Experimental study on the radiation characteristics of downhole acoustic phased combined arc array transmitter

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Abstract
A new kind of acoustic phased combined arc array transmitter with controllable directivity presented can be used in 3D acoustic image logging. The phased combined arc array is composed of numerous phased arc arrays placed equally along an axis. Each phased arc array contains several array elements arranged around a circumference. The phased combined arc array is considered as the combination of phased arc arrays and linear phased arrays. A directional radiation acoustic beam in the space is generated by simultaneously controlling the phase delay of excitation signals exerted on array elements located in the circumferential and axial directions. To investigate the radiation characteristics, an acoustic transmitter comprising four eight-element phased arc arrays was assembled to conduct physical simulation experiments in a water tank. Experimental results show that the main lobe width of the horizontal radiation energy narrows significantly by exerting phase delayed excitation signals on array elements of phased arc arrays. Adjusting the delay time of excitation signals applied on neighboring-phased arc arrays allows the main lobe direction of the vertical radiation energy to be steered and facilitates the change in the main lobe width of the vertical radiation energy. The phased combined arc array is characterized by controllable horizontal directivity, vertical directivity, and main lobe width of the radiated acoustic beam. More importantly, the acoustic phased combined arc array transmitter is applicable to 3D acoustic image logging, which is helpful in the enhancement of the reliability and accuracy of complex reservoir exploration.

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