Ultrabroadband Acoustic Logging Tool for Deep Reading Formation Evaluation

Abstract

Abstract This paper introduces an ultrabroadband array sonic logging tool and related processing for wireline logging in both open and cased holes. The tool consists of six broadband monopole and dipole transmitters and 104 highly sensitive wideband receivers, enabling deep-reading formation evaluation in axial, radial, and azimuthal directions around the tool. The transmitter drive pulses from the six broadband monopole and dipole transmitters are dynamically optimized and controlled to cover a large dynamic range in formation slowness. The low-frequency monopole source is designed for measuring Stoneley dispersion curves. A high-frequency monopole source array helps enable extraction of compressional slowness and arrivals that can generate enhanced radial compressional slowness profiles. These deep readings are then used to evaluate the formation in three directions around the sonic logging tool. The orthogonal dipole sources help enable direct measurement of the shear slowness from the low-frequency flexural asymptotes without the need for dispersion correction. Real-time processing, including quality control of transmitter and receiver sensitivities, delivers high-quality compressional, shear, and Stoneley wave slowness. Subsequent post-acquisition answer products include formation compressional and shear slowness, shear anisotropy, and Stoneley reflections and permeability. Further interpretation of low-frequency compression waves helps enable measurement through high attenuation gas zones and also measure the true formation compressional slowness in very slow formations where leaky compressional modes are prominent. Also, shear slowness measurements through very slow formations allow improved seismic ties from mudline to depth. This next-generation ultrabroadband array sonic logging tool allows for deeper reading and more comprehensive formation evaluation in cased and open holes. In addition to discussing the process for using the tool in wireline logging, this paper provides examples for logs of both slow and fast formations.