Drilling fluid activation correction methodolgy
AssigneeSchlumberger Technology Corporation
InventorsMarie-Laure Mauborgne, Christian Stoller
Life of this patent
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Abstract
A method for making natural gamma ray measurements of a subterranean formation includes causing a natural gamma ray sensor on an LWD tool to acquire a spectral gamma ray measurement while a neutron source emits neutrons. The measurements are evaluated to compute first and second drilling fluid activation corrections using corresponding first and second correction methodologies. The first and second corrections are processed to compute a third drilling fluid activation correction which is applied to the gamma ray measurements to compute a corrected total natural gamma ray measurement.
Claims20
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;
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- (h) applying the third drilling fluid activation correction to the gamma ray measurement to obtain a corrected total natural gamma ray measurement.
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) evaluating the gamma ray measurement over a first accumulation interval to extract (i) a total gamma ray count and (ii) a gamma ray count above a predetermined energy threshold;
- (e) evaluating the gamma ray measurement over a second accumulation interval to fit the gamma ray measurement to standard spectra including at least first and second oxygen activation spectra corresponding to oxygen activation gamma rays emitted by activated drilling fluid circulating inside and outside the logging tool;
- (f) computing first and second oxygen activation counts from said fit in (e), the first and second oxygen activation counts corresponding to the oxygen activation gamma rays emitted by activated drilling fluid circulating inside and outside the logging tool;
- (g) processing the first and second oxygen activation counts computed in (f) to compute a modified R value;
- (h) processing (i) the total gamma ray count and (ii) the gamma ray count above the predetermined energy threshold extracted in (d) in combination with the modified R value to compute an oxygen activation correction;
- and
- (i) applying the oxygen activation correction to the gamma ray measurement to obtain a corrected gamma ray measurement.
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 natural gamma ray sensor to acquire a spectral gamma ray measurement;
- (c) evaluating the gamma ray measurements acquired in (b) to compute first and second drilling fluid activation corrections using corresponding first and second correction methodologies;
- (d) processing the first and second drilling fluid activation corrections to compute a third drilling fluid activation correction;
- and
- (e) applying the third drilling fluid activation correction to the gamma ray measurements made in (b) to compute a corrected total natural gamma ray measurement.
Dependencies are inferred from the claim text.