MXPA99009828A - Apparatus and method for generating a pu sequence - Google Patents

Abstract

The present invention relates to a method for generating a pulse sequence using a probing tool. A pulse programmer is provided to adaptively control the creation and application of a sequence of pulses of magnetic field from FR to a terrestrial formation. To control the RF pulses, a portion of a memory device is divided into a plurality of tables and the control information is stored in the tables. The pulse programmer creates the pulse sequence using information found in the memory device and the operating conditions of the tool. The structure of the split memory device allows the pulse programmer to adapt and change the time of the pulse sequences autonomously in the drill hole

Description

APPARATUS AND METHOD FOR GENERATING A PULSE SEQUENCE This is a partial continuation of the United States Serial Patent Application (Priority Document) No. 09 / 033,965 (Attorney Registration List No. 24,787), consigned March 3, 1998.

BACKGROUND OF THE INVENTION In general, the present invention relates to an apparatus and a method for measuring the nuclear magnetic resonance properties of a ground formation traversed by a borehole, and more particularly with an apparatus and a method for generating a pulse sequence. . It is well recognized that the atomic particles of a ground formation have magnetic moment of non-zero nuclear spin; for example, protons have a tendency to align with a static magnetic field in the formation. A magnetic field of this type can be generated naturally, as is the case for the ground magnetic field BE. A radio frequency pulse that applies a second transverse magnetic field to BE creates a magnetization component in the transverse plane (perpendicular to BE) that experiences precision around the vector BE with a characteristic resonance known as the Larmor frequency, DL, which depends on the strength of the static magnetic field and the gyromagnetic ratio of the particle. Hydrogen nuclei (protons) having a precession around a magnetic field BE of 0.5 gauss, for example, have a characteristic frequency of approximately 2 kHz. If a population of hydrogen nuclei were made to undergo precession in phase, the combined magnetic fields of the protons can generate a detectable oscillating voltage in a receiver coil, conditions that are known to those skilled in the art to be known as free induction decay or a spin echo. Hydrogen and water hydrocarbon nuclei that occur in rock pores produce nuclear magnetic resonance (NMR) signals other than signals that originate from other solids. U.S. Patents No. 4,717,878 issued to Taicher et al. And No. 5,055,787 issued to Kleinberg et al. Describe NMR tools that use permanent magnets to polarize hydrogen nuclei and generate a static magnetic field, B0, and radio frequency antennas for exciting and detecting nuclear magnetic resonance in order to determine the porosity, free fluid ratio, and permeability of a formation. The atomic nuclei are aligned with the applied field, B0, with a time constant of Tx. After the polarization period, the angle between the nuclear magnetization and the applied field can be changed by applying a radio frequency field, Bi, perpendicular to the static magnetic field B0, in the Lamor frequency fL = DB0 / 2D, where D is the gyromagnetic ratio of the proton and B0 designates the strength of the static magnetic field. After the radio frequency pulse ends, the protons have a precession in the plane perpendicular to B0. A sequence of new radio frequency pulse approaches generates a sequence of spin echoes that produce a detectable NMR signal on the antenna. U.S. Patent No. 5,280,243 issued to Melvin Miller describes a nuclear magnetic resonance tool for evaluating a formation while drilling. The tool includes a probe section that is composed of a permanent magnet placed in an annular cavity extending longitudinally out of the drill collar and an antenna placed in a non-conductive magnetic sleeve outside the drill collar. The antenna produces a magnetic field of radio frequency essentially perpendicular to both the longitudinal axis of the tool and the direction of the static field. With the apparatus * 243, the magnet should have a long extension compared to its diameter for the magnetic fields to approximate its expected 2-D bipolar behavior. U.S. Patent No. 5,757,186 issued to Taicher et al. Describes a simultaneous measurement tool with the perforation that includes a sensor apparatus for making nuclear magnetic resonance measurements of the ground formation. The NMR sensor apparatus is mounted in an annular cavity formed within the outer surface of the drill collar. In an incorporation, a flow closure is inserted into the cavity. A magnet is placed on the outer radial surface of the flow closure. The magnet is constructed of a set of radial segments that are magnetized radially outward of the longitudinal axis of the tool. Flow closure is required to provide adequate directional orientation of the magnetic field.

The tools disclosed in patents? 243 and x186 suffer from common problems: both tools require the use of a non-conductive magnet and the placement of the magnet outside the drill collar. For tool * 243, the outer surface of the drill collar must contain a recessed area to accommodate the non-conductive magnet. For tool x186, the outer surface of the drill collar must contain a recessed area to house the flow lock, the non-conductive magnet and the antenna. Because the strength of the drill collar is a function of its spokes, reducing the outer diameter to accommodate the magnet only or the flow lock, the non-conducting magnet and the antenna results in an unacceptably weak section of the drill collar that It can bend or break during the drilling operation. U.S. Patent No. 5,055,787 issued to Kleinberg et al. Describes a pulsed nuclear magnetism tool for evaluating a formation while drilling. The tool includes a drill bit, a drill rod and a pulsed nuclear magnetic resonance device housed within a drill collar made of a non-magnetic alloy. The tool includes a channel, inside the drilling rod and pulsed nuclear magnetic resonance device, through which drilling mud is pumped into the borehole. The pulsed nuclear magnetic resonance device comprises two tubular magnets, which are mounted with similar poles facing each other, surrounding the channel, and an antenna coil mounted on an outer surface of the drilling rod between the magnets. This tool is designed to resonate nuclei in a measurement region that those skilled in the art know as the saddle point. U.S. Patent No. 5,705,927 issued to Sezginer et al. Describes a pulsed nuclear magnetism tool for evaluating a formation while drilling. The tool includes compensation magnets, placed either inside or outside the tool, which suppress the magnetic resonance signal of the borehole fluids by increasing the magnitude of the static magnetic field in the borehole so that the frequency of Lar or in the borehole is above the frequency of the oscillating field produced by a radio frequency antenna located in a recessed area of the tool. The compensation magnets also reduce the gradient of the static magnetic field in the research region.

COMPENDIUM OF THE INVENTION.

A substantially asymmetric static magnetic field is generated within a ground formation traversed by a borehole. A pulse programmer is provided to control in an adjustable manner the creation of a sequence of magnetic frequency pulses of radio frequency and the application thereof to the formation. In order to control the radio frequency pulses, a portion of a memory device is divided into a set of tables and the control information is stored in the tables. The tables may include the following: a buffer table describing the arrangement of the stacking buffers, an acquisition table defining the acquired signals accumulated in buffers, a filter coefficient table describing the detection filter used with an acquisition signal, a spin dynamics correction table that designates the spin dynamics correction to be used for each buffer, and a data processing table that designates the calculated nuclear magnetic resonance characteristic of the buffers acquired. In addition to the pulse scheduler, other tasks may share the control information stored in the tables. The pulse programmer further comprises a pulse sequence template, which is used to generate pulse sequences, which includes a sequence of states that depend on repetition and time variables. These variables are calculated from sequence configuration parameters that use a calculation block. The time variables include the waiting time, echo separation, and the number of echoes acquired. The configuration parameters include the duration of an excitation pulse, the pulse amplitude, and the shape of the pulse. The sequence of states further comprises multiple alternative states for portions of the pulse sequence. In real time, one of the alternative states can be selected based on the external conditions of the device.

BRIEF DESCRIPTION OF THE DRAWINGS The advantages of the present invention will become apparent from the following description of the accompanying drawings. It is understood that the drawings are to be used only for purposes of illustration and not as a definition of the invention. In the drawings: Figure 1 illustrates a simultaneous logging apparatus with the perforation; Figure 2 describes the low gradient probe; Figures 2a-2d illustrate the contour lines | OB0 | corresponding to four configurations of low gradient magnets; Figures 3a-3d illustrate the contour lines of the gradient | DB0 | corresponding to four configurations of low gradient magnets; Figure 4 describes the high gradient probe; Figure 4a represents the contour lines ILTBol corresponding to the high gradient magnet configuration; Figure 4b represents the contour lines of the gradient I DB01 corresponding to the high gradient magnet configuration; Figure 5 describes the simple mode of data acquisition; Figure 6 describes the interleaved data acquisition mode; Figure 7 describes the full mode of data acquisition; and Figure 8 represents a block diagram of the pulse programmer.

DETAILED DESCRIPTION OF THE INVENTION Referring to Figure 1, a tool 10 of simultaneous logging with nuclear magnetic resonance drilling is illustrated.

(RMN). The tool 10 comprises a drilling bit 12, a drilling rod 14, a set of radio frequency antennas 36, 38, and at least one gradient coil 56. The tool 10 further comprises an electronic circuitry 20 housed inside the piercing collar 22. Electronic circuitry 20 comprises radio frequency resonance circuitry for antennas 36, 38, a microprocessor, a digital signal processor, and a low voltage collective conductor. The tool 10 further comprises a series of tubular magnets 30, 32 and 34 which are polarized in a direction parallel to the longitudinal axis of the tool 10 but opposite each other, ie with similar magnetic poles facing each other. The magnets 30, 32 and 34 are a material whether conductive or non-conductive. The configuration of the magnets 30, 32 and 34 and the antennas 36, 38 provides at least two research RMN regions 60, 62 with a static magnetic field and an essentially asymmetric radio frequency. A means for drilling a borehole 24 in the formation comprises a drill bit 12 and a drill collar 22. The drill collar 22 may include a stabilization means (not shown) to stabilize the radial movement of the tool 10 during drilling; however, the stabilization medium is not necessary; therefore, the tool 10 can operate stabilized or not stabilized. The mud flow sleeve 28 defines a channel 90 for carrying the drilling fluid through the drilling rod 14. A steering mechanism 26 rotates the drill bit 12 and - the drilling rod 14. This steering mechanism is suitably described in U.S. Patent No. 4,949,045 issued to Clark et al. However, an engine for the bottom mud can be placed in the drill rod as the steering mechanism 26. It is intended within the scope of the invention to combine N + l magnets to obtain at least N regions of research in the formation . The combinations provided by this invention include, but are not limited to, a low gradient of low gradient, a high gradient of high gradient, a high gradient of low gradient, a low gradient of high gradient, or a combination of high gradient, gradient low and saddle point regions. The combination of static magnetic field regions of high and low gradient in the formation offers several advantages. For example, the high gradient region may have a higher signal-to-sound ratio, but may experience signal loss when the tool 10 experiences lateral movement in the borehole. On the other hand, the low gradient region has less susceptibility to signal loss problems when the tool 10 is in motion. Likewise, with a moderate movement of the tool, longer echo tails can be acquired in the low gradient region than in the high gradient region, whereby more information is provided about permeability, linked flow and free, and types of hydrocarbons. Moreover, the combination of acquired data with the regions of both gradients can provide quantitative information about the amount of lateral movement experienced by the tool 10 and can be used to correct the movement of the NMR data, or, at least, do quality control of the data. Measurements of instruments, such as strain gauges, accelerometers or magnetometers, or any combination of these devices, can be integrated with nuclear magnetic resonance information to do quality control of the data or make corrections to the spin-echo tail. With the combination of static magnetic fields of low and high gradient, the high gradient region shows greater diffusion effect and therefore is of greater interest for hydrocarbon typing techniques than the low gradient region. Finally, the low gradient region has a static magnetic field that has a low amplitude, and therefore this region with its lower Larmor frequency is less affected by the formation and background flow conductivity.

LOW GRADIENT PROBE Referring to Figure 2, in a section of the tool which we will now call the low gradient probe, a central magnet 30 is axially spaced from a lower magnet 32. These magnets 30, 32 generate a substantially asymmetric static magnetic field whose polarization is radial, and on a reasonably long cylindrical envelope, the static magnetic field has a fairly constant magnitude. It is envisaged within the object of the invention to excite a series of cylindrical spin envelopes in the formation where each envelope is resonant at a different radio frequency, and to interrogate each envelope in sequence with radio frequency pulse sequences. The area between the magnets 30, 32 is suitable for housing elements such as electronic components, a radio frequency antenna, and other similar devices. For example, a series of electronic pockets 70 can form an integral part of the mud flow sleeve 28. These electronic pockets 70 can accommodate the radio frequency circuitry (eg, Q switch, duplexer and preamplifier), preferably in close proximity to the radio frequency antenna. In a preferred embodiment of the invention, the pockets 70 form an integral part of the magnetically permeable unit 16. In this case, to maintain the axial symmetry of the magnetic field, a cover 72 highly permeable to magnetism is placed on each of the pockets 70. The magnetically permeable unit 16 is placed inside the drill collar 22 between the magnets 30, 32. The unit 16 may be composed of a single piece or a series of combined sections between the magnets 30, 32. The unit 16 is constructed of a suitable magnetically permeable material, such as ferrite, permeable steel, or other iron-nickel alloy, corrosion-resistant permeable steel, or permeable steel that has a structural function in the design of the unit, such as stainless steel 15 -5 Ph. The magnetically permeable unit 16 concentrates the magnetic field and can also carry drilling fluid through the perf prayer or provide structural support to the drill collar. In addition, the unit 16 improves the shape of the static magnetic field generated by the magnets 30, 32 and minimizes the variations of the static magnetic field due to the vertical and lateral movement of the tool during the acquisition period of the nuclear magnetic resonance signal. The sleeve segment 28 between the magnets 30, 32 may comprise the magnetically permeable unit 16. In that case, the sleeve segment 28 between the magnets 30, 32 will consist of a non-magnetic unit. Alternatively, a magnetically permeable frame surrounding the sleeve segment 28 between the magnets 30, 32 defines the unit 16. In this case, the segment may consist of a magnetic or non-magnetic material. It is provided within the object of the invention to integrate the frame and the segment to form the unit 16. The magnets 30, 32 are biased in a direction parallel to the longitudinal axis of the tool 10 with the similar magnetic poles facing each other. For each of the magnets 30, 32, the magnetic induction lines travel outward from one end of the magnet 30, 32 into the formation, along the axis of the tool 10, and travel inward to the end of the magnet 30, 32 In the region between the central magnet 30 and the lower magnet 32, the induction magnetic lines travel from the center outwardly between the formation, creating a static field in a direction substantially perpendicular to the tool axis 10. The magnetic lines of induction they then travel inwardly symmetrically above the central magnet 30 and below the lower magnet 32 and converge in the longitudinal direction within the sleeve 28. Because of the separation, the static magnetic field magnitude in the central region between the central magnet 30 and the lower magnet 32 is spatially homogeneous compared to a field in saddle stitch. The amount of separation between the magnets , 32 is determined based on several factors: (1) selecting the necessary strength characteristics and magnetic field homogeneity; (2) generate a field that has small radial variations in the region of interest, such that echoes received during a pulse sequence (eg, CPMG, CPI, or other sequences) are less sensitive to lateral movement of the tool; (3) depth of investigation; and (4) minimizing the interference between the resonance circuitry and the collective low-voltage telemetry conductor in order to improve the isolation of the receiving antenna that detects nuclear magnetic resonance signals from the array. As the separation between the magnets 30, 32 decreases, the magnetic field becomes stronger and less homogeneous. Conversely, as the separation between the magnets 30, 32 increases, the magnetic field becomes weaker and more homogeneous. Figures 2a-2d illustrate the contour lines I DBo I corresponding to four configurations of the central magnet 30 and the lower magnet 32 modeled in the laboratory. These modeled results were calculated using a tool having a preselected diameter (a constant diameter was used to model all configurations). The configuration corresponding to Figure 2a comprises a magnetically non-permeable unit separating a central magnet 30 and a lower magnet 32 by 25 inches. The configuration corresponding to Figure 2b comprises a non-magnetically permeable unit separating a central magnet 30 and a lower magnet 32 by 18 inches. The configuration corresponding to Figure 2c comprises a magnetically non-permeable unit separating a central magnet 30 and a lower magnet 32 by 8 inches. The low gradient probe, corresponding to Figure 2d, comprises a magnetically permeable unit 16 separating a central magnet 30 and a lower magnet 32 by 25 inches. The aforementioned dimensions were modeled solely to illustrate the effect of distance and / or a magnetically permeable or non-permeable unit on I OB01. Figures 3a-3d represent the contour lines of the gradient! DB01 corresponding respectively to the configurations illustrated in Figures 2a-2d. In the low gradient probe, the unit 16 derives a significant portion of the magnetic flux toward the center of the tool 10. For purposes of illustration, the magnitude of the B0 field shown in Figure 2d at a distance of approximately seven inches radially from the longitudinal axis of the tool 10 it is twice as large as the field Bo shown in Figure 2a, which was generated by the same configuration of magnets separated by a non-magnetically permeable unit. Moreover, the low gradient probe produces a longer and more uniform extension of the static magnetic field in the axial direction. The nuclear magnetic resonance signal measured in this section of the tool is substantially less sensitive to the vertical movement of the tool. Referring to figure 3d, with the low gradient probe a relatively sticky gradient of approximately 3 Gauss / cm is measured at a distance of approximately seven inches radially from the longitudinal axis of the tool 10. This low gradient results in a nuclear magnetic resonance signal measured that is substantially less sensitive to the vertical movement of the tool 10. When the movement is moderate, longer echo tails can be acquired in this region by means of which more information about the permeability is provided, bound and free flow, and types of hydrocarbons. In the case of the low gradient probe, as with other gradient designs, the region of the proton-rich probe well surrounding the tool 10 will resonate only at higher frequencies than those being applied to the research volume, this is, there is no probe well proton signal. Other NMR-sensitive nuclei found in drilling mud, such as sodium-23, resonate to magnetic field forces significantly higher than hydrogen when excited at the same radio frequency. For the low gradient probe, these higher field strengths do not occur in the region of the borehole surrounding the tool or near the antenna where such unwanted signals could be detected.

HIGH GRADIENT PROBE Reference to figure 4, in another section of the tool which we will now call the high gradient probe, a central magnet 30 is axially separated from an upper magnet 34. The magnets 30, 34 are polarized in a direction parallel to the longitudinal axis of tool 10 with similar magnetic poles facing each other. These generate a substantially asymmetric static magnetic field whose polarization is radial, and on a reasonably long cylindrical envelope, the static magnetic field has a fairly constant magnitude. It is envisaged within the object of the invention to excite a series of cylindrical spin envelopes in the formation wherein each envelope is resonant at a different radio frequency. As shown in Figure 2c, if the separation between the magnets 30 and 34 is approximately eight inches, the contour lines of the static magnetic field force are essentially straight and the force of I DB01 is greater than the force of the field. static magnetic field of the low gradient. However, the gradient I DB01 is enlarged, as shown in Figure 3c, at a distance of approximately seven inches radially from the longitudinal axis of the tool. The boundary lines of I D oo I are curved denoting variation of the gradient in the axial direction. The high gradient probe is improved by inserting a magnetically permeable unit 16 between the magnets 30, 34. Figure 4a represents the contour lines | DB01 corresponding to a configuration in which the magnetically permeable unit 16 separates the upper magnet 34 and the central magnet 30 by eight inches. The contour lines of Figure 4a show a slightly stronger field indicating a better signal-to-sound ratio and less curvature in the axial direction than the contour lines of Figure 2c. Also, as illustrated in FIG. 4b, the magnetically permeable unit 16 produces a more constant I DB01 gradient in the axial direction that can simplify the interpretation of nuclear magnetic resonance measurements influenced by diffusion.

In the case of the high gradient probe, as with other gradient designs, the region of the proton-rich sounding well surrounding the tool 10 will resonate only at higher frequencies than those being applied to the research volume, this is, there is no probe well proton signal. The high gradient wave is sensitive to a small part of the sodium in the borehole fluid. For a drilling well fluid of 30% concentration of NaCl, possibly the worst case, the estimated porosity error due to the sodium signal is approximately 0.08 pu. In the low gradient probe, the sodium signal is substantially lower than in the high gradient probe. Consequently, the sodium signal is negligible for both NMR probes.

GRADIENT ANTENNAS AND COILS With reference to Figures 2 and 4, a magnetic field of radio frequency is created in the investigation regions by the antennas 36, 38 provided in the recessed areas 50, 52. The radio frequency field can be produced by one or more antenna segments that transmit and / or receive from different sectors of circumference of the recording device. See U.S. Patent Applications Nos. 08 / 880,343 and 09 / 094,201 (Attorney Registry Lists Nos. 24,784 and 24,784-CIP) assigned to Schlumberger Technology Corporation. Preferably, each of the antennas 36, 38 comprises a coil 18 wound circularly around the recessed areas 50, 52. The radio frequency field created by a coil array of this type is substantially asymmetric. It is provided within the object of the invention to use the antennas 36, 38 to detect magnetic resonance signals. However, a separate antenna or receiver can be used to detect the signals. A non-conductive material 54 is supplied in the recessed areas 50, 52. The material 54 is preferably a ferrite in order to increase the efficiency of the antennas 36, 38. Alternatively, the material 54 may comprise plastic, rubber or a reinforced epoxy composite. The antennas 36, 38 are resonated by radio frequency circuitry in order to create a magnetic field in the research regions. The recessed area 50 forms a shallow groove in the drill collar without reducing the internal diameter of the drill collar, which is normally done to increase the strength in a region of the drill collar where the outer diameter has been recessed to provide an antenna The recessed area 50 has a greater depth than the recessed area 52. Due to mechanical constraints, it is only possible to have a deeply recessed area where the internal diameter of the piercing collar is substantially reduced. It is provided within the object of the invention that the recessed areas 50, 52 have substantially the same depth or that the recessed area 52 has a greater depth than the recessed area 50. The cylindrical sheaths of spins in the research region can be axially segmented or , preferably, preferably using at least one direction sensitive gradient coil 56 arranged in recessed areas 50 and / or 52. In a preferred embodiment of the invention, three gradient coils are arranged circularly around the recessed area and separated by an angular distance segment of 120 °. Other gradient amounts may be defined, either more or less than three, and said coils may be separated by angular distances other than 120 ° and / or unequal angular segments. Each coil 56 is constructed with turns of wire, which adapt to the curvature of the outer surface of the material 54. The magnetic field produced by each of the gradient coils 56 in a region of the formation facing the coil is substantially parallel to the static magnetic field produced by the magnets. As is known to those skilled in the art, in the basic NMR measurement, pulse sequence is applied to the training under investigation. In U.S. Patent No. 5,596,274 issued to Abdurrahman Sezginer and in U.S. Patent No. 5,023,551 issued to Kleinberg et al., A pulse sequence, such as the Carr-Meiboo-Gill sequence (CPMG) ), first apply an excitation pulse, a 90 ° pulse, to the formation that spins the spins between the transverse plane. After the spins are rotated 90 ° and begin to phase out, the protractor of the new focus pulses, the 180 ° pulses, is phase shifted relative to the 90 ° pulse sequence conveyor according to the following relation: tgo '- t0 - [t18Q ° and - i - ß COmax - t2] where the expression in brackets is repeated for n = 1,2, ... N, where N is the number of echoes collected in a single CPMG sequence and the echo separation is teco = 2tcp = t180 ° and + ti + t2. . 90 ° ± x denotes a radio frequency pulse that causes the spins to rotate at a 90 ° angle around the + x axis, as is commonly defined in the rotation frame of nuclear magnetic resonance measurements (alternating phase). The time between the application of the 90 ° pulse and the 180 ° pulse, t0 is less than tcp, half of the echo separation. The CPMG sequence enables the acquisition of a symmetric measurement (that is, a measurement without using the gradient coils). The exact time parameters, t0, ti and t2, depend on several factors (for example, the shape of the applied pulses). In the present invention, a current pulse applied to a gradient coil 56 generates an additional magnetic field, substantially parallel to the static magnetic field. The current pulse is applied between the first 90 ° pulse and the 180 ° phase reversal pulse. This additional field causes an additional phase change for the spins. Since the 180 ° phase-reversal pulse does not compensate for the additional phase change, the spins attached to the additional field do not form a spin echo. However, for spins not subject to the additional field, a spin echo occurs at 2tcp time, with spin echoes of successively smaller amplitudes occurring at 2tcp time after each phase reverse pulse. The pulse sequence is a b n t90. * - tO-D - tO - [tiso-y - ti - ecom x - t2] na where to is the time between the 90 ° pulse and the b gradient pulse of duration D, toes the time between the pulse of gradient and the 180 ° reversal pulse, by to + D - to = t0. Due to the 180 ° ° pulse and that Signal = 3 * j + ¡M¡) (r) ttqA? -i) G (, r) d)? :( r) J, they happen, and due to the lack of homogeneity of the fields, the x component of the signal of Nuclear magnetic resonance disintegrates within a few echoes. Therefore, we concentrate only on the component and the signal. In this way, neglecting relaxation, the first echo signal of nuclear magnetic resonance can be represented as: where i is the imaginary complex unit; D is or or the gyromagnetic ratio; M * and My are respectively the components x and y of the magnetization at the location r at the time of the first echo in the absence of the gradient pulse; G (r) is the component of the gradient field parallel to BOD in the same location; D is the duration of the gradient pulse; and (r) denotes the differential sensitivity of the nuclear magnetic resonance probe. The gradient coil 56 offers several advantages for obtaining azimuthal measurements. First, because the asymmetric antenna detects spin echoes, long echo tails can be recorded as the tool rotates in the borehole. Second, gradient coil 56 simplifies the design of an LWD-NMR tool because gradient coil 56 does not have the tuning requirements of a radio frequency antenna 36, 38. Third, the same radio frequency antenna 36 , 38 can be used to make symmetric and asymmetric measurements. Fourth, gradient coil 56 can be used to obtain NMR measurements with excellent spatial resolution, particularly vertical resolution. The present invention contemplates different ways to obtain azimuthal NMR measurements. For example, a "simple perturbation" mode uses at least one gradient coil 56 to disturb the spins in a selected quadrant where one quadrant is defined as an angular distance segment around the periphery of the tool 10; however, more coils 56 can be used to disturb multiple quadrants. In either case, two measurements are obtained: a symmetric phase alternating pulse sequence (PAFS) with a fixed timeout followed by a gradient PAFS that has a variable wait time, the disturbed quadrant being firing the coil 56 in the quadrant. In the preferred embodiment of the invention, the aforementioned gradient pulse sequence is used. Subtracting the gradient measurement from the asymmetric measurement creates the azimuth measurement. In this mode, an asymmetric measurement is obtained for every two PAFS and an azimuth sweep is obtained for every eight PAFS. The measurement noise for azimuthal measurement is greater than the noise in the symmetric or gradient measurement because the two measurements are combined. It is possible to reduce the presence of noise by combining different measures of simple quadrant perturbation. For example, four PAFS gradient measurements can be obtained by perturbing each quadrant. The measurements are combined to create a synthetic azimuth measurement and a symmetric measurement. By combining measurements made without firing the gradient coils 56 with measurements made by firing one or more gradient coils 56, "images" of the formation resolved axially or azimuthally can be generated. The acquired data, particularly in the form of azimuth images of porosity and flow linked, are very desirable for 'an improved petrophysical interpretation in highly deviated and horizontal drilling wells, and for decision making while drilling for the location of drilling wells based on geological data.

OPTIMIZE THE PULSE LENGTH AND THE FREQUENCY OPERATING For a selected operating frequency of radio frequency, there is an optimal duration for the 90 ° pulse, t90, as well as for the 180 ° pulse, which guarantees a desired signal-to-noise ratio. The search for an optimal pulse length can be performed during the master calibration of the tool, so that all pulse lengths will start correctly, or when the static magnetic field changes in an unpredictable manner, such as a change due to the Magnetic slag accumulation during the drilling process. See U.S. Patent Application No. 09 / 031,926 (Attorney Registry List No. 24,786) assigned to Schlumberger Technology Corporation. This technique can also be used to select the appropriate frequency in order to satisfy other criteria, such as keeping the depth of the investigation constant. The optimal pulse length can be determined by measuring the NMR response of a sample using at least two different pulse durations and using a predefined mode independent of the NMR properties of the array. Alternatively, the optimal pulse length can be determined using at least two different pulse durations and additionally using a mode calculated from the NMR properties of the array. In the first case, data stacking improves the signal-to-noise ratio; however, the stacking procedure may require a long period of time to acquire training data. Preferably, the measured data is accumulated during a stationary time window when the tool 10 pauses during the drilling operation, such as during the time when a new section of pipe is added to the drilling rod. In the second case, if the T2 distribution of the formation is known, a better acquisition mode can be constructed that provides the highest signal-to-noise ratio for a unit of acquisition time and provides an optimal linear combination of the acquired data. . Laboratory simulations show that the optimum time for the best acquisition mode is achieved when the duration of the echo tail is approximately equal to T2, ma ?, the dominant T2 of the formation, and when the waiting time, t ", is approximately equal to 2.5 x T2, ma? (assuming a constant Tx / T2 ratio of 1.5). The best acquisition mode determines the optimal pulse length at a range of a small percentage over several seconds. A similar technique can be used to optimize the NMR signal with respect to frequency (for example saddle stitch design). The T2 distribution effectively helps the efficient tuning of the pulse lengths for the tool 10.

DATA ACQUISITION MODES As described above, the tool 10 has a set of antennas 36, 38. In a preferred embodiment of the invention, these antennas 36, 38 do not transmit or acquire data simultaneously. Preferably, after an antenna 36 acquires data, the other antenna 38 experiences a minimum wait time while the power supply is recharged to transmit the next pulse sequence. The object of this invention provides for the simultaneous transmission or acquisition of data. Moreover, this invention contemplates the acquisition of data without a waiting time being necessary. Based on these design preferences, many data acquisition modes can be used. By way of example, three representative times for data acquisition are described below: a fast time suitable for sandy and wet areas, a slow time suitable for carbonated zones, and a very slow time designed for areas that have hydrocarbons (or invasion) of mud supported in oil). The times are set forth in Table I.

TABLE I With each data acquisition time, several modes can be used, including, but not limited to, the following: simple, interleaved and bursts. The simplest way to acquire T2 information with the tool 10 is to perform CPMG measurements with both antennas 36, 38 using the same time. Figure 5 illustrates the simple mode of data acquisition with the times of fast decomposition, slow decomposition and very slow decomposition of Table I. Each antenna 36, 38 alternatively acquires a long pulse sequence that provides an effective porosity measurement from of each antenna 36, 38. With the interleaved mode, the high-gradient antenna measures at least two cylindrical shells at two different frequencies while the low-gradient antenna obtains a measurement using a single frequency. Figure 6 shows an interleaved measurement for samples of fast decomposition, slow decomposition components and very slow decomposition components using the times in Table I. The burst mode increases the signal-to-noise ratio, especially for the decomposition components slow. In addition, the burst mode provides a useful fluid-based measurement based on i. See WO 98/29639 assigned to Numar Corporation [describes a method for determining longitudinal relaxation times, i]. See also United States Patent Application No. 09 / 096,320 (Attorney Registration List No. 24,785) assigned to Schlumberger Technology Corporation [describes a method for polarizing the bound fluid of a formation]. Figure 7 illustrates burst measurements for fast decomposition samples, slow decomposition components and very slow decomposition components using the times' of Table I slightly modified. In addition to the simple, interleaved and burst modes, with the present invention it is possible to optimize the evaluation measurements of a formation by detecting drilling well conditions that produce a pause during the drilling operation, determining the drilling mode, and using the mode to control the acquisition of data. Normal rotary drilling operations contain many natural breaks in which the tool remains stationary: connection time when a new section of drill pipe is added to the drilling rod, circulation time when mud is circulated and there is the possibility of turning the drilling pipe, and the idle time of small inconveniences while the drilling rod is stuck and has to be released before the drilling can be re-started. These natural pauses, which occur without interrupting normal drilling operations, or deliberately initiated pauses, are used to make nuclear magnetic resonance measurements. Drilling modes include, but are not limited to, drilling, sliding, travel, circulation, exploration, a short path (up or down), and drill pipe connections. Determining the drilling mode increases the ability to obtain NMR measurements that take a long time or that benefit from a quiet environment, for example, Ti, T2, antenna tuning and hydrocarbon typing. See also United States Patent Application No. 09 / 031,926 (Attorney Registry List No. 24,786) assigned to Schlumberger Technology Corporation. It is also possible to adjust adguisance modes based on changes in the environment (eg flooded stretch, salinity, etc.) and / or changes in NMR properties of the formation (eg, short Ti see its long Ti, etc.). .). The spin echo amplitudes are obtained by integrating the hardware of the reception voltages during a time window. Tool 10 uses phase sensitive detection to measure the phase and quadrature components of the signal-plus-spin echo amplitudes. The techniques disclosed in U.S. Patent 5,381,092 issued to Robert Freedman can be used to calculate window sums in the drilling well and transmit the window sums to the surface for the processing and presentation of T2. Likewise, the techniques described in U.S. Patent No. 5,363,041 issued to Abdurrahman Sezginer can be implemented to use a linear operator in order to map a relaxation time distribution for spin echoes, produce a decomposition of value singular (DVS) of the linear operator, determine vectors of the DVS and compress the spin echo data using the vectors. Preferably, the spectrum of T2 is calculated in the drilling well and transmitted to the surface. This offers the advantage of eliminating a telemetry bottleneck created by the transmission to the surface of the data required to calculate the spectrum of T2. A digital signal processor can be used to invert the T2 data. The amplitudes of the spin echoes, AD, are characterized by the following relationship: Kí A, ~ - where -jj is the noise in measurement A3, ax is the amplitude the distribution of T2 taken in T2? r Xj i represents the elements of matrix x, where tw is the waiting time and c is a constant (the ratio T? / T2), pt is the echo separation, and j = l, 2, ... N, in where N is the number of echoes collected in a single pulse sequence. In matrix notation, the equation becomes • ~ - * - a + .. Since noise, D, is unknown, a can be approximated by finding a solution of least squares, that is, a minimum of the function} = \\ A - Xa \\ _ The solution of this equation is strongly affected by the noise present in the data and the solution may contain negative components even when the T2 spectrum has no negative components. To overcome this problem, a regularization term, the function is added, and the function "* ~ + 'is minimized using a suitable minimization algorithm (for example, the Conjugate Gradient Projection Method) under the constraint that a2 DO for i = l ... M. See Ron S. Dembo and Ulrich Tulowitzki, On the Minimization of Quadratic Functions Subject to Box Constrain ts, Yale Computer Department (September 1984) (describes the Conjugate Gradient Projection Method). The time required to carry out the T2 inversion using a digital signal processor is very reasonable. For example, assuming 1800 echoes and 30 samples in the T2 domain, the investment in a digital signal processor requires less than two seconds.

PULSE PROGRAMMER For the basic measurement of NMR with the tool 10, an electronic circuitry applies a pulse sequence to the formation under investigation. The tool 10 includes a pulse programmer 80, which selectably controls and controls the pulse sequence applied to the array. The pulse scheduler 80 establishes the pulse sequence using the information found in the Measurement Control Block 82 (see FIG. 8) and the operating conditions of the tool 10. Preferably, the Measurement Control Block 82 is stored in a Drilling well memory device. The structure of the block 82 is fixed to allow the programmer 80 to adapt easily and change the time of the pulse sequence autonomously in the drill hole. It is advantageous to divide a portion of the block 82 into a series of tables 84, 86 and 88. Instead of controlling all of the tool operations that depend on the pulse sequence from the pulse scheduler 80, tables 84 are used, 86 and 88 to control these operations. This allows the pulse programmer 80 to vary the pulse sequences without introducing contradictions in the tool configuration. The series of tables 84, 86 and 88 may include, but is not limited to, the following: a buffer table which describes the arrangement of the stacking buffers, an acquisition table defining the acquired signals accumulated in the memories intermediate, a filter coefficient table that prescribes the detection filter used with a signal acquisition, a spin dynamics correction table that designates the spin dynamics correction to be used for each buffer, and a table of data processing that designates the nuclear magnetic resonance characteristic calculated from the acquired buffers. The pulse programmer 80 includes a template 94, useful for the generation of pulse sequences, which comprises a sequence of repetitive and time dependent variables. These variables are calculated from sequence configuration parameters using the calculation block 92. The calculation block 92 can be implemented as an executable or interpretive structure. Based on the physical quantity that will be measured, for example, T2, you can define time variables such as the waiting time tw, the echo separation, and the number of acquired echoes. The configuration parameters include, but are not limited to, t9o, pulse width and pulse shape.

These parameters can be calculated periodically during the calibration of the tool 10 or during the operation of the tool 10 since these parameters can vary as the operating conditions of the tool 10 vary. For example, the amplitude and pulse shape they depend on the quality factor of the antenna and, consequently, on the conductivity of the formation surrounding the tool 10. Normally, after the pulse programmer 80 initiates a pulse sequence, the pulse sequence is executed in a deterministic manner. until it ends. To implement certain azimuth measurement modes with the tool 10, the pulse programmer 80 has the ability to vary the pulse sequence during the execution of the sequence. The pulse programmer 80 can stop the execution of the pulse sequence and enter a STOP state until an external signal ends that state at time tc, or until a maximum period of time tmax has ended. As already discussed in the section on Data Acquisition Modes of this specification, since at least one of the various modes (interleaving) that can be used with the time control for data acquisition contemplates intercalating several measurements, the Pulse programmer 80 compensates for the time it spent during the STOP state. Preferably, the compensation is carried out by grouping HIGH events. For example, a cluster may comprise a pair of HIGH events where one HIGH event operates as previously described and the other HIGH event is a normal event of duration tmax-tc. The grouping of events allows the programmer 80 to combine sequences having variable and deterministic times. In addition, the sequence of states, as defined in template 94, may include several alternatives for parts of the sequence. In real time, one of the alternatives (branching) is selected depending on external conditions of the tool (for example, the azimuth of the tool). The foregoing description of the preferred embodiment and alternative embodiments of the present invention has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise form disclosed. Obviously, many modifications and variations may be evident to those skilled in the art. These additions were selected and described in order to better explain the principles of the invention and their practical application by means of which other experts in the art are allowed to understand the invention for various incorporations and with various modifications as appropriate for the invention. private use contemplated. It is intended that the scope of the invention be defined by the appended claims and their equivalents.

Claims (18)

R E I V I N D I C A C I O N S

1. A method for determining a nuclear magnetic resonance property in a research region of each formation surrounding a drill hole, comprising the steps of: a) generating a substantially axial symmetric static magnetic field in a formation traversed by the borehole; b) control with adaptation of the creation and application of a sequence of pulses of magnetic field of FR to the formation; and c) detection of nuclear magnetic resonance signals from the formation. The method of Claim 1 further comprising the steps of partitioning a portion of a memory device into a plurality of tables and storing control information in the tables. 3. The method of Claim 2 further comprising the defining step of a pattern for executing the magnetic field pulse sequence of FR. The method of Claim 3 further comprising the steps of defining at least one state sequence and storing the state sequences in the pattern. The method of Claims 3-4 further comprising the steps of defining a plurality of alternative state sequences and storing the state sequences in the pattern. The method of Claims 3-5 further comprising the steps of selecting at least one of the state sequences or alternate state sequences and executing the selected state sequences or alternative selected state sequences. The method of Claim 1 further comprising the step of executing the sequence of magnetic field pulses of FR by causality upon completion of the sequence. The method of Claim 7 further comprising the step of varying the sequence of the magnetic field pulses of FR during the execution of the sequence. 9. The method of Claim 7-8 further comprising the steps of stopping the execution of the sequence for a period of time; resumption of sequence execution; and the compensation for that period of time. 10. An apparatus for the determination of a nuclear magnetic resonance property in a region of investigation of terrestrial formations that surround the hole of the perforation, comprising: a) means for the generation of a substantially axial symmetrical static magnetic field in a traversed formation by drilling; b) means for control with adaptation of the creation and application of a sequence of pulses of magnetic field of FR to the formation; and c) means for the detection of nuclear magnetic resonance signals from the formation. The apparatus of Claim 10 further comprising a memory device, means for partitioning a portion of the memory device into a plurality of tables and storing control information in the tables. 1

2. The apparatus of Claim 11 further comprising means for defining a pattern for executing the magnetic field pulse sequence of FR. The apparatus of Claim 12 further comprising means for defining at least one state sequence and means for storing the state sequences in the pattern. The apparatus of Claim 12-13 further comprising means for defining a plurality of alternative state sequences and means for storing the alternative state sequences in the pattern. 15. The apparatus of Claim 12-14 further comprising means for selecting at least one of the state sequences or alternate state sequences and means for executing the selected state sequences or selected alternative state sequences. 16. The apparatus of Claim 10 further comprising means for executing the sequence of magnetic field pulses of FR by causality upon completion of the sequence. 17. The apparatus of Claim 16 further comprising means for varying the sequence of magnetic field pulses of FR during the execution of the sequence. 18. The apparatus of Claims 16-17 further comprising means for stopping the execution of the sequence for a period of time; means for resuming the execution of the sequence; and means for compensation for that period of time.