Abstract:
An agitator for agitating drilling fluid or other slurries or mixtures in a tank includes a pressurized and fluid-free compartment within the tank. The motor driving the agitator is housed in the fluid-free compartment. Control apparatus senses fluid levels and, in conjunction with a compressed gas source, maintains the compartment fluid-free. Additionally, when the fluid level in the enclosure drops to a predetermined minimum, the speed of the agitator may be slowed.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     Not applicable.  
       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 the field of liquid and slurry agitation, and more specifically to the agitation of drilling fluid stored in tanks and as employed in the drilling industry.  
         [0005]     2. Background Information  
         [0006]     A key component or system that is employed in the drilling of oil and gas wells is the mud system, which circulates drilling fluid (mud) through the wellbore. The circulation system is also used to maintain the density of the drilling fluid by removing drilled cuttings from the fluid, and adding other solids to the fluid as may be desired. The density of the drilling fluid is critical to hole cleaning, rate of penetration, and pressure control in the well. Hole cleaning and rate of penetration are important factors in the efficiency of the drilling process, while pressure control is critical to drilling a well safely.  
         [0007]     In general operation, drilling fluid is pumped by high-pressure pumps through the drill string and into the wellbore. The fluid exits the drill string at the bit and returns to the surface through the annulus between the drill string and the wellbore, carrying cuttings from the hole to the surface. The hydrostatic pressure from the column of drilling fluid prevents fluids from the surrounding earthen formation from entering the wellbore and potentially causing well blow out.  
         [0008]     At the surface, the drilling fluid is then processed, in order to maintain the desired density, before it is pumped back through the drill string into the hole. The drilling fluid, including a reserve volume, is typically stored in mud tanks at the surface before being recirculated through the well.  
         [0009]     The mud tanks are typically fabricated of steel and have a top or ceiling that serves as a deck upon which equipment is placed and personnel can walk and perform various duties. The mud tanks may have agitators or stirrers provided to keep the fluid circulating within the tank in order to minimize settling of the solids and other additives that are used to control the density and viscosity of the liquid slurry.  
         [0010]     The conventional agitator has a motor that drives a shaft and an impeller. The motor is normally placed on the top surface of the deck with the shaft and impeller extending down into the drilling mud. This conventional placement of the agitator motor, bearing and associated components on the deck of mud tanks presents operational difficulties and drawbacks. For example, space on the deck is limited during drilling operations. By positioning the agitator motor and related components on the top surface of the deck, the available space for other equipment and operating space for rig personnel is reduced. Deck-mounted equipment also presents trip hazards to personnel working or walking on the deck.  
         [0011]     Therefore, it is highly advantageous to increase the available space on the decking that serves as the ceiling or top of the mud tank. Submerged agitators have been used in the past to increase the available space on the top of the mud tank. The submerged agitators are submerged in the drilling mud and are typically secured to a side wall of the mud tank. Drawbacks of using submerged agitators include difficulties in removal of the agitator from the mud tank, as when servicing is required. Further drawbacks include the typical high initial expense of the submerged agitator. In addition, when the submerged agitator is secured to a side wall of the mud tank, the submerged agitator may not properly stir the drilling mud because of the horizontal motion of its impellers in relation to the mud tank. Moreover, the impeller speed of the submerged agitator is generally not adjusted depending on the mud level in the tank, which can result in a reduced life for the agitator motor if it must consistently operate at a high speed even at low mud levels, for example.  
         [0012]     Consequently, there is a need for an agitator that provides greater space on the top or deck of the mud tank. Further, there is a need for an agitator mounted below the deck of the mud tank that is more easily removed from the mud tank for service. In addition, there is a need for a more effective way of stirring the drilling mud with an agitator mounted below the deck of the mud tank. Moreover, there are additional needs for extending the life of the agitator motor.  
       BRIEF SUMMARY OF SOME OF THE PREFERRED EMBODIMENTS  
       [0013]     Preferred embodiments described herein include agitator apparatus for agitating a fluid or slurry contained within a tank or other enclosure. A vessel or chamber is disposed in the tank and includes a fluid-free compartment housing a motor. A shaft is connected to the motor and extends from the fluid-free compartment into the fluid. Blades and/or impellers are attached to the shaft at a position outside of the vessel for agitating the fluid in the tank.  
         [0014]     The fluid-free compartment may be pressurized to maintain the fluid level in the vessel below the motor. This enables a non-submersible and thus, less costly, motor to be employed. A hatch or other accessway may be provided in the enclosure to allow access into the fluid-free compartment for servicing the agitator motor and related components.  
         [0015]     In certain embodiments, the apparatus includes a controller and a level detector in the vessel for sensing the fluid level and sending a signal to the controller when the fluid level in the vessel rises to a predetermined level. In this arrangement, the controller is electrically coupled to a compressed gas source and causes the source of compressed gas to communicate gas into the fluid-free compartment to maintain the fluid level below the predetermined level and thus below the motor.  
         [0016]     In certain embodiments, the apparatus further includes a pressure relief valve coupled electrically to the controller and adapted to open to cause gas to escape from the fluid-free compartment upon receipt of a control signal from the controller. The apparatus may include a second level detector in the vessel adapted to sense when the fluid in the vessel reaches a second predetermined level that is below the first predetermined level. The second or “low” level detector is also electrically coupled to the controller and, in this preferred embodiment, the controller actuates the pressure relief valve when the second level detector has detected that the fluid level in the vessel has reached the second predetermined or “low” level. Additionally, in certain embodiments of the invention, when the fluid level in the enclosure reaches the second predetermined or “low” level, as sensed by the second level detector, the second level detector signals the controller and the controller slows the speed of the motor and thus the speed of agitation in the enclosure or tank.  
         [0017]     In certain preferred embodiments, the vessel is sealed and is pressurized to a pressure exceeding the ambient air pressure. The pressurized gas in the vessel maintains the fluid level in the vessel below the first predetermined level, and thus below the motor, and thereby maintains the compartment in a fluid-free and dry condition.  
         [0018]     The agitator motor may be an electric or hydraulic motor. It is believed that slowing the speed of the motor and agitator shaft and blades upon sensing of a low level condition has the advantage of increasing the life of the agitator as compared to similar agitators which continue to operate at relatively high speeds even when the fluid level in the enclosure has dropped significantly.  
         [0019]     Further, as understood from the following more detailed discussion, positioning the agitator motor in the fluid-free compartment inside the enclosure, as opposed to conventional apparatus where the motor is placed on top of the enclosure, provides a valuable savings in working space for personnel, reduces trip hazards for personnel, and provides or frees space for other required equipment.  
         [0020]     Thus the disclosed devices and methods are believed to comprise a combination of features and advantages which enable them to overcome certain drawbacks inherent the prior art devices and methods. The various characteristics described above, as well as other features, will be readily apparent to those skilled in the art upon reading the following detailed description, and by referring to the accompanying drawings. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0021]     For a detailed description of the preferred embodiments of the invention, reference will now be made to the accompanying drawings in which:  
         [0022]      FIG. 1  shows, in schematic form, a cross-sectional view of one embodiment of a pressurized compartment housing an agitator motor within a mud tank; and  
         [0023]      FIG. 2  shows an enlarged view of the compartment and agitator apparatus of  FIG. 1 . 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0024]     The following discussion is directed to various specific embodiments of the invention. Unless otherwise specified, the embodiments disclosed should not be interpreted as limiting, or otherwise used to limit, the scope of the disclosure or claims. In addition, one skilled in the art will understand that the following description has broad application. The discussion of any specific embodiment is meant only to be exemplary of that embodiment and is not intended to suggest that the scope of the disclosure or claims is limited to that particular embodiment. In this disclosure, numerous specific details may be set forth to provide a sufficient understanding of the embodiment. However, those skilled in the art will appreciate that the invention as claimed may be practiced without such specific details. In other instances, well-known elements may have been illustrated in schematic or block diagram form in order not to obscure the disclosure in unnecessary detail. Additionally, some details may have been omitted where such details were not considered necessary to obtain a complete understanding of the embodiment, and are considered to be within the understanding of persons of ordinary skill in the relevant art.  
         [0025]     As used herein, the terms “couple” or “couples” or “coupled” are intended to mean either a direct or an indirect connection or link between devices that communicate with one another. Thus, for example, if a first device “couples” to a second device, that connection may be through a direct connection, or through an indirect connection via intermediate devices and connections. Further, the terms “electrically coupled” or “coupled electrically” mean that the components are coupled for communications either by wire conductors, fiber optic means, or may be connected by radio signals, or other communication means.  
         [0026]     Referring to  FIG. 1 , there is shown a schematic representation of a fluid-containing tank which, in this embodiment, constitutes mud tank  25  containing drilling mud  24 . Mud tank  25  includes vessel  10  housing agitator apparatus  5 . Vessel  10  includes fluid-free compartment  16 . Agitator apparatus  5  includes agitator motor  37 , supported on platform  15  within compartment  16 , and agitator  20  extending downwardly from compartment  16  to agitate drilling mud  24 . As explained in more detail below, agitator  20  extends downward from compartment  16  and into the body of drilling mud  24  contained in mud tank  25 . Tank  25  includes bottom  22 , sides  23  and top  30 . As conventional, bottom  22  and four sides  23  (two shown in  FIG. 1 ) are welded together to form a fluid-tight enclosure or tank. Top  30  may likewise be welded or otherwise suitably attached to sides  23 .  
         [0027]     Referring now to  FIG. 2 , attached to top  30  and extending downwardly into the drilling mud  24  is vessel  10 . Vessel  10  includes side walls  11  and a support or platform  15  attached to and extending between walls  11 . Vessel  10  is bolted or otherwise attached to tank top  30 . In certain embodiments, vessel  10  and platform  15  may be supported by a frame (not shown) attached to tank top  30  so as to simplify assembly and service of the system.  
         [0028]     A gasket or other suitable seal (not shown) is disposed between vessel  10  and top  30  to allow compartment  16  to be pressurized. Vessel  10  includes lowermost end  13  that includes opening  34  allowing the drilling mud in tank  25  to communicate into vessel  10 . As explained in more detail below, the level of drilling mud within vessel  10  is controlled, such that the level remains beneath platform  15 . Vessel  10  may be cylindrical, rectangular, or any other suitable shape. Platform  15  may be sized and shaped to match the cross-sectional shape of vessel  10 , or may simply comprise, for example, transverse or cantilevered beams or other members that extend across chamber  10 . In this embodiment, platform  15  is attached to sides  11  and also attached to braces  14  that extend from walls  11 . Platform  15  further includes an aperture  60  for receiving agitator shaft  40 .  
         [0029]     Referring still to  FIG. 2 , agitator apparatus  5  generally includes agitator motor  37  and agitator  20 . Agitator  20  includes impeller  45  and extends between bearing  35  in vessel  10  and bearing support  42  disposed on the bottom  22  of the mud tank  25 .  
         [0030]     Motor  37  and bearing  35  are mounted within fluid-free compartment  16  and supported by platform  15 . In this embodiment, it is preferred that motor  37  be a hydraulic motor, although other types of driving apparatus may be employed, such as an electric motor. Bearing  35  helps support the weight of shaft  40  and impeller  45 . Shaft  40  extends from bearing  35  through platform aperture  60  to drive and thereby rotate impeller  45 . Motor  27  and bearing  35  are mechanically coupled in a conventional manner. Motor  37  may drive shaft  40  through a gearbox (not shown for clarity). Impeller  45  includes a plurality of blades or paddles  46  (four shown in this embodiment).  
         [0031]     Top  30  of tank  25  includes an accessway into chamber  10  which, in this embodiment, comprises hatch  38  that is removably attached to tank top  30 . Hatch  38  and the accessway that it covers is sized so as to allow access into compartment  16  to allow removal of motor  37  and bearing  35  as repair or maintenance so requires. A gasket (now shown) or another seal is disposed between hatch  38  and tank top  30  to enable compartment  16  to be pressurized and sealed. The weight of the drilling mud  24  seals compartment  16  at opening  34 .  
         [0032]     The upper surface of tank top  30  forms deck  39  that is used as a walkway by operating personnel and as a surface for supporting various equipment utilized in the operation and control of agitator apparatus  5 . More specifically, in this particular embodiment, supported atop deck  39  is controller  75 , compressor  80  and pressure-relief valve  85 . Controller  75  preferably is a computer or programmable controller. Compressor  80  is a conventional gas compressor that is adapted to pressurize compartment  16  in vessel  10  by means of the interconnecting conduit  82 . As shown in  FIG. 2 , the lowermost end of conduit  82  extends to and opens into compartment  16  above opening  34 .  
         [0033]     Referring still to  FIG. 2 , mounted within vessel  10  are minimum and maximum level detectors  65 ,  70 , respectively. Level detectors  65  and  70  are electrically coupled to controller  75  via conductors  90 , it being understood that each conductor  90  shown in  FIG. 2  may represent a pair of wires, a control cable, multiple conductors or other means for conducting electrical signals. Controller  75  is also electrically coupled to compressor  80  via conductor  91  so as to turn on and off the compressor when required, as described below. Conductor  92  electrically couples pressure-relief valve  85  with controller  75  such that controller  75  may cause pressure-relief valve  85  to open and release pressure within compartment  16 , or close so as to maintain a desired pressure within the compartment  16 .  
         [0034]     A hydraulic control module  36  for actuating hydraulic motor  37  is electrically coupled to controller  75  via conductor  93  such that, upon receipt of the appropriate electrical signal from controller  75 , the hydraulic control module  36  will actuate to cause operation of hydraulic motor  37  by communicating pressurized fluid to motor  37  via hydraulic lines  33 . Conductors  91 ,  92 ,  93  shown in  FIG. 2  may be multiple conductor cables, wire pairs, or other suitable electrical conductors.  
         [0035]     In operation, controller  75  actuates compressor  80  to pressurize the interior volume  32  of compartment  16  and to maintain the drilling mud level  50  at a level that is beneath platform  15 . Due to this pressurization, mud level  50  is thus well below the level  55  to which the drilling mud extends elsewhere in mud tank  25 . Essentially then, compartment  16  is dry or fluid-free such that a conventional motor (as opposed to a more expensive submersible motor) may be employed in vessel  10  to actuate the agitator  20  within the tank  25 . Level detectors  65 ,  70  in conjunction with controller  75 , operate to control mud level  50  within chamber  10  within predetermined limits. Should the level  50  within chamber  10  reach maximum level detector  70 , the detector transmits a control signal to controller  75  via conductors  90 . Upon receipt of such signal, controller  75  actuates compressor  80  to increase the gas pressure within chamber  10  to drive the mud level  50  down below level detector  70 . Similarly, should the level  50  within chamber  10  reach a predetermined minimum level, a control signal from level detector  65  to controller  75  signals controller  75  to cause pressure-relief valve  85  to open and thereby release pressure from within compartment  16  to allow the fluid level  50  to rise. Valve  85  can comprise any known valve suitable for releasing pressure. In alternative embodiments, more than one valve  85  can be used to release pressure from compartment  16 .  
         [0036]     The present invention is not limited to securing vessel  10  to tank ceiling  30  but includes alternative embodiments comprising securing vessel  10  to any surface in mud tank  25 , such as side walls  23 .  
         [0037]     In alternative embodiments, more than one compressor  80  may be used to supply gas to compartment  16 . The gas can include atmospheric air, stored air, processed air, air that has been purified of flammable or hazardous gases and vapors, and the like. In addition, the present invention is not limited to supplying air to vessel  10  but may include supplying nitrogen or other gas suitable for use in drilling mud operations. Additionally, other sources for supplying compressed gas can be employed in place of the compressor  80 .  
         [0038]     With compartment  16  sealed, pressure within the compartment prevents the drilling mud  24  from rising up and enveloping motor  37 . As shown on  FIG. 2 , the drilling mud level  50  in compartment  16  is lower than or beneath the drilling mud level  55  in mud tank  25 .  
         [0039]     The rotational speed of agitator  20  may be adjusted depending on the level  55  of drilling mud in mud tank  25 . More specifically, when the drilling mud level  50  drops below minimum level detector  65  in vessel  10 , compressor  80  is shut off as previously described. Controller  75  will record that compressor  80  is off. With compressor  80  off, if low level detector  65  again detects a low level condition within vessel  10 , then the level  55  within tank  25  has dropped to the level of low level detector  65 . Detector  65  again communicates or signals the low level condition to controller  75  which, in this instance, communicates with hydraulic control module  36  to lower the rotational speed of agitator  20 . This will have the potential to extend life of the agitator  20 . When drilling mud is added to tank  25  such that the mud level  55  in mud tank  25  again increases above minimum level detector  65 , controller  75  is signaled by detector  65  of the new, higher level and controller will then signal hydraulic control module  36  to increase the rotational speed of agitator  20  to a desired rotational speed.  
         [0040]     The communications between control box  75  and level detectors  65  and  70 , compressor  80 , hydraulic control module  36  and valve  85  can be sent by hardwire  90 ,  91 ,  92 ,  93  as previously described. Such communications however are not limited to hardwire, but instead may be sent by any other suitable means including fiber optic cables, radio signals and the like.  
         [0041]     It will be understood that the present invention is not limited to an arrangement including both minimum level detector  65  and maximum level detector  70 . In alternative embodiments, a single detector may be used to measure the drilling mud level in compartment  16  and to signal controller  75  when the level reaches a predetermined maximum level that is below the level of motor  27 . In still other alternative embodiments, three or more level detectors can be used to monitor and control the drilling mud levels  30  in chamber  10 .  
         [0042]     Even though the preferred embodiments described above describe mounting agitator  20  in a sealed and fluid-free chamber  16  below the drilling mud level  55  in a mud tank, the present invention is expressly not limited to use with mud tanks and will be useful in various other applications. For instance, the present invention would prove useful in waste treatment operations by mounting an agitator motor  37  in a sealed compartment  16  below the waste level and stirring the waste with agitator  20  that extends from the fluid-free compartment into the waste slurry. In addition, the present invention can be used in any application in which an agitator may be used to stir a liquid in a tank, pit, or the like.  
         [0043]     Although certain preferred embodiments of the present invention and some of their advantages have been described in detail, it should be understood that various changes, substitutions and alterations can be made herein without departing from the spirit and scope of the invention as defined by the appended claims.