Abstract:
The flowability of asphalt particles may be improved by mixing the particles with comprises further compound comprises Portland cement, calcium aluminate cement, fly ash, blast furnace slag, lime/silica blends, silica, ground limestone, cement kiln dust, chemically bonded phosphate ceramics, zeolites, geopolymers, cellulose, starch, calcium carbonate, colloidal silica, aluminosilicates, and combinations thereof. Treating the asphalt particles with at least one of these compounds inhibits caking during storage and enhances transportability.

Description:
BACKGROUND 
       [0001]    The statements in this section merely provide background information related to the present disclosure and may not constitute prior art. 
         [0002]    This disclosure relates to methods for improving the flowability of solid asphalt particles. Asphalt has a low specific gravity, making it useful as an extender for reducing the density of cement slurries. Asphalt particles may also be used to control lost circulation in subterranean wells. When wellbore fluids such as drilling muds and cement slurries are pumped into a wellbore, the asphalt particles may enter voids in the subterranean-well formation through which wellbore fluids escape, and form a seal that limits further egress of wellbore fluid from the wellbore into the formation. 
         [0003]    For many years, asphaltite minerals such as unitaite have been used in wellbore fluids. Unitaite is mined in underground shafts and resembles shiny black obsidian. Ground unitaite particles are also hard and free flowing; thus, engineers have little difficulty transporting them or incorporating them into dry blends of cement or drilling-fluid solids. 
         [0004]    At present, most unitaite is produced from one principal deposit in the Unitah Basin of Utah, in the United States. This geographic limitation impedes the worldwide use of unitaite. As a result, alternate materials have been identified. One example that is commercially available around the world is hard asphalt. Hard asphalt has a specific gravity similar to that of unitaite, and it can be ground into fine particles. 
         [0005]    Unlike unitaite, hard asphalt particles are cohesive and tend to agglomerate. Upon storage, the particles form cakes that are difficult to break up. In addition, during dry blending operations, the particles do not readily disperse and distribute themselves evenly throughout the blend. It would therefore be desirable to develop means by which the agglomerative tendency of hard asphalt may be suppressed. 
       SUMMARY 
       [0006]    In an aspect, embodiments relate to methods for improving the flowability of asphalt particles, the methods comprising providing asphalt particles with a penetration grade below about 20; and mixing with at least one further compound comprising Portland cement, calcium aluminate cement, fly ash, blast furnace slag, lime/silica blends, silica, ground limestone, cement kiln dust, chemically bonded phosphate ceramics, zeolites, geopolymers, cellulose, starch, calcium carbonate, colloidal silica, aluminosilicates, and combinations thereof. 
         [0007]    In a further aspect, embodiments relate to methods for storing asphalt particles, the methods comprising providing asphalt particles with a penetration grade below about 20; and mixing the particles with at least one further compound comprising Portland cement, calcium aluminate cement, fly ash, blast furnace slag, lime/silica blends, silica, ground limestone, cement kiln dust, chemically bonded phosphate ceramics, zeolites, geopolymers, cellulose, starch, calcium carbonate, colloidal silica, aluminosilicates, and combinations thereof; and placing the blend in a storage container. 
         [0008]    In yet a further aspect, embodiments relate to methods for transporting asphalt particles, the methods comprising providing asphalt particles with a penetration grade below about 20; mixing the particles with at least one further compound comprising Portland cement, calcium aluminate cement, fly ash, blast furnace slag, lime/silica blends, silica, ground limestone, cement kiln dust, chemically bonded phosphate ceramics, zeolites, geopolymers, cellulose, starch, calcium carbonate, colloidal silica, aluminosilicates, and combinations thereof; placing the blend in a transport container; and transporting the blend from a first location to a second location. 
     
    
     DETAILED DESCRIPTION 
       [0009]    At the outset, it should be noted that in the development of any such actual embodiment, numerous implementation-specific decisions must be made to achieve the developer&#39;s specific goals, such as compliance with system related and business related constraints, which will vary from one implementation to another. Moreover, it will be appreciated that such a development effort might be complex and time consuming but would nevertheless be a routine undertaking for those of ordinary skill in the art having the benefit of this disclosure. The description and examples are presented solely for the purpose of illustrating the preferred embodiments and should not be construed as a limitation to the scope and applicability of the disclosed embodiments. While the compositions of the present disclosure are described herein as comprising certain materials, it should be understood that the composition could optionally comprise two or more chemically different materials. In addition, the composition can also comprise some components other than the ones already cited. 
         [0010]    The Applicants have determined that the agglomerative tendency of hard asphalt particles may be suppressed by blending one or more materials with the particles. The materials may include (but would not be limited to) Portland cement, calcium aluminate cement, fly ash, blast furnace slag, lime/silica blends, silica, ground limestone, cement kiln dust, chemically bonded phosphate ceramics, zeolites, geopolymers, cellulose, starch, calcium carbonate, colloidal silica, aluminosilicates, or combinations thereof Such materials act as anti-caking agents in this disclosure. The hard asphalts particles may be blended with Portland cement, fly ash, blast furnace slag, lime/silica blends, silica, ground limestone or combinations thereof. 
         [0011]    Embodiments relate to methods for improving the flowability of asphalt particles. Asphalt particles provided may have a penetration grade below about 20,or below about 10. The penetration grade of asphalt is determined by using a needle penetrometer, according to ASTM method D5—“Penetration of Bituminous Materials.” The method consists of subjecting an asphalt sample to a 100-g load for 5 seconds with a standard needle. The depth of needle penetration is measured in units of 0.1 mm and reported in penetration units. For example, if the needle penetrates 8 mm, the asphalt penetration value is 80. 
         [0012]    The particles are mixed with an anti-caking agent. The anti-caking agent concentration may be between about 0.1% and 10.0% by weight of asphalt particles, it may be between about 1.0% and 6.0% by weight of asphalt particles, and it may be between about 3.0% and 5.0% by weight of asphalt particles. 
         [0013]    For use in wellbore fluids, the hard asphalt particles may be smaller than about 2500 μm. For example, less than 2 weight percent of the particles are larger than about 2400 μm, and less than about 5 weight percent of the particles are smaller than about 105 μm. Furthermore, the specific gravity of the asphalt particles may be between about 0.95 and 1.15, or between about 1.0 and 1.1. The melting point of the hard asphalt may be higher than about 99° C. 
         [0014]    Embodiments relate to methods for storing asphalt particles. Asphalt particles provided may have a penetration grade below about 20, or below about 10. The particles are mixed with an anti-caking agent, and the resulting blend is placed in a storage container. The temperature of the storage container may be maintained at a level below about 90° C. 
         [0015]    The anti-caking agent concentration may be between about 0.1% and 10.0% by weight of asphalt particles, it may be between about 1.0% and 6.0% by weight of asphalt particles, or it may be between about 3.0% and 5.0% by weight of asphalt particles. 
         [0016]    For use in wellbore fluids, the hard asphalt particles may be smaller than about 2500 μm. For example, less than 2 weight percent of the particles are larger than about 2400 μm, and less than about 5 weight percent of the particles are smaller than about 105 μm. Furthermore, the specific gravity of the asphalt particles may be between about 0.95 and 1.15, or between about 1.0 and 1.1. The melting point of the hard asphalt may be higher than about 99° C. 
         [0017]    Embodiments relate to methods for transporting asphalt particles. Asphalt particles provided may have a penetration grade below about 20, or below about 10. The particles are mixed with an anti-caking agent, the resulting blend is placed in a transport container, and the blend is transported from a first location to a second location. The container may be a vessel suitable for transporting the blend on roads, rail, by air or by sea. Alternatively, transporting the blend may comprise pneumatic transfer from one vessel to another. The temperature of the transport container may be maintained at a level below about 90° C. 
         [0018]    The anti-caking agent concentration may be between about 0.1% and 10.0% by weight of asphalt particles, or between about 1.0% and 6.0% by weight of asphalt particles, or between about 3.0% and 5.0% by weight of asphalt particles. 
         [0019]    For use in wellbore fluids, the hard asphalt particles may be smaller than about 2500 μm. For example, less than 2 weight percent of the particles are larger than about 2400 μm, and less than about 5 weight percent of the particles are smaller than about 105 μm. Furthermore, the specific gravity of the asphalt particles may be between about 0.95 and 1.15, or between about 1.0 and 1.1. The melting point of the hard asphalt may be higher than about 99° C. 
       EXAMPLE 
       [0020]    The following example serves to further illustrate the disclosure. 
         [0021]    500 g of hard asphalt were ground to a particle size distribution wherein less than 2 wt % of the particles were larger than about 2400 μm, and less than 5 wt % of the particles were smaller than about 100 μm. The asphalt was “Special Hard Asphalt,” available from Gulf States Asphalt Company, South Houston, Tex., USA. 
         [0022]    The ground asphalt sample was split into two 250-g portions. One portion was placed in a plastic cup such that the depth of the sample in the cup was about 1.6 cm. The other portion was mixed with an anti-caking agent composed of Portland cement. The anti-caking agent concentration was 5 percent by weight of asphalt particles. The treated portion was placed in another plastic cup, again such that the depth of the sample in the cup was about 1.6 cm. Stainless steel lids were placed on top of the samples such that the asphalt particles were subjected to a 7.6-kPa load. 
         [0023]    Both cups were placed in an oven at a temperature of 43° C. The samples remained in the oven for 7 days. After the samples were removed from the oven, the untreated asphalt particles were observed to have agglomerated into a cohesive cake that was difficult to disperse with a spatula. It was not free flowing. On the other hand, the asphalt sample treated with the anti-caking agent was free flowing and could be easily poured from the beaker. 
         [0024]    Although only a few example embodiments have been described in detail above, those skilled in the art will readily appreciate that many modifications are possible in the example embodiments without materially departing from this invention. Accordingly, all such modifications are intended to be included within the scope of this disclosure as defined in the following claims.