LWD LOGGING TOOL ACOUSTIC TRANSMITTER WHOSE FREQUENCY RESPONSE IS DETERMINED BY THE MASSES OF THE END-CAPS CONSTRAINING A PIEZOELECTRIC DISC STACK

摘要

A logging tool acoustic transmitter 151 with at least one disc assembly 51 comprising a plurality of piezoelectric discs 50 configured to optimize acoustic pressure output within a desired frequency range while meeting physical restrictions of LWD and MWD logging systems. The disc stack is clamped between end-caps 50a and 50b, the masses of which are selected to obtain a predetermined transmitter frequency response. It is disposed in a recess 83 in the logging tool wall 89 in order to optimize acoustic energy transmission into the borehole environs and reduce transmission along the tool housing. In order to increase acoustic pressure output, the discs in each assembly are connected electrically in parallel and fired simultaneously; and their polarity and wiring arrangements are such that each disc then expands or contracts in a common direction. The axis of the disc assembly may be parallel or perpendicular and the transmitter may comprise two such assemblies mechanically and acoustically coupled by an arch-shaped mass (76, Fig. 3) that functions as an end-cap.