Gas formation in sand and clay during electrical resistance heating

A series of electrical resistance heating (ERH) experiments were performed in a two-dimensional test cell to investigate gas production within clay lenses composed of specified mass fractions of kaolin and #20-30 silica sand (40%, 70% and 100% kaolin by mass). Temperature, electrical, photographic and piezometric data were collected during the heating of the test cell by ERH, followed by local electrical resistance measurements during cooling. In each experiment the clay lens heated more rapidly than the surrounding sand, with gas production originating at the clay-sand interface and subsequently extending outwards. The Waxman-Smits model was used to interpret electrical properties to assess the production of gas within the lens. Gas saturations immediately after ERH were estimated in the lens interiors as Sg = 0.38 ± 0.07, 0.25 ± 0.05 and 0.09 ± 0.02 (for the 40%, 70% and 100% clay mass fractions). Gas saturations sufficient to produce a connected gas phase can be generated during ERH in lenses containing moderate amounts of clay.