Finding hydrocarbon reserves with cyclopropane EU-funded research has identified cyclopropane as an environmentally-friendly gas tracer ideal for use in exploration for underground hydrocarbon reservoirs. Energy © Shutterstock Locating new reserves of hydrocarbons deep below the Earth's surface requires the use of gas tracers. Unfortunately, the gases commonly used, such as sulphur hexafluoride and perfluorocarbons, have global warming potentials (GWPs) several orders of magnitude greater than carbon dioxide. A search for replacement tracer species was initiated in the context of ENVITRACER, an RTD project supported by the Fifth Framework Programme. A number of prospective tracer gases were investigated in the course of the project. In addition to not damaging the Earth's climate, the new compounds also had to meet the criteria of not being radioactive. The research was headed by scientists with the Institute for Energy Technology (IFE) in Norway. Analysis of experimental data collected in the laboratory and in the field revealed that cyclopropane was the best candidate tracer gas. Its lifetime and flow characteristics resemble those of perfluorocarbons, but the GWP drawbacks are avoided. IFE thereforerecommended cyclopropane for use as an environmentally-friendly gas tracer. On the basis that other potentially suitable gases were identified, work continued in collaboration with the other ENVITRACER partners to pinpoint alternative tracer species.