| dc.description.abstract | Organic-rich mudrocks can have heterogeneous pore networks that affect hydrocarbon saturation and fluid flow. Organic porosity, a term used to describe pores within organic matter, contributes to a substantial proportion of the total porosity in some mudrock reservoirs. However, predicting organic pore distribution remains enigmatic. This thesis explores possible geochemical controls on organic porosity distribution and abundance with regard to organic matter type and thermal maturity using RockEval, Raman spectroscopy, focused ion beam – scanning electron microscopy (FIB-SEM), and Helium pycnometry. Comparison of RockEval and porosity data from three mudrock reservoirs were analyzed: the Ordovician Viola Group, the Cretaceous Niobrara Formation, and the Silurian “hot shale” indicates that organic porosity increases with increasing thermal maturity and decreasing hydrogen index (HI) values. Increases in both measured porosity and observed porosity (from FIB-SEM and Helium pycnometry data) with decreasing HI values (from Rock Eval data) are interpreted to result from differences in the molecular structure of Type III organic matter versus Type II organic matter. Higher organic porosity in Type III organic matter samples with low HI values is the result of increasing aromaticity, which is interpreted from RockEval and Raman spectroscopic data. Several different organic matter morphologies (lamellar and isolated macerals) coexist in certain samples, organic porosity is only located within isolated organic macerals. Based on Raman spectroscopic data, the interpreted mechanism for which increasing aromaticity develops organic pore space is the restructuring of organic macromolecules which results in the formation of aromatic islands surrounded by void space (created by the release of volatiles). With this conceptual model, reservoirs with more Type III organic matter should have a greater proportion of organic porosity, and potentially higher total porosity, than those with Type II organic matter. These results impact organic porosity prediction and interpretation of total porosity measurements by showing that both the intrinsic cellular structure of the organic matter in a rock and thermal maturity influence the nature, amount, and distribution of organic porosity. | |
