Low Resistivity Pay Carbonate Reservoirs Water Saturation Estimation Problems and Solutions (A Case Study in the Middle East, Shuaiba Carbonate Reservoir)

The low resistivity pays (LRP) have been a long-standing problem in formation evaluation. In LRPs, the reserve calculation and balanced production and reservoir development is a challenging, and risky. The LRPs evaluation with only conventional logs is difficult and overestimates water saturation (Sw), meanwhile the rock produce oil. The LRP reasons must be investigated and determined before appropriate applied solutions. The identification of actual hydrocarbon and actual water saturation is different and need an integration work with advance core data (CCAL, SCAL) and advance logs (ECS, NMR, RST, FMI). The LRP reservoirs mostly originated with high immobile Sw in thin interbed laminate sands and bounded saline water in the micro pores of the carbonates. Also, the presence of metallic conductive minerals and invasion of saline water in natural fractures are other reasons for LRP reservoir. The primary indications such as oil stain in the cuttings, oil in the mud pit and production tests all account toward for final understanding of reservoir potential. Shuaiba is a complex carbonate oil reservoir and a type of (LRP) reservoir. The resistivity tool read low values in the oil bearing above transition zone so, the conventional log analysis method cannot give reliable response to Sw. This paper proposes available mathematical approaches and methodologies and tools for identification range of overestimated Sw. The produced Sw from core (saturation height) and Sw estimated by cased hole tools (TDT, RST, PNN) are used for solving the problem. In this case study these tools were used to overcome this problem.