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You are an expert at summarizing long articles. Proceed to summarize the following text: 
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application claims priority to U.S. Provisional Patent Application No. 60/707,351, filed on Aug. 11, 2005 and titled “Portable Mast Structure,” which is hereby incorporated by reference herein. 
     
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT  
       [0002]     Not Applicable.  
       BACKGROUND  
       [0003]     The present invention relates generally to mast structures used in drilling wells. More particularly, the present invention relates to portable mast structures used for drilling wells.  
         [0004]     In land-based drilling operations it is often desirable to be able to transport a drilling rig to a site where the drilling operations will take place and then be able to move the rig to the next site once operations are complete. Drilling rigs comprises a plurality of systems that all must be interconnected and assembled to support drilling activities The process of disassembling, transporting, and reassembling a drilling rig is complex and time consuming.  
         [0005]     The components and systems that make up a drilling rig are generally transported on trailers between drilling sites. Once on site, the components have to be unloaded and assembled. Drilling can not commence until the entire rig is unloaded and assembled. In many instances, the operators of the drilling rigs only collect rental fees when the rigs are involved in drilling operations Therefore, the time and expenses involved in transporting and assembling a drilling rig are preferably minimized. In many cases, auxiliary equipment, such as a crane and/or forklift, is required to assemble the drilling rig This auxiliary equipment must also be transported between drilling sites, further adding to the complexity and cost of moving a rig.  
         [0006]     Thus, there remains a need in the art for systems and methods for transporting and assembling portable drilling rigs, which overcome some of the foregoing difficulties while providing more advantageous overall results.  
       SUMMARY OF THE PREFERRED EMBODIMENTS  
       [0007]     Embodiments of the present invention include a portable drilling mast structure comprising a lower drilling mast having a lower end pivotally coupled to a base. A hinge is coupled to an upper end of the lower drilling mast and a lower end of an upper drilling masts The drilling mast structure has a first position wherein the lower drilling mast is parallel to the base and the upper drilling mast is disposed between the lower drilling mast and the base. The drilling mast structure has a second position wherein the lower drilling mast is perpendicular to the base and the upper drilling mast is aligned with the lower drilling mast.  
         [0008]     Thus, the embodiments of present invention comprise a combination of features and advantages that enable substantial enhancement of drilling rig transportation and assembly. These and various other characteristics and advantages of the present invention will be readily apparent to those skilled in the art upon reading the following detailed description of the preferred embodiments of the invention and by referring to the accompanying drawings. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0009]     For a more detailed description of the preferred embodiment of the present invention, reference will now be made to the accompanying drawings, wherein:  
         [0010]      FIG. 1  is an elevation view of an erected drilling mast constructed in accordance with embodiments of the present invention;  
         [0011]      FIG. 2  illustrates the drilling mast of  FIG. 1  collapsed for transport;  
         [0012]      FIG. 3  illustrates the drilling mast of  FIG. 1  collapsed and positioned at a drill site;  
         [0013]      FIG. 4  illustrates the drilling mast of  FIG. 1  in an upright position with the upper drilling mast folded down;  
         [0014]      FIG. 5  illustrates the drilling mast of  FIG. 1  as the upper drilling mast is rotated relative to the lower drilling mast;  
         [0015]      FIG. 6  illustrates the drilling mast of  FIG. 1  in a horizontal position with the upper drilling mast aligned with the lower drilling mast;  
         [0016]      FIG. 7  illustrates a folding drilling mast configured for use with a elevated substructure;  
         [0017]      FIG. 8  illustrates the folding drilling mast of  FIG. 7  connected to the substructure; and  
         [0018]      FIG. 9  illustrates the drilling mast of  FIG. 7  in an operational position. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0019]     Referring now to  FIG. 1 , drilling rig  100  comprises folding drilling mast  200 , drawworks  300 , top drive  310 , iron roughneck  320 , mud pumps  340 , hydraulic power unit  350 , hydraulic control unit  360 , and compressor  370 . Folding drilling mast  200 , drawworks  300 , hydraulic power unit  350 , hydraulic control unit  360 , and compressor  370  are mounted to trailer  110 , which is positioned on ramp  112 . Top drive  310  and iron roughneck  320  are mounted to folding drilling mast  200 . Top drive  310  is coupled to cable  304 , which is run over sheaves  302  at the top of folding drilling mast  200  to drawworks  300 . Mud pumps  340  are mounted to skids  342  having upper surface  344 .  
         [0020]     Folding drilling mast  200  comprises lower drilling mast  202  and upper drilling mast  204  connected by hinge  206 . Lower drilling mast  202  is rotatably coupled to trailer  110  by pivot  208 . Main hydraulic cylinder  210  is coupled to trailer  110  and lower drilling mast  202 . Support structure  212  couples lower drilling mast  202  to ramp  112  once drilling mast  200  is fully erected. Sheaves  302  are mounted to the top of upper drilling mast  204 .  
         [0021]     Referring now to  FIG. 2 , folding drilling mast  200  can be collapsed and transported on trailer  110  via truck  114 . Top drive  310  and iron roughneck  320  may remain installed on folding drilling mast  200  during transport and installation. When collapsed for transport, upper drilling mast  202  is stored below and latched to lower drilling mast  204 . Upper drilling mast  202  remains coupled to lower drilling mast  204  at hinge  206 . Lower drilling mast  204  is coupled to trailer  110  at pivot  208 .  
         [0022]     Once at the drilling site, trailer  110  is driven onto ramp  112  and secured in place, as is shown in  FIG. 3 . Mud pumps  340  are also placed adjacent to ramp  112  such that their upper surfaces  344  are aligned with the upper surface  116  of trailer  112 . Folding drilling mast  200  is erected by extending hydraulic cylinder  210  so as to rotate the drilling mast about pivot  208 . Drilling mast  200  is rotated until in a substantially vertical position, as shown in  FIG. 4 . Once in the vertical position, upper drilling mast  204  is unlatched from lower drilling mast  202  by releasing connection  214 .  
         [0023]     Once upper drilling mast  204  is unlatched, hydraulic cylinder  210  is retracted so that lower drilling mast  202  moves back toward a horizontal position. As lower drilling mast  202  rotates, the force of gravity will cause upper drilling mast  204  to rotate about hinge  206 . As upper drilling mast  204  rotates, upper cylinder  216  and pivot aim  218  engage the upper drilling mast. As lower drilling mast  202  is lowered upper drilling mast  204  will contact upper surfaces  114  and  344 . Pivot arm  21   8  acts to control the rate at which upper drilling mast  204  rotates and makes sure the upper drilling mast rotates past vertical as it contacts upper surfaces  114  and  344 .  
         [0024]     As lower drilling mast  202  moves toward horizontal, upper drilling mast  204  slides along upper surfaces  114  and  344  until both the upper and lower drilling masts are aligned and in a substantially horizontal position, as shown in  FIG. 6 . Once aligned, upper drilling mast  204  is fixably connected to lower drilling mast  202  and folding drilling mast  200  can be configured for drilling operations. Once upper drilling mast  204  is fixably connected to lower drilling mast  202 , hydraulic cylinder  210  can be extending, which will rotate folding drilling mast  200  to the vertical position, as shown in  FIG. 1 . Once fully vertical, support structure  212  can be connected to drilling mast  200  so as to reinforce the drilling mast during drilling operations.  
         [0025]     Folding drilling mast  200  is collapsed for storage and transport by essentially reversing the installation procedure described above. Support structure  212  is removed and hydraulic cylinder  210  is retracted to lower folding drilling mast  200  to the horizontal position of  FIG. 6 . Once horizontal, upper drilling mast  204  is partially disconnected from lower drilling mast  202  so that it can rotate about hinge  206 . Hydraulic cylinder  210  is then extended to raise lower drilling mast  202  back toward a vertical position. As lower drilling mast  202  is raised, upper drilling mast  204  will rotate about hinge  206  as is shown in  FIG. 5 .  
         [0026]     As lower drilling mast  202  reaches vertical, as shown in  FIG. 4 , upper drilling mast  204  will be positioned adjacent to the lower drilling mast. Connector  214  is then engaged so that the position of upper drilling mast  204  relative to lower drilling mast  202  is maintained as hydraulic cylinder  210  is retracted The retraction of hydraulic cylinder  210  lowers drilling mast  200  back to a horizontal position where it is fully collapsed and ready for transport, as shown in  FIGS. 2 and 3 .  
         [0027]      FIGS. 7-9  illustrate a folding drilling mast  400  being installed on substructure  500 . Folding drilling mast  400  is transported to a drilling site via trailer  410 . Folding drilling mast  400  comprises lower drilling mast  402  and upper drilling mast  404  that are rotatably coupled at hinge  408 . Substructure  500  comprises platform  502 , hydraulic cylinder  504 , and legs  506 . Connections  508  and  510  extend from the top of platform  502 .  
         [0028]     Referring now to  FIG. 7 , folding drilling mast  400  is moved into a position adjacent to substructure  500 . The base of folding drilling mast  400  is moved onto platform  502  such that lower drilling mast  402  is rotatably coupled to connection  508 , as shown in  FIG. 8 . Erecting arm  406  is extended from lower drilling mast  402  and is connected to cable  512 . Folding drilling mast  400  is erected using substantially the same process as described in reference to  FIGS. 3-6 . As hydraulic cylinder  504  is extended, platform  502  will raise and cable  512  will pull arm  406  such that drilling mast  400  rotates about connection  508 . Once drilling mast  400  is fully vertical, as shown in  FIG. 9 , lower drilling mast  402  is coupled to connection  510  and the drilling mast is secured for drilling operations.  
         [0029]     While preferred embodiments of this invention have been shown and described, modifications thereof can be made by one skilled in the art without departing from the scope or teaching of this invention. The embodiments described herein are exemplary only and are not limiting. Many variations and modifications of the system and apparatus are possible and are within the scope of the invention. Accordingly, the scope of protection is not limited to the embodiments described herein, but is only limited by the claims that follow, the scope of which shall include all equivalents of the subject matter of the claims.

Summary:
A portable drilling mast structure comprising a lower drilling mast having a lower end pivotally coupled to a base. A hinge is coupled to an upper end of the lower drilling mast and a lower end of an upper drilling mast. The drilling mast structure has a first position wherein the lower drilling mast is parallel to the base and the upper drilling mast is disposed between the lower drilling mast and the base. The drilling mast structure has a second position wherein the lower drilling mast is perpendicular to the base and the upper drilling mast is aligned with the lower drilling mast.