Velocity distribution of slow fluid flows in Bentheimer sandstone: an NMRI and propagator study.
This work addresses the special problems of measuring flow velocity distributions in rock by NMR methods. Specifically, these problems are to measure very slow flows as well as flows in the presence of background magnetic field gradients caused by heterogeneities of the rock. We modify a stimulated echo sequence for use in diffusion measurements, in order to maximize velocity sensitivity and minimize background gradient effects. Accurate velocity images of Soltrol 220 oil in sandstone were made for flow velocities up to around 0.04 mm/s with an imager that does not have echo-planar capability. Accurate velocity distributions by the propagator method can be obtained even with stimulated echo delays of 1.9 T1 by phase cycling combined with suitable crusher gradients.
The performance in mobile systems is in many aspects dependent on mobility patterns. For instance the number of hand-of and signaling load is likely to increase as the subscriber mobility raises. Most performance analysis in the literature are based on constant motion models which is considered to be unrealistic. In this paper a fractional Brownian motion (FBM) model for mobile subscribers is presented providing a more realistic phenomena description.