Filtration fronts in pressure compliant reservoirs

Abstract

Hydrofracturing is believed to be the major mechanism responsible for the migration of crust fluids and for the transport of hydrocarbons from overpressured fluid compartments. In their analysis of the process of porosity reduction in the earth’s crust and crustal pore pressure generation, Walder and Nur (1984) point out that elevated pore pressure generated as a result of local porosity reduction may lead to brittle failure with partial relief of high pore pressure. Such episodic fracturing accompanied by crack healing, may be a common process throughout most of the crust. Hunt (1990) also speculates that the generation of oil and gas within the compartments plus the thermal expansion of pore fluids eventually causes fracturing of the top compartment seal during periods of basin sinking. Seal fracturing causes a pressure drop with compartment fluids rushing to the breakout point. Episodic cycles of resealing and breakout may occur in intervals of thousands of years in rapidly sinking basins such as the United States Gulf coast.