WO2010129173A2 - Procédé et appareil pour les mesures de rmn dans des petits forages et pendant le forage sous-pression - Google Patents

Procédé et appareil pour les mesures de rmn dans des petits forages et pendant le forage sous-pression Download PDF

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Publication number
WO2010129173A2
WO2010129173A2 PCT/US2010/031903 US2010031903W WO2010129173A2 WO 2010129173 A2 WO2010129173 A2 WO 2010129173A2 US 2010031903 W US2010031903 W US 2010031903W WO 2010129173 A2 WO2010129173 A2 WO 2010129173A2
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Prior art keywords
borehole
earth formation
regions
examination
formation
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PCT/US2010/031903
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English (en)
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WO2010129173A3 (fr
Inventor
Thomas Kruspe
Martin Blanz
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Baker Hughes Incorporated
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Publication date
Priority claimed from US12/763,624 external-priority patent/US8330459B2/en
Application filed by Baker Hughes Incorporated filed Critical Baker Hughes Incorporated
Publication of WO2010129173A2 publication Critical patent/WO2010129173A2/fr
Publication of WO2010129173A3 publication Critical patent/WO2010129173A3/fr

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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01V—GEOPHYSICS; GRAVITATIONAL MEASUREMENTS; DETECTING MASSES OR OBJECTS; TAGS
    • G01V3/00—Electric or magnetic prospecting or detecting; Measuring magnetic field characteristics of the earth, e.g. declination, deviation
    • G01V3/18—Electric or magnetic prospecting or detecting; Measuring magnetic field characteristics of the earth, e.g. declination, deviation specially adapted for well-logging
    • G01V3/32—Electric or magnetic prospecting or detecting; Measuring magnetic field characteristics of the earth, e.g. declination, deviation specially adapted for well-logging operating with electron or nuclear magnetic resonance
    • 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
    • E21B47/10—Locating fluid leaks, intrusions or movements

Definitions

  • the present disclosure relates generally to determining geological properties of subsurface formations using Nuclear Magnetic Resonance ("NMR") methods for logging wellbores, particularly for correcting for the effects of fluid flow during underbalanced drilling on NMR signals.
  • NMR Nuclear Magnetic Resonance
  • a variety of techniques are currently utilized in determining the presence and estimation of quantities of hydrocarbons (oil and gas) in earth formations. These methods are designed to determine formation parameters, including among other things, the resistivity, porosity and permeability of the rock formation surrounding the wellbore drilled for recovering the hydrocarbons.
  • the tools designed to provide the desired information are used to log the wellbore. Much of the logging is done after the well bores have been drilled. More recently, wellbores have been logged while drilling, which is referred to as measurement-while-drilling (MWD) or logging- while-drilling (LWD).
  • MWD measurement-while-drilling
  • LWD logging- while-drilling
  • NMR Nuclear Magnetic Resonance
  • the NMR logging tools are utilized to excite the nuclei of the fluids in the geological formations surrounding the wellbore so that certain parameters such as nuclear spin density, longitudinal relaxation time (generally referred to in the art as Ti) and transverse relaxation time (generally referred to as T 2 ) of the geological formations can be measured. From such measurements, porosity, permeability and hydrocarbon saturation are determined, which provides valuable information about the make-up of the geological formations and the amount of extractable hydrocarbons.
  • Ti longitudinal relaxation time
  • T 2 transverse relaxation time
  • the NMR tools generate a static magnetic field in a region of interest surrounding the wellbore.
  • NMR is based on the fact that the nuclei of many elements have angular momentum (spin) and a magnetic moment.
  • the nuclei have a characteristic Larmor resonant frequency related to the magnitude of the magnetic field in their locality.
  • magnetization Over time the nuclear spins align themselves along an externally applied static magnetic field creating a macroscopic magnetization, in short: magnetization. This equilibrium situation can be disturbed by a pulse of an oscillating magnetic field, which tips the spins with resonant frequency within the bandwidth of the oscillating magnetic field away from the static field direction.
  • B 0 is the static magnetic flux density.
  • the magnetization returns to the equilibrium direction (i.e., aligned with the static field) according to a characteristic recovery time known as the "spin-lattice relaxation time" or T 1 .
  • T 1 is controlled by the molecular environment and is typically one millisecond to several seconds in rocks.
  • a receiving coil is designed so that a voltage is induced by the precessing spins. Only that component of the nuclear magnetization precesses that is orthogonal to the static magnetic field. The precessing component induces a signal in the receiving coil if its orientation is appropriate. After a 180° tipping pulse (an
  • inversion pulse the spins on resonance are aligned opposite to the static field and the magnetization relaxes along the static field axis to the equilibrium direction. Hence, a signal will be generated after a 90° tipping pulse, but not after a 180° tipping pulse in a generally uniform magnetic field.
  • a series of pulses is applied to repeatedly refocus the spin system, canceling the T 2 * effects and forming a series of spin echoes.
  • the decay of echo amplitude is a true measure of the decay due to material properties. Furthermore it can be shown that the decay is in fact composed of a number of different decay components forming a T 2 distribution.
  • the echo decay data can be processed to reveal this distribution which is related to rock pore size distribution and other parameters of interest to the well log analyst.
  • One embodiment of the disclosure is an apparatus configured to evaluate an earth formation having a fluid therein.
  • the apparatus includes: a carrier configured to be conveyed into a borehole in the earth formation wherein a pressure of a fluid in the formation exceeds a pressure of a fluid in the borehole; a magnet assembly on the carrier configured to produce a static magnetic field in the earth formation and define a region of examination; an antenna on the carrier configured to be activated with a pulse sequence and produce signals from nuclear spins in the region of examination; and a processor configured to estimate a value of a property of the earth formation using the produced signals; wherein a magnetic field gradient in the region of examination is selected to suppress an effect of a formation fluid flow on the produced signals, the fluid flow being caused by the excess pressure.
  • Another embodiment of the disclosure is a method of evaluating an earth formation having a fluid therein.
  • the method includes: conveying a carrier into a borehole in the earth formation wherein a pressure of a fluid in the formation exceeds a pressure of a fluid in the borehole; using a magnet assembly on the carrier for producing a static magnetic field in the earth formation and defining a region of examination; activating an antenna on the carrier with a pulse sequence and producing signals from nuclear spins in the region of examination; and using a processor for estimating a value of a property of the earth formation using the produced signals; wherein a magnetic field gradient in the region of examination is selected to suppress an effect of a formation fluid flow caused by the excess pressure on the produced signals.
  • Another embodiment of the disclosure is a computer-readable medium product having stored thereon instructions that when executed by a processor cause the processor to execute a method.
  • the method includes: estimating a value of a property of the earth formation using signals produced from a region of examination in the earth formation responsive to activation of an antenna in a borehole in the earth formation by a pulse sequence; wherein a pressure of a fluid in the formation exceeds a pressure of a fluid in the borehole; and wherein a magnetic field gradient in the region of examination is selected to suppress an effect of a formation fluid flow caused by the excess pressure on the produced signals.
  • One embodiment of the disclosure is an apparatus configured to evaluate an earth formation.
  • the apparatus includes: a carrier configured to be conveyed in a borehole in the earth formation; a magnet assembly on the carrier configured to produce a static magnetic field in the earth formation and define a plurality of regions of examination; a plurality of antennas on the carrier configured to be activated with a pulse sequence, each of the antennas configured to produce a signal from nuclear spins from an associated one of the plurality of regions of examination; and a processor configured to estimate a value of a property of the earth formation using the produced signal from each of the plurality of regions of examination.
  • Another embodiment of the disclosure is a method of evaluating an earth formation.
  • the method includes: conveying a carrier into a borehole in the earth formation; using a magnet assembly on the carrier configured for producing a static magnetic field in the earth formation and defining a plurality of regions of examination; activating a plurality of antennas on the carrier with a pulse sequence, each of the antennas configured to produce a signal from nuclear spins from an associated one of the plurality of regions of examination; and using a processor for estimating a value of a property of the earth formation using the produced signal from each of the plurality of regions of examination.
  • Another embodiment of the disclosure is a computer-readable medium product having stored thereon instructions that when executed by a processor cause the processor to execute a method.
  • the method includes: estimating a value of a property of the earth formation using signals produced from each of a plurality of regions of examination in the earth formation responsive to activation of a plurality of antennas in a borehole by a pulse sequence.
  • One embodiment of the disclosure is an apparatus configured to evaluate an earth formation.
  • the apparatus includes: a carrier configured to be conveyed in a borehole in the earth formation; a magnet assembly on the carrier configured to produce a static magnetic field in the earth formation and define a plurality of regions at different radial distance from the borehole; at least one antenna on the carrier configured to be activated with at least one pulse sequence, the at least one pulse sequence configured to produce a signal from nuclear spins from an associated one of the plurality of regions of examination; and a processor configured to estimate a value of a property of the earth formation at the different radial distances using the produced signal from each of the plurality of regions of examination.
  • Another embodiment of the disclosure is a method of evaluating an earth formation.
  • the method includes: conveying a carrier into a borehole in the earth formation; using a magnet assembly on the carrier for producing a static magnetic field in the earth formation and defining a plurality of regions at different radial distance from the borehole; activating at least one antenna on the carrier with at least one pulse sequence, the at least one pulse sequence configured to produce a signal from nuclear spins from an associated one of the plurality of regions of examination; and using a processor for estimating a value of a property of the earth formation Oat the different radial distances using the produced signal from each of the plurality of regions of examination.
  • Another embodiment of the disclosure is a computer-readable medium product having stored thereon instructions that when executed by a processor cause the processor to execute a method.
  • the method includes: estimating a value of a property of the earth formation at each of a plurality of regions of examination at different radial distances from a borehole using signals produced signal from each of the plurality of regions of examination responsive to activation of at least one antenna with at least one pulse sequence, the at least one pulse sequence configured to produce a signal from nuclear spins from an associated one of the plurality of regions of examination.
  • FIG. 1 shows a measurement-while-drilling tool suitable for use with the present disclosure
  • FIG. 2 shows a sensor section of a measurement-while-drilling device suitable for use with the present disclosure
  • FIG. 3 shows an NMR sensor having multiple regions of examination
  • FIG. 4(a) shows an NMR sensor having axially spaced apart multiple regions of examination of different depths into the formation
  • FIG. 4(b) shows an NMR sensor having multiple regions of examination of different depths into the formation a the same axial depth
  • FIG. 5 shows three different regions of examination from which T 2 distributions are obtained and shown schematically by 501, 503 and 505 in (a), (b) and (c), and the estimate NMR porosity versus depth of investigation shown in (e);
  • FIG. 6 shows a flow chart for estimating different formation properties using
  • FIGS. 7(a)-(e) shows different hardware configurations to reduce the radial field gradient.
  • FIG. 1 shows a schematic diagram of a drilling system 10 with a drillstring 20 carrying a drilling assembly 90 (also referred to as the bottomhole assembly, or "BHA") conveyed in a "wellbore" or “borehole” 26 for drilling the wellbore.
  • the drilling system 10 includes a conventional derrick 11 erected on a floor 12 which supports a rotary table 14 that is rotated by a prime mover such as an electric motor (not shown) at a desired rotational speed.
  • the drillstring 20 includes a tubing such as a drill pipe 22 or a coiled-tubing extending downward from the surface into the borehole 26. The drillstring 20 is pushed into the wellbore 26 when a drill pipe 22 is used as the tubing.
  • a tubing injector such as an injector (not shown), however, is used to move the tubing from a source thereof, such as a reel (not shown), to the wellbore 26.
  • the drill bit 50 attached to the end of the drillstring breaks up the geological formations when it is rotated to drill the borehole 26.
  • the drillstring 20 is coupled to a drawworks 30 via a Kelly joint 21, swivel 28, and line 29 through a pulley 23.
  • the drawworks 30 is operated to control the weight on bit, which is an important parameter that affects the rate of penetration.
  • the operation of the drawworks is well known in the art and is thus not described in detail herein.
  • axial velocity rate of penetration or ROP
  • Depth information and ROP may be communicated downhole from a surface location.
  • the method disclosed in U.S. Patent 6,769,497 to Dubinsky et al. having the same assignee as the present application and the contents of which are incorporated herein by reference may be used.
  • the method of Dubinsky uses axial accelerometers to determine the ROP.
  • a suitable drilling fluid 31 from a mud pit (source) 32 is circulated under pressure through a channel in the drillstring 20 by a mud pump 34.
  • the drilling fluid passes from the mud pump 34 into the drillstring 20 via a desurger (not shown), fluid line 38 and Kelly joint 21.
  • the drilling fluid 31 is discharged at the borehole bottom 51 through an opening in the drill bit 50.
  • the drilling fluid 31 circulates uphole through the annular space 27 between the drillstring 20 and the borehole 26 and returns to the mud pit 32 via a return line 35.
  • the drilling fluid acts to lubricate the drill bit 50 and to carry borehole cutting or chips away from the drill bit 50.
  • a sensor Si typically placed in the line 38 provides information about the fluid flow rate.
  • a surface torque sensor S 2 and a sensor S 3 associated with the drillstring 20 respectively provide information about the torque and rotational speed of the drillstring. Additionally, a sensor (not shown) associated with line 29 is used to provide the hook load of the drillstring 20.
  • the drill bit 50 is rotated by only rotating the drill pipe 22.
  • a downhole motor 55 (mud motor) is disposed in the drilling assembly 90 to rotate the drill bit 50 and the drill pipe 22 is rotated usually to supplement the rotational power, if required, and to effect changes in the drilling direction.
  • the mud motor 55 is coupled to the drill bit 50 via a drive shaft (not shown) disposed in a bearing assembly 57.
  • the mud motor rotates the drill bit 50 when the drilling fluid 31 passes through the mud motor 55 under pressure.
  • the bearing assembly 57 supports the radial and axial forces of the drill bit.
  • a stabilizer 58 coupled to the bearing assembly 57 acts as a centralizer for the lowermost portion of the mud motor assembly.
  • a drilling sensor module 59 is placed near the drill bit 50.
  • the drilling sensor module contains sensors, circuitry and processing software and algorithms relating to the dynamic drilling parameters. Such parameters typically include bit bounce, stick-slip of the drilling assembly, backward rotation, torque, shocks, borehole and annulus pressure, acceleration measurements and other measurements of the drill bit condition.
  • a suitable telemetry or communication sub 72 using, for example, two-way telemetry, is also provided as illustrated in the drilling assembly 90.
  • the drilling sensor module processes the sensor information and transmits it to the surface control unit 40 via the telemetry system 72.
  • the communication sub 72, a power unit 78 and an MWD tool 79 are all connected in tandem with the drillstring 20. Flex subs, for example, are used in connecting the MWD tool 79 in the drilling assembly 90. Such subs and tools form the bottom hole drilling assembly 90 between the drillstring 20 and the drill bit 50.
  • the drilling assembly 90 makes various measurements including the pulsed nuclear magnetic resonance measurements while the borehole 26 is being drilled.
  • the communication sub 72 obtains the signals and measurements and transfers the signals, using two-way telemetry, for example, to be processed on the surface. Alternatively, the signals can be processed using a downhole processor in the drilling assembly 90.
  • the surface control unit or processor 40 also receives signals from other downhole sensors and devices and signals from sensors S 1 -S 3 and other sensors used in the system 10 and processes such signals according to programmed instructions provided to the surface control unit 40.
  • the surface control unit 40 displays desired drilling parameters and other information on a display/monitor 42 utilized by an operator to control the drilling operations.
  • the surface control unit 40 typically includes a computer or a microprocessor-based processing system, memory for storing programs or models and data, a recorder for recording data, and other peripherals.
  • the control unit 40 is typically adapted to activate alarms 44 when certain unsafe or undesirable operating conditions occur.
  • a suitable device for use of the present disclosure is disclosed in U.S. Patent 6,215,304 to Slade, the contents of which are fully incorporated herein by reference. It should be noted that the device taught by Slade is for exemplary purposes only, and the method of the present disclosure may be used with many other NMR logging devices, and may be used for wireline as well as MWD applications.
  • drillstring underbalanced drilling is commonly carried out using a coiled tubing instead of a drillstring.
  • drilling tubular is intended to include both a drillstring as well as coiled tubing.
  • the tool has a drill bit 107 at one end, a sensor section 102 behind the drill head, and electronics 101.
  • the sensor section 102 comprises a magnetic field generating assembly for generating a B 0 magnetic field (which is substantially time invariant over the duration of a measurement), and an RF system for transmitting and receiving RF magnetic pulses and echoes.
  • the magnetic field generating assembly comprises a pair of axially spaced main magnets 103, 104 having opposed pole orientations (i.e. with like magnetic poles facing each other), and three ferrite members 109, 110 axially arranged between the magnets 103, 104.
  • the ferrite members are made of "soft" ferrite which can be distinguished over “hard” ferrite by the shape of the BH curve which affects both intrinsic coercivity (H j the intersection with the H axis) and initial permeability ( ⁇ l5 the gradient of the BH curve in the unmagnetized case).
  • Soft ferrite ⁇ ! values typically range from 10 to 10000 whereas hard ferrite has ⁇ l5 of about 1. Therefore the soft ferrite has large initial permeability (typically greater than 10, preferably greater than 1000).
  • the RF system comprises a set of RF transmit antenna and RF receive antenna coil windings 105 arranged as a central "field forming" solenoid group 113 and a pair of outer “coupling control" solenoid groups 114.
  • the tool has a mud pipe 160 with a clear central bore 106 and a number of exit apertures 161-164 to carry drilling mud to the bit 107, and the main body of the tool is provided by a drill collar 108.
  • Drilling mud is pumped down the mud pipe 160 by a pump 121 returning around the tool and the entire tool is rotated by a drive 120.
  • Coiled tubing or a drillstring may be used for coupling the drive to the downhole assembly.
  • the drill collar 108 provides a recess 170 for RF transmit antenna and RF receive antenna coil windings 105. Gaps in the pockets between the soft ferrite members are filled with non-conducting material 131, 135 (e.g: ceramic or high temperature plastic) and the RF coils 113, 114 are then wound over the soft ferrite members 109, 110.
  • the soft ferrites 109, 110 and RF coil assembly 113, 114 are pressure impregnated with suitable high temperature, low viscosity epoxy resin (not shown) to harden the system against the effects of vibration, seal against drilling fluid at well pressure, and reduce the possibility of magnetoacoustic oscillations.
  • the RF coils 113, 114 are then covered with wear plates 111 typically ceramic or other durable non-conducting material to protect them from the rock chippings flowing upwards past the tool in the borehole mud.
  • the device of Slade has an axisymmetric magnetic field and region of investigation 112 that is unaffected by tool rotation. Use of the ferrite results in a region of investigation that is close to the borehole. This is not a major problem on a MWD tool (except for special situations discussed below that are the focus of this disclosure) because there is little invasion of the formation by borehole drilling fluids prior to the logging.
  • the region of investigation is within a shell with a radial thickness of about 20 mm and an axial length of about 50 mm.
  • the gradient within the region of investigation is less than 2.7 G/cm.
  • This field gradient of less than 2.7 G/cm may be considered to be a "near zero" field gradient for the purposes of the present disclosure as discussed below.
  • Two magnetic fields are used to conduct a typical NMR measurement: a static magnetic field B 0 and an alternating magnetic field Bi having a component orthogonal to Bo- Pulsed NMR is used in which the alternating field Bi is applied into the sample as a sequence of bursts (usually called pulses): TW - TP - Ti - (RP - T 2 - echo - ⁇ 2 ) n wherein TW is a (long) wait time of usually several times the spin lattice relaxation time, TP is a tipping pulse for tipping the nuclear spins at an angle substantially equal to ninety degrees to cause precession thereof, T 1 , T 2 are waiting times, RP is a refocusing pulse for tipping the nuclear spins greater than 90° and n is the number of echoes to be acquired in one sequence.
  • bursts usually called pulses
  • the duration of the events between the echos is called the interecho time TE.
  • the echoes manifest themselves as rotating macroscopic magnetizations and can be detected with a receiver coil.
  • the induced voltages/currents in this coil are the desired NMR signals.
  • B 0 and Bi amplitudes As well as pulse phases and shapes need to be chosen correctly as known to people familiar with the art of NMR.
  • An exemplary optimized echo sequence called ORPS is discussed, for example, in Hawkes '013.
  • the tipping pulse is typically 90°, but the refocusing pulses are less than 180°. This is in contrast to the CPMG sequence in which the refocusing pulses are 180° pulses.
  • the geometry of the NMR measurement device gives rise to a volume in the earth formation where the B 0 field has the correct strength to fulfill a resonance condition and in which an RF field can be presented with a substantial strength and orientation to reorient nuclear spins within the volume.
  • This volume is often referred to as the sensitive volume.
  • the volume containing those protons excited by the excitation pulse first pulse of the echo sequence
  • the number of spins available to contribute to the subsequent NMR signal is reduced with each subsequent echo.
  • those echoes obtained later in an echo sequence with axial tool motion appear small compared to those echoes obtained later in an echo sequence acquired with no tool motion.
  • “Later echoes" does not mean that only the last echoes of a sequence are affected. In fact, the loss of signal starts right at the beginning of a sequence and develops over time in a unique pattern. This phenomenon is called outflow.
  • NMR echo sequences are repeated several times for the purpose of increasing the final signal-to-noise ratio. Even without concern over signal-to-noise ratio, an echo sequence is usually repeated at least once in order to form a phase- alternated pair (PAP) for the purpose of removing offset and ringing effects.
  • PAP phase- alternated pair
  • the magnetization of the sensitive volume is substantially zero.
  • a wait time TW during which re- magnetization of the formation occurs is used as part of the sequence of pulses. Choosing a wait time of at least 5 times the longest Ti of the formation ensures that the formation is fully magnetized (>99% magnetization) immediately prior to the excitation pulse of the ensuing sequence. However, shorter wait times are often chosen in order to achieve a higher NMR data rate, leading to an improved axial resolution or signal-to-noise ratio.
  • the drawback of shortening TW is that the formation may not be fully magnetized immediately prior to the ensuing sequence. As a consequence, the total porosity that is measured in a tool having axial motion can be too low, and the measured T 2 -distribution is generally distorted, mainly for the longer T 2 components.
  • a similar solution can be used for a different problem, that of making NMR measurements in small boreholes.
  • a BHA designed for use in a small borehole is limited to a small magnet size, so that a normal tool would have a small region of investigation. With small sensitive regions it is difficult to achieve a sufficient signal to noise ratio, which is required to have a high accuracy of the measurement combined with a good vertical resolution.
  • one embodiment of the disclosure combines multiple resonance areas to one big sensitive region, where the measurement is carried out. This combination can be done by designing one common antenna covering all areas.
  • FIG. 3 shows an exemplary logging tool 301.
  • Three magnets 303 are shown. Adjacent magnets have like poles facing each other so as to define two regions of examination 309a, 309b.
  • Antennas 307 are used for generating the RF pulses and measuring the spin echo signals.
  • the electronics module 305 that includes a processor is used for processing the signals received by the antennas. In the configuration shown, the signals from the two antennas are summed, so that effectively, signals from a region of examination that is a combination of 309a and 309b are obtained. This increases the signal to noise ratio, but also reduces the vertical resolution of the NMR measurements.
  • the BHA may be considered to be a "carrier” and the magnet assembly produces a static magnetic field in one or more regions of examination.
  • the static field gradient in the region of examination is nearly zero, so that during the length of the pulse sequence given by eqn. (1), the "outflow" effect is small and signals are obtained from nuclear spins that have been polarized.
  • Another factor to be considered is that the outflow during the time TE should also be small, so that the spin echo signals are without phase distortion.
  • Fig. 3 is directed towards the problem of obtaining an adequate signal in a small borehole.
  • the same design with a single region of examination can be used to address the problem of fluid inflow by selecting the combination of field gradient, and echo train length to satisfy the outflow condition.
  • the spin echo signals from 309a and 309b are stored separately in the electronics module. Depth determinations may be conveniently made by having synchronized clocks downhole and uphole and measuring the length of the drill string at the surface. When drilling has progressed so that the measurements made in one region of examination (say 309b) are at the same depth as those made earlier in the other region of examination (say 309a), then the data corresponding to the same depth are combined. This method of summing data from the same depth increases the signal to noise ratio without reducing the vertical resolution.
  • the formation contains gas which is flowing to the borehole because the pressure in the borehole is lower than the pressure in the formation, we may measure the NMR-properties in a transition zone. Applying a tool with several resonance areas as shown in FIG. 4, having different depths of investigation, would allow characterizing the transition zone. Shown in FIG. 4a is a tool with three regions of investigation 409a, 409b and 409c that can be obtained using a tool 401 having four magnets 403 and three RF coils 407. Different depths of investigation can be obtained by changing the static magnetic field (using different magnet configurations)
  • a pair of magnets 453 and one antenna 457 can be configured to get NMR signals from a multitude of sensitive regions 459a, 459b, 459c having different radial depths of investigation.
  • the different sensitive regions may be selected by using different carrier frequencies for the radio-frequency magnetic field.
  • FIG. 5(a) shows three different regions of examination.
  • FIG. 5(b) shows an exemplary T 2 distribution 501 estimated from signals from the first region
  • FIG. 5(c) shows an exemplary T 2 distribution 503 estimated from signals from the second region
  • FIG. 5(d) shows an exemplary T 2 distribution 505 estimated from signals from the third region.
  • FIG. 5(e) shows estimated porosities 511, 513, 515 from FIGS.
  • FIG. 6 a schematic flow chart illustrates different formation properties that can be estimated from NMR measurements at different depths of investigation.
  • NMR measurements are made at a plurality of depths of investigation 601 and the borehole pressure is measured 603. From these, it is possible to estimate the formation permeability from Ti or T 2 .
  • the permeability can be estimated using Coates' method, or a value from an offset well may be used. It is also possible to determine the fluid volume in the pore space, compressible gas volume and porosity at each of the depths of investigation and extrapolate to the formation away from the borehole as discussed above: methods for estimation of water saturation, oil saturation, gas saturation and porosity from T 2 distributions are known in prior art.
  • FIG. 7(a) shows the important components of the NMR tool. They are the permanent magnets 701, the soft magnetic antenna core 703 and the RF antenna 705.
  • FIG. 7(b) the length of the antenna cores is reduced relative to the length in FIG. 7(a).
  • FIG. 7(c) thickness of the antenna cores is reduced relative to FIG. 7(a).
  • FIG. 7(d) the gap between the magnets and the antenna core is increased relative to FIG. 7(a).
  • FIG. 7(e) the gap between the magnets and the antenna core are the same as in FIG. 7(a) while the cross sectional area of the magnets is reduced. All of these design modifications result in different sizes of the region where the magnetic field gradient is near zero.
  • the disclosure has been described with reference to a NMR device that is part of a BHA conveyed on a drillstring.
  • the disclosure is equally applicable for NMR devices conveyed on coiled tubing.
  • the processing described herein may be done using a downhole processor and the results stored on a suitable memory downhole or telemetered to the surface.
  • the data may be stored on a downhole memory and processed when the BHA is tripped out of the borehole. With improved telemetry capability, it should be possible to telemeter the NMR measurements to a surface location and do the processing there.
  • the results of the processing may be used to estimate, using known methods, properties of interest such as a T 2 distribution, volumetrics, permeability, bound volume irreducible, effective porosity, bound water, clay-bound water, total porosity, pore size distribution, and other rock and fluid properties that are based on NMR data. These are all used in reservoir evaluation and development.
  • the processing of the data may be conveniently done on a processor.
  • the processor executes a method using instructions stored on a suitable computer-readable medium product.
  • the computer-readable medium may include a ROM, an EPROM, an EAROM, a flash memory, and/or an optical disk.

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Abstract

Des signaux d'écho de spin de RMN sont mesurés dans un forage pendant le forage en sous-pression. Un gradient de champ magnétique dans la région d'examen est sélectionné pour supprimer un effet d'un écoulement de fluide de formation sur les signaux produits, l'écoulement de fluide étant provoqué par l'excès de pression de formation sur la pression de fluide de forage. Les mesures de RMN pendant le forage de petits trous sont effectuées en combinant les signaux de plusieurs régions d'examen. En procédant à des mesures dans une pluralité de régions espacées radialement les unes des autres, un profil radial d'une propriété de formation peut être évalué. De plus, une alerte de bouchon de gaz peut être prévue.
PCT/US2010/031903 2009-05-08 2010-04-21 Procédé et appareil pour les mesures de rmn dans des petits forages et pendant le forage sous-pression WO2010129173A2 (fr)

Applications Claiming Priority (8)

Application Number Priority Date Filing Date Title
US17679109P 2009-05-08 2009-05-08
US61/176,791 2009-05-08
US12/763,624 2010-04-20
US12/763,711 2010-04-20
US12/763,597 2010-04-20
US12/763,624 US8330459B2 (en) 2009-05-08 2010-04-20 Method and apparatus for NMR measurements in small boreholes
US12/763,711 US8604783B2 (en) 2009-05-08 2010-04-20 Method and apparatus for NMR measurements while drilling with multiple depths of investigation
US12/763,597 US8587303B2 (en) 2009-05-08 2010-04-20 Method and apparatus for NMR measurements in underbalanced drilling

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US6650114B2 (en) * 2001-06-28 2003-11-18 Baker Hughes Incorporated NMR data acquisition with multiple interecho spacing
US7180288B2 (en) * 2004-11-10 2007-02-20 Schlumberger Technology Corporation Downhole NMR flow and formation characterization while sampling fluids
US7358725B2 (en) * 2004-08-16 2008-04-15 Baker Hughes Incorporated Correction of NMR artifacts due to axial motion and spin-lattice relaxation

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US6429654B1 (en) * 1998-09-11 2002-08-06 Baker Hughes Incorporated Nuclear magnetic resonance pulse sequence for improving signal-to-noise ratio
US6650114B2 (en) * 2001-06-28 2003-11-18 Baker Hughes Incorporated NMR data acquisition with multiple interecho spacing
US7358725B2 (en) * 2004-08-16 2008-04-15 Baker Hughes Incorporated Correction of NMR artifacts due to axial motion and spin-lattice relaxation
US7180288B2 (en) * 2004-11-10 2007-02-20 Schlumberger Technology Corporation Downhole NMR flow and formation characterization while sampling fluids

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