Effects of testing method, lithology and fluid-rock interactions on shale permeability: A review of laboratory measurements

Shale permeability is very important for the prediction and evaluation of shale reservoir performance. In this paper, we review recent work on how shale permeability is affected by testing method, lithology, and fluid-rock interaction. Both the steady-state method and the pulse-decay method are used for shale permeability tests. However, the steady-state method is time-consuming, and the unsteady-state method may over-estimate permeability. Permeability is strongly affected by mesopores, macmpores and clays, rather than porosity and minerals like quartz and carbonates. Water/brine-rock interactions, CO2-rock interactions, and CO2-liquid-rock interactions occur when hydraulic fracturing, CO2 fracturing, and mixed fracturing respectively, are applied. For hydraulic fracturing, clay welling and water lock decrease permeability, while carbonates dissolution increases permeability. In CO2 fracturing, shale permeability is affected by CO2 adsorption, CO2 phase, and imbibition time. For mixed fracturing, permeability variations are complex because of the violent physical and chemical reactions.