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sponge cored. This hole section was then logged with a triplecombo for basic formation evaluation, and NMR determinedpore size distribution. Subsequently, the hole was underreamedto a 10” size with mud doped with MnCl 2 at a concentrationof 1.59 lb/bbl. The underreaming step is essential to removethe mud cake and allow the dopant to invade near thewellbore area and mix with the water. The mud density wascarefully designed to allow slightly overbalance drilling, typicallynot more than 500 psi, to avoid stripping the oil from thenear wellbore region. After enlarging and doping the well,NMR was run again. Figure 3 shows the relaxation time, T2,before and after doping. A clear shift in the water signal can beseen in the “after doping” relaxation time. A T2 cutoff was applied,and remaining oil volume and saturation were computed.A subsequent wireline formation tester (WFT) run indicateda water pressure gradient, and water samples werecollected. In this well, the ROS values from NMR are probablynear the SOR values, Condition 3 in Fig. 1. Sponge core measurements,which later became available, confirmed the previousfinding from NMR and WFT. Additionally, collected watersamples by WFT were analyzed at the laboratory for salinitymeasurements. This salinity data was used later on to refinethe resistivity-based saturation calculation. Water salinity informationis also useful for understanding the regional fluid’sdisplacement, and it can also to be used as a best estimate forfuture wells and as input for resistivity-based saturation calculation.Well #2Almost the same procedure used in Well #1 was followed inWell #2, except the hole size; here it was drilled at 5 7 ⁄8” andthen underreamed to 8 3 ⁄8”. Following the formation evaluationand ROS determination from NMR, a C/O log was run underflowing condition across the open hole. The flowing conditionis necessary to minimize potential fluid reinvasion effects onthe C/O logs 19 . In Fig. 4, the ROS determined from the C/Olog compared well with its counterpart from the NMR LILlog. ROS determined from laboratory tests of the sponge corealso showed good comparison with that from the NMR andC/O logs. In the area around this well, not much displacementis expected as the ROS values are probably very close to theSOR values, showing excellent sweep near the injectors.Well #3In this well, the new dielectric technology was utilized for ROSapplication and compared with NMR-LIL results. The dielectriclog was run before and after doping to ensure no side effectson the dielectric measurements. Figure 5 shows a compositeplot of the ROS from the NMR-LIL and dielectricmeasurements. Dielectric technology measures the water filledporosity, which is then displayed alongside total porosity takenfrom formation evaluation analysis. The ROS was then computedfrom the NMR and dielectric measurements, andshowed a very good match.Well #4Fig. 3. Track #4 shows the NMR relaxation time, T2, before doping; note the oiland water signals overlap at the long T2. After doping, T2 is shown in Track #3;the water signal is shortened and shifted to the left, splitting from the oil signal.The T2 cutoff (in magenta color) was applied, allowing the remaining oil andwater volumes computation in Track #2. Track #1 shows a comparison betweenROS from NMR and from sponge core measurements.Instead of the LIL procedure, the inject-log (IL) procedure wasfollowed. IL is an optimized program in which the open holesection is drilled across the target zone with the doped mud,eliminating the need for a subsequent underreaming run withthe dopant and the NMR relogging part. It saves rig time andSAUDI ARAMCO JOURNAL OF TECHNOLOGY WINTER 2011 49