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A WORLDWIDE LOOK AT THE CAP‐ROCK PROBLEM
Author(s) -
Grunau Hans R.
Publication year - 1987
Publication title -
journal of petroleum geology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.725
H-Index - 42
eISSN - 1747-5457
pISSN - 0141-6421
DOI - 10.1111/j.1747-5457.1987.tb00945.x
Subject(s) - geology , oil shale , caprock , evaporite , lithology , slumping , geotechnical engineering , seal (emblem) , mining engineering , fracture (geology) , petroleum engineering , geochemistry , petrology , paleontology , art , visual arts , sedimentary rock
Geological aspects of the cap‐rock problem were investigated on a worldwide scale in order to provide guide‐lines for assessing the sealing and retention risk in exploration ventures. The most common caprock lithologies are shales and evaporites, which have typical thicknesses of tens to hundreds of meters. Regional seals are often provided by evaporitic sabkha environments and transgressive and regressive shales. Cap‐rocks must be placed in the frame of a hydrocarbon habitat which evolves with time to judge properly the retention risk. Important parameters are rate of diffusion of hydrocarbons through cap‐rocks, and fracture development as a function of the intensity of geomechanical deformation. When losses due to seal failure and diflusion occur, replenishment from an active generation‐migration system may counter‐balance the loss. “Giant” oil‐ and gasfields serve as a yardstick for measuring shale—evaporite ratios and seal depths. Surface seepages can provide a measure of seal failure. As the cap‐rock problem is in an initial stage of research, many uncertainties affect the reliability of semi‐quantitative statements on risks of sealing and retention.