Cased-Hole Formation Resistivity (CHFR) technique improves hydrocarbon saturation monitoring

The ability to detect and evaluate bypassed hydrocarbon and track fluid movement in sandstone reservoir is vital in the quest to improve production and increases recovery. The main technique, which has been used for monitoring reservoir saturations, is Thermal Decay Time (TDT) tool. But, it was hard to interpret the TDT data in the low formation water salinity reservoirs. This problem can not be solved because it is related to the theory itself of TDT measurement, which depends on salt content in formation brine. The problem of low formation water salinity was solved by Carbon Oxygen Ratio (COR) technique, which was latterly combined with TDT technique in the same tool, called Reservoir Saturation Tool (RST). This tool was not widely used due to its short depth of investigation (6-8 inches) in addition to its long logging time. A Technique called Cased Hole Formation Resistivity tool (CHFR) was proposed to overcome many of the pulsed neutrons tool limitations. Based on the actual CHFR logs recorded through wells studied in an oil field in Egypt, which are presented and discussed in the present work, a comparison study was done between the two available techniques, TDT and CHFR as methods for reservoir saturation monitoring, in addition to the results of open-hole resistivity logs as reference runs. It was found that water saturations calculated from CHFR logs were more accurate than TDT log in most of the cases, and that the quick look of CHFR logs always agrees with its quantitative interpretation, which gives the trust to relay on quick look of CHFR log, if a fast decision is required. While the quick look of TDT log was found to be very tricky, in most of the cases: often does not agree with its quantitative interpretation.