Depositional and Diagenetic Control on Porosity and Permeability in Deeply-Buried Sandstone Reservoirs as Exemplified by North Sea Data

Mogens Ramm

Burial diagenesis and reservoir quality modification in North Sea Jurassic reservoirs are shown to be largely controlled by the pre-burial composition of the sandstones. Mechanical compaction at shallow burial, chemical compaction and quartz cementation at deep burial, and clay mineral authigenesis are the three most important reservoir quality modifying diagenetic processes, and all these can largely be considered as being isochemical or partially isochemical. It follows that reservoir quality prediction will be successful if the initial mineralogy and texture of the reservoir rocks, the quantitative effects of changing rock composition, and the burial history are known. Although a highly accurate prediction of initial sandstone composition is rarely achievable, an under tanding of the effect of varying mineralogy on the most important reservoir quality modifying processes will in most cases provide the necessary basis for adequate reservoir quality prediction.

The initial composition of the sandstones is controlled by the sedimentological environment, depositional processes, climate and the type of material transported into the sedimentary basin. Hence, integrated sedimentological and petrological studies, addressing the links between three-dimensional distributions of depositional facies, initial sandstone composition and reservoir quality models are the key to successful reservoir quality prediction prior to drilling in frontier areas as well as detailed reservoir characterization during field development.

AAPG Search and Discover Article #91019©1996 AAPG Convention and Exhibition 19-22 May 1996, San Diego, California