Hydraulic Fracturing Method

Abstract

A method is given for diverting injected slickwater in a hydraulic fracturing treatment. The diversion fluid is preferably a substantially proppant free viscous fluid that causes a net pressure increase and plugging of some of the microfractures in the initial fracture system created, which induces formation of supplementary microfractures connected to the initial fracture network and in-creases the contact area with the formation rock. The method generates a greater fracture network complexity and thus a higher contact area with the reservoir during a single treatment cycle.

Having thus described our invention, we claim: 
     
         1 . A method for fracturing a subterranean formation comprising a first cycle comprising (a) injecting a pad fluid having a viscosity of less than about 50 mPa·s at a shear rate of 100 s −1  under ambient conditions, (b) injecting proppant slurry having a viscosity of less than about 50 mPa·s at a shear rate of 100 s −1  under ambient conditions, (c) injecting a thickened fluid having a viscosity of greater than about 50 mPa·s at a shear rate of 100 s −1  under ambient conditions, and one or more than one subsequent cycles comprising repeating steps (b) and (c). 
     
     
         2 . The method of  claim 1  wherein the pad fluid is injected first. 
     
     
         3 . The method of  claim 1  wherein the thickened fluid has a viscosity of less than about 20 mPa·s as pumped and then thickens. 
     
     
         4 . The method of  claim 3  wherein the reservoir contains carbonate and the thickened fluid is initially acidic. 
     
     
         5 . The method of  claim 1  wherein the thickened fluid further comprises proppant. 
     
     
         6 . The method of  claim 1  wherein the total volume of the fluid injected in steps (b) comprises at least 75 percent of the total volume of fluid injected in the treatment. 
     
     
         7 . The method of  claim 1  wherein the fluid injected in steps (b) carries at least 90 percent of the total proppant injected in the treatment. 
     
     
         8 . The method of  claim 1  wherein the permeability of the formation is less than about 1 mD. 
     
     
         9 . The method of  claim 1  wherein the proppant has a shape selected from spheres, rods, cylinders, plates, sheets, spherocylinders, ellipsoids, toruses, oblongs, fibers, arches/cells, meshes, meshes/cells, honeycombs, bubbles, sponge-like or foam structures, and mixtures of these shapes. 
     
     
         10 . The method of  claim 1  wherein the size of the proppant ranges from about 5 to about 1000 microns. 
     
     
         11 . The method of  claim 1  wherein at least one of the injected fluids comprises solid degradable materials. 
     
     
         12 . The method of  claim 11  wherein the degradable materials comprise polylactic acid, polyglycolic acid, copolymers of polylactic acid and polyglycolic acid, copolymers of glycolic acid with other hydroxy-, carboxylic acid-, or hydroxycarboxylic acid-containing moieties, copolymers of lactic acid with other hydroxy-, carboxylic acid-, or hydroxycarboxylic acid-containing moieties, and mixtures thereof. 
     
     
         13 . The method of  claim 11  wherein the degradable materials are used in the form of fibers, plates, flakes, beads and combinations thereof. 
     
     
         14 . The method of  claim 1  wherein the fluid of step (a) or the fluid of step (b) or both comprise a friction reducing agent. 
     
     
         15 . The method of  claim 1  wherein the fluid of step or steps (c) comprises less than about 0.024 kg proppant per liter of clean fluid. 
     
     
         16 . The method of  claim 1  wherein the fluid of step or steps (c) is substantially proppant free. 
     
     
         17 . The method of  claim 1  wherein one or more than one cycle is followed by injection of a fluid having a viscosity of greater than about 50 mPa·s at a shear rate of 100 s −1  under ambient conditions comprising a coarse proppant. 
     
     
         18 . The method of  claim 17  wherein the one or more steps of injection of a fluid having a viscosity of greater than about 50 mPa·s at a shear rate of 100 s −1  under ambient conditions comprising a coarse proppant is followed by injection of a fluid comprising a proppant flowback control agent. 
     
     
         19 . The method of  claim 1  comprising a final step of injecting a flush fluid. 
     
     
         20 . The method of  claim 1  wherein at least one of the fluids is viscosified with a degradable viscosifying agent. 
     
     
         21 . The method of  claim 1  wherein at least one step (b) after the first step (b) is preceded by a step (a). 
     
     
         22 . The method of  claim 1  wherein each step (b) is preceded by a step (a). 
     
     
         23 . The method of  claim 1  wherein the total volume of the fluid injected in steps (c) comprises less than 10 percent of the total volume of fluid injected in the treatment. 
     
     
         24 . The method of  claim 1  wherein in each cycle the ratio of the volume of fluid in stage C to the volume of fluid in stage B is less than about 1/10.