Summary
Carbon/oxygen (C/O) logs have been run in open hole to assess zones that are potentially swept with fresh injection water in several infill wells offshore Cabinda, Angola.
Interpretation of these logs has been challenging because of the invasion of oil-based mud (OBM) filtrate, mixed sand/carbonate lithology, variable water salinity, large boreholes, and lack of clean wet zones in which to normalize. We discuss the impact of these factors and our experiences in managing them. An example is included in which the results of time-lapse logging suggest that the invasion of OBM filtrate in water zones dissipates slowly or not at all. We show comparisons between saturations derived from the resistivity and the C/O ratio (COR) for these various conditions.