Cratering – a sudden spring of fluid (mainly – gas) moving under high pressure inside the well annulus to the surface. Develops due to violation of natural hydrodynamic equilibrium due to injection of heat transfer agent under pressure close to rock pressure during oil and gas fields development or underground sulfur burn-out.

Such spring leads to craters with dozens or even hundreds meters in diameter. Sometimes several springs occur around a killed well. Often such situations lead to fires. To prevent springs the ways of fluid movement should be sealed by using different methods of killing the well and its further plugging. Often this spring-prevention measures eventually lead to well abandonment. Such work is especially complicated at off-shore fields.