A Thermal Simulation of the Influence of Volcanic Fluids on Source Rock

Abstract

In the Songliao Basin, Cretaceous Yingcheng volcanic rock is an important natural gas reservoir. Volcanic rocks and source rocks interspersed in the fault depressions represent ideal places for studying the interactions between volcanic fluids and source rock. Thermal simulations for this study include the dry system and the fluid system. The characteristics of the gas yield and gas composition were analyzed under four temperature gradients: 300°C, 350°C, 400°C, and 450°C. The results of the experiment showed that in both systems, the gas yield increases with an increase in temperature. The gas compositions are similar, containing H₂, CO, CO₂, and gaseous C₁-C₅ hydrocarbons. Compared with the dry system, the gas yield of the volcanic fluid to mudstone system has a critical temperature between 350°C and 450°C. When the temperature is below the critical temperature, the gas yield increases, and vice versa. The generation of CO₂ is promoted by the volcanic fluids, but the generation of H₂ and C₁–C₅ series gaseous hydrocarbons is simultaneously restrained. In the fluid system, the content of H₂ and gaseous C₁–C₅ hydrocarbons is lower, but CO₂ content is greater than in the dry system. This can explain the fact that a huge amount of CO₂ gas is present as a reservoir in the Songliao Basin.

Keywords:

• volcanic fluid
• source rock
• thermal simulation
• Songliao basin
• gas yield