A method of enhancing the productivity of a subterranean formation penetrated by a gas, oil or geothermal well consists of introducing into the formation and/or well a pumpable polymerizable fluid comprising a crosslinkable, monofunctional alkene, multi-functional alkene (such as a difunctional alkene), a heat inducible free radical initiator and brine. The fluid may be used in the thermal insulation of production tubing or transfer pipes and hydraulic fracturing.