Fluid Identification in Complex Clastic Reservoirs Using 2D NMR Maps: A Case Study from Saudi Arabia

Abstract

Abstract The formation evaluation of Saudi Arabian reservoirs presents multiple challenges. The complexities encountered include varying mineralogy and mixed lithologies, a wide range of porosities and pore types, hydrocarbon viscosity, and variable formation water salinities. Two-dimensional (2D) analysis of NMR data acquired with simultaneous T1-T2 has proven to be beneficial for the identification and quantification of hydrocarbon-bearing reservoirs and providing valuable information about porosity and reservoir quality. NMR porosity measurements are free from mineralogical effects and, therefore, provide a very good estimate of formation porosity. Moveable and bound fractional fluid porosities from NMR provide additional reservoir information and are used for estimating permeability. Simultaneous T1-T2 acquisition and two dimensional analyses provide graphic 2D identification for the presence of hydrocarbons and hydrocarbon type, as well as a volumetric estimate of near wellbore hydrocarbons independent of formation water resistivity. Results from a simultaneous NMR T1-T2 acquisition are compared to formation tester results. The strong correlation between the NMR predictions and the formation tester results suggests this method is effective in the evaluation of challenging formations and might also be applicable to other reservoirs.