Influential factors and mechanisms of hydrogen production via in-situ heavy oil gasification

This study aims to determine the reaction mechanisms behind the in-situ gasification （ISG） of heavy oil and assess the feasibility of hydrogen production using exhaust heat from the steam chamber of steam-assisted gravity drainage （SAGD） and from in-situ combustion. Through experiments with a high-temperature high-pressure （HTHP） autoclave， we systematically explore the impacts of different atmospheres ［air， nitrogen （N2）， and carbon dioxide （CO2）］， varying temperatures （200 ℃ to 300 ℃）， and core powder catalysts of the same sandstone sample on hydrogen production from heavy oil. Using experiments with a fixed pressure （4 MPa）， constant temperatures， and a reaction time of 6 h under multiple atmospheres， as well as mass spectrometry， we reveal the potential and reaction mechanisms of hydrogen production under low temperatures ranging from 200 ℃ to 300 ℃. The results show that the N2 atmosphere yields the highest hydrogen production performance （hydrogen concentration： 4.4%） at a temperature of 300 ℃ attributed to the inert nature of N2， which inhibits hydrogen consumption. In contrast， the CO2 atmosphere shows relatively low hydrogen production efficiency. This occurred primarily because CO2 reacted with heavy oil to generate CO， thereby consuming part of the available hydrogen. The temperature-dependent hydrogen production process can be divided into three stages： the initial stage （150 ℃ to 250 ℃）， the pyrolysis stage （250 ℃ to 300 ℃）， and the high-efficiency stage （above 300 ℃）. Under the N2 atmosphere， core powder demonstrates a significant catalytic effect， increasing hydrogen production by 33%. This highlights the role of formation minerals in promoting low-temperature hydrogen production. This study clarifies the hydrogen production mechanisms under different conditions， providing a novel strategy for converting heavy oil into green resources.