Physico-chemical variations of shale with artificial maturation: In the presence and absence of water

Abstract

Pyrolysis is widely employed to simulate the oil generation process in the lab. This method has been used so far to study systematic evolution of pore structures or geochemical properties of source rocks during thermal maturation. Although the importance, variations in mechanical properties of shale samples during the pyrolysis which plays important role in unconventional reservoir development are rarely studied. Herein, we combined grid nanoindentation method with gas adsorption, organic petrology and bulk geochemical analysis to evaluate changes in mechanical properties of shale samples under anhydrous pyrolysis (AHP) and hydrous pyrolysis (HP). The results showed that thermal maturity (%BRo) of the products is different under these two separate pyrolysis methods. Moreover, at the same pyrolysis temperature, mechanical parameters (i.e., Young's modulus, hardness, and fracture toughness) of the HP product were found to be smaller than those of the AHP product. During the pyrolysis (temperature from 300 to 450 °C), the reduction in the mechanical parameters (mean Young's modulus, mean hardness, and mean fracture toughness) following AHP and HP are more than 40%, which must be considered in the development of unconventional reservoirs where mechanical parameters are critical for successful field operations. Most importantly, this study confirmed that water is a significant factor in physico-chemical parameters of the pyrolyzates, which should be considered in the development plans of the formations that will undergo in situ conversion.