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.

This paper investigates the influence of reaction atmosphere and operation parameters of the lightening process under high temperature and high pressure on high-viscosity shale oil using an experimental approach. Two types of experiments were implemented, one involving a thermogravimetric analyzer and another using an autoclave to carry out the lightening process. By these two kinds of experiments, the effects of reaction atmosphere and operation parameters on the lightening efficiency were clarified. As for the reaction atmosphere, the effects of CO₂, N₂ and air were separately evaluated. As for the operation parameters, the effects of heating rate and formation rock were investigated. The results indicate that under a CO₂ atmosphere, the lightening reaction is more intense than that under the other two gas phases, and it gains the highest reaction rate. Part of the minerals in the formation rock can be treated as catalyst in the shale oil lightening process. With the formation rock being present, the reaction rate increases significantly and higher contents of light components are obtained in both the lightened shale oil and gas phase. For the kinetic parameters in the lightening process, proportional relationships between the kinetic parameters and heating rates under CO₂ atmosphere with and without formation rock were identified. The findings of this study can provide guidance for enhancing high-viscosity shale oil using an in-situ lightening process.

The high recovery performance of steam-assisted gravity drainage (SAGD) makes it a popular option for heavy oil resources. Currently, most of the heavy oil reservoirs developed by SAGD in China are in the late development phase, with high energy consumption due to reduced thermal efficiency. The use of SAGD wind-down processes involving CO₂ in combination with steam for heavy oil recovery is considered as a viable alternative to limit energy consumption, and also reduce the amount of greenhouse gas emissions by leaving CO₂ behind in the reservoir. Study reveals that the dissolution and demulsification of CO₂ in crude oil can reduce the viscosity of emulsified heavy oil by more than 50%. When the steam chamber temperature reaches 200 ${}^{\circ }$C, the amount of solid phase deposition induced by CO₂ extraction is only 0.016 kg/m ${}^3$, the rock wettability changes from lipophilic to hydrophilic, and the higher the reservoir temperature, the stronger the hydrophilicity is, which reduces the adhesion power of the oil phase and facilitates the stripping of crude oil from the rock surface. Numerical simulation studies have been carried out utilizing STARS to obtain energy efficient utilization and improved steam chamber characteristics. Heat loss from SAGD baseline is 1.77 times that with CO₂ injection process, but the recovery factor is only 2.48% higher. At the initial stage with CO₂ injection, the steam chamber continues its lateral expanding, which increases the recovery factor at the initial stage of CO₂ injection by about 6%. One year after CO₂ injection, gas channeling results in lower recovery than traditional SAGD process, and 38.4% of the injected CO₂ is stored in the reservoir from this study.