Factors Necessary to Define a Pressure Seal

Abstract

ABSTRACT A pressure seal is a rock layer capable of confining anomalous pressure over geologic time. In general, three factors are necessary to define a pressure seal: time, thickness, and permeability. The time over which a seal may confine a pressure transient is directly proportional to the square of the seal thickness and inversely proportional to the seal permeability. A seal cannot be defined solely on the basis of its hydraulic resistance unless it can be shown that sufficient time has passed that steady-state conditions are approximated. The minimum permeability needed for a geologic unit to act as a pressure seal over a time span of about 1 m.y. is in the range of 10–21–10–23 m2. This range is generally lower than most measurements of shale permeability.