Top Seal

For a review of top seal analysis see Skerlec, G.M. (1999) Evaluating Fault Seal & Top Seal in Exploring for Oil & Gas Traps (Beaumont/Foster eds.), the newest volume in the AAPG Treatise of Petroleum Geology
also

Skerlec, G.M. (1992) Snap, Crackle & Pop: risking top seal integrity: AAPG Annual Convention program abstracts, p. 21

Brittle failure is the most common cause of the loss of top seal integrity. Brittle failure may be caused by deformation and/or overpressure (including HC buoyancy). Most important is the necessity for estimating the mechanical properties of the seal at the time of failure. Methods for risking brittle failure include:

	Incremental Strain Analysis
	Paleo-Ductility Analysis
	Mohr Circles and Fracture Gradients
	Fracture Mechanics
	Curvature & Second Derivatives
	Finite-element and Boundary-element Numerical Modeling
	Analog models including photoelastic and "clay" materials

The seal capacity of intact top seals is limited by the capillary properties of the seal, the physical character of the hydrocarbons, and seal continuity. Good seals have displacement pressures capable of trapping 1000's of feet of hydrocarbon. Seals with low displacement pressures may traps 0-10's of feet of hydrocarbon. Seal capacity and capillary properties are related to:

	Rock Type
	Sedimentary Facies
	System Tracts
	Log Properties
	Depth
	Interfacial Tension, Wettability and Density of the hydrocarbon phase
	overpressure

MECHANICAL PROPERTIES OF SEALS

CAPILLARY PROPERTIES OF SEALS

SEALS COURSE OUTLINE

"When top seals are good, they are very, very good; but when they are bad, they are awful."

Student Summary