Patent Publication Number: US-2009238643-A1

Title: Method Of Disposing Of Drill Cuttings In Roads

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application is a continuation of pending International patent application PCT/CA2007/001166 filed on Jun. 29, 2007, which designates the United States and claims the benefit under 35 U.S.C. §119 (e) of U.S. Provisional Patent Application Ser. No. 60/806,124, filed on Jun. 29, 2006. The present application also claims the benefit under 35 U.S.C. §119 (e) of the U.S. Provisional Patent Application Ser. No. 60/825,707 filed on Sep. 14, 2006. All prior applications are herein incorporated by reference in their entirety. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to a method of using oil-contaminated drill cuttings from drilling operations in roads and primarily in gravel or dirt roads to provide dust suppression or as a component of the top course of a road. In particular, the invention relates to various compositions and processes in which drill cuttings are mixed with virgin aggregates, asphalt compounds and/or recycled hydrocarbons including recycled rubber from tires and recycled asphalt shingles for incorporation into a road bed to provide a structurally satisfactory road and/or dust suppression. The invention thereby provides an effective use of oil-contaminated drill cuttings that would otherwise require remediation or disposal at a landfill. 
     BACKGROUND OF THE INVENTION 
     In the past, the disposal of drill cuttings has been a significant issue for drill site operators. For example, in a typical drilled well in the oil industry, upwards of 100 m 3  of drill cuttings may be produced from a single well. Typical drill cuttings will contain a variety of contaminants including hydrocarbons, salts, metals, soaps and other agents that have been added to the drilling fluid to assist in the drilling and hydrocarbon recovery processes or that have become mixed with the drilling fluid from the formation. In the past, it has been understood that as a result of the wide range of contaminants in drilling fluids, that the drill cuttings from a well could not be used within roads due to the leaching of volatile organics and metals from the road to the surrounding environment. 
     In a drilling process, recovered and dried drill cuttings will typically include approximately 15% (w/w) hydrocarbon contaminants that may range in viscosity from highly viscous bitumens through to less viscous lighter fractions as well as numerous metals and metal salts. Hydrocarbon contaminants may in some drilling situations be as high as 40% (w/w). 
     In view of this understanding and level of contamination, currently acceptable methods of disposal of drill cuttings are usually dictated by various jurisdictional regulations and will usually require that the drill cuttings are properly remediated into the local soil or alternatively, removed to a landfill site. Local remediation is expensive requiring specially designed containment systems to be built on-site that require regular and on-going monitoring of soil contamination levels. Off-site disposal requires that the drill cuttings are initially stabilized prior to transportation to prevent hydrocarbon release from the vibration and compaction of the drill cuttings within a truck bed. Current methods for adsorbing or absorbing free oil prior to transportation and/or remediation include mixing the drill cuttings with sawdust. 
     However, both on-site and off-site disposal will often lead to environmental contamination as the various contaminants within the drill cuttings may ultimately leach into the local soil or groundwater, particularly for example as the stabilizing sawdust decomposes. Moreover, both techniques are expensive in terms of handling. 
     Further still, the use of sawdust as an agent to stabilize drill cuttings substantially increases the volume of the drill cuttings as in order to stabilize drill cuttings prior to transportation, it is necessary to mix the drill cuttings with approximately a double volume of sawdust, thus tripling the volume of disposal material. In addition, the use of sawdust for disposal is not an effective or high-value use of sawdust and that may also contribute to the unnecessary consumption of trees. 
     The use of landfills is also not a desired long term solution. With increasing difficulty in licensing new landfills, there is greater pressure to utilize existing landfills as efficiently as possible and to extend the life of these facilities. 
     Thus, neither off-site transportation of drill cuttings to a landfill nor on-site soil remediation provides an environmentally sound solution to the issue of disposing of drill cuttings. 
     As noted above, in the past, the use of drill cuttings in roads has not been permitted due to the understanding that the contaminants will leach from the road to the ground. Of particular concern are single aromatic contaminants including benzene, ethylbenzene, toluene and xylene (collectively referred to as BETX) and various metal salts. 
     As a result, there has been a need for effective disposal methods wherein the drill cuttings are disposed of in a manner that meets environmental regulations and that does not increase the overall cost of disposing of such drilling cuttings. More specifically, there has been a need for a disposal method in which drill cuttings provide a useful product wherein the contaminants may be encapsulated or incorporated with other products such that the likelihood of such contaminants leaching to the environment is reduced while also providing useful and beneficial properties to the road. The use of oil based drilling fluid cuttings in road structures can provide a low cost alternative to traditional disposal methods while providing an effective road structure that does not cause contaminants to leach into the ground at undesirable levels. 
     SUMMARY OF THE INVENTION 
     In accordance with the invention, there is provided a method of disposal of hydrocarbon-contaminated drill cuttings in a road comprising the steps of: mixing hydrocarbon-contaminated drill cuttings with virgin aggregates and asphalt binder to form a blended mixture; and incorporating the blended mixture into the road. 
     In further embodiments, the degree of hydrocarbon contamination of the drill cuttings is less than 40% (w/w) (hydrocarbon/drill cuttings). 
     The blended mixture may be incorporated as the base and/or top course of a road. 
     Preferably, the blended mixture of hydrocarbon-contaminated drill cuttings to virgin aggregate is 5-25% (w/w). 
     In one embodiment, the hydrocarbon-contaminated drill cuttings are pre-mixed with an elastomeric material to stabilize the drill cuttings prior to mixing with virgin aggregate. The elastomeric material is preferably 1-25% (w/w) of the mass of the drill cuttings and more preferably 5-10% (w/w) of the mass of the drill cuttings. 
     The asphalt binder is preferably selected from a hot mix, anionic cold mix, cationic cold mix, non-ionic cold mix or asphalt emulsion binder. 
     In yet another embodiment, the invention provides a method of stabilizing oil contaminated drill cuttings or earthen material comprising the step of blending 1-25% (w/w) (more preferably 5-10% (w/w)) rubber crumb or asphalt material with the drill cuttings or earthen material. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention is described with reference to the drawing in which: 
         FIG. 1  is bar graph showing the total level of C10-C40+ leachate for a number of road mix samples. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Methods of incorporating drill cuttings into a road structure are described. As is known, a typical road construction includes a sub-grade of supporting native rock, soil, sand, clay or other material onto which a base course generally comprising a depth of crushed gravel or aggregate is placed and compacted. The aggregate will usually range in depth from 12 inches to several feet depending on the engineering requirements of the road. Roads may be sealed or unsealed. In an unsealed road the aggregate may include various binders or additives that provide dust suppression. 
     In a sealed road, a surface course of a concrete (usually an asphalt concrete) is applied and compacted over the aggregate to seal and bind the upper surface of the road. As is known, many different formulations of cements or binders including various asphalts may be blended with aggregate to create an asphalt concrete. Asphalt is a complex mixture of hydrocarbons primarily comprised of bitumen which in itself is generally comprised of asphaltenes as the dispersed phase and maltenes as the continuous phase. Mixed with various aggregates or mixtures of aggregates, different blends of asphalt concrete can be produced depending on the desired qualities for the road surface. 
     The classes of asphalt binders generally used in road construction include asphalt cements, cutback asphalts and asphalt emulsions as known to those skilled in the art. 
     In accordance with the invention, drill cuttings are incorporated into a road bed either as part of the base course or surface course in conjunction with appropriate quantities of virgin aggregates, binder and/or an elastomeric material. The use of drill cuttings as described herein is particularly effective in dust suppression for gravel roads and within a top course of a road. In addition, the invention provides an effective means of stabilizing drill cuttings for transportation. 
     As noted above, drill cuttings may include hydrocarbon contaminants or diluents, various metals, salts, soaps and other contaminants coated upon the native rock chips removed from the drilled well. 
     In a first embodiment, the drill cuttings are blended with virgin aggregate to 5-25% (w/w) and asphalt binder for use as the base course of a road bed with or without a surface course. The blended drill cuttings and aggregate may be applied to the road bed in the usual manner with graders and compaction vehicles. In this embodiment, as a result of the hydrocarbon contaminants, the blended drill cuttings, aggregate and binder provide effective dust suppression when used in an unsealed road. 
     In a second embodiment, drill cuttings are blended with virgin aggregate to 5-25% (w/w) and blended with an asphalt binder such that the asphalt binder is 4-8% (w/w) of the total mass of the resulting asphalt concrete. 
     The blending of drill cuttings with virgin aggregate may be achieved through use of appropriate mixing equipment including reclaimers either at the road construction site, aggregate quarry or an asphalt plant. 
     The actual proportions of drill cuttings relative to virgin aggregate are determined through assessment of the relative amounts of and properties of the contaminants. Generally, more viscous hydrocarbon contaminants can be incorporated at a higher weight % whereas less viscous more volatile hydrocarbon contaminants are incorporated at a lower weight %. Contaminants other than hydrocarbons are encapsulated within the structure by the asphalt binder. 
     In a further embodiment, the drill cuttings (or a similar material such as soil, sand or other earthen material) are blended with elastomeric materials as a means to stabilize the drill cuttings for transportation and to absorb excess free oil that may be contained within the drill cuttings. Preferred elastomeric materials would include recycled hydrocarbon materials such as recycled rubber from tires and/or recycled asphalt shingles. These materials may be mixed with the drill cuttings at an appropriate proportion (0-25% (w/w), preferably 5-10% (w/w) to reduce the free oil content within the drill cuttings and thereby impart further binding properties to the aggregate and/or asphalt binder. The use of rubber crumb as a blending agent to absorb free oil provides the further advantage of stabilizing drill cuttings during transport from a drill site to a road construction site without the need for using sawdust. For soils and sands that may have been contaminated with spilt oil, the elastomeric materials are effective in absorbing free oil within the soil or sand thereby imparting stability to these materials and further enabling the contaminated materials to be more readily collected for removal. 
     Leachate Tests 
     Leachate tests were performed to quantify and compare the leaching of various contaminants including hydrocarbons and metals from blends of rubber crumb and drill cuttings, sawdust and drill cuttings, “road mixes” containing drill cutting materials and virgin aggregates and standard “broad mixes” using virgin aggregates alone together with various commonly used binders known to those skilled in the art. 
     The leachate tests were conducted using known leachate testing protocols including hot water soluble boron, Toxicity Characteristic Leaching Procedure (TCLP), strong acid digestion, mono-aromatic hydrocarbons and volatile petroleum hydrocarbons testing protocols. 
     Hot water soluble tests performed in accordance with Hot Water Soluble Boron-Azomethine-H Method, 4.61 confirmed boron was within acceptable limits for all samples. 
     TCLP analysis performed in accordance with TCLP, SW-846, EPA 1311 confirmed that each of antimony, arsenic, barium, beryllium, boron, cadmium, chromium, cobalt, copper, iron, lead, mercury, nickel, selenium, silver, thallium, uranium, vanadium, zinc and zirconium were within TCLP limits for all samples. 
     Metals strong acid digestion test performed in accordance with US EPA test 3050B confirmed acceptable EPA levels for each of mercury, antimony, arsenic, barium, beryllium, cadmium, chromium, cobalt, copper, lead, molybdenum, nickel, selenium, silver, thallium, tin, vanadium and zinc for all samples. 
     Mono-aromatic hydrocarbon tests performed in accordance with US EPA test 8260B/5035 and CCME-Canada wide standard for PHC in Soil, CWS PHC confirmed acceptable EPA levels for each of benzene, toluene, ethylbenzene and xylenes (BTEX) for all samples. 
     Representative drill cuttings samples with blended rubber crumb and sawdust were analyzed for volatile hydrocarbon content using standard leachate testing protocols as described above. Total leachate concentrations of benzene, toluene, ethylbenzene and xylene (BETX) were measured and are shown in Table 1. 
     
       
         
           
               
             
               
                 TABLE 1 
               
             
            
               
                   
               
               
                 Total BETX Leachate Concentrations 
               
               
                 for Rubber Crumb, Sawdust Blends 
               
            
           
           
               
               
               
               
            
               
                   
                   
                 Amount 
                 Detection 
               
               
                 Sample 
                 VHC 
                 mg/kg 
                 Limit 
               
               
                   
               
            
           
           
               
               
               
               
            
               
                 500 g Drill Cuttings 
                 Benzene 
                 0.21 
                 0.02 
               
               
                 50 g Rubber Crumb 
               
               
                   
                 Toluene 
                 3.08 
                 0.02 
               
               
                   
                 Ethylbenzene 
                 1.61 
                 0.02 
               
               
                   
                 Xylene 
                 13.8 
                 0.02 
               
               
                 200 ml Drill Cuttings 
                 Benzene 
                 0.33 
                 0.02 
               
               
                 400 ml Sawdust 
               
               
                   
                 Toluene 
                 6.15 
                 0.02 
               
               
                   
                 Ethylbenzene 
                 3.76 
                 0.02 
               
               
                   
                 Xylene 
                 33.2 
                 0.02 
               
               
                   
               
            
           
         
       
     
     The results from Table 1 show that rubber crumb is a more effective absorbant agent as compared to the industry standard of sawdust. 
     Road Mix Leachate Testing 
     A series of “road mixes” including aggregates and binders were prepared and tested for BETX leachate as summarized in Table 2. In each of samples 1-3 and 5, 476.7 g of virgin aggregate was blended with 23.8 g of binder. For sample 4, 10% of the total weight of aggregate was drill cuttings. Samples 1-3 utilized standard road oils typically used in dust suppressant blends as known to those skilled in the art. Sample 4 utilized a cationic cold mix asphalt-based emulsion and Sample 5 used a hot mix asphalt known to those skilled in the art. 
     
       
         
           
               
             
               
                 TABLE 2 
               
             
            
               
                   
               
               
                 BETX Leachate for Road Mix Samples 
               
            
           
           
               
               
               
               
               
               
            
               
                   
                 Sample 1 
                 Sample 2 
                 Sample 3 
                 Sample 4 
                 Sample 5 
               
               
                   
               
               
                 Binder 
                 HF 500 m 
                 MC 250 
                 Crude Oil 
                 Cationic Cold 
                 Hot Mix Asphalt 
               
               
                   
                   
                   
                   
                 Mix 
               
               
                 Benzene (mg/L) 
                 0.012 
                 0.032 
                 0.015 
                 &lt;0.001 
                 &lt;0.001 
               
               
                 Toluene (mg/L) 
                 0.117 
                 0.224 
                 0.211 
                 0.001 
                 &lt;0.001 
               
               
                 Ethyl-Benzene 
                 0.049 
                 0.069 
                 0.113 
                 &lt;0.001 
                 &lt;0.001 
               
               
                 (mg/L) 
               
               
                 m,p-xylene (mg/L) 
                 0.216 
                 0.312 
                 0.208 
                 0.001 
                 &lt;0.001 
               
               
                 o-xylene 
                 0.143 
                 0.183 
                 0.091 
                 0.001 
                 &lt;0.001 
               
               
                 Total xylenes 
                 0.359 
                 0.495 
                 0.299 
                 0.002 
                 &lt;0.001 
               
               
                   
               
            
           
         
       
     
     The results show that BETX leachate from the drill cutting sample 4 was lower than presently acceptable leachate levels or substantially equivalent to leaching levels from aggregate/binder mixes presently used in gravel road (Samples 1-3) and sealed road construction (Sample 5). When compared to the total concentrations of BETX within typical drill cutting samples shown in Table 1, the leachate levels are very low. 
     A further series of road mixes including aggregates and binders were prepared and tested for C11-C40+ hydrocarbon leachates and are summarized in Table 3 and  FIG. 1 . In each sample, total binder was 5% (w/w) of the total mass of aggregate. In sample 2, 10% (w/w) of the total mass of aggregate was drill cuttings. 
     
       
         
           
               
             
               
                 TABLE 3 
               
             
            
               
                   
               
               
                 Hydrocarbon Leachate for Road Mix Samples 
               
            
           
           
               
               
               
            
               
                   
                   
                 Hydrocarbon 
               
               
                 Sample 
                 Binder 
                 Leachate (mg/L) 
               
               
                   
               
            
           
           
               
               
               
            
               
                 1 
                 Hot Mix 
                 19.4 
               
               
                 2 
                 Cationic Cold Mix with Drill Cuttings 
                 37.5 
               
               
                 3 
                 Cationic Cold Mix 
                 25.1 
               
               
                 4 
                 MC 30 
                 114 
               
               
                 5 
                 Crude Oil 
                 47.4 
               
               
                 6 
                 HF 500 mLD 
                 176 
               
               
                 7 
                 Anionic Cold Mix 
                 24.2 
               
               
                   
               
            
           
         
       
     
     The results from Table 3 and  FIG. 1  show that C10-C40+ leachate from the drill cutting sample 2 was acceptable compared to road mix samples incorporating commonly used binders. 
     In summary, the results show that the use of drill cuttings as an additive to virgin aggregates for use in various road mixes do not result in adverse leaching of volatile organic contaminants to the environment. 
     The above-described embodiments of the invention are intended to be examples only. Alterations, modifications and variations may be effected to the particular embodiments by those of skill in the art without departing from the scope of the invention which is defined by the following claims.