Field Measurements of Remaining Oil Saturation

Abstract

ABSTRACT Some of the most promising techniques proposed for evaluating the remaining oil saturation (RÛS) of watered-out formations were tested in a few wells of three different fields Chuelles (Prance), Cortemaggiore (Italy) and a field in the Gulf of Guinea (Africa). The work was carried out with the following main objectives : – to identify a screening for selecting the best ROS measurement method(s) to be applied under different reservoir and/or well conditions; – to compare for the same well the results obtained applying different methods with various investigation depths; – to emphasize the importance of the in-situ ROS determination in heterogeneous reservoirs. The techniques selected were: – conventional carbon-oxygen logging; – pulsed neutron capture tool (log-inject-log); – single well tracer test; – interwell tracer test. The logging methods give results in good agreement in the high-porosity reservoirs conside red and can reveal a heterogeneous distribution of the oil saturation. The single well tracer test may be difficult to interpret when a significant heterogeneity and/or fluid drift occurs. In other cases, this tracer method can be very accurate. The interwell tracer test can give interesting results about flow behaviour in the reservoir, despite difficulties of test analysis. It can also measure an average ROS value at the end of a flooding process. From this series of on-site experiments, we conclude that: using more than one method improves the accuracy of in-situ ROS determinations; ROS measurements performed on one well are representative of the surrounding area; in-situ ROS measured at the end of the flooding process may be quite different from the residual oil saturation (Sor) measured in laboratory.