This study used simulated formation water (15 g/L CaCl₂) from a certain area of Xinjiang Oilfield as the experimental medium., and employed a high-pressure sealed reaction vessel and a sapphire window to systematically investigate the effects of water content (30%–70%), initial pressure (2–14 MPa), and the intervention of CH₄ on the critical point of CO₂ hydrate formation. The differences between the ‘visual confirmation’ method and the temperature-pressure curve inflection point method for determining hydrate formation were also compared. The study found that in a single CO₂ system under a constant pressure of 5 MPa and a water content of 30%–70%, no visible hydrate was observed with the naked eye. However, the inflection point method showed that the theoretical critical temperature and pressure increased with the increase in water content. For a 50% water content system, there was a threshold pressure range of 8–11 MPa. Only when the initial pressure was higher than this threshold would visible hydrates form, and the critical point shifted upward with the increase in pressure. In the CO₂-CH₄ mixed system, the critical point under a constant pressure of 10 MPa showed a V-shaped trend with changes in gas ratio, with a minimum point at a 1:1 ratio; the constant ratio and variable pressure experiment indicated that the intervention of CH₄ significantly increased the critical temperature and pressure. Furthermore, the introduction of CH₄ changed the growth position of hydrates, shifting them from the gas-liquid interface to the liquid phase matrix. The study revealed the pressure threshold effect of CO₂ hydrate formation in high mineralization degree formation water systems and the gas component competition mechanism: when the ratio of the two components is balanced, the competitive effect is minimized, forming the optimal formation conditions; as the proportion of CH₄ increases, its competitive advantage strengthens, not only increasing the critical temperature and pressure, but also driving the shift of the hydrate growth position, demonstrating the decisive regulatory role of gas components on the equilibrium and formation kinetics of hydrates, providing experimental basis for the risk prevention of hydrates in the CO₂ flooding process.

Accurate prediction of the composition of pyrolysis products is the prerequisite for achieving directional regulation of organic-rich shale pyrolysis and conversion products. In this paper, the classical segmented pyrolysis kinetics model and a new refined pyrolysis kinetics model were used to forecast the composition distribution of hydrocarbon generation products co-heated by supercritical water and medium and low maturity organic-rich shale. The prediction accuracy of the two reaction kinetics models for the composition of pyrolysis products of organic-rich shale was compared. The reaction path of hydrocarbon generation in centimeter sized organic-rich shale under the action of supercritical water was identified. The results show that the prediction accuracy of the classical segmented pyrolysis kinetics model was poor at the initial stage of the reaction, and gradually increased with increasing time. The prediction error can reach less than 25% when the reaction time was 12 h. The new refined model of reaction kinetics established is better than the classical reaction kinetics model in predicting the product distribution of pyrolysis oil and gas, and its prediction error is less than 14% in this paper. The reaction paths of hydrocarbon generation in centimeter sized organic-rich shale under supercritical water conversion mainly include organic-rich shale directly generates asphaltene and saturated hydrocarbon, asphaltene pyrolysis generates saturated hydrocarbon, aromatic hydrocarbon and resin, saturated hydrocarbon, aromatic hydrocarbon and resin polymerization generates asphaltene, and saturated hydrocarbon, resin and asphaltene generates gas. The reason for the difference of centimeter sized and millimeter sized medium and low maturity organic-rich shales hydrocarbon generation in supercritical water is that the increase of shale size promotes the reaction path of polymerization of saturated hydrocarbon and aromatic hydrocarbon to asphaltene.