Print this pageDifferential Diagenesis and Reservoir Quality in a Sequence Stratigraphic Framework: Evidence from the Depositional Environment Controls in Santonian Sandstones, Santos Basin, Southeastern Brazil
Recent studies in Santonian sandstones of the Santos Basin, Southeastern Brazil, have provided evidence showing that both diagenesis and reservoir quality evolution of such sandstones are mostly controlled by the depositional environment conditions during eodiagenesis. Over lie
The Santonian sandstones lie on the top of a sequence boundary representing a low stand system tract (LST) sequence, and are covered by mudstones of a transgressive system tract (TST).
The proximal sandstones deposited under coastal marine environments show isopacous coating of illite (formerly smectite as infiltrated clay), feldspar dissolution, kaolinite and quartz cement as the major diagenetic phases. The geometric pore walls and secondary porosity provide better reservoir quality to these sandstones when compared to distal counterparts.
Conversely, the diagenesis in sandstones deposited by hyperpicnal flows in mixed meteoric/marine water on the shelf, most likely initiated as a Fe-rich smectite rim, evolving into well developed chlorite coatings preventing quartz cementation. As a final result these sandstones have turned out into a very low permeability reservoir rocks.
The integration of diagenesis and sequence stratigraphic framework of clastic sequences should improve the ability to predict the spatial and temporal distribution of diagenetic alterations, and related reservoir-quality modifications of sandstone deposits.
AAPG Search and Discover Article #90100©2009 AAPG International Conference and Exhibition 15-18 November 2009, Rio de Janeiro, Brazil