Abstract
The ability to accurately map injected seawater in waterflood operations is an essential goal of reservoir monitoring. This capability improves reservoir management practices by helping to delineate the oil-water interface in new wells, locate bypassed oil pockets, minimizing water fingering and proactively enabling identification of early water breakthrough events. Our approach involves loading the injected water with magnetic nanoparticles, called Magnetic NanoMappers (MNMs) to function as electromagnetic (EM) contrast agents. Detection is accomplished by EM means, similar to cross-well and borehole-to-surface EM imaging, but at higher frequencies. The strategy for developing this technology focuses on forward modeling and travel-time tomographic inversion software. We have previously shown in the laboratory — using a reservoir model — that MNMs slow the group velocity of transiting EM signals [1]. Our results demonstrated the capability of imaging targets filled with different fluids, with high resolution using EM means, which supports the idea of high resolution saturation mapping using MNMs. This paper proposes a novel method to address the challenge of long range EM propagation in the reservoir, in the presence of conductive media.
The proposed method relies on the use of natural planar transmission lines present in the carbonate reservoirs of the GCC area. An EM pulse traveling through a relatively non-conductive layer between two more conductive layers, will propagate with relatively low attenuation, and the pulse's travel time will depend upon the electromagnetic properties of the layers above and below. MNMs will provide velocity contrast for EM pulses traveling through regions of the reservoir saturated with MNMs-loaded injection water. Similarly, changes in oil and water saturation will result in changes in travel time. By performing full waveform inversion one would be able to produce a saturation map with higher resolution than conventional cross-well EM methods.
This paper details a series of Finite Element Method (FEM) simulations to investigate the feasibility of the proposed method. The results show that long range EM propagation can be achieved through non-conductive layers, acting as planar transmission lines. In addition, the results show that the pulses are modulated by the EM properties of the layers above and below the transmission line. These results open up a new possibility for long range high resolution saturation mapping using EM means.
