Publications

The Miocene Kais reefal bank reservoirs in Salawati Basin, West Papua, consists of series of rock type with extremely varying porosity. As a mature field, identifying missed pay opportunities behind casing is extremely challenging. Traditionally, pulsed neutron data has been used to monitor gas/water contacts using techniques such as curve overlays and to calculate water saturation from Carbon/Oxygen (C/O) measurements. They have been used for oil/water saturation calculations in such low or unknown salinity environments with porosity greater than 15%. In Salawati Basin, the low porosity are typically less than 15% which is approximately below the threshold to which C/O logging is applicable, and the water salinity is less than 10 kppm. In 2016, a campaign cased hole technology was undertaken to help solve some of the problems encountered in the Salawati Basin. As part of this, pulsed neutron instrumentation and methodology were used for through-casing water saturation measurements. Low porosity reservoir are still contributing to oil gain although C/O estimation of formation saturation in such low porosity might be not quantitative. The C/O ratio stayed well within the computed envelope, even at such low porosity. This paper reviews the results of C/O measurement from shut in wells wherein low porosity reservoir demonstrates high C/O and positioned very close to oil line. Well-A, for instance, contributed to produce oil from the low porosity zone that had 98% water cut and could produce 35 BOPD after putting the well back online. Another case was Well-C, contributed to produce oil from the low porosity zone that had 83% on water cut, then produced 38 BOPD after the producing well back online. Based on these, C/O measurement still able to identify the remaining potential of untapped oil in the low porosity reservoir and considered as reliable approach extend the lifetime of the field.