Gas and water relative permeability in different coals: Model match and new insights

• Published relative permeability data for different coals have been well matched.
• The fitted cleat size distribution index falls in the range of 0.3 to 8.8.
• The fitted tortuosity parameter falls in the range of 0 to 2.
• U shape correlation between cleat size distribution index and coal rank observed.

A recently derived relative permeability model for coal reservoirs has been applied to fit the published gas–water relative permeability data for different coals from Europe, China, Australia and the U.S., which exhibit a myriad of shapes and curvatures. The two-parameter model is shown to be capable of describing a total of 32 sets of data, including those history-matched from field production and laboratory core flooding tests as well as laboratory-measured ones. The fitted values of the two model parameters, namely cleat tortuosity parameter (η) and cleat size distribution index (λ), fall in the range between 0 and 2, and 0.3 and 8.8, respectively. For the European and Chinese coals whose rank information is available, there is tentative evidence that a U shape correlation between λ and coal rank exists, whereas no discernible trend is observed for η. This U shape dependency on coal rank has also been reported for some other coal properties such as total porosity.