Rock physics interpolation used for velocity modeling of chalks: Ontong Java Plateau example

Chalks are pelagic carbonate sediments that are deposited in deep-water environments. Their elastic behaviour is controlled by a combination of depositional conditions and subsequent diagenesis. In this paper, we incorporate geological information into rock physics modeling by constraining the pore structure (aspect ratio) variability. The strategy is to define a pore-model that reflects lithology, porosity and velocity. Then, a background velocity cube is constructed based on information about the lithologies and the velocity data from some reference wells. This approach may be further used to obtain a gridded velocity model of a reservoir sequence. Well and core data from 14 wells on the Ontong Java Plateau, obtained through the deep sea drilling program and the ocean drilling program, are used to examine this approach. Velocity predictions based on the pore-models derived from six reference wells in the area, show a good correlation with measured velocities at some blind wells. This indicates a homogeneous and predictable pore structure in the area.