Displacement of shale gas confined in illite shale by flue gas: A molecular simulation study

The shale gas is an unconventional supplementary energy to traditional fossil energy, and is stored in layered rocks with low permeability and porosity, which leads to the difficulty for exploration of shale gas. Therefore, using CO2 gas to displace shale gas has become an important topic. In this work, we use molecular simulations to study the displacement of shale gas by flue gas rather than CO2, in which flue gas is modeled as a binary mixture of CO2 and N2 and the shale model is represented by inorganic Illite and organic methylnaphthalene. CH4 is used as a shale gas model. Compared to the pure CO2, flue gas is easily available and the cost of displacement by flue gas would become lower. Results indicate that the pore size of shale is an important factor in the process of displacing shale gas and simultaneously sequestrating flue gas, while the flue gas N2-CO2 ratio shows a small effect on the process of CH4 displacement, because the high partial pressure of flue gas is the main driving force for displacement of shale gas. Moreover, the geological condition also has a significant effect on the process of CH4 displacement by flue gas. Therefore, we suggest that the burial depth of 1 km is suitable operation condition for shale gas displacement. It is expected that this work provides a useful guidance for exploitation of shale gas and sequestration of greenhouse gas.