Physical Changes Associated with Maturation in Organic Rich Rocks
Zargari, Saeed; Prasad, Manika
Potential sources of hydrocarbon are often bodies of sediment which contain considerable fraction of preserved organic matter. Kerogen, which is the metamorphosed form of organic matter, gets preserved in anoxic environments with low grazing pressure. This kerogen generates hydrocarbon when is buried deep enough to reach high temperatures. The process of thermal maturation results in alteration of the petrophysical properties of the kerogen itself and the organic rich shale containing the kerogen. Thermal maturation also controls the storage capacities and hydrocarbon expulsion of the rocks. In addition to thermal maturation, diagenetic effects alter physical properties as well.
Thermal maturity produces largest changes in the organic content while diagenetic effects also alter the inorganic components of a rock. Furthermore, changes in organic matter can be coupled with diagenetic alterations in the inorganic components. Depending on the kerogen type and composition of the source rock, the interaction may vary. In order to use seismic and log measurements to locate organic rich rocks and to differentiate between thermal maturity and inorganic diagenesis, we must understand organic richness and maturation byproducts effect on petrophysical properties and seismic response.
In this study, we present changes in texture, composition, and petrophysical properties of organic rich rocks at different maturity levels. We find significant textural differences and mineral re-orientations in more mature rocks in comparison with immature samples.
Laminated kerogen particles appear to be load bearing in immature state; they become more isolated and scattered at higher maturity levels. Volume changes in kerogen also cause significant differences in bulk mechanical properties of the rock. We also recognize considerable bitumen generation during the course of maturation that changes the volumetric composition of the rock. Using our textural models, we develop appropriate rock models that can aid in seismic and well log interpretations as function of organic richness and maturity.
AAPG Search and Discovery Article #90163©2013AAPG 2013 Annual Convention and Exhibition, Pittsburgh, Pennsylvania, May 19-22, 2013