Low-resistivity beds may produce water-free

Abstract

To analyze whether a zone will produce water-free from a low-resistivity formation, shaly sand models that correct log-indicated water saturations to obtain true formation water saturation can be used. Low-resistivity readings can by caused by microporosity or from clay minerals and pyrite. Shale models relating resistivity to water saturation are described. The effects of laminated shales, dispersed shales and structured shales on the resistivity are considered. The total shale model, Patchett, and Rausch model and effective-medium resistivity model are described. Three examples relating to tertiary sandstone, shaly sandstone and a Pleistocene sandstone are presented