Predicting flow properties in diagenetically-altered media with multi-scale process-based modeling: A Wilcox Formation case study

Abstract

Two approaches to capture the complex texture of Wilcox sandstone samples in a pore-scale model are employed: a process-based method and an image-based method. In the process-based method, petrographic analyses from transmitted light microscopy are used to infer the diagenetic history of the rock. Key steps in the diagenesis are quantitatively followed using a multi-scale pore-network modeling method to reconstruct the porous medium at different times in its history, including the final state. Further information about pore sizes is gathered from scanning electron microscopy and nitrogen adsorption hysteresis measurements. The ability to incorporate texture information of each diagenetic stage of a tight gas sandstone into a predictive multi-scale pore-network model is a novel aspect of this work. In the image-based method, a micro-CT image of the sample is acquired and a pore-network model is extracted based on skeletonizing the resolvable pore space and mapping clusters of micropores to the unresolved porous areas. The paragenesis of the formation was not captured using the image-based method since sufficient details of its history could not be extracted. The process-based and image-based methods produce comparable drainage capillary pressure curves. While the drainage relative permeability curves in both methods display permeability jail effect, they considerably differ from each other quantitatively. The process-based method produced a higher porosity and permeability compared to the image-based method which is potentially due to the lower degree of its disorder. High uncertainties in the petrophysical properties of tight gas sandstones is a costly challenge in their reservoir development. Our work provides insights into the effect of pore texture from different scales on rock fluid properties. Furthermore, the methods demonstrated in this work can be pursued to extrapolate tight gas sandstone petrophysical properties between wells and throughout paragenetic sequences. • An algorithm for the inclusion of oversize pores in process-based modeling is introduced and implemented. • A comparison of process-based and image-based multi-scale pore-network modeling methods in predicting several petrophysical properties is conducted. • Sedimentary rock fragments and dissolving feldspars can be crucial for fluid flow for the Wilcox Formation. • Permeability jail effect is observed during primary drainage using both methods.