--> Abstract: Prediction of Diagenetic Reactions and Reservoir Properties of North Sea Reservoir Sandstones, by K. Bjorlykke; #91004 (1991)

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Prediction of Diagenetic Reactions and Reservoir Properties of North Sea Reservoir Sandstones

BJORLYKKE, KNUT, University of Oslo, Oslo, Norway

The shallowest Jurassic reservoirs at 1.5 km down to 2.5-3 km burial depth have very little quartz cement (<3%). Between 3.0 and 4.5 km there is a rather sharp increase in the amount of quartz cement, and stylolites are very common indicating important internal sources of silica.

In the shallow marine and fluvial Jurassic sandstones kaolinite is the most abundant diagenetic clay mineral and secondary porosity owing to leaching of feldspars is well developed. In sandstones representing deeper water facies, also those closely associated with the source rocks, diagenetic kaolinite is often absent and there is less evidence of feldspar leaching. This suggests that release of acids from the source rocks had little effect on the development of secondary porosity and precipitation of kaolinite.

In the Permian and Triassic reservoirs smectite and illite are usually more abundant than kaolinite suggesting that in the dry climate prevailing when these sandstones were deposited, meteoric water flushing was not very effective.

From 3.5 to 4 km burial there is often a sharp increase in the content of diagenetic illite, probably owing to illitization of kaolinite and dissolution of K-feldspar causing a rapid deterioration of reservoir properties.

Pore water analyses show increasing salinities and more positive O(18) values with depth suggesting that large-scale convective flow or compactional flow has not taken place, thus limiting the potential for mass transfer by advection.

 

AAPG Search and Discovery Article #91004 © 1991 AAPG Annual Convention Dallas, Texas, April 7-10, 1991 (2009)