Abstract:
The present invention allows a well to be produced through a screen without the need for a gravel pack. This is accomplished by the placement of an expandable screen that can move radially outwardly when placed at the desired location against the wellbore and be porous enough with sufficient open area to allow production from the formation. The screen is placed in the desired location by using coiled tubing which can be preperforated for a support for the screen. The screen is protected during delivery to the desired location in the wellbore by providing a disposable or removable outer cover which can be disposed of after proper location on the screen in the wellbore.

Description:
This application claims the benefit of U.S. Provisional Application No. 60/081,711 filed Apr. 14, 1998. 
    
    
     FIELD OF THE INVENTION 
     The field of this invention relates to downhole screens preferably delivered on coiled tubing where the tubing can also be expanded against the screen to push it against the wellbore. 
     BACKGROUND OF THE INVENTION 
     In typical completions in the past, metallic screens have been inserted on rigid or coiled tubing into a zone in the wellbore for production. Prior to producing the zone, sand particles were delivered outside the screen in a technique known as gravel packing. Screens have also been used that come prepacked with a sand layer as an alternative to the traditional gravel packing techniques or to be used in conjunction with the placement of sand outside the screen. The gravel packing procedures especially in horizontal completions left uncertainties as to whether the sand had been sufficiently distributed uniformly in the annular space so as to provide an effective gravel pack. Additionally, the gravel packing procedure took valuable time to accomplish and required the use of surface equipment to handle the material for placement in the wellbore. Another disadvantage of traditional gravel packing procedures is that an annular space around the screen had to be left so that the gravel could be placed there. The end result was the inside diameter within the screen was necessarily small to allow for the presence of the annular space. This constriction in size could also adversely affect the production of the formation to the surface. 
     In using certain drilling techniques, particularly in unconsolidated formations, the drilling mud would form a barrier adjacent the wellbore which cause subsequent plugging when the production began, even with screens and gravel packs being deployed. 
     A more ideal situation for producing a formation is to leave the wellbore in its drilled state so as to create the least amount of disturbance to the formation which has just been drilled. Traditional techniques leaving an annular gap which would be gravel packed, further involved risks of damaging the formation in the gravel packing process, such as when situations occurred that would allow fluid to convey the gravel to also apply hydraulic forces on the formation as well as incompatibilities between the formation and the fluids used to convey the gravel. 
     SUMMARY OF THE INVENTION 
     One of the objects of the present invention is to allow a well to be produced through a screen without the need for a gravel pack. This objective is accomplished by the placement of an expandable screen that can move radially outwardly when placed at the desired location against the wellbore and be porous enough with sufficient open area to allow production from the formation. Another objective is to be able to easily place the screen in the desired location. This objective is met in one way by using coiled tubing which can be preperforated for a support for the screen. Another objective is to protect the screen during delivery to the desired location in the wellbore by a providing a disposable or removable outer cover which can be disposed of after proper location of the screen in the wellbore. These and other objectives and the manner in which the apparatus and method accomplishes the objectives are further described below in the description of the preferred embodiment. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a sectional view of a deviated wellbore showing the apparatus expanded against the wellbore. 
     FIG. 2 is the section view along lines  2 — 2  of FIG.  1 . 
     FIG. 3 is the section view of FIG. 2 shown before expansion of the inner tube against the filtering material. 
     FIG. 4 is a segment which can be rolled longitudinally or spirally into flexible tubing which gives underlying support to the filter or media. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The preferred embodiment is illustrated in operation in FIG. 1. A coiled tubing reel  10  carries a continuous length of tubing  20 , at least a portion of which is preferably made from a perforated material as shown in FIG.  4 . As seen in FIG. 4, segment  12  has a plurality of perforations  14  which can be arranged in any order either random or in repeating pattern. The segment  12  can be punched for the holes  14  or the holes  14  can be placed there in any other known technique and in any order. The desirable goal is to have approximately a 30 or 40 percent open area when the segment  12  is rolled into a tubular shape. The segment  12  can be rolled longitudinally so that edges  16  and  18  are brought together to make a longitudinal seam which is welded or otherwise closed up. Alternatively, the segment  12  can be spirally wound so that edges  16  and  18  come together in a continuous spiral seam, with the advantage in spiral winding being that a particular outside diameter of a tubular configuration can be obtained with any given width of segment  12 . This should be compared to rolling the segment  12  into a tube where its width determines the diameter of the tube that is formed when edges  16  and  18  are aligned and joined in a technique well known in the art. 
     The openings or holes  14  can be put on the tubing made from segment  12  for only a portion of the coiled tubing string  20 . The segment  12  can be as long as the finished coiled length of the tubing  20  with openings  14  placed at the desired locations. Using conventional surface equipment and reel  10 , the flexible tubing  20  can be quickly run into the wellbore  22  to place the perforated segment or segments at the desired locations. 
     FIG. 2 shows in section the tube  20  made from the segment or segments  12  along with openings  14 . Wrapped around the openings  14  is an opened grid structure which can be made from metallic or composite or other nonmetallic materials. The purpose of the grid  26  is to provide a support off of tube  20  for the open cell filter media  28 . In the preferred embodiment, the media  28  is made of Viton® and is an open cell structure akin to a sponge material such as is available from Mosites Rubber Company of Fort Worth, Tex. under Product No. 10292. The filter media  28  is in the form of a cylinder over grid  26  so that upon expansion, one portion of filter media  28  does not exhibit sliding movement with respect to another portion. The opening size can be made to suit. The significant feature of the filtering material  28  is that it is flexible. Thus, when the string  20  is preformed into a corrugated shape as shown in FIG. 3, by using known techniques such as pulling it through a die, the filter material  28  can then be applied over it as shown in FIG.  3 . Thereafter, when the material  28  is properly positioned in the wellbore, a known expansion tool illustrated schematically as  30  in FIG. 1 can be inserted into the string  20  to take the initial shape shown in FIG.  3  and expand the string  20  under the filter material  28  to a rounded shape as shown in FIG.  2 . As a result, the filter material which is flexible expands with the underlying tubular  20  as the shape of tubular  20  changes from that of FIG. 3 to that of FIG.  2 . 
     A cover material  32  can overlay the filter material  28  for running in, so as to protect the filter material  28  from gauges or cuts during run-in. The material can be a thin sheet which snaps upon the slightest expansion of the corrugated tubular  20 . It can be a elastomeric material that literally rips at the slightest expansion of the underlying corrugated tubular  20  as shown in FIG.  3 . Other materials for the cover  32  can be employed without departing from the spirit of the invention or, in a particular application, the cover itself can be eliminated. A material which dissolves or is chemically attacked over time can also be employed as a cover  32  such that it will no longer be in the way when it is desired to put the well in production. 
     Significant expansions volumetrically can be obtained in changing the shape of the tubular  20  from the corrugated shape, such as shown for example in FIG. 3 to the rounded shape as shown in FIG.  2 . While a particular four-lobe arrangement of the corrugated shape is shown in FIG. 3, other initial shapes are within the purview of the invention. The significant thing is that the underlying support structure which comprises the corrugated segment of the string  20 , as shown in FIG. 3, is capable of volumetrically expanding as to bring the filter material  28  into contact with the wellbore as drilled. The initial corrugated shape also permits insertion in smaller wellbores. The initial shape does not have to be corrugated. It can be round and be expanded downhole. 
     This technique is particularly advantageous in under-balanced drilling where circulating mud is not used. In these situations, particularly where shale is encountered, the advantage of this type of drilling can be retained by use of the apparatus and method as described. The initial shape of the wellbore is retained by the assembly when the string  20  is expanded under the filter material  28  so as to push the filter material  28  up against the wellbore  22 . In so doing, the formation can be allowed to flow through the filter material  28  without the presence of an annular space around the outside of the filter material. The traditional gravel packing is eliminated and the flow area within the tubular  20  after it has been expanded to a rounded shape is larger than it otherwise would have been using a traditional gravel pack which requires the annular space for the gravel necessitating a smaller inside diameter inside the screen. 
     It should be noted that it is within the purview of this invention to produce a formation through the use of a coiled tubing string such as  20  which is perforated with openings or holes  14 . A tubing string  20  so perforated with openings  14  can be used in conjunction with traditional gravel pack techniques to produce a formation. In the preferred embodiment, the open cell filter material  28  preferably made of an elastic preferably elastomeric material such as Viton® is overlaid on the corrugated tubular  20  as shown in FIG.  3 . The stretchable qualities of the filter material  28  allow its use in conjunction with an initially corrugated tube  20  as shown in FIG. 3 or a noncorrugated tube, and allow tube  20  to act as a sufficiently rigid support for the filter material  28  when expanded to its rounded form. The openings in material  28  do not expand substantially when the base pipe  20  expands. Additionally, open areas in tube  20  can be as high as 20 to 40 percent while still giving the tube  20  in the perforated area sufficient column strength to be advanced to the proper depth. 
     It is also within the purview of the invention to provide a filter material  28  over a coiled tubing string such as  20  which is perforated with holes  14  without initially corrugating the tube  20  under the filter material  28 . This assembly can be expanded in an initial rounded state to push material  28  against the wellbore. 
     Various known techniques to expand the base pipe  20  can be used. The use of a flexible material for the filter material  28  gives predictable opening sizes and holds the formation in its natural state when in the expanded position, as shown in FIG.  2 . Upon expansion, the tube material  20  with the filter material  28  around it act as a perforated casing for the purposes of production from the formation. 
     The reinforcing grid  26  can be a layer that overlays the tube  20  as shown in FIG. 2, or it can be a structural component within the filter material  28 . The reinforcement  26  can be made from metallic and nonmetallic materials and is generally an open weave. However, other structures can be employed without departing from the spirit of the invention. 
     It is also within the purview of the invention to use an initially round cross section for the tube  20  under the filter material  28  and mechanically expand the combination against the wellbore. However, the preferred embodiment involves the use of a corrugated tube under filter  28  material so that greater volumetric expansions can occur underneath the filter material  28  to better position it against the wellbore. 
     In the preferred embodiment, the openings  14  are round. Rounded openings provide a better structural integrity of the tube after expansion than initial openings which are slotted. Using materials such as stainless steel 316L, yield strengths of 30,000 to 80,000 psi can be obtained. 
     It is also within the scope of the invention to provide a sufficient expansion force on the corrugated tube  20  to get it into the rounded position shown in FIG. 2 such that the filter  28  engages the wellbore with a residual force and, in certain conditions, pushes back the formation materials defining the wellbore to enlarge it. 
     The expansion techniques which are known can be used to change the configuration of the corrugated tube  20  under the filter material  28  to a rounded shape. These can include devices which employ a wedge which is pushed or pulled through the tubular or any other driving device which entails the use of rollers which can be actuated radially outwardly to initiate the expansion of the corrugated tubular as the driver advances. 
     Those skilled in the art will appreciate the advantages of the apparatus and method as described above. In lateral completions there is some uncertainly as to the distribution of the gravel around a screen. Additionally, the necessity of leaving an annular gap for placement of the gravel acts as a limitation on production from the zone in the wellbore. In certain applications involving unconsolidated shale formations, drilling with mud can create an impervious cake on the wellbore walls which will be detrimental to future production when used with traditional gravel packing techniques. Accordingly, since it is more advantageous to allow the formation to begin producing when it is as close to its natural state as possible, the concept of producing through coiled tubing with the apparatus and method as described greatly enhances the production possible from the formation. Accordingly, an open cell filtering material such as  28  which can be stretched is preferred in combination with an underlying coiled tubing material which can be expanded from the corrugated initial condition to a rounded final condition. The open cell filter material  28  can be pushed firmly against the formation where it can easily resist longitudinal flow due to the small pressure increments involved in flow in that direction. The opening size in the filter material  28  is predictable and the assembly can be protected for delivery to the desired location with the cover structure eliminated prior to or during the expansion of the filter material  28  with the underlying tube  20  below it. While various types of mechanical expansions of the underlying tube  20  from a corrugated state to a rounded state have been described, other techniques to push the filter material  28  against the wellbore while supporting it with an underlying perforated support pipe having a large open area, in the order of 20 to 40 percent, are also in the purview of the invention. The reinforcing layer which can be between the tube and the filter material  28 , or within the filter material  28 , prevents extrusion of the filter material  28  through the openings  14  in the base pipe or tube  20 , as shown in FIG.  2 . 
     The foregoing disclosure and description of the invention are illustrative and explanatory thereof, and various changes in the size, shape and materials, as well as in the details of the illustrated construction, may be made without departing from the spirit of the invention.