Liquified petroleum gas fracturing system

Abstract

A fracturing system for a well, in which a stream of LPG, a mixture of propane and butane, is injected into the well at frac pressure. Proppant is supplied into the LPG stream, and carried by the LPG mix into the formation. Inert gas such as nitrogen is used for purging system components of LPG, and to help protect against risk of explosion. Nitrogen may also be added to the LPG mix during a frac of shale gas or coal gas formations.

1 . Apparatus for fracturing a formation penetrated by a well, the apparatus comprising:
 a frac pressure pump connected to a well;   a frac fluid source connected to supply a stream of frac fluid comprising predominantly propane, butane or a mixture of propane and butane to the frac pressure pump;   an inert gas source connected to supply inert gas to the frac fluid source and the frac pressure pump; and   a controller connected to control operation of the frac fluid source, frac pressure pump and inert gas source.   
     
     
         2 . The apparatus of  claim 1  further comprising:
 a proppant supply source connected to supply proppant into the stream of frac fluid from the frac fluid source, the proppant supply source being controlled by the controller. 
 
     
     
         3 . The apparatus of  claim 2  further comprising a gellant supply source connected to supply gellant into the stream of frac fluid from the frac fluid source, the gallant supply source being controlled by the controller. 
     
     
         4 . The apparatus of  claim 2  in which the proppant supply source comprises a positive pressure vessel. 
     
     
         5 . The apparatus of  claim 2  in which the proppant supply source comprises a centrifugal pump. 
     
     
         6 . The apparatus of  claim 2  in which the inert gas source is connected to supply inert gas to the proppant supply source. 
     
     
         7 . The apparatus of  claim 2  in which proppant is metered into the frac fluid stream by an auger. 
     
     
         8 . The apparatus of  claim 1  in which the frac fluid source comprises an insulated tank. 
     
     
         9 . The apparatus of  claim 2  in which the proppant supply source comprises:
 a centrifugal pump connected to pump the stream of frac fluid from the frac fluid source to the high pressure pump, the centrifugal pump having an entry port connected to a metered supply of proppant. 
 
     
     
         10 . The apparatus of  claim 9  in which the centrifugal pump incorporates one or more control valves that are located to control flow of material through the entry port into the centrifugal pump from the metered supply of proppant. 
     
     
         11 . A method for fracturing a formation penetrated by a well, the method comprising the steps of:
 prior to commencing the frac, purging system components with an inert gas and pressure testing all system components that are to be supplied with frac fluid;   supplying a stream of frac fluid comprising predominantly propane, butane or a mixture of propane and butane from a frac fluid source into a well;   pressurizing frac fluid in the well to create fractures in the formation;   purging system components with inert gas; and   releasing pressure from the well to allow frac fluid to vaporize and return to surface.   
     
     
         12 . The method of  claim 11  in which the system components comprise a proppant supply source, the method further comprising:
 supplying proppant from the proppant supply source into the stream of frac fluid from the frac fluid source; 
 adding gellant to the stream of frac fluid, and 
 pumping the proppant containing frac fluid stream into the well with the frac pressure pump. 
 
     
     
         13 . The method of  claim 11  further comprising supplying a controlled amount of inert gas to the frac fluid source. 
     
     
         14 . The method of  claim 12  in which the proppant supply source comprises a pressure vessel. 
     
     
         15 . The method of  claim 14  in which proppant is metered into the frac fluid stream from the frac fluid source by an auger in cooperation with a valve. 
     
     
         16 . The method of  claim 12  in which the proppant supply source comprises a centrifugal pump. 
     
     
         17 . The method of  claim 11  in which the frac fluid source comprises an insulated tank. 
     
     
         18 . The method of  claim 11  in which the frac fluid comprises nitrogen. 
     
     
         19 . The method of  claim 18  applied to fracturing a coal formation that contains gas. 
     
     
         20 . The method of  claim 18  applied to fracturing a shale formation that contains gas. 
     
     
         21 - 29 . (canceled)