Abstract:
A shaker for separating solids from a drilling fluid includes a top screening deck ( 130 ), a flow-back pan ( 160 ) positioned beneath the top screening deck ( 130 ) for receiving an initially separated drilling fluid from the top screening deck. The flow-back pan ( 160 ) is divided into a plurality of channels (A, B, C, D). The shaker further includes a fluid distribution box ( 210 ), which includes a plurality of conduits (A, B, C, D). Each channel (A, B, C, D) of the flow-back pan ( 160 ) corresponds to one of the plurality of conduits (A, B, C, D) in the fluid distribution box ( 210 ) and each channel communicates a stream of the initially separated drilling fluid to the corresponding conduit. The shaker further includes a middle screening deck ( 140 ) and a bottom screening deck ( 150 ). Each conduit (A, B, C, D) routes the stream of initially separated drilling fluid to a corresponding one of the middle screening deck ( 140 ) and the bottom screening deck ( 150 ).

Description:
BACKGROUND 
     1. Field of the Disclosure 
     Embodiments disclosed herein relate to apparatus and methods for distributing fluid in a shaker. 
     2. Description of the Related Art 
     Oilfield drilling fluid, often called “mud,” serves multiple purposes in the industry. Among its many functions, the drilling mud acts as a lubricant to cool rotary drill bits and facilitate faster cutting rates. Typically, the mud is mixed at the surface and pumped downhole at high pressure to the drill bit through a bore of the drill string. Once the mud reaches the drill bit, it exits through various nozzles and ports where it lubricates and cools the drill bit. After exiting through the nozzles, the “spent” fluid returns to the surface through an annulus formed between the drill string and the drilled wellbore. 
     Furthermore, drilling mud provides a column of hydrostatic pressure, or head, to prevent “blow out” of the well being drilled. This hydrostatic pressure offsets formation pressures, thereby preventing fluids from blowing out if pressurized deposits in the formation are breached. Two factors contributing to the hydrostatic pressure of the drilling mud column are the height (or depth) of the column (i.e., the vertical distance from the surface to the bottom of the wellbore) itself and the density (or its inverse, specific gravity) of the fluid used. Depending on the type and construction of the formation to be drilled, various weighting and lubrication agents are mixed into the drilling mud to obtain the right mixture. Typically, drilling mud weight is reported in “pounds,” short for pounds per gallon. Generally, increasing the amount of weighting agent solute dissolved in the mud base will create a heavier drilling mud. Drilling mud that is too light may not protect the formation from blow outs, and drilling mud that is too heavy may over invade the formation. Therefore, much time and consideration is spent to ensure the mud mixture is optimal. Because the mud evaluation and mixture process is time consuming and expensive, drillers and service companies prefer to reclaim the returned drilling mud and recycle it for continued use. 
     Another significant purpose of the drilling mud is to carry the cuttings away from the drill bit at the bottom of the borehole to the surface. As a drill bit pulverizes or scrapes the rock formation at the bottom of the borehole, small pieces of solid material are left behind. The drilling fluid exiting the nozzles at the bit acts to stir-up and carry the solid particles of rock and formation to the surface within the annulus between the drill string and the borehole. Therefore, the fluid exiting the borehole from the annulus is a slurry of formation cuttings in drilling mud. Before the mud can be recycled and re-pumped down through nozzles of the drill bit, the cutting particulates must be removed. 
     Apparatus in use today to remove cuttings and other solid particulates from drilling fluid are commonly referred to in the industry as shale shakers or vibratory separators. A vibratory separator is a vibrating sieve-like table upon which returning solids laden drilling fluid is deposited and through which clean drilling fluid emerges. Typically, the vibratory separator is an angled table with a generally perforated filter screen bottom. Returning drilling fluid is deposited at the feed end of the vibratory separator. As the drilling fluid travels down the length of the vibrating table, the fluid falls through the perforations to a reservoir below, leaving the solid particulate material behind. The vibrating action of the vibratory separator table conveys solid particles left behind to a discharge end of the separator table. The above described apparatus is illustrative of one type of vibratory separator known to those of ordinary skill in the art. In alternate vibratory separators, the top edge of the separator may be relatively closer to the ground than the lower end. In such vibratory separators, the angle of inclination may require the movement of particulates in a generally upward direction. In still other vibratory separators, the table may not be angled, thus the vibrating action of the separator alone may enable particle/fluid separation. Regardless, table inclination and/or design variations of existing vibratory separators should not be considered a limitation of the present disclosure. 
     SUMMARY OF THE DISCLOSURE 
     In one aspect, the present disclosure relates to a shaker for separating solids from a drilling fluid. The shaker includes a top screening deck, a flow-back pan positioned beneath the top screening deck for receiving an initially separated drilling fluid from the top screening deck. The flow-back pan is divided into a plurality of channels. The shaker further includes a fluid distribution box, which includes a plurality of conduits. Each channel of the flow-back pan corresponds to one of the plurality of conduits in the fluid distribution box and each channel communicates a stream of the initially separated drilling fluid to the corresponding conduit. The shaker further includes a middle screening deck and a bottom screening deck. Each conduit routes the stream of initially separated drilling fluid to a corresponding one of the middle screening deck and the bottom screening deck. 
     In another aspect, the present disclosure relates to an apparatus for distributing an initially separated drilling fluid in a shaker. The shaker includes a top screening deck, onto which a solids laden drilling fluid is deposited and through which the initially separated drilling fluid comprising undersized solids passes, a middle screening deck, and a bottom screening deck. The apparatus includes a flow-back pan positioned beneath the top screening deck, wherein the flow-back pan is divided into a plurality of channels. The apparatus further includes a fluid distribution box including a plurality of conduits. Each channel of the flow-back pan directs the initially separated drilling fluid comprising undersized solids to a corresponding conduit of the fluid distribution box. Each conduit routes the initially separated drilling fluid comprising undersized solids to a corresponding one of the plurality of secondary screening surfaces. 
     In another aspect, the present disclosure relates to a method of separating solids from a drilling fluid. The method includes depositing the drilling fluid onto a top screening deck in a shaker, vibrating the shaker, separating the drilling fluid into an initially separated drilling fluid component and a first solid component on the top screening deck, discharging the first solid component from the shaker, receiving the initially separated drilling fluid component onto a flow-back pan comprising a plurality of channels, dividing the initially separated drilling fluid component into a plurality of streams defined by the channels on the flow-back pan, directing each stream of the initially separated drilling fluid component in each channel to a corresponding conduit in a fluid distribution box, and routing each stream of the initially separated drilling fluid component in each conduit to one of a middle screening deck and a bottom screening deck in the shaker. 
     Other aspects and advantages of the disclosure will be apparent from the following description and the appended claims. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1A  shows a discharge end of a shaker in accordance with an embodiment of the present disclosure. 
         FIG. 1B  shows an assembly view of a shaker with different configurations of a rib in accordance with embodiments of the present disclosure. 
         FIG. 2A  shows an internal view of a fluid distribution box for the shaker shown in  FIG. 1  in accordance with an embodiment of the present disclosure. 
         FIG. 2B  shows a cut-away side view of the shaker shown in  FIG. 1A . 
         FIG. 3A  shows an internal view of the fluid distribution box for the shaker shown in  FIG. 1  in accordance with an embodiment of the present disclosure. 
         FIG. 3B  shows a cut-away side view of the shaker shown in  FIG. 1A . 
         FIG. 4  shows a cut-away side view of a shaker in accordance with an embodiment of the present disclosure. 
         FIGS. 5A and 5B  show a cut-away perspective view of a shaker in accordance with an embodiment of the present disclosure. 
         FIGS. 6A and 6B  show a partial cut-away view of a shaker in accordance with an embodiment of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     In one aspect, embodiments disclosed herein relate to apparatus and methods for distributing fluid in a shaker. In particular, embodiments of the present disclosure provide fluid distribution apparatus and methods to distribute drilling fluid amongst multiple screening decks in the shaker. 
       FIGS. 1A, 1B, 2A, 2B, 3A, and 3B  show a shaker in accordance with embodiments of the present disclosure.  FIG. 1A  is a view from the discharge end of the shaker.  FIGS. 2A and 3A  are views from the feed end of the shaker.  FIGS. 2B and 3B  are cut-away side views of the shaker illustrating parallel flow paths for drilling fluid within the shaker. 
     As shown in  FIGS. 2B and 3B , the shaker includes a top screening deck  130 , a middle screening deck  140 , and a bottom screening deck  150 . At least one motor  110  is attached to the shaker to provide vibratory motion while separating solids from drilling fluid. A mesh screen (not shown) is provided on each of the screening decks in order to filter out solids of various sizes from the drilling fluid according to the size of the respective mesh. In some embodiments, the mesh screen may be part of screen assemblies  135 ,  145 ,  155  ( FIG. 1A ) disposed on the top screening deck  130 , the middle screening deck  140 , and the bottom screening deck  150 , respectively. Those of ordinary skill in the art will appreciate that the present disclosure is not limited to any particular screen assembly or mesh screen arrangement. 
     A flow-back pan  160  is provided to distribute drilling fluid between the middle screening deck  140  and the bottom screening deck  150 . For illustration purposes in  FIG. 1A , the screen assemblies  135 ,  145 ,  155  are removed from the right side to provide a view of the flow-back pan  160 . The left side of the flow-back pan may be a mirror image of the right side. Further, the flow-back pan  160  may comprise two separate portions for the right side and the left side, divided by a partition wall  180 . Those having ordinary skill in the art will appreciate that the arrangement and assembly of flow-back pan  160  may vary without departing from the scope of the present disclosure. 
     Continuing with  FIG. 1A , flow-back pan  160  is disposed below top screening deck  130  and includes a plurality of channels for partitioning the flow of drilling fluid after initial separation of solids by top screening deck  130 . In this particular embodiment, four channels (A, B, C, D) are included in the flow-back pan  160 . The channels may be formed, for example, by providing a rib  161  between adjacent channels. Referring to  FIG. 1B , different configurations of rib  161  ( FIG. 1A ) are shown in accordance with embodiments of the present disclosure. As shown, rib  161 A extends along a fill length of flow-back pan  160  and may be welded in place or secured with common fasteners. In alternate embodiments, rib  161 B extends along only a portion of the entire length of flow-back pan  160 , allowing a fluid to be more evenly distributed across flow-back pan  160  before being divided by rib  161 B. Rib  161 B may be welded onto a rear portion of flow-back pan  160 . Those of ordinary skill in the art will appreciate that the channels may be formed in several ways without departing from the scope of the present disclosure. For example, either a full length rib  161 A or a partial length rib  161 B may be used in both compartments, or a combination of full length ribs  161 A and short length ribs  161 B may be used as shown. Further, in alternate embodiments, flow-back pan  160  may include upward bends between the channels to partition the channels from each other. 
     The flow distribution of the embodiment shown in  FIGS. 1A, 1B, 2A, 2B, 3A , and  3 B will now be described. For orientation purposes, the alphabetical labels for the channels (A, B, C, D) in  FIG. 1A  are also used for arrows illustrating corresponding flow paths. After initial separation of solids by the top screening deck  130 , the initially separated drilling fluid flows into the plurality of channels in the flow-back pan  160 . The initially separated drilling fluid then flows downward on the flow-back pan  160  from the discharge end of the shaker to the feed end of the shaker, as best seen in  FIGS. 2B and 3B . At the feed end of the shaker, a fluid distribution box  210  is provided to route the flow from the plurality of channels to corresponding locations on the middle screening deck  140  and the bottom screening deck  150 . In this embodiment, parallel flow is provided by the fluid distribution box  210  in conjunction with the flow-back pan  160 , meaning that portions of the initially separated drilling fluid is routed to either the middle screening deck  140  or the bottom screening deck  150 , not both. 
     The fluid distribution box  210  includes a plurality of conduits (A, B, C, D) corresponding to the plurality of channels in the flow-back pan  160 . The plurality of conduits may be formed, for example, by horizontal partitions  221  and vertical partitions  222  in combination with a cover  201 , which is removed for illustrative purposes in  FIGS. 2A and 3A . The plurality of conduits in the fluid distribution box  210  route the drilling fluid from the corresponding channels in the flow-back pan  160  to the middle screening deck  140  or the bottom screening deck  150  in the parallel flow configuration shown in  FIGS. 2A, 2B, 3A, and 3B . 
       FIGS. 2A and 2B  illustrate the flow path for drilling fluid routed to the middle screening deck  140 .  FIGS. 3A and 3B  illustrate the flow path for drilling fluid routed to the bottom screening deck  150 . In the parallel flow configuration in this particular embodiment, the flow-back pan  160  includes four channels labeled A, B, C, and D from left to right when viewed from the discharge end of the shaker ( FIG. 1A ). After flowing towards the feed end of the shaker, drilling fluid in channels A and C is routed by the fluid distribution box  210  to the middle screening deck  140 , as shown in  FIGS. 2A and 2B . The drilling fluid flows through the middle screening deck  140  to separate smaller solids not initially separated by the top screening deck  130 . Drilling fluid from the middle screening deck  140  then flows along a middle flow-back pan  170  towards the feed end of the shaker, where the drilling fluid then exits the shaker. A skid or sump (not shown) may be provided below the shaker to recover the drilling fluid for further use. 
     Continuing with the parallel flow configuration, drilling fluid in the channels B and D is routed by the fluid distribution box  210  to the bottom screening deck  150 , as shown in  FIGS. 3A and 3B . The drilling fluid flows through the bottom screening deck  150  to separate smaller solids not initially separated by the top screening deck  130 . Drilling fluid from the bottom screening deck  150  may be allowed to immediately flow out of the bottom of the shaker onto the skid (not shown) provided below the shaker to recover the drilling fluid for further use. 
     In one or more embodiments, the flow-back pan  160  may be configured to alternately allow series flow between the middle screening deck  140  and the bottom screening deck  150 , meaning that at least a portion of the drilling fluid flows through both the middle screening deck  140  and the bottom screening deck  150 , as shown in  FIG. 4 . In the series flow configuration, separation of solids from the drilling fluid may be accomplished in three stages using finer mesh with each successive screening deck to filter out smaller solids. For example, the mesh size for the top screening deck  130  may be selected to serve as a “scalping deck” to remove large drill cuttings from the drilling fluid. After initial separation, the middle screening deck  140  may have a mesh size selected to separate solids that can be recycled for further use. For example, the solids separated by the middle screening deck may include lost circulation material, which is used to avoid the loss of drilling fluid into the earth formation during drilling operations. Lost circulation material may be an expensive component of drilling fluid, and as such, the recovery of lost circulation material may result in decreasing total drilling expenditures. After flowing through the middle screening deck  140 , the drilling fluid is further screened by the bottom screening deck  150 , which may have a mesh size selected to remove fine solids. Fine solids in the drilling fluid may negatively affect the physical properties of the drilling fluid. Thus, removal of at least some of the fine solids may reduce negative effects on drilling, such as incorrect fluid weight and damaged drilling components. After flowing through the bottom screening deck  150 , the drilling fluid exits through the bottom of the shaker to be recovered for further use. In one embodiment, solids separated by the middle screening deck  140  may be returned to the drilling fluid after screening by the bottom screening deck  150 . 
     Switching between parallel and series flow may be accomplished in several ways. For example, the flow-back pan  160  and the middle flow-back pan  170  may include removable panels  501  and  502 , respectively, as shown in  FIGS. 5A and 6A . Removal of the removable panels  501  and  502  allows drilling fluid to flow through each of the screening decks in series, as shown in  FIGS. 5B and 6B . To prevent drilling fluid from bypassing the middle screening deck  140 , all or some of the conduits in the fluid distribution box  210  may be blocked. Embodiments of the present disclosure are not limited by the manner in which the conduits in the fluid distribution box  210  are blocked. For example, additional panels (not shown) may be inserted into the fluid distribution box  210 . In one embodiment, the fluid distribution box  210  may be removable. Those having ordinary skill in the art will also appreciate that the configuration of removable panels  501  and  502  may vary without departing from the scope of the present disclosure. For example, the flow-back pan  160  and the middle flow-back pan  170  may each include one removable panel or several removable panels. Further, the removable panels may be attached to the shaker by bolts, latches, or other attachment mechanisms in order to be removable. In further embodiments, the flow-back pan  160  and the middle flow-back pan  170  may include slidable or otherwise movable panels, which may be moved between a parallel flow and a series flow position to vary the fluid distribution in the shaker. 
     Although the above embodiments describe shakers with three screening decks, those of ordinary skill in the art will appreciate that the above teachings may be scaled to apply to additional screening decks. Accordingly, the present disclosure is not limited to only three screening decks. Furthermore, the number of channels provided by the flow-back pan is not limited to the four channels shown in the above embodiments. In other embodiments, two channels may be provided by the flow-back pan. Alternatively, more than four channels may be provided by the flow-back pan. 
     While the present disclosure has been described with respect to a limited number of embodiments, those skilled in the art, having benefit of this disclosure, will appreciate that other embodiments may be devised that do not depart from the scope of the disclosure as described herein. Accordingly, the scope of the disclosure should be limited only by the attached claims.