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 highefficiency 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.