Patent Publication Number: US-2007114020-A1

Title: Robust sand screen for oil and gas wells

Description:
RELATED CASE  
      This application claims the benefit of U.S. Provisional Patent Application Ser. No. 60/738,197 filed on Nov. 18, 2005, and incorporates said provisional application by reference into this disclosure as if fully set out at this point. 
    
    
     FIELD OF THE INVENTION  
      This invention pertains generally to the field of oil and gas production and, more particularly, to production of oil and gas in formations containing unconsolidated sands.  
     BACKGROUND OF THE INVENTION  
      Those of ordinary skill in the well completion and well production arts will recognize that the presence of sand grains or other small items of particulate matter that can be found within oil or gas that is taken from a subsurface formation can be a major operational problem that could lead to premature equipment failure, among other things. By way of explanation, if the producing formation is not sufficiently well consolidated it can yield small fragments of detritus in the vicinity of the wellbore as the reservoir is produced. Loose sand and other particulate matter that might be extracted from the formation can then be drawn along with the fluid (e.g., oil, gas, water, etc.) into the wellbore. The hazards associated having materials such this in the wellbore are well known and include, for example, possible erosion of the surface equipment, damage to the downhole equipment, the creation of cause blockages in the production facilities, etc. One consequence of this sort of damage, of course, is that it can necessitate the costly removal of accumulated solid debris from separators. In other instances, it can cause equipment failures and/or severe malfunction of same, together with the inevitable associated down time, lost production, and costly repairs.  
      Of course, others have considered this problem. However, the solutions proposed heretofore are not without difficulties. For example, frac packs or gravel packs which are often used to inhibit the movement of debris into the well bore can be expensive and risky to install. These sorts of solutions are more complex to install and require a greater amount of time than would be necessary if a stand-alone screen is used. For example, in a gravel pack operation, the gravel must be pumped around the screen which, especially for long horizontal wells, is a tedious and costly operation. Further, the uniformity and quality of the gravel pack can also be questionable.  
      Thus, generally speaking it is more cost effective—in terms time and money—to install a stand-alone sand screen. However, one of the disadvantages of conventional stand-alone screens is that they are not as sturdy as, for example, a gravel pack or frac pack. As a consequence, they are subject to being damaged during installation, with such damage quickly leading to failure in many circumstances. In other instances, screens that have been installed over highly pressurized and productive formations may be subject to rapid erosion and subsequent failure, e.g., where a screen is installed in a high productivity gas well in a heterogeneous formation with high permeability streaks. Of course, a screen provides a single level of protection, i.e., there is no redundancy, so if the screen fails at any point the well will eventually have to be shut in to perform repairs.  
      Heretofore, as is well known in the hydrocarbon production arts, there has been a need for an invention to address and solve these and other difficulties or limitations in the prior art. Accordingly, it should now be recognized, as was recognized by the present inventor, that there exists, and has existed for some time, a very real need for a system that would address and solve the above-described problems.  
      Before proceeding to a description of the present invention, however, it should be noted and remembered that the description of the invention which follows, together with the accompanying drawings, should not be construed as limiting the invention to the examples (or preferred embodiments) shown and described. This is so because those skilled in the art to which the invention pertains will be able to devise other forms of this invention within the ambit of the appended claims.  
     SUMMARY OF THE INVENTION  
      According to a first preferred aspect of the invention, there is provided a down hole sand screen device for use in well completions that comprises a plurality of isolated individual sand screens. Further, in the preferred arrangement the instant invention consists of two screens, one concentrically nested inside of the other, and further wherein the screened sections are not continuous but rather are periodically interrupted by sections of blank pipe. Further, the screened and blank pipe sections are preferably arranged so that a screened section on the outer pipe will be matched by a corresponding blank pipe section on the inner pipe and vice versa. As a consequence, if a hole develops in one of the outer screen sections the movement of sand will be blocked from entering the wellbore by a second/inner screen. Finally, the different pairs/groups of communicating inner and outer screen sections are preferably isolated from other screen sections through the use of spacers or packers that block the flow of fluid between adjacent sections of screen.  
      In the preferred arrangement the instant invention consists of two sand screens, one nested inside of the other, and further wherein the screened sections are not continuous but rather sections of blank pipe and screen are staggered so that if a hole develops in one of the outer screen sections the movement of sand will be blocked from directly entering the wellbore by a second/inner screen. According to the preferred embodiment, in the event that there is a failure in the outer screen, sand will begin filling the gap between the outer and the inner screens, which will in due course block off that part of the screen. Thus, rather than producing sand through a damaged section of screen, the instant invention will tend to block off that section of screen by accumulating debris therein. Thus, the screen of the instant invention can be said to be self-healing to the extent that it tends to block flow through damaged screen sections. Of course, one consequence of this planned blockage is that the well will thereafter be marginally less productive but that is a small price to pay when the alternative may be to shut down the well and repair the screen.  
      To reiterate, the modular screen of the instant invention will tend to repair itself (i.e., isolate and block off the damaged module) if there is a failure in the outer screen. In the preferred embodiment, the instant invention uses alternating sections—preferably on the order of 1-2 feet in length—of screen and blank pipe. Preferably, the screen and blank pipe sections will be staggered, with a section of screen on the outside member being matched with a section of blank pipe on the inside member and vice versa. Preferably, the screen sections will not overlap each other, thereby creating a backup system in case the outer screen fails. Further, in the preferred arrangement if the outer screen fails due to a local high velocity interval, the point of failure in the screen will be located over a corresponding section of blank pipe section on the inner member. Then, axial flow will take place along the outer surface inner blank pipe section until the fluid reaches an inner screen section, at which point sand being carried by the fluid will begin to accumulate and eventually block off any production through the damaged section. As has been discussed previously, in the preferred embodiment the staggered sections of pipe and screen will all be of the same size and will be on the order of one or two feet so that the filtering section is compartmentalized/discretized on a foot-by-foot basis.  
      By way of comparison, screen sections in the prior art are on the order of 30 or 40 feet in length and, thus, a failure at any point along their length will eventually cause the entire screen to fail and result in a need for replacement  
      According to another preferred aspect of the instant invention, the inner screen will preferably be made coarser (e.g., have a larger mesh opening size) than the outer screen. Thus, during normal operations, i.e., when both the inner and outer screens are undamaged, the inner screen will not accumulate sand particles that have been passed through the outer screen and become plugged or otherwise blocked. This will result in less erosion because, among other reasons, the velocity is lower within the inner screen.  
      Another aspect of the instant invention and something that is preferably added between the inner and outer cylindrical members, and preferably at the point where a section transitions from a screen to blank pipe, is a solid ring or toroid that has two primary functions. First, it will tend to act as a spacer and will function to keep the inner and outer cylindrical members uniformly separated. However, a second preferable aspect of this element is that this element could be given flow channels or other pathways which are designed to create a specific pressure loss/pressure differential between the internals of the completion and the formation pressure outside of the completion. s  
      In the preferred arrangement, there will be a gap between the inner and outer screens on the order of, for example, a few millimeters to an inch or more. Standard screens could be utilized, as could custom-made screens. When standard screens are used (e.g., two nested cylindrically shaped screens), the “blank pipe” sections in the inner and outer screen could be created by filling the appropriate part of the screen with a material such as epoxy or, perhaps, some sort of metal that would harden so that that portion of the screen becomes solid/impermeable to the fluid that is being produced. That could be used to produce the blank pipe sections.  
      The foregoing has outlined in broad terms the more important features of the invention disclosed herein so that the detailed description that follows may be more clearly understood, and so that the contribution of the instant inventor to the art may be better appreciated. The instant invention is not to be limited in its application to the details of the construction and to the arrangements of the components set forth in the following description or illustrated in the drawings. Rather, the invention is capable of other embodiments and of being practiced and carried out in various other ways not specifically enumerated herein. Further, the disclosure that follows is intended to apply to all alternatives, modifications and equivalents as may be included within the spirit and scope of the invention as defined by the appended claims. Finally, it should be understood that the phraseology and terminology employed herein are for the purpose of description and should not be regarded as limiting, unless the specification specifically so limits the invention.  
      While the instant invention will be described in connection with a preferred embodiment, it will be understood that it is not intended to limit the invention to that embodiment. On the contrary, it is intended to cover all alternatives, modifications and equivalents as may be included within the spirit and scope of the invention as defined by the appended claims.  
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      Other objects and advantages of the invention will become apparent upon reading the following detailed description and upon reference to the drawings in which:  
       FIG. 1  contains a general view of the invention as it might appear as part of a completion string.  
       FIG. 2  is a longitudinal cross section of a preferred embodiment of the instant invention.  
       FIG. 3  contains transverse cross section of a preferred embodiment of the instant invention.  
       FIG. 4  contains an idealized flow diagram that indicates how fluids would move through one preferred embodiment of the instant invention.  
       FIG. 5  is illustrates preferred variation of the instant invention wherein two screen sections are interconnected by an internal passage or pathway.  
       FIG. 6  contains still another preferred variation wherein the screen regions on the outer and inner pipes are relatively small in comparison with the size of the blank pipe regions.  
       FIG. 7  illustrates another preferred embodiment where the outer pipe is comprised almost entirely of screen material and the inner pipe contains alternating sections of screen and blank pipe, separated by an internal flow inhibitor.  
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
      According to a preferred aspect of the instant invention, the instant robust sand screen module  100  will be most useful in the completion of production or injection wells including, for example, water injectors, gas injectors, or mostly oil and gas producers will be suitable for use with the instant invention. The instant invention will typically be used in connection with well completions in formations that have the potential to produce sand absent some sort of sand preventive technology.  
      According to a first preferred embodiment and as is generally indicated in  FIG. 1 , the instant invention  100  will be preferably be installed as one component of a section of a well completion. However, it should be clear that multiple sections of the invention could be used where, for example, the potential sand problem extends over some distance (e.g., in a horizontal well). In a typical arrangement, the instant invention  100  will preferably be about 30-40 feet in length. One or more pipe lengths of the instant invention  100  could be included in this length.  FIG. 2 , discussed hereinafter, provides additional details.  
      Those of ordinary skill in the art will understand that, for purposes of the instant invention, a screen is a porous material that acts as a filter to keep sand that originates in the producing or other formation from entering the wellbore. Typical screen thickness would be on the order of around a few millimeters to maybe an inch or so in thickness and a few (e.g. 1-2) feet in length. That being said, those of ordinary skill in the art will understand that the thickness of the particular screen that is used and its length is immaterial to the operation of the instant invention. The screen itself might be made, for example, of stainless steel, aluminum, or any other suitable material.  
      As is generally indicated in  FIGS. 2-7 , in the preferred embodiment the instant invention will be comprised of two concentrically nested hollow cylindrical members  270  and  280 . Each of the cylindrical members  270  and  280  is comprised of alternating sections of permeable filter material  210 / 215  and nonpermeable blank pipe  220 / 225 . In the preferred arrangement, each section (e.g., blank pipe section  220 ) will be on the order of 1-2 feet in length, although these dimensions should be understood as having been offered for purposes of illustration only. However, and as is made especially clear in  FIGS. 2 and 4 , according to the instant embodiment the sections of filter material  210  and blank pipe  220  will be positioned so that they are staggered with respect to the inner members  215  and  225 . That is, where the outer pipe  270  has a filter element  210 , this will be matched with a blank pipe section  225  in the inner pipe  280  and vice versa. Thus, in this embodiment there is never a straight fluid path between the producing formation and the interior of the innermost cylinder  280 .  
      The spacing between the inner cylinder  280  and outer cylinder  270  is preferably on the order of a few millimeters, although a wide range of spacings might be utilized depending on the particular circumstances. In the preferred embodiment, the spacing between the two cylindrical members will be maintained throughout by the use of a spacer  230  which will preferably completely encircle the inner cylindrical member  280 . One preferred spacer embodiment will have flow channels placed therein so that fluids can pass through the outer screen  465 , along the outer surface of the blank pipe  455 , until it reaches and passes through the inner screen  440 . This might also be accomplished by placing grooves in the outer surface of the inner blank pipe that will allow for the flow of liquid (including gas) in such grooves along the inner side of the corresponding screen. This embodiment will be discussed in greater detail below.  
      In another preferred arrangement, an outer screen element screen  210  will directly butt up against an inner blank pipe section  225 , i.e., the spacing between the inner  280  and outer  270  cylindrical members will be effectively zero. In such an instance, preferably channels will be cut down into the outer surface of the inner blank pipe section  225 , thereby providing for passage of the produced fluid (to include the production of gas) axially along the outer surface of the inner blank pipe section  220  until the adjacent inner filter section  220  is reached. In such an embodiment, the channels would allow for axial flow along the inside of the outer screen  210  until such flow reached an area where the inner pipe element  280  is permeable.  
      As is indicated in  FIG. 2 , which is a schematic illustration of a longitudinal cross section of a preferred embodiment of the instant invention, each outer screen  210  is paired with an inner blank pipe section  225  and each outer blank pipe section  220  is paired with an inner screen  225 . Thus, the screen  210 / 215  and blank pipe  220 / 225  sections are staggered with respect to each other. Said another way, the embodiment of  FIG. 2  alternates screens and blank sections such that there are screen sections in the inner  280  and outer  270  cylindrical sections never overlap.  
      In one preferred embodiment, the blank pipe sections  220  and  225  will be formed by injecting epoxy or a similar product at about one foot intervals into the interior of a continuous section of screen. After the injected material has hardened, the formerly permeable screen will have been rendered impermeable. This suggested method of manufacture provides a relatively inexpensive way to manufacture sections of the instant invention  100 . That being said, those of ordinary skill in the art will recognize that this is just one of many ways that the instant invention might be manufactured.  
      Turning next to  FIG. 3 , this figure contains a schematic transverse cross section of a preferred embodiment of the instant invention. The view of  FIG. 3A  has been taken across a section of pipe wherein the outer cylindrical member is permeable and the inner cylindrical member is non-permeable. Similarly,  FIG. 3  is a transverse cross section that has been taken across a section of pipe wherein the outer member is blank pipe  220  and the inner member is a screen  215 .  
       FIG. 4  illustrates in greater detail how one preferred embodiment of the instant invention would operate in practice. In more particular, this figure illustrates how fluid flow is controlled through the use of impermeable spacers or packers  420  (blocking elements), certain ones of which, in some preferred embodiments, will be designed to have one or more flow channels placed therein which allows some fluid to move longitudinally along the pipe face. As can be readily seen in this figure, in one preferred embodiment the fluid flow pattern  410  accepts fluid in through outer screen  405 , said fluid is then turned upon encountering the inner blank pipe section  450 , it travels axially along the face of the blank pipe section  450  through the void created between the inner and outer pipes, and then, enters the central core of the instant invention through inner screen  415  where it is carried away  480  from its point of entry and eventually removed from the well. In another preferred embodiment, which might be used instead of or in conjunction with the previous embodiment, fluid will enter through screen  465 , will be turned and move axially along the outer face of blank pipe section  455  until it encounters permeable spacer  435 , move though permeable spacer  435  (through such movement will preferably be retarded at least somewhat), and into the center of the instant invention through screen  440 . Note that the amount of permeability in the spacer  435  could be varied to suit the occasion and, preferably, will consist of a plurality of flow channels that are designed control in a predictable way the pressure differential between the formation and the interior of the well.  
      In another preferred embodiment, there will be no spacers/packers between the inner and outer screens/blank pipe. Although this figure does not show it, in some preferred embodiments the screen  405  will be in direct contact with the blank pipe section  450 , with grooves having been cut into the face of the blank pipe section  450  to allow fluids to pass longitudinally along its upper surface after they have passed through the outer filter element  405 .  
      One particularly favorable aspect of the instant invention is its ability to “repair” itself. Said another way, in the event that screen  405  develops a hole therein, unfiltered fluid will enter through the hole, pass longitudinally/axially through the gap between the cylindrical members, through filter  415 , and into the center of the pipe. Note that the larger particles in the unfiltered materials will tend accumulate on the outer surface of filter  415  and eventually stop the passage of fluid therethrough. One important consequence of this is that a hole in one of the filter sections  405 / 465  will not disable the entire 30-foot joint section. Instead, only the, say, four foot section of filter and blank pipe elements  405 ,  460 ,  450 , and  415  will eventually become blocked and unusable. Thus, only one filter section, i.e., the filter/blank pipe elements between two impermeable spacers will be disabled.  
       FIGS. 5 and 6  contain some additional embodiments. For example, in the embodiments considered above the equal sized screens/blank pipe sections have been presented as discrete cylinders which are staggered with respect to each other and then isolated from each other with packers that prevent flow to other parts of the screen. For example, and as is illustrated generally in  FIG. 6 , two nested cylindrical pipes  630  and  640  could be made to be permeable by way of windows that have been strategically placed in both the outer and inner screen, with screen  610  being in the outer pipe  630  and screen  620  being in an inner pipe  640 . As is generally indicated in this figure, the screens will preferably occupy only a relatively small portion of the pipe&#39;s outer  630  and inner  640  surfaces. Obviously, many such screens  610 / 620  could be used in the inner  640  or outer  630  pipe, with their shape, size, and relative positioning being selected to suit the intended application. In a preferred embodiment, each group of windows will be isolated from the other (e.g., through the use of a spacer  660 ).  
      As another example, in  FIG. 5  an outer filter panel  510  in outer pipe  550  is connected by a groove  530  or other passageway to an inner filter panel  520  in inner pipe  560 , the two pipes being nested closely together so as to prevent (or greatly retard) fluid flow between their surfaces. In this embodiment, one or several windows  510  in the outer pipe  540  could be connected to one or several of the windows  520  in the inner pipe  550  through a flow channel  530 . Thus, once again, if the outer filter window  510  erodes or fails, then a second filter/screen  520  will be available to block the passage of particulate matter therethrough. Further, if the outer screen  510  fails, the instant embodiment will be similarly “self repairing” to the extent that the accumulation of debris within the channel  530  on the outer surface of the screen  520  will eventually close of that passageway, thereby making a complete failure very unlikely.  
      The screens of  FIGS. 5 and 6  could be any shape and need not be rectangular (e.g., they could be round, oblong, etc.) nor do the intake  510 / 610  and output  520 / 620  filters need be the same size. Additionally, the passageways between the input and output filter elements could be designed to help control pressure between the formation and the interior of the pipe, i.e., that structure could be used to create a controlled pressure differential between the internals of the completion and the outside of the completion.  
      Those of ordinary skill in the art will recognize that, although two nested cylindrically shaped elements  270  and  280  are preferred, more nested cylinders (e.g., 3, 4, etc.) could similarly be used, with the consequence that additional protection against failure would be obtained. Obviously, this process could be continued up to the ability of the hole diameter to accommodate multiple pipes (e.g., nested cylinders) within. Of course, by adding additional cylinders/filters, further protection could be provided against leakage/damage to one of the outer filters. Similarly, this would give more of an opportunity to use the preferred structure to control the pressure that is entering the center of the pipe.  
      According to still another preferred embodiment, and as is generally indicated in  FIG. 7 , there is provided a variation of the instant invention (shown in cross section) wherein the outer member is substantially comprised of one or more screen sections  705 . In this variation, generally speaking fluid takes one of two paths from the exterior of the pipe into its central cavity, depending on where it enters. In some instances, it will take a curved path (e.g., paths  710  and  730 ) as a consequence of encountering inner blank pipe sections  750  and  755 . In other cases, (e.g., fluid flow paths  755  and  765 ) it will take a more direct route. However, what is critical is that the flow of fluid downward (or upward) inside of the void  735  must be terminated and redirected by spacer  720 . This sort of configuration, although it has certain disadvantages as compared with other embodiments, will be similarly self healing, in that if the outer screen  705  is breached, sand will tend to accumulate within the void  735  until eventually access to the inner screens  715  and  740  is blocked. Obviously, a high-pressure region could conceivable punch through both the inner and outer screen members in those regions where they overlap. However, this embodiment still implements a key aspect of the instant invention, in that in many cases after a breach of the outer screen the breached section will eventually be blocked off, thus keeping sand away from the central pipe cavity.  
      Returning to  FIG. 4 , and to reiterate, note that if the outer screen fails at some point sand will potentially be produced through the failed screen. However, the inner filter typically will be undamaged and will continue to stop sand from traveling therethrough. Preferably, the inner screen will be a bit coarser than the outer screen. As has been discussed previously, if the outer screen fails larger particles will come through the failed section of the outer screen and it will be blocked by—and accumulated on the surface of—the inner screen. Thus, the inner screen will help ensure that sand will accumulate between either an inner space or the grooves between the inner and outer screen and will eventually block off the failed section. Sand from a failed outer screen will begin to accumulate against an inner screen and eventually will stop the flow of fluid through that section or reduce it to the point where the inner screen will not erode and cause a second failure. Thus, two different filter elements must be breached in order for a complete failure to occur.  
      Another advantage of the instant invention is that the flow path through the outer screen will immediately encounter a blank pipe surface which is much harder or resistant to erosion than a screen. In the event that two overlapping screens are used, if the outer screen is damaged (e.g., by high pressure) then the inner screen is also at risk of erosion. However, with the instant invention if the outer screen is breached the inrushing fluid will be met with an unyielding or hard surface, rather than a similarly fragile inner screen. This is because of the staggered design discussed previously. Thus, a subsurface hot spot where there is a very high flow from the formation that erodes through the outer screen will likely be stopped at the blank pipe surface and will tend to not erode the inner screen.  
      Finally, the mesh size or opening size or coarseness of the inner screen will preferably be larger than that of the outer screen—preferably large enough to prevent accumulation of the particles between the screens.  
     CONCLUSIONS  
      The instant invention has been specifically designed to increase the reliability in downhole screens by creating a structure that is in some sense self-healing or self-correcting. It is an important aspect of the invention that it is comprised of a plurality of hydraulically isolated pairs/groups of communicating screen sections—i.e., one or more inner screen sections and one or more outer screen sections—such that even a catastrophic failure in one of screen pairs does not allow sand to pass into the produced fluid and will affect only an insignificant part of the completion. Preferably, each screen section will be isolated from the other and will be arranged in screen/blank pipe pairs. As a consequence, if a hole develops in one of the outer screen sections the movement of sand will be blocked from entering the wellbore by a second/inner screen section. Finally, the different sections of screen are preferably isolated from pairs/groups through the use of spacers or packers that block the flower of fluid between adjacent sections.  
      Further, although the preferred embodiment of the instant invention has generally described the instant downhole sand screen pipe as having roughly equal amounts of blank pipe and screen, that is not strictly required. In some embodiments there might be much more (or less) blank pipe than screen (e.g., see the embodiment of  FIG. 5 ).  
      Still further, although the inner pipe has been generally pictured as being identical in relative composition to the outer pipe (i.e., having the same relative proportions of blank pipe and screen) that is also not a requirement. Obviously, the relative amounts of blank pipe and screen in the inner and outer pipes could be much different from each other. All that is required is that in each instance where there is a region of sand screen on the outer pipe there should be a corresponding region of blank pipe opposite it on the inner pipe, such that fluids cannot pass through a screen section and into the interior of the pipe without encountering a section of blank pipe on the inner member.  
      Additionally, it should be noted that when the term “blank pipe” is used herein, that term should be broadly understood to include plain tubing of the sort traditionally used in sand control completions, as well as any other sort of pipe that is at least relatively impervious to the passage of fluids therethrough. For example, in some applications a slotted liner with very fine slots could be used as a blank pipe section.  
      Finally, although the preferred embodiment utilizes nested coaxial cylindrical pipes, such a configuration is not required. In some instances, the inner and outer pipes might not be coaxial, i.e., the central axis of the inner pipe could be offset from the central axis of the outer pipe.  
      Thus, it is apparent that there has been provided, in accordance with the invention, a sand screen that fully satisfies the objects, aims and advantages set forth above. While the invention has been described in conjunction with specific embodiments thereof, it is evident that many alternatives, modifications and variations will be apparent to those skilled in the art and in light of the foregoing description. Accordingly, it is intended to embrace all such alternatives, modifications and variations as fall within the spirit of the appended claims.