Complementary imaging of oil recovery mechanisms in fractured reservoirs

Abstract

Complementary imaging techniques used to study enhanced oil recovery (EOR) processes in fractured oil reservoirs have provided new and improved fundamental understanding of how oil recovery is affected by fractures. The combination of two imaging techniques such as magnetic resonance imaging (MRI) and nuclear tracer imaging (NTI) enables a complementary investigation on materials and processes, where large scale (∼m) phenomena are controlled by small scale (μm) heterogeneities. MRI provides high spatial resolution and fast data acquisition necessary to capture the processes that occur inside fractures less than 1 mm wide, while NTI provides information on macro-scale saturation distribution in larger fractured systems. The oil recovery mechanisms involved with waterflooding fractured chalk blocks were found to be dependent on the wettability of the chalk, as the wettability had great impact on the fracture/matrix hydrocarbon exchange. The MRI images of oil saturation development inside the fractures clearly revealed two distinct transport mechanisms for the wetting phase across the fracture at several wettability conditions, and provided new and detailed information on fluid fracture crossing previously observed in block scale experiments investigated by NTI. The ability to obtain rapid (∼s) 1D saturation profiles, high spatial resolution 2D images (sagital, transverse and coronal) within minutes and detailed 3D images within a couple of hours, makes MRI a powerful tool in studies of multiphase flow in fractured porous rocks, and provides excellent dynamic information of enhanced oil recovery efforts.