Abstract:
A downhole debris filtering apparatus has the flow diverter retracted as the tool is run in. Settling velocity is the rate at which debris will fall through the fluid. Settling velocity is dependent on the density of the fluid and the debris density. If the fluid velocity exceeds the settling velocity, the debris will rise. The restricted annular area outside the screens raises the fluid velocity. Above the cup sleeve, the annular area increases significantly and the fluid velocity is reduce to below the settling velocity to allow debris to settle to the bottom of the tool. On run in, the fluid merely bypasses on the outside of the filter. Large debris will settle into the tool as described. When pulled out of the hole the swab cup/flow diverter is actuated into casing or liner wall contact and a large passage is opened to allow flow though the filter. Small debris that has risen above the tool will be captured as the fluid is filtered through the screen. Another embodiment with a non-retractable cup uses a sliding sleeve valve with a large open area.

Description:
FIELD OF THE INVENTION 
     The field of this invention is downhole cleanup of casing and liners and more particularly after cementing and before completion. 
     BACKGROUND OF THE INVENTION 
     The cementing process is known to leave debris such as cement lumps, rocks, and congealed mud in the casing or liner. Other debris can be suspended in the mud and it can include oxidation lumps scale, slivers, shavings and burrs. A variety of well cleaning tools have been developed particularly to dislodge such debris from the casing or liner walls. Jet tools are used to blow such debris loose. A variety of casing scrapers and brushes have been developed to accomplish the same purpose. These tools have more recently been combined with additional tools to filter the downhole fluid and capture the debris therein for removal to the surface. 
     One such debris filtering tool is described in UK Application 2 335 687 and is called the Well Patroller, a trademark of the owner Specialised Petroleum Services of Aberdeen, Scotland. This device generally features a wiper cup that rides the inside of the casing. The cup prevents flow around a mandrel. As the tool is lowered, flow is directed through a plurality of ball check valves into an annular space behind a screen and out though the center of the cup and around the mandrel. In this embodiment, no filtration occurs as the tool is inserted and the cup wipes the casing wall. When the tool is brought out of the wellbore, the ball check valves close and fluid above the cup is directed to the annular space inside the filter and out through the filter. The annular space acts as a reservoir for debris retained by the filter. If the filter clogs pressure can be built up to blow a bypass rupture disc, or, in some embodiments to simply shear screws and blow the cup off the mandrel. There are shortcomings in this design. The most significant is that the opening size in the check valves is small and is prone to plugging with debris. When running in the Well Patroller, downhole progress is stopped every 90 feet or so as another stand of tubulars is added at the surface. During these times the fluid flow through the tool stops and debris suspended in the fluid will settle to the bottom of the tool. The debris will eventually accumulate to the point which the ball check valves can not open. Once fluid can not pass though the check valves, the annular restriction at the top of the tool will force the annular fluid to pass through the screen. Any debris in the fluid will not be able to pass through the screen. When the tool is pulled out of the well, the debris will be left in the well. The Well Patroller tool is used in conjunction with a separate tool to scrape debris off the inside casing wall. The wiper cup&#39;s purpose, in this tool, is to divert flow as opposed to scraping or swabbing the inner casing wall. 
     Other debris removal tools are shown in UK Application 2 335 218; U.S. Pat. Nos. 4,515,212 and 5,330,003. The tool in UK Application 2 335 218 requires forced circulation through a plurality of eductors coupled with a deflector for the induced flow to encourage solids to drop into an annular space. Boot baskets, such as those made by Tri-State Oil Tools Industries Inc., now a part of Baker Hughes Incorporated featured an annular space defined between a solid basket and a mandrel. Solids were capable of being captured on the trip downhole solely due to the velocity decrease as the flow emerged above the boot so that solids could drop into the annular space between the mandrel and the boot. Since the boot was solid, no meaningful capture of solids occurred on the trip out of the hole. 
     One of the objects of the present invention is to eliminate or, at least minimize, the shortcomings of the Well Patroller device and the other tools previously used to filter downhole debris. The objective is addressed by providing an improved open area in the valving to reduce the potential problems from plugging. Another feature is the retractable flow diverter which allows rapid insertion into the wellbore, and provides easy passage of suspended debris past the tool. Yet another feature improves the valve structure in this application to get away from spring loaded balls which can create maintenance concerns. These and other advantages of the present invention will be more readily apparent to those skilled in the art from a review of the preferred embodiment which appears below. 
     SUMMARY OF THE INVENTION 
     A downhole debris filtering apparatus is disclosed. In a preferred embodiment, the flow diverter is retracted as the tool is run in to provide easy passage for debris. Settling velocity is the rate at which debris will fall through the fluid. Settling velocity is dependent on the density of the fluid and the debris density. If the fluid velocity exceeds the settling velocity, the debris will rise. The restricted annular area outside the screens raises the fluid velocity. Above the cup sleeve, the annular area increases significantly and the fluid velocity is reduce to below the settling velocity to allow debris to settle to the bottom of the tool. On run in, the fluid merely bypasses on the outside of the filter. Large debris will settle into the tool as described. When pulled out of the hole the swab cup/flow diverter is actuated into casing or liner wall contact and a large passage is opened to allow flow though the filter. Small debris that has risen above the tool will be captured as the fluid is filtered through the screen. Another embodiment with a non-retractable cup uses a sliding sleeve valve with a large open area which promotes free flow and minimizes fouling from deposited debris. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIGS. 1 a - 1   e  illustrate in section a first embodiment of the tool in the run in position. 
     FIGS. 2 a - 2   e  illustrate the same tool being pulled out of the well. 
     FIGS. 3 a - 3   b  illustrate the distinct features of the preferred tool which differ from FIGS. 1 a - 1   e , showing the retractable feature, in the run in position. 
     FIGS. 4 a - 4   b  are the tool portions of FIGS. 3 a - 3   b  in the pulling out of the well position. 
     FIGS. 5 a - 5   e  illustrate the preferred tool in the run in position with the sliding sleeve covering the screen. 
     FIGS. 6 a - 6   e  is the tool of FIGS. 5 a - 5   e  being pulled from the well. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring to FIGS. 1 a - 1   e , the apparatus A, has a mandrel  10  with a top thread  12  and a lower thread  14 . Top thread  12  can be used to attach a string (not shown) to run the apparatus A into wellbore  16 . Those skilled in the art will appreciate that the wellbore  16  represents casing, liners, or any other tubular string downhole and will henceforth be referred to collectively as “casing  16 ”. Bottom thread  14  as well as top thread  12  can also accommodate other known cleaning tools such as scrapers and jets to name a few. 
     Mandrel  10  has a passage  18  that extends from bottom sub  20  to top sub  22 . Outside of mandrel  10  is a screen  24  which defines an annular space  26  around the mandrel  10  for the purpose of accumulating filtered debris, as will be explained below. Annular space  26  has a lower end  28  shown in FIG. 1 e  adjacent bottom sub  20 . As shown in FIG. 1 c , screen  24  terminates in a sleeve  30  at its upper end. At its lower end, screen  24  is supported by the mandrel  10  via bottom sub  20 . Mandrel  10  has a valve member  32  which engages a seat  34  on cup sleeve  36  during run in as shown in FIG. 1 c . Cup sleeve  36  has a plurality of slotted openings  38  which are open at least in part to allow flow in the annular passage  40  between the casing  16  and the screen  24  to enter the cup sleeve  36  as shown by arrow  42 . The screen  24  is bypassed during run in because the annular space  26  is closed off at its upper end  44  by contact of valve member  32  on seat  34 . 
     A cup  46  acts as a seal and is retained by retainer  48  which is in turn mounted to cup or seal sleeve  36 . A series of drag blocks  50  support the cup sleeve  36  against the casing  16  in a sliding manner well known in the art. Cup sleeve  36  has a rupture disc  52  which can be broken with applied pressure if the screen  24  gets clogged as to avoid pulling a wet string from the wellbore. Those skilled in the art will appreciate that other devices that will allow bypass of a clogged screen  24  can be employed instead of rupture disc  52  without departing from the invention. Finally, bolts  54  prevent relative rotation between the sleeve  30  and the cup sleeve  36  while allowing relative longitudinal movement. 
     The major components now having been described, the run in operation can now be explained. The mandrel  10  is advanced into casing  16 . The cup  46  rides on the inside wall of casing  16  and the spring loaded drag blocks  50  do the same. This resistance allows the mandrel  10  to advance with respect to the cup sleeve  36  until the valve member  32  engages the seat  34 . At that time further advancement of the mandrel  10  downhole is made possible by fluid moving in the annular space  40  around the outside of the screen  24  and through the openings  38 . Fluid simply bypasses cup  46  which closes off annular passage  40  by passing through the cup sleeve  36 , as shown by arrows  42 . 
     FIGS. 2 a - 2   e  illustrate what happens on the trip out of the casing  16 . An upward force on mandrel  10  brings it up and with it, screen  24  and sleeve  30 . Because the cup  46  and the drag blocks  50  hold the cup sleeve  36  momentarily, relative movement occurs. As a result of this relative movement, the sleeve  30  covers the openings  38  and the valve member  32  moves away from the seat  34 . The latter movement opens the upper end  44  of the annular space  26  to passage  58 . As the mandrel moves uphole fluid flows through passage  58  through screen  24 , as shown by arrows  60 . If screen  24  plugs, pressure is applied to passage  58  to blow rupture disc  52  so that fluid can exit to the annular space  40  and bypass the screen  24 . This prevents pulling a wet string if the annular space fills with debris or if for any other reason, the screen  24  plugs. When the tool is removed from the wellbore, the accumulated debris can be easily removed by removing bolts  25  near lower end  28  of annular space  26 . At that point the sleeve  27  which has windows  29  can be rotated until windows  29  align with openings  31  adjacent the lower end  28  of annular space  26  (see FIG. 1 e ). 
     The preferred version of the apparatus has some changes illustrated in FIGS. 3 a - 3   b , in the run in position. In other respects than those mentioned below, the embodiments are virtually identical. In the preferred version, drag blocks  62  support wiper sleeve  64  during run in, allowing the mandrel  66  to be advanced relative to it. This relative motion, on run in, places the valve member  68  in bore  70  of wiper sleeve  64 , closing off passage  72 . Wiper  74  is sufficiently rigid to maintain its cylindrical shape flanked above and below by support rings  76  and  78 . The assembly of the wiper  74  with rings  76  and  78  can move longitudinally on wiper sleeve  64  during run in. Thus, running in will not cause the wiper  74  to collapse and extend outwardly to the position shown on FIG. 4 a  until an upward force is put on the mandrel  66 . Those skilled in the art will appreciate that moving the mandrel  66  downhole will direct fluid outside of screen  80  in annular passage  82  as shown by arrow  84 . As the apparatus A advances downhole, fluid will pass around the outside of the wiper  74 . No flow will go through screen  80  to speak of because the annular space  86  is blocked by valve member  68  in bore  70 . Some flow could pass through bore  88  in mandrel  66  but the path of least resistance will be through annular passage  82 . Screen  80  has a sleeve  90  which contains a rupture disc  92  or an equivalent device that can provide an emergency bypass of screen  80  if it becomes necessary when coming out of the well. 
     When it is time to trip out of the well, an upward force is placed on the mandrel  66  and it moves with respect to wiper sleeve  64 . This movement shifts valve member  68  away from bore  70  to open up passage  72 . Additionally, sleeve  90  engages ring  78  which buckles wiper  74  into contact with the casing or downhole tubular  94 . Sleeve  90  moved up because it is attached to screen  80  which is in turn attached to mandrel  66 . Since drag blocks  62  hold back wiper sleeve  64  the wiper  74  can collapse into the contact position for effective sealing of the inner wall of the casing or tubular  94 . The filtering occurs as the apparatus A is pulled uphole. Fluid is forced to pass downwardly through passage  72  through screen  80  as shown by arrow  96 . 
     The embodiment shown in FIGS. 5 a - 5   e  and  6   a - 6   e  has a valving variation as compared to the embodiment of FIGS. 3 a - 3   b  and  4   a - 4   b . In FIGS. 5 a -e the valve member  68  is eliminated in favor of sleeve  98 , the top of which appears in FIG. 5 b . Sleeve  98  is connected to sleeve  100 , which is, in turn connected to mandrel  104 . Sleeve  98  has a plurality of openings  106 . Openings  106  are misaligned with openings  108  in the run in position so that screen  110  is completely covered on its exterior. Flow, represented by arrow  112  goes around the tool as the tool is advanced downhole (see FIG. 5 c ). Referring to FIG. 5 b , the flow  112  goes past the flow diverter  114  which is in the relaxed position for run in. Due to the high velocity, the solids are retained by the flow  112  past the drag blocks  116 , which have gaps between them to allow the flow  112  to progress. The larger solids  118  can drop into annular space  120  due to the velocity reduction as the flow area suddenly increases. It should be noted that the outer surface of the screen  110  is fully protected against deposition of solids during the trip downhole. On the trip uphole, the drag blocks facilitate the expansion of the fluid diverter  114  against the wellbore to create a seal around the exterior of the tool. Openings  106  are pulled up into alignment with openings  108  due to the upward force on mandrel  104 . Sufficient relative movement occurs to compress fluid diverter  114  as it is retained sufficiently by the drag blocks  116 . With the fluid diverter  114  in the position shown in FIG. 6 b , tandem movement resumes and flow through screen  110  proceeds as illustrated by arrow  124 . The flow  124  must pass through annular space  120  where additional solids, including the smaller particles, which did not previously drop out on the trip downhole, can be retained. Those skilled in the art will appreciate that although a windowed sleeve has been shown as the screen isolation member, other techniques are also within the scope of the invention. These could involve dissolvable coatings and cover sleeves which increase diameter under a twist akin to the action of a child&#39;s toy known as a finger trap. One way to accomplish this is to use interlocking elements such as a weave. When the elements a re twisted in a first direction they close up the openings between them. When the twist force is reversed the weave defines openings to allow flow through the screen. The advantage of having the screen  110  covered as solids-laden fluid flows past it is that there is a reduced chance of plugging and a lager flow at reduced pressure drop through the screen  110  on the trip up the wellbore. 
     Those skilled in the art will appreciate that wiper  74  can have a cup profile, or it can be a solid elastomer block or a bladder, as illustrated. The valving used in both embodiments and its location above the screen permits large flow areas which can let debris pass with minimal risk to clogging the valve structure. In both embodiments, if the increase in annular area is great enough to reduce the fluid velocity below the settling velocity of the debris, the debris will settle into the tool when running into the well. When stopping to add drill pipe, the tool will be pulled up enough to allow any debris that has accumulated above the wiper sleeve  64  to passthrough passage  96  and settle to the bottom of the tool. As distinguished from the Well Patroller, the flow through the screen is effectively stopped when running in the hole. In the Well Patroller, the fluid can pass through the screen at the same time that it passes through the ball valves. Debris is likely to be trapped to the outside of the screen and remain in the wellbore when the Well Patroller is pulled out. 
     Those skilled in the art will appreciate that the parts orientation of either embodiment could be reversed so that the cup  46  is open toward downhole with filtering occurring on the same trip down or on the trip up. Similarly the wiper  74  can be expanded on the trip down and retracted for the trip up. Filtration can occur on the trip up for example. It is also within the scope of the invention to coat the screen such as  24  with a removable material which can be dissolved or otherwise removed on the trip downhole or when the proper depth is reached. Coating the screen for the trip into the wellbore will reduce any tendency of buildup of debris on the outside of the screen on the way down. In the figures, the screens  24  or  80  are shown schematically and should be understood to contemplate the inclusion of such removable layers or coatings. Additionally, sealing can be accomplished with shapes different than cup  46 . Other valving arrangements to close upper end  44  are also contemplated. Openings  38  may have different shapes and are preferred to be sufficiently large to allow loose debris to pass there through. When used herein, “screen” refers to any device which can let some material pass while retaining another and can include such structures as mesh, weave and porous materials, to name a few. 
     It is to be understood that this disclosure is merely illustrative of the presently preferred embodiments of the invention and that no limitations are intended other than as described in the appended claims.