Pore Geometry as an Indicator of Depositional Texture and Velocity Variations in Chalks

The complex pore geometry in carbonates makes their velocity behavior difficult to predict. Integration of geology information can help to make a predictive pattern for pore geometry and as a result for velocity. In this paper, based on available diagenetic models for chalks, an integrated modeling strategy is developed for velocity variation in a mineralogically uniform chalk. It can be shown that different depositional texture in chalks can be expressed by different depositional pore aspect ratio. This depositional aspect ratio transforms to other aspect ratio by post-depositional processes. This transformation of pore aspect ratio in chalks can be predicted from geology information and mostly from foraminifer’s contents and sorting information of the sediment. Mechanical compaction and cementation although both decrease porosity with depth but may increase the velocity by different rates, since one makes more compliant pore throats while another one close cracks and makes stiffer pore bodies, respectively. These show the relevance of pore geometry consideration in velocity interpretation, since some variations in velocity data may results from pore geometry (depositional texture) and its transformation (post-depositional process) through different diagenetic environments rather than mineralogy, fluid or porosity.