Abstract:
An LCM recovery system that relies on gravity and density or specific gravity differences between three of the main components of drilling fluids, i.e., the mud and chemicals, lost circulation material (LCM) or additives, and drill solids or cuttings. Fluid enters the LCM recovery tank from the well via a flow line or mud gas separator return leg. Cuttings, having a greater density than additives, tend to settle and become trapped on the input side of the LCM recovery tank. The less dense fluid and entrained or suspended LCM tends to travel over the baffle near the center of the tank. LCM can then be efficiently returned to the active mud system for reconditioning or pumping downhole again.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation-in-part application of U.S. patent application Ser. No. 14/296,324 filed Jun. 4, 2014, which claims priority to U.S. Provisional Patent Application Ser. No. 61/830,672 filed Jun. 4, 2013 entitled “LCM RECOVERY SYSTEM,” the contents of which are hereby incorporated by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to a method and system for separating and recovering lost circulation material from well sites during drilling. 
     2. Prior Art 
     Drilling fluid is typically used when boreholes are drilled into the earth. For example, drilling fluid is typically used when drilling oil and natural gas wells, but it may also be used for simpler boreholes, such as water wells. Liquid drilling fluid of the sort considered herein will be referred to as “drilling mud”. There are three main categories of such drilling fluids: water-based muds (dispersed and non-dispersed), and non-aqueous muds (i.e., oil-based mud, and gaseous drilling fluid), and synthetics or hybrids. Among the many benefits of using drilling fluids are that they provide hydrostatic pressure to prevent formation fluids from entering into the well bore, as well as assisting in stabilizing the wellbore. Additionally, drilling fluids cool and clean the drill bit during drilling and carry drill cuttings away from the bit to the surface. Drilling fluids additionally aid in suspending the lighter drill cuttings while drilling is paused, such as when the drilling assembly is brought in and out of the hole. 
     The ability of a drilling fluid to carry the rock excavated by the drill bit up to the surface depends on cutting size, shape, and density, and speed of fluid traveling up the well, i.e., it is a function of the annular velocity. The viscosity, surface tension or yield point of the drilling mud is another important consideration, since cuttings will settle to the bottom of the well if the viscosity is too low. 
     Lost circulation is one of the more serious problems that can arise during the drilling of an oil well or gas well. Lost circulation can be complete or partial in nature, the latter of which is usually referred to as seepage. Circulation is said to be lost when the drilling fluid, or mud, flows into the geological formations or fractures instead of returning up the annulus. 
     Lost circulation results in the loss of drilling fluid, which is undesirable for many reasons, including economics, wellbore stability, hole cleaning, rate of penetration, and other reasons. At times of severe seepage or lost circulation, sweeps may not sufficiently provide the relief or results desired. Additionally, loss of drilling fluids can be expensive. Hybrid water based drilling fluids, diesel based muds potassium or polymer, and even synthetic oil muds are extremely costly to lose. Lost circulation may also result in a dangerous well blowout. Therefore, well operators closely monitor tanks, pits, and flow from the well to quickly assess and control any lost circulation. If the fluid in the wellbore drops for any reason, such as lost circulation, hydrostatic pressure is reduced. The reduced hydrostatic pressure can allow a gas or fluid, which is under a higher pressure than the reduced hydrostatic pressure, to flow into the wellbore. 
     Another consequence of lost circulation is called “dry drilling”. Dry drilling occurs when fluid is completely lost from the well bore without actual drilling coming to a stop. Dry drilling may destroy a bit or may even require a new well to be drilled. Dry drilling can also damage the drill string, whether from increased vibration or by thermal generation and thus strength degradation. 
     Lost circulation material (LCM) is used to control or cease lost circulation by sealing formation pores, small holes, or fractures in the wellbore. Although fine carbonates are the most common additive used, other LCM additives are employed, depending on the fluid being used and the depth of drilling in relation to desired production zones. Other LCM additives used might include, by way of example, sawdust, flaked cellophane, crushed or ground gypsum, shredded newspaper, cotton seed hulls, cedar fiber, rubbers, etc. 
     To avoid loss of drilling fluids and LCM, rig vibrating separators or shale shakers are often “bypassed” completely in an effort to reclaim all or some of the LCM being directly added to the active drilling system. For short intervals this method is effective and acceptable, but over time the active pits and sand traps will become completely filled with drilled cuttings causing a loss of surface pit capacity, and an increase in drill solids within the mud system. The result can be costly time consuming pit cleanings before the next hole interval or after reaching the target depth (TD) of the well, as well as reduced rate of penetration (ROP) due to an increase in drilled and low gravity solids, increased drillstring and tool wear, reduced carrying capacity of mud, or even reduced pit volumes at the surface. 
     As is well known in the drilling industry, there has been a need for a system and method that would provide a better way of recovering LCM material. Accordingly, it should now be recognized, as was recognized by the present inventors, that there exists, and has existed for some time, a very real need for a method of LCM recovery would address and solve the above-described problems. 
     Before proceeding to a description of the present invention, however, it should be noted and remembered that the description of the invention which follows, together with the accompanying drawings, should not be construed as limiting the invention to the examples (or embodiments) shown and described. This is so because those skilled in the art to which the invention pertains will be able to devise other forms of this invention within the ambit of the appended claims. 
     SUMMARY OF THE INVENTION 
     Other embodiments and variations are certainly possible within the scope of the instant invention and can readily be formulated by those of ordinary skill in the art based on the disclosure herein. 
     The LCM recovery system of the invention is a simple design that alleviates or reduces the impact of all or most of the issues discussed above, while maintaining a desired LCM concentration in an active mud system. 
     The LCM recovery system of the invention relies on gravity and large density or specific gravity differences between three of the main components of drilling fluids, i.e., the mud and chemicals, lost circulation material (LCM) or additives, and drill solids or cuttings. In one embodiment, fluid enters the LCM recovery tank directly from the well via the flow line or mud gas separator return leg. Cuttings, having a greater density than the additives, i.e., having a typical specific gravity of 2.4-2.8, will tend to settle and become trapped on the cuttings side or input side of the LCM recovery tank. The less dense fluid and entrained or suspended LCM will tend to travel over the baffle plate or plates near the center of the tank. The drilling fluid with LCM can then be efficiently returned to the active mud system for reconditioning or pumping directly downhole again. 
     Cuttings can be collected by mud loggers during drilling. Background gas is monitored and sampled as drilling fluid enters the LCM recovery tank. The cuttings are also typically sampled at 10′ intervals. The mud loggers separate and clean the samples, e.g., by collecting a sample at the sample interval directly to the LCM tank versus what is typically done at the shale shakers. 
     In one embodiment, the fluid level and the tendency of the LCM and drilling fluid to travel from the input side to the recovery side of the LCM recovery tank is controlled by adjusting a height of the baffle plate or plates, e.g., by raising or lowering. The adjustability allows for varying flow rates to be managed while maintaining sufficient fluid and material recovery when used in conjunction with a wide range of hole sizes and drilling conditions observed throughout the well. 
     In one embodiment, an agitator provided within the cutting side or input side of the LCM recovery tank aids in pushing lighter LCM, such as carbonates and/or cedar fiber, to the recovery side across the baffle. Fluid and LCM from the recovery side are returned to the active mud system, e.g., via a centrifugal pump. The cuttings side or input side mixture of cuttings and marginal fluid volumes are returned to shale shakers for further separation. 
     If cuttings buildup on the cuttings side or input side becomes too great, there are two suggested options for removal. First is the use of a track-hoe, which is typically on location for dipping of the cuttings box. The track-hoe can simply remove excess cuttings during “off-pump” events such as connections, surveys, and/or rig services. Further options or embodiments to aid in the removal of cuttings from the tank include augers, fluid, jets, angled tanks, or the use of multiple suctions, which are and have been used but nonetheless are not required for successful use of the LCM recovery tank. 
     The foregoing has outlined in broad terms the more important features of the invention disclosed herein so that the detailed description that follows may be more clearly understood, and so that the contribution of the instant inventors to the art may be better appreciated. The instant invention is not to be limited in its application to the details of the construction and to the arrangements of the components set forth in the following description or illustrated in the drawings. Rather, the invention is capable of other embodiments and of being practiced and carried out in various other ways not specifically enumerated herein. Finally, it should be understood that the phraseology and terminology employed herein are for the purpose of description and should not be regarded as limiting, unless the specification specifically so limits the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Other objects and advantages of the invention will become apparent upon reading the following detailed description and upon reference to the drawings in which: 
         FIG. 1  is a schematic representation of the LCM recovery system of the invention in conjunction with the typical fluid handling components and pits typically found on drilling operations; 
         FIG. 2  is an enlarged schematic representation of the LCM recovery tank of the LCM recovery system of  FIG. 1 . 
         FIG. 3  is a perspective view of the LCM recovery tank of  FIG. 2 ; 
         FIG. 4   a  is a partial top or overhead view of the LCM recovery tank of  FIG. 2 ; 
         FIG. 4   b  is an enlarged view of the inlet/cuttings chamber of the LCM recovery tank of  FIG. 2 ; 
         FIG. 5  is an enlarged perspective view of the baffle and inlet/cuttings chamber of the LCM recovery tank of  FIG. 2 ; 
         FIG. 6  is a cross-sectional perspective view of the baffle and inlet/cuttings chamber of the LCM recovery tank of  FIG. 2 ; 
         FIG. 7  is a perspective view of the LCM recovery tank of  FIG. 2 ; 
         FIG. 8   a  is a partial top or overhead view of the LCM recovery tank of  FIG. 2 ; 
         FIG. 8   b  is an enlarged view of the cuttings chamber of the LCM recovery tank of  FIG. 2 ; 
         FIG. 9  is an enlarged perspective view of the baffle and inlet/cuttings chamber of the LCM recovery tank of  FIG. 2 ; and 
         FIG. 10  is a cross-sectional perspective view of the baffle, agitators, and inlet/cuttings chamber of the LCM recovery tank of  FIG. 2 . 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     While this invention is susceptible of embodiment in many different forms, there is shown in the drawings, and will herein be described hereinafter in detail, some specific embodiments of the instant invention. It should be understood, however, that the present disclosure is to be considered an exemplification of the principles of the invention and is not intended to limit the invention to the specific embodiments or algorithms so described. 
     Referring to the particular embodiment of  FIG. 1  in this figure the instant lost cuttings material (LCM) recovery system is designated generally as part number  10 , when considering tank and lines, and part number  26  when considering just the LCM recovery tank. This variation of the LCM recovery system  10  includes flow line  12  for delivering mud cuttings and LCM material from wellbore  14  or from mud gas separator  20 . 
     According to this embodiment, a trip tank  16  is provided in selective communication with flow line  12 . A trip tank valve  18  is provided for opening or closing a pathway from the flow line  12  to the trip tank  16 . 
     Continuing with the current example, a mud gas separator  20  may be provided. Choke line  22  extends from wellbore  14  to mud gas separator  20 . Mud gas return leg  25  connects mud gas separator  20  with the flow line  12 . A vent valve  27  is provided for selectively opening or closing vent line  25  from flow line  12  to mud gas separator  20 . Mud gas return leg  25  and return leg valve  27  are provided to selectively deliver mud, cuttings, and LCM to flow line  12 . 
     LCM recovery tank  26  defines an inlet chamber  28  or cuttings chamber and a recovery chamber  30  or LCM and fluid chamber. 
     Inlet chamber  28  receives mud, cuttings and LCM material from the flow line  12 , either directly from the wellbore  14  or from mud gas separator  20  via mud gas return leg  25 . In one embodiment, flow line  12  delivers mud, cuttings, and LCM material by dropping it into the open top of inlet chamber  28 . 
     A baffle  32  or weir plate is provided for separating recovery chamber  30  and inlet chamber  28 . The baffle  32  is preferably adjustable in height to account for varying flow rates through flow line  12  that may be encountered while drilling. In this embodiment, baffle  32  is oriented vertically, but it could also be sloped toward or away from the recovery chamber  30  according to the desires or needs of the designer. In a preferred embodiment, the adjustable baffle  32  is a worm driven gasket sealed gate valve. In another embodiment, baffle  32  may also be fixed rather than adjustable, and in yet another embodiment, use of multiple baffles may be employed. 
     In operation, a height of baffle  32  or weir plate is proportional to a flow rate of material pumped into wellbore  14 . However, the most efficient height of baffle  32  may also be affected by the type and amount of LCM. Therefore, the height of baffle  32  may be determined by observation and direct recovery measurements. Sensors for determining fluid level may be provided in the LCM recovery tank  26 . Examples of suitable sensors include sonic type and ball tether type. 
     Optionally, a cuttings auger  34  ( FIG. 2 ) may be provided in inlet chamber  28 . Further options or embodiments to aid in the removal of cuttings from the tank include augers, fluid jets, angled tanks, or the use of multiple suctions, which are and have been used but nonetheless are not required for successful use of the LCM recovery tank. Alternatively, a track-hoe may be utilized for secondary removal during connections as noted and discussed above. 
     An optional agitator  36  is shown in inlet chamber  28 . Agitator  36  is driven by an electric motor in some embodiments. Agitator  36  aids in pushing relatively less dense LCM material over adjustable baffle  32  as an alternative aid to collecting the LCM material in recovery chamber  30 . 
     The LCM recovery system  10  of the current embodiment additionally includes an active steel mud pit  38 . LCM and fluid line  40  communicates recovery chamber  30  with mud pit  38 . In one embodiment, fluid side discharge pump  41  ( FIGS. 3 and 7 ) delivers fluid into fluid line  40 . Discharge pump  41  may be connected to intake pipe  43  ( FIGS. 3 and 7 ) that extends over or through a wall of recovery tank  26 . 
     Vibrating separators or shale shakers  50  are typically positioned above mud pit  38 . Shaker line(s)  52  communicates shaker  50  with flow line  12 . Shaker valve(s)  54  are provided to selectively permit flow from the flow line  12  to shaker  50 . Cuttings line  60  communicates inlet chamber  28  with shaker  50 . Cuttings line  60  is provided to flow mud and cuttings slurry from the inlet chamber of LCM recovery tank  26  to shaker  50 . In one embodiment, cuttings side discharge pump  61  ( FIGS. 3-10 ) delivers mud and cuttings slurry into cuttings line  60 . Cuttings side discharge pump  61  may be connected to an intake pipe  63  ( FIGS. 6 ,  9 , and  10 ) that extends over or through a wall of recovery tank  26 . 
     In  FIG. 1 , steel open top cuttings box  62  is provided adjacent to mud pit  38 . Chute  64  communicates shaker  50  with cuttings box  62 . Mud is delivered from shaker  50  into mud pit  38 . Separated cuttings are delivered by chute  64  into cuttings box  62 . Cuttings delivered to cuttings box  62  are typically removed by a track-hoe or by other means. 
     Continuing with the present example, first flow line valve  70  is provided on flow line  12  downstream of trip tank  16  and upstream of mud gas return leg  25 . Second flow line valve  72  is provided on flow line  12  downstream of mud gas return leg  25  and upstream of shaker line  52 . Third flow line valve  74  is provided on flow line  12  downstream from shaker line  52  and upstream of LCM recovery tank  26 . An igniter  80 , such as a flare stack, may be provided to receive gas from mud gas separator  20  through mud gas vent line  23 , which may be regulated by mud gas vent line valve  24 . 
     In use, the LCM recovery system  10  of the invention receives mud, cuttings, and LCM from wellbore  14  through flow line  12  into inlet chamber  28  of LCM recovery tank  26 . The adjustable baffle  32  is height adjusted to a level suitable to accommodate a flow rate through flow line  12  to allow a desired amount of mud, cuttings and LCM to flow over adjustable baffle  32  from inlet chamber  28  into recovery chamber  30  of LCM recovery tank  26 . Alternatively, baffle  32  may be fixed rather than adjustable. Further, one or more baffles  32  may be used. Mud, cuttings, and LCM remaining in inlet chamber  28  can be agitated with agitator  36  (FIGS.  1 , 2 ,  7 - 10 ) to aid in pushing relatively less dense LCM over baffle  32 . Relatively heavier cuttings tend to remain in inlet chamber  28  rather than passing over baffle  32 . Cuttings auger  34  ( FIG. 2 ) may be provided in inlet chamber  28  to aid in removal of cuttings that settle within inlet chamber  28 . Other contemplated or proven devices include fluid jets  82 , that receive cleaning fluid from charging fluid lines  83 , angled tanks, or the use of multiple suctions, which are and have been used but nonetheless are not required for successful use of the LCM recovery tank may be used to aid in the removal of cuttings that settle away from the cutting suction(s), e.g., intake pipe  63 , within the inlet chamber  28 . Alternatively, cuttings may be removed from inlet chamber  28  with a track-hoe for secondary removal during connections. 
     Mud and LCM flow from recovery chamber  30  to mud pit  38  through LCM and fluid line  40 . The mud and cuttings flow from inlet chamber  28  to shaker  50  through cuttings line  60 . Shaker  50  then separates mud and cuttings wherein the mud drops into mud pit  38  and cuttings are delivered to cuttings box  62  via chute  64 . 
     In addition to receiving mud, cuttings, and LCM directly from wellbore  14 , LCM recovery tank  26  may recover mud, cuttings, and LCM through flow line  12  from mud gas separator  20  through mud gas return leg  25 . Mud gas separator  20  may be provided to receive mud, cuttings, and LCM through choke line  22 . Separated gas is then delivered through flare line  23  to igniter  80  for disposal. Remaining mud, cuttings, and LCM are delivered from mud gas separator  20  through mud gas return leg  25 . In one embodiment, mud gas return leg  25  communicates with flow line  12  upstream of second flow line valve  72 , as shown in  FIG. 1 . Flow through mud gas return leg  25  is controlled by return leg valve  27 . In other embodiments, mud gas return leg  25  may communicate directly with shakers  50  and/or with LCM recovery tank  26  for delivery of mud, cuttings, and LCM to inlet chamber  28  of LCM recovery tank  26 . * * * Thus, the present invention is well adapted to carry out the objectives and attain the ends and advantages mentioned above as well as those inherent therein. While presently preferred embodiments have been described for purposes of this disclosure, numerous changes and modifications will be apparent to those of ordinary skill in the art. Such changes and modifications are encompassed within the spirit of this invention as defined by the claims.