Delivery of Particulate Material Below Ground

Abstract

A wellbore fluid is an aqueous carrier liquid with first and second hydrophobic particulate materials suspended therein. The first hydrophobic particles have a higher specific gravity than the second hydrophobic particles and the fluid also comprises a gas to wet the surface of the particles and bind them together as agglomerates. The fluid may be a fracturing fluid or gravel packing fluid and the first particulate material may be proppant or gravel. The lighter second particulate material and the gas both reduce the density of the agglomerates which form so that they settle more slowly from the fluid, or are buoyant and do not settle. This facilitates transport and placement in a hydraulic fracture or gravel pack. One application of this is when fracturing a gas-shale with slickwater. The benefit of reduced settling is better placement of proppant so that a greater amount of the fracture is propped open.

1 . A wellbore fluid comprising an aqueous carrier liquid and first and second hydrophobic particulate materials suspended therein, where the first hydrophobic particles have a higher specific gravity than the second hydrophobic particles, the fluid also comprising a gas to wet the surface of the particles and bind them together as agglomerates. 
     
     
         2 . A fluid according to  claim 1  wherein the first particles have a specific gravity of at least 1.8 and the second particles have a specific gravity of less than 1.5. 
     
     
         3 . A fluid according to  claim 2  wherein the second particles have a specific gravity of less than 1.0. 
     
     
         4 . A fluid according to  claim 1  wherein agglomerates of the first and second hydrophobic particles in the proportions present in the fluid, containing the gas in the maximum amount which the agglomerates can retain, have a density of 1.1 or less. 
     
     
         5 . A fluid according to  claim 1  wherein the ratio of the first and second particles lies in a range from 4:1 to 1:4 by volume. 
     
     
         6 . A fluid according to  claim 1  wherein the first hydrophobic particles have a higher strength to resist crushing than the second hydrophobic particles. 
     
     
         7 . A fluid according to  claim 1  wherein the first particulate material comprises solid particles with a hydrophobic surface coating. 
     
     
         8 . A fluid according to  claim 1  wherein the second particulate material comprises solid particles of hydrophobic material. 
     
     
         9 . A fluid according to  claim 1  wherein the second particulate material comprises porous particles with a hydrophobic exterior. 
     
     
         10 . A fluid according to  claim 1  wherein the second particulate material comprises hollow particles with a hydrophobic exterior. 
     
     
         11 . A fluid according to  claim 10  wherein the second particulate material comprises hollow glass particles with a hydrophobic surface coating. 
     
     
         12 . A fluid according to  claim 1  wherein the aqueous carrier liquid is substantially free of viscosity-enhancing polymeric thickener and has a viscosity which is less than 15 centipoise when viscosities are measured at 20° C. and a shear rate of 100 sec −1 . 
     
     
         13 . A fluid according to  claim 1  wherein the aqueous carrier liquid is aqueous and contains one or more friction reducing additives in a total amount which is not greater than 1% by weight. 
     
     
         14 . A fluid according to  claim 1  further comprising a hydrophobic oil in an amount which is not more than 1% of the volume of the gas. 
     
     
         15 . A fluid according to  claim 1  wherein the gas is air or nitrogen.