In-Hole Vaporization of Liquid Gas for Well Stimulation

Abstract

An illustrative stimulation method includes: displacing a predetermined volume of liquified gas through a wellhead valve into a service tubing string providing access to a stimulation zone of a well; and closing the wellhead valve to confine the liquified gas and pressurize the stimulation zone as the service tubing string vaporizes the liquified gas. An illustrative well configured for stimulation includes: well casing within a borehole; a stainless-steel wellhead with a valve for receiving a liquified gas; and a stainless-steel service tubing string coupled to the valve to receive and vaporize the liquified gas. The service tubing string acts as a heat exchanger, using the downhole temperatures to vaporize the liquified gas.

What is claimed is: 
     
         1 . A stimulation method that comprises:
 displacing a predetermined volume of liquified gas through a wellhead valve into a service tubing string providing access to a stimulation zone of a well; and   closing the wellhead valve to confine the liquified gas and pressurize the stimulation zone as the service tubing string vaporizes the liquified gas.   
     
     
         2 . The stimulation method of  claim 1 , wherein the predetermined volume is sufficient to pressurize the stimulation zone to at least 8,000 psi. 
     
     
         3 . The stimulation method of  claim 1 , further comprising, prior to said displacing, evacuating gas from an annulus around the service tubing string to reduce a vaporization rate of the liquified gas. 
     
     
         4 . The stimulation method of  claim 1 , further comprising, prior to said displacing, adding fluid to an annulus around the service tubing string to increase hydrostatic pressure on a packer sealing the stimulation zone. 
     
     
         5 . The stimulation method of  claim 1 , further comprising, prior to said displacing:
 installing a stainless-steel wellhead;   setting a packer configured to tolerate exposure to cryogenic liquid; and   running stainless steel tubing as the service tubing string anchored by the packer.   
     
     
         6 . The stimulation method of  claim 1 , further comprising, prior to said displacing:
 installing a stainless-steel wellhead;   installing a production tubing string anchored by a downhole packer configured to tolerate exposure to cryogenic liquid;   running, inside the production tubing string, stainless steel tubing as the service tubing string anchored by a seating nipple configured to tolerate exposure to cryogenic liquid.   
     
     
         7 . The stimulation method of  claim 1 , wherein said closing is for a close-in period of at least 24 hours, and wherein the method further includes returning the well to production after the close-in period. 
     
     
         8 . The stimulation method of  claim 1 , wherein said displacing uses one or more pressure sensors and one or more flow rate monitors to provide control of the displacing, and wherein the displacing includes reducing a flow rate if a derivative of the borehole pressure exceeds a predetermined threshold. 
     
     
         9 . The stimulation method of  claim 1 , wherein the liquified gas is liquified natural gas (LNG) or liquified methane. 
     
     
         10 . The stimulation method of  claim 1 , wherein the liquified gas is liquified nitrogen. 
     
     
         11 . A well that comprises:
 well casing within a borehole;   a stainless-steel wellhead with a valve for receiving a liquified gas; and   a stainless-steel service tubing string coupled to the valve to receive and vaporize the liquified gas.   
     
     
         12 . The well of  claim 11 , further comprising a packer seated within the casing to anchor a lower end of the service tubing string and provide a pressure seal. 
     
     
         13 . The well of  claim 12 , further comprising a vacuum pump to evacuate an annulus around the service tubing string. 
     
     
         14 . The well of  claim 12 , further comprising a thermal insulation coating on an upper portion of the service tubing string to reduce a vaporization rate. 
     
     
         15 . The well of  claim 11 , further comprising a cryogenic liquid transfer pump to transfer the liquified gas to the service tubing string. 
     
     
         16 . The well of  claim 15 , further comprising:
 a pressure sensor coupled to the service tubing string; and   a control system coupled to the pressure sensor and configured to responsively regulate a transfer rate of the liquified gas.   
     
     
         17 . The well of  claim 16 , further comprising:
 a flow sensor coupled to the valve,   wherein the control system is configured to close the valve or otherwise halt delivery of the liquified gas after a predetermined volume has been transferred to the service tubing string.   
     
     
         18 . The well of  claim 11 , further comprising:
 a stainless steel production tubing string anchored to a downhole packer, the production tubing string providing a seating nipple that anchors a lower end of the service tubing string.   
     
     
         19 . The well of  claim 11 , wherein the liquified gas is liquified natural gas (LNG) or liquified methane. 
     
     
         20 . The well of  claim 11 , wherein the liquified gas is liquified nitrogen.