Method and system for treating a flow back fluid exiting a well site

Abstract

The present invention relates to a method and system for treating a flow back fluid exiting a well site following stimulation of a subterranean formation. More specifically, the invention relates to processing the flow back fluid, and separating into a carbon dioxide rich stream and a carbon dioxide depleted stream, and continuing the separation until the carbon dioxide concentration in the flow back stream until the carbon dioxide concentration in the flow back gas diminishes to a point selected in a range of about 50-80 mol % in carbon dioxide concentration, after which the lower concentration carbon dioxide flow back stream continues to be separated into a carbon dioxide rich stream which is routed to waste or flare, and a hydrocarbon rich stream is formed.

1 - 10 . (canceled) 
     
     
         11 . A system for processing the flow back fluid from a well site following stimulation of a subterranean formation, comprises:
 a pretreatment unit to receive and process the flow back fluid from the well site and remove any one of water, solid particulates, liquid hydrocarbons, hydrogen sulfides or a combination thereof;   a membrane unit downstream of the pretreatment unit to receive the pretreated flow back fluid therefrom and separate the pretreated flow back fluid into a carbon dioxide rich permeate stream and a carbon dioxide depleted retentate stream;   a permeate cooling unit to receive the carbon dioxide rich permeate stream and reduce the temperature of the stream to a temperature ranging from about −40 to 20° F.; and   a phase separator to receive the lower temperature carbon dioxide rich permeate stream from the permeate cooling unit and separate the stream into a first liquid stream of predominantly carbon dioxide and a first gaseous stream enriched in methane.   
     
     
         12 . The system of  claim 11 , further comprising a second phase separator to receive the first liquid stream of predominantly carbon dioxide and further separate into a second liquid carbon dioxide product stream and a second gaseous phase stream enriched in methane. 
     
     
         13 . The system of  claim 11 , further comprising a pressure reducing valve disposed between the cooling unit and the phase separator to reduce the pressure to a range of about 60-500 psig, and lower the temperature of the carbon dioxide rich permeate stream. 
     
     
         14 . The system of  claim 11 , further comprising a chiller unit in communication with the cooling unit providing additional refrigeration to the cooling unit. 
     
     
         15 . The system of  claim 12 , further comprising a heat exchanger disposed between the phase separators to warm the first liquid stream of predominantly carbon dioxide routed to the second phase separator. 
     
     
         16 . The system of  claim 11 , further comprising a manifold where the carbon dioxide depleted retentate stream is mixed with the first and second gaseous phase streams to produce a cool process stream which is routed to the cooling unit. 
     
     
         17 . The system of  claim 11 , wherein the entire system or parts of the system are mobile. 
     
     
         18 . The system of  claim 11 , wherein the phase separator is selected from one that either has two or more separation stages, a vessel or column with trays and heaters, a distillation column with a reboiler or a combination thereof. 
     
     
         19 . The system of  claim 11 , wherein the carbon dioxide depleted retentate stream, the first and second gaseous phase streams individually or in any combination is routed to the cooling unit. 
     
     
         20 . The system of  claim 17 , wherein the parts of the system disposed downstream of the membrane are removed from operation upon switching to a second mode where the flow back fluid is separated into a carbon dioxide rich stream and the carbon dioxide rich stream is routed to waste or flared, while the carbon dioxide lean stream, rich in hydrocarbons is recovered as a product. 
     
     
         21 . The system of  claim 11 , wherein the membrane unit is a polyether ether ketone (PEEK) membrane.