Abstract: Subterranean oil and gas producing formations are fractured at vertically spaced intervals utilizing perforating guns forced down the well casing in tailing off "trains" comprising tamping and spacing water columns respectively positioned above and below each perforating gun, a perforation plugging slurry positioned below the spacing water column, and a concentrated proppant slurry column positioned below the perforation plugging slurry column. The perforation plugging and proppant slurry columns are sealed at their upper and lower ends by specially designed gel plug seals each comprising a short column of strong gel solution in which a spaced pair of casing size rock salt balls are disposed to provide the seal with structural reinforcement.