Method and system for providing fuel gas to a topside facility

Abstract

A method for providing fuel gas to a top-side processing system of a sub-sea well stream is provided. The method comprises separating the sub-sea well stream in a sub-sea arranged three phase separator obtaining a crude oil stream, and a crude natural gas stream, separating acid gasses and/or water from the crude natural gas, pressurizing the gas stream sub-sea, adding at least part of the pressurized gas to the crude oil stream subsea, transporting the added gas together with the oil to the topside, separating the gas from the oil in a first stabilization stage and providing the separated gas as fuel gas to a fuel gas system.

1 . A method for providing fuel gas to a topside processing system for a subsea well stream, the method comprising:
 separating the subsea well stream in a subsea arranged three phase separator to thereby obtain a crude oil stream and a crude natural gas stream;   separating at least one of acid gasses and water from the crude natural gas stream;   pressurizing the crude natural gas stream subsea;   adding at least part of the pressurized gas to the crude oil stream subsea;   transporting the added pressurized gas together with the crude oil to the topside processing system;   separating the pressurized gas from the crude oil in a first stabilization stage; and   providing the separated gas as fuel gas to a fuel gas system.   
     
     
         2 . The method according to  claim 1 , further comprises removing water from the crude oil stream subsea to obtain dry crude oil, and transporting the dry crude oil to the topside processing system. 
     
     
         3 . The method according to  claim 2 , wherein the step of removing water from the crude oil stream subsea comprises passing the crude oil through a subsea arranged electrostatic coalescer. 
     
     
         4 . The method according to  claim 1 ,  2  or  3 , further comprising stabilizing the crude oil stream for tanker transport in the topside, processing system through removal of dissolved gas from the crude oil stream. 
     
     
         5 . The method according to  claim 4 , wherein the stabilizing step is performed at a gas pressure equal to a pressure required for the topside fuel gas system. 
     
     
         6 . The method according to  claim 4 , wherein the crude oil is stabilized in first and second stages and is heated with interstage heating. 
     
     
         7 . The method according to  claim 1 , wherein the step of separating acid gasses or water from the crude natural gas is performed subsea. 
     
     
         8 . A subsea well topside fuel gas-providing system which comprises:
 a subsea arranged three phase separator which includes a well stream inlet, a crude natural gas outlet and a crude oil outlet;   a riser which includes a subsea riser inlet in fluid communication with the crude oil outlet and the crude natural gas outlet;   the riser further comprising a topside riser outlet in fluid communication with a topside arranged stabilization unit which includes a stabilized crude oil outlet and a fuel gas outlet.   
     
     
         9 . The system according to  claim 8 , further comprising a subsea gas treatment system located downstream of the three phase separator, the subsea gas treatment system comprising an inlet in fluid communication with the crude natural gas outlet and a treated gas outlet in fluid communication with the riser. 
     
     
         10 . The system according to  claim 8  or  9 , further comprising a subsea arranged water removal unit located downstream of the three phase separator, the water re oval unit comprising a crude oil inlet in fluid communication with the crude oil outlet, a dry crude oil outlet in fluid communication with the riser, and a water outlet. 
     
     
         11 . The system according to  claim 10 , wherein the water removal unit comprises an electrostatic coalescer. 
     
     
         12 . The system according to  claim 8 , herein the fuel gas outlet is in fluid communication with a fuel gas net inlet of a topside arranged power generating unit. 
     
     
         13 . The system according to  claim 8 , further comprising a subsea natural gas compressor with an inlet in fluid communication with the natural gas outlet and a pressurized gas outlet in communication with the riser.