Abstract:
In one embodiment, a wellbore completion method includes disposing an expandable screen into a well bore and disposing a fluid into an annular space between a wall of the wellbore and the expandable screen. The fluid contains a plurality of near neutrally-buoyant particles. The method further includes radially expanding the screen, whereby the near neutrally-buoyant particles exert a force against the wall of the wellbore.

Description:
RELATED APPLICATIONS  
       [0001]     This application claims the benefit of Ser. No. 60/532,933, entitled “Expandable Sand Screen Utilizing Near Neutrally Buoyant Particles Outside of Screen,” filed provisionally on Dec. 29, 2003. 
     
    
     TECHNICAL FIELD OF THE INVENTION  
       [0002]     This invention relates generally to the field of well bore completion and, more particularly, to an expandable screen utilizing near neutrally-buoyant particles outside of the screen.  
       BACKGROUND OF THE INVENTION  
       [0003]     Sand control is important during completion and subsequent production of a wellbore that is in hydraulic communication with Earth formations susceptible to production of solid materials from the formation. Such formations are known in the art as “unconsolidated” and, if not protected with suitable wellbore equipment, may produce solid materials of a character and quantity so as to damage the wellbore, or at least reduce its capacity to produce oil and gas from the formation. Devices known in the art as “sand screens” are typically used to protect such unconsolidated formations. Sand screens include a structural member, called a “base pipe”, having apertures therein to maintain the mechanical integrity of the sand screen (meaning to provide mechanical support for the screen. A “filter layer” is typically disposed outside the base pipe. Many different types of filter layer are used, including, for example, wound wire and mesh screen.  
         [0004]     More recently, radially plastically deformable sand screens, called “expandable sand screens” have been used in some wellbores to increase productivity of wellbores completed in unconsolidated Earth formations. A principal reason for the use of expandable sand screens is to mechanically support the unconsolidated formation prior to initiating fluid production. By supporting the formation prior to initiating production, it is possible to reduce loss of formation permeability due to movement of solid materials against the screen during fluid production. A conventional (non-expandable) sand screen must necessarily have an external diameter smaller than the drilled out diameter of the wellbore (“open hole”) prior to insertion of the sand screen, in order for the screen to fit in the wellbore. The smaller screen diameter results in an annular space between the outer surface of the screen and the wall of the wellbore, which may become filled with formation solids moved from the formation during fluid production. Expandable sand screens are intended to provide a way to close the annular space prior to beginning fluid production, and thus prevent movement of formation solids. Expandable sand screens are run into the wellbore in an unexpanded state, wherein the external diameter of the screen is less than the drilled out diameter of the wellbore. After insertion, the screen is expanded using one or more types of expansion tools, preferably to cause the screen to be placed into firm contact with the wellbore wall.  
         [0005]     During the expansion of expandable sand screens, it is advantageous to push the sand screen outward to an extent so that it “conforms” to, and applies pressure to, the wellbore wall in order to hold the sand in place and increase oil and/or gas flow into the wellbore. Many wellbores may include sections where the actual diameter of the wellbore exceeds the drilled out diameter (drill bit diameter) due to washout or other cause. In such sections, it maybe necessary to expand a screen to 35 or 40 percent greater than its unexpended diameter in order to place the screen in form contact with the wall of the wellbore.  
         [0006]     One problem with expandable screens known in the art is that they are difficult to expand more than about 30 to 35 percent because the base pipes made out of carbon steel or stainless steel begin to fail. As a result, these screens may often not be expanded enough to apply the high contact pressures needed to hold the sand in place in enlarged wellbores, thus resulting in failure of the sand screen or inadequate production. Conversely, if expanded to the degree necessary to provide a suitable amount of contact pressure, the base pipe may be weakened to an extent so as to have very little resistance to crushing under external pressure, thus leaving the wellbore susceptible to failure.  
       SUMMARY OF THE INVENTION  
       [0007]     It is desirable to have an expandable sand screen that can be made to conform to the wall of a wellbore, even if it is necessary to expand the screen to 35 percent or more beyond the unexpanded diameter of the screen, while maintaining sufficient mechanical integrity to resist failure of the screen and consequent loss of the wellbore.  
         [0008]     In one embodiment, a wellbore completion method includes disposing an expandable screen into a wellbore and disposing a fluid into an annular space between a wall of the wellbore and the expandable screen. The fluid contains a plurality of near neutrally-buoyant particles. The method further includes radially expanding the screen, whereby the near neutrally-buoyant particles exert a force against the wall of the wellbore.  
         [0009]     Embodiments of the invention may provide a number of technical advantages. In one embodiment, placement of neutrally-buoyant or near-neutrally-buoyant particles in the annular space outside of the screens makes the screens compliant and allows them to exert a force against the wall of a wellbore and hold the sand particles in place. This facilitates the use of strong base pipe with high torsional, axial, and collapse strength.  
         [0010]     Other technical advantages are readily apparent to one skilled in the art from the following figures, descriptions, and claims.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0011]      FIGS. 1 and 2  are cross-sectional elevation views illustrating a wellbore completion method in accordance with one embodiment of the present invention.  
     
    
     DETAILED DESCRIPTION  
       [0012]      FIGS. 1 and 2  are cross-sectional elevation views illustrating a wellbore completion method in accordance with one embodiment of the present invention. Referring first to  FIG. 1 , a wellbore completion system  100  is utilized in completing a wellbore  101  drilled within a formation  102 . Wellbore  101  may be drilled using any suitable drilling techniques and may have any suitable diameter, length, and direction. Formation  102  may be any suitable geological formation; however, the present invention is particularly suitable for unconsolidated formations, such as sandstone.  
         [0013]     Holding the sand or other particles from formation  102  in place during the completion process is important for effective oil and/or gas flow into wellbore  101 . Thus, expandable sand screens are sometimes utilized to hold the sand in place. A major problem with prior expandable sand screens is that they are difficult to expand more than about 30-35% before the base pipes from which they are made begin to fail. Thus, these prior screens may often not be expanded enough to apply high contact pressures to hold the sand in place.  
         [0014]     Therefore, according to the teachings of one embodiment of the invention, a plurality of near neutrally-buoyant particles  106  are disposed within an annular space  108  between a wall  109  of wellbore  101  and an expandable screen  104  prior to expanding expandable screen  104 . Near neutrally-buoyant particles  106  reduce the amount of expansion required by expandable screen  104  and increases the contact force between expandable screen  104  and wall  109 . In the illustrated embodiment, near neutrally-buoyant particles  106  are disposed within a fluid  115 .  
         [0015]     Expandable screen  104  may be any suitable screen of any suitable size and configuration, and may be formed from any suitable material. For example, expandable screen  104  may be formed from a suitable carbon steel and include a fine screen or coarse screen (or both) inside of a suitable sleeve (sometimes referred to as a “shroud”) having suitable apertures formed therein. Expandable screen  104  may also have any suitable length and may be formed from one or more sections. If expandable screen  104  is formed from more than one section, then expandable threads  112  may be utilized to couple the sections together. Expandable screen  104  may be disposed in wellbore  101  by any suitable method, such as the utilization of a suitable work string  110 . Any suitable method may be utilized to expand expandable screen  104 , such as a cone expander  114  or other suitable expander element.  
         [0016]     Near neutrally-buoyant particles  106  may be any suitable particles formed from any suitable material. As used herein, the term “near neutrally-buoyant” means that particles  106  each have a density that is equal to or very near the density of fluid  115  in which they are suspended. As examples, near neutrally-buoyant particles  106  may be hollow or low density particles. Although near neutrally-buoyant particles  106  may have any suitable size and shape, in one embodiment, near neutrally-buoyant particles  106  are generally spherical in shape having any suitable diameters. In a particular embodiment of the invention, the near neutrally-buoyant particles  106  are generally spherical in shape and have diameters larger than the diameters of the pores existing within formation  102  adjacent wall  109  in order to prevent them from flowing into and plugging the pores in formation  102 . With respect to expandable screen  104 , in one embodiment, near neutrally-buoyant particles  106  may be generally spherical in shape and have diameters larger than the diameters of the holes formed within the outermost member of expandable screen  104 , such as a shroud. In one embodiment, this prevents the near neutrally-buoyant particles from damaging the fine screen inside of the shroud.  
         [0017]     Fluid  115  may be any suitable fluid. For example, in one embodiment, fluid  115  is a suitable completion fluid. In addition, fluid  115  may be disposed within annular space  108  between wall  109  and expandable screen  104  in any suitable manner using any suitable equipment, such as a pump.  
         [0018]     In some embodiments, fluid  115  develops “gel” strength when it is not being circulated. This gel strength allows near neutrally-buoyant particles  106  to be suspended in fluid  115  even though their densities are slightly different than fluid  115 . Therefore, in some embodiments, the densities of near neutrally-buoyant particles  106  do not have to equal the density of fluid  115  to be suspended therein.  
         [0019]     In one embodiment, some of the near neutrally-buoyant particles  106  each have a density slightly greater than fluid  115  such that they tend to fall within fluid  115  prior to expansion of expandable screen  104 , and some of the near neutrally-buoyant particles  106  each have a density slightly less than fluid  115  such that they will tend to rise within fluid  115  prior to expansion of expandable screen  104 . This may improve the placement of particles  106  in annular space  108  around screen  104 . In another embodiment, near neutrally-buoyant particles  106  each have a density equal to fluid  115  such that particles  106  substantially remain in place around expandable screen  104  prior to expansion thereof with no tendency to rise or fall within fluid  115 . Other methods for moving and/or locating particles  106  within fluid  115  are contemplated by the present invention. It should be noted that larger near neutrally-buoyant particles  106  may tend to sink or float faster than smaller particles. Thus, as near neutrally-buoyant particles  106  get larger, the difference in density between near neutrally-buoyant particles  106  and fluid  115  may be smaller in order to suspend them in fluid  115 .  
         [0020]     System  100  may also include a first barrier  118  coupled near a top of expandable screen  104  and a second barrier  120  coupled near a bottom of expandable screen  104 . Barriers  118 ,  120  may be utilized to confine the near neutrally-buoyant particles  106  to a particular vertical space within annular space  108  of wellbore  101 . Barrier  118  and barrier  120  may be any suitable barriers formed from any suitable material, such as an elastomer. Barriers  118 ,  120  are typically coupled to the outside of expandable screen  104  before expandable screen  104  is disposed within wellbore  101 .  
         [0021]     A bottom sub  122  may also be coupled to a bottom of expandable screen  104  to prevent any fluid  115  from exiting expandable screen  104 . Bottom sub  122  may be any suitable plug formed from any suitable material and may coupled to expandable screen  104  in any suitable manner.  
         [0022]     Also illustrated in  FIG. 1  is a casing  124 , which may case any suitable portion of wellbore  101 , and an expandable liner hanger  126  that functions to hang any suitable lining within casing  124 . The present invention contemplates more, fewer, or different components than those illustrated in  FIG. 1 .  
         [0023]     In operation of one embodiment of the invention, and with reference to  FIGS. 1 and 2 , wellbore  101  is first drilled by any suitable method within formation  102  and the upper portion thereof cased with casing  124 . Expandable liner hanger  126  is utilized to position expandable screen  104  within wellbore  101 . Work string  110  with cone expander  114  coupled thereto is then run-in-hole and fluid  115  is circulated down into wellbore  101 . Fluid  115 , with near neutrally-buoyant particles  106  suspended therein, fills annular space  108 .  
         [0024]     Work string  110  then is utilized to apply weight to cone expander  114 , which translates downward and starts radially expanding expandable screen  104 , as illustrated best in  FIG. 1 . Cone expander  114  plastically deforms expandable screen  104 . As expandable screen  104  is radially expanded out towards wall  109 , near neutrally-buoyant particles  106  exert a force against wall  109  in order to hold the sand associated with formation  102  in place. In the illustrated embodiment, the near neutrally-buoyant particles  106  have diameters larger than the pores existing in formation  102  in order to prevent them from flowing into and plugging the pores. Once cone expander  114  reaches the end of its desired travel, then work string  110  and cone expander  114  are pulled out of wellbore  101 , thereby leaving the arrangement illustrated in  FIG. 2 .  
         [0025]     As shown in  FIG. 2 , expandable screen  104  is radially expanded outward towards wall  109  and applies a force to near neutrally-buoyant particles  106  so that they may exert a force on wall  109  of wellbore  101 . Expandable screen  104  is thus plastically deformed from a smaller diameter to a larger diameter. Any suitable expansion is contemplated by the present invention.  
         [0026]     Thus, near neutrally-buoyant particles  106  within annular space  108  facilitate expandable screen  104  being compliant and holds sand particles associated with formation  102  in place by exerting a force against wall  109 . This may allow the use of a strong base pipe with expandable screen  104  with high torsional, axial and collapse strength. Efficient production from wellbore  101  may then be realized.  
         [0027]     Although embodiments of the invention and their advantages are described in detail, a person of ordinary skill in the art could make various alterations, additions, and omissions without departing from the spirit and scope of the present invention as defined by the appended claims.