MXPA00010569A - Acoustic logging tool - Google Patents

Abstract

A sleeve for an acoustic logging tool has a structure with a window section having fewer bars than a conventional sleeve separated by a slotted region with thin circumferential slots which are stress-relieved at the ends ("dumb-bell"shaped). Steel receiver mounts are provided for hydrophone pressure sensors and this, together with the axially oriented hydrophones makes the tool less susceptible to interfering vibration.

Description

ACOUSTIC DIAGNOSTIC PROBE TECHNICAL FIELD The present invention relates to acoustic logging probes, in particular to aspects of a receiving section for an acoustic logging probe in which the interference effect of the bending waves is minimized. BACKGROUND OF THE INVENTION Acoustic diaphragm probes are used in the evaluation of formations around perforations such as those used for the extraction of hydrocarbons. The Figure 1 shows a schematic view of a prior art acoustic logging probe such as the DSI Dipole Sonic Shear Imager by Schlumberger. The probe comprises a probe 10 which is lowered to a bore 12 by means of a wire cable 14. The cable is used to support the probe 10 and to provide power, control signal and the data transmission path for the surface unit 16. Probe 10 includes a transmitter section TX capable of generating dipole and monopolar acoustic signals, a SU sound isolation joint, an RX receiving section, and an EC electronic circuit cartridge. The receiver section RX includes a number of spaced receiving stations, eight stations are commonly used, and each station typically has four piezoelectric sensors for pressure measurement in the perforation due to the passage of acoustic waves. Examples of the various aspects of such a probe can be found in U.S. Patent No. 4,850,450; U.S. Patent No. 4,862,991; U.S. Patent No. 4,872,526; U.S. Patent No. 5,036,945 and U.S. Patent No. 5,043,952. In the dipolar log, the TX transmitter generates a dipole acoustic signal that propagates along a number of possible paths to the RXi, RX receivers (only two stations are shown here instead of the usual eight for clarity purposes). These paths shown schematically in Figure 2 are (1) along the same probe, (2) through the filling of drilling fluid, and (3) as a formation / drilling mode in which the signal passes from the transmitter through the fluid in the perforation to the formations around the perforation where a superficial wave mode of the perforation is established (this is a dispersed mode whose dispersion characteristics of the slowness are determined by the properties of the formation around the perforation, the dimensions of the perforation and the properties of the drilling fluid), then back to the drilling fluid and then to the RXi, RX2 receivers. Since the purpose of the acoustic record is to determine the properties of the training around the performance, it is the last road which is of interest, the signals paying along the roads (1) and (2) not giving information about the formations and in this way interfering with the evaluation. The speed (or "slowness") of propagation of the acoustic signal depends on the physical nature of the medium through which it propagates; usually, the more rigid the faster means is the propagation. The slowness of the pressure field signal through the drilling fluid is usually around 200 μs / ft. The slowness of the bending wave of the probe depends on a particular design of the probe but will commonly be > 700 μs / ft. The slowness of the bending wave signal of the formation / perforation (the signal of interest) can reach from about 100 μs / ft to 1000 μs / ft in common formations recorded by these probes. The presence of the SIJ sound insulation junction between the TX transmitter and the RX receiver goes in some way, to reduce the propagated signal along the body of the probe (the "probe signal"), an example of this is described in U.S. Patent No. 4,862,991. However, this by itself is not enough, especially when handling the propagation of bending waves along the probe. One method is to provide a housing for the probe that is configured to delay the signal from the probe sufficiently that it can not interfere with the signal of the probe. training. An example of this is found in U.S. Patent No. 4,850,450 and in the Schlumberger DSI probe. The receiver section of the DSI probe includes a central mandrel around which alternate Teflon hydrophilic mounts are mounted and the steel spacers connected together to form a continuous structure. The hydrophones are aligned radially (the polarization of the piezoelectric cell is aligned with the radius of the probe). The slotted sleeve has an alternate window and slotted structures. The window section has 10 bars defining the windows (each window defining an arc of 20 °) and four rows of regular circumferential grooves (each slot defining an arc of 70 °). The slotted sleeve is shown in Figures 3a and 3b. Another method is to avoid using a rigid, continuous housing in the receiving section. U.S. Patent No. 5,289,433, U.S. Patent No. 5,343,001 and U.S. Patent No. 5,731,550 describe acoustic probes wherein the receiver includes receiver stations separated by connectors or spacers that include some acoustic or elastic insulating material on the contact surfaces. The method described in the patents * 433 and 001 is that the receiving section lacks sufficient strength or rigidity to be used in rigid recording conditions or non-vertical wells. In such conditions, you must use a sleeve and find the problem of interference of the probe signal. The connectors in the patent * 550 are configured to allow greater compression rigidity but retain an acoustic insulation element in tension, which is the normal recording condition.

While grooved sleeve probes have good mechanical properties, certain problems can be encountered in slow formations, when the sleeve arrives in interference with the arrivals in the slow formations, and when inconsistencies arise in the waveforms from the receiving section due to to the vibration of the probe excited by the perforation waves. An objective of the present invention is an attempt to face such problems. DESCRIPTION OF THE INVENTION The present invention adopts certain principles for providing a structure having a flexural dispersion (slowness vs. frequency) that does not overlap with the flexural dispersion of the perforation in the formations of interest, and in which the receiving section is it constructs in a way that optimizes the detection of the signal of interest while minimizing the interference signal and the sensitivity of the receiving section to couple with the drilling vibration mode. According to one aspect of the invention, a sleeve for encircling the receiving section of a diagnostic probe acoustic, at least in the region of the receiving stations, has alternating first and second portions with openings spaced along its length, wherein: (a) the first portion with openings has bar elements extended axially separated by windows in a circumferential arrangement, the windows being wider than the bars, and (b) the second opening portion having rows of elongated slots in the circumferential direction, the slots having a relatively narrow central portion and relatively enlarged end portions. In a second aspect of the invention, a receiver section for an acoustic logging probe comprises a number of receiving stations along the body of the probe, each station including a number of polarized pressure sensors spaced around the body circumference of the probe, the polarization axes of the sensors are parallel to the axis of the probe body. The first portion with openings of the sleeve (the window section) has a reduced number of bars of increased length and larger windows compared with a normal sleeve. This tends to reduce the spring constant and the increase in flexibility of this portion, increasingthis way the slowness in the flexion of the sleeve (speed of the propagation of the flexion along the sleeve). In one embodiment, two window widths are alternated, for example windows alternating 45 ° and 25 °. It is preferred to configure the window section to inhibit coupling with higher modes of vibration (such as hexagons). This is achieved by selecting the number of windows and the relative dimensions of the windows (for example, alternating sizes as described above). The second apertured portion (the grooved section) is commonly provided with three rows of thin circumferential grooves with enlarged portions at the ends (dumbbell or fungiform grooves). The axial length of the slotted section can be reduced while the mass is almost the same as the corresponding structure of the sleeve with regular slots of the prior art. The radius of the width of the central portion of the grooves at the radius of the end portions is most preferably at least 1: 4, 1: 6. Slots commonly define 70 ° arcs. Each row of slots is offset relative to the adjacent row (s). This displacement is conveniently 90 ° even though other angles may be appropriate. In the receiving section, the pressure sensor (hydrophone) assemblies are preferably made solid, built of steel. The hydrophones themselves are mounted in the axial direction (vertically) as well as to be less susceptible to probe vibrations caused by the coupling of the perforation modes. The receiving section has a central mandrel to which spacers are attached, each spacer loading the weight of the receiver assembly through an adaptable pad. Thus, each receiver assembly is essentially independent of the neighbors. A basic concept that is used in the construction of a probe incorporating the present invention is to ensure that the dispersion of the flexion (slowness vs. frequency) of the probe does not overlap with the dispersion of the bending of the formations of interest at the frequencies of interest. For example, when the formations that have a delay of 1200 μs / ft are going to be measured, the probe is designed so that the arrivals of the bending probe do not occur under such speed. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 shows a schematic view of the acoustic diag- nostic probe of the prior art; Figure 2 shows the paths for the dipole signals from a transmitting acoustic logging probe to a receiver; Figures 3a and 3b show views in general section and partial of a sleeve of the prior art for use in an acoustic logging probe; Figures 4a to 4e show a general and detailed view of a sleeve according to an aspect of the invention; Figures 5a and 5b show partial and general section views of a receiving section according to an aspect of the invention. BEST MODE FOR CARRYING OUT THE INVENTION A sleeve for an acoustic speech probe incorporated in the present invention is shown in Figures 4a to 4e. The sleeve is formed from a steel cylinder with a number of openings or holes cut in it by means of laser machining. The sleeve structure has two main parts, a first portion A having windows cut into the sleeve, and a second portion B defining a slotted section. This sleeve behaves conceptually as a spring-mass-spring-mass system ... in bending mode; the bars in the window sections A act like the springs and the slotted sections B act like the masses. Each window portion A has eight rectangular windows W separated by bars B. In the embodiment of Figures 4a and 4b, alternating window sizes (25 ° and 45 °) are used with regular bars (10 °) (see Figure 4c (section on line AA of Figure 4b)). These dimensions give consequently low constant of springs for this section. The dimensions and number of bars or windows can be chosen to optimize this aspect of sleeve behavior. In this particular case, the windows and bars are around 8 cm in length. By selecting alternating window sizes and reducing the number of windows to eight, the coupling of higher vibration modes (such as hexapolo) in the probe is inhibited. The particular dimensions and the number of windows, and the symmetry of the window section if required can vary to optimize operation. The simple slots of the sleeves of the prior art (Figures 3a and 3b) are relatively easy to manufacture but have a concentration of tension near the end portions. This affects the resistance of the sleeve and places a limitation on the proximity of the slot space. Making the grooves wider but maintaining the same length can decrease the concentration of the tension but it can also decrease the mass of the grooved section (ie, the "mass" in the "mass-spring-mass" system) and has an effect negative in the operation of the flex. The sleeve shown in Figures 4a to 4e use grooves in the form of a "dumbbell", the narrow central portions. Increased mass is given to the grooved portion B while the extreme portions are increased from the slots act to release the concentration of tension. The end portions of the sleeve have a radius of 8 mm but can be increased to 12 mm without significant loss of sleeve strength; the central portion has a width of 2 mm. This can be compared with the slots in the sleeve of the prior art which are approximately 6.4 mm wide. As a result of a lower tension, the axial space between the slots can be reduced, as in the present case the slotted sections are about 7.2 cm long. This results in a slower extension mode. Due to the slower extension mode along the grooved section, the number of rows of grooves can be reduced (from four to three) without sacrificing much compression sluggishness. The shorter grooved section means a decrease in mass but more elongated bars in the window section. The decrease of the bar constant is proportional to the third power of the length dimension (L3) while the decrease of the mass is only proportional to the length dimensions themselves (L). In this way, it will increase the system's slow global flexion. The grooves define arcs of 70 ° in centers spaced 90 ° around the circumference of the sleeve. Each row is displaced with respect to its neighbor (s) by 90 ° (see Figures 4d and 4e (sections on lines BB and CC of Figure 4b, respectively)). The ends of the sleeve have grooved sections with two and four rows of grooves respectively. A receiver section for use in an acoustic logging probe according to the invention is shown in Figures 5a and 5b. The section comprises a central mandrel 20 around which alternating receiver assemblies 22 and spacers 24 are located. The mandrel 20 is formed from a central rod 26 having a Teflon coating 28 in which a number of notches are provided through of which an electrical installation can be connected. The liner provides a forced fit with the receiver or spacer mounts to prevent radial movement. The spacers 24, which comprise massive steel bodies with a central ring around the outer circumference, are firmly connected to the center rod 26 by means of a fixing screw (not shown) extending through the liner 28. Form cavities square 32 are provided at the upper and lower ends of each spacer 24. Receiving mounts 22 are also formed of steel and have four cavities 34 located for hydrophone stacks 36 spaced around the outer circumference. An installation is routed from the hydrophones 36 within the notches in the liner 28 and along the probe to an electronic cartridge. The square cavities 38 are provided at the ends of the receiver assemblies 22, corresponding to the cavities 32 in the spacers 24. The receiver assemblies are not firmly connected to the mandrel 20 as are the spacers 24, but are free to slide along the mandrel 20. An elastic contact pad 40 is located between the adjacent ends of a spacer 24 and a receiver assembly 22. These pads 40 have the same shape and size as the cavities 32, 38 and the spacers 24 and receiver assemblies 22. When the receiver is completely assembled, the spacers 24 are positioned so that there is sufficient space between the consecutive spacers 24 for a receiver assembly 22, leaving a small amount of space above. The receiver assemblies 22 do not directly contact the spacers 24 but support the pads 40 which settle in the cavities 32, 38 of the spacer 24 and the receiver assembly 22. The pads 40 consequently serve not only to provide an elastic contact, but also maintain the relative orientation of the receiver assemblies 22 and the spacers 24 (and by extension, the orientation between all the receiver assemblies 22 and the receiver section). In this way, when the receiving section is vertical, each receiver assembly 22 is free to support in the spacer 24 below through the pad 40. The probability of vibration of the receiving section 5 due to the coupling of the bending mode of the piercing is reduced in two ways . First, receiver assemblies 22 are made of steel which means that it is more difficult for the piercing method to cause the probe to vibrate (greater impedance incompatibility). Second, the The structure of the receiving section is constructed of alternating receiver assemblies 22 and spacer sections 24. In the prior art probe, the receiver assemblies and the steel spacers are all connected together to make a single structure. At the moment In accordance with the invention, each steel spacer 24 is firmly connected to the central mandrel 20 of the probe. The receiver assemblies 22 are separated from the spacers 24 by means of elastic pads 40 forming a single connection. In this way, each spacer 24 carries the assembly 22 on top of it but can not stand the assembly below. This structure prevents the receiving section from acting as a rigid body and coupling with the vibration methods of the perforation. Piezoelectric receivers (hydrophones) in the The present invention is aligned axially opposite to radial direction in the prior art probe. This probe uses piezoelectric ceramic cells as pressure sensors. Given the intrinsic anisotropy of the polarized ceramic material and the volume of the cell, it is not negligible that the detector can be expected to exhibit non-isotropic behavior and have an output that changes depending on the orientation of the polarization axis of the cell in the presence of a field of tension / pressure not uniform. If a stack of sensors of this type is attached to a vibrating rigid body, the measurement of body vibration will depend on the orientation of the stack axis and the direction of vibration. If the battery is polarized along the direction of vibration, its output will be maximum and in phase with the field induced by the vibration. If, on the contrary, the battery is polarized in a direction perpendicular to the direction of movement, the signal will be much smaller and will have the opposite phase. This operation can be considered in the context of a vibrating body (probe) in the presence of a pressure field, not uniformly applied suddenly .. In such a case, the field induced by the probe (the field induced by the vibration of the body) will have initially a phase opposite to that of the external field (if the probe remains perfectly rigid, the pressure accumulated around it will be maximum, any initial movement caused by the external field the initial accumulated pressure around the probe will decrease). For a stack attached to the body with its axes aligned with the direction of vibration, the output of the stack will contain a weighted subtraction of the two fields (the contribution of the output due to the field induced by the body will be in phase with the induced field by the body and, therefore, out of phase with the external field). In contrast, if the stack is polarized perpendicular to the direction of vibration, the output will initially contain a weighted addition of the two fields (the contribution of the field induced by the body is out of phase with the field induced by the body and, consequently, in phase with the external field). Consequently, the initial response to a field applied externally will be maximum when the pile is polarized in a direction perpendicular to the induced vibration of the body to which it is attached. In the vicinity of a dipolar diag- nostic probe, the waves (compression, bending and dipolar short) propagating along the perforation will induce probe vibrations that are predominantly bending, that is, the probe movement is predominantly perpendicular to the axis of the perforation / probe. Therefore, if piezo batteries are used as receivers oriented along the drilling axis, there will be a double benefit. First, because the sensitivity of the battery output to any field induced by the vibration of the probe is minimized, and second, because the initial response of the stack to the perforation waves will increase to the maximum. The change of the mounting material and the orientation of the hydrophone affects the functioning of the receivers somewhat but does not affect the ability of the probe to make the required measurements. The receiving section described here addresses the problem of vibration of the probe in two ways: by adopting a structure which is more difficult for the waves of the perforation to excite in vibrations; and by orienting the sensors to be less sensitive to any vibration of the probe which is excited by the drilling modes. INDUSTRIAL APATION The present invention finds apation in the field of acoustic logging probes that can be used to evaluate formations around perforations, such as those drilled for the extraction of hydrocarbons or geothermal energy.

Claims (32)

1. CLAIMS 1. A sleeve for the receiving section of an acoustic logging probe including a probe body with receiving stations; the sleeve being able to surround the probe's ceupo at least in the region of the receiving stations and having alternate first and second portions with openings spaced along its length, the first portion with openings having elements in bars increased in length. axial direction separated by windows in a circumferential arrangement, the windows being wider than the bars, and the second portion with openings has rows of grooves increased circumferentially; characterized in that each slot has a central portion and end portions, the central portion is narrower than the end portions, and the end portions are wider compared to the central portion.
2. 2. The sleeve as mentioned in claim 1, wherein the grooves of the second portion with openings have parallel sides in the central portion and approximately circular end portions.
3. The sleeve as mentioned in claim 2, wherein the ratio of the width of the groove in the central portion to the radius of the end portion is at least 1: 4.
4. 4. The sleeve as mentioned in claim 3, in where the ratio is approximately 1: 6.
5. The sleeve as recited in claim 1, 2 or 3, wherein each second portion with openings has three rows of grooves.
6. The sleeve as mentioned in any of claims 1 to 5, wherein each first portion with openings has eight windows.
7. The sleeve as mentioned in any of claims 1 to 6, wherein the first portion with openings has windows of two alternating widths.
8. The sleeve as mentioned in claim 7, wherein the windows have widths of 25 ° and 45 °, respectively.
9. The sleeve as mentioned in any of claims 1 to 8, when forming part of an acoustic logging probe having a probe body with a transmitting section and a receiving section.
10. 10. An acoustic logging probe comprising a probe body with a transmitter section and a receiver section comprising a number of receiver stations spaced along a probe body, each station including a number of polarized pressure sensors spaced apart around the circumference of the body of the probe, and a sleeve surrounding the body of the probe at least in the region of the receiving stations and having a first and second portions with openings spaced along their length; the first portion with openings has enlarged axially shaped bar members, separated by windows in a circumferential arrangement, the windows are wider than the bars, and the second open portion has rows of circumferentially enlarged grooves, characterized in that the The sleeve comprises a sleeve as claimed in any of claims 1 to 9 and the polarization axes of the sensors are parallel to the axis of the body of the probe.
11. The probe as recited in claim 10, wherein the pressure sensors comprise piezoelectric cells.
12. The probe as recited in claim 10 or 11, wherein each station has four pressure sensors spaced equidistantly around the body of the probe.
13. The probe as recited in claim 10, 11 or 12, comprising a central mandrel around which are mounted alternately, assemblies of pressure sensors and spacers, the spacers are firmly connected to the mandrel and the sensor assembly is maintained in position by the spacers.
14. The probe as mentioned in claim 13, wherein the spacers and the pressure sensor assemblies They are made of steel.
15. 15. The probe as recited in claim 13 or 14, wherein each mounting of the pressure sensor makes contact with its neighboring spacers by means of elastic contact pads.
16. 16. The probe as mentioned in any of claims 13, 14 or 15 where, when arranged vertically, the weight of each mounting of the pressure sensor is charged by the spacer located under the mounting.
17. 17. The receiving section for an acoustic logging probe comprising a number of receiving stations spaced along a probe body, each station including a number of polarized pressure sensors spaced around the circumference of the probe body, characterizes in which the polarization axes of the sensors are parallel to the axis of the body of the probe.
18. 18. The receiving section as recited in claim 17, wherein the pressure sensors comprise piezoelectric cells.
19. 19. The receiver section as recited in claim 17 or 18, wherein each station has four pressure sensors spaced equidistantly around the body of the probe.
20. 20. The receiving section as mentioned in claim 17, 18 or 19, comprising a central mandrel around which the pressure sensor assemblies and spacers are mounted alternately, the spacers are firmly connected to the mandrel and the sensor assembly being held in place by the spacers .
21. 21. The receiving section as recited in claim 20, wherein the spacers and the pressure sensor assemblies are made of steel.
22. 22. The receiving section as shown in claim 20 or 21, wherein each mounting of the pressure sensor makes contact with its closest spacer by means of elastic contact pads.
23. 23. The receiving section as claimed in claim 20, 21 or 22, wherein, when arranged in a vertical position, the weight of each mounting of the pressure sensor is loaded by the spacer located below the assembly.
24. 24. The receiving section as claimed in claims 17 to 23, when forming part of an acoustic logging probe has a probe body which also includes a transmitting section.
25. 25. The receiving section as claimed in claims 17 to 24, further comprises a sleeve that is capable of encircling the body of the probe at least in the region of the receiving stations and having alternating a iafet. first and second portions with openings spaced along their length, wherein: (a) the first portion with openings has bar members extended axially separated by windows in 5 a circumferential arrangement, the windows being wider than the bars, and (b) the second portion with openings having rows of circumferentially elongated slots, the slots having a central portion and end portions, the portion 10 relatively narrow center and the end portions being enlarged in comparison with the central portion.
26. 26. The receiving section as claimed in claim 25, wherein the grooves of the second portion with openings have parallel sides in the portion 15 central and external portions approximately circular.
27. 27. The receiving section as claimed in claim 26, wherein the ratio of the width of the groove in the central portion to the spokes of the end portion is at least 1: 4.
28. 28. The receiving section as claimed in claim 27, wherein the ratio is about 1: 6.
29. 29. The receiving section as claimed in claim 25, 26 or 27 wherein each second portion with openings has three rows of grooves. 25.
30. 30. The receiving section as claimed in any of claims 25 to 29, wherein each first portion with openings has eight windows.
31. 31. The receiver section as claimed in any of claims 25 to 30, wherein the first portion with openings has windows of two alternating widths.
32. 32. The receiving section as claimed in claim 31, wherein the windows have widths of 25 ° and 45 °, respectively.