Abstract:
A non-metallic element system is provided which can effectively seal or pack-off an annulus under elevated temperatures. The element system can also resist high differential pressures without sacrificing performance or suffering mechanical degradation, and is considerably faster to drill-up than a conventional element system. In one aspect, the composite material comprises an epoxy blend reinforced with glass fibers stacked layer upon layer at about 30 to about 70 degrees. A downhole tool, such as a bridge plug, frac-plug, or packer, is also provided. The tool comprises a first and second support ring having one or more tapered wedges, a first and second expansion ring, and a sealing member disposed between the expansion rings and the support rings.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The present invention relates to a downhole non-metallic sealing element system. More particularly, the present invention relates to downhole tools such as bridge plugs, frac-plugs, and packers having a non-metallic sealing element system.  
           [0003]    2. Background of the Related Art  
           [0004]    An oil or gas well includes a wellbore extending into a well to some depth below the surface. Typically, the wellbore is lined with tubulars or casing to strengthen the walls of the borehole. To further strengthen the walls of the borehole, the annular area formed between the casing and the borehole is typically filled with cement to permanently set the casing in the wellbore. The casing is then perforated to allow production fluid to enter the wellbore and be retrieved at the surface of the well.  
           [0005]    Downhole tools with sealing elements are placed within the wellbore to isolate the production fluid or to manage production fluid flow through the well. The tools, such as plugs or packers for example, are usually constructed of cast iron, aluminum, or other alloyed metals, but have a malleable, synthetic element system. An element system is typically made of a composite or synthetic rubber material which seals off an annulus within the wellbore to prevent the passage of fluids. The element system is compressed, thereby expanding radially outward from the tool to sealingly engage a surrounding tubular. For example, a bridge plug or frac-plug is placed within the wellbore to isolate upper and lower sections of production zones. By creating a pressure seal in the wellbore, bridge plugs and frac-plugs allow pressurized fluids or solids to treat an isolated formation.  
           [0006]    [0006]FIG. 1 is a cross sectional view of a conventional bridge plug  50 . The bridge plug  50  generally includes a metallic body  80 , a synthetic sealing member  52  to seal an annular area between the bridge plug  50  and an inner wall of casing there-around (not shown), and one or more metallic slips  56 ,  61 . The sealing member  52  is disposed between an upper metallic retaining portion  55  and a lower metallic retaining portion  60 . In operation, axial forces are applied to the slip  56  while the body  80  and slip  61  are held in a fixed position. As the slip  56  moves down in relation to the body  80  and slip  61 , the sealing member is actuated and the slips  56 ,  61  are driven up cones  55 ,  60 . The movement of the cones and slips axially compress and radially expand the sealing member  52  thereby forcing the sealing portion radially outward from the plug to contact the inner surface of the well bore casing. In this manner, the compressed sealing member  52  provides a fluid seal to prevent movement of fluids across the bridge plug  50 .  
           [0007]    Like the bridge plug described above, conventional packers typically comprise a synthetic sealing element located between upper and lower metallic retaining rings. Packers are typically used to seal an annular area formed between two co-axially disposed tubulars within a wellbore. For example, packers may seal an annulus formed between production tubing disposed within wellbore casing. Alternatively, packers may seal an annulus between the outside of a tubular and an unlined borehole. Routine uses of packers include the protection of casing from pressure, both well and stimulation pressures, as well as the protection of the wellbore casing from corrosive fluids. Other common uses include the isolation of formations or leaks within a wellbore casing or multiple producing zones, thereby preventing the migration of fluid between zones. Packers may also be used to hold kill fluids or treating fluids within the casing annulus.  
           [0008]    One problem associated with conventional element systems of downhole tools arises in high temperature and/or high pressure applications. High temperatures are generally defined as downhole temperatures above 200° F. and up to 450° F. High pressures are generally defined as downhole pressures above 7,500 psi and up to 15,000 psi. Another problem with conventional element systems occurs in both high and low pH environments. High pH is generally defined as less than 6.0, and low pH is generally defined as more than  8 . 0 . In these extreme downhole conditions, conventional sealing elements become ineffective. Most often, the physical properties of the sealing element suffer from degradation due to extreme downhole conditions. For example, the sealing element may melt, solidify, or otherwise loose elasticity.  
           [0009]    Yet another problem associated with conventional element systems of downhole tools arises when the tool is no longer needed to seal an annulus and must be removed from the wellbore. For example, plugs and packers are sometimes intended to be temporary and must be removed to access the wellbore. Rather than de-actuate the tool and bring it to the surface of the well, the tool is typically destroyed with a rotating milling or drilling device. As the mill contacts the tool, the tool is “drilled up” or reduced to small pieces that are either washed out of the wellbore or simply left at the bottom of the wellbore. The more metal parts making up the tool, the longer the milling operation takes. Metallic components also typically require numerous trips in and out of the wellbore to replace worn out mills or drill bits.  
           [0010]    There is a need, therefore, for a non-metallic element system that will effectively seal an annulus at high temperatures and withstand high pressure differentials without experiencing physical degradation. There is also a need for a downhole tool made substantially of a non-metallic material that is easier and faster to mill.  
         SUMMARY OF THE INVENTION  
         [0011]    A non-metallic element system is provided which can effectively seal or pack-off an annulus under elevated temperatures. The element system can also resist high differential pressures as well as high and low pH environments without sacrificing performance or suffering mechanical degradation. Further, the non-metallic element system will drill up considerably faster than a conventional element system that contains metal.  
           [0012]    The element system comprises a non-metallic, composite material that can withstand high temperatures and high pressure differentials. In one aspect, the composite material comprises an epoxy blend reinforced with glass fibers stacked layer upon layer at about 30 to about 70 degrees.  
           [0013]    A downhole tool, such as a bridge plug, frac-plug, or packer, is also provided that consists essentially of a non-metallic, composite material which is easier and faster to mill than a conventional bridge plug containing metallic parts. In one aspect, the tool comprises a non-metallic element system, comprising a first and second support ring having one or more tapered wedges, a first and second expansion ring, and a sealing member disposed between the expansion rings and the support rings.  
           [0014]    A method is further provided for sealing an annulus in a wellbore. In one aspect, the method comprises running a body into the wellbore, the body comprising a non-metallic sealing system having a first and second support ring, a first and second expansion ring, and a sealing member disposed between the expansion rings and the support rings, wherein the support ring comprises one or more tapered wedges. The method further comprises expanding the one or more tapered wedges to engage an inner surface of a surrounding tubular, and flowing the expansion ring to fill voids between the expanded wedges. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0015]    So that the manner in which the above recited features, advantages and objects of the present invention are attained and can be understood in detail, a more particular description of the invention, briefly summarized above, may be had by reference to the embodiments thereof which are illustrated in the appended drawings.  
         [0016]    It is to be noted, however, that the appended drawings illustrate only typical embodiments of this invention and are therefore not to be considered limiting of its scope, for the invention may admit to other equally effective embodiments.  
         [0017]    [0017]FIG. 1 is a partial section view of a conventional bridge plug.  
         [0018]    [0018]FIG. 2 is a partial section view of a non-metallic sealing system of the present invention.  
         [0019]    [0019]FIG. 3 is an enlarged isometric view of a support ring of the non-metallic sealing system.  
         [0020]    [0020]FIG. 4 is a cross sectional view along lines A-A of FIG. 2.  
         [0021]    [0021]FIG. 5 is partial section view of a frac-plug having a non-metallic sealing system of the present invention in a run-in position.  
         [0022]    [0022]FIG. 6 is section view of a frac-plug having a non-metallic sealing system of the present invention in a set position within a wellbore.  
         [0023]    [0023]FIG. 6A is an enlarged view of a non-metallic sealing system activated within a wellbore.  
         [0024]    [0024]FIG. 7 is a cross sectional view along lines B-B of FIG. 6. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0025]    A non-metallic element system that is capable of sealing an annulus in very high or low pH environments as well as at elevated temperatures and high pressure differentials is provided. The non-metallic element system is made of a fiber reinforced polymer composite that is compressible and expandable or otherwise malleable to create a permanent set position.  
         [0026]    The composite material is constructed of a polymeric composite that is reinforced by a continuous fiber such as glass, carbon, or aramid, for example. The individual fibers are typically layered parallel to each other, and wound layer upon layer. However, each individual layer is wound at an angle of about 30 to about 70 degrees to provide additional strength and stiffness to the composite material in high temperature and pressure downhole conditions. The tool mandrel is preferably wound at an angle of 30 to 55 degrees, and the other tool components are preferably wound at angles between about 40 and about 70 degrees. The difference in the winding phase is dependent on the required strength and rigidity of the overall composite material.  
         [0027]    The polymeric composite is preferably an epoxy blend. However, the polymeric composite may also consist of polyurethanes or phenolics, for example. In one aspect, the polymeric composite is a blend of two or more epoxy resins. Preferably, the composite is a blend of a first epoxy resin of bisphenol A and epichlorohydrin and a second cycoaliphatic epoxy resin. Preferably, the cycloaphatic epoxy resin is Araldite® liquid epoxy resin, commercially available from Ciga-Geigy Corporation of Brewster, N.Y. A 50:50 blend by weight of the two resins has been found to provide the required stability and strength for use in high temperature and pressure applications. The 50:50 epoxy blend also provides good resistance in both high and low pH environments.  
         [0028]    The fiber is typically wet wound, however, a prepreg roving can also be used to form a matrix. A post cure process is preferable to achieve greater strength of the material. Typically, the post cure process is a two stage cure consisting of a gel period and a cross linking period using an anhydride hardener, as is commonly know in the art. Heat is added during the curing process to provide the appropriate reaction energy which drives the cross-linking of the matrix to completion. The composite may also be exposed to ultraviolet light or a high-intensity electron beam to provide the reaction energy to cure the composite material.  
         [0029]    [0029]FIG. 2 is a partial cross section of a non-metallic element system  200  made of the composite, filament wound material described above. The element system  200  includes a sealing member  210 , a first and second cone  220 ,  225 , a first and second expansion ring  230 ,  235 , and a first and second support ring  240 ,  245  disposed about a body  250 . The sealing member  210  is backed by the cones  220 ,  225 . The expansion rings  230 ,  235  are disposed about the body  250  between the cones  220 ,  225 , and the support rings  240 ,  245 , as shown in FIG. 2.  
         [0030]    [0030]FIG. 3 is an isometric view of the support ring  240 ,  245 . As shown, the support ring  240 ,  245  is an annular member having a first section  242  of a first diameter that steps up to a second section  244  of a second diameter. An interface or shoulder  246  is therefore formed between the two sections  242 ,  244 . Equally spaced longitudinal cuts  247  are fabricated in the second section to create one or more fingers or wedges  248  there-between. The number of cuts  247  is determined by the size of the annulus to be sealed and the forces exerted on the support ring  240 ,  245 .  
         [0031]    Still referring to FIG. 3, the wedges  248  are angled outwardly from a center line or axis of the support ring  240 ,  245  at about 10 degrees to about 30 degrees. As will be explained below in more detail, the angled wedges  248  hinge radially outward as the support ring  240 ,  245  moves axially across the outer surface of the expansion ring  230 ,  235 . The wedges  248  then break or separate from the first section  242 , and are extended radially to contact an inner diameter of the surrounding tubular (not shown). This radial extension allows the entire outer surface area of the wedges  248  to contact the inner wall of the surrounding tubular. Therefore, a greater amount of frictional force is generated against the surrounding tubular. The extended wedges  248  thus generate a “brake” that prevents slippage of the element system  200  relative to the surrounding tubular.  
         [0032]    Referring again to FIG. 2, the expansion ring  230 ,  235  may be manufactured from any flexible plastic, elastomeric, or resin material which flows at a predetermined temperature, such as Teflon® for example. The second section  244  of the support ring  240 ,  245  is disposed about a first section of the expansion ring  230 ,  235 . The first section of the expansion ring  230 ,  235  is tapered corresponding to a complimentary angle of the wedges  248 . A second section of the expansion ring  230 ,  235  is also tapered to compliment a slopped surface of the cone  220 ,  225 . At high temperatures, the expansion ring  230 ,  235  expands radially outward from the body  250  and flows across the outer surface of the body  250 . As will be explained below, the expansion ring  230 ,  235  fills the voids created between the cuts  247  of the support ring  240 ,  245 , thereby providing an effective seal.  
         [0033]    The cone  220 ,  225  is an annular member disposed about the body  250  adjacent each end of the sealing member  210 . The cone  220 ,  225  has a tapered first section and a substantially flat second section. The second section of the cone  220 ,  225  abuts the substantially flat end of the sealing member  210 . As will be explained in more detail below, the tapered first section urges the expansion ring  230 ,  235  radially outward from the body  250  as the element system  200  is activated. As the expansion ring  230 ,  235  progresses across the tapered first section and expands under high temperature and/or pressure conditions, the expansion ring  230 ,  235  creates a collapse load on the cone  220 ,  225 . This collapse load holds the cone  220 ,  225  firmly against the body  250  and prevents axial slippage of the element system  200  components once the element system  200  has been activated in the wellbore. The collapse load also prevents the cones  220 ,  225  and sealing member  210  from rotating during a subsequent mill up operation.  
         [0034]    The sealing member  210  may have any number of configurations to effectively seal an annulus within the wellbore. For example, the sealing member  210  may include grooves, ridges, indentations, or protrusions designed to allow the sealing member  210  to conform to variations in the shape of the interior of a surrounding tubular (not shown). The sealing member  210 , however, should be capable of withstanding temperatures up to 450° F., and pressure differentials up to 15,000 psi.  
         [0035]    In operation, opposing forces are exerted on the element system  200  which causes the malleable outer portions of the body  250  to compress and radially expand toward a surrounding tubular. A force in a first direction is exerted against a first surface of the support ring  240 . A force in a second direction is exerted against a first surface of the support ring  245 . The opposing forces cause the support rings  240 ,  245  to move across the tapered first section of the expansion rings  230 ,  235 . The first section of the support rings  240 ,  245  expands radially from the mandrel  250  while the wedges  248  hinge radially toward the surrounding tubular. At a predetermined force, the wedges  248  will break away or separate from the first section  242  of the support rings  240 ,  245 . The wedges  248  then extend radially outward to engage the surrounding tubular. The compressive force causes the expansion rings  230 ,  235  to flow and expand as they are forced across the tapered section of the cones  220 ,  225 . As the expansion rings  230 ,  235  flow and expand, they fill the gaps or voids between the wedges  248  of the support rings  240 ,  245 . The expansion of the expansion rings  230 ,  235  also applies a collapse load through the cones  220 ,  225  on the body  250 , which helps prevent slippage of the element system  200  once activated. The collapse load also prevents the cones  220 ,  225  and sealing member  210  from rotating during the mill up operation which significantly reduces the required time to complete the mill up operation. The cones  220 ,  225  then transfer the axial force to the sealing member  210  to compress and expand the sealing member  210  radially. The expanded sealing member  210  effectively seals or packs off an annulus formed between the body  250  and an inner diameter of a surrounding tubular.  
         [0036]    The non-metallic element system  200  can be used on either a metal or more preferably, a non-metallic mandrel. The non-metallic element system  200  may also be used with a hollow or solid mandrel. For example, the non-metallic element system  200  can be used with a bridge plug or frac-plug to seal off a wellbore or the element system may be used with a packer to pack-off an annulus between two tubulars disposed in a wellbore. For simplicity and ease of description however, the non-metallic element system will now be described in reference to a frac-plug for sealing off a well bore.  
         [0037]    [0037]FIG. 5 is a partial cross section of a frac-plug  300  having the non-metallic element system  200  described above. In addition to the non-metallic element system  200 , the frac-plug  300  includes a mandrel  301 , slips  310 ,  315 , and cones  320 ,  325 . The non-metallic element system  200  is disposed about the mandrel  301  between the cones  320 ,  325 . The mandrel  301  is a tubular member having a ball  309  disposed therein to act as a check valve by allowing flow through the mandrel  301  in only a single axial direction.  
         [0038]    The slips  310 ,  315  are disposed about the mandrel  302  adjacent a first end of the cones  320 ,  325 . Each slip  310 ,  315  comprises a tapered inner surface conforming to the first end of the cone  320 ,  325 . An outer surface of the slip  310 ,  315 , preferably includes at least one outwardly extending serration or edged tooth, to engage an inner surface of a surrounding tubular (not shown) when the slip  310 ,  315  is driven radially outward from the mandrel  301  due to the axial movement across the first end of the cones  320 ,  325  thereunder.  
         [0039]    The slip  310 ,  315  is designed to fracture with radial stress. The slip  310 ,  315  typically includes at least one recessed groove (not shown) milled therein to fracture under stress allowing the slip  310 ,  315  to expand outwards to engage an inner surface of the surrounding tubular. For example, the slip  310 ,  315  may include four sloped segments separated by equally spaced recessed grooves to contact the surrounding tubular, which become evenly distributed about the outer surface of the mandrel  301 .  
         [0040]    The cone  320 ,  325  is disposed about the mandrel  301  adjacent the non-metallic sealing system  200  and is secured to the mandrel  301  by a plurality of shearable members  330  such as screws or pins. The shearable members  330  may be fabricated from the same composite material as the non-metallic sealing system  200 , or the shearable members may be of a different kind of composite material or metal. The cone  320 ,  325  has an undercut  322  machined in an inner surface thereof so that the cone  320 ,  325  can be disposed about the first section  242  of the support ring  240 ,  245 , and butt against the shoulder  246  of the support ring  240 ,  245 .  
         [0041]    As stated above, the cones  320 ,  325  comprise a tapered first end which rests underneath the tapered inner surface of the slips  310 ,  315 . The slips  310 ,  315  travel about the tapered first end of the cones  320 ,  325 , thereby expanding radially outward from the mandrel  301  to engage the inner surface of the surrounding tubular.  
         [0042]    A setting ring  340  is disposed about the mandrel  301  adjacent a first end of the slip  310 . The setting ring  340  is an annular member having a first end that is a substantially flat surface. The first end serves as a shoulder which abuts a setting tool described below.  
         [0043]    A support ring  350  is disposed about the mandrel  301  adjacent a first end of the setting ring  340 . A plurality of pins  345  secure the support ring  350  to the mandrel  301 . The support ring  350  is an annular member and has a smaller outer diameter than the setting ring  340 . The smaller outer diameter allows the support ring  350  to fit within the inner diameter of a setting tool so the setting tool can be mounted against the first end of the setting ring  340 .  
         [0044]    The frac-plug  300  may be installed in a wellbore with some non-rigid system, such as electric wireline or coiled tubing. A setting tool, such as a Baker E-4 Wireline Setting Assembly commercially available from Baker Hughes, Inc., for example, connects to an upper portion of the mandrel  301 . Specifically, an outer movable portion of the setting tool is disposed about the outer diameter of the support ring  350 , abutting the first end of the setting ring  340 . An inner portion of the setting tool is fastened about the outer diameter of the support ring  350 . The setting tool and frac-plug  300  are then run into the well casing to the desired depth where the frac-plug  300  is to be installed.  
         [0045]    To set or activate the frac-plug  300 , the mandrel  301  is held by the wireline, through the inner portion of the setting tool, as an axial force is applied through the outer movable portion of the setting tool to the setting ring  340 . The axial forces cause the outer portions of the frac-plug  300  to move axially relative to the mandrel  301 . FIGS. 6 and 6A show a section view of a frac-plug having a non-metallic sealing system of the present invention in a set position within a wellbore.  
         [0046]    Referring to both FIGS. 6 and 6A, the force asserted against the setting ring  340  transmits force to the slips  310 ,  315  and cones  320 ,  325 . The slips  310 ,  315  move up and across the tapered surface of the cones  320 ,  325  and contact an inner surface of a surrounding tubular  700 . The axial and radial forces applied to slips  310 ,  315  causes the recessed grooves to fracture into equal segments, permitting the serrations or teeth of the slips  310 ,  315  to firmly engage the inner surface of the surrounding tubular.  
         [0047]    Axial movement of the cones  320 ,  325  transfers force to the support rings  240 ,  245 . As explained above, the opposing forces cause the support rings  240 ,  245  to move across the tapered first section of the expansion rings  230 ,  235 . As the support rings  240 ,  245  move axially, the first section of the support rings  240 ,  245  expands radially from the mandrel  250  while the wedges  248  hinge radially toward the surrounding tubular. At a pre-determined force, the wedges  248  break away or separate from the first section  242  of the support rings  240 ,  245 . The wedges  248  then extend radially outward to engage the surrounding tubular  700 . The compressive force causes the expansion rings  230 ,  235  to flow and expand as they are forced across the tapered section of the cones  220 ,  225 . As the expansion rings  230 ,  235  flow and expand, the rings  230 ,  235  fill the gaps or voids between the wedges  248  of the support rings  240 ,  245 , as shown in FIG. 7. FIG. 7 is a cross sectional view along lines B-B of FIG. 6.  
         [0048]    Referring again to FIGS. 6 and 6A, the growth of the expansion rings  230 ,  235  applies a collapse load through the cones  220 ,  225  on the mandrel  301 , which helps prevent slippage of the element system  200  once activated. The cones  220 ,  225  then transfer the axial force to the sealing member  210  which is compressed and expanded radially to seal an annulus formed between the mandrel  301  and an inner diameter of the surrounding tubular  700 .  
         [0049]    In addition to frac-plugs as described above, the non-metallic element system  200  described herein may also be used in conjunction with any other downhole tool used for sealing an annulus within a wellbore, such as bridge plugs or packers, for example. Moreover, while foregoing is directed to the preferred embodiment of the present invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow.