Seal Failure Related to Basin-scale Processes
The leakage of trapped petroleum is a major concern in hydrocarbon exploration and has led to a large number of exploration failures. Changes in stress state, fluid pressure, and cap rock permeability may all result in a loss of trapped hydrocarbons. Such changes may result from several different subsurface processes.
This chapter describes an examination of important processes that control compaction, fluid flow in reservoirs, fault reactivation, and their influence on leakage from hydrocarbon reservoirs. It was concluded that seal-failure analysis is seldom based on more than a few of the operating processes and therefore does not reach its full potential. Especially, the effects of overpressures on sediment compaction and hydrocarbon leakage seem to have been oversimplified and commonly overstated. The conditions for hydrofracturing and the corresponding loss of hydrocarbons from structural crests are also commonly considered too superficially in sealing analyses.
It was concluded that inadequate leakage assessments can result from neglect of some subsurface processes that influence stress, pore pressure, and hydrocarbon permeability in the seal. Seal integrity predictions can be improved if thorough analyses of the relevant subsurface processes routinely precede the sealing analyses.