(1) Institut Français du Pétrole, Rueil-Malmaison, France
ABSTRACT: Origin and Distribution of Pore-Lining Chlorite in Siliciclastic Reservoirs
Diagenetic chlorite is a variety of authigenic clay that commonly coats the surface of detrital grains in sandstones. As it prevents silicification, it can be responsible for the preservation of favorable reservoir properties in deeply buried sediments. Its formation, stability, and distribution in sediments are still debated questions. Sedimentological, petrographical, mineralogical and geochemical data were acquired from core samples of six sandstone sequences : from Silurian, Lower Devonian and Upper Devonian series of the Saharian platform ; from a Lower Jurassic formation of the Haltenbanken area, North Sea ; from a Cretaceous formation of the Neuquen Basin, Argentina ; and from Paleocene sediments of the North Sea. It appeared that a/ chloritic sandstones exhibit a large diversity of facies, depositional environment and detrital composition ; b/ the total amount of diagenetic chlorite is not related to the sedimentary facies ; c/ few textures of pore-lining and pore-filling chlorite are typical, including the ooidal texture ; d/ morphology and texture of the chlorite evolve with compaction ; e/ chlorite composition, very constant at the reservoir-unit scale, varies both with sedimentary context and burial depth. Integrating the considered dataset with a thorough review of literature revealed that chloritic sandstones occur preferentially a/ in intracontinental platforms and seaways ; b/ in stratigraphic correlation with oolitic ironstones, for which a global geochemical model does exist. A tentative sedimentological model is discussed. Thermodynamics helps in understanding the conditions of formation of the chlorite precursor during early diagenesis and of chlorite stability during compaction.
AAPG Search and Discovery Article #90906©2001 AAPG Annual Convention, Denver, Colorado