You are an expert at summarizing long articles. Proceed to summarize the following text:

You are an expert at summarizing long articles. Proceed to summarize the following text: 
RELATED APPLICATIONS  
       [0001]    This application is a Continuation application of PCT Application Serial No. PCT/BE02/00031 entitled Reamer filed on Mar. 12, 2002, which claims priority to Belgium Application Serial No. 2001/0157 filed on Mar. 12, 2001. 
     
    
     
       TECHNICAL FIELD OF THE INVENTION  
         [0002]    The present invention relates to a bore hole opener, particularly for enlarging a bore hole underneath a casing in the field of oil prospecting.  
         BACKGROUND OF THE INVENTION  
         [0003]    Underreamers are typically used to enlarge the diameter of a bore hole, for one or more of a variety of reasons. It is often necessary for the underreamer to first travel through a casing(s), having a diameter smaller than the diameter desired down-hole of the casing. Accordingly, underreamers are provided with cutting arms that may be retracted during travel through the casing. When a predetermined depth is reached, the cutting arms are actuated to an extended position, and drilling with the underreamer commences. Before an underreamer is brought into service on each occasion, it may be necessary that each arm be locked distinctly in the inactive position. This is to prevent the arms from being deployed unintentionally following variations in the pressure of the fluid passing through the underreamer, until a particular time and/or depth chosen by the operator. In particular therefore, for each new use of a typical underreamer, it is often necessary to remove each arm on each occasion, and possibly the housing thereof, in order to renew the distinct locking means.  
           [0004]    In addition, this type of equipment is subjected to very harsh forces under working conditions that are known to be very difficult and therefore very expensive. Firstly, an equipment breakdown may cost significant time, money and resources in attempting to save the equipment, for example jammed at a great depth, and in particular saving the bore hole made at great expense and which, otherwise, could be definitively condemned. Secondly, when the equipment is recovered, an equipment breakdown must be able to be repaired very easily because the technical repair means available on or close to a drilling platform are sometimes limited.  
         SUMMARY OF THE INVENTION  
         [0005]    In accordance with a particular embodiment of the present invention, a bore hole opener comprises a body of longitudinal axis., a duct for drilling fluid, formed longitudinally in the body, and having a fluid passage cross section of inside radius i, and at least two hole-opening arms which have an active part equipped with cutting mechanisms, which are arranged in such a way that they can slide between a position of rest in the body and an active position partially out of the body, which are guided and supported for this purpose in the body over a distance g and which, in the active position, project from the body by a length o.  
           [0006]    This kind of opening tool has, for example, a body diameter of, for example, between 119 and 427 millimeters. That leaves only a small amount of space in which to build a simple mechanism, provide the aforesaid elements, and give these proportions which give them, and the opener as a whole, a balanced relative solidity.  
           [0007]    It is an object of the present invention to provide a solution to this problem and the present invention proposes to observe a given proportional relationship between, on the one hand, the respective values mentioned above for the inside radius i, distance g, length o and, on the other hand, the sum s of these three values.  
           [0008]    To this end, according to the invention, the values of i, g and o are chosen to simultaneously satisfy the following conditions:  
           [0009]    I+g+o=s;  
           [0010]    0.30&lt;i/s&lt;0.45, 0.40&lt;g/s&lt;0.60, 0.07&lt;o/s&lt;0.20.  
           [0011]    It has been found that these conditions can advantageously be successfully applied to various sizes of hole opener, as explained hereinbelow.  
           [0012]    According to one embodiment of the invention, for its sliding guidance in the body, each arm may comprise a cylindrical portion of diameter d, the value of which is at least equal to the value of g above.  
           [0013]    According to a particular embodiment of the invention, in order to move it from the position of rest into the active position, each hole-opening arm has a face, internal to the body, designed to be subjected directly, in the same way as an active face of a piston, to the pressure of the drilling fluid flowing through the body.  
           [0014]    Other details and particular features of the invention will become apparent from the appended claims and from the description of the schematic drawings attached to this text and which illustrate, by means of non-limiting example, at least one preferred embodiment of the hole opener of the invention.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0015]    [0015]FIG. 1 shows, in axial section, a hole opener, an arm visible in the figure being in the position of rest.  
         [0016]    [0016]FIG. 2 shows a partial axial section in which the visible arm is in the active position.  
         [0017]    [0017]FIGS. 3 and 4 each show a cross section in which three hole-opening arms are depicted in the position of rest, and in the active position, respectively.  
         [0018]    [0018]FIG. 5 shows, to a larger scale and in longitudinal section, an assembly comprising an arm and an intermediate support so that arms can be mounted and exchanged quickly.  
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0019]    In the various figures, the same references denote similar or analogous elements.  
         [0020]    The hole opener  1 , as depicted by way of example in FIGS.  1  to  4 , comprises a body  2  of longitudinal axis  3 , a duct  4  for drilling fluid, formed longitudinally in the body  2 , and at least two hole-opening arms  5  which are distributed symmetrically in the body  2  about the longitudinal axis  3  to make sure that the operation of the hole opener  1  is approximately balanced. FIGS. 3 and 4 show that three arms  5  can easily be arranged in the body  2  with angles of 120° between two successive arms  5 .  
         [0021]    The arms  5  each have an active part  7  equipped with cutting mechanisms  8  (FIGS.  3  to  5 ) which are known and explained hereinbelow. The arms  5  are arranged in the body  2  so that they can be moved between a position of rest  9  in this body  2  and an active position  10  partially out of this same body  2 .  
         [0022]    Each arm  5  may comprise, for moving it from the position of rest  9  into the active position  10 , a face  12  internal to the body  2  and designed to be subjected directly, in the same way as an active face of a piston, to the pressure of the drilling fluid flowing through the body  2 . Through this arrangement, it is possible to avoid having intermediate mechanical parts between the fluid which is to actuate the arm  5  and this arm, and the problems known to those skilled in the art which may ensue.  
         [0023]    The internal face  12  of the arm  5  should be understood as meaning any face/surface in contact, at any moment in the drilling and/or hole-opening operation, with the pressurized fluid flowing through the duct  4 . Some of these faces/surfaces subjected to the same pressure will compensate for each other but, overall, there remains enough positive area that, for example with a positive pressure differential of the order of 2 MPa (about 300 psi) between the pressure of the fluid in the duct  4  and that of the fluid outside the body  2  in the region of the arm or arms  5 , a thrust force of the order of 2000 kg can be obtained, in order to deploy the arm  5  from the body  2 .  
         [0024]    The arm  5  is mounted in such a way that it can slide parallel to itself in the body  2 , so as to move from the position of rest  9  into the active position  10  and vice versa. The choice of a movement of this kind is one of the more favorable types of movement, for operation in the manner of a piston.  
         [0025]    The movement of the arm  5  can be directed radially and/or in any other favorable direction, whether this be upward or downward with respect to a direction of work of the hole opener, and/or forward or backward with respect to a direction of rotation of the hole opener, possibly in any combination of these directions of movement.  
         [0026]    A movement of pivoting about an axis (not depicted) perpendicular to the longitudinal axis  3  and to the direction of the travel of the arm  5 , and arranged somewhat away from the arm  5  is, however, also possible, but would require special machining of significantly higher cost than the machining of the previous embodiment in order to implement it.  
         [0027]    In order to provide the aforementioned piston function, sealing means  11  are provided at places which are known to those skilled in the art.  
         [0028]    To move it from the active position  10  into the position of rest  9  when the pressure in the duct  4  decreases, the or each arm  5  advantageously comprises elastic return means  13 , for example compression coil springs  14  as depicted in the drawings. This arrangement allows the hole opener  1  to be withdrawn from the bore hole without difficulty.  
         [0029]    The arm  5  may, in the active position  10  out of the body  2 , have a posterior face  16  (with reference to a direction F of advance for opening out the hole) which is at an angle, designed, for example if the springs  14  should be deficient, to help the arm  5  back into the body  2  when the hole opener  1  is being withdrawn from the bore hole.  
         [0030]    The arm  5  can be mounted in the body  2  by means of an intermediate support  15  which acts as a housing and a guide for the arm  5  in the body  2  and which is fixed to the latter, for example by screws  17 . Sealing means  18  may then be provided between the body  2  and said intermediate support  15 .  
         [0031]    The fluid duct  4  has (FIGS. 2 and 4) a passage cross section of inside radius i. The term radius is to be understood in a broad sense, for example half the mean linear dimension of this passage cross section.  
         [0032]    The arms  5  are guided, at least in the active position, in the body  2  or, as appropriate, in their respective intermediate support  15  over a distance g. These same arms  5 , in the active position, project from the body  2  by a length o.  
         [0033]    As FIGS. 2 and 4 show,  
         [0034]    the sum s of the three values i, g and o corresponds to the radius or half the diameter of opening of the arms  5 ,  
         [0035]    the outside diameter of the body  2  is equal to (i+g)×2 or to (s−o)×2,  
         [0036]    thus, the projecting length o is equal to s−g−i.  
         [0037]    The invention proposes to keep the three values i, g and o related to their sum s within respective determined values. This stems from various experiments which yielded fairly narrow ranges for the following three proportions:  
         [0038]    0.30&lt;i/s&lt;0.45, 0.40&lt;g/s&lt;0.60, 0.07&lt;o/s&lt;0.20.  
         [0039]    The value of o considered is the maximum possible value for the movement of the arm  5  in the hole opener.  
         [0040]    Table 1 appended hereto gives, for seven hole openers of different sizes, ranging, in increasing size, from size  1  to size  7 , characteristic dimensions and the corresponding proportions. It is evident from this that preference may be given to the following respective ranges for said proportions:  
         [0041]    0.34&lt;i/s&lt;0.39, 0.45&lt;g/s&lt;0.53, 0.10&lt;o/s&lt;0.16.  
         [0042]    For any other identical construction condition, proportions outside these ranges gave rise to hole openers which did not perform as well as those whose proportions fell within the above ranges, whether in terms of operational reliability, life, quality of work, performance, etc.  
         [0043]    For its sliding guidance in the body  2  or in the intermediate support  15 , each arm  5  may comprise a portion, preferably cylindrical, of diameter d, the value of which is advantageously at least equal to the value of g above. In doing this, attempts are made at making a weighty and robust arm  5 .  
         [0044]    This advantageously cylindrical portion of the arm  5 , in the form of a piston, may be made of a steel, for example surface-hardened on the guide surface so as to reach a hardness of the order of at least 120 or even 140 or as much as 240 kg/mm2. The guide cavity of the body  2  or of the intermediate support  15 , acting as cylinder for said piston, may be formed in a steel treated, for example, by through-hardening of the guide surface to obtain a hardness of at least 120 or preferably 140 kg/mm2.  
         [0045]    Of course, the most favorable technical and economical combination is sought when choosing these hardnesses.  
         [0046]    Prior to a hole-opening operation, each arm  5  is kept in the position of rest  9  in the body  2  by at least one pin  19  designed to break when the pressure of the drilling fluid flowing through the body  2  exceeds a predetermined value higher than a maximum usual boring value.  
         [0047]    For this purpose, the pin  19  may have a region  19 A of calibrated weakness, at the or each point of transition  20  where the pin  19  passes, as the case may be, either from the body  2  or from the intermediate support  15  into the arm  5 . It is obvious that, unlike what has been depicted in FIGS. 3 and 4, the pin  19  does not necessarily have to emerge from both sides of the arm  5 .  
         [0048]    This pin  19  may fix the arm  5  merely to the intermediate support  15  (FIGS. 3 and 4).  
         [0049]    [0049]FIG. 4 shows the pin  19  broken into one part  19 B in the arm and two parts  19 C in the intermediate support  15 .  
         [0050]    The intermediate support  15 , the arm  5 , the aforementioned elastic means  14  and the pin  19  may therefore constitute an assembly  21  (FIG. 5) designed to be assembled beforehand outside the body  2  and then installed therein. This then makes the hole opener  1  not only easier to assemble, but also easier to maintain or repair in the event of damage, etc.  
         [0051]    It must be understood that the present invention is not in any way restricted to the embodiments described hereinabove and that many modifications may be made thereto without departing from the scope of the claims given hereinbelow.  
         [0052]    On its outer face, between two successive arms  5 , the body  2  may have a longitudinal passage  22  for returning drilling fluid to the surface, and a boss  23  arranged in this passage  22  so as to divert and/or deflect the drilling fluid which is rising back up toward the surface onto that part of the wall of the hole on which the arms  5  are acting. The passage  22  and the boss  23  are produced in such a way as not to form too great a restriction to the passage of the returning fluid.  
         [0053]    In a particular embodiment of the hole opener  1 , the travel of an arm  5  between the position of rest  9  and the active position  10  is limited in both directions of travel by stops. In the position of rest  9 , the arm  5  is usually completely retracted into the body  2  and is held therein by reciprocal stop surfaces  
         [0054]    (FIG. 3) or, as appropriate, by the pin  19 . In the active position  10 , the arm  5 , retained by reciprocal stop surfaces  26  (FIGS. 2 and 4), sweeps through an area, the largest diameter of which is equal to between 1.05 and 1.3 times, preferably 1.2 times the nominal diameter of a drill bit associated with the hole opener  1  for a combined drilling and hole-opening operation.  
         [0055]    The cutting mechanisms  8  on the arms  5  are arranged by the person skilled in the art in such a way as, for example, to obtain cutting efficiency similar to that of the cutting means of the associated drill bit.  
         [0056]    The reciprocal stop surfaces  26  may be arranged on exchangeable or adjustable elements so as to allow a user of the hole opener  1  to choose the extent to which the arms  5  can deploy out of the body  2  during service.  
                                                                                           TABLE 1                                       Hole-opener           size                                                    1   2   3   4   5   6   7                        Diameter of   133.4   177.8   250.8   311.2   355.6   431.8   508.0       opening of       the arms =       s × 2       Diameter of   119.1   149.2   212.7   266.7   308.0   371.5   428.6       the body =       (s − o) × 2       Length by   7.15   14.3   19.05   22.25   23.8   30.15   39.7       which the       arms project       out of the       body = o       i.e.       (2s − (2s −       2o)) :2       Guide   36.5   41.9   60.35   75.35   86.0   104.65   115.8       distance = g       Inside   23.05   32.7   46.0   58.0   68.0   81.1   98.5       passage       radius =i       Sum s =   66.7   88.9   125.4   155.6   177.8   215.9   254.0       o + g + i       o/s   0.107   0.161   0.152   0.143   0.134   0.140   0.156       g/s   0.547   0.471   0.481   0.484   0.484   0.485   0.456       i/s   0.346   0.368   0.367   0.373   0.382   0.375   0.388                  
 
         [0057]    Key to the Figures  
         [0058]    [0058] 1  hole opener  
         [0059]    [0059] 2  body  
         [0060]    [0060] 3  longitudinal axis  
         [0061]    [0061] 4  duct  
         [0062]    [0062] 5  hole-opening arms  
         [0063]    [0063] 7  active part  
         [0064]    [0064] 8  cutting means  
         [0065]    [0065] 9  position of rest  
         [0066]    [0066] 10  active position  
         [0067]    [0067] 11  sealing means  
         [0068]    [0068] 12  internal face  
         [0069]    [0069] 13  elastic return means  
         [0070]    [0070] 14  coil springs  
         [0071]    [0071] 15  intermediate support  
         [0072]    [0072] 16  posterior face  
         [0073]    [0073] 17  screws  
         [0074]    [0074] 18  sealing means  
         [0075]    [0075] 19  pin  
         [0076]    [0076] 19 A weakened region(s)  
         [0077]    [0077] 19 B part of the pin  
         [0078]    [0078] 19 C part of the pin  
         [0079]    [0079] 20  transition point  
         [0080]    [0080] 21  assembly  
         [0081]    [0081] 22  longitudinal passage  
         [0082]    [0082] 23  boss  
         [0083]    [0083] 25  reciprocal stop surfaces  
         [0084]    [0084] 26  reciprocal stop surfaces  
         [0085]    S direction of advance of a hole-opening/boring process

Summary:
A bore hole opener for enlarging a bore hole includes a longitudinal body, a duct for drilling fluid, formed longitudinally in the body, having a fluid passage cross-section of inside radius i, and at least two hole-opening arms, borne by the body, which have an active part equipped with cutting mechanisms, which are arranged therein in such a way that they can slide between a position of rest in the body and an active position partially out of the body, and which are guided and supported for this purpose in the body over a distance g and which, in the active position, project from the body by a length o, in which the values of i, g and o are chosen to simultaneously satisfy the conditions i+g+o S;  
     0.30&lt;i/s&lt;0.45, 0.40&lt;g/s&lt;0.60, 0.07&lt;o/s&lt;0.20.