Abstract:
A gerotor and bearing apparatus for a whirling mass orbital vibrator which generates vibration in a borehole. The apparatus includes a gerotor with an inner gear rotated by a shaft having one less lobe than an outer gear. A whirling mass is attached to the shaft. At least one bearing is attached to the shaft so that the bearing engages at least one sleeve. A mechanism is provided to rotate the inner gear, the mass and the bearing in a selected rotational direction in order to cause the mass, the inner gear, and the bearing to backwards whirl in an opposite rotational direction. The backwards whirling mass creates seismic vibrations.

Description:
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
   This invention was made with U.S. Government support under Prime Contract No. DE-FG26-00BC15191 awarded by the United States Department of Energy. The U.S. Government has certain rights in the invention. 

   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a gerotor and bearing system for a backwards whirling mass orbital vibrator. In particular, the present invention is directed to a gerotor and bearing apparatus and method to use a whirling mass orbital vibrator to generate vibrations. 
   2. Prior Art 
   Subterranean seismic vibration signals are known to be used in order to allow investigation of the geology surrounding subterranean boreholes. For example, the energy industry is known to utilize downhole vibration signals as a seismic energy source for generating information to evaluate the potential for deposits of oil and gas accumulation and other information. Seismic profiles of the earth may be generated from this information. 
   Seismic signals can be generated by various devices that may employ vibration which generates a sound wave directly or indirectly through the earth. 
   The use of downhole mechanical vibrations to increase the mobility of petroleum and gas deposits is also known. Vibrations are believed to decrease fluid interfacial tension as well as capillary forces, thereby allowing hydrocarbons to flow more easily. 
   Mechanical mechanisms to generate vibrations by spinning a shaft to create rotational energy are also known. For example, see Assignee&#39;s patents such as U.S. Pat. No. 5,159,160, U.S. Pat. No. 5,305,405, U.S. Pat. No. 5,210,381 and U.S. Pat. No. 5,515,918. The mechanical means may be provided by rotating a shaft in a selected rotational direction which causes a mass to backwards whirl in a direction opposite to rotational direction. Backwards whirl is defined as the motion of a circle having a diameter (d) whirling within another circle having a diameter (D), which generates a hypocycloid with multiple vibrations per rotation as follows: 
   
     
       
         
           d 
           
             D 
             - 
             d 
           
         
       
     
   
   In the past, various types of mechanisms were used to insure a controlled backwards whirling motion. In one example, small, involute gears were utilized. It was important to assure that the mass did not encourage the gears to become misaligned, jump the gear teeth and then grind or destroy the gears over time due to misalignment. 
   Gerotors are one type of known gearing system. A typical gerotor includes an inner gear and an outer gear section. The gerotor is a system wherein the outer gear set has one more gear tooth or lobe than the inner gear set. In the past, gerotors have been used as fluid pumps and/or as hydraulic motors. In fluid pump applications, a fluid porting mechanism is utilized such that when the inner gear section is rotated in relation to the outer gear section, the fluid is pressurized. As the inner gear set rotates, a volume is created. This motion creates a volume of reduced pressure and fluid is drawn in. In a hydraulic motor application, a porting mechanism is used to force hydraulic fluid between the inner and outer gear sections imparting a rotary motion to the inner gear section. 
   For example, U.S. Pat. No. 6,336,317 to Holtzapple et al discloses use of a gerotor in an engine. 
   There remains a need to provide a gerotor and bearing system for a whirling mass orbital vibrator that will transmit vibrational energy. 
   There remains a need to provide a gerotor and bearing system for a whirling mass orbital vibrator that is efficient and will operate effectively downhole with minimal maintenance. 
   There also remains a need to provide a continuous drip lubrication system for a whirling mass orbital vibrator having a self contained lubricating system. 
   SUMMARY OF THE INVENTION 
   The present invention provides a gerotor and bearing apparatus for a whirling mass orbital vibrator. The apparatus is contained in a housing which encloses an upper end of the device through which an upper drive shaft extends. Suspended from the upper drive shaft is a drive shaft connected by a pair of opposed U-joints on each end. The arrangement of the U-joints allows off center or eccentric axial movement. Attached to the drive shaft and U-joints is an upper gerotor set having an inner gear with one less lobe than an outer gear. Attached below the inner gear of the upper gerotor is an upper track roller bearing which engages a cylindrical sleeve mounted on the housing. Attached below the upper track roller bearing is a cylindrical mass. The upper track roller bearing is parallel and axially aligned to the mass. 
   A lower gerotor set having an inner gear and an outer gear are similar in configuration to the upper gerotor set. The inner gear is attached to the cylindrical mass. The upper gerotor set and lower gerotor set are radially aligned and parallel. 
   Attached below the lower gerotor set is a lower track roller bearing. The lower track roller bearing is parallel and is axially aligned with the cylindrical mass and with the upper track roller bearing. Attached below the lower track roller bearing is a pump shaft having a pair of U-joints on each end. A pump suspended from the pump shaft and rotated by the drive shaft serves to provide oil and lubrication for the apparatus. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  illustrates a front elevational view of a portion of a gerotor and bearing apparatus for a whirling mass orbital vibrator constructed in accordance with the present invention; 
       FIG. 2  is a perspective view of a portion of the apparatus taken along section lines  2 — 2  of  FIG. 1 ; 
       FIG. 3  illustrates a top view, and  FIG. 4  illustrates a perspective view of a gerotor set which is a part of the gerotor and bearing apparatus of the present invention; 
       FIG. 5  is a simplified diagrammatic view of the gerotor and bearing apparatus within a housing; and 
       FIG. 6  is an elevational, sectional view of the gerotor and bearing apparatus within a housing set inside casing. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   The embodiments discussed herein are merely illustrative of specific manners in which to make and use the invention and are not to be interpreted as limiting the scope of the instant invention. 
   While the invention has been described with a certain degree of particularity, it is to be noted that many modifications may be made in the details of the invention&#39;s construction and the arrangement of its components without departing from the spirit and scope of this disclosure. It is understood that the invention is not limited to the embodiments set forth herein for purposes of exemplification. 
   Referring to the drawings in detail,  FIG. 1  illustrates a front view of a portion of a gerotor and bearing apparatus  10  for a downhole whirling mass orbital vibrator constructed in accordance with the present invention. In  FIG. 1 , an external housing  12  of the apparatus has been removed for clarity. 
   The present invention will be utilized downhole in a cased borehole which extends from the earth&#39;s surface and has been drilled in a usual, known manner in drilling for oil, gas or other wells. The present invention will generate vibrations downhole which may be used in a number of applications. One application of the present invention is to generate a seismic energy signal which can be used to generate compression and shear wave signals that travel in the earth and can be detected. Another application of the present invention is for enhanced oil recovery. Seismic stimulation of oil-bearing strata is known to increase fluid recovery. 
   In one embodiment, extending from an upper drive shaft  18  is a shaft  24  surrounded by a pair of U-joints  26  and  28 . A housing  12  (shown in  FIG. 5 ) encloses an upper end of the device  10 . Rotation of the drive shaft  18  will translate into rotation of the shaft  24 . The shaft may be rotated by mechanical, electrical, or hydraulic systems as are well known. The arrangement of the U-joints  26  and  28  with the shaft  24  allows the shaft to make off center or eccentric movement. Accordingly, while the shaft  18  produces centered rotation, the gerotor is permitted to rotate out of axial alignment. 
   Attached to the shaft  24  and U-joints  26  and  28  is a gerotor set  30  having an inner gear  32  (visible in  FIG. 1 ). An outer gear  34  (not seen in  FIG. 1 ) surrounds the inner gear and is attached to the housing. As will be seen, the gerotor inner gear  32  has one less lobe than the outer gear. Attached below the upper gerotor  30  is an upper track roller bearing  36 . As will be seen, the upper track roller bearing  36  contacts a cylindrical sleeve. 
   Attached below the upper track roller bearing  36  is a parallel and axially aligned cylindrical mass  38 . Attached below the cylindrical mass  38  is an inner gear  44  (visible in  FIG. 1 ) of a lower gerotor set. An outer gear  44  (not seen in  FIG. 1 ) surrounds the inner gear and is attached to the housing. Attached below the lower gerotor is a lower track roller bearing  40 . The lower track roller bearing  40  is parallel and is axially aligned with the cylindrical mass  38  and the upper track roller bearing  36 . 
   Attached below the lower track roller bearing is a second shaft having a pair of U-joints  50  and  52  on opposing ends of the shaft  48 . A lower drive shaft  16  of the apparatus is suspended below the second shaft  48 . 
   It will be observed from the foregoing that the inner gears and the track roller bearings and mass are axially aligned. The track roller bearings can rotate independently relative to the inner gears and mass. 
     FIG. 2  shows a perspective view taken along sectional line  2 — 2  of  FIG. 1  showing a portion of the gerotor and bearing apparatus  10  in an enlarged view. Referring to  FIG. 1  and with continuing reference to  FIG. 2 , the U-joint  28  permits the inner gear of the upper gerotor set, upper roller bearing  36  and cylindrical mass  38  to be eccentric to the drive shaft  18 . 
     FIG. 3  shows a top view and  FIG. 4  shows a perspective view of one of the gerotor sets, for example, the upper gerotor set  30 . The inner gear  32  resides and operates within the outer gear  34 . As can be seen, the inner gear  32  has one less lobe than the outer gear  34 . For example, inner gear  32  has ten lobes while outer gear  34  has eleven lobes. The lower gerotor set  42  (not shown) would be similar in arrangement. 
     FIG. 5  illustrates a simplified, diagrammatic view of the gerotor and bearing apparatus  10  of the present invention. The apparatus  10  is contained in a fluid tight housing and operates and resides downhole within casing  20  in a borehole (shown in  FIG. 6 ). 
   The cylindrical mass  38  has an exterior diameter less than the interior diameter of the housing  12  of the apparatus. Extending from the second shaft  48  and U-joints  50  and  52  is a pump  54  (a diagrammatic view seen in  FIG. 5 ). The pump  54  serves to provide oil and, in turn, lubrication for the gerotor and bearing apparatus  10  of the present invention. 
   The upper track roller bearing  36  rolls on and operates within an upper cylindrical sleeve  56  while the lower track roller bearing  40  rolls on and operates within a lower sleeve  58 . 
     FIG. 6  shows a detailed sectional view of one embodiment of the gerotor and bearing apparatus  10 . The illustration of the apparatus  10  has been split in two as shown by dashed line  60 . 
   A housing  12  of the apparatus  10  surrounds the components shown in  FIGS. 1 and 2  and forms a fluid tight enclosure. A seal  62  creates a fluid tight seal with the shaft. A series of bearings  66  surround the shaft. 
   As the mass is rotated, the roller bearings  36  and  40  contact the sleeves  56  and  58 . The housing  12  includes a pair of cones  68  and  70  which have larger diameters than the housing  12 . A plurality of slips  72  are lowered and follow the cones and engage the casing  20 . 
   Returning to consideration of  FIGS. 3 and 4 , when the cylindrical mass  38  is rotated in a clockwise direction, for example, the rotation of the inner gears of the upper gerotor and lower gerotor forces the cylindrical rotating mass  38  within the housing to move in a counterclockwise, backwards whirling motion. 
   The mass will backwards whirl at a speed defined by a backward whirl multiplier factor according to the following formula: 
   
     
       
         
           
             K 
             = 
             
               n 
               
                 N 
                 - 
                 n 
               
             
           
           ⁢ 
           
               
           
         
       
     
     
       
         
           
             where  n 
           
           = 
           
             
               number  of  lobes  on  inner  rotor  and  N 
             
             = 
             
                 
             
             ⁢ 
             
               
 
             
             ⁢ 
             
               number  of  lobes  on  outer  rotor 
             
           
         
       
     
   
   In order to prevent the gerotors  30  and  42  from having to support the high force loads generated by the backwards whirling mass, the heavy-duty track roller bearings  36  and  40  are utilized to transmit the centrifugal force created by the whirling mass to the sleeves  56  and  58  and then the housing of the apparatus  10 . The vibrations generated by the centrifugal force created by the backwards whirling mass are transmitted to the cones  68  and  70  of the housing and then through the slips  72  to the casing  20 . It will be observed that the slips  72  are directly in line with the sleeves  56  and  58  so that a direct load path exists from the applied load of the rotating mass through the casing to the well formation. The track rolling bearings  36  and  40  and the upper gerotor and lower gerotor are specially sized in order to allow the gerotors to force or pull the mass into a backwards whirling motion and have the bearings support the centrifugal force generated by the whirling mass. 
   The lower drive shaft  16  is surrounded by bearings  74  to retain the lower shaft in axial alignment. Below the lower drive shaft  16  and connected thereto is a fluid pump. Lubricating oil is contained in an oil sump  76 . A filter  78  prevents solids from entering the pump  54 . The pump  54  delivers oil through a passageway  80  in the housing  12 . The passageway  80  may have certain openings or perforations to allow oil to drip into the interior of the housing so that the gerotors, bearings and the other components of the apparatus are lubricated at all times. A self-contained drip lubrication system is thereby provided. 
   Whereas, the present invention has been described in relation to the drawings attached hereto, it should be understood that other and further modifications, apart from those shown or suggested herein, may be made within the spirit and scope of this invention.