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

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 (eta) and cleat size distribution index (lambda), 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 lambda and coal rank exists, whereas no discernible trend is observed fors. This U shape dependency on coal rank has also been reported for some other coal properties such as total porosity. (C) 2013 Elsevier B.V. All rights reserved.