Fractures serve as important conduits for subsurface fluid flow and their presence can transform an otherwise unproductive rock formation into an economic hydrocarbon reservoir. Large through going fracture zones are targeted for wellbore intersection because of their high transmissivity and ability to drain a large volume of reservoir rock. On the other hand, gouge filled faults may serve as permeability barriers that inhibit flow to the wellbore. Thus, fractures represent major heterogeneities within the reservoir. Predicting the spatial distribution and fluid flow properties of fracture systems in the subsurface is an integral component of reservoir characterization, and is the primary goal of our research project. Work to date can be divided into two main efforts: (1) evaluating the effects of mechanical stratigraphy on fracture scaling relations, and (2) spatial analysis of secondary porosity from limestone core. In the first project, we are analyzing veins (mineral-filled fractures) at the microscopic scale from samples taken from an outcrop of the Monterey Formation, California. Samples were collected from various stratigraphic layers, as well as at different structural positions around a small fold. We are also quantifying the fracture-related porosity from digital images of thin sections. This will enable us to map the distribution of porosity and fracture permeability around the fold, thus providing important constraints on fluid flow in subsurface reservoirs. In the microstructural analysis of fracture aperture, fracture length, and fracture related strain, we have analyzed 18 samples by conducting 1770 scanline surveys of digital images. The image processing software we are employing allows for the rapid collection of fracture aperture, length and spacing measurements as well as for their direct transfer into spreadsheets. A total of 15,766 individual measurements have been taken from these samples. The dataset will provide the opportunity to address a wide range of important issues, such as the ability to predict rock properties beyond the scale of observation, factors that lead to breaks in scaling relations, and fluid flow through fractured rock masses. For the second research component, we are characterizing the distribution and geometry of solution-enhanced pores in limestones, an important reservoir rock that is notorious for its irregular production history. Using a GIS (Geographic Information System) software package, we are mapping the density of pores, pore geometry and pore size from a 30 foot section of the Biscayne aquifer. The Biscayne aquifer is a porous limestone that serves as the primary source of water for the rapidly growing population of South Florida. Preliminary results reveal a heterogeneous distribution of pore density, which can be directly related to stratigraphic layering in the limestone. Further analysis will quantify the extent of high-density pore zones, and their contribution to enhanced fluid flow.