Reducing Water Saturation Uncertainties in a Low Resistivity Pay Carbonate Reservoir

Abstract

Abstract Water saturation is a key input in the determination of hydrocarbon resource estimations among many other uses. Evaluating water saturation is a huge challenge in heterogenous carbonate because of its diverse pore types. In order to find suitable evaluation techniques, a proper identification of the source and the characterization of these reservoirs is essentially required. There are several known causes of the low resistivity pay phenomenon namely: micro-porosity, fractures, paramagnetic minerals, and deep conductive borehole mud invasion. In Carbonates main cause is the presence of micritic pores or microporosity which strongly suppress or mask resistivity log response making water saturation evaluated from this type of reservoir rock inaccurate or over-estimated using the Archie equation. To compute a more accurate and realistic water saturation from such reservoir requires, an alternative resistivity independent approach is required to reduce the uncertainty in water saturation estimations. This paper demonstrated a simple alternative and pragmatic approach in evaluation of water saturation in complex carbonate reservoir with varying presence of micro porosity formed from micritization. The approach an integrated workflow based on geological(lithofacies/diagenesis) and petrophysical rock typing with other petrophysical methods to build a realistic saturation model in this challenging environment. The integration of various subsurface and dynamic data has contributed significantly to identification of the source of LRP, the distribution and the impact on the water saturation in oil and gas zones of the reservoir. Thus, reducing uncertainty, improving the reservoir characterization and HCIIP significantly most especially in the oil zone where LRP effect is more pronounced.