TECHNOLOGY FOCUS - INORGANIC CHEMISTRY - Preferred Components: The precursor is a salt having a low water-solubility that can be converted into a salt having a high water-solubility, where precursor may be converted by contacting with an acidic or a basic solution. The precursor is tricalcium diphosphate, barium carbonate, magnesium oxide, zinc sulfide, ferric hydroxide and/or barium sulfate. The fluid is water and where the precursor can be converted into a compound that is soluble in water.    TECHNOLOGY FOCUS - POLYMERS - Preferred Components: The elastomer matrix comprises an elastomer comprising rubber materials which, apart from swelling in water, also swell in crude oil and/or rubber materials which do not swell in crude oil. The rubber material which swells in crude oil is: ethylene propylene rubber (EPM) and ethylene propylene diene monomer (EPDM); ethylene-propylene-diene terpolymer rubber (EPT); butyl rubber (IIR); brominated butyl rubber (BIIR); chlorinated butyl rubber (CIIR); styrene butadiene copolymer rubber (SBR); and/or silicone rubbers (VMQ). The rubber material which does not swell in crude oil is butadiene acrylonitrile copolymer (nitrile rubber, NBR); Zetpol (RTM: Hydrogenated nitrile butadiene rubber), Therban (RTM: Hydrogenated nitrile butadiene rubber); NBR with reactive groups (carboxylated nitrile butadiene rubber)(X-NBR); chlorinated polyethylene (CM or CPE); neoprene rubber (CR); epichlorohydrin ethylene oxide copolymer (CO, ECO); chloro sulfonated polyethylene (CSM); ethylene acrylate rubber (EAM or AEM); Kalrez (RTM: Fluorosilicone rubber (FVMQ)); Chemraz (RTM: Perfluoro rubbers (FFKM)); Viton (RTM: Fuoro rubbers), Fluorel (RTM: Fluoro rubbers); and/or Aflas (RTM: Tetrafluoroethylene/propylene). EXAMPLE - Typical elastomer composition comprised of: 100 g of ethylene propylene diene monomer rubber; 25 g of paraffinic plasticizer; 37.5 g of fast extruding furnace carbon black; 1.56 g of peroxide crosslinker; 1.25 g of triallyl isocyanurate (coagent for crosslinking); and 181.25 g of tricalcium diphosphate.