A scanning electron microscope study of textures in several companion pairs of uncompacted and experimentally compacted Ekofisk chalk samples has documented two principal mechanisms of chalk matrix compaction. The dominant mechanism — which we have quantified through processing and analysis of digitized backscattered electron images — is simple grain displacement, which results in larger pore spaces being partially filled in by single calcite rhombohedra and other small fragments of bioclasts as the matrix porosity becomes more homogeneous with compaction. A second mechanism — which we have quantified by counting intact coccoliths in 100 secondary electron images per sample — involves the mechanical breakup (cataclasis) of bioclasts. The second mechanism contributes to the first. However, it clearly played a more significant role in the natural process of compaction over geologic time and is likely to be of only secondary importance relative to simple grain displacement during production-related compaction of the reservoir.

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