CO2-Enhanced Gas Recovery (CO2-EGR): Multi-Scale Simulation of Rarefied Gas Flows in Porous Media

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The shale gas revolution in North America has transformed the energy sector in terms of prices, consumption, and helped to reduce CO2 emission. In the UK, unconventional gas could replace rapidly depleting North Sea reserves and help to build a stronger and more competitive economy. However, although many countries/regions want to copy this success, limited progress has been made, due to the short history of shale gas extraction (started from this century) and long production span (usually larger than 20 years) of unconventional reservoirs. The shale gas extraction process is currently trial-and-error, as limited engineering experience has been gained.To make shale gas extraction and carbon sequestration in unconventional reservoirs economical and safe, we need to quantify the gas transport in the ultra-tight porous media typically found in unconventional reservoirs. Understanding of the gas flow helps to determine the drainage area and life span of the shale formations, which leads to optimized production process. For example, we can better determine the distance between the wells to achieve the same production goal but with much reduced numbers of drilling wells and the corresponding environmental impact. We can also determine how much CO2 should be injected and how long the well should be sealed in CO2-enhanced gas recovery (CO2-EGR) stage. Finally, new gas transport results are needed to assess how much CO2 can be stored, and hence to design long-term carbon storage strategies. Experimental measurement of gas permeability is extremely difficult for ultra-tight porous media. Numerical simulation, based on digital images of shale samples, becomes key to understanding the non-trivial gas transport. This is supported by recent advances in obtaining high-resolution images of shale rocks by using Focused-Ion-Beam/Scanning Electron and Helium-Ion Microscopes. With this technology advancement, this research project will develop new kinetic models and high-performance computer codes to investigate CO2-EGR in ultra-tight porous media, where the conventional Navier-Stokes equations fail and Molecular Dynamics simulations are too expensive. Based on the digital image of shale rocks, we will investigate factors that could optimise the production process for maximum recovery of methane from shale. This fundamental research will enable us to make well-informed predictions of shale gas production rates, and, in particular, help to assess the economic and environmental value of CO2-EGR and subsequent long-term CO2 sequestration.