Patent Publication Number: US-2013248465-A1

Title: Return Fluid Separator

Description:
BACKGROUND OF INVENTION 
     1. Field of the Invention 
     Embodiments disclosed here generally relate to a separator for drilling wastes. Specifically, embodiments disclosed herein relate to a separator for receiving a return fluid from a well and separating a solids phase from an effluent phase. More specifically, embodiments disclosed herein relate to separator for separating gumbo from drilling return fluid. 
     2. Background 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 drillstring. 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 drillstring 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 breeched. 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 drillstring 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.” A shale shaker, also known as 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. 
     In the North Sea and the United States Gulf Coast, drillers commonly encounter argillaceous sediments in which the predominant clay mineral is sodium montmorillonite (commonly called “gumbo shale” or “gumbo”). Such heavy, high-volume solids are usually encountered when drilling top-hole sections of formation. If not removed, the soft, sticky, swelling clay cuttings, i.e., gumbo, may clog separator screens and/or otherwise adhere to surfaces of the processing equipment, fouling tools and plugging piping. Those of ordinary skill in the art will appreciate that gumbo is typically only encountered in approximately 1% of the entire well; however, removal of the gumbo may prolong the life of the equipment and is often necessary for efficient processing of the returned drilling waste. 
     Accordingly, there exists a need for more separators that more efficiently process drilling waste or drilling muds. 
     SUMMARY OF INVENTION 
     In one aspect, embodiments disclosed herein relate to a separator for drilling waste including a tank having an inlet and an outlet; a screening device disposed within the tank; a conduit coupled to the outlet; and a rotary valve coupled to the conduit. 
     In another aspect, embodiments disclosed herein relate to a separator for drilling waste including a tank having an inlet and an outlet; a trough in fluid communication with the tank; and a screening device having a plurality of members disposed within the tank, wherein the screening device is configured to direct an effluent phase through the plurality of members into the trough and a solids phase to the outlet. 
     In another aspect, embodiments disclosed herein relate to a method of separating drilling waste including flowing a return fluid from a well to an inlet of a tank; and directing the return fluid against a screening device disposed within the tank, wherein an effluent phase of the return fluid passes through the screening device and wherein a solids phase of the return fluid falls to an outlet of the tank. 
     Other aspects and advantages of the invention will be apparent from the following description and the appended claims. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a perspective view of a separator in accordance with embodiments disclosed herein. 
         FIG. 2  is a perspective view of a rotary valve in accordance with embodiments disclosed herein. 
     
    
    
     DETAILED DESCRIPTION 
     In one aspect, embodiments disclosed herein relate to a separator for drilling wastes. Specifically, embodiments disclosed herein relate to a separator for receiving a return fluid from a well and separating a solids phase from an effluent phase. More specifically, embodiments disclosed herein relate to separators for separating gumbo from drilling return fluid. 
     Referring to  FIG. 1 , a separator  100  is shown. Separator  100  includes a tank  102  having an inlet  104  and an outlet  106 . The inlet  104  is configured to receive a fluid for separating a fluids phase and a solids phase. In one embodiment, inlet  104  receives a return fluid from a well. More specifically, in certain embodiments, inlet  104  receives a return fluid comprising gumbo. 
     Separator  100  further includes a screening device  106  disposed within tank  102 . Screening device  106  may include a plurality of members disposed within the tank, wherein the screening device  106  is configured to separate a solids phase from an effluent phase of a return fluid. The plurality of members of the screening device  106  may include axially aligned longitudinal members  108 , as shown in  FIG. 1 . The plurality of axially aligned longitudinal members  108  may be evenly spaced or may be spaced at varying distances. In one embodiment, the plurality of members of the screening device  106  may be tubulars. For example, screening device  106  may include a plurality of 2 inch diameter tubulars spaced approximately 2 inches apart. In other embodiments, the plurality of members may be solid bars. 
     In an alternate embodiment, the screening device  106  may include a plurality of members, wherein the members are axially aligned horizontal members (not shown). In yet other embodiments, the screening device  106  may include a plurality of axially aligned longitudinal members and axially aligned horizontal members, thereby forming a mesh of members. One of ordinary skill in the art will appreciate that the spacing between the plurality of members of the screening device  106  may be selected based on the size of the desired solids phase to be separated from the return fluid. 
     The plurality of members of the screening device  106  may be individually installed and aligned within the tank  102 . Alternatively, screening device  106  may include an assembled screen which includes the plurality of members. In this embodiment, the screen may be placed inside the tank  102  and secured in place by any mechanism known in the art. For example, tank  102  may include a track (not shown) in which the screen of the screening device  106  slides into. Additionally, the screen may be mechanically fastened, e.g., by bolting, screwing, riveting, etc., welding the screen into place, or any combination thereof. 
     As shown, the screening device  106  extends across a length L of the tank  102 , such that fluid entering the separator  100  may not bypass the screening device  106  around ends of the screening device  106 . Additionally, the screening device  106  extends across a width w of the tank  102 , such that fluid entering the separator  100  may not bypass the screening device  106  around sides of the screening device  106 . Accordingly, gumbo or solids larger than the spacing between the plurality of members of the screening device  106  are prevented from flowing up and out of, i.e., bypassing, the separator  100 . The screening device  106  may be disposed within tank  102  at a predetermined angle a with respect to a wall of the tank  102 . The predetermined angle a may vary based on the size and shape of the tank  102 , the specific configuration of the screening device  106  (e.g., the number and spacing of the plurality of members), and the solids phase to be separated from the return fluid (e.g., the size and expected quantity of gumbo to be filtered). For example, screening device  106  may be disposed at an angle a between about 10 and about 80 degrees from the side of the tank. In other embodiments, the screening device  106  may be disposed at an angle a of between about 20 and about 45 degrees from the side of the tank. 
     Specifically, screening device  106  may be disposed within tank  102  such that a first end  110  is positioned higher than a second end  112  within the tank  102 . As used herein, first end  110  and second end  112  may refer to all ends of the plurality of aligned members of the screening device  106 , an end of a screen having a plurality of aligned members, or both. For example, the first end  110  of the screening device  106  may be disposed proximate a first upper edge  114  of the tank  102  and the second end  112  may be disposed proximate an opposite lower end  116  of the tank  102 . 
     As shown, the inlet  104  of the tank  102  is located below the first end  110 , i.e., the upper end, of the screening device  106 . Thus, as fluid enters the tank  102  through inlet  104 , the fluid is directed against the screening device  106 . An effluent phase of the fluid passes through the screening device  106  and a solids phase sized larger than the spacing between the plurality of members of the screening device  106  is trapped or separated from the effluent phase and falls to the bottom of the tank  102 . As shown in  FIG. 1 , tank  102  may include a non-flat bottom surface  118  to assist in guiding the separated solids phase toward the outlet  106  of the tank  102 . For example, the bottom surface  118  of the tank  102  may be conical or angled toward the outlet  106 . 
     The effluent phase of return fluid that passes through the screening device may then be transferred from the tank  102  to a separate container, distribution vessel, or secondary separators (not shown). A trough  120  or other conduit may be coupled to the tank  102  along a side of the screening device  106  opposite the inlet  104 . The trough  120  is configured to transfer the effluent phase to the separate container, distribution vessel, or secondary separators. 
     A conduit  122  is coupled to the outlet  106  of the tank  102  and configured to transfer the separated solids phase from the separator  100  to other process equipment, for example, a secondary separator  126 , storage container, or an overboard line. An isolation valve  124  may be coupled to the conduit  122  to close the conduit  122 , thereby stopping flow of the solids phase through the conduit  122 . The flow of solids phase may be stopped to allow, for example, maintenance to be performed on one or more components of the process equipment, e.g., secondary separator  126 , downstream of the conduit  122 . Although the isolation valve  124  is shown disposed proximate the center of the conduit  122 , one of ordinary skill in the art will appreciate that the isolation valve  124  may be disposed anywhere along the length of the conduit  122 . For example, in one embodiment, the isolation valve  124  may be disposed proximate the outlet  106  or between the outlet  106  and a first end  129  of the conduit  122 . The isolation valve may be any type of valve known in the art, for example a knife gate valve. 
     A rotary valve  128  is coupled to a second end  130  of the conduit  122 . One example of a rotary valve  128  is a DM 500  Airlock, commercially available from Mac Equipment, Kansas City, Mo. As shown in  FIG. 2 , the rotary valve  128  includes a material inlet  132  into a housing  134 . A rotor  136  extends into a chamber  135  of the housing  134 . A plurality of vanes  138  are coupled to the rotor  136  and extend therefrom into the chamber  135 . The rotor  136  is coupled to a motor (not shown) that rotates the rotor  136  and, therefore, the vanes  138  inside the chamber  135 . Accordingly, the separated solids phase  144  of the return fluid flows from the conduit  122  ( FIG. 1 ) to the material inlet  132  of the rotary valve  128  and into a partitioned segment of the chamber  135  disposed between the vanes  138  of the rotary valve  128 . As the motor turns the rotor  136  and vanes  138 , the solids phase  144  is rotated or moved, as indicated by arrow R, through the housing  134  of the rotary valve  128  from the material inlet  132  to a material outlet  140  of the rotary valve  128 . 
     The rotary valve  128  may be operated at varying speeds based on, for example, the consistency of the solids phase, the size of the rotary valve, and the flow rate of the solids phase. In one embodiment, the rotary valve  128  may be operated at  19  revolutions per minute. The rotary valve  128  may also include various features that allow the valve  128  to process gumbo material. For example, in certain embodiments, the rotary valve  128  may be modified to include a radiused pocket rotor, thereby smoothing out the portion where the blades are welded to the shaft, a Nedox coating to improve the resistance to abrasive particles in the gumbo, and air jets along the discharge to aide in removing material that might otherwise stick to the discharge. The Nedox coating is a chrome compound that may be sprayed onto the rotor  136  and vanes  138  and includes a Teflon compound infused into the pores to provide an abrasion resistant, slick surface to assist in transferring the solids phase (e.g., gumbo) through the rotary valve  128  from the separator  100  ( FIG. 1 ). One of ordinary skill in the art will appreciate that other coatings may be applied to the rotor  136  and vanes  138  to reduce adhesion of the solids phase to the rotary valve  128 . Arrows  142  in  FIG. 2  show introduction of air into the chamber  135  of the rotary valve  128  to assist in removing material from the rotary valve  128 . Rotary valve  128  may thus be used to facilitate the transference of gumbo from separator  100  ( FIG. 1 ) to secondary process equipment, such as secondary separator  126  ( FIG. 1 ). 
     Referring back to  FIG. 1 , while solids phase is separated from a primarily effluent phase of the drilling waste, the solids phase may be directed to a secondary separator  126 . In one embodiment, secondary separators  126  may include separators for high-volume solids, such as the Mongoose® Shaker, commercially available from M-I Swaco, L.L.C., in Houston, Tex. The effluent phase may pass through separator  100  through trough  120  to a flow distribution vessel (not shown). The flow distribution vessel (not shown) may be used to divert the flow of effluent phase between various separators (not shown). 
     A method of separating drilling waste is now disclosed with reference to  FIG. 1 . A return fluid from a well is flowed to inlet  104  of tank  106 . The return fluid may include drilling muds and drilling waste, including gumbo. Due to the position of the screening device  106  in the tank  102 , the return fluid is directed against the screening device  106 . As the return fluid hits the screening device  106 , an effluent phase of the return fluid passes through the screening device, thereby filtering out or separating the solids phase of the return fluid, which, as mentioned above, may include gumbo. The effluent flows through the trough  120  coupled to the tank  102  for further processing or storage. In one embodiment, the effluent may be transferred by the trough  120  to a flow distribution vessel (not shown), which directs the effluent to one or more separators. These separators may include multiple deck separators, such as the MD-3 Shale Shaker, commercially available from M-I Swaco, L.L.C., in Houston, Tex. 
     Due to the position or alignment of the screening device  106  in the tank  102 , as described above, the solids phase separated by the screening device  106  falls to the bottom surface  108  of the tank  102 . The curvature or angling of the bottom surface  108  of the tank  102  helps direct the solids phase of the return fluid to the outlet  106  of the tank  122 . The solids phase is transferred to the rotary valve  128  which is operated to transfer the solids phase to secondary process equipment. For example, rotary valve  128  may be operated to transfer the solids phase to a secondary separator  126 , which may further filter or dry the solids phase. In one embodiment, a distribution box  146  may be disposed downstream of the rotary valve  128  and configured to separate the solids phase between one of a plurality of secondary separators  126   a ,  126   b,    126   c.  Those of ordinary skill in the art will appreciate that depending on the type of secondary separation required, the type and/or number of secondary separators  126  may vary. 
     The isolation valve  124  may be actuated to close the valve  124  to prevent solids phase from flowing to the rotary valve  128 . The isolation valve  124  may be closed to allow maintenance or cleaning work on the secondary process equipment, e.g., secondary separator  126 . 
     Advantageously, embodiments disclosed herein provide for a separator for receiving a return fluid from a well and separating a solids phase from an effluent phase that reduces or prevents splash-over or bypassing of the screening device. Furthermore, embodiments disclosed herein may provide a separator for efficiently separating gumbo from a drilling return fluid. Advantageously, embodiments disclosed herein provide a separator that allows gumbo to settle down in a tank rather than flowing over a shaker. Additionally, embodiments disclosed herein provide a separator having a rotary valve configured to gradually feed gumbo from a receiving tank to a shaker, overboard, or other processing equipment. 
     While the invention 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 can be devised which do not depart from the scope of the invention as disclosed herein. Accordingly, the scope of the invention should be limited only by the attached claims.