Abstract:
The invention relates to base pipe with slots cut into the peripheral wall to form compaction absorber segments that are arranged to permit the base pipe to be compacted in length without buckling or transferring excessive compressive forces to other pipe sections when a poorly consolidated formation shrinks due to production from the formation. Over time, the slots close as the base pipe shrinks in length and production continues through conventional holes in the base pipe.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a non-provisional application which claims benefit under 35 USC §119(e) to U.S. Provisional Application Ser. No. 61/165,304 filed Mar. 31, 2009, entitled “Compaction Tolerant Basepipe for Hydrocarbon Production,” which is incorporated herein in its entirety. 
     
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
       [0002]    None. 
       FIELD OF THE INVENTION 
       [0003]    This invention relates to base pipe which is used in a production tubing/liner string in a fluid production well and especially a hydrocarbon production well where the base pipe is positioned in the proximity of the fluid production formation and has holes and typically a screen around the base pipe to allow the fluid into the production string while substantially excluding sand and other solid particles. 
       BACKGROUND OF THE INVENTION 
       [0004]    Prior to extracting fluids from a downhole formation, the fluids occupy space within the formation. In the process of producing fluids from a formation, the fluid pressure will generally decline. Reduced pore pressure in the reservoir rock will increase the effective stress and thereby cause the rock itself to shrink, and thus the reservoir will compact. Reservoir compaction may then cause subsidence at the surface. Subsidence is a substantial concern in the production of hydrocarbons, especially where the formation is comprised of unconsolidated sands or does not have significant structural integrity. Offshore platforms mounted to the seafloor and arranged to stand well above sea level and above any wave action at the sea surface have settled toward the sea because of subsidence. Actually, the amount of subsidence could be alarming if a substantial safety zone wasn&#39;t established in the design phase of the well development plan and such subsidence has been measured in as much as tens of feet. 
         [0005]    The thickness of the producing zone typically diminishes to some extent during production of well fluids, but in poorly consolidated sands and high porosity rocks may diminish by a substantial amount such as about 10% over the life of the production operation. Compaction of the producing zones exerts powerful forces on equipment and pipe in the well. Conventional base pipe is subject to buckling when the compaction of the production string is less than 2 to 3% with relatively good lateral confinement supports and it is likely that the well will have to be abandoned or recompleted if the production string has buckled. 
       SUMMARY OF THE INVENTION 
       [0006]    The invention more particularly includes a base pipe for use in a wellbore to tolerate compaction of the production zone where the base pipe includes an elongated generally cylindrical hollow body with an upper end, a lower end, a peripheral exterior wall and in interior space and at least one connector at the upper end for connecting to production tubing or liner. The base pipe further includes holes in the peripheral wall through which production fluid may pass from the outside of the base pipe into the interior space and screen mesh mounted around the peripheral wall to prevent sand and other particles from being carried by production fluids through the holes in the peripheral wall and into the interior space. Additionally, the base pipe includes compaction absorber segments spaced along the generally cylindrical hollow body to absorb longitudinal stresses and reduce the length of the elongated generally cylindrical hollow body. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0007]    The invention, together with further advantages thereof, may best be understood by reference to the following description taken in conjunction with the accompanying drawings in which: 
           [0008]      FIG. 1  is a fragmentary cross sectional view of a wellbore undergoing the stresses and illustrating a failure of a drillstring with conventional base pipe; 
           [0009]      FIG. 2  is a fragmentary perspective view of the base pipe of the present invention; 
           [0010]      FIG. 3  is a cross sectional end view of the base pipe of the present invention; and 
           [0011]      FIG. 4  is an enlarged, fragmentary side view of the base pipe particularly illustrating a compaction absorber segment. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0012]    Turning now to the preferred arrangement for the present invention, reference is made to the drawings to enable a more clear understanding of the invention. However, it is to be understood that the inventive features and concept may be manifested in other arrangements and that the scope of the invention is not limited to the embodiments described or illustrated. The scope of the invention is intended only to be limited by the scope of the claims that follow. 
         [0013]    Turning now to  FIG. 1 , a wellbore is generally indicated by the arrow  10  and extends deep into the ground G and into hydrocarbon bearing formation F. A drill string comprising pipe  15  extends down into wellbore  10  with base pipe  20  attached at the lower end. The screens and screen base pipes can be run as a part of production liner separately from the tubing string. Base pipe  20  includes holes that are not shown and a wire wrapped screen surrounding the base pipe  20  to keep sand and other solids out of the production string. Within the production string is a pump may be arranged to pump liquids to the surface for transporting to a refinery. 
         [0014]    As fluid from formation F is withdrawn to the surface  12 , the thickness of formation F may shrink over time as shown by the reduced vertical dimension of formation F in the proximity of base pipe  20 . The upper portion of the formation F has subsided along with the layers of earth over top of the formation so that the surface actually sinks or subsides. The subsidence exerts a substantial amount of compression on the length of the production string and can force a buckle as shown at  17  in the pipe  15  effectively closing off the production string and stopping or severely limiting further production. 
         [0015]    Turning now to  FIG. 2 , a section of compaction tolerant base pipe  30  is shown with compaction absorber segments  32 . The compaction absorption segments are comprised of cross cut slots  34  that extend for a substantial portion of a circumferential arc of the pipe  30 . Preferably, each cross cut slot  34  extends for about 120 degrees or about ⅓ of the circumference of the pipe  30  and are perpendicular to the axis of the pipe  30 . However, the compaction absorber segments  32  include a number of overlapping cross cut slots  34  that will work together to preferential collapse the length of the base pipe  30  without buckling or conveying excessive compressive forces up the production string to a weak point where a buckling failure or other failure may occur. 
         [0016]    The overlaps of slots  34  are preferably at least 50% the circumferential length of the tangential cuts and spaced apart by two to three times the width of the cross cuts. While the compaction absorber segments  32  are intended to accommodate the reduction in length of the base pipe  30 , they are also intended to maintain necessary strength parameters in other respects. The base pipe  30  of the present invention must retain sufficient compressive and tensile strength to be put into and withdrawn from wellbore  10  in the event the production string must be withdrawn and re-installed. Also, the base pipe  30  must have sufficient radial strength to resist forces that would tend to collapse the base pipe and close the hollow space through which fluids are produced to the surface. 
         [0017]    It should be understood that base pipe  30  includes conventional holes  36  and a screen such as wire wrap screen  38 . Wire wrap screen  38  is removed from the end of the base pipe  30  to reveal the holes  36  and slots  34 , but in practice would cover the portions of base pipe  30  that would include any openings Base pipe  30  would preferably include screw threads at each end or at the top end to connect to other lengths of base pipe in a large producing formation and to the conventional production tubing to form the production string. The bottom end of the base pipe  30  is typically closed, but may be open with screen or other mesh to prevent sand and other solids from entering the hollow interior of the base pipe  30 . 
         [0018]      FIG. 3  shows the wire wrapped screen  38  surrounding base pipe  30  with spacers  39  attached to the outside of the peripheral wall of base pipe  30  to create a space for fluids to pass fully through the screen  38  and then move toward holes  36 . It should be understood that the wire wrapped screen  38  may also be closely attached to base pipe  30  without spacers, if desired. 
         [0019]    In  FIG. 4 , the compaction absorber segments  32  are more clearly illustrated where it can be seen that each of the slots  34  have a dimension called slot width  44 . Also, the slots  34  are spaced by a dimension called slot spacing  42  and overlap one another by a dimension called slot overlap  40 . With the slot overlap  40 , slot spacing  42  and slot width  40 , some relative ratios can be identified. For example, it is preferred for the slot spacing to be at least two times the slot width and preferably at most four times the slot width. 
         [0020]    The segments  32  are illustrated with four perfectly transverse slots, but three, four, five or six or more substantially transverse slots that overlap with suitable slot width and slot overlap to slot spacing ratios may perform adequately. In this example, the slots are cut slightly offline from the circumference of the base pipe  30  such that each slot overlaps one adjacent slot closer to the bottom end of the base pipe while the other end overlaps the other adjacent slot closer to the top end of the base pipe. Also, it should be understood that six or eight nearly transverse overlapping slots may be used for reservoirs that are highly likely to compact during fluid production. 
         [0021]    It is preferred that each slot is at least three millimeters in width and up to about ten millimeters in width. 
         [0022]    Another parameter of the base pipe of the present invention is segment spacing which is the distance one compaction absorber segment  32  is from the next adjacent compaction absorber segment  32 . While the spacing may be irregular, it is preferred that the segment spacing would be less than four times the diameter of the base pipe  30  and more preferably less than three times the diameter. At the same time, it is preferred that the segment spacing is at least the diameter of the base pipe  30  and more preferably at least twice the diameter of the base pipe  30 . 
         [0023]    Finally, the scope of protection for this invention is not limited by the description set out above, but is only limited by the claims which follow. That scope of the invention is intended to include all equivalents of the subject matter of the claims. Each and every claim is incorporated into the specification as an embodiment of the present invention. Thus, the claims are part of the description and are a further description and are in addition to the preferred embodiments of the present invention. The discussion of any reference is not an admission that it is prior art to the present invention, especially any reference that may have a publication date after the priority date of this application.