Classifications

• • 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
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
  • G01R33/00—Arrangements or instruments for measuring magnetic variables
  • G01R33/20—Arrangements or instruments for measuring magnetic variables involving magnetic resonance
  • G01R33/60—Arrangements or instruments for measuring magnetic variables involving magnetic resonance using electron paramagnetic resonance

Definitions

• This invention relates to locating subterranean formations of crude oil, and more particularly to determining porosity and permeability parameters of such formations.
• NMR nuclear magnetic resonance
• NMR techniques may be used to determine pore size distribution and the porosity and the permeability of the rock. With this information, a decision can be made whether a particular rock formation contains a sufficient amount of recoverable fluid such that drilling is profitable.
• NMR porosity and permeability estimates do not typically attempt to differentiate between the effect of varying proportions of oil and water in the fluid.
• the invention uses a magnetic resonance technology, specifically electron paramagnetic resonance (EPR) , also known as electron spin resonance (ESR) , to detect and measure the concentration of crude oil and certain other hydrocarbon solids and liquids contained within underground formations.
• EPR electron paramagnetic resonance
• ESR electron spin resonance
• Such detection and measurement may be obtained from the surface of the earth to appreciable depths below the surface. They may also be obtained from locations adjacent to the walls of natural openings in the earth's surface (such as caves, open faults, cliffs, sink holes, and hillsides) or in man made earth penetrations (such as tunnels, wells, trenches or boreholes) .
• EPR data is particularly advantageous in that EPR response signals emanate only from unpaired electrons, such as those due to broken bonds in high molecular weight (MW) hydrocarbon compounds, in paramagnetic and ferromagnetic materials, and in a few metals.
• unpaired electrons such as those due to broken bonds in high molecular weight (MW) hydrocarbon compounds, in paramagnetic and ferromagnetic materials, and in a few metals.
• broken bonds and paramagnetic ions are commonly found in, but not limited to, many crude oils, asphalts, and coals.
• the presence of these materials in the earth, or elsewhere, may be detected and measured by the invention.
• the invention provides rapid detection and measurement as compared to other magnetic resonance methods, such as nuclear magnetic resonance (NMR) .
• NMR nuclear magnetic resonance
• the time required to polarize and measure such electrons is commonly on the order of a few microseconds or less.
• the invention also includes the use of EPR in combination with nuclear magnetic resonance (NMR) to provide additional advantages
• FIGURE 1 illustrates an NMR/ESR detector in accordance with the invention.
• FIGURES 2A - 2K illustrate various embodiments of antenna of FIGURE 1.
• FIGURES 3A - 3G illustrate various embodiments of the magnet of FIGURE 1.
• FIGURE 4 illustrates the magnet and antenna of FIGURE 1, and a second antenna, such that the generation of the B- field and the detection of response signals are performed by two different antennas.
• FIGURES 5A - 5D illustrate EPR signals from four different crude oil fields, respectively.
• ESR electronic spin paramagnetic resonance
• FIGURE 1 illustrates an EPR detector 100 in accordance with the invention.
• FIGURE 1 is an illustrative embodiment, and many variations of this embodiment are within the scope of the invention.
• detector 100 generates the magnetic fields for obtaining an EPR response signal, and receives and analyzes the EPR response signal to determine the crude oil content of an underground formation.
• the EPR analysis performed by detector 100 can be supplemented with an NMR analysis, by also using the same detector 100 to generate the magnetic fields appropriate for obtaining, receiving and analyzing an NMR response signal.
• FIGURE 1 is in terms of EPR detection, detector 100 may also be used for NMR detection.
• the use of both EPR and NMR response signals permits not only crude oil content to be determined, but also characteristics of the underground formation, such as pore size.
• a magnet 101 produces a magnetic field of intensity B 0 (in gauss) in a sensitive region.
• B 0 in gauss
• EPR signals may be detected from materials in the sensitive region.
• a transmitter 102 provides power at frequency f 0 , through duplexer 103 (or circulator or coupler) to antenna 104.
• the result is an electromagnetic field of intensity B ⁇ (in gauss) in the sensitive region.
• B ⁇ in gauss
• the plane of the B x field is perpendicular to that of the B 0 field.
• the sensitivity of detector 100 generally varies as a function of sin ⁇ where ⁇ is the angle between the B 1 and B 0 field vectors.
• antenna 104 receives an EPR response signal from the material in the sensitive zone.
• the incoming signal is delivered via duplexer 103 and filter 105 to a radio frequency (RF) amplifier/detector 106.
• RF radio frequency
• a second (receiving) antenna may be used for reception of the EPR response signal.
• This receiving antenna would be located in view of the sensitive zone, and connected through filter 105 to RF amplifier/detector 106.
• the receiving antenna could be oriented and located to reject direct pickup of the transmitter signal from the transmitting antenna 104, while obtaining maximum pickup of the cross polarized component of the EPR response signal from the sensitive zone. If a separate receiving antenna is used, then duplexer 103 is not required and transmitter 102 may be connected directly to the transmitting antenna 104.
• detector 100 may incorporate a modulation feature.
• modulation feature A variety of different modulation techniques may be used either singly or in combination.
• Coils 107 may be used for this purpose, energized with ac current.
• One modulation technique involves modulation of the intensity of the magnetic field, B 0 .
• B 0 may be slowly swept through resonance, and the peak amplitude of the detected signal detected and recorded. The presence of a signal at a specific range of the sweep is detected.
• a fixed B 0 field for electron magnetic resonance on the transmitter frequency, f 0 may be modulated by a high frequency current of frequency, f lf in coils 107.
• any EPR response from material in the sensitive region will contain spectral components of f 0 as well as of f 0 ⁇ £ ⁇ .
• filter 105 may be set to pass only the upper (f 0 + f ⁇ ) or lower (f 0 -f x ) sideband and to reject the strong direct transmitter signal at frequency f 0 .
• the sideband signal amplitude will be proportional to the unpaired electrons in the sensitive region.
• Quadrature detection means may be used to recover both upper and lower sidebands simultaneously while rejecting f 0 for more sensitive detection.
• a frequency controller 109 uses detected data to maintain the frequency of transmitter 102 on the EPR frequency.
• Another modulation method uses transmitter 102 to produce pulsed RF signals of the EPR frequency, f 0 .
• the pulses are short compared to a relaxation time, T 2 , which is explained below.
• T 2 a relaxation time
• the pulse duration might be the reciprocal of the spectral line width.
• EPR such conditions typically require pulses having a duration within a range of 2 to 10 nanoseconds.
• the field modulation coils 107 and field modulator 108 are not required for the pulse mode.
• the EPR response signal is received by amplifier/detector 106.
• a data processor 110 stores and executes programming appropriate to perform various calculations, which are explained below. As explained below, processor 110 analyzes the EPR response signal, and may also analyze an NMR response signal . It is assumed that processor 110 has appropriate processing memory and program memory for executing the programming.
• a user interface 111 may provide a display and/or printout of the results of the calculations.
• FIGURES 2A - 2K illustrate a variety of embodiments of antenna 104. In the following discussion, each different antenna 104 is identified as antenna 104 [2X] , with the 2X corresponding to the associated figure number 2A -2K.
• FIGURE 2A illustrates a loop antenna 104 (2A) .
• the loop 201 is tuned to the ESR frequency by a capacitor 202.
• the loop 201 may be round, square, rectangular or any shape and may be open or closed as shown. It may be of a single turn or multiple turns and may be fed by an impedance matching coupler or by a section of open transmission line to form a high "Q' resonant cavity with the loop unshielded.
• FIGURE 2B illustrates a capacitive loaded loop antenna 104 (2B) , which is made up of wire or metal strip segments 203 separated by capacitors 204, which tune out part of the reactance. This allows a larger area to be made resonant at a higher EPR frequency than would be possible without capacitors 204.
• Loop antenna 104 (2B) is coupled to detector 100 through an impedance matching network which may also act with antenna 104 (2B) as a high "Q" resonator.
• FIGURE 2C illustrates a resonant half-wavelength dipole antenna 104 (2C) , which is coupled to detector 100 through a matched transmission line.
• Antenna 104 (2C) may be located in close proximity and parallel to the plane of a metal plate to improve the directivity and increase the
• FIGURE 2D illustrates a crossed dipole antenna
• the two dipoles 205 and 206 are perpendicular to each other and electronically phased at 90 degrees to each other to produce a circularly polarized wave or at 0 or 180 degrees to produce a linear polarization.
• the crossed dipole antenna 104 (2D) may also be located in close proximity to the plane of a metal plate 207 to improve the directivity and increase the Q.
• FIGURE 2E illustrates a microstrip "patch" antenna 104 (2E), which has a metal conducting layer 209 separated by a thin low-loss dielectric 210, from a metal backing plate 211.
• Layer 209 is approximately one-half wavelength electrically square and may be fed by an impedance matched coaxial transmission line from a tap point and the backing plate 211 to produce a vertical H-plane wave, a horizontal H-plane wave, or circular polarized wave, as selected by the position of the tap point.
• Layer 209 may be round or elliptical or rectangular.
• Patch antenna 104 (2E) has a high Q and a directivity that are controlled by its physical size, the thickness of insulation layer 210, the dielectric constant of insulator layer 210, and the size of backing plate 211. Multiple patch antennas 104 (2E) may be used in an array and appropriately phased to produce greater directivity, a larger near field sensitive region, and a far field of reduced beamwidth.
• the layer structure of antenna 104 (2E) may be curved to fit around a portion of a round pipe or rod.
• FIGURE 2F illustrates a rectangular patch antenna 104 (2F) and
• FIGURE 2G illustrates a rectangular patch antenna 104 (2G) on a curved backing.
• the metal conducting layer 212 is resonant at the frequency f 0 being substantially one-half wavelength long, but substantially less than one-half wavelength wide. These antennas may be used to generate a linear polarized wave, but not a circularly polarized wave.
• FIGURE 2H illustrates a phased dipole array antenna 104 (2H) , comprising a configuration of phased, vertical dipoles 220 mounted around the periphery of a metal tube or rod 221.
• the 220 dipoles are spaced from rod 221 by a distance selected to meet physical size, impedance, and Q constraints.
• Antenna 104 (2H) is intended for use in bore holes to determine properties of the formation outside the bore hole.
• the dipoles 220 are electrically phased at 90 degrees relative to each other by feed line network 222 to produce a circular pattern about rod 221 with the H-field encircling the rod 221.
• Rod 221 could be magnetized axially to produce H-field lines parallel to the rod.
• Additional encircling arrays of dipoles 220 may be used around rod 221 to extend the axial length of a sensitive region in the formation that is coaxial with and along the axial direction of rod 221.
• FIGURE 21 illustrates a phased patch array antenna 104 (21) , which is similar in concept to the antenna of FIGURE 2H, except that patch type antennas 223 are used in the phased encircling array.
• Antenna 104(21) is particularly advantageous because it may be mounted to directly fit the contour of the rod 224 (or magnet) due to a metal backing plate.
• the encircling patches 223 are electrically phased at 90 degrees by a feed line network to produce a circular sensitive zone that is coaxial with the magnet. By selection of the feed point the H-field from the patch array may be made vertical, horizontal or circular to allow a match to the requirements of different magnetic field directions and configurations. Patch arrays may be stacked vertically along the rod to extend the length of the sensitive region.
• FIGURE 2J illustrates a horn antenna 104 (2J) , which provides a directive pattern and field concentration that can extend the useful range between the ESR sensor and the sensitive region of the material .
• the H component of the B : field may be vertical or horizontal, as required to make the Bj_ field perpendicular to the B 0 field.
• FIGURE 2K illustrates a solenoid coil or helical antenna 104 (2K) .
• the helical configuration is approximately one wavelength in diameter.
• the sensitive region extends along the axis from one end of the coil.
• the directivity increases with number of turns.
• a backing plate (reflection) is used at the feed end.
• FIGURES 3A - 3G illustrate a variety of embodiments of magnet 101.
• Each of these magnets 101 provides the B 0 field required to establish resonance at the selected EPR frequency.
• each different magnet 101 is identified as magnet 101 [3X] , with the 3X corresponding to the associated figure number 3A -3G.
• FIGURE 3A is a loop type electromagnet 101 (3A), which carries an electrical current and produces a magnetic field that is oriented perpendicular to the plane of the loop.
• the current may be a DC current to provide a static magnetic field, in particular, a static magnetic field that adds to the earth's magnetic field intensity in the area of the loop and in the spatial volume extending both above and below and around the loop area.
• the current may be an AC current of a selected frequency to modulate the magnetic field intensity as described above.
• the loop may have a round, square, rectangular, triangular, or non-uniform shape. Its size is comparable to the maximum distance to the desired locations of the sensitive region outside the 10
• Electromagnet 101 could be oriented to provide a polarized B 0 field in the desired spatial region.
• Two loop antennas 101 (3A) may be used side by side in the same plane to produce a magnetic field component, parallel to the plane and both above and below the loops, in the space between the loops .
• Antenna 104 would be oriented to provide the properly polarized B 1 field in this region.
• FIGURE 3B illustrates a rod magnet 101 (3B) , which provides a field along the axis and a near coaxial B 0 field along its length.
• the B 0 field intensity decreases as a function of distance away from the diameter of rod antenna 101 (3B) , but is constant at all angles in a plane perpendicular to the axis.
• the magnetic field varies symmetrically above and below the center of magnet 101 (3B) .
• the magnetic field is generally oriented parallel to the axis but deviates substantially near the end of the rod magnet 101 (3B).
• the antenna 104 used with magnet 101 (3B) should produce a B ⁇ field that is oriented parallel to a plane that is perpendicular to the B 0 field lines.
• Bj . is generally perpendicular to the axis of magnet 101 (3B) .
• the most sensitive region is where the B 0 and B x lines are perpendicular and where B 0 causes an EPR response (and/or NMR response, if used) at the desired frequency (s) .
• Rod magnet 101 (3B) may be a permanent magnet or a solenoid type of electromagnet .
• FIGURE 3C illustrates a U-shaped magnet 101 (3C) , whose open faces are its poles.
• the B x field of interest is oriented vertically.
• the sensitive region is outside the physical extent of the poles and in the vertical region corresponding to the area of the gap.
• the field intensity generally decreases as a function of distance away from the plane of the poles.
• a ferromagnetic plate 31 between the N and S poles provides a spatial region over a specific 11
• Magnet 101 may have a square or rectangular cross section as shown, or it may be round.
• FIGURE 3D illustrates another U-shaped magnet 101 (3D) , which provides a uniform field, as a function of angle about the axis, over 360 degrees.
• the poles are of uniform magnetic intensity around the complete circumference and polarized radically with the connecting rod (or tube) , providing additional magnetic field or a ferromagnetic return path.
• the B 0 field is oriented from pole-to-pole and extends radially outward from the magnet about the gap between the poles. The B 0 field generally decreases with radial distance.
• the antenna 104 is located in the gap between the poles and outside the ferromagnetic shunt and produces a B 1 field perpendicular to the B 0/ preferably of uniform intensity as a function of angle about the axis.
• the antenna of FIGURES 2B and 21 are particularly useful with magnet 101 (3D) and produce a sensitive region of a "donut" or cylindrical shape at a selected distance about magnet 101 (3D).
• the B 0 field is appropriate for EPR (or NMR) at the selected transmitter frequency.
• FIGURE 3E illustrates an enhancement for certain of the above-described magnets to minimize the loss of magnetic flux out of the top and bottoms of the magnets. 12
• the main magnet 32 could be magnet 101 (4B) , 101 (3C), or 101 (3D) .
• Auxiliary magnets 33 and 34 are polarized similar to the ends of the main magnets to force more lines of flux outward, radially, and increase the intensity of the B 0 field.
• FIGURE 3F illustrates a magnet 101 (3F) that is polarized perpendicular to the axis, and that produces a B 0 field that is also polarized perpendicular to the axis.
• the B 0 field region of interest is perpendicular to the plane of the poles and decreases in intensity as a function of distance away from magnet 101 (3F) .
• the B 1 field is polarized along the plane of the axis.
• the sensitive zone is perpendicular to the plane of the poles and along the axis at a selected distance from the center line.
• FIGURE 3G illustrates a magnet 101 (3G), which is similar to magnet 101 (3F), except that it is round to better fit in a bore hole. A slot on each side permits antenna 104 to be within the selected overall diameter.
• FIGURE 4 illustrates one example of a magnet 101 and antenna 104 combined for stimulating and sensing EPR response signals.
• the U-shaped magnet 101 (3C) provides the B 0 field in the sensitive zone.
• Antenna 104 (2C) mounted in the gap, provides the B x field.
• a second antenna 104 (2C) oriented perpendicular to the first antenna may be used.
• the two antennas 104 (2C) are shielded from each other to the extent possible.
• One antenna 104 (2C) is the transmit antenna to generate the B 1 field.
• the other antenna 104 (2C) is the receive antenna to intercept the EPR response signals from the materials being measured. Both antennas have a direct and unshielded path to the sensitive region.
• the configuration of FIGURE 3 is an alternative to the embodiment of FIGURE 1, where a single antenna 104 (2C) functions both to generate the B 1 field and to intercept the EPR response signals from the material in the sensitive region. 13
• the method of the invention involves obtaining and analyzing EPR response data from an underground rock formation.
• the result is a determination of the crude oil concentration in the underground formation.
• NMR response data may also be obtained and analyzed to provide additional information about characteristics of the formation, such as its porosity and the total hydrocarbon materials in the formation.
• Equipment for obtaining NMR data is known in the art of oil exploration.
• the same magnets 101 and antennas 104 as those described above for obtaining EPR response signals may be used.
• different control electronics will be more suitable for NMR because of the difference in polarization times, excitation frequency, and response signal sensitivity.
• NMR polarization times are typically 0.2 to 0.8 seconds for oil and 2.0 to 2.5 seconds for water, whereas polarization times for EPR are in the order of microseconds.
• EPR frequency is greater than that of NMR by a factor of about 658 and the sensitivity is proportionally greater.
• the material to be evaluated is located in a static magnetic field B 0 .
• the material is also preferably exposed to one or more pulses of a radio frequency (RF) field, Bi .
• RF radio frequency
• Selected nuclei in the material will absorb energy from the B ⁇ field, and will produce a detectable response when the RF frequency, v 0 , is related to the B 0 field, by the Larmor equation:
• NMR signals are the magnetization decay signals. This method is generally called time domain NMR, and the peak amplitude of the response signal is proportional to the concentration of selected atomic specie (e.g. hydrogen) in the measured volume of material .
• selected atomic specie e.g. hydrogen
• T 1# is related to the time required for nuclei in the material being measured to become polarized in a magnetic field.
• T x also sets the minimum time that the material must be exposed to a magnetic field prior to an NMR measurement and it determines how rapidly NMR measurements can be beneficially repeated on the same sample.
• T 2 determines how rapidly the NMR signal decays in a perfect magnetic field.
• low-field NMR measures three useful parameters: the equilibrium nuclear magnetization, M n , which is proportional to the total signal amplitude and to the fluid- filled porosity, and T 2 and T 2 , which are the two relaxation time constants. These parameters can be correlated with petrophysical properties such as pore size, producible fluid, and permeability. In fluid- saturated porous rock, the fluids may interact with the rock surface to promote NMR relaxation. As a result, the T 2 values for fluids in pores can be shorter than for bulk fluids. In the fast diffusion limit, the T 2 relaxation rate, l/T 2 , is proportional to the surface-to-volume (S/V) ratio of a pore, such that: 15
• the factor p is the surface relaxivity, which is a measure of the rock surface's ability to enhance the relaxation rate. It falls within a reasonably narrow band for a broad sampling of sedimentary rocks and is typically a few micrometers per second. For example, p is approximately 0.0005 cm/s for carbonates, and is approximately 0.0015 cm/s for sandstone.
• the volume, V is the pore size.
• the surface area, S varies depending on the shape of the pore and the roughness of the surface.
• Permeability estimation using NMR is based on the fact that permeability has dimensions of length squared, and uses the pore size obtained from NMR data. By knowing S/V for the pore, the permeability of a porous medium can be estimated. For carbonate, the following estimate for permeability, k, can be used:
• the permeability is proportional to (1/T 2 ) 2 .
• Porosity also may be measured from the NMR signal amplitude.
• NMR proton magnetization amplitude is directly proportional to the fluid-filled porosity.
• the excitation sequence 90° - t - 180° - echo - delay
• the echo following the 180° rotation of the magnetization vector is given by:
• NMR transverse relaxation (T 2 ) data can be expressed as a sum of exponential functions:
• M(t) is the sum of all NMR magnetization decays of the fluid-saturated rock.
• T 2 The relaxation time, T 2 , is a function of the type of fluid, proton frequency, temperature, pore surface chemistry, and pore size. For a porous rock, the observed magnetization will depend upon the T 2 (i.e., pore size) of all pores. The variation of magnetization with time may be obtained by summing over all T 2 ' s :
• T 2m ⁇ n and T 2max represent the smallest and largest values of T 2 expected for the particular rock.
• T 2max may be taken to be the value for the bulk fluid used to saturate the pores.
• the function, f(T 2 ) is the desired T 2 distribution, which is related to the pore volume distribution. The extraction of f (T 2 ) from the 17
• the bulk water relaxation rate, (l/T 2B ) is often negligible because the bulk water relaxation time, T 2bulk , is about 2-3 seconds.
• T 2 is only from several milliseconds to a few hundred milliseconds, and the distribution of T 2 arises from the distribution of surface-to-volume ratios of the pores, as shown above.
• T 2 depends linearly on pore size, the T 2 distribution corresponds to pore size distribution, with the largest pores having the longest relaxation times. It can be concluded that if M in the preceding equation is plotted against T 2l , it can be rescaled according to the above equation for l/T 2 to obtain the pore size distribution. This M versus T 2l data is a useful way to present NMR relaxation data.
• EPR Electron paramagnetic resonance
• g is a spectroscopic splitting factor and ⁇ 0 is the Bohr magneton of the electron.
• ⁇ 0 is the Bohr magneton of the electron.
• measurements in the laboratory are made at X-band.
• the B 0 field is around 3300 gauss and the EPR frequency is centered about 9.25 GHz (nominal) .
• EPR occurs at a nominal frequency of 2.8 MHZ per gauss of the static magnetic field, which is about 658 times as great as for NMR in the same magnetic field. Consequently most laboratory EPR work is carried out at microwave frequencies (GHz) . For better (deeper) penetration of the formation, EPR for borehole and other earth measurements uses relatively low frequencies and modest magnetic fields. These range from 28 to 2800 MHZ and 10 to 1000 gauss, respectively.
• FIGURES 5A -5D illustrate EPR signals from crude oil obtained from four different oil fields.
• the static magnetic field strength (in gauss) is plotted against the amplitude of the EPR response signal.
• EPR signals are not produced by water or gas, but are produced by many, if not all, crude oils.
• the amplitude of the EPR signal is proportional to the amount of the oil inside the rock.
• a concentration of crude oil per unit volume can be determined.
• calibration factors for the type of oil can be readily determined and applied.
• EPR spectra can 19
• FIGURE 5D there is an additional resonance peak, which is possibly due to contributions from two or more radical species with different heteroatom compositions.
• the components of water and oil in the NMR signal can be separated. Specifically, by subtracting the concentration of crude oil from the concentration of total hydrogen- bearing material, the concentration of water is known. Based on a number of facts, the components of water and oil in a rock sample can each be accurately measured from a combination of EPR and NMR measurements. These facts include: an EPR response signal is produced by crude oils but not by water, the proton density in oil is about 5 - 15% higher than water on a volumetric basis, and the surface relaxivity for oil is about one-third that of water.
• the relationship between pore size and the T 2 relaxation rate, as expressed above, can be rewritten as:
• I / ⁇ 2 f fc ( S /V) pore + fc l Po ⁇ .1 ( S /V) pore
• the relaxation rate is a sum of two terms: one representing the effect of crude oil and one representing the effect of water.
• the relaxation rate (l/T 2 ) of fluid in contact with rock surfaces is enhanced by those surfaces.
• the fraction of oil in a water- oil mixture can be used to increase the accuracy of the calculation of l/T 2 .
• This increases the accuracy of estimates of pore size distribution and permeability of the rock formation about boreholes or in fluid-saturated cores .
• p water is 0.0005 cm/s
• p 011 is (1/3)0.0005 cm/s
• the calculated pore diameter is 10 microns. However, if only NMR measurements were used, the calculated pore diameter would be 15 microns. The permeabilities for 10 and 15 micron pore sizes are 0.04 and 0.09 microns squared, respectively, resulting in a nearly 2:1 difference.

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• 1999
  • 1999-04-22 JP JP2000545048A patent/JP2002512376A/ja active Pending
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