Methods for recovering natural gas using nitrogen rejection units

Abstract

A method and system for enhanced oil recovery by performing the steps of feeding a mixture of nitrogen from a primary nitrogen supply and an optional supplemental nitrogen supply into an oil field; separating recovered oil from a gas mixture comprising nitrogen, natural gas and C2+ hydrocarbons; feeding the gas mixture to a nitrogen rejection unit operating at elevated pressures; and recovering the nitrogen, natural gas and C2+ hydrocarbons. A method for the recovery of natural gas is also described herein.

Having thus described the invention, what we claim is: 
     
         1 . A method for enhanced oil recovery comprising the steps of (a) feeding nitrogen from a primary nitrogen supply into an oil field; (b) recovering oil and a gas mixture comprising nitrogen, natural gas and C2+ hydrocarbons from the oil field; (c) separating the oil from the gas mixture (d) feeding the gas mixture to a nitrogen rejection unit; and (d) recovering nitrogen, natural gas and C2+ hydrocarbons. 
     
     
         2 . The method as claimed in  claim 1  further comprising feeding a supplemental nitrogen supply into the oil field. 
     
     
         3 . The method as claimed in  claim 1  wherein the primary nitrogen supply is from an air separation unit. 
     
     
         4 . The method as claimed in  claim 2  wherein the supplemental nitrogen supply is from a supplemental air separation unit. 
     
     
         5 . The method as claimed in  claim 1  wherein the primary nitrogen supply is fed to a high pressure compressor. 
     
     
         6 . The method as claimed in  claim 1  wherein the high pressure compressor operates at a pressure up to 6700 pounds per square inch. 
     
     
         7 . The method as claimed in  claim 1  wherein the oil and the gas mixture are fed to an oil separation and sour gas removal unit, thereby separating the recovered oil from the gas mixture. 
     
     
         8 . The method as claimed in  claim 1  wherein the recovered oil is fed to a storage system. 
     
     
         9 . The method as claimed in  claim 1  wherein the nitrogen rejection unit will separate the nitrogen from the natural gas and C2+ hydrocarbons. 
     
     
         10 . The method as claimed in  claim 1  wherein the nitrogen rejection unit is operating at high pressures. 
     
     
         11 . The method as claimed in  claim 10  wherein the high pressure is 30 bar. 
     
     
         12 . The method as claimed in  claim 1  wherein the recovered nitrogen is fed to an intermediate pressure compressor before being fed to the high pressure compressor. 
     
     
         13 . The method as claimed in  claim 1  wherein a mixture of nitrogen and methane is recovered from said nitrogen rejection unit and is fed to the high pressure compressor. 
     
     
         14 . The method as claimed in  claim 9  further comprising feeding the C2+ hydrocarbons along with the nitrogen and methane to the high pressure compressor. 
     
     
         15 . The method as claimed in  claim 1  wherein the recovered C2+ hydrocarbons are fed to a recycle or fractioning unit. 
     
     
         16 . A method for the recovery of natural gas from an enhanced oil recovery operation comprising the steps of (a) feeding a primary nitrogen supply into an oil field; (b) recovering oil and a gas mixture comprising nitrogen, natural gas and C2+ hydrocarbons from the oil field; (c) separating the oil from the gas mixture; (d) feeding the gas mixture to a nitrogen rejection unit operating at elevated pressures: and (e) separating natural gas from nitrogen and C2+ hydrocarbons. 
     
     
         17 . The method as claimed in  claim 16  further comprising feeding a supplemental nitrogen supply into the oil field. 
     
     
         18 . The method as claimed in  claim 16  wherein the primary nitrogen supply is from an air separation unit. 
     
     
         19 . The method as claimed in  claim 17  wherein the supplemental nitrogen supply is from a supplemental air separation unit. 
     
     
         20 . The method as claimed in  claim 16  wherein the primary nitrogen supply is fed to a high pressure compressor. 
     
     
         21 . The method as claimed in  claim 16  wherein the high pressure compressor operates at a pressure up to 6700 pounds per square inch. 
     
     
         22 . The method as claimed in  claim 16  wherein the oil and the gas mixture are fed to an oil separation and sour gas removal unit, thereby separating the recovered oil from the gas mixture. 
     
     
         23 . The method as claimed in  claim 16  wherein the recovered oil is fed to a storage system. 
     
     
         24 . The method as claimed in  claim 16  wherein the nitrogen rejection unit will separate the natural gas from the nitrogen and C2+ hydrocarbons. 
     
     
         25 . The method as claimed in  claim 16  wherein the nitrogen rejection unit is operating at elevated pressures. 
     
     
         26 . The method as claimed in  claim 25  wherein the high pressure is 30 bar. 
     
     
         27 . The method as claimed in  claim 16  wherein the recovered nitrogen is fed to an intermediate pressure compressor before being fed to the high pressure compressor. 
     
     
         28 . The method as claimed in  claim 16  wherein the natural gas is recovered from said nitrogen rejection unit and is fed to the high pressure compressor. 
     
     
         29 . The method as claimed in  claim 16  wherein the recovered C2+ hydrocarbons are fed to a recycle or fractioning unit. 
     
     
         30 . A system for enhanced oil recovery comprising a source of nitrogen, a supplemental source of nitrogen, and a nitrogen rejection unit. 
     
     
         31 . The system as claimed in  claim 30  wherein the source of nitrogen is a primary air separation unit. 
     
     
         32 . The system as claimed in  claim 30  wherein the supplemental source of nitrogen is a supplemental air separation unit. 
     
     
         33 . The system as claimed in  claim 30  wherein the nitrogen rejection unit operates at high pressure. 
     
     
         34 . The system as claimed in  claim 30  wherein the high pressure is 30 bar. 
     
     
         35 . The system as claimed in  claim 30  wherein the nitrogen rejection unit separates a gas mixture or nitrogen, natural gas and C2+ hydrocarbons. 
     
     
         36 . The system as claimed in  claim 30  further comprising an intermediate pressure compressor. 
     
     
         37 . The system as claimed in  claim 30  further comprising a high pressure compressor.