A downhole assembly with spring isolation filter

Abstract

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 being characterized by an operational frequency spectrum. The apparatus has a housing assembly including a first end, a second end, and one or more protective enclosures configured to accommodate one or more devices. The housing assembly is configured to be rotationally registered to the structural member when coupled to the structural member, and 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.

What is claimed is: 
     
         1 . 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 being characterized by an operational frequency spectrum, the apparatus comprising:
 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 configured to be rotationally registered to the structural member when coupled to the structural member, the housing assembly being characterized by a predetermined housing mass; and   a spring arrangement 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 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 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.   
     
     
         2 . The apparatus of  claim 1 , wherein 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. 
     
     
         3 . The apparatus of  claim 2 , wherein 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. 
     
     
         4 . The apparatus of  claim 2 , wherein 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. 
     
     
         5 . The apparatus of  claim 4 , wherein the plurality of first spring elements includes four spring elements or the plurality of second spring elements includes four spring elements. 
     
     
         6 . The apparatus of  claim 1 , wherein the spring arrangement includes at least one compression spring, the at least one compression spring being configured to oppose compression along the longitudinal axis. 
     
     
         7 . The apparatus of  claim 1 , wherein the at least one device includes at least one sensor device or at least one magnetic source element. 
     
     
         8 . The apparatus of  claim 7 , wherein 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. 
     
     
         9 . The apparatus of  claim 7 , wherein 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. 
     
     
         10 . The apparatus of  claim 1 , wherein the isolation filter is a low pass filter and the passband includes frequencies substantially between 0 Hz 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 1/f 2  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. 
     
     
         11 . The apparatus of  claim 1 , wherein 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.   
     
     
         12 . The apparatus of  claim 11 , wherein 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. 
     
     
         13 . The apparatus of  claim 12 , wherein the magnetic source device is selected from a group of magnetic source devices including a permanent magnet and an electromagnet. 
     
     
         14 . The apparatus of  claim 11 , further comprising a protective cover disposed over the housing assembly in the operational state, the protective cover substantially configured to conform to the exterior housing surface. 
     
     
         15 . The apparatus of  claim 14 , wherein the protective cover is disposed over the spring arrangement in the operational state. 
     
     
         16 . The apparatus of  claim 1 , wherein the predetermined force-displacement relationship includes a constant spring rate or a variable spring rate. 
     
     
         17 . 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; and   an apparatus coupled and rotationally registered to the structural member, the apparatus comprising,
 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; and 
 a spring arrangement 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 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 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. 
   
     
     
         18 . The assembly of  claim 17 , wherein 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. 
     
     
         19 . The assembly of  claim 18 , 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. 
     
     
         20 . The assembly of  claim 18 , wherein 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. 
     
     
         21 . The assembly of  claim 20 , wherein the plurality of first spring elements includes four spring elements and/or wherein the plurality of second spring elements includes four spring elements. 
     
     
         22 . The assembly of  claim 17 , wherein 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. 
     
     
         23 . The assembly of  claim 17 , wherein 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. 
     
     
         24 . The assembly of  claim 23 , wherein 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. 
     
     
         25 . The assembly of  claim 17 , wherein 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. 
     
     
         26 . The assembly of  claim 25 , wherein 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. 
     
     
         27 . The assembly of  claim 17 , wherein the at least one device includes at least one sensor device or at least one magnetic source element. 
     
     
         28 . The assembly of  claim 27 , wherein 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. 
     
     
         29 . The assembly of  claim 27 , wherein 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. 
     
     
         30 . The assembly of  claim 17 , wherein the isolation filter is a low pass filter and the passband includes frequencies substantially between 0 Hz 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 1/f 2  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. 
     
     
         31 . The assembly of  claim 17 , wherein the predetermined force-displacement relationship includes a constant spring rate or a variable spring rate. 
     
     
         32 . 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 assembly is substantially isolated from the stress wave energy.   
     
     
         33 . The method of  claim 32 , wherein the isolation filter is a low pass filter and the passband includes frequencies substantially between 0 Hz 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 1/f 2  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.