Rock-physics characterization of chalk by combining acoustic and electromagnetic properties

Abstract

The characterization of shallow subsurface formations is essential for geologic mapping and interpretation, reservoir characterization, and prospecting related to mining/quarrying. To analyze elastic and electromagnetic (EM) properties, we characterize near-surface chalk formations deposited on a shallow seabed during the Late Cretaceous-Early Paleogene (Maastrichtian-Danian). EM and elastic properties, both of which are related to mineralogy, porosity, and water saturation, are combined to characterize the physical properties of chalk formations. We also perform rock-physics modeling of elastic velocities and permittivity and analyze their relationships. We then use measured ground-penetrating radar and P-wave velocity field data to determine the key model parameters, which are essential for the validity of the models and can be used to evaluate the consolidation degree of the rocks. Based on the models, a scheme is developed to estimate the porosity and water saturation by combining the two rock-physics templates. The predictions are consistent with previous findings. Our templates facilitate fast mapping of near-surface porosity and saturation distributions and represent an efficient and cost-effective method for near-surface hydrologic, environmental, and petrophysical studies. In the current formulation, the method is only applicable to rock type (chalk) comprising a single mineral (pure calcite). It is possible to tailor the formulation to include more than one mineral; however, this will increase the uncertainty of the results.