Knowing the wetting condition of a reservoir at an early stagernis crucial for selecting optimum field development options.rnPaying insufficient attention to the wetting condition e.g.rnAssuming water wet behavior) may result in incorrect STOIIPrnestimates, and in unexpected dynamic behavior, e.g. underrnwater flooding.rnA novel method is presented to determine the in-siturnwettability of rocks from NMR logs. The method is based onrnthe fact that fluids experience additional relaxation when inrndirect contact with the rock surface. A reduction of the oilrnrelaxation time away from its bulk value is generally known asrna qualitative wettability indicator. Through detailed modelingrnof the NMR response, this concept has been further developedrnto provide a quantitative wettability index. It is based on arnmodel for the microscopic distribution of the crude oil and thernwetting state of the rock at any given overall saturation. Thernmethod requires an NMR measurement on a samplerncontaining two reservoir fluids, I.e. Brine and crude oil. Multiacquisitionrnschemes including diffusion effects make therninterpretation more robust, but a normal NMR acquisitionrnsuffices and can be made with all available NMR toolsrn(wireline and LWD).rnThe new NMR based method has been extensivelyrnverified on core data against standard wettability tests.rnApplication to NMR logs from several fields, and in particularrncarbonates, show continuous profiles of varying wettability,rnranging from fairly oil-wet, through intermediate, to waterwet,rnall in line with the available core data.
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