Delivery of particulate material below ground

Abstract

A wellbore fluid comprises an aqueous carrier liquid, hydrophobic particulate material suspended therein and a gas to wet the surface of the particles and bind them together as agglomerates. The hydrophobic particulate material has a specified maximum particle size and/or minimum surface area: namely a volume median particle size d 50 of not more than 200 micron, determined as median diameter of spheres of equivalent volume and/or a surface area of at least 30 m 2 per litre (0.03 m 2 per milliliter), determined as surface area of smooth spheres of equivalent volume. The agglomeration of the particles by gas leads to the formation of agglomerates which contain gas and so have a bulk density lower than the density of the particles. This reduces the rate of settling. The fluid is particularly envisaged as a slickwater fracturing fluid in which the suspended particles are proppant. We have found that the small particle size and/or substantial surface area increases the amount of gas which can be retained within agglomerates and so enhances the buoyancy of the agglomerates. The end result is that a greater proportion of a hydraulic fracture is propped open.

1 . A wellbore fluid comprising an aqueous carrier liquid and hydrophobic particulate material suspended therein, wherein the hydrophobic particulate material has a volume median particle size d50 of not more than 200 micron, determined as median diameter of spheres of equivalent volume, 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 hydrophobic particulate material has a specific gravity of at least 1.8. 
     
     
         3 . A fluid according to  claim 1  wherein agglomerates of the hydrophobic particles in the fluid, containing the gas in the maximum amount which the agglomerates can retain, have a density of not more than 1.4 gm/ml. 
     
     
         4 . A fluid according to  claim 1  wherein the hydrophobic particulate material comprises solid particles with a hydrophobic surface coating. 
     
     
         5 . 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. 
     
     
         6 . A fluid according to  claim 1  wherein the aqueous carrier liquid contains one or more friction reducing additives in a total amount which is not greater than 1% by weight. 
     
     
         7 . A wellbore fluid comprising an aqueous carrier liquid and hydrophobic particulate material suspended therein, wherein the hydrophobic particulate material has a surface area of at least 30 m2 per litre (30,000 m2 per m3 or 0.03 m2 per milliliter), determined as surface area of smooth spheres of equivalent volume, the fluid also comprising a gas to wet the surface of the particles and bind them together as agglomerates. 
     
     
         8 . A fluid according to  claim 7  wherein the hydrophobic particulate material has a specific gravity of at least 1.8. 
     
     
         9 . A fluid according to  claim 7  wherein agglomerates of the hydrophobic particles in the fluid, containing the gas in the maximum amount which the agglomerates can retain, have a density of not more than 1.4 gm/ml. 
     
     
         10 . A fluid according to  claim 7  wherein the hydrophobic particulate material comprises solid particles with a hydrophobic surface coating. 
     
     
         11 . A fluid according to  claim 7  wherein the aqueous carrier liquid is substantially free of viscosity-enhancing polymeric thickener and has a viscosity which is less than ten times the viscosity of water when viscosities are measured at 20 QC and a shear rate of 10 sec−1. 
     
     
         12 . A fluid according to  claim 7  wherein the aqueous carrier liquid contains one or more friction reducing additives in a total amount which is not greater than 1% by weight. 
     
     
         13 . A fluid according to  claim 1  wherein the gas is air or nitrogen. 
     
     
         14 .- 26 . (canceled)