NMR T1 and T2 Relaxation in Oil-Based Mud Filtrates at Reservoir Temperatures

Abstract

AbstractKnowledge of the nuclear magnetic resonance (NMR) properties of the near-wellbore fluids at reservoir temperature is needed for planning and interpretation of an NMR logging program. If the oil-based mud filtrate (OBMF) is the nonwetting pore phase, it will exhibit long, bulk fluid-like relaxations that can strongly affect the NMR response of the flushed zone. Knowledge of the NMR T1 and T2 relaxations at reservoir temperature is needed, since these parameters have significant temperature dependences. In this work, the bulk-fluid NMR T1 and T2 responses of six oil-based mud filtrates and three drilling fluid base oil samples were measured over a range of elevated temperatures. The present work also has application to NMR lab measurements on core taken with low invasion oil-based coring fluids.All samples were degassed using a standard helium sparging technique, since dissolved paramagnetic oxygen can greatly reduce the NMR relaxations of refined oil products. The experimental temperature range was approximately 30100 C (546-670 °R). The temperature dependence of the bulk viscosity of each sample was measured using a rolling ball viscometer. The NMR relaxation data was collected on a 2 MHz permanent magnet spectrometer.There were no important NMR relaxation differences between base oils and their derived mud filtrates. Sample viscosity had an approximately linear inverse relationship with temperature. The sample relaxations varied approximately as the inverse cube power of viscosity, steeper than has been observed in dead crude oils. For all samples, T1 and T2 increased approximately linearly with temperature, tripling from 30 to 100 C (546-670 °R).