Abstract:
A solid body contains a surfactant and crushed walnut hulls. The solid body is shaped to predetermined dimensions that permit passage through the central interior opening of drill pipe. The solid body dissolves in drilling mud for delivery of a pill to the annulus through the drill bit nozzles. The pill is an effective treatment against bit balling.

Description:
BACKGROUND 
   1. Field of the Invention 
   The field of the invention pertains to drilling fluid additives that may be used to remediate bit balling that otherwise occurs in clay and shale (hereafter referred to collectively as ‘clay’) zones as a well is drilled. 
   2. Description of the Related Art 
   Water-based drilling mud systems are usually employed during the drilling of a well, such as an oil or gas well. The well bore may penetrate a clay zone, and this circumstance exposes naturally occurring clay minerals. Water in the mud is able to hydrate the clay minerals, which then typically swell to cause a number of known problems. 
   The clay problems may be addressed by using chemical treating agents. This is done using salts and/or polymers in the drilling mud. Salts, such as KCl or CaCl, reduce the clay swelling and dispersion. Such polymers as partially hydrolyzed polyacrylamide are sometimes added to the drilling mud used to encapsulate the clay, thus keeping the clay from hydrating and swelling. Alternatively, oil-based mud may be used to prevent the swelling phenomenon, but since oil mud also contains water, it is necessary that the salinity of the water be sufficiently high to prevent water from entering the clay by osmosis. 
   Bit balling is one problem that is frequently encountered when drilling through clay. The problem is caused by the tendency of hydrated clay minerals to stick or adhere to the bit and bottom-hole assembly of a drill string. Although this problem may also occur in oil based mud, it is relatively rare as compared to water-based mud. From an operations standpoint, bit balling is evidenced by increased pump pressures as the flow pathway through the well bore annulus becomes blocked, reduced rates of penetration, blocked shaker screens, a required over-pull tension that occurs due to a restricted annulus when tripping pipe, and possible stuck pipe. 
   Once bit balling is diagnosed, conventional methods of remediation are to increase the weight on the bit, add chemicals and perhaps pull the drill pipe out of the hole to clean the bit and bottom hole assembly. For a water-based mud, a detergent may be added to the drilling mud to reduce the ability of the hydrated clay to stick to the bit and bottom hole assembly. Glycol may also be added at about 3% to 4% of system volume. This often fails to cure the problem. 
   Preventative measures against bit balling include the review of prior drilling reports to ascertain and adopt procedures that have previously worked in the geographic area to overcome bit balling. A KCl/polymer or CaCl/polymer mud may be used to inhibit the swelling of clays. The selection of a bit may also affect bit balling, where it is known that polycrystalline diamond compact bits are more prone to balling than are tri-cone bits, and it is further the case that the arrangement of teeth structures on tri-cone bits may affect bit balling. This is shown for example, in U.S. Pat. No. 4,984,643 issued to Isbell et al. 
   Another way to address the problem of bit balling is to optimize the mud system hydraulics. This may be done for either large or small bore bits. In addition to sizing the nozzles for optimum delivery of hydraulic horsepower, it is also possible to direct the nozzle discharge to optimize bottom-hole cleaning in a ‘mud pick’ configuration. This is reported, for example, in Smith et al., Hydraulics Optimization Research in Large Diameter Bits Reduces Operator&#39;s Variable Costs, AASDE-05-NTCE-58 (2005). 
   It has also been reported that maintaining a negative potential of a few volts on the drill string assembly may liberate water at the interface between the bit and the hydrated clay. See Sanjit et al., The effect of electro-osmosis on the indentation of clays, Proceedings of the 32nd US Rock Mechanics Symposium, Norman Okla. (July 1991). 
   Although the art does provide remedial measures, bit balling continues to be a significant factor affecting the costs of drilling new wells. It is particularly difficult to pump pills of material to remediate the problem of bit balling, and any such measures often provide only temporary relief. 
   SUMMARY 
   The present instrumentalities overcome the problems outlined above and advances the art by providing a compact and easy to use article of manufacture for introducing treatments to a drilling mud system. 
   In one embodiment, the article is formed as a solid body that contains a combination of nut hulls and a surfactant that are bound together with an optional carrier. As used herein the term “solid” also encompasses a gel unless specifically noted otherwise. The carrier may be a soft wax, such as beeswax, having a melting temperature much less than is expected at the bit. Beeswax generally melts at a temperature of 144° to 149° F. Thus, in an area where there exists a geothermal gradient of 1.8° F. per 100 feet of well, it may be expected that a well in excess of 8000 feet of depth will reach this temperature. A plasticizer, such as glycerol or castor oil, may be added to reduce the melting temperature. Alternatively, a water soluble polymer may be used as the carrier. This may be, for example, an ethylene/vinyl alcohol copolymer with a de-structured starch composition and a plasticizer, such as glycerin, with urea as a de-structuring agent. Suitable compositions are reported in EP0400532A1 to Bastioli et al., which is incorporated by reference to the same extent as though fully disclosed herein. The carrier is nonessential, since the surfactant itself may bind the nut hulls. 
   In dissolved form, the solid body forms a pill. A “pill” is hereby defined as any relatively small quantity, less than 200 bbl, of a special drilling fluid that is provided to accomplish a specific task that the regular drilling fluid cannot perform. Examples of conventional pills include the use of high-viscosity pills to help lift cuttings out of a vertical well bore, pipe-freeing pills to destroy filter cake and relieve differential sticking forces and lost circulation material pills to plug a thief zone. The pill that is formed of the dissolved solid body is used against bit balling. 
   The surfactant may be any surfactant; which may be a detergent, a wetting agent, or an emulsifier. Detergents are preferred. The detergent may be a soap, such as a sodium soap of a fatty acid. The detergent may also be classified as an ionic, anionic, or cationic detergent depending upon the mode of action. Sulfonates are especially preferred, and particularly linear alkyl sulfonates for their biodegradability. Soaps may be particularly useful, as a saponification reaction may be used to react and harden a glycerol ester as a soap during the casting process. In some embodiments, a potassium or sodium lye may be used to saponify a C15 to C20 fatty acid. The C18 fatty acids are particularly preferred where, for example, the resultant soap may be a saponified castor oil comprised mostly of ricinoleic acid, or oleic acid. 
   The nut hulls may be any nut hulls, but the use of walnut hulls is particularly preferred. Crushed walnut hulls that have been screened through −30/+60 US mesh are commonly purchased on commercial order and used to remediate lost circulation in wells. These may be mixed with other hull materials, including similarly sized cottonseed hulls, pecan shells, and almond shells. Use of the walnut hulls in the present instrumentality differs in that the walnut hulls are generally hard and lightweight, and may be used to blast hydrated clay from the bit and bottom hole assembly, once softened by the surfactant. 
   The article of manufacture may be used in a method of treating a drilling mud system to overcome bit balling 
   The following disclosure makes these and other advantages are apparent to those skilled in the art. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  shows a solid body that may be used to provide a pill for the treatment of bit balling; 
       FIG. 2  is a cross-sectional view taken along line  2 - 2 ′ of  FIG. 1 ; 
       FIG. 3  shows another embodiment of the solid body; 
       FIG. 4  shows the solid body being inserted into a drill string; 
       FIG. 5  is a top view of the solid body inserted into the drill string; 
       FIG. 6  shows an improvement in a rate of penetration obtained form use of a pill that contains a combination of a detergent and crushed nut hulls; 
       FIG. 7  shows a system for molding the solid body; and 
       FIG. 8  provides additional detail for the molding system of  FIG. 7 ; 
   

   DETAILED DESCRIPTION 
   There will now be shown and described an article for use in treating a bit balling problem.  FIG. 1  shows an article  100  that is formed as a generally cylindrical tube having a diameter D and a length L. A center hole  102  presents a diameter D′. A wall  104  is made of a surfactant, crushed hulls, and a dissoluble carrier.  FIG. 2  presents a sectional view taken along line  2 - 2 ′ of  FIG. 1 . 
   Dimensions are not critical, except the diameter D must be sufficiently small to pass through the interior of a drill pipe. Hole  102  is provided to assist circulation of mud through the article  100 , in order to facilitate dissolution. By way of example, suitable dimensions for most applications include a diameter D of 1 to 1.5 inches, a length L of about 20 to 30 inches, with 27 inches being most preferred, and a diameter D′ of about 1/16 to ½ inch. 
   Article  100  contains a combination of nut hulls and a surfactant that are bound together with a carrier. The carrier may be a soft wax, such as beeswax, having a melting temperature much less than is expected at the bit. Beeswax generally melts at a temperature of 144° to 149° F. Thus, in an area where there exists a geothemal gradient of 1.8° F. per 100 feet of well bore, it may be expected that a well in excess of 8000 feet of depth will reach this temperature. A plasticizer, such as glycerol, may be added to reduce the melting temperature suitably for shallower depths. Alternatively, a water soluble polymer may be used as the carrier. This may be, for example, an ethylene/vinyl alcohol copolymer with a de-structured starch composition and a plasticizer, such as glycerin. Urea may be used as a de-structuring agent. Suitable polymeric compositions for this use are reported in EP0400532A1 to Bastioli et al. 
   In some cases, the carrier may be a soap. It is possible to combine the nut hulls with the glycerol ester of a fatty acid, or another ester, pour the mixture into a mold, and cast the article  100  to saponify and harden the mixture, then release from the mold. In this case, the resultant soap holds together the nut hulls. 
     FIG. 3  shows another embodiment as article  300  with center hole  302 . In this case, half of the article  300  is a surfactant  304  and the other half  306  contains nut hulls bound with a carrier, as described above in context of the wall  104  that is shown in  FIG. 1 . The respective halves  304 ,  306  are cast together in a common mold. 
     FIG. 4  shows article  100  in use. Drill pipe  400  is retained by slips  402  in a rotary table  404 . The drill string, as represented by drill pipe  400 , is broken to make a new connection. Tongs  406  are in position for use in assembling the next connection, as is required to advance the drill pipe  400  down the well-bore as the well is drilled. The article  100  is being placed into a female joint  408  that will receive a male pin of the next piece of drill pipe (not shown) as the connection proceeds. Any number of articles  100  may be manually placed in the drill pipe  400  in this manner. 
     FIG. 5  shows the article  100  positioned in the female joint  408 . A threaded surface  500  transitions to a curved wall  502  and conduit  504 . Article  100  resides within conduit  504 . From this position, the connection may be assembled with joint  408 , and active drilling may recommence. The recommencement of drilling necessarily entails the pumping of mud through conduit  504 . The mud drives article  100  down hole towards the bit. As article  100  proceeds down hole the water in the mud and/or temperature of the mud tends to dissolve article  100  to release the surfactant and the nut hulls, providing what is known in the art as a ‘pill’. The surfactant and the nut hulls pass through the nozzles of a drilling bit and enter the annulus of the well-bore where they work against bit balling. The hole  102  and the space between article  100  and the walls of conduit  504  assures that mud pumped through conduit  504  is able to bypass article  100 , in order that article does not fully obstruct conduit  504  if article  100  has not completely dissolved by the time it reaches the drill bit (not shown) at the bottom of the hole. 
     FIG. 6  shows an improvement in rate of penetration that was obtained using a pill of this nature where the pill contained 0.1 gallons of crushed walnut hulls and 0.3 gallons of liquid soap. The “after” penetration rate shows comparatively that a bit balling problem has been overcome. 
     FIG. 7  shows a system  700  that may be used to make article  100 . An injection system  702  disburses liquid material through line  704  into to mold system  706 . A nut hull hopper  708  provides nut hull material for combination with the liquid in the mold system  706 . The injection system  702  may be, for example, a screw extruder system for the liquefaction of water soluble polymer material, as described above in context of EP0400532A1. The injection system  702  may also be a metering system for pumping a soap precursor that may be saponified in the mold system  706 . Initially cast with a liquid, the articles  100 ,  300  harden in the mold system  706 . 
     FIG. 8  provides additional detail with respect to one embodiment of the mold system  706 . A bivalve mold  800  is formed of respective halves  802 ,  804 , which are notched as at  806 ,  808  to accommodate line  704 . Upon opening of the mold  800 , a robotic arm  810  imparts motion  812 ,  814  to swing the halves  802 ,  804  away from line  704 . With the mold  800  removed in this way, a pneumatic cylinder  816  is mounted on line  704 , and is capable of extending head  818  in direction  820  to release cast articles  100  from line  704 . The arm  810  then positions the mold  800  as shown in  FIG. 8  for receipt of nut material from nut hopper  708  (not shown in  FIG. 8 ). With the mold  800  subsequently closed, line  704  receives liquid material from the injection system  702  and disburses the same into mold cavity  822  through perforations  824 . The mold halves  802 ,  804  may be configured with a heating structure, such as resistive electrical coils or a water jacket (not shown) to heat materials in the mold, for example, to perform a saponification reaction. 
   EXAMPLES 
   Table 1 provides various formulations of materials that may be used as articles  100  or  300 : A 1.5″ diameter stick that is 27″ long contains 0.27 gallons of material. Although this is less than the total of 0.4 gallons used in actual testing reported herein. two or more sticks may be used at one time in a stacked sequential order. The calculations below are based on a total stick volume of 0.27 gallons. 
   
     
       
             
           
             
             
             
             
           
             
             
             
             
             
           
         
             
               TABLE 1 
             
           
           
             
                 
             
             
               Example compositions 
             
           
        
         
             
               Article 
               Material 
               Amount 
               Processing Comments 
             
             
                 
             
           
        
         
             
               A 
               Saponified Castor Oil 
               0.2 
               gal 
               Heat to 115°. Mix .01 gal 
             
             
                 
               (SCO) 
             
             
                 
               Crushed walnut 
               0.07 
               gal 
               of the SCO together with 
             
             
                 
               hulls sized - 
                 
                 
               the walnut hulls. Inject 
             
             
                 
               30/+60 US mesh 
                 
                 
               remainder of the SCO into 
             
             
                 
                 
                 
                 
               one end of the mold and 
             
             
                 
                 
                 
                 
               the SCO/ Walnut hull 
             
             
                 
                 
                 
                 
               mixture into the other end. 
             
             
                 
                 
                 
                 
               Cool for 360 minutes. 
             
             
                 
                 
                 
                 
               Remove from mold. 
             
             
               B 
               Beeswax 
               .01 
               gal 
               Heat Beeswax to 144° 
             
             
                 
                 
                 
                 
               and mix with walnut hulls. 
             
             
                 
               Saponified Castor Oil 
               0.19 
               gal 
               Heat SCO to 115°. Inject 
             
             
                 
               (SCO) 
             
             
                 
               Crushed walnut 
               0.07 
               gal 
               each mixture into opposite 
             
             
                 
               hulls sized - 
                 
                 
               ends of the mold. Cool for 
             
             
                 
               30/+60 US mesh 
                 
                 
               360 minutes. Remove 
             
             
                 
                 
                 
                 
               from mold. 
             
             
               C 
               Oleic Acid 
               0.14 
               gal 
               Add Lye to water. Mix 
             
             
                 
               Lye 
               0.02 
               gal 
               lye/water solution into 
             
             
                 
               Crushed walnut hulls 
               0.07 
               gal 
               Oleic Acid. Stir until 
             
             
                 
               sized - 
                 
                 
               thick. Mix .01 gal of this 
             
             
                 
               30/+60 US mesh 
                 
                 
               solution together with the 
             
             
                 
                 
                 
                 
               walnut hulls. Inject 
             
             
                 
                 
                 
                 
               remainder of the solution 
             
             
                 
                 
                 
                 
               into one end of the mold 
             
             
                 
                 
                 
                 
               and the Walnut hull 
             
             
                 
                 
                 
                 
               mixture into the other end. 
             
             
                 
                 
                 
                 
               Cool for 360 minutes. 
             
             
                 
                 
                 
                 
               Remove from mold. 
             
             
                 
               Water 
               0.04 
               gal 
             
             
                 
             
           
        
       
     
   
   Those skilled in the art appreciate that the foregoing instrumentalities teach by way of example, and not by limitation. Accordingly, what is claimed as the invention also encompasses insubstantial changes with respect to what is claimed. The inventor hereby states his intention to rely upon the Doctrine of Equivalents to protect the scope and spirit of the invention.