Lightweight proppant and method of making same

Abstract

A method of forming lightweight, high-strength proppants is disclosed, comprising the steps of: homogeneously blending at least one ceramic precursor and at least one pore former; pelletizing the blend to form microspheres; heating the microspheres to less than sintering temperatures, to evaporate volatile components and pyrolyze fugitive components; further heating the microspheres to temperatures sufficient to sinter the continuous phase of the ceramic precursor, to form sintered particles; and then forming the sintered particles into generally spheroid proppants. The generally spheroid proppants, which have preferably been sintered to near theoretical density, may then be coated. Heating of the microspheres may comprise a series of heating stages.

1 . A method of forming lightweight, high-strength proppants comprising the steps of: 
 (a) blending at least one ceramic precursor and at least one pore former to form a blend;    (b) pelletizing the blend to form a plurality of microspheres;    (c) heating the plurality of microspheres to less than sintering temperatures, to evaporate volatile components and pyrolyze fugitive components;    (d) heating the plurality of microspheres to temperatures sufficient to sinter the continuous phase of the at least one ceramic precursor, to form sintered particles; and    (e) forming the sintered particles into generally spheroid proppants.    
   
   
       2 . The method of  claim 1  wherein the at least one ceramic precursor is a ceramic oxide selected from the group consisting of alumina, aluminum hydroxide, boehmite, pseudo boehmite, kaolin clay, kaolinite, silica, clay, talc, magnesia, cordierite, and mullite.  
   
   
       3 . The method of  claim 1  further comprising the step of selecting the at least one pore former on the basis of particle size, particle size distribution, morphology, specific gravity, and reactivity at elevated temperatures.  
   
   
       4 . The method of  claim 1  wherein the at least one pore former is an inert pore former.  
   
   
       5 . The method of  claim 1  wherein the at least one pore former is a fugitive pore former.  
   
   
       6 . The method of  claim 1  wherein the at least one pore former is selected from the group consisting of finely divided natural materials, finely divided man-made materials, walnut shells, alginates, saccharides, polymers, and carbon modifications.  
   
   
       7 . The method of  claim 1  wherein the at least one ceramic precursor is homogeneously blended with the at least one pore former to form a homogeneous blend.  
   
   
       8 . The method of  claim 1  wherein at least one additional component is blended with the at least one ceramic precursor and the at least one pore former to form the blend.  
   
   
       9 . The method of  claim 8  wherein the at least one additional component is selected from the group consisting of inorganic and organic additives.  
   
   
       10 . The method of  claim 8  wherein the at least one additional component is selected from the group consisting of fillers, fibres, binders, fugitive binders, surfactants, plasticizers, and thickeners.  
   
   
       11 . The method of  claim 1  wherein each of the plurality of microspheres is a generally spherical body less than 5 mm in diameter.  
   
   
       12 . The method of  claim 1  wherein the heating of the plurality of microspheres to sinter the continuous phase of the at least one ceramic precursor causes the at least one ceramic precursor to reach near theoretical density.  
   
   
       13 . The method of  claim 1  wherein the blending of the at least one ceramic precursor with the at least one pore former to form a blend is achieved by milling the at least one ceramic precursor and the at least one pore former in dry form.  
   
   
       14 . The method of  claim 1  wherein the blending of the at least one ceramic precursor with the at least one pore former to form a blend is achieved by dispersing the at least one ceramic precursor and the at least one pore former with a liquid.  
   
   
       15 . The method of  claim 1  wherein the pelletizing of the blend to form the plurality of microspheres is achieved by a process selected from the group consisting of agglomeration, spray granulation, wet granulation, spheronizing, extruding and pelletizing, vibration-induced dripping, spray nozzle formed droplets, and selective agglomeration.  
   
   
       16 . The method of  claim 1  comprising the further step after step (e) of coating the generally spheroid proppants.  
   
   
       17 . The method of  claim 16  wherein the coating of the generally spheroid proppants employs a material selected from the group consisting of organic coating, epoxy, furan, phenolic resins and combinations thereof.  
   
   
       18 . The method of  claim 1  wherein the at least one pore former is less than 5 microns in size.  
   
   
       19 . The method of  claim 18  wherein the at least one pore former is less than 1 micron in size.  
   
   
       20 . The method of  claim 1  wherein the at least one pore former is produced by a process selected from the group consisting of grinding, ball milling, precipitating, dispersing, flame pyrolysis, gas condensation, spray conversion, crystallization, polymerization, chemical synthesis, and sol-gel techniques.  
   
   
       21 . The method of  claim 1  wherein the at least one ceramic precursor is less than 10 microns in size.  
   
   
       22 . The method of  claim 21  wherein the at least one ceramic precursor is less than 5 microns in size.  
   
   
       23 . The method of  claim 1  wherein the at least one ceramic precursor is produced by a process selected from the group consisting of grinding, ball milling, precipitating, dispersing, flame pyrolysis, gas condensation, spray conversion, crystallization, chemical synthesis, and sol-gel techniques.  
   
   
       24 . The method of  claim 14  wherein the liquid has a boiling point of less than 150.degrees.C.  
   
   
       25 . The method of  claim 14  wherein the liquid is water.  
   
   
       26 . The method of  claim 14  wherein concentration of the liquid is 2 to 75 wt. percent.  
   
   
       27 . The method of  claim 10  wherein the fillers are selected from the group consisting of fly ash, sludges, slags, volcanic aggregates, expanded perlite, pumice, obsidian, diatomaceous earth mica, borosilicates, clays, oxides, fluorides, sea shells, silica, inorganic pore formers, mineral fibres, and chopped fibreglass.  
   
   
       28 . The method of  claim 27  wherein the inorganic pore formers are selected from the group consisting of carbonates, acetates, nitrates, silica and alumina hollow spheres.  
   
   
       29 . The method of  claim 10  wherein the binders are selected from the group consisting of acrylic polymers, alginates, saccharides, silicates, and monomer-catalyst combinations.  
   
   
       30 . The method of  claim 1  wherein the step of heating the plurality of microspheres to less than sintering temperatures comprises a series of heating stages.  
   
   
       31 . The method of  claim 1  wherein the temperatures sufficient to sinter the continuous phase of the at least one ceramic precursor are above 800.degrees.C.  
   
   
       32 . The method of  claim 1  wherein the heating of the plurality of microspheres to sinter the continuous phase of the at least one ceramic precursor causes the at least one ceramic precursor to achieve less than theoretical density.