Print this pageInfluence 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.