Technologies merging enhanced oil recovery with in situ upgrading can significantly increase the economic and environmental efficiency of unconventional oil exploitation. This work targets understanding the effects of thermal processing in a porous medium at moderate temperatures (340-370 degrees C) and residence time between 12 and 48 h for Athabasca bitumen. The main limitation for upgrading via thermal cracking in the reservoir is the formation of coke precursors. Vacuum residue (VR) conversions above 32% fail to produce a stable product. Below 32% VR conversion transporting oil properties are just slightly improved. Product viscosity is reduced by 1-2 orders of magnitude, while moderate improvement in other properties are achieved such as 3 points increase in API gravity when stable product is the limit and 7-23% reduction in sulfur content. Additionally, coke precursors are significantly retained by the sand matrix, as analyzed by Microcarbon residue testing of the sand. This retention may in time cause damage to the porous media, thus limiting the applicability of thermal cracking as an in situ upgrading process. The presence of the porous media increases the apparent reaction order for the Vacuum Residue conversion to a second order reaction. A five lump kinetic model with seven reactions was successfully used to predict the product distribution with an overall error of 7% and excellent correlation to Arrhenius law. Obtained activation energies are in the range of 100-250 kJ/mol. (C) 2017 Elsevier Ltd. All rights reserved.