Fracturing methods and systems

Abstract

Hybrid gas fracturing methods and systems utilizing an early stage gas treatment fluid, which may contain a dispersed phase of fluid loss control agent particles, followed by a proppant stage(s) to form a fracture system having a branched tip region and a propped region between the branched tip region and the wellbore. Also, treatment fluids suitable for use in the methods and systems are disclosed.

We claim: 
     
         1 . A method for treating a subterranean formation traversed by a wellbore, comprising:
 injecting a substantially proppant-free early stage comprising a continuous gas phase into the formation above a fracturing pressure to form a fracture system comprising a branched tip region; and   injecting a proppant stage comprising a treatment fluid comprising proppant, wherein the viscosity of the proppant stage is greater than the early stage, wherein the injecting the proppant stage behind the early stage forms a propped region of the fracture system for communication between the wellbore and the branched tip region.   
     
     
         2 . The method of  claim 1 , wherein the early stage comprises particles dispersed in the continuous gas phase as a fluid loss control agent. 
     
     
         3 . The method of  claim 2 , wherein the particles dispersed in the continuous gas phase comprise fines having a diameter of less than 50 microns and are substantially free of solids having a diameter greater than 100 microns. 
     
     
         4 . The method of  claim 2 , wherein the particles dispersed in the continuous gas phase comprise from 0.5 to 10 percent by volume based on the total volume of the gas stage. 
     
     
         5 . The method of  claim 1 , wherein the early stage comprises liquid or foam phase particles dispersed as a mist in the gas phase. 
     
     
         6 . The method of  claim 5 , wherein the dispersed liquid or foam phase particles comprise microdroplets having a diameter of less than 100 microns. 
     
     
         7 . The method of  claim 5 , wherein the particles dispersed in the continuous gas phase are aqueous and comprise a foaming agent. 
     
     
         8 . The method of  claim 5 , wherein the mist further comprises fines having a diameter of less than 50 microns and is substantially free of solids having a diameter greater than 100 microns. 
     
     
         9 . The method of  claim 1 , wherein the one or more proppant stages comprise slickwater and a proppant loading from 0.01 to 0.6 g/mL of carrier fluid (0.1-5 ppa). 
     
     
         10 . The method of  claim 1 , wherein the one or more proppant stages comprise an aqueous or oil-based carrier fluid, a viscosifier and a proppant loading of at least 0.6 g/mL of carrier fluid (5 ppa). 
     
     
         11 . The method of  claim 1 , wherein the one or more proppant stages comprise a high solid content fluid. 
     
     
         12 . The method of  claim 1 , wherein the one or more proppant stages comprise alternating proppant concentration between successive proppant stages. 
     
     
         13 . The method of  claim 1 , further comprising injecting one or more substantially proppant-free stages between successive ones of the proppant stages. 
     
     
         14 . The method of  claim 1 , wherein the one or more proppant stages comprise carrier fluid, proppant and agglomerant, wherein injection of the one or more proppant stages forms a substantially uniformly distributed mixture of the proppant and the agglomerant, and wherein the proppant and the agglomerant have dissimilar velocities in the fracture system to transform the substantially uniformly distributed mixture into areas that are rich in proppant and areas that are substantially free of proppant. 
     
     
         15 . The method of  claim 1 , wherein the one or more proppant stages comprise proppant and shapeshifting particles dispersed in a carrier fluid, and further comprising changing a conformation of the shapeshifting particles in the fracture system. 
     
     
         16 . The method of  claim 1 , further comprising:
 continuously distributing the proppant into the fracture system during the injection of the one or more proppant stages;   aggregating the proppant distributed into the fracture to form spaced-apart clusters in the fracture system;   anchoring at least some of the clusters in the fracture system to inhibit aggregation of at least some of the clusters;   reducing pressure in the fracture system to form interconnected, hydraulically conductive channels between the clusters in the propped region of the fracture system.   
     
     
         17 . The method of  claim 1 , further comprising:
 injecting the one or more proppant stages at a continuous rate with a continuous proppant concentration;   while maintaining the continuous rate and proppant concentration, successively alternating concentration modes of an anchorant in the one or more proppant stages between a plurality of relatively anchorant-rich modes and a plurality of anchorant-lean modes.   
     
     
         18 . The method of  claim 1 , wherein the early stage is injected as a pre-pad stage and the method further comprises injecting a foam or liquid pad stage into the fracture system following the pre-pad stage prior to the one or more proppant stages. 
     
     
         19 . The method of  claim 1 , further comprising injecting a flush stage into the fracture system following the one or more proppant stages. 
     
     
         20 . A reservoir fluid production system comprising:
 a wellbore penetrating a subterranean formation; and   the fracture system obtained by the method of  claim 1  in fluid communication with the wellbore.   
     
     
         21 . The system of  claim 20 , wherein the branched tip region of the fracture system is substantially proppant-free. 
     
     
         22 . A system to treat a subterranean formation, comprising:
 a subterranean formation penetrated by a wellbore;   a gas injection unit to supply a gas treatment fluid stage, substantially free of proppant and comprising a continuous gas phase, to the formation above a fracturing pressure to form a fracture system comprising a branched tip region; and   a pump system to supply one or more proppant stages, comprising a treatment fluid comprising proppant and having a viscosity greater than the gas treatment fluid stage, into the fracture system behind the gas treatment fluid stage to form a propped region of the fracture system to communicate between the wellbore and the branched tip region.