Pulsed neutron spectral oxygen logging for 2-phase and 3-phase saturation determination

Abstract

A process (200) for the determination of 2-phase and 3-phase saturations using oxygen count rates obtained using a downhole tool (102). A 2-phase saturation measurement of gas and wet (oil-water) separation may be determined (210) using short space (SS) and long space (LS) oxygen count ratio and porosity. A 2-phase saturation measurement of oil and water-gas separation may be determined (214) using a normalized short space (SS) or long space (LS) oxygen count rate, and a short space (SS) and long space (LS) oxygen count ratio. The 2-phase saturation determinations may be combined to determine (216) a 3-phase determination.

Description

Attorney Docket No.: 610NUK-510438-WO-2 (000250)PULSED NEUTRON SPECTRAL OXYGEN LOGGING FOR2-PHASE AND 3-PHASE SATURATION DETERMINATION CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to and the benefit of U. S. Provisional Application No. 63 / 735,085, filed December 17, 2024, and titled “PULSE NEUTRON SPECTRAL OXYGEN LOGGING FOR2-PHASE AND 3-PHASE SATURATION DETERMINATION.”BACKGROUNDField of the Disclosure

[0002] The present disclosure generally relates to wellbore logging. More specifically, embodiments of the disclosure relate to using a pulsed neutron spectral oxygen logging to determine 2-phase and 3-phase saturations of downhole fluids.Description of the Related Art

[0003] Wellbore (also referred to as “well”) logging systems are typically used in hydrocarbon exploration. Such systems provide data for use by geologists and petroleum engineers in making determinations relating to tire extraction and production of hydrocarbons from hydrocarbon-bearing reservoirs. These systems may include different types of tools and instruments that are disposed in a wellbore to perform various tasks and measurements. Such tools and instruments may include resistivity tools, gamma density tools, neutron porosity tools, sonic and acoustic logging tools, and pulsed neutron tools. Pulsed neutron measurement tools are utilized in downhole environments for a variety of purposes, such as neutron based formation density and porosity measurements, and neutron induced gamma-ray spectral measurements. Pulsed neutron tools typically include a nuclear radiation source and associated nuclear radiation detectors that are conveyed into the wellbore via a rigid or non-rigid conveyance device.SUMMARY

[0004] The most common pulsed neutron measurement technique relies on the cross section for tire absorption of thermal neutrons by a substance and is referred to as a “sigma” measurement. Logs produced by this technique are referred to as sigma logs. Although these sigma measurements may be recorded at relatively fast speeds, the measurements are most effective in situations of relatively high water salinity. Use of sigma measurements are-1- IM-#10933321.1Attorney Docket No.: 610NUK-510438-WO-2 (000250)increasingly ineffective with decreasing water salinity because the thermal neutron attenuation cross section of fresh water is comparable to oil cross sections, thus rendering oil / water separation practically impossible.

[0005] In relatively low water salinity environments, an alternative pulsed neutron measurement technique for determining saturation is carbon / oxygen (C7O) logging. However, C / 0 logging has a relatively slow' logging speed and requires multiple passes for saturation determination. Other saturation determination techniques exist but are limited to gas saturation or require a combination with C / 0 logging and is subject to its limitations.

[0006] Embodiments of the disclosure generally relate to the determination of 2-phase and 3 -phase saturations using an oxygen count measurement obtained from a downhole tool. The embodiments describes in the disclosure provide effective 2-phase and 3-phase saturation determinations that are not limited by water salinity levels and relatively slow logging speeds.

[0007] Disclosed herein is a method of determining a saturation of a formation. The method includes obtaining inelastic energy spectra through a downhole tool inserted in a wellbore of a well accessing a formation, the downhole tool having a pulsed neutron source, a first detector and a second detector, and the inelastic energy spectra including a first inelastic energy spectrum obtained through the first detector and a second inelastic energy spectrum obtained through the second detector, such that the first detector is a short space (SS) detector. The method also includes determining a first oxygen count rate from the first inelastic energy¬ spectrum and determining a second oxygen count rate from the second inelastic energy spectrum. The method further includes determining a ratio of the first oxygen count rate to the second oxygen count rate and determining a 2-phase gas in oil -water saturation using the ratio of the first oxygen count rate to the second oxygen count rate and a porosity of the formation. The second detector may be a long space (LS) detector or an extra long space (XLS) detector. Determining a first oxygen count rate from the first inelastic energy spectrum optionally includes deconvolving the first inelastic energy spectrum into a first oxygen spectrum, determining a first oxygen yield from the first oxygen spectrum, and converting the first oxygen yield into the first oxygen count rate. Additionally, determining a second oxygen count rate from the second inelastic energy spectrum optionally includes deconvolving the second inelastic energy spectrum into a second oxygen spectrum, determining a second oxygen yield from the second oxygen spectrum, and converting the second oxygen yield into the secondIM-#10933321.1Attorney Docket No.: 610NUK-510438-WO-2 (000250)oxygen count rate. The method also optionally includes inserting the downhole tool into the wellbore.

[0008] Also disclosed is another method of determining a saturation of a formation. The method includes obtaining inelastic energy spectra through a downhole tool inserted in a ■wellbore of a well accessing a formation, the downhole tool having a pulsed neutron source, a first detector and a second detector and the inelastic energy spectra including a first inelastic energy spectrum detected by the first detector and a second inelastic energy spectrum detected by the second detector, such that the first detector is a short space (SS) detector. The method includes determining a first oxygen count rate from the first inelastic energy spectrum and determining a second oxygen count rate from tire second inelastic energy spectrum. The method also includes determining a ratio of the first oxygen count rate to the second oxygen count rate, and determining a 2-phase oil in water-gas saturation using a normalized first oxygen count rate or a normalized second oxygen count rate, and the ratio of the first oxygen count rate to the second oxygen count rate. The second detector may be a long space (LS) detector or an extra long space (XLS) detector. Determining a first oxygen count rate from the first inelastic energy spectrum optionally includes deconvolving the first inelastic energy¬ spectrum into a first oxygen spectrum, determining a first oxygen yield from the first oxygen spectrum, and converting the first oxygen yield into the first oxygen count rate. Additionally, determining a second oxygen count rate from the second inelastic energy spectrum optionally includes deconvolving the second inelastic energy spectrum into a second oxygen spectrum, determining a second oxygen yield from the second oxygen spectrum, and converting the second oxygen yield into the second oxygen count rate. The method also optionally includes inserting the downhole tool into the wellbore. Tire method may include normalizing the first oxygen count rate to a porosity with a known saturation to determine the normalized first oxygen count rate. Additionally, the method may include normalizing the second oxygen count rate to a porosity with a known saturation to determine the normalized second oxygen count rate.

[0009] Additionally, another method of determining a saturation of a formation is provided. The method includes obtaining inelastic energy spectra through a downhole tool inserted in a wellbore of a well accessing a formation, the downhole tool having a pulsed neutron source, a first detector and a second detector, and the inelastic energy spectra including a first inelastic energy spectrum obtained through the first detector and a second inelastic energy spectrum-3- IM-#10933321.1Attorney Docket No.: 610NUK-510438-WO-2 (000250)obtained through the second detector, such that the first detector is a short space (SS) detector. The method also includes determining a first oxygen count rate from the first inelastic energy spectrum and determining a second oxygen count rate from the second inelastic energy¬ spectrum. The method further includes determining a ratio of the first oxygen count rate to the second oxygen count rate and determining a 2-phase gas in oil-water saturation using the ratio of the first oxygen count rate to the second oxygen count rate and a porosity of the formation. The method also includes determining a 2-phase oil in water-gas saturation using a normalized first oxygen count rate and the ratio of the first oxygen count rate to the second oxygen count rate and determining a 3-phase saturation from the 2-phase gas in oil-water saturation and the 2-phase oil in water-gas saturation. The second detector may be a long space (LS) detector or an extra long space (XLS) detector. In some embodiments, the method includes normalizing the first oxygen count rate to a porosity with a known saturation to determine the normalized first oxygen count rate. Determining a first oxygen count rate from the first inelastic energy spectrum optionally includes deconvolving the first inelastic energy spectrum into a first oxygen spectrum, determining a first oxygen yield from the first oxygen spectrum, and converting the first oxygen yield into the first oxygen count rate. Additionally, determining a second oxygen count rate from the second inelastic energy spectrum optionally includes deconvolving the second inelastic energy spectrum into a second oxygen spectrum, determining a second oxygen yield from the second oxygen spectrum, and converting the second oxygen yield into the second oxygen count rate. The method also optionally includes inserting the downhole tool into the wellbore. Tire method may include normalizing the second oxygen count rate to a porosity with a known saturation to determine the normalized second oxygen count rate.BRIEF DESCRIPTION OF THE DRAWINGS

[0010] FIG. 1 is a schematic side-sectional view- of a production well environment in accordance w ith an embodiment of tire disclosure;

[0011] FIG. 2 is a flowchart of a process for determining 2-phase and 3 phase saturations using oxygen count rates obtained through a downhole tool in accordance with embodiments of the disclosure;

[0012] FIGS. 3A-3C depict plots of the SS oxygen count rate / LS oxygen count ratio as a function of porosity (in porosity- units (p.u.)) for various formation lithologies in a 6 inch water borehole in accordance with an embodiment of the disclosure;-4- IM-#10933321.1Attorney Docket No.: 610NUK-510438-WO-2 (000250)

[0013] FIGS. 4A-4C depict plots of the SS oxygen count rate / LS oxygen count ratio as a function of porosity for various formation lithologies in a 6 inch oil borehole in accordance with an embodiment of the disclosure;

[0014] FIGS, 5A-5C depict plots of oxygen count rate as a function of porosity for various lithologies in a 12.25 inch water borehole in accordance with an embodiment of the disclosure;

[0015] FIGS. 6A-6C depict plots of oxygen count rate as a function of porosity for various lithologies in a 12.25 inch oil borehole in accordance with an embodiment of the disclosure;

[0016] FIGS. 7A-7C depict plots of normalized SS oxygen count rate as a function of SS / LS oxygen count rate ratio for various lithologies in a 6 inch water borehole in accordance w ith an embodiment of the disclosure;

[0017] FIGS. 8A-8C depict plots of normalized LS oxygen count rate as a function of SS / LS oxygen count rate ratio for various lithologies in an 6 inch oil water borehole in accordance ■with an embodiment of the disclosure; and

[0018] FIGS. 9 A and 9B depict envelope saturation lines for normalized LS oxygen count rates in accordance with an embodiment of the disclosure.DETAILED DESCRIPTION

[0019] The present disclosure will be described more fully with reference to the accompanying drawings, which illustrate embodiments of the disclosure. This disclosure may, however, be embodied in many different forms and should not be construed as limited to tire illustrated embodiments. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the disclosure to those skilled in the art.

[0020] It is to be further understood that the scope of the present disclosure is not limited to the exact details of construction, operation, exact materials, or embodiments shown and described, as modifications and equivalents will be apparent to one skilled in the art. In the drawings and specification, there have been disclosed illustrative embodiments and, although specific terms are employed, they are used in a generic and descriptive sense only and not for the purpose of limitation.-5- IM-#10933321.1Attorney Docket No.: 610NUK-510438-WO-2 (000250)

[0021] Embodiments of the disclosure include a process for the determination of 2 -phase and 3 -phase saturations using oxygen count rates obtained through a downhole tool. Embodiments may include the determination of a 2 -phase saturation measurement of gas and wet (oil-water) separation (referred to as “gas in oil-water saturation” or “gas and oil-water saturation”) using short space (SS) and long space (LS) oxygen count rate ratio and porosity. Embodiments may also include the determination of a 2 -phase saturation measurement of oil and water-gas separation (referred to as “oil in water-gas saturation” or “oil in water gas¬ saturation”) using a normalized short space (SS) or long space (LS) oxygen count rate and a short space (SS) and long space (LS) oxygen count ratio. The 2 -phase saturation determinations may be combined to determine a 3-phase determination.

[0022] FIG. 1 depicts a production well environment 100 in a side sectional view in accordance with an embodiment of the disclosure. Tire well environment 100 includes an example of a downhole tool 102 that is disposed in a wellbore 104 that intersects a subterranean formation 106. In the example, a string of casing 108 lines wellbore 104, and which can be cemented in place in wellbore 104. Production tubing I 10 is shown inserted within casing 108, However, it should be appreciated that although FIG. 1 depicts a production well environment, embodiments of the disclosure are applicable to other well environments such as drilling, exploration, and development,’

[0023] Downhole tool 102 is disposed within wellbore 104 on a wireline 112 shown extending up to the opening of wellbore 104 and being threaded through a wellhead assembly 114. Optionally, coiled tubing, slick line, cable, or other means may be used for deploying downhole tool 102 within wellbore 104. A controller 116 is shown on surface for communicating with the downhole tool 102. A communication means 118 communicatively couples controller 116 with wellhead assembly 114 and is shown as a hardwired assembly. In other embodiments, the communication means 118 may be wireless, fiber optic, or other means of relaying signals or data communication. In the example of FIG. 1, downhole tool 102 has an outer housing 120 and in which a neutron source 122 is shown provided within its lower end. A series of detectors 124, 126, and 128 are also disposed within housing 120. Thus, the downhole tool 104 may be or be referred to a as pulsed neutron tool. As will be appreciated, neutrons emitted from the neutron source 122 may interact with fluids and other substances and cause the release of gamma radiation received by the detectors 124, 126, and 128.-6- IM-#10933321.1Attorney Docket No.: 610NUK-510438-WO-2 (000250)

[0024] The detector 124 closest to the neutron source 122 may be referred to as a “short space detector" with corresponding measurements from this detector referred to as “short space” measurements. The detector 126 farther away from the neutron source 122 may be referred to as a “long space detector” with corresponding measurements from this detector referred to as “long space” measurements. The detector 128 farthest away the neutron source 122 may be referred to as an “extra long space detector” with corresponding measurements from this detector referred to as “extra long space” measurements. As will be appreciated gamma rays travel through more of the formation to reach the long space detector than they do to reach the short space detector, and through more of the formation to reach the extra long space detector than the long space detector.

[0025] As described in the disclosure the downhole tool 102 may be used in 2 -phase and 3-phase saturation determinations in formations accessed by the wellbore 104 through measurements of oxygen count rates. The determinations include a 2-phase saturation measurement of gas and wet (oil-water) separation and a 2-phase saturation measurement of oil and water-gas separation. These 2-phase saturation determinations may be combined to determine a 3-phase determination.

[0026] FIG. 2 is a process for determining 2-phase and 3 phase saturations using oxygen count rates obtained through the downhole tool 102 in accordance with embodiments of the disclosure. Initially, an inelastic energy spectrum may be obtained using the downhole tool 102 (block 202). For example, as discussed supra, the downhole tool 102 may be lowered into a wellbore of a well (for example, a development well or production well) accessing a formation via a wireline or other mechanism. Spectra measurements may be obtained using the neutron source 122 and detectors 124, 126, and 128, and may be communicated to a controller 116 via communication means 118. Inelastic spectra may be determined by processing the measured spectra. As will be appreciated, each detector 124, 126, and 128 may provide a spectrum measurement that may be referred to as short space (SS), long space (LS), and extra long space (XLS) spectra respectively depending on the detector used,

[0027] Hie inelastic energy spectrum may be deconvolved into individual elements, such as oxygen, carbon, magnesium, hydrogen, silicon, and iron to provide “yields” of each element (block 204). As used herein, the term “yield” refers to the fraction of a specific element spectrum in the normalized total spectrum. The individual elements may include oxygen, carbon, magnesium, hydrogen, silicon, and iron. Other embodiments may include other -7- IM-#10933321.1Attorney Docket No.: 610NUK-510438-WO-2 (000250)elements that contribute to the measured energy spectra. An elemental yield may then be converted into an elemental count rate by multiplying the yield by the total count rate. As shown in FIG. 2, the oxygen yields may be converted into oxygen count rates in this manner (block 206). As will be appreciated, oxygen count rates may be determined for oxygen yields corresponding to the measured spectra form each detector. Thus, embodiments of the disclosure may include short space (SS) oxygen count rates, long space (LS) oxygen count rates, and (XLS) oxygen count rates.

[0028] Next, the ratio of SS oxygen count rate to LS oxygen count rate (referred to as “the SS oxygen count rate / LS oxygen count ratio”) may be determined (block 208) and used in the subsequent determinations of saturations. Each of these determinations are discussed infra.

[0029] in some embodiments, the 2-phase gas in wet (oil-water) saturation may be determined using the SS oxygen count rate / LS oxygen count ratio and a measured porosity of the formation (block 210). The oxygen count rate may be a function of porosity at different lithologies, borehole sizes, pore space fluids, and borehole fluids. For example, FIGS. 3A-3C depict plots of the SS oxygen count rate / LS oxygen count ratio as a function of porosity (in porosity units (p.u.)) for various formation lithologies in a 6 inch water borehole in accordance with an embodiment of the disclosure. FIG. 3A depicts a plot 300 of SS oxygen count rate / LS oxygen count ratio vs porosity for gas, oil, and water in sandstone, FIG. 3B depicts a plot 302 of SS oxygen count rate / LS oxygen count ratio rate vs porosity for gas, oil, and water in limestone, and FIG. 3C depicts a plot 304 of SS oxygen count rate / LS oxygen count ratio vs porosity for gas, oil, and water in dolomite.

[0030] In another example, FIGS. 4A-4C depict plots of the SS oxygen count rate / LS oxygen count ratio as a function of porosity for various formation lithologies in a 6 inch oil borehole in accordance with an embodiment of the disclosure. FIG. 4A depicts a plot 400 of SS oxygen count rate / LS oxygen count ratio vs porosity for gas, oil, and water in sandstone, FIG. 4B depicts a plot 502 of SS oxygen count rate / LS oxygen count ratio rate vs porosity for gas, oil, and water in limestone, and FIG. 4C depicts a plot 404 of SS oxygen count rate / LS oxygen count ratio vs porosity for gas, oil, and water in dolomite.

[0031] In another example, FIGS. 5A-5C depict plots of oxygen count rate as a function of porosity for various lithologies in a 12.25 inch water borehole in accordance with an embodiment of the disclosure. FIG. 5A depicts a plot 500 of SS oxygen count rate / LS oxygen-8- IM-#10933321.1Attorney Docket No.: 610NUK-510438-WO-2 (000250)count ratio vs porosity for gas, oil, and water in sandstone, FIG. 5B depicts a plot 502 of SS oxygen count rate / LS oxygen count ratio rate vs porosity for gas, oil, and water in limestone, and FIG. 5C depicts a plot 504 of SS oxygen count rate / LS oxygen count ratio vs porosity for gas, oil, and water in dolomite.

[0032] In the final example, FIGS. 6A-6C depict plots of oxygen count rate as a function of porosity for various lithologies in a 12.25 inch oil borehole in accordance with an embodiment of the disclosure. FIG. 6A depicts a plot 600 of SS oxygen count rate / LS oxygen count ratio vs porosity for gas, oil, and water in sandstone, FIG. 6B depicts a plot 602 of SS oxygen count rate / LS oxygen count ratio rate vs porosity for gas, oil, and water in limestone, and FIG. 6C depicts a plot 604 of SS oxygen count rate / LS oxygen count ratio vs porosity for gas, oil, and water in dolomite.

[0033] As shown in FIGS. 3A-6C, tire oxygen count rate ratio is generally linear vs. porosity with respect to oil, gas, and water. Moreover, the gas lines in the plots are distinct and separate from the wet (oil-water) lines. Thus, the gas saturation in oil-water may be determined from the oxygen count rates by comparing the oxygen count rate ratios at certain porosities. The porosity may be determined using techniques known in the art, such as acoustic logging, nuclear magnetic resonance logging, other techniques, or combinations thereof.

[0034] Additionally, the process 200 shown in FIG, 2 may include the determination of the 2-phase saturation of oil in water-gas. In some embodiments, the normalized SS oxygen count rate (or normalized LS oxygen count rate) may be determined by normalizing the SS oxygen count rate (or LS oxygen count rate) to a porosity with a known saturation (block 212). In other embodiments, the SS oxygen count rate (or LS oxygen count rate) may be normalized to the 0 p.u. (also referred as the “matrix point”) count rates. After obtaining the normalized values, the 2-phase oil in water-gas saturation may be determined using the normalized SS oxygen count rate (or normalized LS oxygen count rate) and the SS oxygen count rate / LS oxygen count ratio (block 214). Tire normalized SS oxygen count rate may be a function of SS / LS oxygen count rate ratio at different lithologies, borehole sizes, pore space fluids, and borehole fluids. For example, FIGS. 7A-7C depict plots of normalized SS oxygen count rate as a function of SS / LS oxygen count rate ratio for various lithologies in a 6 inch water borehole in accordance with an embodiment of the disclosure. FIG. 7A depicts a plot 700 of normalized SS oxygen count rate as a function of SS / LS oxygen count rate ratio for gas, oil, and water in sandstone, FIG. 7B depicts a plot 702 of normalized SS oxygen count rate as a function of SS / LS oxygen -9- IM-#10933321.1Attorney Docket No.: 610NUK-510438-WO-2 (000250)count rate ratio for gas, oil, and water in limestone, and FIG. 7C depicts a plot 704 of normalized SS oxygen count rate as a function of SS / LS oxygen count rate ratio for gas, oil, and water in dolomite.

[0035] In another example, FIGS, 8A-8C depict plots of normalized LS oxygen count rate as a function of SS / LS oxygen count rate ratio for various lithologies in an 6 inch water borehole in accordance w ith an embodiment of the disclosure. FIG. 8A depicts a plot 800 of normalized LS oxygen count rate as a function of SS / LS oxygen count rate ratio for gas, oil, and water in sandstone, FIG. 8B depicts a plot 802 of normalized LS oxygen count rate as a function of SS / LS oxygen count rate ratio for gas, oil, and water in limestone, and FIG. 8C depicts a plot 804 of normalized LS oxygen count rate as a function of SS / LS oxygen count rate ratio for gas, oil, and water in dolomite. As in FIGS, 7A-8C, the oil lines in the plots are distinct and separate from the gas and water lines. Thus, the oil saturation in water-gas may be determined from the normalized SS or LS oxygen rates as a function of the SS / LS oxygen count rate ratio. In other embodiments, the ratio of SS oxygen count rates to extra long space (XLS) oxygen count rates obtained via an XLS detector may be used instead of the SS / LS oxygen count rate.

[0036] FIGS. 9 A and 9B depict envelope saturation lines for normalized LS oxygen count rates in accordance with an embodiment of the disclosure. FIG. 9A depicts a plot 900 of normalized LS oxygen count rate vs SS / LS oxygen count rate ratio and oil-gas envelope saturation lines, and FIG, 9B depicts a plot 902 of normalized LS oxygen count rate vs SS / LS oxygen count rate ratio and oil-water envelope saturation. As shown in FIGS. 9A and 9B, the saturation lines are not vertical; however, the deviation in the orientation of the saturation lines may be determined using modeling techniques to provide oil and wet saturation lines as function of the SS and LS oxygen count rates (or, in other embodiments, as a function of SS and XLS oxygen count rates).

[0037] As shown in FIG. 2, after determining the 2 -phase gas in wet (oil-water) saturation, and the 2 -phase oil in water-gas saturation, these saturations may be combined to determine a 3 phase saturation (block 216).

[0038] Embodiments of the disclosure, such as aspects of the process 200, may be implemented in a processing system or processing device (for example, controller 116), Such systems or devices may include a central processing unit (CPU), a computer-readable media-10- IM-#10933321.1Attorney Docket No.: 610NUK-510438-WO-2 (000250)(for example, random access memory (RAM), read only memory (ROM), solid state memory (SSD) drives, hard drives), input and output control units, and a network interface (for example, wired or wireless network interface). Such systems and device may, in some embodiments, include, a display, a user interface, input device, and other components. Such systems and devices may include executable code stored in the computer-readable media. The executable code according to the present disclosure is in the form of computer operable instructions causing the data processor to receive input data and provide outputs based on processing the input data. The computer operable instructions of the executable code may execute processes and determine 2 -phase saturations and a 3-phase saturation.

[0039] Ranges may be expressed in the disclosure as from about one particular value, to about another particular value, or both. When such a range is expressed, it is to be understood that another embodiment is from the one particular value, to the other particular value, or both, along with all combinations within said range.

[0040] Further modifications and alternative embodiments of various aspects of the disclosure will be apparent to those skilled in the art in view of this description. Accordingly, this description is to be construed as illustrative only and is for the purpose of teaching those skilled in the art the general manner of carrying out the embodiments described in the disclosure. It is to be understood that the forms shown and described in the disclosure are to be taken as examples of embodiments. Elements and materials may be substituted for those illustrated and described in the disclosure, parts and processes may be reversed or omitted, and certain features may be utilized independently, all as would be apparent to one skilled in the art after having the benefit of this description. Changes may be made in the elements described in the disclosure without departing from the spirit and scope of the disclosure as described in the following claims. Headings used in the disclosure are for organizational purposes only and are not meant to be used to limit the scope of the description.-II- IM-#10933321.1

Claims

Attorney Docket No.: 610NUK-510438-WO-2 (000250)CLAIMSWhat is claimed is:

1. A method of determining a saturation of a formation, compri sing:obtaining inelastic energy spectra through a downhole tool inserted in a wellbore of a well accessing a formation, the downhole tool comprising a pulsed neutron source, a first detector and a second detector, the inelastic energy spectra comprising a first inelastic energy spectrum detected by the first detector and a second inelastic energy spectrum detected by the second detector, wherein the first detector is a short space (SS) detector;determining a first oxygen count rate from the first inelastic energy spectrum; determining a second oxygen count rate from the second inelastic energy spectrum; determining a ratio of the first oxygen count rate to the second oxygen count rate; and determining a 2-phase gas in oil- water saturation using the ratio of the first oxygen count rate to the second oxygen count rate and a porosity of the formation.

2. The method of claim 1, wherein the second detector is a long space (LS) detector or an extra long space (XLS) detector.

3. The method of any one of the preceding claims, wherein determining a first oxygen count rate from the first inelastic energy spectrum comprising:deconvolving the first inelastic energy spectrum into a first oxygen spectrum; determining a first oxygen yield from the first oxygen spectrum; andconverting the first oxygen yield into the first oxygen count rate.

4. The method of any one of the preceding claims, wherein determining a second oxygen count rate from the second inelastic energy spectrum comprising:deconvolving the second inelastic energy spectrum into a second oxygen spectrum; determining a second oxygen yield from the second oxygen spectrum; and converting the second oxygen yield into the second oxygen count rate.

5. The method of any one of the preceding claims, comprising inserting the downhole tool into the wellbore.

6. A method of determining a saturation of a formation, comprising:obtaining inelastic energy spectra obtained through a downhole tool inserted in a wellbore of a well accessing a formation, the downhole tool comprising a pulsed neutron -12- IM-#10933321.1Attorney Docket No.: 610NUK-510438-WO-2 (000250)source, a first detector and a second detector, the inelastic energy spectra comprising a first inelastic energy spectrum detected by the first detector and a second inelastic energy spectrum detected by the second detector, wherein the first detector is a short space (SS) detector;determining a first oxygen count rate from the first inelastic energy spectrum; determining a second oxygen count rate from the second inelastic energy spectrum; determining a ratio of the first oxygen count rate to the second oxygen count rate; determining a 2-phase oil in water-gas saturation using a normalized first oxygen count rate or a normalized second oxygen count rate, and the ratio of the first oxygen count rate to the second oxygen count rate.

7. The method of claim 6, wherein the second detector is a long space (LS) detector or an extra long space (XLS) detector.8, The method of claims 6 or 7, wherein determining a first oxygen count rate from the first inelastic energy spectrum comprising:deconvolving the first inelastic energy spectrum into a first oxygen spectrum; determining a first oxygen yield from the first oxygen spectrum; andconverting the first oxygen yield into the first oxygen count rate.9, Tire method of claims 6, 7, or 8, wherein determining a second oxygen count rate from the second inelastic energy spectrum comprising:deconvolving the second inelastic energy spectrum into a second oxygen spectrum; determining a second oxygen yield from the second oxygen spectrum; and converting the second oxygen yield into the second oxygen count rate.10, Tire method of claims 6, 7, 8, or 9, composing inserting the downhole tool into the wellbore.

11. The method of claims 6, 7, 8, 9, or 10, comprising normalizing the first oxygen count rate to a porosity with a known saturation to determine the normalized first oxygen count rate.

12. The method of claims 6, 7, 8, 9, 10, or 11, comprising normalizing the second oxygen count rate to a porosity with a known saturation to determine the normalized second oxygen count rate.-13- IM-#10933321.1Attorney Docket No.: 610NUK-510438-WO-2 (000250)13, A method of determining a saturation of a formation, comprising:obtaining inelastic energy spectra obtained through a downhole tool inserted in a wellbore of a well accessing a formation, the downhole tool comprising a pulsed neutron source, a first detector and a second detector, the inelastic energy spectra comprising a first inelastic energy spectrum detected by the first detector and a second inelastic energy spectrum detected by the second detector, wherein the first detector is a short space (SS) detector;determining a first oxygen count rate from the first inelastic energy spectrum; determining a second oxygen count rate from the second inelastic energy spectrum; determining a ratio of the first oxygen count rate to the second oxygen count rate; determining a 2 -phase gas in oil-water saturation using the ratio of the first oxygen count rate to the second oxygen count rate and a porosity of the formation;determining a 2-phase oil in water-gas saturation using a normalized first oxygen count rate or a normalized second oxygen count rate, and the ratio of the first oxygen count rate to the second oxygen count rate; anddetermining a 3 -phase saturation from the 2-phase gas in oil-water saturation and the 2-phase oil in water-gas saturation.14, The method of claim 13, wherein the second detector is a long space (LS) detector or an extra long space (XLS) detector.15, Tire method of claims 13 or 14, wherein determining a first oxygen count rate from the first inelastic energy spectrum comprising:deconvolving the first inelastic energy spectrum into a first oxygen spectrum; determining a first oxygen yield from the first oxygen spectrum; andconverting the first oxygen yield into the first oxygen count rate.16, Tire method of claims 13, 14, or 15, wherein determining a second oxygen count rate from the second inelastic energy spectrum comprising:deconvolving the second inelastic energy spectrum into a second oxygen spectrum; determining a second oxygen yield from the second oxygen spectrum: and converting the second oxygen yield into the second oxygen count rate.17, Tire method of claims 13, 14, 15, or 16, comprising inserting the downhole tool into the wellbore.-14- IM-#10933321.1Attorney Docket No.: 610NUK-510438-WO-2 (000250)18. The method of claims 13, 14, 15, 16, or 17, comprising normalizing the first oxygen count rate to a porosity with a known saturation to determine tire normalized first oxygen count rate.

19. The method of claims 13, 14, 15, 16, 17, or 18, comprising normalizing the second oxygen count rate to a porosity with a known saturation to determine the normalized second oxygen count rate.-15- IM-#10933321.1

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