CA2755229C - Borehole logging system and method - Google Patents
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- CA2755229C CA2755229C CA2755229A CA2755229A CA2755229C CA 2755229 C CA2755229 C CA 2755229C CA 2755229 A CA2755229 A CA 2755229A CA 2755229 A CA2755229 A CA 2755229A CA 2755229 C CA2755229 C CA 2755229C
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- 238000000034 method Methods 0.000 title claims abstract description 22
- 230000005484 gravity Effects 0.000 claims abstract description 101
- 238000005259 measurement Methods 0.000 claims abstract description 54
- 239000000523 sample Substances 0.000 claims abstract description 47
- 230000015572 biosynthetic process Effects 0.000 claims abstract description 45
- 238000005755 formation reaction Methods 0.000 claims abstract description 45
- 230000000694 effects Effects 0.000 claims abstract description 39
- 238000001739 density measurement Methods 0.000 claims abstract description 28
- 238000012545 processing Methods 0.000 claims abstract description 12
- 230000008569 process Effects 0.000 claims description 5
- 239000000463 material Substances 0.000 description 10
- 230000005855 radiation Effects 0.000 description 7
- 239000004215 Carbon black (E152) Substances 0.000 description 6
- 229930195733 hydrocarbon Natural products 0.000 description 6
- 150000002430 hydrocarbons Chemical class 0.000 description 5
- 238000012937 correction Methods 0.000 description 4
- 238000005065 mining Methods 0.000 description 4
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- 238000001514 detection method Methods 0.000 description 2
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- TVFDJXOCXUVLDH-RNFDNDRNSA-N cesium-137 Chemical compound [137Cs] TVFDJXOCXUVLDH-RNFDNDRNSA-N 0.000 description 1
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Classifications
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- 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
- E21B49/00—Testing the nature of borehole walls; Formation testing; Methods or apparatus for obtaining samples of soil or well fluids, specially adapted to earth drilling or wells
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01V—GEOPHYSICS; GRAVITATIONAL MEASUREMENTS; DETECTING MASSES OR OBJECTS; TAGS
- G01V11/00—Prospecting or detecting by methods combining techniques covered by two or more of main groups G01V1/00 - G01V9/00
- G01V11/002—Details, e.g. power supply systems for logging instruments, transmitting or recording data, specially adapted for well logging, also if the prospecting method is irrelevant
- G01V11/005—Devices for positioning logging sondes with respect to the borehole wall
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01V—GEOPHYSICS; GRAVITATIONAL MEASUREMENTS; DETECTING MASSES OR OBJECTS; TAGS
- G01V5/00—Prospecting or detecting by the use of ionising radiation, e.g. of natural or induced radioactivity
- G01V5/04—Prospecting or detecting by the use of ionising radiation, e.g. of natural or induced radioactivity specially adapted for well-logging
- G01V5/08—Prospecting or detecting by the use of ionising radiation, e.g. of natural or induced radioactivity specially adapted for well-logging using primary nuclear radiation sources or X-rays
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01V—GEOPHYSICS; GRAVITATIONAL MEASUREMENTS; DETECTING MASSES OR OBJECTS; TAGS
- G01V7/00—Measuring gravitational fields or waves; Gravimetric prospecting or detecting
- G01V7/005—Measuring gravitational fields or waves; Gravimetric prospecting or detecting using a resonating body or device, e.g. string
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Abstract
A borehole logging method comprises processing density measurements taken by at least one probe at intervals along a borehole to determine the gravitational effects of geologic formations intersected by the borehole; and removing the determined gravitational effects from gravity measurements taken by at least one probe at intervals along the borehole to determine the gravitational efforts of geologic formations from the borehole.
Description
BOREHOLE LOGGING SYSTEM AND METHOD
Field of the Invention [0001] The present invention relates to borehole logging and in particular to a borehole logging system and method.
Background of the Invention
Field of the Invention [0001] The present invention relates to borehole logging and in particular to a borehole logging system and method.
Background of the Invention
[0002] Changes in the gravitational field of the Earth from place to place reflect the distribution of its diverse geologic materials, as a result of their differences in density. These gravitational changes can be observed through precise measurements by means of gravimeters, on the Earth's surface and, more recently, from aircraft and in boreholes. In mining applications, gravitational measurements have played an important role in the exploration, evaluation and development of mineral resources, including both metallics and non-metallics. Gravitational measurements are also of use in the exploration and production phases in the hydrocarbon field.
[0003] Surface gravity measurements naturally provide more information about the distribution of densities of geologic material closer to the Earth's surface than about geologic material at greater depths. It is now common practice to explore and mine mineral deposits at depths of up to 1-2 km below the Earth's surface, and hydrocarbon bearing horizons are being exploited to even much greater depths.
Gravity measurements made at the Earth's surface are of limited help in such deep programs. For this reason, borehole gravity sondes have been developed which are capable of providing high quality gravity measurements at such great depths, even under the extreme conditions of pressure and temperature prevailing at those depths.
Gravity measurements made at the Earth's surface are of limited help in such deep programs. For this reason, borehole gravity sondes have been developed which are capable of providing high quality gravity measurements at such great depths, even under the extreme conditions of pressure and temperature prevailing at those depths.
[0004] Borehole gravity measurements are affected by the distribution of rock densities, both in the vicinity of the borehole and remote from the borehole.
For some applications, borehole gravity measurements are employed to provide quantitative, bulk-density data about the geologic formations being intersected by the borehole, and about fluids in reservoirs. Accurate bulk-density measurements can be of material value in several stages of mining activity. In the hydrocarbon field, they can yield information of great value in the evaluation of the hydrocarbon potential of specific horizons, or to monitor the progress of secondary recovery methods.
For some applications, borehole gravity measurements are employed to provide quantitative, bulk-density data about the geologic formations being intersected by the borehole, and about fluids in reservoirs. Accurate bulk-density measurements can be of material value in several stages of mining activity. In the hydrocarbon field, they can yield information of great value in the evaluation of the hydrocarbon potential of specific horizons, or to monitor the progress of secondary recovery methods.
[0005] For other applications, borehole gravity measurements can be interpreted to indicate the presence of density changes that are either remote from the borehole or that lie below the bottom of the borehole. Remote detection of non-intersected ore bodies is a common objective of borehole gravity measurements in mining applications. In the hydrocarbon field, information may be sought about the presence of salt domes and structural features, such as faults and folds, which have not been intersected by the borehole. Whereas the effects of remote geologic features are inherent in gravity measurements taken at intervals along the borehole, for lack of any unique interpretation of gravity data, it is theoretically impossible to resolve the contribution of remote density variations from the much larger contributions due to proximal sources, that is, the geologic formations actually intersected by the borehole.
Only in the rare case that the geologic founations intersected by the borehole all have a uniform density, will the gravity effects of more remote geologic formations become resolvable.
Only in the rare case that the geologic founations intersected by the borehole all have a uniform density, will the gravity effects of more remote geologic formations become resolvable.
[0006] As will be appreciated, being able to determine the effect remote geologic formations have on gravity measurements taken along a borehole is desired as it provides insight as to the nature of the remote geologic formations. It is therefore an object of the present invention to provide a novel borehole logging system and method.
Summary of the Invention
Summary of the Invention
[0007] According to the following, the gravitational effects of geologic formations intersected by a borehole may be determined and removed from the gravity measurements taken along the borehole allowing the gravitational effects of geologic formations remote from the borehole to be resolved and revealed.
[0008] Accordingly, in one aspect there is provided a borehole logging method comprising: running a density probe down a borehole, and at intervals during the running, using the density probe to take density measurements; processing the density measurements taken at intervals by the density probe using a processor to determine gravitational effects of geologic formations intersected by the borehole;
running a gravity probe down the borehole, and at intervals during the running, using the gravity probe to take gravity measurements; processing the gravity measurements taken at intervals by the gravity probe using the processor to remove the determined gravitational effects of geologic formations intersected by the borehole from the gravity measurements thereby to determine gravitational effects of geologic formations remote from the borehole; and utilizing the determined gravitational effects of geologic formations remote from the borehole to determine the nature of the remote geologic formations based on remote density variations.
running a gravity probe down the borehole, and at intervals during the running, using the gravity probe to take gravity measurements; processing the gravity measurements taken at intervals by the gravity probe using the processor to remove the determined gravitational effects of geologic formations intersected by the borehole from the gravity measurements thereby to determine gravitational effects of geologic formations remote from the borehole; and utilizing the determined gravitational effects of geologic formations remote from the borehole to determine the nature of the remote geologic formations based on remote density variations.
[0009] In one embodiment, the density and gravity measurements are taken independently, at either different times or simultaneously. The method may further comprise, prior to the processing, taking density measurements at first vertical intervals along the borehole and taking gravity measurements at second longer vertical intervals along the borehole. The method may further comprise pre-processing the gravity measurements prior to the processing to compensate for the effects of at least one of instrumental drift, effects of the Earth's tides and the normal variation with depth of the Earth's gravitational attraction.
[00010] According to another aspect, there is provided a borehole logging system comprising: a density probe configured to take density measurements at intervals when run-in along a borehole; a gravity probe configured to take gravity measurements at intervals when run-in along the borehole; and a processor communicating with the density probe and the gravity probe and configured to:
process the density measurements taken at intervals by the density probe to determine gravitational effects of geologic formations intersected by the borehole;
process the gravity measurements taken at intervals by the gravity probe to remove the determined gravitational effects of geologic formations intersected by the borehole from the gravity measurements thereby to determine gravitational effects of geologic formations remote from the borehole; and utilize the determined gravitational effects of geologic formations remote from the borehole to determine the nature of the remote geologic formations based on remote density variations.
Detailed Description of the Drawings
process the density measurements taken at intervals by the density probe to determine gravitational effects of geologic formations intersected by the borehole;
process the gravity measurements taken at intervals by the gravity probe to remove the determined gravitational effects of geologic formations intersected by the borehole from the gravity measurements thereby to determine gravitational effects of geologic formations remote from the borehole; and utilize the determined gravitational effects of geologic formations remote from the borehole to determine the nature of the remote geologic formations based on remote density variations.
Detailed Description of the Drawings
[00011] Embodiments will now be described more fully with reference to the accompanying drawings in which:
[00012] Figure 1 is a side elevational view of a gamma-gamma density probe that has been lowered into a borehole;
[00013] Figure 2 is a side elevational view of a gravity sensor that has been lowered into the borehole; and
[00014] Figure 3 is a side elevational view of a sonde, comprising a gamma-gamma density probe and a gravity sensor that has been lowered into the borehole.
Detailed Description of the Embodiments
Detailed Description of the Embodiments
[00015] According to the following, a borehole logging system and method are provided that allow the gravitational effects of geologic formations remote from a borehole to be resolved and revealed. During the method, density measurements are taken along the borehole at intervals to yield a density log and are processed to determine the gravitational effects of the geologic formations intersected by the borehole. Gravity measurements are also taken at intervals along the borehole to yield a gravity log. The determined gravitational effects of the geologic formations intersected by the borehole are removed from the gravity measurements allowing the gravitational effects of geologic formations remote from the borehole to be determined. These determined gravitational effects signify density variations remote from the borehole and provide insight as to the nature of remote geologic formations.
[00016] A number of techniques may be used to acquire the density measurements at intervals along the borehole in order to generate the density log. For example, gamma-gamma (GG) density measurements, neutron gamma (ND) density measurements or other non-acceleration based density measurements that provide information about the density of geologic formations within one meter or less of the borehole maybe used. GG density measurements however are the one most commonly preferred in practice for wallrock density determination and will be referred to hereinafter by example only.
[00017] The model 2GDA-1000DX device, manufactured by Mt. Sopris Instruments, Denver, Colorado, USA, is a suitable device to take GG density . .
measurements at intervals along a borehole in order to generate the density log. This device comprises a source of gamma radiation (e.g. 100milliCuries of Cesium 137), and one or two radiation detectors (typically thalium- activated NaI
crystals), separated from the radioactive source by a distance of between about 20-35cm.
The detectors are shielded from direct gamma radiation emitted by the radioactive source.
The emitted gamma radiation creates both back-scattered Compton radiation and photoelectric absorption in the geologic material surrounding the borehole.
This secondary radiation impinges on the detectors. For a range of common densities of geologic materials (1-4 gm/cc), the count rate sensed by the detectors provides a reasonable linear estimate of the density of the geologic material surrounding the borehole, out to about 7-12cm into the surrounding geological material. The typical accuracy of such gamma-gamma density measurements is of the order of 0.1 gin/cc, with a resolution of about 0.05 gm/cc.
100018] The Gravilog sonde offered by Scintrex Limited, Concord, Ontario, Canada is a suitable device to take gravity measurements at intervals along the borehole in order to generate the gravity log. The gravity measurements are typically pre-processed to undergo certain corrections in order to more accurately provide useful geologic infoiniation. These corrections include instrumental drift with time, the effects of the Earth's tides and the normal variation, with depth, of the Earth's gravitational attraction (the so-called Free-Air correction). After such corrections have been made to the gravity measurements, changes (Ag) in the resultant gravity data with depth are predominantly dependent on the density of the geologic formations being traversed by the borehole, and are given by the formula shown in Equation (1) below:
Ag = -0.08382 pAz (1) where:
Ag is in units of milliGals;
p is the local geologic formational density, in units of gm/cc; and Az is the change in depth, in meters [00019] The change of resultant gravity with depth reflects the upward attraction (i.e. the reduction of gravity) of the geologic formations which overlie the gravity station (i.e. the position along the borehole at which the gravity measurement is made), and may be inverted to derive the mean bulk density of the geologic formations, for those applications where this is the factor of greatest interest.
Inverting Equation (1) provides Equation (2) as follows:
p = 11.93Ag / Az (2) where:
p is the mean geologic formational density, in units of gm/cc.
[00020] According to Equation (2), p is the mean value of the geologic formational density, the so-called "bulk density" between two gravity stations Az meters apart in depth. The effective radius from the borehole of these bulk-density values is several times the separation between the two gravity stations, i.e.
normally 10-100 meters.
[00021] However, for applications requiring the detection of remote density variations, a basic impediment is the dominant effect of the near-borehole geologic formational densities on the gravity measurements. Attempts may be made to estimate the mean value of p to be used for the near-borehole geologic formation densities, in Equation (1) and therefore to estimate their contribution to the observed gravity measurements, but this is an exercise which is subject to considerable subjective error.
[00022] It has been found that the gravity contribution of the near-borehole geologic formations can be removed through the use of the GG density log. Due to the shallow depth penetration of GG density measurements into the geologic material .. surrounding the borehole, the densities in the density log pertain only to the geologic formations actually intersected by the borehole. The densities derived from the GG
density log can be designated as py and can be used in Equation (1) to determine the gravity effects that arise from these geologic formations, on the assumption of their being of a uniform GG density, tabular, horizontally lying and of very large horizontal extent.
[00023] These calculated gravity effects can then be subtracted from the corrected gravity log measurements, on the basis of the measured GG densities.
The residual gravity after this subtraction is attributed to density changes that are remote from the borehole. This GG-derived residual gravity is referred to as GRG and embodies the effect of any departures, at a distance from the borehole, of the actual density distribution from the idealized, one-dimensional density model based on py.
[00024] Typically, in a gravity log of a borehole, the gravity station highest in the borehole is designated as a base station for drift determination, and also is the arbitrary base level for all subsequent relative gravity measurements. If the corrected gravity values are defined as g, and the GG calculated gravity values are defined as gy, then based on Equation (1), Equation (3) can be derived as follows:
gy = -0.08382 E py8 (3) where:
the 1, summation is over the vertical depth from the base station to the moving station; and 8 is the vertical spacing between successive values of py.
[00025] Based on the above, GG-derived residual gravity GRG may be resolved as shown in Equation (4) below:
GRG = g - = g + 0.08382 Epy8 (4) [00026] The graph of GRG may be interpreted to derive basic information about density changes occurring remote from the borehole, not just laterally but also at depths below the bottom of the borehole.
[00027] As well, the bulk-density values of p determined by Equation (2) using the gravity measurements, may be compared with the mean GG density values py over the same vertical intervals. Any differences between these two density values indicates an increase or decrease of density away from the borehole (usually laterally) from the geologic formations intersected by the borehole. These differences may be designated as GG-derived residual densities, or GRD, equal to p- py. However, GRD
data are of lesser value than the GRG values, because they are not as readily subject to quantitative modeling.
[00028] The practice of generating a GG density log of a borehole is a long established, standard procedure in the case of boreholes drilled for hydrocarbon purposes, so that in such boreholes at-hole density measurements are usually available for use. In the case of boreholes drilled for mining and other applications, GG density logs are not necessarily commonplace, and a density log may not be available.
For such case, a GG density log will have to be carried out. For example, a GG
sensor may be incorporated in the same sonde as a gravity sensor, or alternatively a GG
density log may be carried out independently, either prior to or subsequent to the gravity log. Where it is intended that a borehole will be metal cased prior to conducting a gravity log, the GG density log will have to be done prior to the insertion of the casing. This is because GG density measurements arc not possible in metal-cased boreholes, due to the effect of the casing. When carried out, GG
density measurements are commonly recorded at short intervals down the borehole, typically of the order of 15 cm. Gravity measurements are typically made at much larger intervals, commonly 10 meters or more. The value of the GG py to be used will be the mean of the GG py values over the gravity station intervals.
[00029] As will be appreciated, the subject method employs density logs to calculate the theoretical gravitational effect of geologic formations in the immediate vicinity of the borehole and then removes these gravitational effects from gravity measurements to reveal the presence of density changes which are remote from the borehole. The mean GG density values, over the vertical interval between successive gravity measurements, are compared with the gravity-derived bulk-density values, thereby to directly indicate an increase or decrease of density away from the borehole.
[00030] Figures 1 to 3 show examples of probes that can be used to acquire density and/or gravity measurements at intervals along a borehole in order to enable density and gravity logs to be generated. In particular, Figure 1 is a schematic drawing of a gamma-gamma density probe 2, having a gamma source 3 and a radiation detector 4 that is suspended in borehole 5 by a cable 1. Cable 1 incorporates a strength member, as well as electrical members which both control the operation of the probe 2 and transmit density measurements from the probe 2 to the top of the .. borehole. The region of geologic material 6 around the borehole 5which influences the gamma-gamma density measurements is shown.
[00031] In Figure 2, a gravity sensor 7 that is suspended in the borehole 5 by the cable 1 is shown. As is suggested by the configurations shown in Figures 1 and 2, the density probe 2 and gravity sensor 7 allow independent density and gravity measurements to be taken along the same borehole. However, as shown in Figure 3, a sonde including both a gamma-gamma density probe 2 and a gravity probe 7 may be used, whereby both gamma-gamma density and gravity measurements can be made in one logging survey of the borehole.
[00032] The gamma-gamma density measurements and the gravity measurements are transmitted via one or more of the electrical members in the cable 1 to processing structure (not shown). The processing structure processes the density and gravity measurements as described above to resolve the gravity contribution due to formations intersected by the borehole from the gravity contribution due to density variations that are remote from the borehole.
[00033] The processing structure in this embodiment is a general purpose computing device comprising a processing unit, system memory (volatile and/or non-volatile memory), other non-removable or removable memory (e.g. a hard disk drive, RAM, ROM, EEPROM, CD-ROM, DVD, flash memory, etc.), a display and a system bus coupling the various computer components to the processing unit. The computing device may also comprise networking capabilities using Ethernet, WiFi, and/or other suitable network format, to enable connection to shared or remote drives, one or more networked computers, or other networked devices.
[00034] Although embodiments have been described, those of skill in the art will appreciate that variations and modifications may be made without departing from the scope thereof as defined by the appended claims.
measurements at intervals along a borehole in order to generate the density log. This device comprises a source of gamma radiation (e.g. 100milliCuries of Cesium 137), and one or two radiation detectors (typically thalium- activated NaI
crystals), separated from the radioactive source by a distance of between about 20-35cm.
The detectors are shielded from direct gamma radiation emitted by the radioactive source.
The emitted gamma radiation creates both back-scattered Compton radiation and photoelectric absorption in the geologic material surrounding the borehole.
This secondary radiation impinges on the detectors. For a range of common densities of geologic materials (1-4 gm/cc), the count rate sensed by the detectors provides a reasonable linear estimate of the density of the geologic material surrounding the borehole, out to about 7-12cm into the surrounding geological material. The typical accuracy of such gamma-gamma density measurements is of the order of 0.1 gin/cc, with a resolution of about 0.05 gm/cc.
100018] The Gravilog sonde offered by Scintrex Limited, Concord, Ontario, Canada is a suitable device to take gravity measurements at intervals along the borehole in order to generate the gravity log. The gravity measurements are typically pre-processed to undergo certain corrections in order to more accurately provide useful geologic infoiniation. These corrections include instrumental drift with time, the effects of the Earth's tides and the normal variation, with depth, of the Earth's gravitational attraction (the so-called Free-Air correction). After such corrections have been made to the gravity measurements, changes (Ag) in the resultant gravity data with depth are predominantly dependent on the density of the geologic formations being traversed by the borehole, and are given by the formula shown in Equation (1) below:
Ag = -0.08382 pAz (1) where:
Ag is in units of milliGals;
p is the local geologic formational density, in units of gm/cc; and Az is the change in depth, in meters [00019] The change of resultant gravity with depth reflects the upward attraction (i.e. the reduction of gravity) of the geologic formations which overlie the gravity station (i.e. the position along the borehole at which the gravity measurement is made), and may be inverted to derive the mean bulk density of the geologic formations, for those applications where this is the factor of greatest interest.
Inverting Equation (1) provides Equation (2) as follows:
p = 11.93Ag / Az (2) where:
p is the mean geologic formational density, in units of gm/cc.
[00020] According to Equation (2), p is the mean value of the geologic formational density, the so-called "bulk density" between two gravity stations Az meters apart in depth. The effective radius from the borehole of these bulk-density values is several times the separation between the two gravity stations, i.e.
normally 10-100 meters.
[00021] However, for applications requiring the detection of remote density variations, a basic impediment is the dominant effect of the near-borehole geologic formational densities on the gravity measurements. Attempts may be made to estimate the mean value of p to be used for the near-borehole geologic formation densities, in Equation (1) and therefore to estimate their contribution to the observed gravity measurements, but this is an exercise which is subject to considerable subjective error.
[00022] It has been found that the gravity contribution of the near-borehole geologic formations can be removed through the use of the GG density log. Due to the shallow depth penetration of GG density measurements into the geologic material .. surrounding the borehole, the densities in the density log pertain only to the geologic formations actually intersected by the borehole. The densities derived from the GG
density log can be designated as py and can be used in Equation (1) to determine the gravity effects that arise from these geologic formations, on the assumption of their being of a uniform GG density, tabular, horizontally lying and of very large horizontal extent.
[00023] These calculated gravity effects can then be subtracted from the corrected gravity log measurements, on the basis of the measured GG densities.
The residual gravity after this subtraction is attributed to density changes that are remote from the borehole. This GG-derived residual gravity is referred to as GRG and embodies the effect of any departures, at a distance from the borehole, of the actual density distribution from the idealized, one-dimensional density model based on py.
[00024] Typically, in a gravity log of a borehole, the gravity station highest in the borehole is designated as a base station for drift determination, and also is the arbitrary base level for all subsequent relative gravity measurements. If the corrected gravity values are defined as g, and the GG calculated gravity values are defined as gy, then based on Equation (1), Equation (3) can be derived as follows:
gy = -0.08382 E py8 (3) where:
the 1, summation is over the vertical depth from the base station to the moving station; and 8 is the vertical spacing between successive values of py.
[00025] Based on the above, GG-derived residual gravity GRG may be resolved as shown in Equation (4) below:
GRG = g - = g + 0.08382 Epy8 (4) [00026] The graph of GRG may be interpreted to derive basic information about density changes occurring remote from the borehole, not just laterally but also at depths below the bottom of the borehole.
[00027] As well, the bulk-density values of p determined by Equation (2) using the gravity measurements, may be compared with the mean GG density values py over the same vertical intervals. Any differences between these two density values indicates an increase or decrease of density away from the borehole (usually laterally) from the geologic formations intersected by the borehole. These differences may be designated as GG-derived residual densities, or GRD, equal to p- py. However, GRD
data are of lesser value than the GRG values, because they are not as readily subject to quantitative modeling.
[00028] The practice of generating a GG density log of a borehole is a long established, standard procedure in the case of boreholes drilled for hydrocarbon purposes, so that in such boreholes at-hole density measurements are usually available for use. In the case of boreholes drilled for mining and other applications, GG density logs are not necessarily commonplace, and a density log may not be available.
For such case, a GG density log will have to be carried out. For example, a GG
sensor may be incorporated in the same sonde as a gravity sensor, or alternatively a GG
density log may be carried out independently, either prior to or subsequent to the gravity log. Where it is intended that a borehole will be metal cased prior to conducting a gravity log, the GG density log will have to be done prior to the insertion of the casing. This is because GG density measurements arc not possible in metal-cased boreholes, due to the effect of the casing. When carried out, GG
density measurements are commonly recorded at short intervals down the borehole, typically of the order of 15 cm. Gravity measurements are typically made at much larger intervals, commonly 10 meters or more. The value of the GG py to be used will be the mean of the GG py values over the gravity station intervals.
[00029] As will be appreciated, the subject method employs density logs to calculate the theoretical gravitational effect of geologic formations in the immediate vicinity of the borehole and then removes these gravitational effects from gravity measurements to reveal the presence of density changes which are remote from the borehole. The mean GG density values, over the vertical interval between successive gravity measurements, are compared with the gravity-derived bulk-density values, thereby to directly indicate an increase or decrease of density away from the borehole.
[00030] Figures 1 to 3 show examples of probes that can be used to acquire density and/or gravity measurements at intervals along a borehole in order to enable density and gravity logs to be generated. In particular, Figure 1 is a schematic drawing of a gamma-gamma density probe 2, having a gamma source 3 and a radiation detector 4 that is suspended in borehole 5 by a cable 1. Cable 1 incorporates a strength member, as well as electrical members which both control the operation of the probe 2 and transmit density measurements from the probe 2 to the top of the .. borehole. The region of geologic material 6 around the borehole 5which influences the gamma-gamma density measurements is shown.
[00031] In Figure 2, a gravity sensor 7 that is suspended in the borehole 5 by the cable 1 is shown. As is suggested by the configurations shown in Figures 1 and 2, the density probe 2 and gravity sensor 7 allow independent density and gravity measurements to be taken along the same borehole. However, as shown in Figure 3, a sonde including both a gamma-gamma density probe 2 and a gravity probe 7 may be used, whereby both gamma-gamma density and gravity measurements can be made in one logging survey of the borehole.
[00032] The gamma-gamma density measurements and the gravity measurements are transmitted via one or more of the electrical members in the cable 1 to processing structure (not shown). The processing structure processes the density and gravity measurements as described above to resolve the gravity contribution due to formations intersected by the borehole from the gravity contribution due to density variations that are remote from the borehole.
[00033] The processing structure in this embodiment is a general purpose computing device comprising a processing unit, system memory (volatile and/or non-volatile memory), other non-removable or removable memory (e.g. a hard disk drive, RAM, ROM, EEPROM, CD-ROM, DVD, flash memory, etc.), a display and a system bus coupling the various computer components to the processing unit. The computing device may also comprise networking capabilities using Ethernet, WiFi, and/or other suitable network format, to enable connection to shared or remote drives, one or more networked computers, or other networked devices.
[00034] Although embodiments have been described, those of skill in the art will appreciate that variations and modifications may be made without departing from the scope thereof as defined by the appended claims.
Claims (10)
1. A borehole logging method comprising:
running a density probe down a borehole, and at intervals during the running, using the density probe to take density measurements;
processing the density measurements taken at intervals by the density probe using a processor to determine gravitational effects of geologic formations intersected by the borehole;
running a gravity probe down the borehole, and at intervals during the running, using the gravity probe to take gravity measurements;
processing the gravity measurements taken at intervals by the gravity probe using the processor to remove the determined gravitational effects of geologic formations intersected by the borehole from the gravity measurements thereby to determine gravitational effects of geologic formations remote from the borehole; and utilizing the determined gravitational effects of geologic formations remote from the borehole to determine the nature of the remote geologic formations based on remote density variations.
running a density probe down a borehole, and at intervals during the running, using the density probe to take density measurements;
processing the density measurements taken at intervals by the density probe using a processor to determine gravitational effects of geologic formations intersected by the borehole;
running a gravity probe down the borehole, and at intervals during the running, using the gravity probe to take gravity measurements;
processing the gravity measurements taken at intervals by the gravity probe using the processor to remove the determined gravitational effects of geologic formations intersected by the borehole from the gravity measurements thereby to determine gravitational effects of geologic formations remote from the borehole; and utilizing the determined gravitational effects of geologic formations remote from the borehole to determine the nature of the remote geologic formations based on remote density variations.
2. The method of claim 1, wherein the density and gravity measurements are taken independently, at different times
3. The method of claim 1, wherein the density and gravity measurements are taken simultaneously.
4. The method of claim 1, wherein the density measurements are taken by the density probe at first vertical intervals along the borehole and wherein the gravity measurements are taken by the gravity probe at second longer vertical intervals along the borehole.
5. A borehole logging system comprising:
a density probe configured to take density measurements at intervals when run-in along a borehole;
a gravity probe configured to take gravity measurements at intervals when run-in along the borehole; and a processor communicating with the density probe and the gravity probe and configured to:
process the density measurements taken at intervals by the density probe to determine gravitational effects of geologic formations intersected by the borehole;
process the gravity measurements taken at intervals by the gravity probe to remove the determined gravitational effects of geologic formations intersected by the borehole from the gravity measurements thereby to determine gravitational effects of geologic formations remote from the borehole; and utilize the determined gravitational effects of geologic formations remote from the borehole to determine the nature of the remote geologic formations based on remote density variations.
a density probe configured to take density measurements at intervals when run-in along a borehole;
a gravity probe configured to take gravity measurements at intervals when run-in along the borehole; and a processor communicating with the density probe and the gravity probe and configured to:
process the density measurements taken at intervals by the density probe to determine gravitational effects of geologic formations intersected by the borehole;
process the gravity measurements taken at intervals by the gravity probe to remove the determined gravitational effects of geologic formations intersected by the borehole from the gravity measurements thereby to determine gravitational effects of geologic formations remote from the borehole; and utilize the determined gravitational effects of geologic formations remote from the borehole to determine the nature of the remote geologic formations based on remote density variations.
6. The borehole logging system of claim 5, wherein the density and gravity probes are configured to take the density measurements and gravity measurements at vertical intervals along the borehole either (i) simultaneously, or (ii) independently at different times.
7. The borehole logging system of claim 5, wherein the density probe is configured to take the density measurements at first vertical intervals and wherein the gravity probe is configured to take the gravity measurements at second vertical intervals, the first vertical intervals being smaller than the second vertical intervals.
8. The borehole logging system of any one of claims 5 to 7, wherein the density probe is one of a gamma-gamma density probe and a neutron gamma density probe.
9. The borehole logging system of claim 5, wherein the density probe and the gravity probe are combined in a single sonde.
10. The borehole logging system of any one of claims 5 to 7, wherein said density probe and gravity probe are separate sondes.
Applications Claiming Priority (4)
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|---|---|---|---|
| US39333910P | 2010-10-14 | 2010-10-14 | |
| US61/393,339 | 2010-10-14 | ||
| US39371710P | 2010-10-15 | 2010-10-15 | |
| US61/393,717 | 2010-10-15 |
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| CA2755229A1 CA2755229A1 (en) | 2012-04-14 |
| CA2755229C true CA2755229C (en) | 2019-02-26 |
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Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA2755229A Active CA2755229C (en) | 2010-10-14 | 2011-10-14 | Borehole logging system and method |
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|---|---|
| US (1) | US20130205887A1 (en) |
| CA (1) | CA2755229C (en) |
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| US11054539B2 (en) * | 2019-10-30 | 2021-07-06 | Vadim Kukharev | Methods of searching for mineral resources by analyzing geochemical and other anomalies during gravitational resonances |
Family Cites Families (11)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US3747403A (en) * | 1970-07-27 | 1973-07-24 | Chevron Res | Gravimetric determination of anomalies lateral to boreholes |
| US4399693A (en) * | 1982-01-08 | 1983-08-23 | Mobil Oil Corporation | Applications of borehole gravimetric techniques to determine residual oil saturation |
| US4419887A (en) * | 1982-05-13 | 1983-12-13 | Mobil Oil Corporation | Distinguishing true basement from dikes and sills encountered in drilling of a borehole through the earth |
| US4475386A (en) * | 1983-06-06 | 1984-10-09 | Mobil Oil Corporation | Borehole gravimetry system |
| US4712424A (en) * | 1984-01-26 | 1987-12-15 | Schlumberger Technology Corp. | Quantitative determination by elemental logging of subsurface formation properties |
| US5218864A (en) * | 1991-12-10 | 1993-06-15 | Conoco Inc. | Layer density determination using surface and deviated borehole gravity values |
| EP1292850A4 (en) * | 2000-04-14 | 2006-11-08 | Lockheed Corp | Method of determining boundary interface changes in a natural resource deposit |
| WO2009036420A1 (en) * | 2007-09-13 | 2009-03-19 | The Trustees Of Columbia University In The City Of New York | Methods of long-term gravimetric monitoring of carbon dioxide storage in geological formations |
| US8113042B2 (en) * | 2007-09-28 | 2012-02-14 | Schlumberger Technology Corporation | Gravity measurment methods for monitoring reservoirs |
| US9442214B2 (en) * | 2008-12-19 | 2016-09-13 | Schlumberger Technology Corporation | System and method for gravity measurement in a subterranean environment |
| US9651708B2 (en) * | 2011-04-21 | 2017-05-16 | Baker Hughes Incorporated | Method of mapping reservoir fluid movement using gravity sensors |
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2011
- 2011-10-14 CA CA2755229A patent/CA2755229C/en active Active
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2013
- 2013-01-21 US US13/745,988 patent/US20130205887A1/en not_active Abandoned
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| Publication number | Publication date |
|---|---|
| US20130205887A1 (en) | 2013-08-15 |
| CA2755229A1 (en) | 2012-04-14 |
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