WO2006014272A1 - Acoustic isolator for downhole applications - Google Patents
Acoustic isolator for downhole applications Download PDFInfo
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- WO2006014272A1 WO2006014272A1 PCT/US2005/022972 US2005022972W WO2006014272A1 WO 2006014272 A1 WO2006014272 A1 WO 2006014272A1 US 2005022972 W US2005022972 W US 2005022972W WO 2006014272 A1 WO2006014272 A1 WO 2006014272A1
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- drilling
- assembly
- acoustic
- masses
- tubular
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01V—GEOPHYSICS; GRAVITATIONAL MEASUREMENTS; DETECTING MASSES OR OBJECTS; TAGS
- G01V1/00—Seismology; Seismic or acoustic prospecting or detecting
- G01V1/40—Seismology; Seismic or acoustic prospecting or detecting specially adapted for well-logging
- G01V1/52—Structural details
- G01V1/523—Damping devices
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01V—GEOPHYSICS; GRAVITATIONAL MEASUREMENTS; DETECTING MASSES OR OBJECTS; TAGS
- G01V1/00—Seismology; Seismic or acoustic prospecting or detecting
- G01V1/40—Seismology; Seismic or acoustic prospecting or detecting specially adapted for well-logging
- G01V1/52—Structural details
Definitions
- the present invention pertains to logging while drilling apparatus and more particularly to acoustic logging while drilling apparatus and attenuation of acoustic pulses that travel parallel to the direction of drilling.
- extended reach boreholes have been drilled to access hydrocarbon reserves at reservoir flanks and to develop satellite fields from existing offshore platforms. Even more recently, attempts have been made to drill boreholes corresponding to three- dimensional borehole profiles. Such borehole profiles often include several builds and turns along the drill path. Such three dimensional borehole profiles allow hydrocarbon recovery from multiple formations and allow optimal placement of wellbores in geologically intricate formations.
- Hydrocarbon recovery can be maximized by drilling the horizontal and complex wells along optimal locations within the hydrocarbon-producing formations.
- Crucial to the success of these wells is establishing reliable stratigraphic position control while landing the well into the target formation and properly navigating the drill bit through the formation during drilling.
- Such well profiles usually limit the horizontal reach and the final well length exposed to the reservoir.
- Modern directional drilling systems usually employ a drill string having a drill bit at the bottom that is rotated by a drill motor (commonly referred to as the "mud motor").
- a plurality of sensors and MWD devices are placed in close proximity to the drill bit to measure certain drilling, borehole and formation evaluation parameters. Such parameters are then utilized to navigate the drill bit along a desired drill path.
- sensors for measuring downhole temperature and pressure, azimuth and inclination measuring devices and a formation resistivity measuring device are employed to determine the drill string and borehole-related parameters.
- the resistivity measurements are used to determine the presence of hydrocarbons against water around and/or a short distance in front of the drill bit. Resistivity measurements are most commonly utilized to navigate the drill bit.
- the depth of investigation of the resistivity devices usually extends only two to three meters and resistivity measurements do not provide bed boundary information relative to the downhole subassembly.
- the location of the resistivity device is determined by some depth measuring apparatus deployed on the surface which has a margin of error frequently greater than the depth of investigation of the resistivity devices.
- it is desirable to have a downhole system which can accurately map the bed boundaries around the downhole subassembly so that the drill string may be steered to obtain optimal borehole trajectories.
- the relative position uncertainty of the wellbore being drilled and the critical near-wellbore bed boundary or contact is defined by the accuracy of the MWD directional survey tools and the formation dip uncertainty.
- MWD tools may be deployed to measure the earth's gravity and magnetic field to determine the inclination and azimuth. Knowledge of the course and position of the wellbore depends entirely on these two angles. Under normal conditions, the inclination measurement accuracy is approximately plus or minus two tenths of a degree. Such an error translates into a target location uncertainty of about three meters per one thousand meters along the borehole. Additionally, dip rate variations of several degrees are common. The optimal placement of the borehole is thus very difficult to bbtain based on the currently available MWD measurements, particularly in thin pay zones, dipping formations and complex wellbore designs.
- a prior art proposal has been to utilize estimates of the acoustic velocities obtained from prior seismic data or offset wells. Such acoustic velocities are not very precise because they are estimates of actual formation acoustic velocities. Also, since the depth measurements can be off by several meters from the true depth of the downhole subassembly, it is highly desirable to utilize actual acoustic formation velocities determined downhole during the drilling operations to locate bed boundaries relative to the drill bit location in the wellbore.
- the most significant noise source is acoustic signals traveling from the source to the receivers via the metallic tool housing and those traveling through the mud column surrounding the downhole subassembly (tube waves and body waves).
- acoustic sensor designs are used to achieve a certain amount of directivity of signals.
- a transmitter coupling scheme with signal processing method may be used for reducing the effects of the tube wave and the body waves. Such methods, however, alone do not provide sufficient reduction of the tube and body wave effects, especially due to strong direct coupling of the acoustic signals between the transmitters and their associated receivers.
- This apparatus includes of a substantially rigid member having interruptions in the longitudinal continuity of the member. These interruptions provide tortuous paths for the passage of acoustic energy along the member.
- a plurality of masses are periodically spaced along the interior of the member and are each mechanically integral with opposite sides of the member at locations chosen to enable the member and masses to cooperate as a mechanical filter.
- United States patent number 5,043,952, titled “Monopole Transmitter For a Sonic Well Tool", issued to David C. Hoyle, et al., relates to a monopole transmitter for a sonic tool which includes an axial tube, a piezoceramic cylinder surrounding the axial tube, an endcap disposed at each end of and firmly contacting the cylinder, and an apparatus for holding the endcaps firmly against the axial tube.
- the endcaps firmly contact the axial tube without simultaneously contacting an upper bulkhead.
- the apparatus may include spring washers disposed between the bulkhead and at least one endcap, or it may include a spring disposed between a nodal mount and each endcap.
- a nodal mounting tube may be disposed around the axial tube, a ring being disposed at each end of the nodal mounting tube, each ring being disposed outside of the cylinder for biasing the endcaps in tension against a ring thereby holding each endcap firmly in contact against the axial tube.
- United States patent number 5,510,582, titled “Acoustic Attenuator, Well Logging Apparatus and Method of Well Logging”, issued to James R. Birchak, et al., relates to a sonic well tool for performing acoustic investigations of subsurface geological formations penetrated by a borehole.
- the well tool generally includes a longitudinally extending body for positioning in the borehole.
- the tool also includes a transmitter supported by the body for transmitting acoustic energy and a receiver supported by the body for receiving acoustic energy.
- the tool includes an acoustic attenuation section positioned on the body between the transmitter and the receiver.
- This section includes one or more cavities defined by the body, inertial mass members positioned inside the cavities in a suitable manner to form a gap between the wall of the cavity and the inertial mass members, and an acoustical attenuation fluid in the gap.
- the method for attenuating sonic waves generally includes transmitting a sonic wave from the transmitter to the tool, passing the sonic wave through the acoustic attenuation section, and receiving attenuated wave at the receivers.
- Receiver Array Including an Attenuation and Delay Apparatus relates to a sonic well tool that includes a transmitter array having at least one monopole transmitter and at least one dipole transmitter and a receiver array for receiving sonic pressure wave signals from a surrounding borehole formation.
- a first attenuation and delay apparatus is positioned above the receiver array and a second attenuation and delay apparatus is positioned below the receiver array in the sonic well tool.
- the first attenuation and delay apparatus includes an attenuation member comprising a plurality of interleaved rubber and metal like washers for attenuating compressional and flexural waves propagating along a metal center support rod to the receiver array and an inner housing comprising a bellows section having a corrugated shape and a thin transverse dimension for delaying the propagation of compressional and flexural waves along the inner housing to the receiver array.
- the second attenuation and delay apparatus includes a plurality of mass loading rings surrounding the outer housing of the sonic well tool for attenuating the flexural waves propagating up the outer housing from a sonic transmitter ad a further inner housing including a further bellows section having a corrugated shape and a thin transverse dimension for delaying the propagation of compressional and flexural waves up the tool, along the inner housing, to the receiver array.
- the sonic well tool also includes a differential volume compensator for changing the quantity of oil encapsulated in the sonic well tool in accordance with changes in oil volume and changes in borehole temperature and pressure.
- the receiver array includes a plurality of hydrophone sets, each hydrophone set including at least one pair and preferably two pair of hydrophones disposed in a cross section of the tool, one hydrophone of a pair being disposed opposite the other hydrophone of the pair in the cross section. .
- United States Patent Application Ser. No. 09/201,988, now United States Patent 6,082,484 to MoIz & Duhinsky, having the same assignee as the present invention discloses the use of a section of a drill collar that has a plurality of shaped cavities filled with oil.
- the passage of an acoustic wave sets up a resonance of the fluid in the shaped cavity.
- the frequency of resonance depends upon the shape and size of the cavity and the properties of the fluid in the cavity.
- the cavities are spherical.
- Another embodiment of the invention uses cylindrical cavities with a piston restrained by a spring within the cavity. Changing the spring constant provides additional control over the frequencies that are attenuated.
- the '988 application also discloses the use of segmented isolators in which the drill collar section is filled with layers of a composite material in which the layers have a different density. The thicknesses of the individual layers is selected to attenuate certain frequencies.
- United States Patent Application Ser. No. 09/583,258 to Egerev et al having the same assignee as the present application and the contents of which are incorporated herein by reference, discloses a system and method for attenuation of acoustic waves that travel through a drill collar in a logging while drilling operation.
- the system includes a plurality of heavy masses attached to an inner wall of the drill collar.
- the heavy masses constitute mass discontinuities that attenuate waves traveling through the drill collar.
- the mass discontinuities are rings and attachment is done by neck pieces. These neck pieces extend out from the outer circumference of the rings and may be an original outer circumference of the ring that has been milled down by cutting out portions of the ring. This allows significantly less than the entire outer circumference of the hanging rings to be in contact with the inner surface of the drill collar. Thus, the rings will more efficiently attenuate the vibrational force of the acoustic pulses coming in contact with the hanging ring.
- the plurality of heavy hanging rings are spaced and sized for the maximum attenuation of acoustic pulses in a predetermined range, preferably in the range of 10 khz to 20 khz.
- the system may include steel rings as the plurality of heavy hanging rings.
- the plurality of heavy hanging rings may be a heavier, more dense material such as tungsten.
- the plurality may have as many as ten rings or as few as six, with eight being another possibility.
- the spacing of the rings may vary between twelve and fourteen centimeters, depending on the material used.
- a pipe may be placed within the inner circumference of the rings to isolate the attenuation rings from the flow of drilling mud.
- the isolation pipe may be of any material, however, a material that is non-rigid that is less likely to conduct vibrational forces is preferred.
- the mass discontinuities are attached to the drill collar over a substantial portion of their individual axial lengths. Such an arrangement acts as a low pass filter.
- the attenuator section comprises a cylindrical body with sections of different inside and/or outside diameters to produce a ringed pipe: the sections of different diameter each have a characteristic pass band and a reject band for attenuation of signals.
- the attenuator system of Egerev is expensive to fabricate and difficult to maintain due to the multiple mass discontinuities incorporated on the inner wall of a drill collar.
- the erosive flow of drilling fluid in the inside of the collar can cause severe damage to the isolators absent an internal sleeve. If would be desirable to have an attenuator system that is less expensive to fabricate and easier to maintain.
- an apparatus for performing acoustic investigations while drilling a borehole in a subsurface geological formation comprises a longitudinally extending assembly conveyed in the borehole on a drilling tubular.
- the assembly and the drilling tubular have a drilling fluid flowing through a longitudinally extending passage in the assembly and the drilling tubular.
- An acoustic transmitter is supported by the assembly.
- the transmitter generates acoustic signals in the assembly, the borehole and the subsurface formation.
- An acoustic receiver is spaced apart from the transmitter and is supported by the assembly for receiving the acoustic signals.
- An attenuator is located in the assembly between the acoustic transmitter and the acoustic receiver for attenuating the acoustic signals in the assembly within a predetermined frequency range.
- the attenuator comprises a tubular element of a composite material having a substantially cylindrical outer surface. The outer surface has a plurality of spaced-apart masses having a predetermined spacing, mass and length firmly attached thereto.
- a method of performing acoustic investigations while drilling a borehole in a subsurface geological formation comprises conveying a logging assembly into the borehole on a drilling tubular.
- the assembly and the drilling tubular having a drilling fluid flowing through a longitudinally extending passage in the assembly and the drilling tubular.
- a transmitter is activated in the assembly for generating acoustic signals in the formation, the borehole, and the assembly.
- Signals passing through the assembly are attenuated using an attenuator comprising a composite tubular element having a plurality of spaced-apart masses firmly attached on an outer diameter surface of the tubular element. The masses are spaced apart a preselected distance to attenuate signals within a specified frequency range.
- a receiver on a side of the attenuator opposite the transmitter receives signals through the formation and the attenuated signals through the assembly.
- Figure 1 is an illustration of a drill system having a measuring while drilling device mounted in the drilling apparatus
- Figure 2 illustrates raypaths of acoustic signals between the transmitter and the receiver
- Figure 3 is an illustration of an attenuation system for use on a well drilling collar
- Figure 4 is a graphical representation illustrating the effects of an increased number of attenuation elements of a system as that illustrated in Figure 1;
- Figure 5 is a graphical representation illustrating the effects of increasing the weight of attenuation elements of a system as that illustrated in Figure 1.
- Figure 6 is a graphical representation illustrating the attenuation effect of the system of Figure 1;
- Figures 7a and 7b show a comparison of the invention of Fig. 2 with one in which the mass discontinuities are attached to the drill collar over a substantial length;
- Figures 8a - 8c show alternate embodiments of the invention in which attenuation is accomplished by means of recesses that produce mass discontinuities in a body of the attenuator;
- Figure 9 shows a comparison of frequency spectra of attenuators having different types of recesses having a fixed length
- Fig. 10 shows alternate embodiments of the invention in which the diameter of the attenuation sections is varied
- Figs. 11 shows an alternate preferred embodiment using an arrangement of mass bodies attached to an external wall of a drill collar
- Fig. 12 shows an asymmetrical arrangement for a mass ring attached to an external wall of a drill collar.
- Figs. 13 shows an embodiment using an arrangement of mass bodies attached to an external wall of a composite tubular element
- Fig. 14 shows an asymmetrical arrangement for a mass ring attached to an external wall of a composite tubular element.
- FIG. 1 is a :, schematic illustration of the use of a Measurement- While-Drilling (MWD) apparatus while drilling a well.
- MWD Measurement- While-Drilling
- a drilling rig 1 is used to drill a borehole 23 through subterranean formations 25a, 25b, 25c etc.
- a drillship or a platform could be used to drill a borehole into subterranean formations covered by a body of water.
- a drilling tubular 13, that could be made of drill pipes or coiled tubing is used to rotate a drillbit 17 at the bottom, the rotating action of the drillbit and axial pressure carving out the borehole.
- a drilling motor (not shown) is used to impart the necessary rotary motion to the drillbit.
- a variety of transducers are used downhole in a sensor assembly 11.
- This sensor assembly makes measurements of properties of the formations through which the borehole is being drilled. These could include electromagnetic, gamma ray, density, nuclear-magnetic resonance, and acoustic sensors.
- acoustic transmitter array 31 and an acoustic receiver array 33 are indicated. Those versed in the art would recognize that other configurations of the acoustic transmitters and receivers could be used.
- the transmitter 31 and the receiver 33 are shown inside the borehole 23.
- the annulus between the drilling tubular 13 and the borehole 23 is filled with a drilling fluid.
- the fluid is conveyed down the borehole inside the drilling tubular to the drillbit and returns up the hole via the annulus.
- Excitation of the transmitter produces acoustic signals.
- a portion of the signal, denoted by the raypath 43 is referred to as the direct arrival and travels through the tool to the receiver.
- the transmitter also produces an acoustic signal in the borehole fluid that enters into the formation. ,One portion of it, illustrated by the raypath 41 travels as a body wave through the formation and carries information about the formation that it traverses.
- the receiver also detects other signals, such as tube waves that involve a coupled wave between the fluid and the formation, Stoneley waves that are surface waves in the fluid, and signals reflected from acoustic reflectors within the formation.
- the body wave 41 through the formation usually arrives before the tube wave and the Stoneley wave.
- the direct arrival 43 through the tool commonly arrives before the desired signal component 41 that carries information about the acoustic properties of the formation.
- the drillbit 17 itself is continuously generating acoustic signals traveling through the drilling tubular 13. Consequently, it becomes very difficult to determine a travel time for the formation body wave 41.
- a pulse attenuator 40 is located in tool 11 between transmitter 31 and an receiver 33. Only one transmitter and receiver are illustrated for demonstration. In practice, there may be several receivers and transmitters and the present invention operates with any arrangement, the only requirement is that attenuator 40 be located between the transmitter and the receiver.
- the acoustic isolator is based upon an array of mass rings attached to the inner wall of the drilling collar.
- Such an array presents an interference filter providing a stop band at a predetermined frequency for longitudinal sound waves propagating along the walls of a collar.
- the device exhibits sufficient damping within the predetermined frequency range as well as good mechanical strength.
- the efficiency of an isolator of this type increases proportionally to the number of the rings N as well as to the ratio M / ⁇ , where M is the mass of a single ring, ⁇ is a mass per unit length of the collar. Hence, the efficiency of the isolator is very sensitive to even minor changes in outer dimensions of the pipe as well as to the changes in demands to its wall thickness.
- the attenuation provided by the isolator section is designed to be minus forty decibels within the frequency range of twelve through eighteen kilohertz.
- the isolator design satisfy the mechanical requirements specified concerning the limitations on inner diameter, outer diameter, minimal cross section area and others.
- FIG. 3 is a partial illustration of an attenuation system 50 for a sound tool (not shown) in a drill collar 52 using an array of hanging mass irregularities 54, 56, 58 ... (may include up to ten elements) mounted on inner wall 60 of drill collar 52.
- Mass irregularities 54, 56, 58, ... are secured to inner wall 60 by neck pieces 62 which extend out from outer circumference 64, 66, 68, ... of mass irregularities 54, 56, 58, ... respectively.
- Neck pieces 62 are smaller both in depth and width than outer circumferences 64, 66, 68, ... of mass irregularities 54, 56, 58, ... so that mass irregularities 54, 56, 58, ... are held firmly against inner wall 60, but not so firmly that acoustic pulses traveling through drill collar 52 are transferred without attenuation. In this manner, mass irregularities 54, 56, 58, ... are held firmly but not tightly.
- an inner pipe 64 may be provided to protect array of mass irregularities 54, 56, 58, ... from mud flow.
- Inner pipe may be of any material to isolate mass irregularities 54, 56, 58 ... from the mud flow, however, a material that is non-rigid and has a degree of flexibility is preferred. A material that is less likely to transfer acoustic pulses toward the receivers is desired.
- the operation of the attenuation filter may be understood by the following discussion.
- the mass of a ringj is nij.
- an incident longitudinal sound wave of a unit amplitude traveling towards the origin of coordinates may be denoted by
- k ⁇ /c is a wavelength constant
- c the velocity of sound.
- Y is the Young's modulus of the pipe material
- S is the cross section area of the pipe wall
- u is the displacement
- ⁇ is the linear mass of the pipe
- x is the longitudinal coordinate.
- the displacement u When considering propagation of a sinusoidal wave, the displacement u may be represented by a function of the form u(x)exp(-i ⁇ t), where, ⁇ is the angular frequency,
- ⁇ is the angular frequency
- N u ⁇ x) Ae ila - ⁇ b j G(x - X j )u(X j )
- G(x - X j ) exp (ix. x - x y. ) / (2 y s k) is Green function, and bj ⁇ M j ⁇ is the magnitude of an irregularity.
- T u (x) / A, which may be expressed in decibels using the usual conversion factor.
- the transmission coefficient of the array may also be obtained by other methods.
- the impedance is calculated with the help of the following recurrence procedure:
- Figures 4 and 5 illustrate plots of transmission vs. frequency.
- the influence of the number of elements is illustrated in Figure 4.
- Transmission curves are shown for six elements, eight elements and ten elements.
- the increase in the number of elements only slightly changes the transmission curve at the borders of the predetermined frequency band.
- the period of an array 1 is important to place the transmission curves at the proper frequency.
- an optimal value for the spacing between elements is 5.12 inches or approximately thirteen centimeters for the inner and outer diameter used.
- other spacings such as fourteen or twelve centimeters may also be used and provide acceptable results.
- the influence of the mass of a single element is illustrated in Figure 5.
- Figure 4 illustrates attenuation curves for arrays of ten elements. Each curve is for elements of different weights. A first curve is for ten elements, each weighing eight kilograms, the second for elements weighing eleven kilograms and a third for elements weighing fourteen kilograms. An increase in the mass IvI results in changing the low frequency border. The high frequency border remains essentially unchanged. All the transmission curves show that transmission loss exceeds forty decibels within the predetermined frequency band between twelve and eighteen kilohertz.
- Transmission coefficient was calculated vs. frequency within the frequency range from five to twenty kilohertz.
- Figure 6 is a graphical representation of the attenuation of a preferred embodiment of the present invention.
- ten elements were used with a spacing of thirteen centimeters between elements. Rings of stainless steel were used as mass irregularities 54, 56, 58 .... It can be seen that the arrangement of the preferred embodiment provides attenuation of waves in the range of eight to eighteen kilohertz. By using his system, interference of waves traveling through the collar of a drilling tool can be greatly reduced and acoustic logging is possible during a drilling operation.
- Figs 7a and 7b show a comparison between the embodiment discussed above with respect to Fig. 2 and an alternate embodiment of the invention using a different arrangement of attaching the mass discontinuities to the drill collar.
- Shown in the upper portion of Fig. 7a is a drill collar 152a to which a mass 154a is attached by means of a neck 158a. This corresponds to the arrangement discussed above with reference to Fig. 2.
- Shown in the upper portion of Fig. 7b is an alternate arrangement in which a mass 154b is attached to the drill collar 152b over substantially the full length of the mass.
- Fig. 7a Shown in the lower portion of Fig. 7a is a schematic representation of the effective mass discontinuity 170a as seen by a propagating wave: typically, such a mass discontinuity provides approximately 6 to 8 dB of attenuation of the wave.
- the lower portion of Fig. 7b shows the effective mass discontinuity 170b as seen be a propagating wave: effectively, an attenuation of 2 - 3 dB of attenuation is provided at each boundary.
- the arrangement of Fig. 7b is shown to act as a low pass filter.
- the effective cutoff frequency can be made to be around 10 kHz.
- body waves through the drill collar may be effectively attenuated.
- Figs. 8a - 8c show alternate embodiments of the invention in which the isolator comprises a machined cylindrical member.
- the cylindrical member has an outer diameter of OD and an inner diameter of ID. The inner diameter allows passage of drilling mud.
- the inside wall if the cylindrical member has recess of length L therein.
- a body wave encounters regions of different cross sectional areas and mass densities, similar to the embodiments discussed above, resulting in attenuation of body waves.
- Fig. 8b shows an arrangement in which the recess are on the outside of the isolator whole
- Fig. 8c shows an arrangement in which there are recess on both the outside and the inside of the isolator.
- Fig. 9 shows the results of a finite element ("FE") simulation of the various embodiments shown in Figs. 8a - 8c.
- the abscissa is the frequency and the ordinate is the normalized amplitude of waves passed by the attenuator. Note that the amplitude scale is linear, rather than being in decibels.
- the curve 301 shows the spectrum for a cylindrical pipe.
- the curve 303 shows the spectrum for cuts on the inside of the pipe, 305 is for recesses on the inside and outside of the pipe while 307 is for recesses on the outside of the pipe. Similar FE simulations have been carried out for various lengths L of the recesses.
- a value of L of 3.15" (8.5cm) with recesses on both the inside and the outside of the isolator is used.
- the results in Fig. 9 are for a plurality of equally spaced recesses having the same length and the same depth of the recesses.
- Other embodiments of the invention use a combinations of sections having different lengths and different depths of inner and outer recesses. Examples are shown in Fig. 10.
- Each section 400 may be considered to be a waveguide with an associated pass-band and a reject band determined by the inner diameter 403 and the outer diameter 401. As may be seen in Fig.
- each section has an axis parallel to the longitudinal axis 405 of the body of the attenuator.
- a broad range of frequencies may be attenuated. This attenuation is in addition to the attenuation produced by reflections between adjacent sections 400.
- the waveguides are "leaky" waveguides that allow energy to propagate into the fluid.
- the inner diameters range from 2" to 6" and the outer diameter ranges from 4" to 10".
- Figs. 11 and 12 show an alternate preferred embodiment using an arrangement of mass bodies attached to an external wall of a drill collar. The effects are similar to those discussed above in reference to Figs. 7 a and 7b, however the external arrangement offers advantages of easier and less expensive fabrication and easier maintenance than masses connected to the internal wall of the drill collar as described previously.
- the mass discontinuities shown in Figs. 11 and 12 are essentially cylindrical rings.
- the rings may be made of steel or, alternatively, may be made of a more dense material such as tungsten.
- the mass rings 505a and 505b have an internal diameter 501 which is greater than the external diameter 503 of the drill collar 504 and are attached to the drill collar 504 by necks 506a and 506b, respectively.
- such a mass discontinuity as shown in Fig. 11 provides approximately 6-8 dB of attenuation of a direct acoustic wave traveling in the drill collar 504.
- the number of rings will typically be between 6 and 10 with a spacing between approximately 12 and 14 cm. for a frequency range of interest of 10 khz to 20 khz. Note that this is an exemplary range and that other frequency ranges may be filtered by the appropriate selection of mass size, number and spacing as previously described.
- an advantage of the external arrangement can be realized because attenuation is related to the mass of each ring 506a, 506b, divided by the mass per unit length of the drill collar, as previously discussed.
- the external rings 506a, 506b can have a smaller thickness t due to the d 2 effect on ring volume.
- the rings 506a,506b are at a.larger diameter than the internal ring described in Fig. 7a, if the length of the rings is the same, rings 506a, 506b will be thinner to have the same mass for the same material.
- the mass of rings 506a if the ring thickness t and the length are held the same as before, then the mass of rings 506a,
- Fig. 12 shows an asymmetrical arrangement for a mass ring attached to a collar.
- Exemplary mass rings 605a, 605b are coupled to collar 604 at shoulder 607 having a raised diameter 606.
- the masses 605a, 605b contact the collar over a portion K of the length L of the masses 605a, 605b such that the masses are supported over a portion of their length and cantilevered for a portion of their length.
- the masses may be attached by welding, brazing, press fitting, shrink fitting or any other suitable technique.
- the number of masses and the spacing of the masses are essentially the same as for those described for Fig. 11.
- the acoustic source is located in the direction of the supported portion of the masses 605a, 605b, typically an uphole direction, as shown in Fig. 12. As acoustic waves from the source travel toward the receiver, or downhole, they encounter a geometry which allows the acoustic wave to enter the masses
- Fig. 12 is preferred for a drilling operation because it provides increased support area for the masses as compared to that of Fig. 11, thereby providing increased stability of the masses as they encounter the significant wall forces involved in downhole drilling.
- the external arrangement of the masses of Fig. 11 and Fig. 12 provide improved cleaning, inspection, and maintenance compared to the internal mass arrangements described previously. While the masses shown in Fig. 11 and Fig. 12 have sharp corners, radiused corners may be provided for stress relief and/or to facilitate ease of manufacturing. Such techniques are known in the art and are not described further.
- the tubular element 704 and 804 is a composite material having mass rings 705 and 805 attached thereto.
- the attenuation is related to the ratio of the density of the mass ring to the density of the tubular member. Therefore, by using a light material, relative to the commonly used steel in downhole tubulars, a greater density ratio between the attenuator rings and the tubular may be realized, resulting in enhanced attenuation. Drilling fluid 710 and 810 flows through the inner passage 711,811 of tubular elements 704 and 804, respectively.
- the composite material utilized may include graphite fibers, aramid fibers, fiberglass, or any other suitable material. Such materials are known and are commercially available from a variety of sources. Multiple layers may be used. A number of methods, known in the art, have been proposed for orientation and thickness of different types of composite materials for use in downhole tubulars. Suitable resins may be used within and between the layers. For the purpose of this invention, any composite tubular may be utilized, whether or not layered. Mass 705, associated with tubular element 704, and mass 805, associated with tubular element 804, may be of a like composite material to that of the tubular elements.
- masses 705 and 805 may be of a density greater than that of tubular elements 704 and 804, such as, for example, steel and/or tungsten.
- the number of elements and their spacing are similar to that described previously.
Abstract
Description
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Priority Applications (3)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
CA002572481A CA2572481A1 (en) | 2004-07-02 | 2005-06-27 | Acoustic isolator for downhole applications |
GB0625820A GB2431005B (en) | 2004-07-02 | 2005-06-27 | Acoustic isolator for downhole applcations |
NO20070616A NO339289B1 (en) | 2004-07-02 | 2007-02-01 | Acoustic insulator for use in a borehole in the underground |
Applications Claiming Priority (2)
Application Number | Priority Date | Filing Date | Title |
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US10/884,850 | 2004-07-02 | ||
US10/884,850 US7028806B2 (en) | 1999-06-03 | 2004-07-02 | Acoustic isolator for downhole applications |
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Publication Number | Publication Date |
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WO2006014272A1 true WO2006014272A1 (en) | 2006-02-09 |
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Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
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PCT/US2005/022972 WO2006014272A1 (en) | 2004-07-02 | 2005-06-27 | Acoustic isolator for downhole applications |
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Country | Link |
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US (1) | US7028806B2 (en) |
CA (1) | CA2572481A1 (en) |
GB (1) | GB2431005B (en) |
NO (1) | NO339289B1 (en) |
RU (1) | RU2362189C2 (en) |
WO (1) | WO2006014272A1 (en) |
Cited By (1)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US8220583B2 (en) | 2006-11-23 | 2012-07-17 | Reeves Wireline Technologies Limited | Acoustic isolator section |
Families Citing this family (19)
Publication number | Priority date | Publication date | Assignee | Title |
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US6615949B1 (en) * | 1999-06-03 | 2003-09-09 | Baker Hughes Incorporated | Acoustic isolator for downhole applications |
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Also Published As
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GB2431005A (en) | 2007-04-11 |
US20050023074A1 (en) | 2005-02-03 |
GB0625820D0 (en) | 2007-02-07 |
NO20070616L (en) | 2007-03-21 |
CA2572481A1 (en) | 2006-02-09 |
US7028806B2 (en) | 2006-04-18 |
GB2431005A8 (en) | 2007-05-08 |
GB2431005B (en) | 2007-12-27 |
RU2007103717A (en) | 2008-08-10 |
NO339289B1 (en) | 2016-11-21 |
RU2362189C2 (en) | 2009-07-20 |
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