U.S. patent application number 13/299818 was filed with the patent office on 2012-12-27 for method of calculating formation characteristics.
This patent application is currently assigned to BAKER HUGHES INCORPORATED. Invention is credited to Anton Nikitin, Alexandr A. Vinokurov.
Application Number | 20120326017 13/299818 |
Document ID | / |
Family ID | 47360948 |
Filed Date | 2012-12-27 |
United States Patent
Application |
20120326017 |
Kind Code |
A1 |
Nikitin; Anton ; et
al. |
December 27, 2012 |
METHOD OF CALCULATING FORMATION CHARACTERISTICS
Abstract
A method of calculating a formation characteristic includes
measuring with at least two detectors spaced apart from each other
an intensity of gamma rays, and calculating the formation
characteristic by calculating a ratio of the intensity of the gamma
rays detected by the two detectors.
Inventors: |
Nikitin; Anton; (Houston,
TX) ; Vinokurov; Alexandr A.; (Novosibirsk,
RU) |
Assignee: |
BAKER HUGHES INCORPORATED
Houston
TX
|
Family ID: |
47360948 |
Appl. No.: |
13/299818 |
Filed: |
November 18, 2011 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61500039 |
Jun 22, 2011 |
|
|
|
Current U.S.
Class: |
250/269.7 ;
250/265 |
Current CPC
Class: |
G01V 5/125 20130101;
G01V 5/101 20130101 |
Class at
Publication: |
250/269.7 ;
250/265 |
International
Class: |
G01V 5/10 20060101
G01V005/10; G01V 5/00 20060101 G01V005/00 |
Claims
1. A method of calculating a formation characteristic, comprising:
measuring with at least two detectors, spaced apart from each
other, an intensity of gamma rays; and calculating the formation
characteristic by calculating a ratio of the intensity of the gamma
rays detected by the two detectors.
2. The method of claim 1, wherein measuring the intensity of the
gamma rays includes measuring gamma rays generated by neutrons
reacting with a boron isotope B10, cadmium or samarium.
3. The method of claim 2, wherein measuring the intensity of gamma
rays includes measuring a spectrum peak intensity of gamma rays
generated by neutrons reacting with the boron isotope B10, cadmium
or samarium.
4. The method of claim 2, wherein each of the at least two
detectors is covered by a separate layer of B10 isotope, cadmium or
samarium.
5. The method of claim 1, wherein each of the at least two
detectors includes a scintillation crystal and a light detector,
and the intensity of the gamma rays is measured by measuring light
emitted by the scintillation crystal when gamma rays react with the
scintillation crystal material.
6. The method of claim 1, wherein the formation characteristic is
porosity.
7. The method of claim 6, wherein the porosity is calculated
according to the formula: GI SS GI LS = f ( .rho. ) , ##EQU00002##
where GI.sub.SS and GI.sub.IS each represent a gamma ray intensity
created in a neutron reaction with a material covering the at least
two detectors and detected by a respective one of the at least two
detectors, and f(.rho.) is a function of the porosity of the
formation.
8. The method of claim 7, wherein the material is a B10 isotope,
cadmium or samarium.
9. A gamma ray measurement system, comprising: a neutron source; a
first detector; a second detector; and a computing device
configured to receive from the first and second detectors detection
signals corresponding to a detected gamma ray intensity of each of
the first and second detectors, and configured to calculate a
formation characteristic based on a ratio of a gamma ray intensity
detected by the first detector to a gamma ray intensity detected by
the second detector.
10. The gamma ray detection system of claim 9, wherein at least one
of the first and second detectors is coated in a layer of boron
isotope B10, cadmium or samarium.
11. The gamma ray detection system of claim 10, wherein each of the
first detector and the second detector includes a scintillation
crystal and a photodetector to detect gamma radiation, and the B10
isotope, cadmium or samarium coating surrounds an outer
circumference of the scintillation crystal and an end of the
crystal facing the neutron source.
12. The gamma ray detection system of claim 11, wherein the
scintillation crystal is one of an NaI, LnBr.sub.3:Ce, GYSO, YAP or
BGO crystal.
13. The gamma ray detection system of claim 9, wherein the neutron
source and the first and second detectors are co-linear.
14. The gamma ray detection system of claim 9, wherein the neutron
source and the first and second detectors are laterally adjacent to
each other.
15. A method of measuring a characteristic of an earth formation,
the method comprising: covering at least two detectors with a layer
of a boron isotope B10, cadmium or samarium; inserting the at least
two detectors and a neutron source into a borehole; emitting
neutrons from the neutron source; detecting gamma rays generated by
a reaction of the B10 isotope, cadmium or samarium and neutrons;
and calculating the characteristic of the formation by detecting a
ratio of intensities of gamma rays detected by the at least two
detectors.
16. The method of claim 15, wherein the characteristic is
porosity.
17. The method of claim 15, wherein the at least two detectors and
the neutron source are arranged co-linearly.
18. The method of claim 17, wherein one of the at least two
detectors is located between another of the at least two detectors
and the neutron source.
19. The method of claim 15, wherein the at least two detectors and
the neutron source are arranged laterally adjacent to each
other.
20. The method of claim 15, wherein detecting the ratio of
intensities of gamma rays includes detecting a ratio of spectrum
peak intensities of gamma rays detected by the at least two
detectors.
Description
REFERENCE TO RELATED APPLICATIONS
[0001] This application claims priority from U.S. Provisional
Application No. 61/500,039 filed Jun. 26, 2011 in the U.S. Patent
and Trademark Office, the entire contents of which are hereby
incorporated by reference in the present application.
BACKGROUND
[0002] Various devices are used to calculate characteristics of
geological formations in drilling operations. Some devices include
radiation emitters to emit radiation into the geological formation
and detectors to detect the by-products of the interaction of the
emitted radiation with a formation. For example, when the radiation
emitter is a neutron emitter, and the emitted neutrons interact
with nuclei in the geological formation, gamma rays are released,
and detectors are used to measure the spectrum of released gamma
rays to determine characteristics of the geological formation.
SUMMARY
[0003] According to one embodiment, a method of calculating a
formation characteristic includes measuring with at least two
detectors spaced apart from each other, an intensity of gamma rays,
and calculating the formation characteristic by calculating a ratio
of the intensity of the gamma rays detected by the two
detectors.
[0004] According to another embodiment, a gamma ray measurement
system includes a neutron source; a first detector; a second
detector; and a computing device configured to receive from the
first and second detectors detection signals corresponding to a
detected gamma ray intensity of each of the first and second
detectors, and configured to calculate a formation characteristic
based on a ratio of a gamma ray intensity detected by the first
detector to a gamma ray intensity detected by the second
detector.
[0005] According to yet another embodiment, a method of measuring a
characteristic of an earth formation includes: covering at least
two detectors with a layer of a boron isotope B10, cadmium or
samarium; inserting the at least two detectors and a neutron source
into a borehole; emitting neutrons from the neutron source;
detecting gamma rays generated by a reaction of the B10 isotope,
cadmium or samarium and neutrons; and calculating the
characteristic of the formation by detecting a ratio of intensities
of gamma rays detected by the at least two detectors.
BRIEF DESCRIPTION OF THE DRAWINGS
[0006] Referring now to the drawings wherein like elements are
numbered alike in the several Figures:
[0007] FIG. 1 illustrates an embodiment of an assembly configured
to perform measurements of formation properties;
[0008] FIG. 2 is an exemplary spectrum of gamma rays detected by a
detector of the assembly of FIG. 1;
[0009] FIG. 3 illustrates a dependence of the ratio of the
intensity of gamma rays with particular energy detected by a first
detector and by a second detector of the assembly of FIG. 1 on
formation porosity measured for formations with sandstone and
limestone lithologies.
[0010] FIG. 4 illustrates a gamma ray measurement system according
to one embodiment;
[0011] FIG. 5 is a flow chart illustrating an embodiment of a
method of detecting formation properties; and
[0012] FIG. 6 illustrates an embodiment of a measurement unit
configured to perform measurements of formation properties.
DETAILED DESCRIPTION
[0013] FIG. 1 illustrates an assembly 20 configured to measure
characteristics of an earth formation. In one embodiment, the
assembly 20 is configured to be inserted into a bore hole 11 in a
geological formation 10 (e.g., via a borehole string, a drill
string or a wireline) to gather data about the geological formation
10, such as density, porosity, and composition. In the embodiment
shown in FIG. 1, the formation detection assembly 20 is disposed in
a shaft 21 and includes a measurement unit 22.
[0014] The assembly 20 may be embodied with any suitable carrier. A
"carrier" as described herein means any device, device component,
combination of devices, media and/or member that may be used to
convey, house, support or otherwise facilitate the use of another
device, device component, combination of devices, media and/or
member. Exemplary non-limiting carriers include drill strings of
the coiled tube type, of the jointed pipe type and any combination
or portion thereof. Other carrier examples include casing pipes,
wirelines, wireline sondes, slickline sondes, drop shots, downhole
subs, bottom-hole assemblies, and drill strings.
[0015] In one embodiment, the measurement unit 22 of the assembly
includes at least one neutron source 23 and a plurality of
detectors, such as a short space (SS) detector 24 and a long space
(LS) detector 25. The neutron source 23 emits fast neutrons 40,
which interact with matter in the borehole and/or formation, lose
energy, and become thermalized. The thermalized neutrons form a
thermal neutron cloud 41, and the characteristics of the thermal
neutron cloud 41, such as special distribution of thermal neutron
flux, correlates with the properties of the matter that makes up
the geological formation 10 such as hydrogen index and formation
porosity. The neutron source 23 may be one of a chemical neutron
source and a pulsed neutron generator.
[0016] The thermal neutron flux passing the detectors is converted
into detectable particles, e.g., gamma rays, which can be detected
by the SS detector 24 and the LS detector 25 by the material 29 and
33 that converts thermals neutrons into gamma rays 29 and 33. The
material 29 and 33 converting neutrons into gamma rays 34 and 35
can be boron isotope B10. In one embodiment, each of the SS
detector 24 and the LS detector 25 are made of a piece of
scintillation material and optically coupled photodetector. For
example, the SS detector 24 and the LS detector 25 include a
respective crystal 26 and 30, and a respective light sensor 27 and
31. In the present embodiment, the crystals 26 and 30 are NaI
crystals, and the light sensors 27 and 31 are photomultiplier
tubes. In alternative embodiments, other scintillation crystals
such as LanBr.sub.3:Ce, YAP, GYSO or BGO are used to detect gamma
rays emitted in the process of neutron interaction with material
converting neutrons into gamma rays.
[0017] In the embodiment shown in FIG. 1, the SS detector 24 is
located closer to the neutron source 23 than the LS detector 25.
According to one embodiment, the neutron source 23, the SS detector
24, and the LS detector 25 are co-linear. According to another
embodiment, the source and/or the detectors are laterally adjacent,
as illustrated in FIG. 6. In FIG. 6, a measurement unit 70 includes
a first detector 71 and a second detector 72 laterally adjacent to
each other. Each of the first detector 71 and the second detector
72 includes a layer of material 73 and 74 that reacts with neutrons
to generate a gamma spectrum, such as a B10 isotope. The detectors
71 and 72 detect the gamma spectra, and the detected spectra are
used to determine characteristics of a geological formation 10. The
measurement unit 70 may also include a neutron source 75, to emit
neutrons to generate a thermal neutron cloud, as discussed above
with respect to FIG. 1.
[0018] Referring again to FIG. 1, in one embodiment, at least a
portion of each of the SS detector 24 and the LS detector 25 is
coated with a layer 29 and 33 of material configured to convert
neutrons into gamma rays, such as a B10 isotope. For example, the
thermal neutrons contact the B10 layers 29 and 33 and generate
gamma rays with a particular energy E.sub..gamma.=0.478 MeV which
are detected by the SS and LS detectors 24 and 25. In one
embodiment, the B10 isotope coating 29 and 33 covers a first end 34
and 35 of the SS and LS detectors 24 and 25 facing the neutron
source 23. The B10 isotope coating 29 and 33 may also cover the
sides of the SS and LS detectors 24 and 25, including selected
surfaces of the crystals and/or photodetectors. In the present
embodiment, a second end 28 and 32 of the SS and LS detectors 24
and 25 facing away from the neutron source 23 is not covered by the
B10 isotope coating 29 and 33. Other materials converting neutrons
into gamma rays can be used instead of the boron isotope B10, such
as cadmium and samarium. In other embodiments the material
converting neutrons into gamma rays can be deposited at the gamma
ray detector surface in the form of axial or circumferential strips
or can have any other shapes.
[0019] Power P can be supplied to the assembly 20 performing
measurement of the formation properties 20 via a wire to power the
neutron source 23, e.g., when the neutron source is a pulsed
neutron generator, and may also provide operating power to the
photodetectors 27 and 31. Data D is transmitted to a computing
device, such as a personal computer or server having a database to
store and generate formation characteristic data based on the data
collected by the SS detector 24 and the LS detector 25. The
computing device may include a processor and another suitable
electronics, and may be disposed at any desired location, such as
at surface location or a downhole location.
[0020] The intensity of gamma rays produced by the neutron reaction
with B10 nuclei is proportional to the intensity of the thermal
neutron flux passing through the detectors 24 or 25. Since the
characteristics of the thermal neutron cloud 41 correspond to
characteristics of the geological formation 10, the intensity of
gamma rays produced in neutron reaction with B10 nuclei provides
information about the characteristics of the geological formation
10. Since the boron peak in the measured spectrum includes the
gamma ray signal generated in a neutron reaction with B10 nuclei,
detecting and measuring the boron peak provides information about
the thermal neutron cloud 41 and the geological formation 10. In
particular, the ratio of the intensity of gamma rays formed in
neutron reaction with B10 nuclei in layer 29 of the SS detector 24
to the intensity of gamma rays formed in neutron reaction with B10
nuclei in layer 33 of the LS detector 25 corresponds to a porosity
of the formation 10, as demonstrated by formula (I).
R = GI SS GI LS .about. FTN SS FTN LS .about. n ( Z 1 ) n ( Z 2 ) =
f ( .rho. ) ( 1 ) ##EQU00001##
[0021] In equation (1), R is a ratio of gamma ray intensities,
GI.sub.xx is the gamma ray intensity emitted in neutron reaction
with layers of B10 coatings 34 and 35 detected of a respective SS
or LS detector 24 or 25, FTN.sub.xx is a flux of thermal neutrons
passing through the respective SS or LS detector 24 or 25,
n(Z.sub.x) is the concentration of thermal neutrons in a point of
detector location Z.sub.x, and f(.rho.) is a function of the
formation porosity.
[0022] FIG. 2 illustrates a gamma ray spectrum measured by a gamma
ray detector with a B10 isotope coating exposed to the thermal
neutrons. Line 53 represents gamma rays generated by the neutron
reaction with B10 nuclei in the B10 isotope coating, which has a
peak C. The gamma ray intensity at peak C is around
E.sub..gamma.=0.478 MeV. Line 52 represents gamma rays born due to
the annihilation of the positrons generated within the crystal of
the detector, and the gamma ray intensity of a corresponding peak B
is around E.sub..gamma.=0.511 MeV. Line 51 includes lines 52 and
53, as well as background radiation. Peak A corresponds to the
combined peaks B and C. Detecting the characteristics of the peak B
provides information about the thermal neutron cloud 41 and the
geological formation 10.
[0023] In the example shown in FIG. 2, the intensity of B peak was
extracted from measured gamma ray spectra through spectra
decomposition using exponential background and 3 Gaussian peaks
(one for unidentified low energy peak and 2 for peaks at energy
E.sub..gamma.=0.478 MeV and E.sub..gamma.=0.511 MeV) for better
convergence of the fit (see FIG. 2). The intensity of A peak was
equal to the sum of intensities of peak B and peak C in the
fit.
[0024] FIG. 3 shows the dependence of a ratio of peak A intensities
GI.sub.SS/GI.sub.LS extracted from the gamma ray spectra measured
by the SS detector 24 and LS detector 25 of the assembly 20 in the
case when assembly was equipped with pulsed neutron generator and
was located in the sandstone and limestone formations of different
porosity when pore space was filled with water. As illustrated in
FIG. 3, the apparent porosity has a correlated relationship with
the calculated ratio of the gamma ray intensity detected by the SS
and LS detectors 24 and 25. In particular, as the ratio of
intensities of peak A (i.e., GI.sub.SS/GI.sub.LS) increases, the
apparent porosity also increases. In FIG. 3, line 54 corresponds to
limestone formations of different porosity and line 55 corresponds
to sandstone formations of different porosities. Accordingly, the
apparent porosity of each type of formation may be determined by
calculating the ratio of the intensities of peak A in gamma ray
spectra detected by the SS and LS detectors 24 and 25.
[0025] FIG. 4 illustrates an embodiment of a gamma ray measurement
system 42 configured to operate the detection assembly 22.
[0026] The gamma ray measurement system 42 includes the measurement
unit 22, a computing device 43, and a communication line 45 to
transmit detected gamma ray data from the measurement unit 22 to
the computing device 43. The computing device 43 includes an input
terminal 44 to receive the gamma ray data from the measurement unit
22, and a processor, memory, and supporting logic to convert the
detected data to information about a geological formation. The
input terminal 44 is one of a wired port, such as a conductive lead
connected to a wire, or a wireless port, such as an antenna.
Likewise, the communication line 45 is one of a wire and air
through which wireless data signals propagate.
[0027] The computing device 43 is configured to receive the
detected gamma ray data and calculates formation characteristics,
such as a porosity of the formation, based at least upon the
portion of the gamma ray data corresponding to gamma rays generated
when neutrons interact with the coating of the detectors 24 and 25,
as discussed above.
[0028] FIG. 5 illustrates a method of calculating formation
characteristics according to an embodiment of the present
invention. In operation 61, the formation analysis assembly 20 is
inserted into a bore hole. In operation 62, the neutron emitter 23
emits neutrons, and a neutron cloud 41 is generated around the
neutron emitter 23 and the measurement unit 22. In operation 63,
the SS detector 24 and the LS detector 25 detect gamma rays
generated when neutrons in the neutron cloud 41 react with a
coating or layer (e.g., a B10 coating) on each of the SS detector
24 and the LS detector 25. In operation 64, a ratio of gamma ray
intensities formed in neutron reaction with B10 material and
detected by the SS detector 24 and the LS detector 25 is
calculated. In operation 65, a formation characteristic, such as
porosity, is calculated based on the calculated ratio of gamma ray
intensities in operation 64. Although FIG. 5 illustrates an
embodiment in which each of operations 61-65 are performed,
according to alternative embodiments one or more operations may be
omitted, or additional operations may be performed.
[0029] In support of the teachings herein, various analysis
components may be used, including a digital and/or an analog
system. The computing device and the detection assembly may have
components such as a processor, storage media, memory, input,
output, communications link, user interfaces, software programs,
signal processors (digital or analog) and other such components
(such as resistors, capacitors, inductors and others) to provide
for operation and analyses of the apparatus and methods disclosed
herein in any of several manners well appreciated in the art. It is
considered that these teachings may be, but need not be,
implemented in conjunction with a set of computer executable
instructions stored on a computer readable medium, including memory
(ROMs, RAMs), optical (CD-ROMs), or magnetic (disks, hard drives),
or any other type that when executed causes a computer to implement
the method of the present invention. These instructions may provide
for equipment operation, control, data collection and analysis and
other functions deemed relevant by a system designer, owner, user
or other such personnel, in addition to the functions described in
this disclosure.
[0030] Further, various other components may be included and called
upon for providing for aspects of the teachings herein. For
example, a power supply (e.g., at least one of a generator, a
remote supply and a battery), cooling unit, heating unit, motive
force (such as a translational force, propulsional force or a
rotational force), magnet, electromagnet, sensor, electrode,
transmitter, receiver, transceiver, antenna, controller, optical
unit, electrical unit or electromechanical unit may be included in
support of the various aspects discussed herein or in support of
other functions beyond this disclosure.
[0031] It will be recognized that the various components or
technologies may provide certain necessary or beneficial
functionality or features. Accordingly, these functions and
features as may be needed in support of the appended claims and
variations thereof are recognized as being inherently included as a
part of the teachings herein and a part of the invention
disclosed.
[0032] While the invention has been described with reference to
exemplary embodiments, it will be understood that various changes
may be made and equivalents may be substituted for elements thereof
without departing from the scope of the invention. In addition,
many modifications will be appreciated to adapt a particular
instrument, situation or material to the teachings of the invention
without departing from the essential scope thereof. Therefore, it
is intended that the invention not be limited to the particular
embodiment disclosed as the best mode contemplated for carrying out
this invention, but that the invention will include all embodiments
falling within the scope of the appended claims.
* * * * *