Wells for Engineered Geothermal Systems (EGS) typically occur in conditions presenting significant challenges for conventional rotary and percussive drilling technologies: granitic rocks that reduce drilling speeds and cause substantial equipment wear. Thermal spallation drilling, in which rock is fragmented by high temperature rather than mechanical means, offers a potential solution to these problems. However, much of the knowledge surrounding this drilling technique is empirical - based on laboratory experiments that may or may not represent field conditions. This paper outlines a new numerical modeling effort investigating the grain-scale processes governing thermal spallation drilling. Several factors affect spall production at the mesoscale, including grain size and size distribution, surface temperatures and material heterogeneity. To investigate the relative influence of these factors, we have conducted a series of simulations using GEODYN - a parallel Eulerian solid and fluid dynamics code. In this paper, we describe a two-dimensional model used to simulate the grain-scale processes and present preliminary results from this modeling effort.