The significant increase in the contribution of unconventional oil and gas reservoirs to the world’s total petroleum production has led to a corresponding interest in the study of these resources over the last decade. Various researchers have focused on the study of storage and transport mechanisms that are unique to these naturally fractured unconventional resources. In this chapter, we show how to extend the MATLAB Reservoir Simulation Toolbox (MRST) to model these physical mechanisms using a shale module that we have developed. Some of the features of this module include the modeling of sorption, molecular diffusion, stress-sensitive permeability, and realistic fractures in any orientation. This chapter starts with a discussion of the design of our shale module. We then present the governing equations for compositional simulation and show how to use the hfm and compositional modules in MRST to perform a compositional simulation in a fractured reservoir. To demonstrate the practicality of our \texttt{shale} module, we model an Eagle Ford shale oil reservoir with hundreds of natural fractures. We conclude this chapter with a discussion of how to implement certain storage and transport mechanisms that are unique to shale oil/gas reservoirs.