CPC G01V 5/06 (2013.01) | 19 Claims |
1. A method for making natural gamma ray measurements of a subterranean formation, the method comprising:
(a) circulating drilling fluid through a logging while drilling string deployed in a subterranean wellbore, the logging while drilling string including a neutron source and a natural gamma ray sensor;
(b) causing the neutron source to emit neutrons while circulating in (a);
(c) causing the natural gamma ray sensor to acquire a spectral gamma ray measurement while the neutron source emits neutrons in (b);
(d) fitting the gamma ray measurement made in (c) to standard spectra to determine a total drilling fluid activation count, at least one of the standard spectra being an oxygen activation spectrum;
(e) processing the total drilling fluid activation count to compute a first drilling fluid activation correction in a first time interval;
(f) processing a count of the gamma ray measurement above at least one predetermined energy threshold to compute a second drilling fluid activation correction in a second time interval;
(g) processing a weighted average of the first drilling fluid activation correction and the second drilling fluid activation correction to computing a third drilling fluid activation correction; and
(h) applying the third drilling fluid activation correction to the gamma ray measurement to obtain a corrected total natural gamma ray measurement.
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