Numerical Modelling of Underground Methane Leakage from the Shale Gas Reservoirs

Shale gas is becoming one of the fastest growing fields of study in the oil and gas industry with global reserves estimated to be more than 200 trillion cubic meters. However, development of shale gas reservoirs potentially contaminates air and underground fresh water particularly due to hydraulic fractures which serve as pathways for gas leakage. In this study, the impact of shale gas leakage in hydraulically fractured reservoirs with improper well plugging and abandonment practices were evaluated. The reservoir under study consisted of 4 zones- Fresh water, Impermeable, Depleted and Shale zones. The results of this simulation study shows that the large volume of shale gas is estimated to be produced in fresh water wells in comparison with the hydraulically fractured shale gas well. Also, the effect of heterogeneity of fracture permeability on underground shale gas leakage was studied. The results show negligible difference in cumulative gas produced for a 20% deviation from reference permeability and 40% deviation from reference porosity. Hence, it can be inferred that for high fracture permeability values modelled in this study, significant variations do not largely influence gas leakage.