We report on the discovery and testing of a downhole sparker source that is able to generate acoustic signals with peak frequencies from 2 to 1000 Hz. The sparker can be configured such that the energy of the produced acoustic signals lies within a spectral band that is suitable for transmission lengths of the order of thousands of feet, making it a viable source for single-well imaging and reverse vertical seismic profiling. The sparker produces repeatable shots and allows a firing rate much less than typical listening times in borehole seismic applications. Together with its robust design and reliability the described sparker can be operated for thousands of shots before spark plug maintenance is needed. This paper summarizes the development of the tool and presents results from recent field tests.
When a plane acoustic wave impinges on a cylindrical array, the leading edge insonifics the first few elements of the array. As the wave front continues past the leading edge of the cylinder, more and more elements are insonified until all elements in the array are insonificd. The time between the first and last clement to be insonificd is called array "fill time." For a cylindrical array with a phase-shift beamformer, in which the insonifying pulse length is long compared to the fill time, the resultant beam pattern is essentially the same as a cylindrical array with a delay line beamformer and is approximately the same as a planar array of similar aperture size. Up to this time there has been no detailed description of how the beam pattern is affected when the pulse length and th.c fill time are approximately the same. This article reports a thorough analysis of array fill time of a cylindrical array; a phase-shift beamformer is compared to a delay line beamformer. The conclusion from this study is that fill time has little effect on the array beam pattern as long as the fill time is no greater than the pulse length.
Single-frequency acoustical estimates of zooplankton biomass are notoriously inaccurate, varying 10–30 dB with variations in sizes of the scatterers. Multifrequency acoustical estimates are much more accurate but require substantial data processing. A compromise system, utilizing wideband acoustical signals (2.5–3.5 MHz) and broadband processing to reduce the sensitivity to scatterer size variations, has been developed. This system offers the advantages of rapid single-channel data rates and high spatial resolution while providing satisfactory accuracy in biomass estimation. System design required development of several novel subsystems: a broadband transducer with an acrylic lens for obtaining reasonable acoustic sample volumes from physically practical elements; a programmable broadband signal generator; and a wideband square-law receiver/detector. [Work supported by ONR Oceanic Biology and NSF Biological Oceanography.]
A curved face hydrophone array has been designed, constructed, and tested for 20 000-ft depth operations. A basic description of the hydrophone design is presented, where the hydrophone consists of a beamforming array of staves mounted on the circumference of a 20-in.-diameter cylindrical housing. Since conventional pressure release materials cannot be used in the construction, solutions to problems encountered, such as flexural waves generated in the housing wall and improper backing impedances for the individual elements, will be briefly discussed. A presentation of the received frequency response and beam patterns show that the transducer properties are insensitive to hydrostatic pressures up to 1000 psi.
The vertical side-lobe structure of cylindrical arrays driven in phase is examined. Experimental results demonstrate that the vertical side-lobe levels are significant when the angular aperture of the array is large.The physical cause of this phenomenon is identified, and a method of eliminating excessi•,e side-lobe levels is explained. Experimental results showing that this method is successful are presented. PACS numbers: 43.30 Yj, 43.30 Vh.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.