TIME-LAPSED DIFFUSIVITY LOGGING FOR MONITORING ENHANCED OIL RECOVERY

摘要

The use of time-lapsed NMR diffusivity measurements in an observation well isdisclosed.The observation well is cased in the zone of interest with non-magnetic andnon-conductivecasing that is invisible to the NMR tool. Second, because NMR measurementshave a deadzone in front of the antenna depending on the spatial variation of the fixedmagnet strength,for example about 2.7 inches, a distance between the casing and the formationis reduced toless than the dead zone length by drilling the observation well at smalldeviation of about 5°and running the casing without centralizers. Both the casing and the pad-typeNMR tool willfollow the low side of the borehole, ensuring the measurement volume of theNMR tool isinside the formation and beyond the annulus. With the appropriate observationwellcompletion, time-lapse diffusivity measurements with pad-type NMR tools canaddressseveral shortcomings in the current practice of monitoring EOR processes thatrely uponchanges in density and hydrogen index (HI). Various uses of NMR imaging inwells casedwith non-metallic casing are also disclosed.