Changes

# Petroleum is displaced from the [[trap]] at the [[spill point]] as the pore volume within the structural closure decreases. If [[porosity]] is lowered sufficiently, the [[accumulation]] may be subeconomic in size.

# Petroleum is displaced from the [[trap]] at the [[spill point]] as the pore volume within the structural closure decreases. If [[porosity]] is lowered sufficiently, the [[accumulation]] may be subeconomic in size.

# Reduced porosity may result in lower [[permeability]] so that production rates are subeconomic, even where economic quantities of petroleum are still trapped.

# Reduced porosity may result in lower [[permeability]] so that production rates are subeconomic, even where economic quantities of petroleum are still trapped.

# As pore size decreases in a petroleum-filled reservoir, the [[capillary pressure]] of the petroleum phase must increase to occupy the pore spaces (assuming no change in [[wettability]]). In low-permeability [[tight gas reservoirs|tight sands]] or carbonates, the capillary [[displacement pressure]] in the reservoir rock may approach that of moderate-quality seals. As a result, a lithology that could seal an accumulation at shallow depth may no longer be effective at deeper depths because it differs little from the reservoir rock.

# As pore size decreases in a petroleum-filled reservoir, the [[capillary pressure]] of the petroleum phase must increase to occupy the pore spaces (assuming no change in [[wettability]]). In low-permeability [[tight gas reservoirs: evaluation|tight sands]] or carbonates, the capillary [[displacement pressure]] in the reservoir rock may approach that of moderate-quality seals. As a result, a lithology that could seal an accumulation at shallow depth may no longer be effective at deeper depths because it differs little from the reservoir rock.

==Predicting spillage by cementation==

==Predicting spillage by cementation==