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fax 01-972-952-9435. AbstractOptimizing production in mature fields depends greatly on proper reservoir characterization. After a certain period of production, a reservoir may exhibit changes in its properties because of changes in formation water salinity arising from water injection, left-behind residual oil in the rock, and changes in pressure regime. These factors, combined with complexities in the original reservoirs properties, such as rapid variations in permeability and oil viscosity, strongly affect the degree of uncertainty in evaluating and predicting productive zones when using only conventional logging methods.These variations affect the responses of most conventional logs. Consequently, traditional log analysis models may fail to provide realistic evaluation results and may not achieve appropriate production forecasts. Common examples of such failures have been recognized when producing high water content from a zone believed to be hydrocarbon or when perforating an interval that does not produce.New logging technologies, such as magnetic resonance imaging (MRI), demonstrate promising formation evaluation results in mature fields. The MRI technology helps to properly distinguish candidate production zones and provide key in-situ reservoir properties, including hydrocarbon type, reservoir quality in terms of permeability and porosity, and barrier zones. The ability of MRI to determine oil viscosity influences the selection and elimination of zones to be produced based on its fluids mobilities. Thus, MRI serves well in the selection of hydrocarbon producing intervals.This paper discusses the effectiveness of applying the MRI technology in characterizing the reservoir fluid properties in the El Furrial field, East Venezuela. It also highlights the value of this technology in minimizing the cost of mis-identified zones for production or testing by identifying best candidate intervals. Verification of the MRI results with actual production testing and/or formation pressure measurements will be demonstrated in the article.