Methods and means for measurement of the water-oil interface within a reservoir using an x-ray source

An x-ray-based reservoir evaluation tool for measurement variations in formation density anticipated at the water-oil interface of a reservoir is provided, the tool including at least: an internal length comprising a sonde section, wherein said sonde section further comprises an x-ray source; radiation measuring detectors; sonde-dependent electronics; and a plurality of tool logic electronics and PSUs. A method of using an x-ray based reservoir evaluation tool for measuring variations in formation density anticipated at the water-oil interface of a reservoir is also provided, the method including at least the following steps: using x-rays to illuminate the formation surrounding the cased borehole; uses detectors to directly measure the density of the formation; using detectors to directly measure the effects on the measurement from tool stand-off or production liner attenuation; and employing techniques for compensating for the production liner and liner-annular region when computing the saturated formation density within the production interval.