Vimal V. Shah

Data communication along the drill string using acoustic waves

A new method of wireless data telemetry in oil well services uses compressional acoustic waves to transmit data along the drill string. Coded wave trains are produced by an acoustic transducer, travel through the drill string and are subsequently decoded to recover the data. Normal drilling operations produce in-band acoustic noise at multiple sources at intensities comparable to the transducer output, while propagation through the long drill string further degrades the signal. We describe a theoretical channel model, and, based on this model, demonstrate that a single receiver system has a capacity of several hundred bits per second in such noisy drilling conditions. We analyze a two-receiver scheme that exploits the fact that the dominant noise source and the signal propagate in opposite directions. We show that with two receivers this dominant noise can be cancelled, which results in a significant improvement in capacity over the single receiver.

Viscosity measurement with laser-generated and detected shear waves

A technique is described in which laser-generated shear waves can be used to measure the viscosity of liquids. The technique involves measuring the shear wave reflection coefficient at a solid–liquid interface. To accommodate this procedure, a wedge was designed to launch laser-generated shear waves into the material at nearly normal incidence to the solid–liquid interface. The reflected laser-generated shear waves are detected at a second interface with a laser interferometer. The angle of incidence at this second interface is at an angle greater than the critical angle. The purpose of this arrangement is to maximize the out-of-plane displacement at this second interface so that detection with the interferometer can be more easily accomplished. Calculations that support the design of the wedge and experiment are outlined and experimental results are presented and discussed. This technique would be most applicable in those situations in which conventional techniques are not suitable, such as those involvi...