A well treatment composition for use in a hydrocarbon-bearing reservoir, optionally as a kill pill, and comprising a reversible aminal gel composition. The reversible aminal gel composition includes a liquid precursor composition. The liquid precursor composition is operable to remain in a liquid state at about room temperature. The liquid precursor composition comprises an organic amine composition; an aldehyde composition; a polar aprotic organic solvent; and a metal salt composition. The liquid precursor composition transitions from the liquid state to a gel state responsive to an increase in temperature in the hydrocarbon-bearing reservoir. The gel state is stable in the hydrocarbon-bearing reservoir at a temperature similar to a temperature of the hydrocarbon-bearing reservoir, and the gel state is operable to return to the liquid state responsive to a change in the hydrocarbon-bearing reservoir selected from the group consisting of: a decrease in pH in the hydrocarbon-bearing reservoir and an addition of excess metal salt composition in the hydrocarbon-bearing reservoir.