Time-gated energy spectra for removal of borehole capture background
A method and systems for taking downhole measurements. The method may include selecting a pulsing scheme for taking one or more measurements using a pulsed neutron logging tool, selecting a neutron burst width for the pulsing scheme based at least in part on a neutron tube utilized by the pulsed neutron logging tool to form at least in part a neutron burst train, and selecting a decay window in which the one or more measurements are performed by the pulsed neutron logging tool. The method may further include selecting a starting time for a late gate in which the one or measurements are taken, disposing the pulsed neutron logging tool into a borehole, performing the neutron burst train with the pulsed neutron logging tool, and performing the one or more measurements with the pulsed neutron logging tool during the late gate.
1 . A method comprising:
selecting a pulsing scheme for taking one or more measurements using a pulsed neutron logging tool;
selecting a neutron burst width for the pulsing scheme based at least in part on a neutron tube utilized by the pulsed neutron logging tool to form at least in part a neutron burst train;
selecting a decay window in which the one or more measurements are performed by the pulsed neutron logging tool;
selecting a starting time for a late gate in which the one or measurements are taken;
disposing the pulsed neutron logging tool into a borehole;
performing the neutron burst train with the pulsed neutron logging tool; and
performing the one or more measurements with the pulsed neutron logging tool during the late gate.
2 . The method of claim 1 , wherein a width of the decay window a time between an end of the neutron burst train and a beginning of a second neutron burst train.
3 . The method of claim 1 , further comprising selecting a starting time for an early gate in the decay window that is initiated immediately after the last burst of the neutron burst train.
4 . The method of claim 3 , further comprising selecting a width for the early gate.
5 . The method of claim 4 , further comprising creating a time-gated energy spectrum from the one or more measurement within the early gate.
6 . The method of claim 5 , wherein the early gate has a duration of 200 microseconds.
7 . The method of claim 1 , wherein the starting time for the late gate is after an early gate.
8 . The method of claim 7 , wherein the late gate is initiated about 400 microseconds after the early gate ends.
9 . The method of claim 7 , further comprising selecting a width for the late gate.
10 . The method of claim 9 , further comprising creating a time-gated energy spectrum which is acquired during the late gate.
11 . A system comprising:
a pulsed neutron logging tool comprising:
a neutron tube disposed in a pulsed neutron generator;
one or more gamma ray scintillator detectors; and
one or more thermal neutron detectors; and
an information handling system in communication with the pulsed neutron logging tool and configured to:
select a pulsing scheme for taking one or more measurements using a pulsed neutron logging tool;
select a neutron burst width for the pulsing scheme based at least in part on a neutron tube utilized by the pulsed neutron logging tool to form at least in part a neutron burst train;
select a decay window in which the one or more measurements are performed by the pulsed neutron logging tool;
select a starting time for a late gate in which the one or measurements are taken;
select a time for a late time gate that is initiated after the neutron burst train in which one or more measurements may be performed;
instruct the neutron tube to emit a neutron burst train; and
instruct the one or more gamma ray scintillator detectors or the one or more thermal neutron detectors to perform one or more measurements during the late time gate.
12 . The system of claim 11 , wherein a width of the decay window a time between an end of the neutron burst train and a beginning of a second neutron burst train.
13 . The system of claim 11 , wherein the information handling system is further configured to select a start time for an early gate in the decay window that is initiated immediately after the last burst of the neutron burst train.
14 . The system of claim 13 , wherein the information handling system is further configured to select a width for the early gate.
15 . The system of claim 14 , wherein the information handling system is further configured to create a time-gated energy spectrum from the one or more measurement within the early gate.
16 . The system of claim 15 , wherein the early gate has a duration of 200 microseconds.
17 . The system of claim 11 , wherein the start time for the late gate is after an early gate.
18 . The system of claim 17 , wherein the late gate is initiated about 400 microseconds after the early gate ends.
19 . The system of claim 17 , wherein the information handling system is further configured to select a width for the late gate.
20 . The system of claim 19 , wherein the information handling system is further configured to create a time-gated energy spectrum which is acquired during the late gate.