Abstract:
The High LCM Positive Pulse MWD Component is designed to reduce the entry of LCM and debris into traditional positive pulse MWD systems by utilizing a screen positioned over the fluid ports. The component modifies the traditional poppet housing utilized in positive pulse MWD systems without changing the parameters of the fluid ports or changing the operation or need to recalibrate standard positive pulse MWD systems.

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. provisional application Ser. No. 61/584,137 filed Jan. 6, 2012 and entitled Protective Screen for Positive Pulse MWD Tool, which is incorporated by reference herein. 
    
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     Not applicable. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an improved lower end for a positive pulse measurement while drilling (MWD) tool. Specifically, the improved lower end has the ability to prevent or reduce the entry of lost circulation material (LCM) and debris into the lower end through standard mud port holes. Reducing the entry of LCM and debris, especially larger sized LCM and debris, helps prevent the signal shaft from clogging or becoming inoperable. 
     2. Description of the Related Art 
     Positive pulse MWD tools are commonly used in the oil and gas industry as an effective means for determining the real-time location of the drill bit for purposes of making adjustments to drilling strategies. The standard positive pulse MWD system is comprised of multiple tubular housings comprising of at least a helix housing, poppet housing, pulser, directional module, and battery housing, among others. 
     The traditional positive pulse MWD system relies on a signal shaft or piston to interrupt the flow of drilling mud within the drilling string. This interruption of the drilling mud flow results in a positive pulse that machinery outside the well interprets to determine the location of the drill. An example of a typical MWD system is described in U.S. Pat. No. 5,333,686. The standard poppet housing is a tube with a substantially uniform outer diameter throughout the length of the poppet housing with a series of fluid ports located near the downwell end. 
     Traditional positive pulse MWD lower ends suffer from repeated clogging from debris or lost circulation material (LCM) entering the fluid ports located on the poppet housing of the lower end. During normal drilling operations, drilling mud is lost into the formation due to cracks in the rock or other geographic features. When enough drilling mud is lost to affect operations, drillers pump LCM down the drill string in an effort to seal up the cracks within the formation. LCM is comprised of numerous different types of material such as pieces of cotton seed hulls, walnut shells, seeds, bark, etc. that have sufficient volume and mass capable of filling the cracks in the formation that result in loss of drilling mud. Other debris also may present in drilling mud from cuttings not properly filtered as drilling mud is recycled. 
     Standard positive pulse MWD tools may become clogged and ineffective due to LCM or other debris entering the drilling fluid port(s). When this occurs, the signal shaft ceases to operate properly and the entire drill string must be removed so the lower end and signal shaft can be cleared of debris. Depending on the depth of the drill string, this clogging may result in a 12 to 24 hour delay, costing tens of thousands of dollars, while the signal shaft is cleared of debris. A secondary result of the common clogging of the lower end is that drillers tend to utilize less LCM which reduces the effectiveness of preventing the loss of drilling mud. As a result, many operators reduce LCM flow rates from the standard of 40 to 50 pounds per barrel to 15 pounds per barrel. 
     BRIEF SUMMARY OF THE INVENTION 
     The present invention is a modified version of the standard positive pulse MWD system for operation in a high lost circulation material (LCM) environment. The present invention maintains the same fluid port holes, at the same outer diameter and size, but is modified to accommodate a cylindrical screen positioned over the fluid port holes. The use of the same size, position, and location of the fluid port holes as a standard poppet housing obviates the need to recalibrate the positive pulse MWD system or conduct testing to ensure proper operation. The screen is prevented from moving longitudinally along the wellbore by a tapered section of the poppet housing and a connector ring attached to the downwell end of the poppet housing. The tapered section of the poppet housing matches the outer diameter of the screen and connector ring to prevent any shoulders that may hinder insertion of the tool into the wellbore or interrupt the flow of drilling mud. 
     The screen has slits that prevent LCM and other debris from entering the fluid ports and disrupting operation of the signal shaft. While fluid ports in standard poppet housings allow particles with a maximum dimension of 3/16 of an inch to enter, the preferred embodiment of the screen only allows particles with a maximum dimension of 1/32 of an inch. This reduction in size of the particles prevents the entry of larger sized particles that are capable of inhibiting the function of the signal shaft. Furthermore, particles that are capable of passing through the screen are generally sufficiently small to not disrupt operation of the signal shaft. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         FIG. 1  is a profile view of the preferred embodiment. 
         FIG. 2  is a side view of the preferred embodiment of the poppet housing. 
         FIG. 3  is a downwell cross sectional view of the preferred embodiment of the first section of the poppet housing at  3 - 3 . 
         FIG. 4  is a downwell cross sectional view of the preferred embodiment of the housing screen at  4 - 4  of  FIG. 5 . 
         FIG. 5  is an exploded profile view of the preferred embodiment. 
         FIG. 6  is a profile view of the preferred embodiment in the lower end of a positive pulse MWD tool including the helix housing. 
         FIG. 7  is an interior cross-sectional view of the preferred embodiment in the lower end of a positive pulse MWD tool including the helix housing. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     When used with reference to the FIG.s, unless otherwise specified, the terms “upwell,” “above,” “top,” “upper,” “downwell,” “below,” “bottom,” “lower,” and like terms are used relative to the direction of normal drilling through a formation. Thus, normal drilling operations result in a production string originating from the surface downwell without regard to whether the tubing string is disposed in a vertical wellbore, a horizontal wellbore, or some combination of both. 
       FIG. 1  shows a side profile view of the preferred embodiment of the present invention  1 . The preferred embodiment 1 comprises a poppet housing  10 , screen  50  and connector ring  60 . The preferred embodiment 1 is generally cylindrical and has a downwell opening  2  located at the downwell end  3  and an upwell opening  4  located at the upwell end  5 . The downwell opening  2  and upwell opening  4  provide access to the substantially cylindrical interior cavity  13  of the preferred embodiment where fluid may flow between various MWD housings, generally flowing from upwell end  5  to downwell end  3 . 
     As will be described herein, screen  50  is concentrically positioned around the poppet housing  10  and prevented from moving upwell or downwell by the poppet housing  10  and connector ring  60 . Slits  51  are arranged along the circumference of the screen  40  and extend longitudinally, or parallel along the well bore. In other embodiments, the slits may be formed of a variety of different openings including but not limited to a plurality of holes or slits positioned latitudinally or perpendicular to the wellbore as long as slits are capable of preventing entry of LCM or other debris that would ordinarily enter through fluid ports (described herein). 
       FIG. 2  shows the side profile of the poppet housing  10  of the preferred embodiment. Poppet housing  10  is generally cylindrical in shape and comprised of three sections comprising a first section  15 , tapered second section  30 , and connecting third section  40 . In the preferred embodiment, the first section  15 , tapered second section  30 , and connecting third section  40  are integral. Poppet housing  10  is generally constructed of beryllium copper. 
     Connecting third section  40  is cylindrical in shape having a terminal upwell end  41  and downwell end  42  that abuts tapered second section  30  at shoulder  33 . External thread connectors  43  are circumferentially positioned on the exterior surface  44  of side wall  45  for purposes of threadably connecting with internally threaded standard upwell MWD componentry, such as batteries or additional housings. 
     The tapered second section  30  has a substantially cylindrical sidewall  35 , an upwell end  31 , and a downwell end  32 . Upwell end  31  abuts connecting third section  40  creating shoulder  33 . The diameter of tapered second section  30  at upwell end  31  is larger than the diameter of connecting third section  40 . Standard upwell MWD componentry, once connected to the threadable connectors  43  of connector third section  40 , abuts shoulder  33  and creates a generally seamless fit with the exterior surface  34  of sidewall  35  at the upwell end  31 . In other words, the exterior diameter of standard upwell MWD componentry threadably connected to connector third section  40  is roughly the same exterior diameter of the sidewall  35  at the upwell end  31  of tapered second section  30 . Thus, no sharp plateaus or shoulders are created between MWD upwell componentry and tapered second section  30  once upwell MWD componentry is threadably connected. 
     Tapered second section  30  has varying thicknesses of sidewall  35  resulting in three distinct sections: small diameter section  36 , tapered section  37 , and large diameter section  38 . Small diameter section  36  is located at the upwell end  31 . Large diameter section  38  is positioned at the downwell end  32 . Connecting the small diameter section  36  and large diameter section  38  is a tapered section  37 . Sidewall  35 , as seen in  FIG. 7 , varies in thickness to accommodate the changing diameter in order to maintain an interior cavity of the poppet housing similar to the standard MWD poppet housing. In the preferred embodiment, exterior surface  34  of sidewall  35  is smooth with no breaks as small diameter section  36 , tapered section  37 , and large diameter section  38  are integral. This allows for ease of insertion into the drill casing and drilling string as the poppet housing  10  does not have any exposed shoulders to get hung up on equipment downhole. 
     First section  15  has a sidewall  23 , an upwell end  16  and a terminal downwell end  17 . Upwell end  16  abuts the downwell end  32  of tapered second section  30 . First section  15  has a smaller diameter than the large diameter section  38  of the tapered section  30 . In the preferred embodiment, the outer diameter of the first section  15  is similar to the small diameter section  36  of the tapered second section  30  and similar to the outer diameter of a traditional poppet housing. Two raised collars  18 ,  19  of equal diameters are located circumferentially around the sidewall  23  of the first section  15 . The upwell raised collar  18  abuts the downwell end  32  of the tapered second section  30 . The diameter of the upwell raised collar  18  is smaller than the large diameter section  38  of the tapered second section  30  but larger than the diameter of the first section  15  which results in a shoulder  20  located between the downwell end  32  of the tapered second section  30  and the upwell raised collar  18 . The downwell raised collar  19  is located near the terminal downwell end  17  but not physically at the terminus. Downwell shoulder  21  is created between the downwell side of the downwell raised collar  19  and the exterior surface  22  of the sidewall  23 . In the preferred embodiment, raised collars  18 ,  19  are integrally made with into the poppet housing  10 . 
     Disposed through the sidewall  23  of first section  15  between the upwell raised collar  18  and the downwell raised collar  19 , but located more proximal to the upwell raised collar  18 , are fluid ports  24 . In the preferred embodiment as seen in  FIG. 3 , there are sixteen identically sized and equidistantly spaced fluid ports  24  circumferentially disposed through sidewall  23  of the first section  15 . In the preferred embodiment, the angle of degree between the center of a fluid port and the center of the next adjacent fluid port is 22.5 degrees and the approximate diameter of each fluid port at the exterior surface  22  is 3/16 of an inch. The location, size, and spacing of the fluid ports  24  are consistent with standard positive pulse MWD componentry. 
     Fluid ports  24  define a pathway for fluid to enter the interior cavity  13  of the poppet housing  10 . The interior cavity  13  includes internal threadable connectors  25  (seen in  FIG. 7 ) positioned on the interior surface  14  of sidewall  23  between the terminal downwell end  17  and the fluid ports  24  on the interior surface of the poppet housing  10 . An interior shoulder  26  (seen in  FIG. 7 ) is positioned within the interior cavity  13  towards the upwell end  31  of the tapered second section  30 . The interior cavity  13  is substantially similar to existing MWD poppet housings and is well known in the art. 
       FIG. 5  is an exploded view of the preferred embodiment 1. Screen  50  is tubular in structure having a sidewall  52  with an inner and outer diameter, a terminal upwell end  53  and a terminal downwell end  54 . In the preferred embodiment, the screen is made of a material with an approximate thickness of 0.075 inches. The outer diameter of the sidewall  52  is approximately equal to the circumference of the large diameter section  38  of the tapered second section  30 . Slits  51  are disposed circumferentially through the sidewall  52  and extend longitudinally from near the terminal upwell end  53  to past the mid-point of the screen  50 . In the preferred embodiment as seen in  FIG. 4 , there are thirty-six identically sized and equidistantly spaced slits  51  disposed circumferentially through the sidewall  52  with the angle of degree between the center of a slit and the center of the next adjacent slit is 10 degrees. In the preferred embodiment, the length of the screen is 2.5 inches with the slits  51  beginning approximately 0.25 inches from the terminal upwell end  53  and extending 1.5 inches towards the terminal downwell end  54 . In the preferred embodiment the approximate width of each slit is 1/32 of an inch. In the preferred embodiment, screen  50  is machined from stainless steel and is heat treated. 
     Connector ring  60  is a layered cylindrical shape with a thin sidewall  61  located on the upwell section  62  having an inner and outer diameter. Connector ring  60  also has a thick sidewall  63  located on the downwell section  64  having an inner and outer diameter. In the preferred embodiment, the upwell section  62  and a downwell section  64  are integral. In the preferred embodiment, the inner diameters of the thin sidewall  61  and thick sidewall  63  are equal whereas the outer diameter of the thin sidewall  61  is smaller than that the outer diameter of the thick sidewall  63  resulting in shoulder  65 . The outer diameter of thin sidewall  61  is smaller than the inner diameter of screen  50  which allows for upwell section  62  to concentrically fit within screen  50 . The outer diameter of thick sidewall  63  is approximately equal to the outer diameter of screen  50 . The length of connector ring  60  is approximately equal to the distance between shoulder  20  and the terminal downwell end  17  of the first section  15 . 
     The inner diameter of connector ring  60  is uniform for both the upwell section  62  and downwell section  64 . The inner diameter of connector ring  60  is slightly larger than the outer diameter of the first section  15  which allows for an interference or frictional engagement between the interior surface of the connector ring  60  and the exterior surface  22  of the first section  15 . 
     Abrasion ring  70  is cylindrical in shape with a sidewall  71 , having an inner and outer diameter, a terminal upwell end  72  and a terminal downwell end  73 . The inner diameter of abrasion ring  70  is substantially equal to the inner diameter of terminal downwell end  17  of first section  15 . The outer diameter of abrasion ring  70 , at the terminal upwell end  72  is substantially equal to the outer diameter of the connector ring  60 , outer diameter of screen  50 , and the outer diameter of the large diameter section  38  of the tapered second section  30 . The thickness of the sidewall  71  at the terminal upwell end  72  is substantially equal to the combined thickness of terminal downwell end  17  of first section  15  and downwell terminal end  68  of connector ring  60 , allowing terminal upwell end  72  of abrasion ring  70  to fit flush against terminal downwell end  17  of first section  15  and downwell terminal end  68  of connector ring  60 . Terminal downwell end  73  of abrasion ring  70  features a tapered or chamfer edge  74 . In the preferred embodiment the chamfer is approximately forty five degrees and 0.188 inches long. 
       FIG. 6  shows the preferred embodiment as viewed as part of the positive pulse MWD lower end assembly comprising a poppet housing  10 , screen  50 , connector ring  60 , abrasion ring  70 , helix housing  80 , and signal shaft  95 . Helix housing  80  is generally tubular in shape with a sidewall  81 , terminal upwell end  82  (seen in  FIG. 7 ) with external threaded connectors  83 , terminal downwell end  84 , raised shoulder  85 , and vents  86 . The exterior diameter of the helix housing  80 , from the terminal upwell end to the raised shoulder  85 , is smaller than the interior diameter of the first section  25 , but large enough for the external threaded connectors  83  and the internal threaded connectors  25  to threadably mate (seen in  FIG. 7 ). 
     A slotted key receptacle  81  is disposed on the exterior surface  88  of the sidewall  81 . Slotted key receptacle  81  is capable of fitting within standard MWD muleshoes to ensure proper placement within the drill string. When fitted in a standard muleshoe, the tapered edge  74  of abrasion ring  70  is positioned against a receiving section of the muleshoe that is inversely proportioned to the tapered edge  74 . 
     Helix housing  80  is well known within the art. Signal shaft  95  is located within interior cavity  89  of helix housing  80  and extends into the interior cavity  13  of poppet housing  10 . Signal shaft  95  is comprised of a hollow shaft  96 , flow plug  97  located at the downwell end, and a piston  98  (as seen in  FIG. 7 ) located on the upwell end of the hollow shaft  96 . Piston  98  has seals  99  located on around its external circumference. Signal shaft  95  is of sufficient length to partially extend beyond terminal downwell end  84  of helix housing  80 . Drilling mud may flow from upwell opening  4  through interior cavity  13  and through signal shaft  95  and out flow plug  97 . 
       FIG. 7  is a cross sectional view of  FIG. 6 . When assembled, screen  50  is concentrically positioned over first section  15  where slits are positioned over fluid ports  24 . Terminal upwell end  53  rests over upwell raised collar  18 , abutting tapered second section  30  at shoulder  33 , and rests over downwell raised collar  19 . Due to the raised collars, gap  56  exists between exterior surface  22  of first section and the interior surface of screen  50 . Thus a gap exists between the screen  50  and fluid ports  24 . Connector ring  60  is then attached to the first section  15  through the frictional engagement as described above. Once in place, terminal upwell end  67  of connector ring  60  abuts downwell raised collar  19  and the downwell terminal end  68  of connector ring  60  lines up with terminal downwell end  17 . Screen  50  is prevented from moving longitudinally by shoulder  33  and downwell section  64  of connector ring  60 . Any upwell force from connector ring  60  is received by the downwell raised collar  19  and not by the screen  50 . This allows the screen  50  to rotate freely around the first section  15  and prevents the slits from opening beyond their designed width as a result of longitudinal compressional forces that occur during assembly and/or insertion of the tool downhole. 
     Abrasion ring  70  is concentrically positioned over the terminal upwell end  82  with the tapered edge  74  slid towards raised shoulder  85 . The terminal downwell end  73  abuts raised shoulder  85  and prevent abrasion ring  70  from moving further downwell. 
     The terminal upwell end  82  of helix housing  80 , with signal shaft  95  located in interior cavity  89 , is inserted into poppet housing  10  through downwell opening  4 . The external threaded connectors  83  of helix housing  80  threadably mate with internal threadable connectors  25  of first section  15  until abrasion ring  70  is flush terminal downwell end  17  of first section  15  and downwell terminal end  68  of connector ring  60 . Raised shoulder  85  further secures the abrasion ring  70  from moving downwell. Seal  90  on helix housing  80  located upwell from external threaded connectors  83  seals against interior surface  14  of poppet housing  10 . 
     Piston  98  of signal shaft  95  has a series of seals  99  that engage the interior surface  14  of poppet housing  10 , creating a barrier to prevent fluid from passing around the outside of the signal shaft  95 . Piston  98  is positioned upwell from fluid ports  24 . Spring  100  engages the head  99  of signal shaft  95  with the other end of the spring  100  positioned against interior shoulder  26  of the poppet housing. Depending on the pressure of drilling mud entering slits  51  and into fluid ports  24 , the signal shaft  95  may move upwell or downwell. In operation, the signal shaft  95  moves longitudinally along the wellbore in relation to the poppet housing  10  and helix housing  80 . 
     In operation, drilling mud flows between slits  51  of screen  50  and into the gap  56 . From gap  56 , drilling mud flows into the fluid ports  24  and into the interior cavity  13  of the poppet housing  10 . Screen  50  prevents LCM and other debris from entering the fluid ports. In the preferred embodiment screen  50  is capable of filtering particles that have a smallest dimension of 1/32 of an inch. Only particles in which the maximum dimension is less than 1/32 of an inch may pass through slits  53 . In contrast, particles in which the maximum dimension is less than 3/16 of an inch may pass through fluid ports  24 . 
     Once the drilling mud enters the interior cavity  13 , it acts on signal shaft  95  in the same manner as traditional positive pulse MWD systems known in the art. In the preferred embodiment, the amount of the drilling mud entering fluid ports  24  is the same as drilling mud entering the standard fluid ports in standard positive pulse MWD systems. 
     Overall the High LCM Positive Pulse MWD Component functions identically in regard to traditional positive pulse MWD components in that functionality and operational aspects of the positive pulse methods function as known in the art. However, due to the screen and design of the high LCM positive pulse MWD component, the system may function in a high LCM environment without suffering from clogging and reduced efficiency in the operation of drilling. A further advantage of the present invention is the ability to replace the screen without having to replace other parts or portions of the lower end assembly. 
     The present invention is described above in terms of a preferred illustrative embodiment of a specifically-described High LCM Positive Pulse MWD Component. Those skilled in the art will recognize that alternative constructions of such an apparatus can be used in carrying out the present invention. Other aspects, features, and advantages of the present invention may be obtained from a study of this disclosure and the drawings, along with the appended claims.