Determination of formation water salinity using time resolved chlorine capture gamma spectroscopy

Patent metadata

Field	Value
Publication number	US-12326536-B2
Application number	US-202318300649-A
Country	US
Kind code	B2
Filing date	Apr 14, 2023
Priority date	Apr 14, 2023
Publication date	Jun 10, 2025
Grant date	Jun 10, 2025

Abstract

Methods and systems for determining formation salinity using pulsed neutron (PN) tools are described. Embodiments of the described methods involve binning chlorine yields or chlorine count rates arising from capture events into early and late capture regimes, which may be used to attribute the events to either the borehole or the formation.

First claim

What is claimed is:

1. A method of determining salinity of water in a formation traversed by a borehole using a pulsed neutron (PN) tool deployable in the wellbore, wherein the PN tool comprises a source configured to issue bursts of fast neutrons, thereby irradiating the borehole and the formation with neutrons, and at least one detector configured to detect gamma photons resulting from the irradiating and arriving at the detector, the method comprising:
(i) receiving data from a first of the at least one of the detectors, wherein the data comprises a time spectrum of gamma photon counts, wherein the time spectrum comprises a burst duration comprising photon counts detected while the source is actively issuing fast neutrons and a capture duration comprising photon counts detected while the source is not actively issuing fast neutrons,
(ii) binning the data into a first plurality of bins comprising gamma photon counts arising during a first duration of the time spectrum and a second plurality of bins comprising gamma photon counts arising during a second duration of the time spectrum, and
(iii) using the first and second pluralities of bins to calculate the salinity.

2. The method of claim 1 , wherein the time spectrum further comprises:
a sigma decay duration comprising photon counts arising from sigma decay, and
a background duration comprising photon counts arising from background radiation.

3. The method of claim 2 , wherein the first and second pluralities of bins each comprise gamma photon counts detected during the capture duration.

4. The method of claim 1 , wherein the first plurality of bins comprises gamma photon counts arising during an early portion of the capture duration and the second plurality of bins comprises photon counts arising during a later portion of the capture duration, wherein the later portion is later in time than the early portion.

5. The method of claim 4 , wherein a majority of photon counts of the first plurality of bins result from irradiation of the borehole and wherein a majority of photon counts of the second plurality of bins result from irradiation of the formation.

6. The method of claim 1 , wherein calculating the salinity comprises determining the fractional contributions of the gamma photon counts of the first and second pluralities bins, respectively, to the total number of capture gamma photon counts.

7. The method of claim 6 , wherein the fractional contribution of the gamma photon counts of the first plurality of bins is determined using the formula:

ECB_Frac
=

ECB
/

(

ECB
+

L
⁢
CB

)

,

where ECB_Frac is the fractional contribution of the gamma photon counts of the first plurality of bins, ECB is the gamma photon counts of the first plurality of bins, and LCB is the gamma photon counts of the second plurality of bins, and wherein the fractional contribution of the gamma photon counts of the second plurality of bins is determined using the formula:

LCB_Frac
+

LCB
/

(

ECB
+
LCB

)

,

where LCB_Frac is the fractional contribution of the gamma photon counts of the second plurality of bins.

8. The method of claim 7 , wherein calculating the salinity comprises determining a formation effect according to the formula:

Formation
⁢

Effect

=

1
-

(

ECB_Frac
/
LCB_Frac

)

.

9. The method of claim 8 , wherein calculating the salinity comprises determining a formation factor by normalizing the formation effect over a logged interval using the PN tool according to the formula:

Formation
⁢

Factor

=

abs
⁡
(

Min_Formation
⁢

Effect

)

/



⁢

(

abs
⁢

(

Min_Formation
⁢

Effect

)

+



⁢



Max_Formation
⁢

Effect

)

where Min_Formation Effect is the minimum formation effect determined over the logged interval and Max_Formation Effect is the maximum formation effect determined over the logged interval.

10. The method of claim 1 , wherein calculating the salinity comprises using an energy spectrum of capture gamma photons to spectrographically determine a chlorine yield.

11. The method of 9 , wherein calculating the salinity comprises determining a chlorine yield attributable to the formation according to the formula:

FM_Chlorine
=

(

Chlorine
⁢

Yield

Assignees

• Weatherford Tech Holdings Llc

Inventors

• Mekic Natasa
• Pemper Richard
• Schmid Gregory

Classifications

• G01V5/102 Primary

  the neutron source being of the pulsed type · CPC title