Patent Abstract:
A rotary blowout preventer has a first and a second fluid circuit. Each of the fluid circuits are defined into and out of a stationary body and between the stationary body, a rotating body, and two seals. The first fluid circuit is physically independent from the second fluid circuit although they share a seal interface. A fluid is introduced into the first fluid circuit at a pressure responsive to the well bore pressure. A fluid is introduced into the second fluid circuit at a pressure responsive to and lower than the pressure of the fluid in the first circuit. Adjustable orifices are connected to the outlet of the first and second fluid circuits to control such pressures within the circuits. Such pressures affect the wear rates of the seals. The system can therefore control the wear rate of one seal relative to another seal. A thrust bearing is added to share the load placed upon the upper bearings. The thrust bearing is connected between the top end of a packer sleeve and the stationary body.

Full Description:
BACKGROUND  
         [0001]    U.S. Pat. No. 5,178,215 serves as a starting point for the departure made by the present invention. The disclosure of U.S. Pat. No. 5,178,215 is intended to be incorporated herein by reference and includes a general discussion of an existing rotary blowout preventer which is fluid actuated to grip a drill pipe or kelly, and the controlled circulation of a fluid to lubricate and cool bearings and seals, and to filter particulate matter.  
           [0002]    These existing rotary blowout preventers have an annulus between an outer housing and a rotary housing. Such systems use rather large bearings which require a rather large clearance. Such an arrangement has positive effects but also results in “wobbling” between the rotary housing and the outer housing. The wobbling creates heat, “nibbles” the seals, etc. A fluid is introduced into and circulates through the annulus between the outer housing and the rotary housing to cool the seal assemblies, the bearings and to counteract heat generated by contact between the seals and the rotary housing (wellhead fluid temperatures may normally be about 200° F., and during rotation, without cooling, the temperature would readily increase to about 350° F. and destroy a seal in a relatively short time). The circulated fluid also removes foreign particulate matter from the system. Pumps are used to maintain a fluid pressure in the annulus at a selected pressure differential above the well bore pressure.  
           [0003]    The bearings in these rotary blowout preventers may normally operate at a temperature of about 250° F. Such bearings are subjected to a significant thrust load, e.g. 2,000 lbs.-force, due in part to an upward force created by well bore pressures and placed upon a packer assembly and a sleeve in the rotary housing. Such a thrust load will generate significant heat in a bearing rotating at, for example, 200 rpm. Heat, and heat over time, are important factors which may lead to bearing failure. For example, bearings may immediately fail if they reach temperatures of about 550° F. Even at temperatures of 250° F. a bearing may fail after a significant period of use, for example, twenty days of rotation at 200 rpm when subjected to a significant thrust load.  
           [0004]    Such existing rotary blowout preventers are very functional at wellhead pressures up to 2000 psi. However, for reasons discussed herein, there are added challenges when wellhead pressures are in the range of, for example, 2500 psi to 5000 psi.  
           [0005]    For example, as suggested, the continued and trouble free operability of such rotary blowout preventers is dependent, in part, upon the life of the seals and bearings within the rotary blowout preventer. The seals have a “pressure/velocity” or “pv” rating which may be used to predict the relative life of a seal given the pressure and velocity conditions to be borne by a seal. When considering “PV” rating, it is significant to note that a linear relationship does not exist between the life of a seal and the increases in pressure or rotational velocity to which a seal will be subjected. Rather, the life of the seal decreases exponentially as the pressure or rotational velocity to which the seal is subjected is increased.  
           [0006]    As such, when well bore pressures increase to ranges from 2500 psi to 5000 psi, the loads, the wear and the heat exerted on seals and bearings within a rotary blowout preventer pose a greater challenge to the operations and life of the seals and bearings. This must be considered in the context of the fact that well bore operations may be shut down for maintenance work when significant wear of seals or bearings, significant “nibbling” of seals, or seal/bearing failure occurs. Such shut downs can significantly affect the profitability of well bore operations.  
         SUMMARY OF THE INVENTION  
         [0007]    This rotary blowout preventer has a first and a second pressurized fluid circuit. Each of the fluid circuits are defined into and out of a stationary body and between the stationary body, a rotating body, and two seals. The first fluid circuit is physically independent from the second fluid circuit although they share a seal interface. A fluid is introduced into the first fluid circuit at a pressure responsive to the well bore pressure. A fluid is introduced into the second fluid circuit at a pressure responsive to and lower than the pressure of the fluid in the first circuit. Adjustable orifices are connected to the outlet of the first and second fluid circuits to control such pressures within the circuits. Such pressures affect the wear rates of the seals. The system can therefore control the wear rate of one seal relative to another seal. A thrust bearing is added to share the load placed upon the upper bearings. The thrust bearing is connected between the top end of a packer sleeve and the stationary body. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0008]    [0008]FIG. 1 is a sectional view of a rotary blowout preventer incorporating the invention(s).  
         [0009]    [0009]FIG. 2 is a sectional view of the rotating body without the packer sleeve.  
         [0010]    [0010]FIG. 3 is an enlarged view of the middle and upper seal carriers shown in FIG. 1.  
         [0011]    [0011]FIG. 4 is a sectional view of the top closure.  
         [0012]    [0012]FIG. 5 is a schematic view of a control system which may be used in the invention(s). 
     
    
     DETAILED DESCRIPTION  
       [0013]    Referring to FIGS. 1 and 2, the rotating blowout preventer  8  generally includes a stationary body  10  which houses a rotating body  12 . The rotating body  12  includes a rotating housing  14 , a rotating housing cover plate  16  and a packer assembly  18 . The packer assembly  18  has a split keeper ring  20 , an outer packer  22 , an inner packer  24  and a packer sleeve  26 . The stationary body  10  generally includes a body  28  with a top closure  30  and a bottom closure flange  32 .  
         [0014]    A lower bearing  34  is mounted between the stationary body  10  and the rotating body  12  in a cup  36 . An upper bearing  38  is mounted between the stationary body  10  and the rotating body  12  against a cup  40 . A bottom thrust bearing  42  is mounted between the stationary body  10  and the rotating body  12  on the bottom closure flange  32 .  
         [0015]    A first or bottom seal carrier  44  is mounted between the stationary body  10  and the rotating body  12  and includes a groove for the mounting of a first seal  46 , which may, for example, be a seal of the type marketed by Kalsi Engineering, Inc. A bearing  48 , for example, a type marketed by Kaydon is mounted between the first seal carrier  44  and the rotating body  12 . A locking nut  50   a  may be used for attaching the bottom closure flange  32  to the body  28 .  
         [0016]    Packer adapters  52  and  54  are connected to the packer sleeve  26 . A packer-pulling sleeve  56  engages the upper end of the packer adapter  54 . A thrust bearing  58  has a lower end  60  connected to a top end  62  of the packer sleeve of the rotating body  12 , and an upper end  64  connected to a top closure  66  of the stationary body  10 . The lower end  60  of the thrust bearing  58  is rotatable. The top closure  66  is held in place by a top closure flange  68  and studs  70 . The thrust bearing  58  is mounted inside a bearing retaining ring  72 . The bearing retaining ring  72  has openings between the thrust bearing o-rings  74  and  76  for introduction, circulation and outlet of a cooling fluid as part of a thrust bearing cooling and lubricating circuit  75 . The thrust bearing  58 , may be a commercially available thrust cylindrical roller bearing or it may be custom built.  
         [0017]    The body  28  defines an inlet orifice  80  and an outlet orifice  82  of a first fluid or actuating, lubricating, cooling and filtering circuit  81 . The first fluid circuit  81  is further defined by the annular space between the rotating body  12  and the stationary body  10  and cools, lubricates and filters the region between the rotating body  12  and the stationary body  10  including the lower bearing  34  and the upper bearing  38 . FIG. 2 shows surfaces  17   a  and  17   b  of the rotating housing cover plate  16  which help define the first fluid circuit  81  between the rotating body  12  and the second seal carrier  92 . FIG. 4 shows annular cup  40  and annular surfaces  31   a,b  and  c  in top closure  30  which also define in part the first fluid circuit  81 . The first fluid circuit  81  loads first seal carrier  44  and one side of first seal  46  as well as second seal carrier  92  and one side of second seal  96 .  
         [0018]    The rotating blowout preventer  8  has a second fluid or lubricating, cooling and filtering circuit  83 . The second fluid circuit  83  has an inlet orifice  84  and an outlet orifice  86  which may be tubular and which may be defined by the stationary body  10  such as by the body  28  and the top closure  30  and may be made, for example, by cross-drilled lines  88   a,b,c,d,e , &amp;  f  in stationary body  10  and top closure  30 . The second fluid circuit  83  further has annular voids defined by the third seal carrier  94  itself, and between the third seal carrier  94  and annular channels  33   a  and  33   b  (FIG. 4) in top closure  30 . FIG. 2 shows surface  17   c  of the rotating housing cover plate  16  which helps define the second fluid circuit  83  between the rotating body  12  and the third seal carrier  94 . The cross-drilled lines  88   b  and  88   e  may be isolated from the first fluid circuit by, for example, plugs  90   a  and  90   b  respectively.  
         [0019]    As discussed above the annular voids defined intermediate top closure  30  and rotating housing cover plate  16  are for the mounting of a second or middle seal carrier  92  and a third or top seal carrier  94  (the first seal carrier  44  is placed in an annular void defined by rotating housing  14  and bottom closure flange  32 ). A second seal  96  is mounted in the second seal carrier  92  and a third seal  98  is mounted in the third seal carrier  94 . The first, second and third seal carriers  44 ,  92 ,  94  are preferably hydraulically balanced floating seal carriers for carrying seals  46 ,  96 ,  98 . Such seals may be, for example, seals of the type marketed by Kalsi Engineering, Inc.  
         [0020]    Referring to FIG. 3 various seal or o-rings  100   a,b,c,d,e,f,g  and  h  are mounted in grooves around the second and third seal carriers  92  and  94 , and the top closure  30 . Bearing  102  is mounted in the second seal carrier  92  and in the first fluid circuit  81 . Bearing  104  is mounted in the second fluid circuit intermediate the third seal carrier  94  and a bearing spacer  101 . As discussed above, annular voids are defined by the top closure  30  and/or by the second and third seal carriers  92  and  94 . These annular voids form part of the first and the second fluid circuits  81  and  83 .  
         [0021]    The rotating blowout preventer  8  and the fluid circulation circuits may be operated as discussed below. This system is especially useful in well bore environments where the pressure of the well bore exceeds 2500 psi on up to and exceeding 5000 psi.  
         [0022]    The description following in the next two paragraphs serves as an example of the implementation of the invention and is not intended to quantify any limits on the value of features expressed in terms of pressure or time. However, such quantified values may be individually or collectively claimed as a preferred embodiment of the invention.  
         [0023]    A fluid for actuating, for cooling, for lubricating and for removing foreign particulate matter is introduced into the first fluid circuit  81  at a pressure P 1 . The pressure P 1  is at or about well bore pressure plus about 300 psi (i.e. P 1  ranges from 300 psi to 5300 psi depending upon well bore pressure). At the same time, a like or a similar fluid is introduced into the second fluid circuit  83  at a pressure P 2  in the range of about 35% to 65% of the pressure P 1 . The second seal  96  experiences a pressure differential from P 1  to P 2  and the third seal  98  experiences a pressure differential from P 2  to atmosphere (or to the pressure of the thrust bearing cooling circuit  75 ). The pressure P 2  may nominally be introduced into the second fluid circuit  83  at approximately one-half the pressure P 1 . Next, data may be gathered by one skilled in the rotating blow out preventer art relating to wear rates and conditions for bearings and seals within the rotary blowout preventer  8 . Then, such data may be used to empirically determine optimal pressure settings, pressure differentials and pressure changes to be made in response to variables such as changes in the well bore pressure in order to maintain the integrity of the seals and bearings. More specifically, it will be advantageous to control the pressure differentials such that the second seal  96  has a wear rate exceeding the wear rate of the third seal  98 . This is because if excessive wear is inflicted upon the second seal  96  prior to being inflicted upon the third seal  98 , a leak past the second seal  96  will create an increase in pressure in the second fluid circuit  83  as detected by controls such as pressure transducers, in the control system  110 . Then, the pressure increase detected in the second fluid circuit  83  may be used to infer or signal the possibility of the infliction of excessive wear on the third seal  98  (the timing of such an infliction of excessive wear on the third seal  98  being dependent upon a variety of variables such as well bore pressure, working rotational velocity, the current condition of the third seal  98 , etc.) thus prompting at least the consideration of maintenance operations. Accordingly, maintenance operations may be fore planned and fore scheduled prior to a leak past third seal  98 . Comparatively, the infliction of excessive wear on the third seal  98  prior to the infliction of excessive wear on the second seal  96  (or the infliction of excessive wear on the upper seal in the existing rotary blowout preventers) can result in a leak to atmosphere and an immediate shutdown or “kill” of well operations.  
         [0024]    In a more specific example, if the well bore pressure is 4000 psi, then the pressure P 1  could be about 4300 psi, and the pressure P 2  could be nominally about 2150 psi (incidentally the pressure seen from above the third seal  98  could be about 60 psi). Then the pressures of the well bore, P 1  and P 2  can be detected (e.g., every fifty to one hundred milliseconds) in the control system  110  and the pressures P 1  and/or P 2  adjusted as suggested by empirical data or experience to, in anticipation of the infliction of excessive wear on a seal, cause the second seal  96  to incur excessive wear prior to the third seal  98 . As mentioned above, this sequence of events will suggest to operators that maintenance work should be planned and conducted within, and dependent upon operational variables, about six hours.  
         [0025]    Referring to FIG. 5, a control system  110  which may be used with the rotary blowout preventer is shown. The control system  110  generally connects via line  112  to the inlet orifice  80  of the first fluid circuit  81  and via line  116  to the outlet orifice  82  of the first fluid circuit  81 . The control system  110  generally connects via line  114  to the inlet orifice  84  of the second fluid circuit  83  and via line  118  to the outlet orifice  86  of the second fluid circuit  83 . The control system  110  generally includes pumps  120  and  122  such as fixed displacement pumps for circulating a cooling and lubricating fluid; filters  124  and  126  for filtering the fluid fluid; and valves, for example, pinch valves,  128 ,  130 ,  132  and  134 . The valves may, for example, be used to create backpressure on the respective first and second fluid circuits  81 ,  83  and to energize the floating seal carriers  46 ,  96 ,  98  by varying the orifice of the valves  128 ,  130 ,  132 , and  134 . The pressure within the circuits  81 ,  83  may be independently adjusted or varied by other means, such as, for example, via pumps (not shown).  
         [0026]    The thrust bearing  58  shares the thrust load, e.g. 2,000 lbs.-force, exerted by well bore pressure and placed upon the packer assembly  18  and consequently the load placed upon the lower and upper bearings  34 ,  38  while allowing the rotable body  12  to rotate. Such results in lowering the heat on lower and upper bearings  34 ,  38  and extending the life of same. By sharing the thrust load, “nibbling” of the first, second and third seals  46 ,  96 ,  98  may be decreased to extend the seal life of same. It is also advantageous to lubricate the thrust bearing  58  to counter the heat effects of the thrust load and rotation upon same. This may be accomplished, for example, by a thrust bearing cooling and lubricating circuit  75  which introduces the cooling fluid to the thrust bearing through the opening between the o-rings  74  and  76 .  
         [0027]    It should be noted that reverse rotation may be utilized during use of the rotary blowout preventer  8  and the invention will be functional under such conditions.  
         [0028]    In conclusion, therefore, it is seen that the present invention and the embodiments disclosed herein are well adapted to carry out the objectives and obtain the ends set forth. Certain changes can be made in the subject matter without departing from the spirit and the scope of this invention. It is realized that changes are possible within the scope of this invention and it is further intended that each element or step recited is to be understood as referring to all equivalent elements or steps. The description is intended to cover the invention as broadly as legally possible in whatever form it may be utilized.

Technology Classification (CPC): 8