Fathoming the mechanics of shale gas production at the microscale

Abstract

Unlocked by advanced technologies, such as hydraulic fracturing and horizontal drilling, gas shale reservoirs constitute one of the most promising hydrocarbon resources around the world. A combination of ultra-small complex pore throat geometries and an incomplete knowledge of the pertinent physics are partly behind underperforming wells. Further progress in terms of gas recovery hinges on a thorough understanding of the gas behaviour in the pores and between them (i.e., permeability). In this work, we propose a geometrically accurate model from a shale formation inspired from Scanning Electron Microscopy (SEM) imaging. The computational model implements the equations of flow, Klinkenberg permeability and gas compressibility. To compare the model results with experimental measurements, a non-dimensionalisation approach was developed which considers the real gas behaviour and shale permeability characteristics. Non-dimensional gas velocity and flow-rate findings demonstrated an intricate but more realistic flowrate-pressure relationship compared to conventional reservoirs. Owing to its versatility, the non-dimensionalisation methodology can be adapted and generalised to other complex geologies such as carbonate formations. Meanwhile, a flowrate sensitivity analysis was conducted in the context of the matrix and the fluid properties. The sensitivity analysis revealed that, although permeability is the most prominent parameter governing flowrate, reservoir pressure requires even more attention, since it changes considerably during gas production and it can be managed by a suitable development strategy.