Microtextural, elastic and transport properties of source rocks [electronic resource]
Keywords: Geophysics

This dissertation addresses recurrent questions in hydrocarbon reservoir characterization. In particular, the major focus of this research volume is microtextural characterization of source rock fabric as well as elastic and transport properties of source rocks. Source rocks are one of the most complicated and intriguing natural materials on earth. Their multiphase composition is continually evolving over various scales of length and time, creating the most heterogeneous class of rocks in existence. The heterogeneities are present from the submicroscopic scale to the macroscopic scale, and all contribute to a pronounced anisotropy and large variety of shale macroscopic behavior. Moreover, the effects of the multiphase composition are amplified within organic-rich rocks that contain varying amounts of kerogen. Despite significant research into the properties of kerogen, fundamental questions remain regarding how the intrinsic rock-physics properties of the organic fraction affect the macroscopic properties of host rocks. Because we do not fully understand the elastic properties of either the organic matter or the individual clay minerals present in source rocks, seismic velocity prediction in organic-rich shales remains challenging. Conventional measurements of 'macroscopic' or 'average' properties on core plugs are not sufficient to fully address the degree of property variation within organic-rich rocks. Alternatively, most analyses of organic matter rely on samples that have been isolated by dissolving the rock matrix. The properties of the organic matter before and after such isolation may be different, and all information about sample orientation is lost. In addition, comprehensive characterization of organic-rich rocks has been hindered by several factors: sample preparation is time-consuming, and the nanogranular nature of this rock type makes it difficult to link effective elastic properties to maceral properties, such as elastic moduli, composition, maturity, and quality. These difficulties have prevented us from building large databases, without which we cannot establish the accurate rock-physics models needed for inverting field geophysical data. I approach this issue using atomic-force microscopy based nanoindentation, coupled with scanning electron and confocal laser-scanning microscopy as a tool for visualization and identification of the organic part within shale, and to perform nanoscale elastic-property measurements. First, the microfabric of a set of source rock samples is characterized. The spatial and temporal link between organic matter and the stiff silicate mineral matrix is established, which leads to proposal of alternative Rock Physics modeling approach to organic-rich source rocks. Based on the nanoindentation measurements, I obtain elastic properties of source rock phases and provide several applications of these (nanoindentation-derived) elastic properties within a number of geomechanical problems. Finally, transport properties of various source rock formations are discussed based on comparison to more conventional reservoir rocks.