oil seeps

Just dug up some information about seeps to get a better understanding about PPL 267......(LOOKING GOOD!!!)


A good definition of a seep is ''the surface expression of a migration pathway, along which petroleum is currently flowing, driven by buoyancy from a sub-surface origin'' (Clarke & Cleverly,1990). Knowledge of where oil and gas seeps are emerging is therefore a key piece of evidence in reducing the risk on source presence in a new basin as seeps originate by leakage from buried oil and gas accumulations (fig 1). At the most basic level, this demonstrates that the basin contains a generating source rock and hence a viable petroleum system.

Work published by BP and others in the early 90's (Clarke & Cleverly,1990; Clayton et al.,1991) demonstrated that over 75% of the world's petroliferous basins contain surface seeps (Fig 2), the exceptions being those with unbroken regional evaporitic seals (such as the Hith Anhydrite in the Arabian-Iranian Foreland basin). Most seeps represent tiny but detectable volumes of oil and gas which are not significantly depleting the reservoir. Exceptions would be in some recent onshore fold and thrust belts where accumulations have either been breached or redistributed to tertiary traps and where the link between surface seeps and the leaking traps is more complex. Such geology, however, is rarely encountered in offshore basins so that problem does not arise. Confirmation of the presence of seeps, therefore especially in offshore basins, is positive and in the vast majority of cases is not indicative of breached or depleted traps.