The Study of Coal Beds within Gas Sandstones of Whicher Range Field in the Perth Basin, Western Australia

Gas reservoir sandstones of the Whicher Range field in the Perth Basin, as a part of unconventional reservoirs, consist of sandstone, siltstone, shale and thin coal interlayers which have been developed in a meandering river system. Thin inerlayers of coal intercalated with fine grained silt and shale sediments are considered as the gas sources within the sandstones. In this study, in order to recognize these coals interlayers based on their well log characteristics, gamma ray, density and sonic logs in one well of the studied field in concordance with core properties were investigated. The results show that these units generally are characterized with low density log, high sonic and medium gamma ray values in comparison with the other reservoir units (i.e., clean sands, shaly sands, shales). Regarding the thin layering attitude and also the association and intercalation of the coal units with fine grained shaly and silty sediments, their gamma and sonic values have been to some extent affected, and have overlapping with the other reservoir rock units. Therefore, density log provides more reliable responses for their study. Also, in reservoir studies of the field for their differentiation, it is better to consider these units as thin coal bearing intervals. The results of this study can be used in the more exact evaluation of petrophysical properties, and sequence stratigraphy studies of the reservoir sandstones in the field.