factor of the drilling fluid to compute a log of the photoelectric factor of the formation and a log of the photoelectric factor of the drilling fluid.