A method and mobile system for cleaning dirty gas from a newly stimulated gas well. The entire system is supported on a trailer or other mobile support so that it can be driven from well site to well site for short-term, post-stimulation use only. The system comprises a gas separator, such as a membrane separator. The system also includes a pretreatment assembly for preparing the gas for the gas separator. The pretreatment assembly may include separators, a heater, a guard vessel and a polishing filter. A chiller or heat exchanger cools the treated gas to a marketable temperature. A generator and a hydraulics plant provide power to the system. Each mobile system will be designed to treat gases with widely different operating conditions varying from well to well.