Sensitivity analysis of effective parameters in water saturation estimation by using Monte Carlo simulation

Water saturation is one of the primary and influential parameters in evaluating the reservoir quality of hydrocarbon formations and is typically calculated by the Archie equation. This equation employs porosity, cementation factor, saturation exponent, tortuosity factor, formation water resistivity and true reservoir resistivity for water saturation calculation. It should be noted that uncertainty in these values can directly affect water saturation calculation, so the correct water saturation calculation in hydrocarbon reservoirs is essential, and any mistakes in its calculation leads to optimistic or pessimistic consideration of interval of interest. In this study, the Monte Carlo simulation method based on well-logging data were used to investigate the uncertainty of effective parameters in water saturation in the framework of Archie's equation. In this regard, the water saturation is calculated in three wells for the Sarvak reservoir in one of southwestern Iran's giant oilfields. The Monte Carlo simulation was implemented using MATLAB software for each parameter causing uncertainty in the water saturation model, and the distribution function is obtained for each parameter. Water saturation is as a distribution for each depth by investigating the uncertainty of each parameter affecting the Archie equation and is calculated in optimistic, probable and pessimistic cases. The results show that using well-logging data, the mentioned method can calculate the uncertainty of water saturation.