--> ABSTRACT: Influence of Over Pressure on Hydrocarbon Trapping Potential, by G. Yardley, P. Ringrose, and P. Corbett; #91021 (2010)

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Influence of Over Pressure on Hydrocarbon Trapping Potential

YARDLEY, G., P. RINGROSE, and P. CORBETT

Several recent publications have defined sealing and leakage classifications for hydrocarbon traps. These give the expected hydrocarbon column height as a function of trap properties, fluid properties and pressure gradients. These treatments have tended to be over simplistic and do not incorporate the full effects of capillary forces in pore networks. It is important to examine the basic physics of multi-phase flow in cap rocks in order to assess the potential of a trap, especially in overpressured cases. We investigate the interaction between water and hydrocarbon phases from the pore scale to the trap scale using a reservoir simulator. We model hydrocarbon trapping, and fluid flow across membrane seals for a realistic range of caprock and reservoir pressure scenarios. The aim was to determine the impact of overpressure on trapping potential and hydrocarbon reserves.

We conclude that overpressure does not affect the hydrocarbon column height needed to break through into the caprock, contrary to some recently published results. However, trapping potential in dynamic membrane seals, where hydrocarbons leak through the caprock, is a function of the pressure gradient, and two phase flow through the caprock. There is little reliable data on caprock permeabilities and especially relative permeabilities; however, we show the influence of different permeability, relative permeability and wettability assumptions on the trapping potential of a given cap rock. Examples from North Sea fields will be shown of how these situations will impact reserves and exploration objectives in overpressured systems.

AAPG Search and Discovery Article #91021©1997 AAPG Annual Convention, Dallas, Texas.