CA2506133C - Logging tool with a parasitic radiation shield and method of logging with such a tool - Google Patents
Logging tool with a parasitic radiation shield and method of logging with such a tool Download PDFInfo
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- CA2506133C CA2506133C CA2506133A CA2506133A CA2506133C CA 2506133 C CA2506133 C CA 2506133C CA 2506133 A CA2506133 A CA 2506133A CA 2506133 A CA2506133 A CA 2506133A CA 2506133 C CA2506133 C CA 2506133C
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- 230000005855 radiation Effects 0.000 title claims abstract description 168
- 230000003071 parasitic effect Effects 0.000 title claims abstract description 9
- 238000000034 method Methods 0.000 title claims description 6
- 230000015572 biosynthetic process Effects 0.000 claims abstract description 55
- 238000005755 formation reaction Methods 0.000 claims abstract description 55
- 238000005286 illumination Methods 0.000 claims abstract description 6
- 239000000463 material Substances 0.000 claims description 36
- 239000003381 stabilizer Substances 0.000 claims description 33
- 230000005251 gamma ray Effects 0.000 claims description 22
- 238000005259 measurement Methods 0.000 claims description 8
- 239000000126 substance Substances 0.000 claims description 7
- 230000002285 radioactive effect Effects 0.000 claims description 5
- WFKWXMTUELFFGS-UHFFFAOYSA-N tungsten Chemical compound [W] WFKWXMTUELFFGS-UHFFFAOYSA-N 0.000 claims description 5
- 229910052721 tungsten Inorganic materials 0.000 claims description 5
- 239000010937 tungsten Substances 0.000 claims description 5
- 238000001739 density measurement Methods 0.000 claims description 4
- 238000001131 gamma-ray scattering spectroscopy Methods 0.000 claims description 3
- ZOXJGFHDIHLPTG-UHFFFAOYSA-N Boron Chemical compound [B] ZOXJGFHDIHLPTG-UHFFFAOYSA-N 0.000 claims description 2
- 239000011358 absorbing material Substances 0.000 claims description 2
- 229910052796 boron Inorganic materials 0.000 claims description 2
- 229910052793 cadmium Inorganic materials 0.000 claims description 2
- BDOSMKKIYDKNTQ-UHFFFAOYSA-N cadmium atom Chemical compound [Cd] BDOSMKKIYDKNTQ-UHFFFAOYSA-N 0.000 claims description 2
- PCHJSUWPFVWCPO-UHFFFAOYSA-N gold Chemical compound [Au] PCHJSUWPFVWCPO-UHFFFAOYSA-N 0.000 claims description 2
- 229910052737 gold Inorganic materials 0.000 claims description 2
- 239000010931 gold Substances 0.000 claims description 2
- 238000001956 neutron scattering Methods 0.000 claims description 2
- JFALSRSLKYAFGM-UHFFFAOYSA-N uranium(0) Chemical compound [U] JFALSRSLKYAFGM-UHFFFAOYSA-N 0.000 claims description 2
- 239000000956 alloy Substances 0.000 claims 1
- 229910045601 alloy Inorganic materials 0.000 claims 1
- 238000005553 drilling Methods 0.000 description 23
- 239000012530 fluid Substances 0.000 description 5
- 239000004215 Carbon black (E152) Substances 0.000 description 3
- 230000002411 adverse Effects 0.000 description 3
- TVFDJXOCXUVLDH-RNFDNDRNSA-N cesium-137 Chemical compound [137Cs] TVFDJXOCXUVLDH-RNFDNDRNSA-N 0.000 description 3
- 229930195733 hydrocarbon Natural products 0.000 description 3
- 150000002430 hydrocarbons Chemical class 0.000 description 3
- 230000004044 response Effects 0.000 description 3
- FVAUCKIRQBBSSJ-UHFFFAOYSA-M sodium iodide Chemical compound [Na+].[I-] FVAUCKIRQBBSSJ-UHFFFAOYSA-M 0.000 description 3
- 238000001228 spectrum Methods 0.000 description 3
- GUTLYIVDDKVIGB-OUBTZVSYSA-N Cobalt-60 Chemical compound [60Co] GUTLYIVDDKVIGB-OUBTZVSYSA-N 0.000 description 2
- 238000010521 absorption reaction Methods 0.000 description 2
- 230000005540 biological transmission Effects 0.000 description 2
- 238000006243 chemical reaction Methods 0.000 description 2
- 230000007423 decrease Effects 0.000 description 2
- 239000002245 particle Substances 0.000 description 2
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 2
- 229910000838 Al alloy Inorganic materials 0.000 description 1
- 229910052790 beryllium Inorganic materials 0.000 description 1
- 230000006378 damage Effects 0.000 description 1
- 230000003247 decreasing effect Effects 0.000 description 1
- 238000001514 detection method Methods 0.000 description 1
- 238000009826 distribution Methods 0.000 description 1
- 230000000694 effects Effects 0.000 description 1
- 230000004907 flux Effects 0.000 description 1
- 238000003780 insertion Methods 0.000 description 1
- 230000037431 insertion Effects 0.000 description 1
- 238000011835 investigation Methods 0.000 description 1
- 238000004519 manufacturing process Methods 0.000 description 1
- 238000005457 optimization Methods 0.000 description 1
- 230000000149 penetrating effect Effects 0.000 description 1
- 230000008569 process Effects 0.000 description 1
- 230000009467 reduction Effects 0.000 description 1
- 239000011435 rock Substances 0.000 description 1
- 230000035945 sensitivity Effects 0.000 description 1
- 235000009518 sodium iodide Nutrition 0.000 description 1
- 239000007787 solid Substances 0.000 description 1
Classifications
-
- E—FIXED CONSTRUCTIONS
- E21—EARTH OR ROCK DRILLING; MINING
- E21B—EARTH OR ROCK DRILLING; OBTAINING OIL, GAS, WATER, SOLUBLE OR MELTABLE MATERIALS OR A SLURRY OF MINERALS FROM WELLS
- E21B47/00—Survey of boreholes or wells
- E21B47/01—Devices for supporting measuring instruments on drill bits, pipes, rods or wirelines; Protecting measuring instruments in boreholes against heat, shock, pressure or the like
- E21B47/017—Protecting measuring instruments
Landscapes
- Geology (AREA)
- Life Sciences & Earth Sciences (AREA)
- Engineering & Computer Science (AREA)
- Physics & Mathematics (AREA)
- Mining & Mineral Resources (AREA)
- Geophysics (AREA)
- Environmental & Geological Engineering (AREA)
- Fluid Mechanics (AREA)
- General Life Sciences & Earth Sciences (AREA)
- Geochemistry & Mineralogy (AREA)
- Geophysics And Detection Of Objects (AREA)
- Analysing Materials By The Use Of Radiation (AREA)
- Measurement Of Radiation (AREA)
Abstract
It is described a logging tool for underground formations surrounding a borehole, comprising an elongated body along a major axis; a collar disposed peripherally around said body having a collar wall defined by an inner and an outer surface; a radiation emitting source arranged to illuminate the earth formation surrounding the borehole; at least one radiation detector arranged to detect radiation reflected by the earth formation resulting from illumination by the source; at least one source collimation -window and one detector collimation window through which the earth formation is illuminated and radiation is detected; and characterized in that it further comprises at least one radiation shield located between said inner collar surface and the outer surface of the tool, said radiation shield positioned so as to eliminate parasitic radiation that has not traversed the outer collar.
Description
LOGGING TOOL WITH A PARASITIC RADIATION SHIELD
AND METHOD OF LOGGING WITH SUCH A TOOL
Field of the invention This invention relates to logging of oil, water or gas well in underground formations surrounding a borehole and more particularly to a logging tool with a parasitic radiation shield such as a logging-while-drilling gamma ray density measurement tool.
Description of the Prior Art In hydrocarbon exploration and production, it is of prime importance to determine if a given earth formation contains hydrocarbon, and the amount of hydrocarbon within the formation.
Therefore, formation properties while drilling or in a freshly drilled hole are measured to predict the presence of oil, gas and water in the formation. These formation properties may be logged with wireline tools, logging while drilling (LWD) tools, or measurement while drilling (MWD) tools.
One method to predict formation properties is to measure the density of material in earth formation using a source of nuclear radiation and a radiation detector. The density of a material can be determined either by a transmission or by a scattering measurement. In a transmission measurement the material, the density of which needs to be determined, is put between the radiation source and the detector. In a scattering measurement the intensity and energy distribution of the radiation scattered back to a detector from the material under investigation is used to determine the density. Downhole measurements of formation density are of the scattering type since it is not usually possible to insert the formation material directly between source and detector, with the possible exception of rock samples removed from the formation.
Gamma-ray scattering systems have been used for many years to measure the density of a material penetrated by a borehole. Typically density is measured as a function of position 25 along the borehole thereby yielding a "log" as a function of depth within the borehole.
The measuring tool typically comprises a source of radiation and one or more radiation detectors, which are in the same plane as the source and typically, mounted within a pressure tight container.
Radiation impinges on and interacts with the material, and a fraction of the impinging radiation is scattered by the material and a traction thereof will return to the detector. After appropriate system calibration, the intensity of the detected scattered radiation can be related to the bulk density of the material.
The radial sensitivity of the density measuring system is affected by several factors such as the energy of the gamma radiation emitted by the source, the axial spacing between the source and the one or more gamma ray detectors, and the properties of the borehole and the formation.
The formation in the immediate vicinity of the borehole is usually perturbed by the drilling process, and more specifically by drilling fluid that invades the formation in the near borehole region. Furthermore, particulates from the drilling fluid tend to buildup on the borehole wall. This buildup is commonly referred to as mudcake, and adversely affects the response of the system. In this way, intervening material between the tool and the borehole wall will adversely affect the tool response. Intervening material in the tool itself between the active elements of the tool and the outer radial surface of the tool will again adversely affect the tool response by producing a background of scattered radiation which is independent of the presence of the borehole fluid, the mudcake or the formation. Typical sources are isotropic in that radiation is emitted with essentially radial symmetry. Flux per unit area decreases as the inverse square of the distance to the source. Radiation per unit area scattered by the formation and back into detectors within the tool also decreases with increasing distance, but not necessarily as the inverse square of the distance. In order to maximize the statistical precision of the measurement it is desirable to dispose the source and the detector as near as practical to the borehole environs, while still maintaining adequate shielding and collimation.
Prior art logging-while-drilHng systems use a variety of source and detector geometries to minimize standoff, such as placing a gamma ray source and one or more gamma ray detectors outside the tool body within a drill collar with a stabilizer disposed between source and detectors and the borehole and formation; or within stabilizer fins that radiate outward from a drill collar.
This tends to minimize intervening material within the tool, and positions source and detectors near the borehole environs, but often at the expense of decreasing the efficiency of shielding and collimation. The signal-to-noise ratio is often degraded by the detection of particles that have not probed the earth formation but instead have traveled trough low-density regions or voids existing in the tool between source and detectors, and especially through collar and stabilizer.
AND METHOD OF LOGGING WITH SUCH A TOOL
Field of the invention This invention relates to logging of oil, water or gas well in underground formations surrounding a borehole and more particularly to a logging tool with a parasitic radiation shield such as a logging-while-drilling gamma ray density measurement tool.
Description of the Prior Art In hydrocarbon exploration and production, it is of prime importance to determine if a given earth formation contains hydrocarbon, and the amount of hydrocarbon within the formation.
Therefore, formation properties while drilling or in a freshly drilled hole are measured to predict the presence of oil, gas and water in the formation. These formation properties may be logged with wireline tools, logging while drilling (LWD) tools, or measurement while drilling (MWD) tools.
One method to predict formation properties is to measure the density of material in earth formation using a source of nuclear radiation and a radiation detector. The density of a material can be determined either by a transmission or by a scattering measurement. In a transmission measurement the material, the density of which needs to be determined, is put between the radiation source and the detector. In a scattering measurement the intensity and energy distribution of the radiation scattered back to a detector from the material under investigation is used to determine the density. Downhole measurements of formation density are of the scattering type since it is not usually possible to insert the formation material directly between source and detector, with the possible exception of rock samples removed from the formation.
Gamma-ray scattering systems have been used for many years to measure the density of a material penetrated by a borehole. Typically density is measured as a function of position 25 along the borehole thereby yielding a "log" as a function of depth within the borehole.
The measuring tool typically comprises a source of radiation and one or more radiation detectors, which are in the same plane as the source and typically, mounted within a pressure tight container.
Radiation impinges on and interacts with the material, and a fraction of the impinging radiation is scattered by the material and a traction thereof will return to the detector. After appropriate system calibration, the intensity of the detected scattered radiation can be related to the bulk density of the material.
The radial sensitivity of the density measuring system is affected by several factors such as the energy of the gamma radiation emitted by the source, the axial spacing between the source and the one or more gamma ray detectors, and the properties of the borehole and the formation.
The formation in the immediate vicinity of the borehole is usually perturbed by the drilling process, and more specifically by drilling fluid that invades the formation in the near borehole region. Furthermore, particulates from the drilling fluid tend to buildup on the borehole wall. This buildup is commonly referred to as mudcake, and adversely affects the response of the system. In this way, intervening material between the tool and the borehole wall will adversely affect the tool response. Intervening material in the tool itself between the active elements of the tool and the outer radial surface of the tool will again adversely affect the tool response by producing a background of scattered radiation which is independent of the presence of the borehole fluid, the mudcake or the formation. Typical sources are isotropic in that radiation is emitted with essentially radial symmetry. Flux per unit area decreases as the inverse square of the distance to the source. Radiation per unit area scattered by the formation and back into detectors within the tool also decreases with increasing distance, but not necessarily as the inverse square of the distance. In order to maximize the statistical precision of the measurement it is desirable to dispose the source and the detector as near as practical to the borehole environs, while still maintaining adequate shielding and collimation.
Prior art logging-while-drilHng systems use a variety of source and detector geometries to minimize standoff, such as placing a gamma ray source and one or more gamma ray detectors outside the tool body within a drill collar with a stabilizer disposed between source and detectors and the borehole and formation; or within stabilizer fins that radiate outward from a drill collar.
This tends to minimize intervening material within the tool, and positions source and detectors near the borehole environs, but often at the expense of decreasing the efficiency of shielding and collimation. The signal-to-noise ratio is often degraded by the detection of particles that have not probed the earth formation but instead have traveled trough low-density regions or voids existing in the tool between source and detectors, and especially through collar and stabilizer.
Shielding of source and detectors mounted in the tool body is well known in the prior art;
chassis is shielded and detectors are mounted in a shielded holder with windows through which radiation is detected. Other prior art patents focus on total radiation shielding of the tool to the detriment of functionality: EP 0160351 describes a shielded tool casing with windows, which receives instrument package, US 6,666,285 describes an apparatus, which has a cavity to receive a solid shielded instrument package. Those apparatus, because they use a framework totally made of high-density materials, are heavy and brittle, and in harsh drilling conditions, can be broken resulting in the destruction and possibly the loss of the instrument package and more critically the loss of the radioactive source. The problem of providing shielding in the collar and 10 the stabilizer has not been yet addressed successfully.
Summary of the Invention According to an aspect of the invention there is provided a logging tool for underground formations surrounding a borehole, comprising: an elongated body along a major axis; a collar disposed peripherally around the body having a collar wall defined by an inner and an outer surface. Further, the tool comprises a radiation emitting source arranged to illuminate the earth formation surrounding the borehole; at least one radiation detector arranged to detect radiation reflected by the earth formation resulting from illumination by the source; at least one source collimation window and one detector collimation window through which the earth formation is illuminated and radiation is detected;
and at least one radiation shield located between the inner collar surface and the outer surface of the tool, the radiation shield positioned so as to eliminate parasitic radiation that has not traversed the outer collar. The radiation shield is located between the emitting radiation source and the radiation detector, the radiation shield has a length along the major axis, which is less than 80% of the distance between the emitting radiation source and the radiation detector.
In a preferred embodiment, the tool further comprises a stabilizer located at the periphery around the outer collar surface, wherein this stabilizer comprises a stabilizer wall defined by an inner stabilizer surface and an outer stabilizer surface, and wherein the radiation shield is located between this inner collar surface and this outer stabilizer surface. The stabilizer enhances the contact between the tool and the formation by reducing the space available for mud between the tool and the formation.
The tool is designed so that the source and the detector are as near as practical to the borehole environs. The radiation shields increase the signal to noise ratio.
And the invention below proposes a robust, secure and functional configuration.
In a preferred embodiment, the radiation shield may have a thickness in the cross section perpendicular to the major axis, which is preferably less than 40% of the width of the tool at the position of the radiation source. This makes it possible to eliminate a significant fraction of the radiation that are coming from source and that have not passed through the borehole fluid and the formation, but whose path was entirely inside the collar and the stabilizer.
In a preferred embodiment, the radiation shield may have an annular shape surrounding the detector window and has a length along the axis, which is less than 40% of the distance between the source and the detector. In a preferred embodiment, the radiation shield may have a thickness in the cross section perpendicular to the major axis, which is less than 40% of the width of the tool at the position of emitting radiation source.
This enables eliminating a part of the radiations passing through the collar to the detecting window and not through the window in the collar to the detector window.
In a preferred embodiment, this invention may be directed toward a radiation density measurement system in underground formations surrounding a borehole with a chemical radioactive source or an electronic radiation source emitting x-ray; or a chemical or electronic neutron source.
In a preferred embodiment, this invention may be directed toward a gamma-ray logging-while-drilling density tool. The system may comprise a source of gamma radiation and one or more gamma detectors. Multiple detectors (2 or more) provide better efficiency and allow compensation for the effect of mud and mudcake intervening between the tool and the formation. It is clear, however, that the basic concepts of the invention could be employed in other types and classes of logging, logging-while-drilling or measurement-while-drilling systems. As an example, the invention can be used in a neutron porosity system for measuring formation porosity, wherein the sensor comprises a neutron source and one or more neutron detectors.
The gamma-ray radiation shield can be fabricated from a high atomic number material, commonly referred to as "high Z" material. High Z material is an efficient attenuator of gamma-ray radiation, and permits the efficient shielding, collimation and optimum disposition of the source and detectors with respect to the borehole environs.
According to another aspect of the invention there is provided a method for logging a well comprising the steps of: lowering a logging tool in a well; and logging the well using the logging tool; wherein the logging tool comprising: an elongated body along a major axis; a collar disposed peripherally around the body having a collar wall defined by an inner and an outer surface; a radiation emitting source arranged to illuminate the earth formation surrounding the borehole; at least one radiation detector arranged to detect radiation reflected by the earth formation resulting from illumination by the source; at least one source collimation window and one detector collimation window through which the earth formation is illuminated and radiation is detected; and at least one radiation shield located between the inner collar surface and an outer surface of the tool, the radiation shield positioned so as to eliminate parasitic radiation that has not traversed the outer surface of the collar and the radiation shield is located between the emitting radiation source and the radiation detector, the radiation shield has a length along the axis, which is less than 80% of the distance between the emitting radiation source and the radiation detector.
Also disclosed is a logging tool for underground formations surrounding a borehole, comprising:
an elongated body along a major axis; a collar disposed peripherally around the body having a collar wall defined by an inner and an outer surface; a radiation emitting source arranged to illuminate the earth formation surrounding the borehole; at least one radiation detector arranged to detect radiation reflected by the earth formation resulting from illumination by the source; at least one source collimation window and one detector collimation window through which the earth formation is illuminated and radiation is detected; at least one radiation shield located between the inner collar surface and an outer surface of the tool, the radiation shield positioned so as to eliminate parasitic radiation that has not traversed the outer surface of the collar; and another radiation shield having an annular shape surrounding the detector collimation window.
Brief description of the drawings Further embodiments of the present invention can be understood with the appended drawings:
= Figure 1 illustrates a logging-while-drilling tool according to the invention.
= Figure 2a is a side view on the major axis of the tool of figure 1 with the radiation shield localized between source and first detector.
= Figure 2b is a side view on the major axis of the tool of figure 1 with the radiation shield localized closed to first detector.
= Figure 2c is a side view on the major axis of the tool of figure 1 with both radiation shields.
= Figure 3 shows pulse-height spectra obtained by numerical modeling of the logging-while-drilling tool of figure 2a and 2c as well as a case in which neither of the shields 30 and 31 is present.
Detailed description Figure 1 illustrates a logging-while-drilling tool, identified as a whole by the numeral 20, disposed by means of a drill string within a well borehole 18 defined by a borehole wall 14 and penetrating an earth formation 16. The upper end of the collar element 22 of the tool 20 is operationally attached to the lower end of a string of drill pipe 28.
The stabilizer element of the tool 20 is identified by the numeral 24. A drill bit 26 terminates the lower end of logging tool 20. It should be understood, however, that other elements can be disposed on either end of the tool 20 between the drill pipe 28 and the drill bit 26. The 5a upper end of the drill pipe 28 terminates at a rotary drilling rig 10 at the surface of the earth 12. The drilling rig rotates the drill pipe 28 and cooperating tool 20 and drill bit 26 thereby advancing the borehole 18. Drilling mud is circulated down the drill pipe 28, through the axial passage in the collar 22, and exits at the drill bit 26 for return to the surface 12 via the annulus defined by the outer surface of the drill string and the borehole wall 14.
Figures 2a, 2b and 2c illustrate conceptually radiation shields on the tool 20 of figure 1 shown in 5b side view on the major axis of the tool. In a first embodiment, the tool is a logging- while-drilling gamma-ray scattering tool with a chemical radioactive source. The tool 20 is made of an elongated tool body 21 and a drill collar 22 disposed peripherally around the tool body 21. In the illustrated tool, a stabilizer 24 is disposed peripherally around the drill collar 22; the stabilizer is optional and reduces the amount of mud between the tool and the formation wall and therefore the influence of the borehole fluid on the measurement. The tool 20 receives one source collimation window 202 through which the earth formation 16 is illuminated by the radiation emitted from the radioactive source, and two detector collimation windows 212 and 222 through which the radiation coming from the outside of the tool 20 is detected. In the illustrated tool, a source of gamma radiation 201 illuminating the earth formation 16 and affixed to a source holder 200, is mounted in the collar wall 22. Though this is the preferred way, other locations for the source 201 are in the tool body 21 or in the stabilizer 24. The source 201 is preferably cesium-137 ('Cs) which emits gamma radiation with an energy of 0.66 million electron volts (MeV).
Alternately, cobalt-60 (60Co) emitting gamma radiation at 1.11 and 1.33 MeV
can be used as source material. The tool 20 receives a first or "short spaced" gamma ray detector 211 disposed at a first axial distance from the source 201, and a second or "long spaced"
gamma ray detector 212 disposed at a second axial distance from the source, where the second spacing is greater than the first spacing. In the illustrated tool, the detectors are mounted in the tool body 21 in holders:
210 for the first detector and 220 for the second detector. Though this is the preferred way, other locations for the detectors 211, 221 are in the collar wall 22 or in the stabilizer 24. The detectors are preferably scintillation type such as sodium iodide (Nat) or Gadolinium-oxy-ortho-silicate (GSO) to maximize detector efficiency for a given detector size.
Insertion of high-density materials in the collar is often undesirable since the collar supports the stresses inherent to logging conditions, in figure 2a, a side view of the tool illustrates a radiation shield 30 located in the collar 22 whose shape is optimized to reduce leakage through the collar without affecting its mechanical strength.
The trajectories of gamma rays traveling from the source to the detector are like broken lines, on which each break corresponds to a collision with an electron within the surrounding material Gamma radiations lose energy by means of the most pertinent reaction here:
Compton scatter reaction. After undergoing one or more Compton scattering events, a small fraction of the emitted with reduced gamma-ray energy returns to the tool and is detected by the gamma radiation detector. The function of the radiation shield 30 is to intercept and attenuate by photoelectric absorption or by Compton scattering and subsequent photoelectric absorption, a significant fraction of those gamma rays that travel through the collar or/and stabilizer and that might otherwise go back to the detector after being scattered in the collar or/and stabilizer.
Figure 2b illustrates a side view of the tool with a radiation shield 31 located on the inner collar surface in the collimation window 212 of the first detector 211. The function of the radiation shield 31 is to intercept and attenuate gamma rays traversing the collar to the detecting window.
Figure 2c illustrates a side view of the tool with both radiation shields 30 and 31.
To estimate the amount of gamma ray leakage that is effectively removed by the radiation shields, a Monte-Carlo N-Particle model is built based on the tool plan of figures 2. A
compromise is found between the effective shielding and the mechanical strength of the tool.
The model of source used is a mono-energetic 0.662 million electron volts (MeV) cesium-137 radiation. Pulse-height spectra for energies between 0.1 and 0.5 MeV for the first Nal detector are computed for three different configurations: (1) tool without extra radiation shield, (2) tool with radiation shield 30 as in figure 2a, (3) tool with radiation shields 30 and 31 as in figure 2c.
One or more pieces of a high-density material, i.e. a material with a high atomic number (more than Z-70) and a high density (more than 15 g/cc) like tungsten, gold or depleted uranium, are inserted in the collar in a particular locations where their shielding efficiency will be maximal and their influence on the mechanical stmigth will be minimal. High Z
materials are efficient attenuators of gamma radiation, and permit the efficient shielding, collimation and optimum disposition of the source and detectors with respect to the borehole environs.
The radiation shield 30 of figure 2a is in a preferred embodiment, placed into a cavity in the outer surface of the collar, wrapped in a rubber envelope and then compressed underneath a cover plate screwed onto the collar between the source and the detector. In a preferred embodiment, better efficiency is obtained when length along the axis of this radiation shield is less than 80% of the first axial distance between source and detector; and when thickness of this radiation shield in the cross section perpendicular to the major axis is less than 40% of the width of the tool at the position of the source. In a second preferred embodiment, best efficiency is obtained when length along the axis of this radiation shield is less than 60%
of the first axial distance between source and detector; and when thickness of this radiation shield in the cross section perpendicular to the major axis is less than 20% of the width of the tool at the position of the source. The radiation shield is disposed circumferentially around the collar outer surface, and preferably covering less than 180 of this surface. The effectiveness of the radiation shield 30 is maximized when its edge is brought closer to that of the collimation window of the first detector.
The effectiveness is also increased when the thickness of the radiation shield is increased or an extension towards the source is made, but at the expense of a lower mechanical strength. As an example of optimization, for a circular part of a tungsten patch, the length along the axis is 58 mm whereas the first axial distance is 170 mm, and the thickness is 7 mm. and for the circular part, the internal radius is 78 mm and the opening angle is 90 .
The radiation shield 30 of figure 2a can be associated with another radiation shield 31 of figure 2b, located at the base and very close to the collimator window of the first detector, this radiation shield 31 has an annular shape surrounding this collimator window and with a trapezoidal section. Both radiation shields in this embodiment are illustrated on figure 2c. The efficiency is maximized with specific angular aperture of the trapezoidal section just as the dimension of the annular shield. Nevertheless, these dimensions of the annular shield are dictated by the requirements for mechanical strength. Therefore, in a preferred embodiment, better efficiency for the radiation shield 31 is obtained when this radiation shield is located between the first detector and the outer stabilizer surface facing the first detector, and when this radiation shield has an annular shape with a length along the axis or a diameter, which is less than 40% of the distance between source and first detector. In a second preferred embodiment, best efficiency for the radiation shield 31 is obtained when this radiation shield has an annular shape with a length along the axis or a diameter, which is less than 20% of the distance between source and first detector. In a preferred embodiment this radiation shield has a thickness in the cross section perpendicular to the major axis, which is less than 40% of the width of the logging-while-drilling tool at the position of emitting radiation source. In a second preferred embodiment, this radiation shield has a thickness in the cross section perpendicular to the major axis, which is less than 20%
of the width of the logging-while-drilling tool at the position of emitting radiation source.
Figure 3 shows the pulse-height spectra obtained by numerical modeling of the tool with optimized radiation Welds 30 and 31 for the three configurations already described above. In order to determine the amount of gamma-radiation passing through the tool to the detectors, without interacting with the materials in the borehole or the formation, the earth formation is assumed to be very dense like tungsten (17.4 g/cm3) so that practically no gamma-rays will return from the formation and the signal is entirely due to gamma-rays traveling through the collar and the stabilizer. From those data and for an energy range between 0.15 and 025 MeV, corresponding to the principal energy used for logging-while-drilling density measurements with a cesium-137 gamma ray source, the percentage of total gamma-ray leakage removed from the total signal by the radiation shields is evaluated. For a stabilizer diameter of 8 inches, the percentage of gamma-ray leakage removed is of 45% with the radiation shield 30 alone and of 54% with both radiation shields 30 and 31; for a stabilizer diameter of 9 3/8 Inches, this percentage is 43% and 51% respectively.
In a second model, the earth formation is assumed to be made of an aluminum alloy (2.805 g/cm3) so gamma-rays will return in this model also from the formation. The percentage of gamma-ray leakage removed from the signal by the radiation shields is evaluated in this model as well and the results are comparable to those obtained with the first model. For a stabilizer diameter of 8 inches, the percentage of gamma-ray leakage removed is 43% with the radiation shield 30 alone and of 57% with both radiation shields 30 and 31; for a stabilizer diameter of 9 3/8 inches, this percentage is 38% and 46%
respectively.
The radiation shield 30 removes almost 50% of gamma-ray leakage and the radiation shield 31 removes an additional 10% of gamma-ray leakage. These radiation shields 30 and 31 mounted offer therefore various mechanical, operational and technical advantages.
Radiation shields between first and second detectors or in the collimation window of the long spaced detector are possible; nevertheless this second detector is less sensitive to gamma-ray leakage and a reduction of the leakage is less important.
In a second embodiment, the tool 20 is a logging-while-drilling density tool with an electronic radiation source. The source 201 is an x-rays generator. The shielding materials need to be inserted into the structural materials of the tool body, collar or stabilizer with the intent to optimize shielding with a minimal impact on the structural strength of the tool.
Shielding materials for lower energy gamma-rays or x-rays could be lighter materials.
In a third embodiment, the tool 20 is a logging-while-drilling neutron scattering tool with a chemical or electronic neutron source. The source 201 is a chemical source, as Radium-Beryllium source or an electronic source like pulsed neutron generator. The shielding materials need to be inserted into the structural materials of the tool body, collar or stabilizer with the 10 intent to optimize shielding with a minimal impact on the structural strength of the tool. Shielding materials for neutrons will typically be hydrogenous materials and/or neutron absorbing materials, like boron or cadmium for slow-neutrons;
and will typically be high atomic number materials like tungsten and/or hydrogenous materials for fast neutrons.
chassis is shielded and detectors are mounted in a shielded holder with windows through which radiation is detected. Other prior art patents focus on total radiation shielding of the tool to the detriment of functionality: EP 0160351 describes a shielded tool casing with windows, which receives instrument package, US 6,666,285 describes an apparatus, which has a cavity to receive a solid shielded instrument package. Those apparatus, because they use a framework totally made of high-density materials, are heavy and brittle, and in harsh drilling conditions, can be broken resulting in the destruction and possibly the loss of the instrument package and more critically the loss of the radioactive source. The problem of providing shielding in the collar and 10 the stabilizer has not been yet addressed successfully.
Summary of the Invention According to an aspect of the invention there is provided a logging tool for underground formations surrounding a borehole, comprising: an elongated body along a major axis; a collar disposed peripherally around the body having a collar wall defined by an inner and an outer surface. Further, the tool comprises a radiation emitting source arranged to illuminate the earth formation surrounding the borehole; at least one radiation detector arranged to detect radiation reflected by the earth formation resulting from illumination by the source; at least one source collimation window and one detector collimation window through which the earth formation is illuminated and radiation is detected;
and at least one radiation shield located between the inner collar surface and the outer surface of the tool, the radiation shield positioned so as to eliminate parasitic radiation that has not traversed the outer collar. The radiation shield is located between the emitting radiation source and the radiation detector, the radiation shield has a length along the major axis, which is less than 80% of the distance between the emitting radiation source and the radiation detector.
In a preferred embodiment, the tool further comprises a stabilizer located at the periphery around the outer collar surface, wherein this stabilizer comprises a stabilizer wall defined by an inner stabilizer surface and an outer stabilizer surface, and wherein the radiation shield is located between this inner collar surface and this outer stabilizer surface. The stabilizer enhances the contact between the tool and the formation by reducing the space available for mud between the tool and the formation.
The tool is designed so that the source and the detector are as near as practical to the borehole environs. The radiation shields increase the signal to noise ratio.
And the invention below proposes a robust, secure and functional configuration.
In a preferred embodiment, the radiation shield may have a thickness in the cross section perpendicular to the major axis, which is preferably less than 40% of the width of the tool at the position of the radiation source. This makes it possible to eliminate a significant fraction of the radiation that are coming from source and that have not passed through the borehole fluid and the formation, but whose path was entirely inside the collar and the stabilizer.
In a preferred embodiment, the radiation shield may have an annular shape surrounding the detector window and has a length along the axis, which is less than 40% of the distance between the source and the detector. In a preferred embodiment, the radiation shield may have a thickness in the cross section perpendicular to the major axis, which is less than 40% of the width of the tool at the position of emitting radiation source.
This enables eliminating a part of the radiations passing through the collar to the detecting window and not through the window in the collar to the detector window.
In a preferred embodiment, this invention may be directed toward a radiation density measurement system in underground formations surrounding a borehole with a chemical radioactive source or an electronic radiation source emitting x-ray; or a chemical or electronic neutron source.
In a preferred embodiment, this invention may be directed toward a gamma-ray logging-while-drilling density tool. The system may comprise a source of gamma radiation and one or more gamma detectors. Multiple detectors (2 or more) provide better efficiency and allow compensation for the effect of mud and mudcake intervening between the tool and the formation. It is clear, however, that the basic concepts of the invention could be employed in other types and classes of logging, logging-while-drilling or measurement-while-drilling systems. As an example, the invention can be used in a neutron porosity system for measuring formation porosity, wherein the sensor comprises a neutron source and one or more neutron detectors.
The gamma-ray radiation shield can be fabricated from a high atomic number material, commonly referred to as "high Z" material. High Z material is an efficient attenuator of gamma-ray radiation, and permits the efficient shielding, collimation and optimum disposition of the source and detectors with respect to the borehole environs.
According to another aspect of the invention there is provided a method for logging a well comprising the steps of: lowering a logging tool in a well; and logging the well using the logging tool; wherein the logging tool comprising: an elongated body along a major axis; a collar disposed peripherally around the body having a collar wall defined by an inner and an outer surface; a radiation emitting source arranged to illuminate the earth formation surrounding the borehole; at least one radiation detector arranged to detect radiation reflected by the earth formation resulting from illumination by the source; at least one source collimation window and one detector collimation window through which the earth formation is illuminated and radiation is detected; and at least one radiation shield located between the inner collar surface and an outer surface of the tool, the radiation shield positioned so as to eliminate parasitic radiation that has not traversed the outer surface of the collar and the radiation shield is located between the emitting radiation source and the radiation detector, the radiation shield has a length along the axis, which is less than 80% of the distance between the emitting radiation source and the radiation detector.
Also disclosed is a logging tool for underground formations surrounding a borehole, comprising:
an elongated body along a major axis; a collar disposed peripherally around the body having a collar wall defined by an inner and an outer surface; a radiation emitting source arranged to illuminate the earth formation surrounding the borehole; at least one radiation detector arranged to detect radiation reflected by the earth formation resulting from illumination by the source; at least one source collimation window and one detector collimation window through which the earth formation is illuminated and radiation is detected; at least one radiation shield located between the inner collar surface and an outer surface of the tool, the radiation shield positioned so as to eliminate parasitic radiation that has not traversed the outer surface of the collar; and another radiation shield having an annular shape surrounding the detector collimation window.
Brief description of the drawings Further embodiments of the present invention can be understood with the appended drawings:
= Figure 1 illustrates a logging-while-drilling tool according to the invention.
= Figure 2a is a side view on the major axis of the tool of figure 1 with the radiation shield localized between source and first detector.
= Figure 2b is a side view on the major axis of the tool of figure 1 with the radiation shield localized closed to first detector.
= Figure 2c is a side view on the major axis of the tool of figure 1 with both radiation shields.
= Figure 3 shows pulse-height spectra obtained by numerical modeling of the logging-while-drilling tool of figure 2a and 2c as well as a case in which neither of the shields 30 and 31 is present.
Detailed description Figure 1 illustrates a logging-while-drilling tool, identified as a whole by the numeral 20, disposed by means of a drill string within a well borehole 18 defined by a borehole wall 14 and penetrating an earth formation 16. The upper end of the collar element 22 of the tool 20 is operationally attached to the lower end of a string of drill pipe 28.
The stabilizer element of the tool 20 is identified by the numeral 24. A drill bit 26 terminates the lower end of logging tool 20. It should be understood, however, that other elements can be disposed on either end of the tool 20 between the drill pipe 28 and the drill bit 26. The 5a upper end of the drill pipe 28 terminates at a rotary drilling rig 10 at the surface of the earth 12. The drilling rig rotates the drill pipe 28 and cooperating tool 20 and drill bit 26 thereby advancing the borehole 18. Drilling mud is circulated down the drill pipe 28, through the axial passage in the collar 22, and exits at the drill bit 26 for return to the surface 12 via the annulus defined by the outer surface of the drill string and the borehole wall 14.
Figures 2a, 2b and 2c illustrate conceptually radiation shields on the tool 20 of figure 1 shown in 5b side view on the major axis of the tool. In a first embodiment, the tool is a logging- while-drilling gamma-ray scattering tool with a chemical radioactive source. The tool 20 is made of an elongated tool body 21 and a drill collar 22 disposed peripherally around the tool body 21. In the illustrated tool, a stabilizer 24 is disposed peripherally around the drill collar 22; the stabilizer is optional and reduces the amount of mud between the tool and the formation wall and therefore the influence of the borehole fluid on the measurement. The tool 20 receives one source collimation window 202 through which the earth formation 16 is illuminated by the radiation emitted from the radioactive source, and two detector collimation windows 212 and 222 through which the radiation coming from the outside of the tool 20 is detected. In the illustrated tool, a source of gamma radiation 201 illuminating the earth formation 16 and affixed to a source holder 200, is mounted in the collar wall 22. Though this is the preferred way, other locations for the source 201 are in the tool body 21 or in the stabilizer 24. The source 201 is preferably cesium-137 ('Cs) which emits gamma radiation with an energy of 0.66 million electron volts (MeV).
Alternately, cobalt-60 (60Co) emitting gamma radiation at 1.11 and 1.33 MeV
can be used as source material. The tool 20 receives a first or "short spaced" gamma ray detector 211 disposed at a first axial distance from the source 201, and a second or "long spaced"
gamma ray detector 212 disposed at a second axial distance from the source, where the second spacing is greater than the first spacing. In the illustrated tool, the detectors are mounted in the tool body 21 in holders:
210 for the first detector and 220 for the second detector. Though this is the preferred way, other locations for the detectors 211, 221 are in the collar wall 22 or in the stabilizer 24. The detectors are preferably scintillation type such as sodium iodide (Nat) or Gadolinium-oxy-ortho-silicate (GSO) to maximize detector efficiency for a given detector size.
Insertion of high-density materials in the collar is often undesirable since the collar supports the stresses inherent to logging conditions, in figure 2a, a side view of the tool illustrates a radiation shield 30 located in the collar 22 whose shape is optimized to reduce leakage through the collar without affecting its mechanical strength.
The trajectories of gamma rays traveling from the source to the detector are like broken lines, on which each break corresponds to a collision with an electron within the surrounding material Gamma radiations lose energy by means of the most pertinent reaction here:
Compton scatter reaction. After undergoing one or more Compton scattering events, a small fraction of the emitted with reduced gamma-ray energy returns to the tool and is detected by the gamma radiation detector. The function of the radiation shield 30 is to intercept and attenuate by photoelectric absorption or by Compton scattering and subsequent photoelectric absorption, a significant fraction of those gamma rays that travel through the collar or/and stabilizer and that might otherwise go back to the detector after being scattered in the collar or/and stabilizer.
Figure 2b illustrates a side view of the tool with a radiation shield 31 located on the inner collar surface in the collimation window 212 of the first detector 211. The function of the radiation shield 31 is to intercept and attenuate gamma rays traversing the collar to the detecting window.
Figure 2c illustrates a side view of the tool with both radiation shields 30 and 31.
To estimate the amount of gamma ray leakage that is effectively removed by the radiation shields, a Monte-Carlo N-Particle model is built based on the tool plan of figures 2. A
compromise is found between the effective shielding and the mechanical strength of the tool.
The model of source used is a mono-energetic 0.662 million electron volts (MeV) cesium-137 radiation. Pulse-height spectra for energies between 0.1 and 0.5 MeV for the first Nal detector are computed for three different configurations: (1) tool without extra radiation shield, (2) tool with radiation shield 30 as in figure 2a, (3) tool with radiation shields 30 and 31 as in figure 2c.
One or more pieces of a high-density material, i.e. a material with a high atomic number (more than Z-70) and a high density (more than 15 g/cc) like tungsten, gold or depleted uranium, are inserted in the collar in a particular locations where their shielding efficiency will be maximal and their influence on the mechanical stmigth will be minimal. High Z
materials are efficient attenuators of gamma radiation, and permit the efficient shielding, collimation and optimum disposition of the source and detectors with respect to the borehole environs.
The radiation shield 30 of figure 2a is in a preferred embodiment, placed into a cavity in the outer surface of the collar, wrapped in a rubber envelope and then compressed underneath a cover plate screwed onto the collar between the source and the detector. In a preferred embodiment, better efficiency is obtained when length along the axis of this radiation shield is less than 80% of the first axial distance between source and detector; and when thickness of this radiation shield in the cross section perpendicular to the major axis is less than 40% of the width of the tool at the position of the source. In a second preferred embodiment, best efficiency is obtained when length along the axis of this radiation shield is less than 60%
of the first axial distance between source and detector; and when thickness of this radiation shield in the cross section perpendicular to the major axis is less than 20% of the width of the tool at the position of the source. The radiation shield is disposed circumferentially around the collar outer surface, and preferably covering less than 180 of this surface. The effectiveness of the radiation shield 30 is maximized when its edge is brought closer to that of the collimation window of the first detector.
The effectiveness is also increased when the thickness of the radiation shield is increased or an extension towards the source is made, but at the expense of a lower mechanical strength. As an example of optimization, for a circular part of a tungsten patch, the length along the axis is 58 mm whereas the first axial distance is 170 mm, and the thickness is 7 mm. and for the circular part, the internal radius is 78 mm and the opening angle is 90 .
The radiation shield 30 of figure 2a can be associated with another radiation shield 31 of figure 2b, located at the base and very close to the collimator window of the first detector, this radiation shield 31 has an annular shape surrounding this collimator window and with a trapezoidal section. Both radiation shields in this embodiment are illustrated on figure 2c. The efficiency is maximized with specific angular aperture of the trapezoidal section just as the dimension of the annular shield. Nevertheless, these dimensions of the annular shield are dictated by the requirements for mechanical strength. Therefore, in a preferred embodiment, better efficiency for the radiation shield 31 is obtained when this radiation shield is located between the first detector and the outer stabilizer surface facing the first detector, and when this radiation shield has an annular shape with a length along the axis or a diameter, which is less than 40% of the distance between source and first detector. In a second preferred embodiment, best efficiency for the radiation shield 31 is obtained when this radiation shield has an annular shape with a length along the axis or a diameter, which is less than 20% of the distance between source and first detector. In a preferred embodiment this radiation shield has a thickness in the cross section perpendicular to the major axis, which is less than 40% of the width of the logging-while-drilling tool at the position of emitting radiation source. In a second preferred embodiment, this radiation shield has a thickness in the cross section perpendicular to the major axis, which is less than 20%
of the width of the logging-while-drilling tool at the position of emitting radiation source.
Figure 3 shows the pulse-height spectra obtained by numerical modeling of the tool with optimized radiation Welds 30 and 31 for the three configurations already described above. In order to determine the amount of gamma-radiation passing through the tool to the detectors, without interacting with the materials in the borehole or the formation, the earth formation is assumed to be very dense like tungsten (17.4 g/cm3) so that practically no gamma-rays will return from the formation and the signal is entirely due to gamma-rays traveling through the collar and the stabilizer. From those data and for an energy range between 0.15 and 025 MeV, corresponding to the principal energy used for logging-while-drilling density measurements with a cesium-137 gamma ray source, the percentage of total gamma-ray leakage removed from the total signal by the radiation shields is evaluated. For a stabilizer diameter of 8 inches, the percentage of gamma-ray leakage removed is of 45% with the radiation shield 30 alone and of 54% with both radiation shields 30 and 31; for a stabilizer diameter of 9 3/8 Inches, this percentage is 43% and 51% respectively.
In a second model, the earth formation is assumed to be made of an aluminum alloy (2.805 g/cm3) so gamma-rays will return in this model also from the formation. The percentage of gamma-ray leakage removed from the signal by the radiation shields is evaluated in this model as well and the results are comparable to those obtained with the first model. For a stabilizer diameter of 8 inches, the percentage of gamma-ray leakage removed is 43% with the radiation shield 30 alone and of 57% with both radiation shields 30 and 31; for a stabilizer diameter of 9 3/8 inches, this percentage is 38% and 46%
respectively.
The radiation shield 30 removes almost 50% of gamma-ray leakage and the radiation shield 31 removes an additional 10% of gamma-ray leakage. These radiation shields 30 and 31 mounted offer therefore various mechanical, operational and technical advantages.
Radiation shields between first and second detectors or in the collimation window of the long spaced detector are possible; nevertheless this second detector is less sensitive to gamma-ray leakage and a reduction of the leakage is less important.
In a second embodiment, the tool 20 is a logging-while-drilling density tool with an electronic radiation source. The source 201 is an x-rays generator. The shielding materials need to be inserted into the structural materials of the tool body, collar or stabilizer with the intent to optimize shielding with a minimal impact on the structural strength of the tool.
Shielding materials for lower energy gamma-rays or x-rays could be lighter materials.
In a third embodiment, the tool 20 is a logging-while-drilling neutron scattering tool with a chemical or electronic neutron source. The source 201 is a chemical source, as Radium-Beryllium source or an electronic source like pulsed neutron generator. The shielding materials need to be inserted into the structural materials of the tool body, collar or stabilizer with the 10 intent to optimize shielding with a minimal impact on the structural strength of the tool. Shielding materials for neutrons will typically be hydrogenous materials and/or neutron absorbing materials, like boron or cadmium for slow-neutrons;
and will typically be high atomic number materials like tungsten and/or hydrogenous materials for fast neutrons.
Claims (13)
1. A logging tool for underground formations surrounding a borehole, comprising:
an elongated body along a major axis;
a collar disposed peripherally around said body having a collar wall defined by an inner and an outer surface;
a radiation emitting source arranged to illuminate the earth formation surrounding the borehole;
at least one radiation detector arranged to detect radiation reflected by the earth formation resulting from illumination by the source;
at least one source collimation window and one detector collimation window through which the earth formation is illuminated and radiation is detected;
at least one radiation shield located between said inner collar surface and an outer surface of the tool, said radiation shield positioned so as to eliminate parasitic radiation that has not traversed the outer surface of the collar and said radiation shield is located between said emitting radiation source and said radiation detector, said radiation shield has a length along the major axis, which is less than 80% of the distance between said emitting radiation source and said radiation detector.
an elongated body along a major axis;
a collar disposed peripherally around said body having a collar wall defined by an inner and an outer surface;
a radiation emitting source arranged to illuminate the earth formation surrounding the borehole;
at least one radiation detector arranged to detect radiation reflected by the earth formation resulting from illumination by the source;
at least one source collimation window and one detector collimation window through which the earth formation is illuminated and radiation is detected;
at least one radiation shield located between said inner collar surface and an outer surface of the tool, said radiation shield positioned so as to eliminate parasitic radiation that has not traversed the outer surface of the collar and said radiation shield is located between said emitting radiation source and said radiation detector, said radiation shield has a length along the major axis, which is less than 80% of the distance between said emitting radiation source and said radiation detector.
2. A tool as claimed in claim 1 further comprising a stabilizer located at the periphery around the outer collar surface, wherein said stabilizer comprises a stabilizer wall defined by an inner stabilizer surface and an outer stabilizer surface, and wherein the radiation shield is located between said inner surface of the collar and said outer stabilizer surface.
3. A tool as claimed in claim 1, wherein another radiation shield has an annular shape surrounding the detector collimation window and has a length along the major axis, which is less than 40% of the distance between said source and said detector.
4. A tool as claimed in claim 1, wherein said radiation shield has a thickness in the cross section perpendicular to the major axis, which is less than 40% of the width of the said logging tool at the position of said emitting radiation source.
5. A tool as claimed in claim 1, wherein the radiation emitting source is chosen in the list of: chemical radioactive source, an electronic radiation source emitting x-ray, a chemical neutron source or an electronic neutron source.
6. A tool as claimed in claim 1, wherein said logging tool is a gamma-ray scattering density measurement tool wherein:
said emitting radiation source is a gamma ray source or an x-ray source;
a first radiation detector is a short spaced gamma ray detector spaced axially at a first distance from said; and a second radiation detector is a long spaced gamma ray detector spaced axially at a second distance, greater than said first distance, from said emitting radiation source.
said emitting radiation source is a gamma ray source or an x-ray source;
a first radiation detector is a short spaced gamma ray detector spaced axially at a first distance from said; and a second radiation detector is a long spaced gamma ray detector spaced axially at a second distance, greater than said first distance, from said emitting radiation source.
7. A tool as claimed in claim 1, wherein said logging tool is a neutron scattering porosity measurement tool wherein:
said emitting radiation source is a neutron source; and said radiation detector is a neutron detector spaced axially at a first distance from said neutron source.
said emitting radiation source is a neutron source; and said radiation detector is a neutron detector spaced axially at a first distance from said neutron source.
8. A tool as claimed in claim 1, wherein said radiation shield is made of high atomic number material.
9. A tool as claimed in claim 8, wherein the high atomic number material includes tungsten, depleted uranium, gold or an alloy thereof.
10. A tool as claimed in claim 1, wherein said radiation shield is made of components selected from the list consisting of: hydrogenous material, neutron absorbing materials, boron and cadmium.
11. A method for logging a well comprising the steps of:
lowering a logging tool in a well; and logging the well using the logging tool;
wherein the logging tool comprising:
an elongated body along a major axis;
lowering a logging tool in a well; and logging the well using the logging tool;
wherein the logging tool comprising:
an elongated body along a major axis;
12 a collar disposed peripherally around said body having a collar wall defined by an inner and an outer surface;
a radiation emitting source arranged to illuminate the earth formation surrounding the borehole;
at least one radiation detector arranged to detect radiation reflected by the earth formation resulting from illumination by the source;
at least one source collimation window and one detector collimation window through which the earth formation is illuminated and radiation is detected; and at least one radiation shield located between said inner collar surface and an outer surface of the tool, said radiation shield positioned so as to eliminate parasitic radiation that has not traversed the outer surface of the collar and said radiation shield is located between said emitting radiation source and said radiation detector, said radiation shield has a length along the axis, which is less than 80% of the distance between said emitting radiation source and said radiation detector.
a radiation emitting source arranged to illuminate the earth formation surrounding the borehole;
at least one radiation detector arranged to detect radiation reflected by the earth formation resulting from illumination by the source;
at least one source collimation window and one detector collimation window through which the earth formation is illuminated and radiation is detected; and at least one radiation shield located between said inner collar surface and an outer surface of the tool, said radiation shield positioned so as to eliminate parasitic radiation that has not traversed the outer surface of the collar and said radiation shield is located between said emitting radiation source and said radiation detector, said radiation shield has a length along the axis, which is less than 80% of the distance between said emitting radiation source and said radiation detector.
13
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| EP04291261.8 | 2004-05-17 | ||
| EP04291261A EP1605281B1 (en) | 2004-05-17 | 2004-05-17 | Logging tool with a parasitic radiation shield and method of logging with such a tool |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| CA2506133A1 CA2506133A1 (en) | 2005-11-17 |
| CA2506133C true CA2506133C (en) | 2013-11-26 |
Family
ID=34684794
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA2506133A Expired - Fee Related CA2506133C (en) | 2004-05-17 | 2005-05-02 | Logging tool with a parasitic radiation shield and method of logging with such a tool |
Country Status (5)
| Country | Link |
|---|---|
| EP (1) | EP1605281B1 (en) |
| AT (1) | ATE328294T1 (en) |
| CA (1) | CA2506133C (en) |
| DE (1) | DE602004001045T2 (en) |
| GB (1) | GB2414296A (en) |
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| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US8211247B2 (en) | 2006-02-09 | 2012-07-03 | Schlumberger Technology Corporation | Degradable compositions, apparatus comprising same, and method of use |
| US10316616B2 (en) | 2004-05-28 | 2019-06-11 | Schlumberger Technology Corporation | Dissolvable bridge plug |
| US8567494B2 (en) | 2005-08-31 | 2013-10-29 | Schlumberger Technology Corporation | Well operating elements comprising a soluble component and methods of use |
| US8231947B2 (en) | 2005-11-16 | 2012-07-31 | Schlumberger Technology Corporation | Oilfield elements having controlled solubility and methods of use |
| US8220554B2 (en) | 2006-02-09 | 2012-07-17 | Schlumberger Technology Corporation | Degradable whipstock apparatus and method of use |
| US8770261B2 (en) | 2006-02-09 | 2014-07-08 | Schlumberger Technology Corporation | Methods of manufacturing degradable alloys and products made from degradable alloys |
| US8211248B2 (en) | 2009-02-16 | 2012-07-03 | Schlumberger Technology Corporation | Aged-hardenable aluminum alloy with environmental degradability, methods of use and making |
| CN101598017B (en) * | 2008-06-04 | 2012-10-31 | 中国石油集团钻井工程技术研究院 | Device for measuring porosity of azimuth neutrons during drilling |
Family Cites Families (7)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US3510654A (en) * | 1965-12-22 | 1970-05-05 | Texaco Inc | Scintillation-type fast neutron well logging device |
| DE3312883C1 (en) * | 1983-04-11 | 1984-08-02 | Preussag Ag Metall, 3380 Goslar | Probe for insertion into boreholes for the purpose of exploring ore deposits |
| US4661700A (en) * | 1985-05-28 | 1987-04-28 | Schlumberger Technology Corporation | Well logging sonde with shielded collimated window |
| US5134285A (en) * | 1991-01-15 | 1992-07-28 | Teleco Oilfield Services Inc. | Formation density logging mwd apparatus |
| GB2252623B (en) * | 1991-01-15 | 1994-10-19 | Teleco Oilfield Services Inc | A method for analyzing formation data from a formation evaluation measurement while drilling logging tool |
| US6300624B1 (en) * | 1999-03-25 | 2001-10-09 | Halliburton Energy Services, Inc. | Radiation detector |
| US6666285B2 (en) * | 2002-02-15 | 2003-12-23 | Precision Drilling Technology Services Group Inc. | Logging-while-drilling apparatus and methods for measuring density |
-
2004
- 2004-05-17 EP EP04291261A patent/EP1605281B1/en not_active Expired - Lifetime
- 2004-05-17 DE DE602004001045T patent/DE602004001045T2/en not_active Expired - Lifetime
- 2004-05-17 AT AT04291261T patent/ATE328294T1/en not_active IP Right Cessation
-
2005
- 2005-05-02 CA CA2506133A patent/CA2506133C/en not_active Expired - Fee Related
- 2005-05-06 GB GB0509221A patent/GB2414296A/en not_active Withdrawn
Also Published As
| Publication number | Publication date |
|---|---|
| ATE328294T1 (en) | 2006-06-15 |
| DE602004001045T2 (en) | 2006-12-28 |
| DE602004001045D1 (en) | 2006-07-06 |
| GB0509221D0 (en) | 2005-06-15 |
| GB2414296A (en) | 2005-11-23 |
| EP1605281A1 (en) | 2005-12-14 |
| CA2506133A1 (en) | 2005-11-17 |
| EP1605281B1 (en) | 2006-05-31 |
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