Petrophysics is the study if the physical properties of the rocks. The main goal of our petrophysical studies is assessment of the controlling parameters, such as porosity, pore structures, pressure, saturation and mineralogy on sonic velocity and permeability in carbonates. Understanding the relative importance of all these parameters is important to assess the uncertainties that arise when using theoretical equations to interpret or predict velocity, porosity and permeability trends from subsurface data sets. 
Our current focus is to test several assumptions in rock physics. For example, experiments have revealed that the basic assumption in Gassmann’s equation, which says that the dry and wet shear moduli are constant, needs to be questioned in carbonates. A series of projects address the causes for this shear modulus variability and the effect of saturation on sonic velocity in carbonates. The results of these experiments will provide a guidance of assessing uncertainties in AVO analysis and time-lapse seismic surveys. 
In earlier studies we documented the importance of pore structures on velocity at a given porosity, and qualitatively related pore types to these velocity variations. Digital image analysis of pore structures yield a quantitative way to estimate their influence on sonic velocity and permeability. In addition, high-resolution CT–scans of plug samples increases our pore structure analysis from 2-D to 3-D. Over the last years we started to assemble a data-base on dolomites and plan to focus on the sonic velocity and permeability in dolomites to get a better understanding of the petrophysical behavior of various types of dolomite. 
Core material from several drill sites are used for integrated studies of the sedimentologic, diagenetic, petrophysical characteristics of oolithic grainstone bodies which determine the influence of early cementation on sonic and hydraulic properties, and the cause for the heterogeneity in such oolithic grainstone settings.

Using a newly developed GPR system with the capability of efficiently acquiring high-resolution data at centimeter precision, we have imaged fractures, deformation bands, and karst features in porous and tight Cretaceous carbonates. The partitioning of the rock by fractures and karst at and below the GPR wavelength, thin vertical fractures and irregular karst features and a faint stratigraphy present a challenging task for GPR imaging. A crucial aspect of fracture imaging is to design surveys with the optimal grid density, frequency and antenna polarization to collect non-aliased data with high- information content

Characterizing fracture patterns of reservoirs in the subsurface is a challenging task that requires a good understanding of the 3D geometry and distribution of the fractures as well as the processes controlling the distribution of fractures. Fracture characterization in outcrops relies mostly on scan line measurements to capture the properties of fractures including the type, orientation, length, aperture, spacing, density and fracture termination.The inability of this technique to visualize and analyze the fracture in three dimensions, however, limits the fracture characterization using this method. Likewise the 3D distribution of karst cavities is not discernable in outcrops but is of paramount importance for fluid flow in the subsurface. This study takes advantage of newly developed high precision and high resolution 3D GPR to image in 3D both fractures and the karst cavities in the shallow subsurface.

The goal of this GPR study is to achieve a full characterization of the subsurface fluid flow in terms of:

1. Water content changes and tracking of flooding/drainage boundaries. Application of the Topp petrophysical transfer function to time shift volumes quantifies the in-situ water content changes over time and space.
2. Flow propagation rates through major fluid conduits and the porous surrounding matrix.
3. Fluid mass balance used to verify the water content change computations.
4. Compare time-lapse GPR results with conventional infiltration and evaporation measurements performed in the field and on samples.

The electrical resistivity in fluid-filled sedimentary rocks is largely controlled by its pore space geometry, as the electric current is conducted predominantly through the pore fluid. Yet, in carbonates, the variation in electrical resistivity and the cementation factor for a given porosity are poorly understood. Many studies have recognized that acoustic velocity and permeability in carbonate rocks is dependent upon pore geometry. In this study we aim to explore the complex relationship between the shape and size of pores and pore throats and the flow of the electric charge. It is postulated that the carbonate pore structure exerts a strong control on the electrical resistivity.

The Pleistocene reefs that developed in the Dominican Republic over the past 1.8 million years provide an unique opportunity to study the complex three-dimensional architecture and controlling factors of fringing reef development during high frequency sea level cycles (see prospectus by Klaus et al.). Coral reefs present special challenges for geological and geophysical studies because reef growth is highly variable even over a small spatial scale. A dedicated ground-truth data set needs to be developed for assessing the variability in petrophysical properties in the reef rocks.