In this paper,anisotropy of resistivity of thin-bedded formation is investigated experimentally and numerically.The experiments consist of measurements of anisotropy of resistivity on twin-plugs of laminated cores as a function of oil/water saturation.Our results show a clear increase of the anisotropy of resistivity when Sw decreases.This result demonstrates that anisotropy of resistivity is induced by the difference of saturation between the sand layer(oil bearing)and the fine grain layers(water bearing).Our modeling work was designed to compare the robustness of various equations for estimating water saturation.Four models have been defined: a thinly laminated coarse grain sand,a thinly laminated fine grain sand,a thinly laminated sand-shale and a turbidite.The vertical and horizontal resistivity of each formation is calculated with a dual water model.This anisotropy of resistivity is used to compare the oil content in the original model and the one obtained from various Sw equations.This work demonstrates that the use of resistivity parallel(ρh)and transverse(ρv)to the bedding planes and an accurate volume of fine grain,gives better Sw values than shaly-sand equations when we know only the horizontal resistivity.In addition,a new Sw equation for shaly sandstone,which uses both ρv and ρh but does not require the knowledge of water resistivity,is proposed.
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