Around the Elmworth gas field, the Falher Member comprises five transgressive and regressive cycles. Coarse sandstones and conglomerates of the shore zone form conventional reservoirs with porosities up to 15% and permeabilities to 1 darcy. The fine-grained shoreface and shallow-marine sandstones are "tight-sands" with permeabilities of 0.001 to 0.5 md. Porosity loss because of (1) formation of quartz overgrowths, (2) crushing of sedimentary rock fragments, and (3) cementation by carbonates and clays. The tight sands have lower permeabilities than some shales and form the seals that trap gas in the basin by retarding updip flow.--Modified journal abstract

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