Abstract:
A wire cross-sectional shape for a wire wrap screen provides a primary and secondary gap with a contained circumferential volume in between. The secondary gap extends screen life by taking the place of the primary gap if erosion opens the primary gap and lets the larger solids get past. The closed space between the primary and secondary gaps also has the effect of reducing velocity due to the enlarged volume before the secondary gap is reached while also creating turbulence between the gaps to slow the fluid velocity to protect the secondary gap. All or parts of the wire outer surface can optionally be coated to extend service life.

Description:
FIELD OF THE INVENTION 
       [0001]    The field of the invention is wire wrap screens for subterranean use and more particularly where the wire section presents dual gaps with a velocity containment feature in between. 
       BACKGROUND OF THE INVENTION 
       [0002]    Screens are employed in completions to retain solids produced with the desired hydrocarbons. There are many styles for such screens but a popular design is commonly known as a wire wrap screen. The design of such a screen involves using a perforated base pipe and securing axially oriented mounting rods to the exterior of the base pipe. The wire is then helically wrapped over the mounting rods and secured to them at each intersection. The spacing between adjacent windings determines the particle size that is allowed to get through the screen. Sometimes punched openings are provided in outer jackets that cover over the wire wrap to protect the screen during running in. 
         [0003]    Many optimizations of the performance of such screens have been attempted in the past. Some of these have focused on the cross-sectional shape of the wire with an eye toward keeping the manufacturing process reliable while attempting to control the flow direction for the stated purposes of enhancing throughput or reliability of operation. One issue that affects such screens is the potential for erosion from high velocity fluids that entrain produced solids. Some designs take a triangular cross-section for the wrapped wire and overlay exterior filtering layers for protection as in U.S. Pat. No. 8,701,757. Another design illustrated in US 20100258300 uses a round section for the wrap wire and varying spacing between the windings along the length of the screen. WO 2010143060 shows triangular or near trapezoidal shapes for wire cross-section with the near trapezoidal formed from taking a triangular shape and trimming one of the angles back to an arc shape. Also of interest regarding the above-mentioned wire cross-sectional shapes are the following references: US 2013/0092391 (note paragraph 36 noting that the wire shape can control flux in the screen); US 2010/0224359 (triangular with a rounded corner or trapezoidal); U.S. Pat. No. 7,188,687 (keystone shaped cross-section); U.S. Pat. No. 8,267,169 (FIGS. 3 and 4 showing triangular with rounded outer face or diamond or arrowhead shapes for the wire section); U.S. Pat. No. 8,291,971 (triangular); US 2014/0158295 (triangular with outer surface coating in FIG. 14B); U.S. Pat. No. 8,267,169 (triangular with rounded outer surface in FIG. 8); US 2005/0082060 (triangular in FIG. 7) and U.S. Pat. No. 7,273,106 (triangular in FIG. 11). 
         [0004]    What is common to all these designs is that regardless of the shape employed for the wire cross-section, there is but a single gap between windings such that when erosion enlarges this gap the larger particles will get through and the base pipe underneath will also be exposed to erosive effects of high velocity fluids with entrained solids. The present invention seeks to improve the existing designs by offering the spacing that defines the size of the particles screened out in duplicate so that the sizing capability for excluded solids remains if one of the spacings is enlarged by erosive effects. Furthermore the backup spacing is further protected from erosive effects of high velocity fluids by virtue of the enclosed circumferential space between the outer and inner gaps because the enlarged volume between the inner and outer gaps reduces fluid velocity by the turbulence that is created to further protect the inner gap of the wire wrap and add longevity to the screen in subterranean environments. The enlarged volume area can be geometrically designed to move the erosion from the primary or secondary gap to an inner sacrificial area that does not compromise sand control. These and other aspects of the present invention will be more readily understood by those skilled in the art from a review of the detailed description and the associated drawings while recognizing that the full scope of the invention is to be determined by the appended claims. 
       SUMMARY OF THE INVENTION 
       [0005]    A wire cross-sectional shape for a wire wrap screen provides a primary and secondary gap with a contained circumferential volume in between. The secondary gap extends screen life by taking the place of the primary gap if erosion opens the primary gap and lets the larger solids get past. The closed space between the primary and secondary gaps also has the effect of reducing velocity due to the enlarged volume before the secondary gap is reached while also creating turbulence between the gaps to slow the fluid velocity to protect the secondary gap. All or parts of the wire outer surface can optionally be coated to extend service life. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0006]      FIG. 1  is a perspective view of adjacent windings of wire wrap screen showing the general I-beam cross-sectional shape; 
           [0007]      FIG. 2  is a section view of another embodiment where the section has the appearance of mirror image homes with sloped roofs and adjacent peaks; 
           [0008]      FIG. 3  is a section view of another embodiment where the section is of dual T-shaped wire where one wire is an inverted T shape and the adjacent is a right side up T-shape; 
           [0009]      FIG. 4  is another alternative design where the passage between inner and outer face gaps makes several turns. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0010]      FIG. 1  shows in perspective two windings as they would be positioned on a wire wrap screen that is not shown. The windings  10  and  12  define a primary gap  14  and a spaced secondary gap  16 . In between, there are facing arcuate surfaces  18  and  20 . Flow through the screen progresses from gap  14  to gap  16  and through openings  24  in base pipe  22 . The flow in production mode is in the direction of arrow  26 . The cross-sectional shape is akin to an I-beam with a circular web. However, a straight web to make the cross-section more akin to a structural I-beam shape is also contemplated. A few support rods  28  and  30  that run axially on the base pipe  22  and are secured with tack welds  32  and  34  are illustrated for reference while those skilled in the art will recognize that additional rod can be used to create the needed structural strength for the assembly. Equipment to continuously wind the windings such as  10  and  12  is also known which also applies the weld or other attachment method to the rods  28  and  30  as the windings make contact in a continuous process. Preferably the gaps  14  and  16  are identical but they can also be different with  14  being larger  16  or  16  being larger than  14 . Along the screen length the preferred pitch is constant although gaps  14  or  16  that change along the length of the screen are also contemplated. A coating  36  can be applied to an outer face  38  and if desired the coating can be wrapped around into the rounded circumferential or annular space defined between curved surfaces  18  and  20  for each of the windings that make up the screen or for less than all of the windings, if desired. The coating has the objective of protecting the windings  12  and  14  from the effects of high fluid velocity. Also along those lines the winding material can be made from a hard metal or a composite or a shape memory alloy. The gaps  14  and  16  can change as between the time of manufacturing and when placed in service if for example a shape memory alloy is used. The gaps can be manufactured at a larger dimension that can close up as the transition temperature is reached if the windings are from a shape memory alloy. 
         [0011]    Those skilled in the art will readily appreciate the differences from known designs. The wire shape creates a primary and a secondary gap so that screening can continue even if there is wear of parts of the primary gap without allowing larger particulates to get through as the secondary gap is still in service to stop such particles. The erosive effects of high fluid velocity are attenuated in two ways. First, the enlargement of the flow area after passing through gap  14  and before reaching gap  16  tends to slow the fluid velocity as does the turbulence that is created due to the change and the enlargement of the flow area between the gaps. Additionally, the enlarged space between the gaps can collect solids that would not have passed through gap  14  but for it wearing during service. Of course if there is a surrounding gravel pack in the annular space around the windings  10  and  12  solids can also accumulate there by design. The provision of multiple gaps provides for a longer service life for excluding solids down to the desired dimension. The enlarged gap creates turbulence and a velocity slowdown from the shape of the space and the fact that the flow area dimension rises either gradually or in a stepwise manner. While straight or arcuate surfaces  18  and  20  have been described, those surfaces can also be smooth or roughened to act more as a velocity deterrent. 
         [0012]    Referring to  FIG. 2  windings  50  and  52  are illustrated on base pipe  54  with the axially oriented support rods omitted for greater clarity. Here again are primary and secondary gaps  56  and  58  with the production flow in the direction of arrow  60 . Surfaces  62  and  64  form a V-shape facing another V-shape made of surfaces  66  and  68 . These surfaces can be rounded as they extend from a middle region  70  or  72 . While regions  70  or  72  look like a narrow ridge, the width of such a ridge can be adjusted for addressing structural integrity issues. Optionally, pass through openings  74  can be provided at the ridges  70  or  72  or offset from those locations to address issues of structural integrity. Cross flow between windings  50  and  52  after gap  56  is contemplated and would occur in the direction of arrow  76 . The cross flow ports such as  74  create further turbulence and reduce the erosion effects on gap  58 . Such openings can also reduce the pressure drop across the screen for a given flow rate as compared with the same design without such openings. Beyond, this the recited variations described with regard to  FIG. 1  are also intended to apply to the design shown in  FIG. 2 . Although spiral windings are contemplated independent adjacent rings of wire are also contemplated. 
         [0013]    Referring to  FIG. 3  two adjacent windings  80  and  82  that together define an outer gap  84  and an inner gap  86 . The wires are preferably the same T-shape with one being upside down and the other being right side up. Together they define an enlarged flow space  88  that is wider than gaps  84  or  86 . Gaps  84  and  86  can be the same size or one can be larger than the other in either order. Arrow  90  represents the direction of incoming fluid flow. Arrow  92  represents the continuation of that flow toward gap  86 . On the way through gap  86  what erosion effects there will be will occur at corners  94  on wire  82  and corners  96  on wire  80 . However, despite erosion at corners  94  and  96  there will still be an original dimension represented by arrow  100  that is the same as the gap  86  initially. Thus as the corners  94  and  96  are sacrificed the original gap  86  dimension is maintained. This extends the longevity of the wire wrap screen that is built according to the  FIG. 3  embodiment. Other options as discussed with regard to  FIGS. 1 and 2  are equally applicable to the  FIGS. 3 and 4  embodiments. 
         [0014]      FIG. 4  shows two adjacent wraps of a single wire design where the wraps are  110  and  112 . Arrow  114  represents flow into the outer face gap  116 . Circle  118  is intended to schematically illustrate the size of the gap  116  and to show that it has some depth in the direction of flow indicated by arrow  114 . Similarly, circle  120  is intended to show that the inner surface gap  122  has a depth to it as well. In between gaps  116  and  122  there is a tortuous path where the flow is forced to make at two turns after entering in the direction of arrow  114 . Some of the flow is turned by surface  124  while the flow pattern is reoriented by surface  126  either of which can be a continuous arc or multiple adjacent flat or curved surfaces that have the result of preferable shooting the flow through gap  122  as close as possible to the skewed orientation of the gap  122  to minimize erosion. Even if erosion removes some of the wire at locations  126  or  128  the effective dimension of the gap  122  is retained as there is a height to the gap between locations  126  and  128  that continues to remain the same despite the onset of erosion at  126  or  128 . 
         [0015]    The above description is illustrative of the preferred embodiment and many modifications may be made by those skilled in the art without departing from the invention whose scope is to be determined from the literal and equivalent scope of the claims below: