Downhole membrane separation system with sweep gas

Abstract

One configuration of a separation system for separating hydrocarbons from contaminants downhole includes a tubular membrane having a fluid inlet end and a fluid outlet end. Between the fluid inlet end and the fluid outlet end of the membrane tube the membrane material selectively permeates contaminants, such as carbon dioxide, through the membrane while preventing the hydrocarbon from passing through the membrane achieving the downhole separation. A driving force of the membrane is increased by passing a sweep gas past the output side of the membrane during membrane separation to remove or dilute the contaminant at the output side of the membrane. The sweep gas improves the driving force of the membrane by increasing a partial pressure difference across the membrane.

What is claimed is:  
     
         1 . A system for separating a hydrocarbon and a contaminant in a wellbore, the system comprising: 
 a membrane for separating a hydrocarbon and a contaminant by passing the contaminant through the membrane from an input side to an output side of the membrane, the membrane configured to be positioned in the wellbore; and    a sweep fluid delivery system for delivering a sweep fluid to the output side of the membrane to improve a driving force driving the contaminant through the membrane.    
     
     
         2 . The system of  claim 1 , wherein the membrane is a tubular membrane.  
     
     
         3 . The system of  claim 2 , wherein the tubular membrane has the input side at the inside of the tubular membrane and the output side at the outside of the tubular membrane.  
     
     
         4 . The system of  claim 1 , wherein the sweep fluid delivery system delivers a liquid into the wellbore and includes an expansion element which expands the liquid in the wellbore to a gas which acts as the sweep fluid.  
     
     
         5 . The system of  claim 4 , wherein the wherein the expansion element is an expansion valve.  
     
     
         6 . The system of  claim 1 , wherein the sweep fluid delivery system delivers a liquid into the wellbore to serve as the sweep fluid.  
     
     
         7 . The system of  claim 1 , further comprising a sweep fluid regeneration system which removes contaminant from the sweep fluid and delivers a regenerated sweep fluid back to the sweep fluid delivery system.  
     
     
         8 . The system of  claim 7 , wherein the sweep fluid regeneration system includes a liquid/gas separator.  
     
     
         9 . A method of separating a hydrocarbon and a contaminant in a wellbore, the method comprising: 
 separating a hydrocarbon and a contaminant in a wellbore with a membrane separator; and    delivering a sweep fluid to an output side of the membrane separator to improve a driving force driving the contaminant through the membrane.    
     
     
         10 . The method of  claim 9 , wherein the sweep fluid is pumped into the wellbore as a liquid and expanded to a gas.  
     
     
         11 . The method of  claim 10 , wherein the sweep fluid is water.  
     
     
         12 . The method of  claim 9 , wherein the contaminant is carbon dioxide.  
     
     
         13 . The method of  claim 9 , wherein the sweep fluid is a liquid containing a complexing agent pumped into the wellbore as a liquid.  
     
     
         14 . The method of  claim 13 , wherein the complexing agent is sodium hydroxide, magnesium hydroxide, a caustic agent, or amine.  
     
     
         15 . The method of  claim 9 , wherein the sweep fluid includes methanol.  
     
     
         16 . The method of  claim 9 , wherein hydrocarbon and contaminant are separated by passing a production stream containing the hydrocarbon and contaminant through a tubular membrane and permeating the contaminate through the membrane.  
     
     
         17 . The method of  claim 9 , wherein the sweep gas and contaminant are disposed of in an underground disposal formation.  
     
     
         18 . The method of  claim 9 , wherein the sweep gas and contaminant are removed to the surface.  
     
     
         19 . The method of  claim 9 , wherein the sweep gas and contaminant are separated by a sweep gas regeneration system.  
     
     
         20 . The method of  claim 19 , wherein the sweep gas regeneration system is positioned downhole.