Groundwater flow-controlled migration of dissolved microbial gas in the Eastern Hungarian Pannonian Basin

The formation of commercial microbial gas accumulations requires specific migration and accumulation conditions which can be effectively provided by groundwater flow systems. Namely, if microbial methane can be gathered and transported in aqueous solution over large lateral distances, great amounts of free gas can be exsolved where flows turn upward, causing a decrease in solubility. Based on this concept and the flow pattern of regional scale topography-driven groundwater flow systems, the present study built a simplistic 2D model in MS Excel including a methane solubility database with 32 000 data points. The model can calculate the required flow pathway length to saturate groundwater with methane, the amount of free gas that can be released in a potential accumulation zone and the necessary time interval for the whole process. Application of the model was demonstrated based on the geological and hydrogeological conditions of a study area in the Central Pannonian Basin (Hungary), focusing on the Hajdúszoboszló gas field. In light of the upscaled results of the 2D model, the known microbial gas accumulations of the study area could be charged according to the model. In addition, parameter sensitivity analysis also provided valuable insights into the complex mechanisms of microbial gas migration.