Many facies assumed to act as seals contain stringers of sand and silt that are potential low–grade reservoir units. The drill–stem tests (DSTs) from these formations generally show them to be “tight,” but many of the wells in these “barrier” facies ultimately become commercial producers after completion. Calculation of the permeability and fluid content of these facies from DSTs has not been a common practice because the facies often do not produce oil or gas when tested, making them unattractive to operators, and because the analysis of DSTs from tight formations can be problematic. However, knowing the permeability of seal facies helps operators determine which of these “barriers” are the leakiest and, hence, are the best potential exploration targets. In this study, the shape of the shut-in curve on pressure charts andothersubtle indicationsareusedtomoreaccurately assess the reservoir quality of these neglectedformations. This paper will attempt to demonstrate that a good approximation of the leakage potential of these facies can be made using published empirical correlations if the permeabili–ty, as from a DST, is known.
Figures & Tables
Seals, Traps, and the Petroleum System
This memoir provides the information to help explorationists greatly increase their understanding of seals and traps and thereby markedly improve their ability to forecast hydrocarbon occurrences.