An acquisition of representative reservoir fluid samples is important for reservoir management and development. During overbalanced drilling, the high hydrostatic pressure causes mud filtrate invasion into the reservoir. This makes the process of acquiring representative reservoir fluid samples challenging due to the miscibility of Oil-Based Mud (OBM) filtrate with the reservoir fluid. The presence of OBM filtrate impacts the characterization of the reservoir fluid, resulting in inaccurate and not representative PVT laboratory measurements. PVT data generated out of contaminated samples should be avoided as they have the potential of harming field development plans.
In this study, OBM level in contaminated samples was quantified and their compositions were restored through skimming and subtraction techniques. Consequently, the key fluid properties of the decontaminated fluid were successfully predicted through an Equation of State (EOS) software.
The results demonstrated the impact of OBM filtrate on bubble point pressure and heavy-end properties, as concluded by the EOS modelling software, which compared the phase behavior properties of the contaminated and decontaminated fluids. Subsequently, modeled properties like Formation Volume Factor (Bo), Gas-Oil Ratio (GOR), API gravity, and mixture density were all compared to the measured fluid properties of clean fluids. Additionally, the capability and robustness of each decontamination methods were confirmed against the measured original clean composition.