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Line 19: − {| class = "wikitable"+ − |-+ − ! Step+ − ! Phenomenon − |- − | 1 − | 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. − |- − | 2 − | Reduced porosity may result in lower [[permeability]] so that production rates are subeconomic, even where economic quantities of petroleum are still trapped. − |- − | 3 − | 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 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. − |}
Postaccumulation cementation (view source)
Revision as of 20:36, 27 October 2014
, 20:36, 27 October 2014→The process
As the pore volume within a trap decreases due to [[burial cementation]], several phenomena combine to destroy the economic accumulation.
As the pore volume within a trap decreases due to [[burial cementation]], several phenomena combine to destroy the economic accumulation.
# 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.
# 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 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==