Patent Description:
In underground drilling operations such as oil and gas drilling operations, it is often desirable to precisely control the drilling path of a new borehole relative to a known location (which may be disposed within the pathway of an existing borehole). To do that, operators may precisely monitor the location of the drill bit forming the new borehole relative to the existing borehole. For example, when a group of wells are drilled from an offshore platform, it is often necessary to drill new wells spaced three meters or less from existing wells for <NUM> meters or more during the initial depth interval. Subsequently, the wells may be directionally deviated and drilled to targets which may be two kilometers or more away in lateral directions. In another example application, this procedure may be useful when twin horizontal wells are drilled for the steam-assisted gravity drainage (SAGD) of heavy oils. In this example, it may be necessary to drill one well directly above the other while maintaining a five meter (±<NUM> meter) spacing over <NUM> meters of horizontal extension at depths of <NUM> or more meters. Moreover, the present invention may be employed in various types of underground drilling operations such as geothermal drilling, mining, hammer drilling and/or other such drilling operations; and the present invention should not be deemed to be limited to the aforementioned examples.

The monitoring system used to control the drilling operations can include a magnetic field sensor that is disposed in the existing borehole and a magnetic source that is disposed in the new borehole. Specifically, the magnetic source assembly may be disposed in a drill string proximate the drill bit/tool. The magnetic source generates rotating magnetic fields. The sensor apparatus typically includes a magnetometer assembly that is configured to measure the magnetic field radiating from the magnetic source assembly. The sensor apparatus precisely calculates the location of the source from the field measurements. In this way, the drilling of the new borehole may be precisely controlled to achieve a desired separation between the existing borehole and the new borehole.

One issue that may be associated with a magnetic source assembly or a sensor assembly relates to their sensitivity to stress waves. Briefly stated, the drilling process may generate stress waves and vibrational forces which propagate along the drill string to the magnetic source or sensor assembly. The stress waves may cause the magnetic source assembly or the sensor assembly to fail.

Another issue relates to the thermal energy generated from various sources. Those skilled in the drilling/mining arts will appreciate that a drill bit may become relatively hot during mining and drilling operations. Magnetic materials may lose their magnetic remanence if temperatures exceed the temperature rating of the magnetic material.

Another issue relates to rotationally registering the magnetic source assembly or the sensor assembly to the drill bit. Rotational registration allows the monitoring system to determine the orientation of the drill bit, as well the location of the drill bit, to more effectively control the drilling process.

<CIT> discloses a drilling apparatus providing isolation from drilling vibration. Further systems and apparatus related to the present invention are disclosed in <CIT>, <CIT>, <CIT>, <CIT> and <CIT>.

The present invention substantially addresses the needs described above by providing an apparatus and method configured to substantially isolate a downhole assembly from the stress waves experienced during drilling operations. The present invention includes cooling means that direct thermal energy away from the apparatus. The present invention is also configured to rotationally register a downhole assembly to a drill bit to thus provide drill bit orientation data during the drilling control operation.

One aspect of the present invention is directed to an apparatus for use on a structural member having a longitudinal axis, the structural member being configured to propagate stress wave energy in an operational state. The stress wave energy is characterized by an operational frequency spectrum. The apparatus comprises a housing assembly including a first end, a second end, and at least one protective enclosure configured to accommodate at least one device. The housing assembly is configured to be rotationally registered to the structural member when coupled to the structural member. The housing assembly is characterized by a predetermined housing mass. A spring arrangement is coupled between the structural member and the first end and/or coupled between the structural member and the second end in the operational state. The spring arrangement is characterized by a predetermined force-displacement relationship. The housing assembly and the spring arrangement form an isolation filter characterized by a predetermined spectral transfer function, the predetermined spectral transfer function being a function of the predetermined housing mass and the predetermined force-displacement relationship. The predetermined spectral transfer function includes a passband having frequencies that are substantially outside the operational frequency spectrum wherein the stress wave energy is substantially attenuated in the operational state so that the housing member is substantially isolated from the stress wave energy.

In one embodiment, the spring arrangement includes at least one first spring element coupled between the first end and the structural member in the operational state, and wherein the spring arrangement includes at least one second spring element coupled between the second end and the structural member in the operational state.

In one version of the embodiment, the housing assembly is substantially cylindrical, and wherein the at least one first spring element and the at least one second spring element have an outer diameter substantially equal to an outer diameter of the housing assembly.

In one version of the embodiment, the at least one first spring element includes a plurality of first spring elements coupled in parallel between the first end and the structural member in the operational state, and the at least one second spring element includes a plurality of second spring elements coupled in parallel between the second end and the structural member in the operational state.

In one version of the embodiment, the plurality of first spring elements includes four spring elements or the plurality of second spring elements includes four spring elements.

In another embodiment, the spring arrangement includes at least one compression spring, the at least one compression spring being configured to oppose compression along the longitudinal axis.

In another embodiment, the at least one device includes at least one sensor device or at least one magnetic source element.

In one version of the embodiment, the at least one sensor device includes at least one accelerometer, at least one magnetometer, a gyro sensor, at least one environmental sensor, a piezoelectric transducer, or a battery device.

In one version of the embodiment, the at least one protective enclosure includes at least one set of pockets orientated in a plane perpendicular to the longitudinal axis, and wherein each pocket of the at least one set of pockets is configured to accommodate a magnetic source element.

In another embodiment, the isolation filter is a low pass filter and the passband includes frequencies substantially between <NUM> and a natural resonant frequency, and wherein the isolation filter includes a stopband having frequencies substantially greater than the natural resonant frequency, and wherein the stress wave energy includes frequencies within the stopband so that the stress wave energy is substantially attenuated in the operational state in accordance with a <NUM>/f<NUM> roll-off attenuation factor, wherein f is a frequency within the operational frequency spectrum, and wherein the attenuation factor increases as the frequency f increases.

In another embodiment, the housing assembly is substantially cylindrical having an inner diameter and an outer diameter respectively defining an interior housing surface and an exterior housing surface; and wherein the housing assembly includes a first housing portion coupled to a second housing portion, each of the first housing portion and the second housing portion having a substantially semicircular cross-section so that the housing assembly has a substantially circular cross-section when the first housing portion is coupled to the second housing portion; and wherein a key channel arrangement is formed in the interior housing surface where the first housing portion coupled to the second housing portion, the key channel arrangement being configured to mate with a portion of the structural member to effect rotational registration.

In one version of the embodiment, the at least one protective enclosure includes a plurality of pockets formed in the interior housing surface or the exterior housing surface, each pocket of the plurality of pockets being configured to accommodate a magnetic source device; or wherein the at least one protective enclosure is formed in the exterior housing surface and configured to accommodate a sensor assembly.

In one version of the embodiment, the magnetic source device is selected from a group of magnetic source devices including a permanent magnet and an electromagnet.

In one version of the embodiment, a protective cover is disposed over the housing assembly in the operational state, the protective cover substantially configured to conform to the exterior housing surface.

In one version of the embodiment, the protective cover is disposed over the spring arrangement in the operational state.

In another embodiment, the predetermined force-displacement relationship includes a constant spring rate or a variable spring rate.

Another aspect of the present invention is directed to an assembly comprising a structural member having a longitudinal axis, the structural member being configured to propagate stress wave energy in an operational state, the stress wave energy being characterized by an operational frequency spectrum. An apparatus is coupled and rotationally registered to the structural member, the apparatus comprises a housing assembly including a first end, a second end, and at least one protective enclosure configured to accommodate at least one device, the housing assembly being characterized by a predetermined housing mass. A spring arrangement is coupled between the structural member and the first end and/or coupled between the structural member and the second end, the spring arrangement being characterized by a predetermined force-displacement relationship. The housing assembly and the spring arrangement form an isolation filter characterized by a predetermined spectral transfer function, the predetermined spectral transfer function being a function of the predetermined housing mass and the predetermined force-displacement relationship. The predetermined spectral transfer function includes a passband having frequencies that are substantially outside the operational frequency spectrum wherein the stress wave energy is substantially attenuated in the operational state so that the housing member is substantially isolated from the stress wave energy.

In an embodiment, the spring arrangement includes at least one first spring element coupled between the first end and the structural member, and at least one second spring element coupled between the second end and the structural member.

In one version of the embodiment, the at least one first spring element and the at least one second spring element have an outer diameter substantially equal to an outer diameter of the housing assembly.

In one version of the embodiment, the at least one first spring element includes a plurality of first spring elements coupled in parallel between the first end and the structural member, and wherein the at least one second spring element includes a plurality of second spring elements coupled in parallel between the second end and the structural member.

In one version of the embodiment, the plurality of first spring elements includes four spring elements and/or wherein the plurality of second spring elements includes four spring elements.

In one version of the embodiment, the structural member is a drill rod or a drill rod attachment including a central fluid channel configured to conduct a pressurized fluid along the longitudinal axis in the operational state, the structural member including a plurality of fluid openings in a region where the structural member is coupled to the housing assembly, the pressurized fluid including a gas or a liquid.

In another embodiment, the structural member includes a carrying region, a first shoulder member being disposed at a first end portion of the carrying region and a second shoulder member being disposed at a second end portion of the carrying region, wherein the housing assembly is coupled to the carrying region between the first shoulder member and the second shoulder member, and wherein the spring arrangement includes at least one first spring element coupled between the first end and the first shoulder member, and at least one second spring element coupled between the second end and the second shoulder member.

In one version of the embodiment, the structural member further comprises a box portion disposed at a first end of the structural member, a pin portion disposed at a second end of the structural member, and a carrying region being disposed between the box portion and the pin portion, the box portion being configured to accommodate a drive element of a drill string and the pin portion being configured to accommodate a tool bit or a drill bit.

In another embodiment, the spring arrangement includes at least one first spring element and at least one second spring element, and wherein the structural member further comprises a first collar member and a second collar member, and wherein the at least one first spring element is coupled between the first end and the first collar member, and wherein the at least one second spring element is coupled between the second collar member and the second end.

In one version of the embodiment, the first collar member includes a first registration feature configured to rotationally register the at least one first spring element to an orientation feature on the structural member, and/or wherein the second collar member includes a second registration feature configured to rotationally register the at least one second spring element to an orientation feature on the structural member.

In one version of the embodiment, the at least one sensor device includes at least one accelerometer, at least one magnetometer module, a gyro sensor, at least one environmental sensor, a piezoelectric transducer, or a battery device.

In another embodiment, the isolation filter is a low pass filter and the passband includes frequencies substantially between <NUM> and a natural resonant frequency, and wherein the isolation filter includes a stopband having frequencies substantially greater than the natural resonant frequency, wherein the stress wave energy includes frequencies within the stopband so that the stress wave energy is substantially attenuated in the operational state in accordance with a <NUM>/f<NUM> roll-off attenuation factor, wherein f is a frequency within the operational frequency spectrum and wherein the attenuation factor increases as the frequency f increases.

Another aspect of the present invention is directed to a method comprising: providing a structural member having a longitudinal axis, the structural member being configured to propagate stress wave energy in an operational state, the stress wave energy being characterized by an operational frequency spectrum; providing a housing assembly including a first end, a second end, and at least one protective enclosure configured to accommodate at least one device, the housing assembly being characterized by a predetermined housing mass; providing a spring arrangement, the spring arrangement being characterized by a predetermined force-displacement relationship, the housing assembly and the spring arrangement forming an isolation filter characterized by a predetermined spectral transfer function, the predetermined spectral transfer function being a function of the predetermined housing mass and the predetermined force-displacement relationship, the predetermined spectral transfer function including a passband having frequencies that are substantially outside the operational frequency spectrum; coupling the housing assembly to the structural member such that the housing assembly is rotationally registered to the structural member; coupling the spring arrangement between the structural member and the first end and/or between the structural member and the second end; and entering an operational state wherein stress wave energy propagates along the structural member, the stress wave energy being substantially attenuated by the isolation filter so that the housing member is substantially isolated from the stress wave energy.

Additional features and advantages of the invention will be set forth in the detailed description which follows, and in part will be readily apparent to those skilled in the art from that description or recognized by practicing the invention as described herein, including the detailed description which follows, the claims, as well as the appended drawings.

It is to be understood that both the foregoing general description and the following detailed description are merely exemplary of the invention, and are intended to provide an overview or framework for understanding the nature and character of the invention as it is claimed. It should also be appreciated that terminology explicitly employed herein that also may appear in any disclosure incorporated by reference should be accorded a meaning most consistent with the particular concepts disclosed herein.

The drawings illustrate various embodiments of the invention and together with the description serve to explain the principles and operation of the invention.

Reference will now be made in detail to the present embodiments of the invention, examples of which are illustrated in the accompanying drawings. An exemplary embodiment of the downhole assembly of the present invention is shown in <FIG>, and is designated generally throughout by reference numeral <NUM>.

As depicted in <FIG>, a cross-sectional view of a measurement system <NUM> featuring a magnetic source apparatus <NUM> and a magnetic field measurement sensor <NUM> is disclosed. The measurement system <NUM> is shown in the context of a pair of horizontal, spaced wells in accordance with an application of the present invention. This view illustrates a method and apparatus for guiding the directional drilling of a second borehole <NUM> relative to a first (previously drilled) borehole <NUM> such that the new borehole <NUM> is separated from the existing borehole <NUM> by a predetermined distance along their respective paths. The new borehole <NUM> contains a drill string <NUM> that carries or includes the downhole apparatus <NUM> equipped with the spring mass isolation filter. The drill assembly includes a drill bit <NUM> which is driven by suitable motors in a conventional manner, to rotate about a longitudinal axis of rotation and/or to reciprocate (axially hammer) along the longitudinal axis. The drill bit <NUM> may be steerable to control the drilling direction in response to control signals provided by a control station <NUM> located at the surface <NUM> (of the Earth). The magnetic source apparatus <NUM> includes a plurality of magnet elements <NUM> that generate an elliptically polarized rotating magnetic field <NUM> that is centered at the magnetic source apparatus <NUM> in the new borehole <NUM>. The magnetic source apparatus <NUM> includes a magnetic field source <NUM>, which may be implemented using a permanent bar magnet <NUM> that is typically mounted in a non-magnetic portion of the assembly (not shown in this view) located at the distal end of the drill string behind the rotating drill bit <NUM>. (The term "non-magnetic" material refers to a material that has a magnetic permeability that is comparable to air or a vacuum). The magnets <NUM> have north-south axes that are perpendicular to the longitudinal axis <NUM> of the drill bit <NUM>. Because assembly <NUM> rotates (and/or reciprocates) about the longitudinal axis <NUM> with the drill bit <NUM>, the elliptically polarized magnetic field <NUM> is an alternating magnetic field at observation point <NUM> (which is radially spaced from the magnets <NUM>).

The existing borehole <NUM> is illustrative of a horizontal well of the type which may be used for steam assisted gravity drainage of heavy oil (SADG). Of course, the present invention may be employed in any type of drilling application (and/or in any orientation) such as oil and gas drilling operations, geothermal, hammer drilling, top-hammer drilling, mining and/or other such drilling operations. In the example depicted in <FIG>, the drill bit <NUM> is controlled so that the borehole <NUM> is drilled directly above borehole <NUM> and is spaced above it by a predetermined, substantially constant distance. Control of the drill bit <NUM> is carried out in response to measurements made in the target borehole <NUM> by a magnetic field sensor <NUM>. The measuring tool <NUM> is lowered into the borehole <NUM> through a casing by means of a suitable wireline <NUM>, with the location, or depth, of the measuring tool being controlled from the earth's surface in conventional manner from an equipment truck <NUM>. In one embodiment, the spring mass isolation filter of the present invention is embodied within the magnetic field sensor <NUM>.

Again, the magnetic field sensor <NUM> is located at an observation point <NUM> and may incorporate a plurality of fluxgate magnetometers having their axes of maximum sensitivity intersecting each other at one or more observation points and substantially at right angles to each other. In one embodiment, the sensor may include two magnetometers; in another embodiment, there may be three magnetometers. If a gradient measurement is required, there may be six magnetometers in the sensor <NUM>. The magnetometers measure the amplitude and the phase of two perpendicular components of the magnetic field <NUM>. The measuring tool <NUM> may also include additional sensors such as earth's field sensors, inclinometers, and/or a gyroscope (depending on the application).

As embodied herein and depicted in <FIG>, a cross-sectional view of a pair of horizontal, spaced boreholes in accordance with another application of the present invention is disclosed. In this example application, an underground rock drilling assembly <NUM> employs a movable carrier <NUM> having one or more booms <NUM>-<NUM> connected to the carrier <NUM>. A drilling unit <NUM>-<NUM> may be disposed at the distal end of the boom <NUM>-<NUM>. The drilling unit <NUM>-<NUM> may comprise a feed beam <NUM>-<NUM> and a rock drilling machine <NUM>-<NUM> which drives the drill rod <NUM> and hence drill bit <NUM> into a rock wall <NUM>. In this application the drilling assembly is used to form a series of boreholes in the rock face, wherein each borehole is formed such that it follows a predetermined path in three-dimensional space within the rock wall/structure <NUM>.

Like the application depicted at <FIG>, the measurement system <NUM> features a magnetic source apparatus <NUM> (that includes the spring mass isolation filter) and a magnetic field measurement sensor <NUM>. (Again, in some applications the sensor <NUM> may include the spring mass isolation filter). In the application depicted at <FIG>, however, a cross-sectional view of a pair of horizontal, spaced boreholes is shown. Like the previous application shown at <FIG>, this view illustrates a method and apparatus for guiding the directional drilling of a second borehole <NUM> relative to a first (previously drilled) borehole <NUM> such that the new borehole <NUM> is separated from the existing borehole <NUM> by a predetermined distance along their respective paths. The new borehole <NUM> contains a carriage assembly having a magnetic source apparatus <NUM>. As before, the magnetic field sensor <NUM> is located at an observation point <NUM> and may incorporate a plurality of fluxgate magnetometers (e.g., up to three) having their axes of maximum sensitivity intersecting each other at the observation point and substantially at right angles to each other. (In another embodiment there can be multiple sets of magnetometers (of up to three per set)). The magnetometers measure the amplitude and the phase of two or more perpendicular components of the magnetic field <NUM>. The measuring tool <NUM> may also include additional sensors such as earth's field sensors, gravity sensors, inclinometers, and/or a gyroscope depending on the application.

As embodied herein and depicted in <FIG>, a diagrammatic depiction of a magnetic source downhole assembly <NUM> in accordance with an embodiment of the present invention is disclosed. The downhole assembly <NUM> includes a carriage apparatus <NUM> coupled to a structural member <NUM>. In one embodiment, the structural member can be a drill rod <NUM>, which is typically employed in the example applications depicted at <FIG>. However, the present invention should not be deemed to be limited to the example applications depicted at <FIG>.

One skilled in the art will appreciate that the present invention may be employed in other applications and thus, the drill rod <NUM> may be implemented using any structural member suitable for the application at hand. One such alternate application includes performing a borehole surveying operation. In another alternate application, the carriage apparatus <NUM> includes a sensor assembly <NUM> for use in a previously drilled borehole, in an extant pipeline, in a borehole survey or any other suitable application.

The drill rod <NUM> (or structural member) may include shoulder members (<NUM>-<NUM>, <NUM>-<NUM>) that are used to accommodate the carriage apparatus <NUM> therebetween. The drill rod <NUM> may include a box portion <NUM>-<NUM> (i.e., a female thread) at one end thereof, and a pin portion <NUM>-<NUM> (i.e., a male thread) at second, opposite end thereof. The pin portion <NUM>-<NUM> may also include a drill bit shoulder <NUM>-<NUM> which abuts the drill bit <NUM> when the drill bit <NUM> is screwed onto the pin portion <NUM>-<NUM>. The box portion <NUM>-<NUM> may be configured to accommodate a drive member associated with the drilling assembly <NUM> (<FIG>). The pin portion <NUM>-<NUM> may be configured to accommodate other tools suitable for a given application as well as a drill bit <NUM>.

The carriage apparatus <NUM> is shown to include a protective cover member <NUM>. The cover member <NUM> is employed to protect a downhole carriage housing <NUM> disposed under the cover member <NUM>, between the shoulders <NUM>-<NUM> and <NUM>-<NUM>. The cover <NUM> may be fastened to the housing <NUM> using any suitable fastener elements or techniques (e.g., screws, rivets, press fit, etc.).

The carriage apparatus also includes a plurality of spring elements <NUM> that are coupled between the carriage apparatus <NUM> and the shoulders (<NUM>-<NUM>, <NUM>-<NUM>). As described below, the spring elements <NUM> and the mass of the carriage apparatus <NUM> form an isolation filter that is characterized by a low pass frequency transfer function (<FIG>) that is substantially below an operational frequency spectrum (See, e.g., <FIG>).

Specifically, the low pass frequency transfer function is a function of a predetermined mass of the carriage apparatus and the total effective spring rate (force-displacement relationship) of springs <NUM>. Specifically, each spring <NUM> may have a spring rate equal to k, where k is some numerical value. Also, the spring may have a variable rate. The springs <NUM> at each end of the carriage apparatus <NUM> can be implemented as four springs <NUM> disposed in a parallel spring arrangement with a composite spring rate being substantially equal to <NUM>. Since there are four springs at each end, the total spring rate would be about <NUM>. The spring rate is selected based on the carriage apparatus mass to obtain a desired low pass frequency transfer function (see <FIG>) relative to the operational frequency spectrum (<FIG>).

The operational frequency spectrum can refer to the frequency content of surface accelerations propagating along the drill rod as a result of a given drilling or mining operation. (The surface accelerations are derived from the stress wave energy produced by drilling/hammering). Because the frequency content of the surface accelerations mostly includes frequencies greater than the low pass frequency (spectral) transfer function, the stress wave energy is attenuated and substantially prevented from disturbing the carriage apparatus <NUM>. Those skilled in the art will appreciate that the resonant frequency is selected so that it is well below the operational frequency spectrum (<FIG>). While there may be some small amount of energy at or near the resonant frequency, it is not enough to induce a carriage failure mode.

As embodied herein and depicted in <FIG>, a detail view of a carriage apparatus <NUM> depicted in <FIG> is disclosed. In this view, the cover member <NUM> is removed from the carriage apparatus <NUM> to show the downhole housing <NUM>. The downhole housing <NUM> includes a first housing portion <NUM>-<NUM> and a second housing portion <NUM>-<NUM>. During assembly, the first housing portion <NUM>-<NUM> is coupled to the second housing portion <NUM>-<NUM> with the drill rod <NUM> therebetween so that the downhole housing <NUM> is spatially registered to the drill bit <NUM>. The gap between each edge of the carriage housing <NUM> and its respective drill rod shoulder (<NUM>-<NUM>, <NUM>-<NUM>) is a function of the spring constant and carriage assembly weight, so that under typical conditions the carriage apparatus <NUM> will not contact the shoulders. If the conditions are such that carriage assembly <NUM> does make contact with a shoulder (<NUM>-<NUM>, <NUM>-<NUM>), each spring <NUM> is configured to fully retract into its respective spring pocket <NUM>-<NUM> (<FIG>) without fully compressing.

In the magnetic source embodiment, each housing portion (<NUM>-<NUM>, <NUM>-<NUM>) includes a plurality of magnetic field source elements (e.g., permanent magnets, electromagnets) <NUM> disposed within respective pockets <NUM>-<NUM>. The permanent magnets <NUM> are configured to generate magnetic field <NUM> (as shown at <FIG>).

As noted above, the downhole housing <NUM> may also be configured to accommodate a sensor assembly <NUM> (<FIG>) wherein the housing portions (<NUM>-<NUM>, <NUM>-<NUM>) may include compartments configured to accommodate various sensor components such as inclinometers (tilt sensors), magnetometers, environmental sensors (pressure, temperature, radiation, etc.), gravity sensors (accelerometers), rotation sensors (gyroscope), a power supply and/or battery, a receiver, transmitter, a processor/controller, memory, etc., depending on the application.

As embodied herein and depicted in <FIG>, a diagrammatic depiction of a drill rod structure <NUM> shown in <FIG> is disclosed. (Here, the carriage apparatus <NUM> is removed for clarity of illustration). The drill rod <NUM> includes a source/sensor carrying region <NUM>-<NUM> disposed between the shoulder members (<NUM>-<NUM>, <NUM>-<NUM>). (Depending on the housing embodiment, region <NUM>-<NUM> either carries the magnetic source housing or the sensor housing). As before, the drill rod <NUM> may include a box portion <NUM>-<NUM> at one end thereof, and a pin portion <NUM>-<NUM> at second, opposite end thereof. Fluid channels <NUM>-<NUM> and key members <NUM>-<NUM> are disposed within the payload carrying region <NUM>-<NUM> between the shoulder members (<NUM>-<NUM>, <NUM>-<NUM>). The remaining features of the drill rod were previously described above.

Referring to <FIG>, a detail view of carrying portion <NUM>-<NUM> of the drill rod depicted in <FIG> is shown. In this embodiment, the carrying region <NUM>-<NUM> includes four fluid channels <NUM>-<NUM> and two key members <NUM>-<NUM> disposed in a central region of the carrying region <NUM>-<NUM>. Specifically, a set of two fluid channels <NUM>-3alternates with a key member <NUM>-<NUM> at <NUM>° increments around the circumference of the central area of the carrying region <NUM>-<NUM>. Thus, a set of two fluid channels <NUM>-<NUM> are disposed <NUM>° away from the second set of fluid channels <NUM>-<NUM>, and one key member <NUM>-<NUM> is disposed <NUM>° away from the second key member <NUM>-<NUM>.

Those skilled in the art will appreciate that the size and number of the fluid channels <NUM>-<NUM> may vary depending on the application. For example, the number and size of the fluid channels <NUM>-<NUM> may be a function of the type of fluid traversing the channels (e.g., air, water, etc.) as well as the application for which the assembly is being used. Those skilled in the art will appreciate that the number of fluid channels <NUM>-<NUM> may vary depending on the thermal energy characteristics of the operating environment. In relatively warmer environments, the drill rod <NUM> will include additional fluid channels <NUM>-<NUM> to better direct the thermal energy away from the carriage <NUM>. In relatively cooler environments, the drill rod <NUM> may include fewer fluid channels <NUM>-<NUM> (or none at all if cooling is not an issue in the application). The number of fluid channels <NUM>-<NUM> shown in <FIG> is merely a representative example.

The number of key members <NUM>-<NUM> may vary depending on the application for which the assembly is being used. Accordingly, more or less channels <NUM>-<NUM> and/or key members <NUM>-<NUM> may be employed depending on the embodiment and/or application.

The existence of fluid channels <NUM>-<NUM> presupposes the existence of a central fluid-flow channel (not shown) that extends through the entire length of the drill rod <NUM> and is centered about the longitudinal axis <NUM> (see, e.g., <FIG>). In one embodiment, the diameter of the central fluid-flow channel may be about <NUM> (<NUM> inches). The outer diameter of the source/sensor carrying region <NUM>-<NUM> may be about <NUM> (<NUM> inches). (The fluid transmitted through via <NUM>-<NUM> may be air or some other suitable fluid).

In one embodiment, the drill rod <NUM> is formed by a machining a steel alloy billet (e.g., using a CNC milling machine) to produce an integrally formed drill rod. In another alternate embodiment, the shoulder members (<NUM>-<NUM>, <NUM>-<NUM>) and/or the key members <NUM>-<NUM> may be formed on a steel alloy rod using a sputter-welding process, wherein layers of steel material are deposited and built-up along the circumference of the rod at appropriate locations. The built-up portions are then machined (using, e.g., a lathe) to form the shoulder portions (<NUM>-<NUM>, <NUM>-<NUM>) and the key members <NUM>-<NUM>. The box portion <NUM>-<NUM> and the pin portion <NUM>-<NUM> may be welded to their respective ends of the drill rod <NUM> by way of a friction-welding process. In the various alternate embodiments, those of ordinary skill in the art will appreciate that the shoulders (<NUM>-<NUM>, <NUM>-<NUM>), key members <NUM>-<NUM>, pin <NUM>-<NUM>, box <NUM>-<NUM>, and other such features may be formed and/or machined using any suitable fabrication method(s).

In one embodiment of the present invention, the drill rod may be formed using a chrome-molybdenum AISI Alloy <NUM> steel bar (which has, e.g., a tensile strength of about <NUM> MPa (<NUM>,<NUM> psi), and an elastic modulus within a range of about <NUM>,<NUM> MPa - <NUM>,<NUM> MPa (<NUM>,<NUM> - <NUM>,<NUM> ksi). Thus, chrome-molybdenum AISI Alloy <NUM> steel bars may be employed in each of the fabrication and machining embodiments described above.

As embodied herein and depicted in <FIG>, an isometric view of the carriage apparatus <NUM> depicted at <FIG> is disclosed. In this view, the non-magnetic cover <NUM> is disposed over the carriage housing <NUM>. Each set of four spring elements <NUM> extend from their respective ends of the carriage housing <NUM>. The non-magnetic cover <NUM> may be formed using any suitable non-magnetic material including stainless steel, titanium, BeCu, aluminum, etc. In one embodiment, the cover <NUM> may be formed using an austenitic nickel-chromium alloy material such as the Inconel alloys manufactured by Special Metals Corporation. The austenitic nickel-chromium alloys are oxidation-corrosion-resistant materials well suited for service in extreme environments subjected to pressure and heat.

Each spring <NUM> may be formed using any suitable material, but in one embodiment, the springs <NUM> are formed from a chrome-silicon steel material. In one embodiment, the spring conforms to a spring pocket <NUM>-<NUM> diameter of about <NUM>/<NUM>" (<NUM>) and has an interior diameter of about <NUM>/<NUM>" (<NUM>). The spring rate may be about <NUM> N/mm. In one embodiment, the springs <NUM> may be manufactured by McMaster-Carr and be implemented by the McMaster-Carr Blue Chrome-Silicon Steel Die Spring PN 9573K11.

Referring to <FIG>, an isometric view of the carriage housing <NUM> depicted at <FIG> is disclosed. The carriage housing <NUM> includes a first housing portion <NUM>-<NUM> connected to a second housing portion <NUM>-<NUM>. As noted previously, the exterior surface of each housing portion includes a plurality of pockets <NUM>-<NUM>, each pocket <NUM>-<NUM> being configured to accommodate a permanent magnet <NUM> (not shown).

A key channel <NUM>-<NUM> is formed in an interior portion of the housing <NUM> at the connection interface <NUM>-<NUM>. Each key channel <NUM>-<NUM> is configured to accommodate one of the key members <NUM>-<NUM> therein. When the key members <NUM>-<NUM> are disposed within their respective key channels <NUM>-<NUM>, the carriage housing <NUM> is rotationally registered to a predetermined portion of the drill bit <NUM>, and is substantially prevented from rotating about the central longitudinal axis <NUM> of the drill string (see, e.g., <FIG>).

Four spring pockets <NUM>-<NUM> are formed in each end of the carriage housing <NUM>, with two spring pockets <NUM>-<NUM> being formed at one end of each housing portion (<NUM>-<NUM>, <NUM>-<NUM>). The depth of each spring pocket can be a function of the spring composition such that a pocket depth can allow a spring <NUM> to fully retract within the pocket <NUM>-<NUM> without the spring becoming fully compressed into a solid cylinder.

Referring to <FIG>, an isometric view of a carriage housing <NUM> in accordance with an alternate embodiment is disclosed. Descriptions of the magnet pockets <NUM>-<NUM>, spring pockets <NUM>-<NUM> and the key channel <NUM>-<NUM> are omitted for brevity's sake since these elements were described above. In this embodiment, the housing portions (<NUM>-<NUM>, <NUM>-<NUM>) include additional features such as mating pins <NUM>-<NUM>, mating holes <NUM>-<NUM>, and rivet holes <NUM>-<NUM>. Moreover, the section B-B, section A-A and section C-C are shown at <FIG>, respectively, and described below.

In this embodiment, the mating holes <NUM>-<NUM> are configured to accommodate mating pins <NUM>-<NUM> that are used to couple the first housing <NUM>-<NUM> to the second housing <NUM>-<NUM>. The rivet holes <NUM>-<NUM> are configured to accommodate rivets which are used to secure the housing cover <NUM> to the carriage housing <NUM>.

Referring to <FIG>, a detail view of a portion <NUM>-<NUM> of the carriage housing <NUM> depicted at <FIG> is disclosed. (This drawing figure is equally applicable to housing portion <NUM>-<NUM>, except that portion <NUM>-<NUM> would be a mirror image of housing portion <NUM>-<NUM> such that each side of the housing <NUM> would include a set of mating pins <NUM>-<NUM>). This view clearly shows that the key channel <NUM>-<NUM> is created by forming a notched region <NUM>-<NUM> along the edges of the housing portions (<NUM>-<NUM>, <NUM>-<NUM>).

Referring to <FIG>, cross-sectional views of the carriage housing depicted at <FIG> are disclosed. <FIG> is a cross-sectional view corresponding to section B-B of <FIG>. Here, the rivet holes <NUM>-<NUM> have an hourglass shape so that the wider portions of the rivet hole <NUM>-<NUM> can accommodate the thicker head portions of a rivet, and wherein the relatively narrow portions of the rivet hole <NUM>-<NUM> are configured to accommodate the relatively narrow body portion of a rivet. This view also provides a sectional view of key channel <NUM>-<NUM> formed at opposite edges of housing <NUM>. <FIG> is a cross-sectional view corresponding to section A-A of <FIG>. In this view, the mating holes <NUM>-<NUM> configured to accommodate mating pins <NUM>-<NUM> are shown. <FIG> is a cross-sectional view corresponding to section C-C of <FIG>. In this view, the section includes three magnet pockets <NUM>-<NUM> per housing portion (<NUM>-<NUM> or <NUM>-<NUM>) for a total of six magnet pockets per section. In reference to <FIG>, therefore, the carriage housing <NUM> includes five magnet sections for a total of about thirty magnet pockets.

In one embodiment, the carriage housing <NUM> may be formed from a cylindrical or tube-shaped material (hereinafter "stock material") that is divided into two halves to form the first housing portion <NUM>-<NUM> and the second housing portion <NUM>-<NUM>. (There is no significance placed on the terms first housing or second housing other than the fact that the housing <NUM> includes two housing portions (<NUM>-<NUM>, <NUM>-<NUM>)). In one embodiment, the stock material may be comprised of a Teflon PTFE resin material that substantially complies with UL 94V0 and ASTM D1710 standards. In other embodiments, the tube material may be comprised of any suitable material; for example, the material may be an acetal homopolymer (Polyoxymethylene POM) material sometimes known as Delrin. In another example, the material may be a Polyether ether ketone (PEEK) material, which is a colorless, organic, thermoplastic polymer. In yet another embodiment, the material may be bronze or a bronze alloy material, titanium, stainless steel, or any suitable non-magnetic material. Those skilled in the art will appreciate that the materials of the tube used to form the magnetic source housing <NUM> may vary in accordance with the application since the environment (vibrations, shock, temperature, etc.) may also differ from application to application.

In one embodiment, the stock material may have an outer diameter (OD) of about <NUM> (<NUM> inches), an inner diameter (ID) of about <NUM> (two inches), and a wall thickness of about <NUM> (one inch). Those of ordinary skill in the art will appreciate that the dimensions of the stock material used to form the downhole housing <NUM> may vary in accordance with the embodiment and/or application.

Before the stock material is separated into two parts (i.e., to form the first housing portion <NUM>-<NUM> and the second housing portion <NUM>-<NUM>), the stock material may be machined to include the various features depicted herein. For example, the stock material may be machined to include the mating pins <NUM>-<NUM>, mating holes <NUM>-<NUM>, rivet holes <NUM>-<NUM>, magnetic source pockets <NUM>-<NUM>, and the sensor assembly pockets <NUM>-<NUM> (See <FIG>). The rivet holes <NUM>-<NUM> may also be configured to accommodate any suitable fastener element (e.g., a pop-rivet, etc.) for connecting the first housing portion <NUM>-<NUM> to the second housing portion <NUM>-<NUM> during assembly. Alternatively, some or all of the features may be machined after the stock material is separated into two parts.

Each magnetic source pocket <NUM>-<NUM> is configured to accommodate a magnetic source element <NUM> and an epoxy (or other) potting material. The potting material is employed to hold the magnetic element <NUM> in place within its respective pocket <NUM>-<NUM>.

The magnetic sources <NUM> employed in the invention may vary in accordance with the application since the environment (vibrations, shock, temperature, etc.) or desired operating parameters may also change in accordance with the application. Some non-limiting examples of operating parameters may be remanence, coercivity, Curie temperature, etc. Accordingly, the magnetic source elements <NUM> may be implemented using neodymium rare earth magnets, samarium cobalt magnets or any suitable magnetic source elements depending on the application. In another embodiment, the magnetic source elements may be implemented by electromagnetic source elements. In this embodiment, a wireline may be fed to carriage apparatus <NUM> via the central fluid channel of the drill rod. The wireline would provide electrical power from an uphole location to the carriage <NUM>. In another embodiment, one of more piezoelectric transducers would be included in the carriage housing <NUM> and be configured to convert the mechanical energy (Wh) generated by the drilling operations into electrical energy. The electrical energy would be stored in a battery which would, in turn, provide power to the electromagnets. In another embodiment, a battery without piezoelectric transducers can be employed.

As described herein, the key channel <NUM>-<NUM> may be configured as a rectangularly-shaped channel that is machined (or otherwise formed) to accommodate the key element <NUM>-<NUM> formed in the carrying region <NUM>-<NUM> of the drill rod <NUM>. (Note that key channel <NUM>-<NUM>, the key element <NUM>-<NUM> and source-carrying region <NUM>-<NUM> may be machined to conform to any suitable geometry and is thus not limited to a rectangular shape). In any event, the key channel <NUM>-<NUM> conforms to the key element <NUM>-<NUM> of the drill rod such that the downhole housing <NUM> is in a fixed spatial relationship and registered to the drill rod <NUM> in at least two-dimensions. On the other hand, the reader should note that the downhole housing <NUM> is configured to slide along the source-carrying region <NUM>-<NUM> between the two shoulders (<NUM>-<NUM>, <NUM>-<NUM>) in a substantially frictionless manner under certain circumstances. A person skilled in the art will appreciate that the term substantially frictionless is predicated on the coefficient of friction of the interior surface of the housing <NUM>, the coefficient of friction of the carrying region <NUM>-<NUM> of drill rod <NUM> and the operational characteristics of the isolation filter. In addition, the interface between the interior surface of the housing <NUM> and the surface of the carrying region <NUM>-<NUM> may be packed with grease or some other lubricant material.

As embodied herein and depicted in <FIG>, a diagrammatic depiction of stress wave propagation in a top-hammer rock drilling application is disclosed. Here, the stress waves are modeled as a sequence of square or rectangular waves for ease of illustration. In diagram <NUM>, a top hammer rock drill is shown to include a hammer/piston <NUM>-<NUM> that is used to impact the drill rod <NUM>. (See, e.g., <FIG>). The hammer <NUM>-<NUM> may be implemented using any suitable hammer type, e.g., such as a pneumatic hammer (which uses compressed air) or a hydraulic hammer (which uses pressurized hydraulic fluid). (The drill rod <NUM> is a depicted in this view as an elongated cylinder; in practice, however, the drill rod <NUM> may be of the type depicted at <FIG>).

During operations, examples of which are shown at <FIG>, the drilling motor <NUM>-<NUM> may simultaneously provide a reciprocating motion and a rotational motion to drive the drill rod <NUM>. The reciprocating motion provides the hammering action to the drill rod <NUM> while the rotational force slowly rotates the drill rod <NUM> and drill bit <NUM> in a drilling motion. As the borehole length increases, additional drill rods can be added to the drill string by screwing a new drill rod onto the drill string that extends into the borehole. The kinetic energy of the hammering action is transmitted by the drill rod <NUM> to the drill bit <NUM> to fragment the rock <NUM> during the drilling action. Accordingly, any sensor instrument package <NUM> or magnetic source package <NUM> attached to a down-hole drill rod <NUM> must be able to with-stand intense stresses and strains.

In this case, the isolation filter of the present invention is configured to substantially isolate the housing <NUM> from the stress, energy and power flow associated with the drilling. To be clear, the spring elements <NUM> do not function as a damping mechanism, but rather as a low pass filter, since the frequency spectrum of the surface accelerations characterizing the hammering/drilling operations are greater than the low pass frequency response spectrum of the isolation filter, and thus, the stress waves are substantially attenuated and substantially prevented from disturbing the carriage apparatus <NUM>. (The surface accelerations are derived from the stress wave energy produced by drilling/hammering).

In step <NUM>, the hammer <NUM>-<NUM> is shown prior to impact and is shown to have a length "LP" (also referred to herein as "L"). In step <NUM>, the hammer <NUM>-<NUM> moves toward the drill rod <NUM> with a velocity v and strikes the drill rod <NUM>. In step <NUM>, a compressive stress wave Cp is generated in the hammer <NUM>-<NUM> and a compressive stress wave C is also generated in the drill rod <NUM>. These stress waves are depicted in the diagram as an increased diameter in each element. The maximum induced compressive stress (σ) is substantially equal to:
<MAT> Where, v is the hammer velocity, E is Young's (elastic) modulus of the material (hammer and drill rod), and c is the speed of sound in the hammer/rod. This assumes that the diameter and material of the hammer <NUM>-<NUM> and the drill rod <NUM> are the same.

In step <NUM>, the stress wave Cp reaches the upper end of the hammer <NUM>-<NUM> and is reflected; and the compressive stress wave C continues to propagate down the length of the drill rod <NUM>. In step <NUM>, the reflected wave Cp propagates down the hammer <NUM>-<NUM> and is transmitted into the drill rod <NUM> such that the stress waves C and Cp are combined. In step <NUM>, the combined stress wave C exits the hammer <NUM>-<NUM>; and in response to being elastically compressed by the stress waves, a portion of the drill rod <NUM> has been displaced. Assuming a square wave shape, the elastic compression (Δ) is substantially equal to: <MAT> In a typical top hammer application, µ<NUM> may be about <NUM> given a velocity (v) of <NUM>/s and a hammer length (L) of about <NUM>.

In step <NUM>, the stress wave has a length <NUM> and propagates along the drill rod <NUM> at the speed of sound c, which is substantially equal to <MAT> wherein ρ is the density of the drill rod material. The stress wave propagates the initial mechanical energy Wh to the drill bit <NUM>, where <MAT> wherein m is the mass of the hammer <NUM>-<NUM>. Of course, only a fraction of the mechanical energy Wh is applied to fragment the rock <NUM> (See, e.g., <FIG>). Another portion or fraction of the mechanical energy is reflected back up the rod <NUM>.

Referring to <FIG>, charts showing another idealized stress wave surface velocity and surface acceleration resulting from the hammer blow stress wave depicted at <FIG> are disclosed. In this analysis, the stress wave is modeled as a sinusoidal wave. Briefly stated, the stress wave surface velocity curve <NUM> can be modeled as a sine wave or a cosine wave over an interval from <NUM> - π radians (<NUM>° - <NUM>°). Those skilled in the art will appreciate that the form of the stress wave <NUM> depends on the rock drill, drilling parameters, the number of drill rods <NUM> in a given drill string, the type of rock being drilled, the hardness and the integrity of the rock material, and etc. Nonetheless, the stress wave surface velocity <NUM> may be reasonably modeled as a sinusoid (over a <NUM> - π radian interval) to ascertain the energy and forces being brought to bear on the downhole housing <NUM> described above. The surface acceleration <NUM> is, of course, the derivative of the stress wave surface velocity <NUM>.

Referring to <FIG>, charts showing the idealized stress wave and acceleration with reflections are shown. In other words, <FIG> shows the stress wave surface velocity <NUM> (at <FIG>) along with the stress wave reflections that develop over time. See <FIG> and the related text above. Similarly, <FIG> shows the surface acceleration signal <NUM> (<FIG>) along with the reflected surface accelerations that develop over time (see <FIG> and the related text). Specifically, <FIG> shows that after a millisecond or so, the reflection waves <NUM> begin to propagate along the drill rod. <FIG> shows the resultant surface acceleration based on the stress wave surface velocity shown at <FIG>.

Referring to <FIG>, charts showing the stress wave surface velocity and acceleration signals for multiple (e.g., ten) top hammer blows are disclosed. In these drawings the stress wave surface velocity signals <NUM> and <NUM> shown at <FIG> are compressed as the time scale is changed from milliseconds to seconds. Specifically, the stress wave surface velocity signals (<NUM> and <NUM>) shown at Fig. C are shown in a compressed form as signal <NUM>. The stress wave surface velocity signal <NUM> is repeated for each hammer blow. <FIG>, therefore, shows ten stress wave surface velocity signals <NUM> propagating down the drill rod, one for each of the ten hammer blows. The surface acceleration signals (<NUM> and <NUM>) shown at <FIG> are likewise shown at Fig. 113F in compressed form as signal <NUM>. There are therefore ten surface acceleration bursts <NUM>, one for each hammer blow.

Briefly stated, therefore, the mathematical model makes the following assumptions: first, it assumes that the stress wave is sinusoidal; and second, it assumes that the geometry and material of the hammer <NUM>-<NUM> and drill rod <NUM> are substantially the same so that they both have the same acoustic impedance. The model is based on the stress wave formulation steps shown at <FIG>, except that a sinusoidal approximation is employed. The stress wave modeled by equation (<NUM>) is at some drill rod element a distance "x" from the top of the rod <NUM> at time "t. " In step <NUM>, e.g., the velocity ("du/dt") of a point on the drill rod can be represented by: <MAT> The velocity du/dt is based on u(x,t), which is a tiny displacement of an element on the drill rod from its equilibrium location x at time t. The factor "(x - ct)" indicates that u(x, t) describes a displacement propagating along the longitudinal axis "x" of the drill rod <NUM> toward the drill bit <NUM>. While the shape of a wave pulse may assume any form, x and t must always appear in the combination with each other to satisfy the governing wave equation (i.e., the argument must include either (x - ct) or (x + ct). If the argument is (x + ct), the stress wave displacement is propagating along the longitudinal axis "x" of the drill rod <NUM> toward the hammer <NUM>-<NUM> and away from the drill bit <NUM>.

Again, while equation (<NUM>) models the stress wave as a sinusoidal wave, those skilled in the art will appreciate that the wave could be modeled as a trapezoidal wave, a square wave or as a rectangular pulse. (Those skilled in the art will appreciate that mathematical models are only approximations of real world mechanical phenomena). The factor <NUM> in equation (<NUM>) indicates that the wave has a length <NUM>, which corresponds to twice the hammer's length, as shown at <FIG>.

Referring to <FIG>, a diagrammatic depiction of a mechanical isolation filter system <NUM> in accordance with the present invention is disclosed. Briefly stated, the stress waves formed by the axial shocks and vibration may be substantially reduced by the isolation filter <NUM>. Before describing the filter <NUM>, and its features and benefits, it may be useful to highlight the differences between the mechanical isolation filter system <NUM> of the present invention and a damping spring mechanism.

The mechanical isolation filter system <NUM> is configured as a low pass axial shock and vibration filter and not as a damping mechanism. Specifically, note that a damping mechanism typically uses significant dissipative forces (frictional or fluid forces) to dampen vibrational motions; however, these dissipative frictional forces generate thermal energy. In contrast, the mechanical isolation filter system <NUM> of the present invention substantially isolates the sensor <NUM> or the magnetic sources <NUM> from potentially damaging shock and vibrations (axial or otherwise) while substantially obviating any frictional forces. Stated differently, because of the filtering operation, the carriage <NUM> will exhibit very little oscillation, if any. As a result, the amount of thermal energy (heat) generated by the spring-mass filter <NUM> is relatively small when compared to a frictional damping device.

In the various drilling applications contemplated by the present invention, such as a reciprocating drilling action (e.g., hammer-drilling), the excitation frequencies propagating along the longitudinal axis <NUM> of the drill rod <NUM> are on the order of approximately <NUM> and above (see <FIG>). The low pass isolation filter <NUM> of the present invention is configured to substantially filter out excitations (shock and vibration) to frequencies well below <NUM>.

As shown in <FIG>, therefore, the mechanical isolation filter system <NUM> is comprised of the carriage apparatus <NUM> and the spring system <NUM> disposed between the carriage apparatus <NUM> and the drill rod shoulders (<NUM>-<NUM>, <NUM>-<NUM>). The carriage <NUM> is modeled as a mass m that is connected between a pair of springs <NUM> (one spring at each end), which have a spring constant "k. " The springs <NUM> are further connected to the drill rod at their respective ends via the shoulders <NUM>. As highlighted by <FIG> and <FIG>, and the associated text, the stress waves generated by a reciprocating drilling operation (such as hammer drilling) are primarily directed along its longitudinal axis <NUM>. The natural frequency of vibration of the mass and spring system (at <FIG> and <FIG>) is [<NUM>/(2π)]*[sqrt (<NUM>/m)], wherein k is the spring constant of one spring. Since there is one spring <NUM> at each end of the carriage housing <NUM> (and two (<NUM>) total springs), the term "<NUM>" is used in the natural frequency equation. (If only one spring <NUM> is employed, the natural frequency is [<NUM>/(2π)]*[sqrt (k/m)]).

Note that in the embodiments depicted <FIG> and <FIG>, there are a set of four (<NUM>) springs at each end (and eight (<NUM>) total), and thus the natural frequency of vibration of the mass and spring system is [<NUM>/(2π)]*[sqrt (<NUM>/m)]. In these embodiments, the spring rate k for one spring is approximately <NUM> N/mm. After converting the spring rate k from mm to meters, the spring rate becomes <NUM>,<NUM> N/m. Accordingly, with the two sets of four springs <NUM> (one set at each end) disposed in parallel, the two sets of springs <NUM> would have a combined spring rate of about <NUM>,<NUM> N/m. With a carriage housing <NUM> having a mass of about <NUM>, the natural or fundamental frequency would be f = [<NUM>/(2π)] * [sqrt (<NUM>,<NUM>/<NUM>)] which equals about <NUM>.

In another example embodiment, the carriage apparatus <NUM> may be coupled between the shoulders (<NUM>-<NUM>, <NUM>-<NUM>) by a set of two springs at each end, i.e., four springs total. In this case the two sets of springs <NUM> would have a rate of about <NUM>,<NUM> N/m; and with a carriage mass of <NUM>, the natural frequency would be about <NUM>. In all of these embodiments, a variable rate spring may be employed.

Accordingly, one skilled in the art will appreciate that the design may be adapted to various environmental scenarios. That is, the stress wave parameters may vary depending on the type of drilling/mining application, and thus, the carriage mass, spring rate and/or total number of springs may be selected in accordance with a given application. Any excitations along the longitudinal axis that are greater than <NUM> times the natural (fundamental) frequency will be substantially attenuated (i.e., filtered out) by the low pass filter <NUM>. The spring rate k used in the above calculations is a constant value; however, the present invention contemplates that the spring rate may be non-constant (i.e., non-linear). Thus, the present invention contemplates that the spring rate may be construed to refer to or encompass any predetermined force-displacement relationship.

In reference to <FIG>, the plots shown in these charts recapitulate the teachings articulated herein, e.g., at <FIG> and the associated text. For example, <FIG> shows a fast Fourier transform (FFT) of the surface accelerations depicted at <FIG>. In <FIG>, most of the frequency content of the surface accelerations is between <NUM> (<NUM><NUM>) and <NUM> (<NUM><NUM>) or less. The peak acceleration is about <NUM> at about <NUM>,<NUM>. (Note that since <NUM> is approximately equal to <NUM>/s<NUM>, <NUM> is approximately equal to about <NUM>/s<NUM>).

<FIG> is a chart showing transfer functions (<NUM>, <NUM>) for the spring mass isolation filter <NUM> of <FIG> (and implemented by spring <NUM> and mass (carriage apparatus <NUM>) system depicted at <FIG> and <FIG>. The transfer function curve <NUM> represents the first filter example wherein the isolation filter has two sets of four springs <NUM> (one at each end) that are disposed in parallel. In this case, the system example is characterized by a natural frequency of about <NUM>. Note that the <NUM> natural frequency is the location of the peak frequency of curve <NUM>, and represents the resonant frequency of the isolation filter <NUM>. Frequencies below the natural frequency represent the filter passband wherein the attenuation factor is equal to one. Frequencies greater than the <NUM> natural frequency are attenuated with the curve falling off at an attenuation rate of <NUM>/f<NUM>.

The transfer function curve <NUM> represents the second filter example wherein the isolation filter has two sets of two springs <NUM> (one at each end) that are disposed in parallel. In this case, the system example is characterized by a natural frequency of about <NUM>. Thus, the adaptability of isolation filter <NUM> to different drilling/mining environments should be readily apparent to the reader. As noted herein, the isolation filter uses very little damping to avoid generating thermal energy. Briefly stated, <NUM>% of critical damping is assumed in the calculations. This damping amount represents small spring losses, minimal friction between the drill rod and the carriage assembly, etc. Also, those skilled in the art will appreciate that this minimal amount of damping is included in the transfer functions of <FIG> so that the motion at resonance remains finite. (If no damping is assumed in the calculations, then the peak attenuation multiple (at <FIG>) will go to infinity at resonance).

<FIG> is a chart showing the output of the spring mass isolation filter when subject to the excitations shown at <FIG>. This chart is directed toward the first example wherein the filter has a <NUM> resonant frequency. The peak filtered acceleration of the filter <NUM> is about <NUM>/s<NUM> (i.e., about <NUM>) at approximately <NUM>. Comparing the surface accelerations of <FIG> to the filter output chart of <FIG>, the surface acceleration curve <NUM> has a peak acceleration of <NUM> (i.e., <NUM>,<NUM>/s<NUM>) whereas the peak filter output is again, only about <NUM>/s<NUM>. As the frequencies of the surface accelerations increase, the surface accelerations of the carriage apparatus <NUM> decrease until they approach <NUM>/s<NUM> at about <NUM>,<NUM>. Essentially, in stark contrast to a damping system, the carriage <NUM> becomes stationary as the vibrational frequencies increase.

Thus, the isolation filter implemented by the carriage apparatus <NUM> is characterized by a low pass frequency transfer function <NUM> (<NUM>) that includes pass band frequencies that are substantially below the operational frequency spectrum (<NUM>) wherein stress waves propagating along the drill rod <NUM> from a predetermined drilling operation are substantially attenuated and substantially prevented from disturbing the carriage apparatus <NUM>.

As embodied herein and depicted at <FIG>, a diagrammatic depiction of a downhole assembly <NUM> in accordance with an alternate embodiment of the present invention is disclosed. Here, the carriage apparatus <NUM> is substantially identical to those described above, and hence, any further description is redundant and omitted for brevity's sake.

On the other hand, in this embodiment the drill rod <NUM> is modified so that the shoulders (<NUM>-<NUM>, <NUM>-<NUM>) are replaced by clamped collar devices (<NUM>-<NUM>, <NUM>-<NUM>). Here, collar <NUM>-<NUM> is shown as having a smaller diameter than collar <NUM>-<NUM>; however, the collar diameter size may be relatively unimportant in this case since the collars <NUM> can be attached to drill rod <NUM> after the carriage apparatus <NUM> is coupled to the drill rod <NUM>. The collars (<NUM>-<NUM>, <NUM>-<NUM>) are two-piece devices that include matching tap holes <NUM>-<NUM> that are configured to accommodate a screw or other such fastener used to tighten the collar pieces around the drill rod <NUM>.

In reference to <FIG>, a diagrammatic depiction of a downhole assembly in accordance with another alternate embodiment of the present invention is disclosed. Again, the carriage apparatus <NUM> is substantially identical to those described above, and hence, any further description is redundant and omitted for brevity's sake. This embodiment features a hybrid drill rod <NUM> that is a cross between the drill rod depicted at <FIG> and the drill rod shown at <FIG>. That is, the drill rod features a shoulder <NUM>-<NUM> (like <FIG>) along with a collar device <NUM> (like <FIG>). In other words, the shoulder <NUM>-<NUM> (<FIG>) is replaced by a collar <NUM>. Thus, the carriage apparatus <NUM> or cover <NUM> may be inserted over the drill pin <NUM>-<NUM> and moved down the drill rod <NUM> until the springs <NUM> are coupled between the carriage <NUM> and the shoulder <NUM>-<NUM>. Then, the collar <NUM> is attached to secure the other set of springs <NUM> between the carriage <NUM> and the collar <NUM>.

Those skilled in the art will appreciate that the collar <NUM> may be implemented as a two-piece shaft collar with a <NUM> bore, <NUM> OD, and <NUM> width. The collar may be manufactured from <NUM> lead free steel having a black oxide finish that increases holding power and resists corrosion. In one embodiment, the collar <NUM> may be implemented by an MSP-<NUM>-F collar arrangement manufactured by the Ruland Manufacturing Company.

In reference to <FIG>, detail views of a clamp keying arrangement employed at <FIG> are disclosed. In <FIG>, a shallow groove <NUM>-<NUM> may be machined or otherwise formed in the drill rod <NUM> to accommodate the collar therein. In <FIG>, a stop portion <NUM>-<NUM> is included to substantially prevent the collar from slipping or rotating about the drill rod <NUM>.

<FIG> shows a collar <NUM> that is disposed in situ within a groove <NUM>-<NUM>. The collar <NUM> includes a proud surface <NUM>-<NUM> that has a larger diameter than the recessed portion <NUM>-<NUM> adjacent thereto. The recessed portion <NUM>-<NUM> may be employed to accommodate an extended-length protective cover <NUM>.

Note that each drawing (<FIG>) shows a sectional view of the drill rod such that the central fluid channel <NUM>-<NUM> is shown. (This channel may be used to direct a pressurized fluid from an uphole region (e.g., control station <NUM> at <FIG>) to the drill bit <NUM>. The fluid may be air pressurized at <NUM> kPa (<NUM> PSI).

Referring to <FIG>, a detail view of the carriage apparatus employing the clamping arrangement depicted at <FIG> is disclosed. In this view, the protective cover <NUM> fits within the recessed portion <NUM>-<NUM> of the collar <NUM>. At the same time, the cover <NUM> is substantially flush with the proud surface <NUM>-<NUM> of collar <NUM>.

<FIG> is a cross-sectional view of the carriage apparatus <NUM> shown at <FIG> and <FIG>. That is, the carriage apparatus <NUM> is coupled to a drill rod <NUM> that employs the clamping arrangement <NUM> depicted at <FIG>. Again, the protective cover <NUM> is disposed within the recessed portion <NUM>-<NUM> of the collar <NUM> such that it extends over the springs <NUM> and the housing <NUM>. The cover <NUM> is substantially flush with the proud surface <NUM>-<NUM>.

As embodied herein and depicted in <FIG>, a diagrammatic depiction of a downhole assembly in accordance with another alternate embodiment of the present invention is disclosed. In this embodiment, the drill rod <NUM> is substantially the same as the one shown at <FIG>. Moreover, the carriage apparatus <NUM> is substantially identical to those described in previous embodiments. Accordingly, only the new elements of the carriage <NUM> are described for the sake of brevity. Here, a bumper arrangement <NUM> is provided at each end of the carriage housing <NUM>. The bumper arrangement <NUM> includes two semi-circular pads (<NUM>-<NUM>, <NUM>-<NUM>) that are applied to each end of the housing portions (<NUM>-<NUM>, <NUM>-<NUM>).

Turning to <FIG>, detail views of a carriage apparatus <NUM> of the downhole assembly depicted in <FIG> is disclosed. These views show the bumper arrangement <NUM> with greater clarity. The semi-circular pads (<NUM>-<NUM>, <NUM>-<NUM>) take the form of a gasket that includes four holes <NUM>-<NUM>. The holes <NUM>-<NUM> accommodate the springs <NUM>. The gasket pads <NUM>-<NUM>, <NUM>-<NUM> may be formed using any suitable material configured to protect the carriage housing <NUM> from a hard impact from the drill rod shoulders (<NUM>-<NUM>, <NUM>-<NUM>); the materials may include rubber, polymer, composite materials, a relatively soft metal, etc..

As embodied herein and depicted in <FIG>, a detail view of a carriage cover <NUM> in accordance with another alternate embodiment of the present invention is disclosed. In this embodiment the cover <NUM> has one end with a relatively large diameter opening (as in previous embodiments) and an opposing end with a relatively small diameter opening. This allows the protective cover <NUM> to slide over the drill rod pin <NUM>-<NUM> and be held in place by the drill bit <NUM> (not shown) when it is screwed onto the pin <NUM>-<NUM>.

<FIG> is a cross-sectional view of a carriage apparatus <NUM> depicted in <FIG>. Note that the cover end (left side of <FIG>) abutting shoulder <NUM>-<NUM> has a larger diameter 30D1; and the cover end that abuts shoulder <NUM>-<NUM> has a smaller diameter 30D2. Thus, the larger diameter opening is large enough to slide over the shoulders (<NUM>-<NUM>, <NUM>-<NUM>) and the carriage <NUM> until an end cap portion <NUM>-<NUM> abuts the shoulder <NUM>-<NUM>. Once the drill bit <NUM> is threaded onto the pin <NUM>-<NUM>, the end cap <NUM>-<NUM> is firmly caught between the shoulder <NUM>-<NUM> and the drill bit <NUM> to secure the cover to the apparatus <NUM>.

As embodied herein and depicted in <FIG>, a detail view of a portion <NUM>-<NUM> of the carriage apparatus in accordance with yet another alternate embodiment of the present invention is disclosed. Most of the housing portion <NUM>-<NUM> is substantially identical to embodiments described above, and hence, a description of previously described elements is omitted for brevity's sake. In this view, a series of spring holes <NUM>-<NUM> are formed in the surface of the key channel <NUM>-<NUM>. Each hole <NUM>-<NUM> is configured to accommodate a spring <NUM>; thus, upon the assembly of housing <NUM>, the springs <NUM> extend into holes <NUM>-<NUM> formed in each housing portion <NUM>-<NUM>, <NUM>-<NUM>. The springs <NUM> and the carriage mass m form another filter that is configured to filter any torqueing forces that may be applied to the housing <NUM> during a rotational drilling process (in a manner similar to the spring isolation filter <NUM> described above). In one embodiment, the springs <NUM> are manufactured using chrome-silicon steel, have a <NUM> (<NUM> inch) long free length, and have a spring rate of <NUM> N/mm. The holes <NUM>-<NUM> may have a <NUM> (<NUM>") diameter. In one embodiment, the springs <NUM> may be manufactured by McMaster-Carr and be implemented by the McMaster-Carr Blue Chrome-Silicon Steel Die Spring PN 9657K49.

As embodied herein and depicted in <FIG>, a diagrammatic depiction of a downhole assembly in accordance with yet another alternate embodiment of the present invention is disclosed. In this view, the carriage housing <NUM> is configured to accommodate a sensor assembly <NUM> instead of a magnetic source assembly. Here, the sensor carriage <NUM> is shown with the protective cover <NUM> removed. The housing portion <NUM>-<NUM> is shown with a protective enclosure <NUM>-<NUM> formed therein. The enclosure <NUM>-<NUM> is configured to accommodate the sensor circuit assembly <NUM> and some potting material. The potting material is employed to hold the circuit elements in place within the protective enclosure <NUM>-<NUM>. The drill rod <NUM> and spring <NUM> arrangement is substantially identical to previous embodiments described above, and thus any description of previously described elements is omitted for brevity's sake.

<FIG> is a detail view of a carriage apparatus <NUM> depicted in <FIG>. In this view, the protective cover <NUM> is shown with a cutaway view that reveals the housing <NUM> underneath. As before, the sensor circuit <NUM> is disposed within the protective enclosure <NUM>-<NUM> and the cover <NUM> serves to protect the circuitry <NUM>.

Referring to <FIG>, a diagrammatic depiction of the sensor assembly depicted at <FIG> is disclosed. The sensor assembly <NUM> includes various components disposed, e.g., on a printed circuit board (PCB) and coupled together by a bus system <NUM>-<NUM>. The bus system <NUM>-<NUM> is coupled to a microprocessor <NUM>-<NUM> and computer readable memory <NUM>-<NUM>. The sensor assembly <NUM> may also include an accelerometer module <NUM>-<NUM>, a magnetometer module <NUM>-<NUM>, an inclinometer <NUM>-<NUM>, a gyro rate sensor <NUM>-<NUM>, as well as an environmental module <NUM>-<NUM>.

As those skilled in the art will appreciate, the accelerometer module <NUM>-<NUM> may be configured to measure the Earth's gravity vector and provide the gravity vector components gx, gy, gz of the Earth's gravity vector g. The gyroscope <NUM>-<NUM> is used for measuring the device's orientation and/or angular velocity. The gyro <NUM>-<NUM> may be configured as a rate gyroscope which is configured to produce an output voltage proportional to a rate of rotation. The magnetometer module <NUM>-<NUM> may include a plurality of fluxgate magnetometers having their axes of maximum sensitivity intersecting each other at one or more observation points and substantially at right angles to each other. (As before, the magnetometer module <NUM>-<NUM> may have a magnetometer sensor having up to three magnetometers; and, the magnetometer module <NUM>-<NUM> may have multiple magnetometer sensors). Magnetometers measure the amplitude and the phase of two perpendicular components of the magnetic field <NUM>. The inclinometer may be employed to measure the angles of slope/tilt of carriage <NUM> with respect to the gravity vector. The environmental sensor module <NUM>-<NUM> may be configured to measure one or more of temperature, pressure, radiation, etc..

The microprocessor <NUM>-<NUM> may be configured to use the sensor inputs to determine the spatial relationships between the borehole axis <NUM>, borehole inclination, roll angle, borehole azimuth, the Earth's rotation vector, and other such spatial relationships.

The sensor assembly <NUM> also includes a piezoelectric transducer <NUM>-<NUM> that is configured to convert the mechanical energy (Wh) generated by the drilling operations into electrical energy. (An expression for the mechanical energy is provided herein). As those skilled in the relevant arts would appreciate, the piezoelectric effect converts mechanical strain into electric current or voltage. The electrical current is provided to an electrical storage device <NUM>-<NUM> which includes a battery for storing the harvested energy. In an alternate embodiment, electrical power may be provided to the carriage <NUM> (and sensor assembly <NUM>) by way of wireline.

Finally, the sensor assembly <NUM> may include a transmitter device <NUM>-<NUM> and a receiver <NUM>-<NUM>. The transmitter <NUM>-<NUM> and receiver may be configured as a wireless or as a wireline transceiver configured to communicate with an uphole telemetry system (not shown in this view). In one embodiment, the uphole telemetry system is configured to manipulate all of the sensor data provided by the sensor assembly <NUM> (disposed down-hole). This information, or some of the information, may be transmitted to a driller controller (<FIG>) so that an appropriate course correction can be made (if necessary). In another embodiment, data transfer may be effected when the device <NUM> is retrieved from the downhole environment.

The microprocessor <NUM>-<NUM> may be configured to bi-directionally communicate with the various components coupled to the bus <NUM>-<NUM>. In this embodiment, the microprocessor <NUM>-<NUM> may include on-board analog-to-digital conversion (ADC) channels that accommodate the analog output signals of the accelerometers (<NUM>-<NUM> - <NUM>-<NUM>). The analog voltage output signal of the gyro sensor <NUM>-<NUM> may also be converted into digital signals.

The sizing and selection of the microprocessor <NUM>-<NUM> is considered to be within the skill of one of ordinary skill in the art with the following proviso: obviously, if the functionality of the up-hole control system is incorporated into the down-hole system, the computational burden of the resultant processor will necessarily be greater. In any event, in accordance with the embodiment of FIG. 5C, the microprocessor <NUM>-<NUM> may be implemented using any suitable processing device depending on processing speed, cost, and durability considerations. In one embodiment, therefore, processor <NUM>-<NUM> may be implemented using a <NUM> bit, a <NUM>-bit, a <NUM> bit, or any suitable microcontroller coupled to any suitable computer readable media <NUM>-<NUM>. As noted above, the microcontroller may be more or less powerful depending on cost/processing speed considerations.

The term "computer-readable medium" as used herein refers to any medium that participates in providing data and/or instructions to the processor <NUM>-<NUM> for execution. Such a medium may take many forms, including but not limited to RAM, PROM, EPROM, EEPROM, FLASH-EPROM or any suitable memory device, either disposed on-board the processor <NUM>-<NUM> or provided separately. In one embodiment, the processor <NUM>-<NUM> may include <NUM> KB of flash memory and <NUM> KB of SRAM.

As embodied herein and depicted in <FIG>, a diagrammatic depiction of a downhole assembly <NUM> in accordance with yet another alternate embodiment of the present invention is disclosed. In this view, the housing <NUM> is configured to provide a protective housing for the magnetic source elements <NUM>. As described below, the magnetic source elements may be disposed within the housing <NUM> via the interior of the housing so that they are protected from the ambient environment. The magnetic source housing <NUM> is coupled to a first spring member <NUM>-<NUM> at a first end thereof, and is coupled to a second spring member <NUM>-<NUM> at a second end portion of the housing <NUM>. In this embodiment, the spring members (<NUM>-<NUM>, <NUM>-<NUM>) may be formed by machining metallic cylinders to form a spring structure.

The spring member <NUM>-<NUM> is coupled to the collar member <NUM>-<NUM> at a first end portion of the magnetic source apparatus <NUM>; the collar members (<NUM>-<NUM>, <NUM>-<NUM>) function as attachment points for the apparatus <NUM>. Stated differently, the collar member <NUM>-<NUM> is fixedly attached to a portion of the drill string <NUM> proximate to the drill bit <NUM> (not shown in this view). Similarly, the spring member <NUM>-<NUM> is coupled to a second collar member <NUM>-<NUM> at a second end portion of the magnetic source apparatus <NUM> distal from the drill bit <NUM>. The second collar member <NUM>-<NUM> is fixedly attached to an up-hole portion of the drill string <NUM>.

As described below, the carriage apparatus <NUM> is configured such that the magnet elements <NUM> are rotationally registered to a registration portion of the drill bit <NUM> such that measurements of the magnetic field by the sensor apparatus <NUM> will include knowledge of the drill bit (tool face) <NUM> orientation. This allows the measurement system <NUM> (<FIG>) to instantaneously control the drilling direction via control station <NUM>. Having said that, note that only the collar portions (<NUM>-<NUM>, <NUM>-<NUM>) are coupled to the drill string <NUM>. The carriage housing <NUM> and the spring members (<NUM>-<NUM>, <NUM>-<NUM>) are spatially separated from a drill rod portion <NUM>-<NUM> and thus configured to float or glide over the drill rod portion <NUM>-<NUM> as the drill string <NUM> rotates (during the drilling process). In one embodiment, the drill rod <NUM>-<NUM> is not deemed to be a component part of apparatus <NUM>, i.e., the apparatus <NUM> may be coupled to any similar structure. In another embodiment, the apparatus may include a drill rod <NUM>-<NUM> manufactured and machined especially for apparatus <NUM>; and in this case, the drill rod <NUM>-<NUM> would be a component part of the apparatus <NUM>.

In reference to <FIG>, a diagrammatic depiction of a magnetic source apparatus <NUM>" shown in <FIG> is disclosed. In this embodiment, a protective sleeve <NUM> may be disposed over the entire assembly <NUM>". The protective sleeve may be formed from any suitable material such as BeCu, stainless steel, plastic, etc..

As embodied herein and depicted in <FIG>, a diagrammatic depiction of a downhole apparatus <NUM>‴ in accordance with another embodiment of the present invention is disclosed. The number of components in assembly <NUM> is identical to the assembly depicted in <FIG>; however, some of the individual members may be implemented differently. For example, in this embodiment, the spring members (<NUM>-<NUM>, <NUM>-<NUM>) may be implemented using a wire spring structure. Both implementations may have similar performance characteristics). As before, the spring members (<NUM>-<NUM>, <NUM>-<NUM>) are configured to register the housing <NUM> so that the magnetic source elements <NUM> are rotationally registered with the drill bit <NUM> and/or an orientation feature on the drill bit <NUM>. Moreover, the collar portions (<NUM>-<NUM>, <NUM>-<NUM>) are configured to be rotationally registered with the spring members (<NUM>-<NUM>, <NUM>-<NUM>). Detail views of the collar assemblies (<NUM>-<NUM>, <NUM>-<NUM>) are described below in conjunction with <FIG>.

<FIG> is a diagrammatic depiction of the drill rod structure <NUM> depicted in <FIG> with the carriage apparatus removed. In one embodiment, the assembly <NUM> may include a specially fabricated drill rod that provides rotational registration features configured to register the source housing <NUM>, the spring elements (<NUM>-<NUM>, <NUM>-<NUM>) with the drill bit <NUM>. Specifically, the drill bit <NUM> may include a drill bit registration feature <NUM>-<NUM> that is configured to be aligned with a registration mark <NUM>-<NUM> formed on drill rod <NUM>-<NUM>. At the same time, the drill rod <NUM>-<NUM> also includes key indents <NUM>-<NUM> at each end thereof. The key indents <NUM>-<NUM> are configured to accommodate a key ring portion of the collars (<NUM>-<NUM>, <NUM>-<NUM>) to thus rotationally register the collars to the rod <NUM>-<NUM>. Moreover, the indent gap <NUM>-<NUM> is configured to accommodate an end portion of the wire spring (<NUM>-<NUM>, <NUM>-<NUM>) to rotationally register the springs (<NUM>-<NUM>, <NUM>-<NUM>) to the drill rod <NUM>-<NUM>. Finally, a plurality of cooling holes <NUM>-<NUM> are formed in the drill rod <NUM>-<NUM>. The cooling holes <NUM>-<NUM> are in communication with the central fluid channel <NUM>-<NUM> of the drill rod <NUM>-<NUM>. The central fluid channel <NUM>-<NUM> extends the length of the drill string <NUM> and allows a cooling fluid (such as air) to be directed from the source <NUM> (<FIG>) to the drill bit <NUM>.

The housing <NUM> is assembled such that each magnetic source <NUM> is positioned over a corresponding cooling hole <NUM>-<NUM>. Thus, the cooling holes <NUM>-<NUM> may be used to rotationally register the magnetic source housing <NUM> to the drill rod <NUM>-<NUM>, and hence to the drill bit registration feature <NUM>-<NUM> formed on the drill bit <NUM>. At this point, a few words concerning the meaning of the term "rotational registration" may be in order. If the drill bit registration feature <NUM>-<NUM> is designated as, for example, <NUM>°, every other feature on the drill rod will have a predetermined angular position θ relative to feature <NUM>-<NUM> when the assembly <NUM> is properly configured. The drill bit orientation feature <NUM>-<NUM> may be an asymmetrical feature or drill orientation that allows the drilling control system <NUM> to perform directional drilling (i.e., precisely control the direction of the borehole as it is being drilled). The orientation is known and programmed in software. The magnetic field orientation relative to the magnet source elements <NUM> is also known and programmed in software. By determining the magnetic field orientation via the sensor assembly (<FIG>), the drill bit orientation may also be determined.

As before, the springs <NUM>-<NUM> and <NUM>-<NUM>, along with the mass of the carriage are configured to form a low pass isolation filter in accordance with the principles outlined above. See <FIG> and the associated text.

In reference to <FIG>, a cross-sectional view of the magnetic source housing <NUM> depicted in <FIG> and <FIG> is disclosed. In this view, the housing portions <NUM>-<NUM> and <NUM>-<NUM> are shown as being disposed around the drill rod <NUM> such that the magnetic sources <NUM> are aligned with the cooling holes <NUM>-<NUM>. In one application, the cooling air is directed down the pipe <NUM>-<NUM> at about <NUM> kPa (<NUM> PSI). Accordingly, the cooling air is directed into the cooling holes <NUM>-<NUM> and into the gap <NUM> that is formed between the inner surface of the housing <NUM> and the outer surface of the drill rod <NUM>-<NUM>. As a result, the cooling air is employed to direct thermal energy away from the magnets <NUM> and thus lower the ambient temperature of the magnetic source elements <NUM>.

In reference to <FIG>, a detail view of a collar assembly <NUM>-<NUM> depicted in <FIG> is disclosed. (Note that the retention collar <NUM>-<NUM> disposed on the other end of drill rod <NUM>-<NUM> (see <FIG> and <FIG>) is of like or similar construction). The retention collar <NUM>-<NUM> may include a first collar portion <NUM>-<NUM> coupled to a second collar portion <NUM>-<NUM> (disposed behind drill rod <NUM>-<NUM> and thus not shown in this view). The first and second collars (<NUM>-<NUM>, <NUM>-<NUM>) may be coupled together using any suitable means such as a weld <NUM>-<NUM> or other suitable fastener means. A first retention key <NUM>-<NUM> is disposed within a key indent <NUM>-<NUM> (see <FIG>) and a retention feature formed within the interior surface of the first collar portion <NUM>-<NUM>, to thus rotationally register the collar <NUM>-<NUM> to the drill rod <NUM>-<NUM>. (The second collar <NUM>-<NUM>, disposed behind the drill rod <NUM>-<NUM> in this view, also accommodates a second retention key <NUM>-<NUM> disposed within its respective key indent <NUM>-<NUM>). Note that a spring registration portion <NUM>-<NUM> is disposed within the indent gap <NUM>-<NUM> to rotationally register the spring <NUM>-<NUM> with the drill rod <NUM>-<NUM>. (In reference to <FIG>, the spring registration portion <NUM>-<NUM> is not depicted for clarity of illustration, but may be employed in that embodiment).

In reference to <FIG>, a detail view of a collar assembly <NUM>-<NUM> depicted in <FIG> in accordance with an alternate embodiment of the present invention is disclosed. In this alternate embodiment, the retention collar <NUM>-<NUM> includes a first collar portion <NUM>-<NUM> that includes a ramped sleeve <NUM>-<NUM> that slides over the drill rod <NUM>-<NUM>. A second collar portion <NUM>-<NUM> slides over the ramped portion <NUM>-<NUM> and is tightened by fasteners <NUM>-<NUM> to exert pressure on the sleeve <NUM>-<NUM>. The ramped sleeve <NUM>-<NUM> features a relatively small angle φ between the ramp and the interior surface of the collar portion <NUM>-<NUM>. The angle φ may be of any suitable amount; for example, in one embodiment the angle φ is between <NUM>° - <NUM>°.

In another embodiment, the attachment collars (<NUM>-<NUM>, <NUM>-<NUM>) may also be implemented as an end portion of the spring members (<NUM>-<NUM>, <NUM>-<NUM>). In this embodiment, the end-collar portion of the spring includes a registration mark or indicia that are aligned to a registration mark/indicia formed on the drill rod. Upon alignment, the end-collar may be welded to the drill rod <NUM>-<NUM>.

In yet another embodiment of the invention, the attachment collars (<NUM>-<NUM>, <NUM>-<NUM>) may be integrally formed with the drill rod <NUM>-<NUM> itself. In this embodiment, each attachment collar includes a spring member interface that accommodates the spring registration portion <NUM>-<NUM> to rotationally register the spring <NUM>-<NUM> with the drill rod <NUM>-<NUM>.

As embodied herein and depicted in <FIG>, detail views of the spring elements depicted in <FIG> are disclosed. In <FIG>, the spring element <NUM>-<NUM> is shown as being disposed over the drill rod <NUM>-<NUM>. In this embodiment the free length F/L may be about <NUM> (<NUM> inches). In <FIG>, the outside diameter (ID) is about <NUM>,<NUM> (<NUM> inches) in order to accommodate the outside diameter of the drill rod <NUM>-<NUM>. The wire diameter in this embodiment may be about <NUM> (<NUM> inches). In this embodiment, the spring members <NUM>-<NUM>, <NUM>-<NUM> are configured as compression springs and are implemented as open-coil helical springs wound or constructed to oppose compression along the longitudinal axis <NUM> (see, e.g., <FIG>). (As noted previously, while the spring registration portion <NUM>-<NUM> (shown at <FIG> and described above) is not depicted in <FIG> for clarity of illustration, the springs (<NUM>-<NUM>, <NUM>-<NUM>) may include the registration feature <NUM>-<NUM> or other such features such as <NUM>-<NUM> to thus provide rotational registration).

While several inventive embodiments have been described and illustrated herein, those of ordinary skill in the art will readily envision a variety of other means and/or structures for performing the function and/or obtaining the results and/or one or more of the advantages described herein, and each of such variations and/or modifications is deemed to be within the scope of the inventive embodiments described herein. More generally, those skilled in the art will readily appreciate that all parameters, dimensions, materials, and configurations described herein are meant to be exemplary and that the actual parameters, dimensions, materials, and/or configurations will depend upon the specific application or applications for which the inventive teachings is/are used. Those skilled in the art will recognize, or be able to ascertain using no more than routine experimentation, many equivalents to the specific inventive embodiments described herein. It is, therefore, to be understood that the foregoing embodiments are presented by way of example only and that, within the scope of the appended claims and equivalents thereto; inventive embodiments may be practiced otherwise than as specifically described and claimed.

All references, including publications, patent applications, and patents, cited herein are hereby incorporated by reference to the same extent as if each reference were individually and specifically indicated to be incorporated by reference and were set forth in its entirety herein.

The use of the terms "a" and "an" and "the" and similar referents in the context of describing the invention (especially in the context of the following claims) are to be construed to cover both the singular and the plural, unless otherwise indicated herein or clearly contradicted by context. The term "connected" is to be construed as partly or wholly contained within, attached to, or joined together, even if there is something intervening.

Accordingly, a value modified by a term or terms, such as "about" and "substantially", are not to be limited to the precise value specified. Here and throughout the specification and claims, range limitations may be combined and/or interchanged; such ranges are identified and include all the sub-ranges contained therein unless context or language indicates otherwise.

The recitation of ranges of values herein are merely intended to serve as a shorthand method of referring individually to each separate value falling within the range, unless otherwise indicated herein, and each separate value is incorporated into the specification as if it were individually recited herein.

The use of any and all examples, or exemplary language (e.g., "such as") provided herein, is intended merely to better illuminate embodiments of the invention and does not impose a limitation on the scope of the invention unless otherwise claimed.

Only the transitional phrases "consisting of" and "consisting essentially of" shall be closed or semi-closed transitional phrases, respectively, as set forth in the United States Patent Office Manual of Patent Examining Procedures, Section <NUM>.

Claim 1:
An apparatus for use on a structural member (<NUM>) having a longitudinal axis, the structural member being configured to propagate stress wave energy in an operational state, the stress wave energy having an operational frequency spectrum, the apparatus comprising:
a housing assembly (<NUM>) including a first end, a second end, and at least one protective enclosure configured to accommodate at least one device (<NUM>, <NUM>), the housing assembly being configured to be rotationally registered to the structural member when coupled to the structural member, the housing assembly having a predetermined housing mass; and
a spring arrangement (<NUM>) coupled between the structural member and the first end and/or coupled between the structural member and the second end in the operational state, the spring arrangement having a predetermined force-displacement relationship, the housing assembly and the spring arrangement forming an isolation filter having a predetermined spectral transfer function, the predetermined spectral transfer function being a function of the predetermined housing mass and the predetermined force-displacement relationship, the predetermined spectral transfer function including a passband having frequencies that are substantially outside the operational frequency spectrum wherein the stress wave energy is substantially attenuated in the operational state so that the housing assembly is substantially isolated from the stress wave energy.