Cased-hole interpretation workflow for determining residual oil saturation for mature fields

Formation evaluation for mature oil fields remains a challenge for operators. Rock-petrophysical properties present large uncertainties following years of production. Formation evaluation becomes even more challenging when there is a lack of open-hole logging data as is typically the case. Logging programs for cased-hole formation evaluation are limited by the size of the well completion. In addition, a metallic casing often prevents the effective use of electric measurements. However, pulsed-neutron tools (PNTs) are a viable option for mature fields. We developed a brief review of PNT theory. The high-energy neutrons output at a high count rate fit the need of cased-hole applications. Application of pulsed-neutron technology for mature fields and a case history from west Texas, in which pulsed neutron technology was used to determine remaining oil saturation are discussed. We documented the best practice for data acquisition and the processing workflow. Having a good collaboration between operator and service provider helps to better understand the logging objectives and in job planning, which is important for the success of the logging operation.