A system and process for producing synthetic crude oil from produced fluids of an oil well is disclosed. The system comprises a separation plant for producing an associated gas stream from produced fluids a membrane unit comprising a plurality of polymer membranes to provide a CO2 enriched permeate stream and a CO2 depleted product gas stream, a gas conversion plant for converting the CO2 depleted product gas stream into a synthetic crude oil and a heat exchanger adding heat to the associated gas stream so that the membrane unit operates at a temperature of at least 80° C. during separation of the associated gas stream using the membrane unit. A process using the aforementioned components, including separation of the associated gas stream using the membrane unit at a temperature >80° C., into a CO2 enriched stream and a CO2 depleted product stream, is also described.