Thin Bed Reservoirs Formation Evaluation without Bimodal Sand-shale Assumption

Thinly bedded reservoirs have been produced for many years, but their identification and quantitative evaluation remains a difficult challenge, since conventional deep induction resistivity lacks sensitivity to thin resistive pay sands. Introduction of vertical resistivity with triaxial induction tools overcame this, but analysis has been built on the simplification of a bimodal formation model because deep resistivity measurements have limited vertical resolution. This model assumes that formation consists of indiscernible thin sand and shale layers and all sand and all shale layers are identical. This assumption leads to significant overestimation of producible hydrocarbon volume if formation is not bimodal. Alternative model free of bimodal assumption is proposed which integrates textural measurements with resistivity via parameterization of the pore water volume. Flags to indicate applicability of bimodal approximation are constructed. Hydrocarbon volume estimates resolution matched to textural data are made. Proposed approach either used just as thin beds indicator in conjunction with known industry methods or used to incorporate higher resolution textural measurements is capable to deliver significantly better-quality estimates for producible hydrocarbons in thinly laminated siliciclastic reservoirs.