Abstract:
A downhole deburring tool is equipped with retractable cutters which permit it to fit through restrictions in a wellbore—e.g., a subsurface safety valve—and subsequently expand to deburr or scrape a section of tubing having an internal diameter greater than that of the restriction. In one preferred embodiment, tapered surfaces on the tool act to effect retraction of the cutters during withdrawal of the tool from a wellbore. Deburring operations with the tool may increase the effectiveness of bridge plugs and/or ball sealer systems to permit chemical treatment of selected zones. Scraping operations with the tool to remove scale, corrosion and other material from the inner surface of a well tubular can increase the effective diameter of the tubing thereby allowing greater production

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    None 
       STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
       [0002]    Not Applicable 
       BACKGROUND OF THE INVENTION 
       [0003]    1. Field of the Invention 
         [0004]    This invention relates to well servicing tools. More particularly, it relates to wireline tools used to finish or repair the interior surface of well casing tubulars. 
         [0005]    2. Description of the Related Art including information disclosed under 37 CFR 1.97 and 1.98 
         [0006]    A burr is a deformation of metal wherein a raised edge forms on a metal part which has been machined or otherwise formed. It may be present in the form of a fine wire on the edge of a freshly sharpened tool or as a raised portion on a surface, after being struck a blow from an equally hard, or heavy object. 
         [0007]    More specifically, burrs are generally unwanted material remaining after a machining operation such as grinding, drilling, milling, or turning. Burr formation in machining accounts for a significant portion of machining costs for manufacturers in America and around the world. Drilling burrs, for example, are common when drilling almost any material. 
         [0008]    Deburring tools may be used where the burr from a previous metal-working operation needs to be removed for cosmetic, safety or performance reasons. 
         [0009]      FIG. 6  depicts a wellbore  10  of the prior art in formation F. Wellbore  10  comprises casing  12  which has been perforated in production zone P with perforations  40 . Fractures  42  in formation F have been created to enhance the flow of hydrocarbon products from formation F into wellbore  10 . Also shown in  FIG. 2  are polymer sealing balls  44  which may be used to selectively plug perforations  40  in certain regions of the well. In this way, different production zones may be selectively treated—e.g. with an acid treatment or a certain proppant. Fluid pressure within wellbore  10  acts to seat balls  44  in perforations  40  thereby preventing the flow of treatment fluid(s) pumped into wellbore  10  from entering production zone P. Certain perforations  40  in casing  12  are shown in the sealed condition with seated balls  44 ′. After treating a different production zone (or region of the well), fluid pressure within wellbore  10  may be reduced thereby permitting fluids to flow from formation F into the wellbore, dislodging seated balls  44 ′ 
         [0010]    It will be appreciated by those skilled in the art that the sealing effectiveness of polymer balls  44  depends, at least in part, on the smoothness of perforations  40 . Inasmuch as perforations  40  are typically formed using shaped-charge explosive devices (“perforating guns”), the holes are often rough. Deburring the holes provides a smoother wellbore (which is less disruptive to fluid flow) and also provides a better seat for polymer sealing balls  44 . 
       BRIEF SUMMARY OF THE INVENTION 
       [0011]    A preferred embodiment of the deburring tool of present invention comprises spring-loaded cutting dogs which expand in a radial direction for deburring or scraping operations and which may retract upon encountering a restriction in the internal diameter of the well casing. The deburring tool may be used in pairs to achieve substantially 360° coverage of the inner surface of a well&#39;s casing (or other tubular element). 
         [0012]    Without deburring, burrs and other particles present on the side walls of the tubing reduce the effectiveness of the elastomeric elements of bridge plugs to seal against and grip the inner wall of the tubing. In practice, valves under the upward force of well pressure and the downward force of acid pumping have became dislodged and blown down or up the well, necessitating major fishing operations costing millions of dollars. In similar fashion, deburring increases the effectiveness of ball sealer systems to be set in the desired area to provide production zone shutoff. Use of a tool according to the invention prior to setting a bridge plug has been shown to provide a significant improvement in bridge plug setting efficiency. The tool may also be used for corrosion removal of perforated tubing. 
         [0013]    In one particular preferred embodiment, the deburring tool comprises a carriage moveable in an axial direction between a first position and a second position. Retractable cutters connected to the carriage move from a first position wherein the tool has a first, smaller outside diameter to a second position in which the tool has a second, larger outside diameter. A shear pin restrains the carriage in a first position until a pre-selected force urging the carriage towards the second position is exceeded. 
         [0014]    In certain embodiments, selected surfaces of the cutter are sloped or tapered to provide a cam-type action when the tool encounters a restricted diameter during withdrawal from a wellbore. The cam-type action urges the cutters into the retracted position, thereby reducing the outside diameter of the tool and permitting to pass through regions of reduced inside diameter, such as subsurface safety valves and the like. 
     
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING(S) 
         [0015]      FIG. 1  depicts a tool string comprising a pair of deburring tools according to the invention being run in hole in a cross-sectioned, subterranean well bore. 
           [0016]      FIG. 2  depicts a tool string comprising a pair of deburring tools according to the invention in operating condition in a cross-sectioned, subterranean well bore. 
           [0017]      FIG. 3  is a cross-sectional view taken along line  3 - 3  in  FIG. 1 . 
           [0018]      FIG. 4  is a cross-sectional view taken along line  4 - 4  in  FIG. 2 . 
           [0019]      FIG. 5  is a cross-sectional view taken along line  5 - 5  in  FIG. 2 . 
           [0020]      FIG. 6  is a cross-sectional view of a perforated section of well casing temporarily plugged with polymer spheres, according to a prior art technique for selective zone well treatment. 
           [0021]      FIG. 7  is an elevation of a pair of deburring tools according to the invention connected together in-phase (for purposes of illustration). 
           [0022]      FIG. 8  is a cross-sectional view of a deburring tool according to the invention in run-in mode with the cutting teeth retracted. 
           [0023]      FIG. 9  is a cross-sectional view of a deburring tool according to the invention in operating mode with the cutting teeth extended. 
           [0024]      FIG. 10  is a cross-sectional view of a deburring tool according to the invention shown as it is being withdrawn from a well bore with the cutting teeth retracted. 
           [0025]      FIG. 11  is an elevation of a pair of deburring tools according to a second embodiment of the invention connected together in-phase (for purposes of illustration). 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0026]    In order to allow hydrocarbons to flow from a formation into a cased wellbore, the casing may be perforated to create holes in the casing or liner to achieve efficient communication between the reservoir and the wellbore. The characteristics and placement of the communication paths (perforations) can have significant influence on the productivity of the well. A perforating gun assembly with the appropriate configuration of shaped explosive charges and the means to verify or correlate the correct perforating depth can be deployed on wireline, tubing or coiled tubing. 
         [0027]    Hydraulic fracturing is a stimulation treatment routinely performed on oil and gas wells in low-permeability reservoirs. Specially engineered fluids are pumped at high pressure and rate into the reservoir interval to be treated, causing a vertical fracture to open. The wings of the fracture extend away from the wellbore in opposing directions according to the natural stresses within the formation. Proppant, such as grains of sand of a particular size, is mixed with the treatment fluid to keep the fracture open when the treatment is complete. Hydraulic fracturing creates high-conductivity communication with a large area of formation and bypasses any damage that may exist in the near-wellbore area. 
         [0028]    Matrix acidizing is the treatment of a reservoir formation with a stimulation fluid containing a reactive acid. In sandstone formations, the acid reacts with the soluble substances in the formation matrix to enlarge the pore spaces. In carbonate formations, the acid dissolves the entire formation matrix. In each case, the matrix acidizing treatment improves the formation permeability to enable enhanced production of reservoir fluids. Matrix acidizing operations are ideally performed at high rate, but at treatment pressures below the fracture pressure of the formation. This enables the acid to penetrate the formation and extend the depth of treatment while avoiding damage to the reservoir formation. 
         [0029]    As described above, bridge plugs or polymer balls (as depicted in  FIG. 6 ) may be used to selectively block perforations in a well casing to permit different treatments to be applied to different portions or production zones of a well without exposing other portions to the treatment agent. 
         [0030]    Subsurface Safety Valves (SSVs) are often deployed in hydrocarbon producing wells to shut off production of well fluids in emergency situations. Such SSVs are typically fitted into production tubing in the wellbore, and operate to block the flow of formation fluids upwardly through the production tubing should a failure or hazardous condition occur at the well surface. 
         [0031]    SSVs are designed either to be slickline retrievable, or tubing retrievable. If a safety valve is configured to be slickline/wireline retrievable (WRSSV), it can be easily removed and repaired. If the SSV forms a portion of the well tubing, it is commonly known as “tubing retrievable” (TRSSV). In this instance, the production tubing string must be removed from the well to perform any safety valve repairs. SSV&#39;s may have a smaller internal diameter than casing below the SSV. The SSV may thereby effectively restrict the diameter of conventional tools which may be deployed below the SSV. The present invention solves the problem of passing a deburring tool through a more narrow portion of a well bore for operation in section of the wellbore having a greater internal diameter. 
         [0032]    The invention may best be understood by reference to the particular preferred embodiment illustrated in the drawing figures. 
         [0033]    Referring to  FIG. 1 , a pair of downhole deburring tools  30  according to one embodiment of the invention is shown as part of a tool string in a wellbore  10  comprised of tubular casing  12  having internal diameter (I.D.)  14 . The well tubing also comprises tubing-retrievable subsurface safety valve (TRSSV)  16  having internal diameter  18  (which may be less than I.D.  14  of casing  12 ). It will be appreciated that TRSSV  16  forms a portion of the well tubing and its internal diameter  18  may be the limiting factor which dictates the maximum outside diameter (O.D.) of conventional downhole tools which may be deployed in the well. 
         [0034]    In addition to deburring tool  30 , the illustrated tool string comprises knuckle joint/crossover  20  (as shown in  FIG. 2 ), fluted centralizer  22 , stem  24 , 5.85-inch fluted centralizer  26 , brush assembly  28  and gauge cutter  32 , all of which are conventional in the art. The gauge cutter is designed to cut away paraffin, scale, or other debris from the ID of the tubing. Cutting operations can be performed with the well flowing or while circulating, so that the debris flows from the well as it is cut. It is good practice to make a gauge cutter run prior to running any downhole tools, particularly prior to setting and retrieving packers and plugs. The gauge cutter size is selected depending on the minimum restriction inside the wellbore completion. It is made up at the bottom of the tool string and run into the well. On its path down the tubing, it cuts paraffin, wax, and other soft debris from the tubing. However, the gauge cutter diameter (gauge) must be selected to accommodate the smallest I.D. of the well tubing. Hence, burrs, scale and other buildup on the interior surface of larger I.D. portions of the well tubing will not be completely removed by a gauge cutter. 
         [0035]    Tool strings comprising a deburring tool according to the invention may include additional or fewer components as the downhole conditions and particular well configuration may dictate. As illustrated in  FIGS. 1 and 2 , deburring tool  30  may typically be paired in a tool string with an additional deburring tool positioned such that its retractable cutters are oriented 90° about the central axis relative to the cutters on the other deburring tool so that deburring may be effected substantially throughout 360 degrees.  FIG. 7  shows deburring tool  30  joined to deburring tool  30 ′. For purposes of illustration only, the tools are shown aligned in the same direction. When in operating configuration, the two tools  30  and  30 ′ are preferably aligned 90° “out of phase” with each other to achieve substantially 360° coverage of the inner wall—i.e., the retractable cutters of tool  30  are oriented 90° about the central axis relative to the cutters on deburring tool  30 ′ 
         [0036]      FIG. 2  shows the tool string illustrated in  FIG. 1  deployed deeper in wellbore  10 —i.e., past TRSSV  16 . Deburring tools  3  are now in production zone P, in position to deburr perforations  40  in casing  12 . 
         [0037]      FIG. 8  shows deburring tool  30  in running mode—i.e., configured so as to be run into a well on a tool string with cutters  52  retracted so as to reduce the O.D. of the tool and permit it to pass through certain restrictions in the well bore. In the illustrated embodiment, the deburring tool  30  has an overall O.D. with its cutters retracted that permits it to pass through a TRSSV having an internal diameter A of 5.963 inches. Tubing  12  is shown in phantom. 
         [0038]    Deburring tool  30  comprises mandrel  50  having externally threaded connecter  70  at a first end and internally threaded connector  72  at a second end. Mandrel  50  may comprise internal cavity  51  in fluid communication with fluid passages  55  which permit the passage of well fluids through the tool. Circulating fluids may be used to remove metal cuttings from the wellbore, as is conventional in the art. 
         [0039]    Deburring cutters or teeth  52  are attached to or formed in the outer circumference of floating carrier  54 . Carrier  54  is mounted on carriage  74  which may move axially on mandrel  50 . Carriage  74  is slidably secured to mandrel  50  with lower retainer  66  at a first end and upper retainer  68  at a second end. Axial movement of carriage  74  in the upward direction is limited by shoulder  53  on mandrel  50 . 
         [0040]    Cavities  61  in carriage  74  contain resilient elements  60  which bias carrier  54  in an outward, radial direction. In the illustrated embodiment, resilient elements  60  comprise coiled springs. 
         [0041]    In the running mode illustrated in  FIG. 8 , outward radial movement of carrier  54  is prevented by the contact of tapered surface  62  with surface  56  on carrier  54 . Axial movement of carriage  74  on mandrel  50  is prevented by shear pin  64 . Thus, when shear pin  64  is intact, cutters  52  are held in a retracted position. 
         [0042]      FIG. 9  depicts deburring tool  30  with its cutters deployed in a section of tubing  12  (shown in phantom) having internal diameter B (which may be greater than internal diameter A shown in  FIG. 8 ). Pin  64  has sheared and carriage  74  has moved in an upward axial direction on mandrel  50 . This axial movement changes the contact position of tapered surface  62  and surface  56  on carrier  54  allowing floating carrier  54  to move radially outward under the influence of springs  60  until cutters  52  contact the interior surface of the well tubing. In the illustrated embodiment, this well tubing has an internal diameter of from about 6.3 to about 6.4 inches, which is larger than the internal diameter of a TRSSV located higher in the well. Radial movement of floating carrier  54  may also be limited by the contact of the upper retainer  68  with shoulder  53  and the resulting contact point of surfaces  62  and  56 . In this way, variations in the internal diameter of the well tubing may be accommodated, to a degree. 
         [0043]    Deployment of cutters  52  on carrier  54  may be effected by lowering the deburring tool  30  until restrictions in the well bore (such as burrs or scale) contact cutters  52  thereby creating a drag force on the tool. This drag force acts to urge carriage  74  towards shoulder  53  as the tool is lowered. When the drag force is sufficient to shear pin  64 , carriage  74  moves axially on mandrel  50  and floating carrier  54  extends in a radial direction. The drag force necessary to effect deployment of cutters  52  may be varied by selecting the shear strength of pin  64 . As will be appreciated by those skilled in the art, the shear strength may be affected by the material of pin  64  and/or its size (diameter). In one particular preferred embodiment, shear pin  64  is brass and the remainder of the deburring tool is steel. 
         [0044]      FIG. 10  depicts deburring tool as it is being withdrawn from the wellbore. Although located in a section of tubing  12  (shown in phantom) having internal diameter C, the tool has an outer diameter D which is less than C. As the tool is pulled up, the drag force acting on cutters  52  acts to urge carriage  74  in a downward axial direction (relative to mandrel  50 ) and away from shoulder  53 . This changes the contact point between surfaces  56  and  62  which returns floating carrier  54  to its retracted position of reduced O.D. Sloped surface  58  on the upper end of carrier  54  also acts as a cam to urge carrier  54  radially inward as the tool encounters restrictions in the inner diameter of the wellbore as it is being withdrawn. This may occur particularly at a subsurface safety valve. 
         [0045]    Upon recovery of the deburring tool  30  at the surface, shear pin  64  may be replaced and the tool reused for another deburring operation. 
         [0046]      FIG. 11  illustrates a second embodiment of the invention having an alternative configuration of cutters  52 ′.  FIG. 11  shows deburring tool  31  joined to deburring tool  31 ′. For purposes of illustration only, the tools are shown aligned in the same direction. When in operating configuration, the two tools  31  and  31 ′ are preferably aligned 90° “out of phase” with each other to achieve substantially 360° coverage of the inner wall—i.e., the retractable cutters of tool  31  are oriented 90° about the central axis relative to the cutters on deburring tool  31 ′. Other cutter configurations will be readily apparent to those skilled in the art. 
         [0047]    Although the invention has been described in detail with reference to certain preferred embodiments, variations and modifications exist within the scope and spirit of the invention as described and defined in the following claims.