The presentation “Using the ‘entire’ acoustic waveform to quantify formation properties beyond just velocity” will be given by Philip Tracadas, from Halliburton.
Abstract
This talk presents how several different advanced signal processing algorithms can extract more information than just velocity from sonic waveform ‘trace’ recordings. Most modern acoustic logging tools record a sonic waveform ‘trace’ of vibrations versus time lasting 5 to 10s of milliseconds per receiver station, much longer than it takes for the arrival time of refracted modes. Petrophysicists recall the primary information extracted from these traces is inference of elastic properties by measurement of velocity (or its inverse, slowness) of various acoustic modes that travel through the formation rock.
This paper focuses on using various interface modes to assess fracture fluid conductivity and two types of formation anisotropy. Interface modes originate due to the borehole fluid and formation rock interface, and exhibit frequency vs. slowness dispersion; that is, their slowness (or 1/velocity) is different depending on frequency during the same trace recording. Using wide bandwidth and high dynamic range trace recordings, along with differential phase processing, the measurement of dispersion can be made over several to more than ten kilohertz. When analyzed in the correct frequency bands, dipole- created flexural interface mode can be interpretated for azimuthal (TIH aka HTI) anisotropy mechanism and polar (TIV aka VTI) anisotropy. Examples of continuous mechanism logs are presented. Low frequency monopole-created Stoneley interface mode is also sensitive to polar anisotropy and a flexural- Stoneley joint inversion process in the frequency domain is presented for Thomsen gamma measurement.
The Stoneley interface mode is also the highest amplitude mode that can be excited. It exerts large pressure changes on the borehole wall interface as it propagates, thus making it ideal as a mini-pressure test of fluid conductive fractures (as investigated by Hornby et.al. 1989). The theory and algorithm to estimate fracture conductivity are presented, which includes frequency spectral analysis of ‘reflections’ recorded later in the waveform trace after the direct Stoneley arrival.
Biography
Philip Tracadas is a geoscientist subject matter expert for borehole acoustics at Halliburton. From 2013-2016 he served as Associate Editor for Acoustics for the SPWLA’s Petrophysics journal. Over the last decade, he has taught internal acoustic training, for wireline and while drilling tools, from basic to advanced products. With eighteen years of industry experience on various acoustic processing algorithms and tools, he liaises between log analysts, software developers, field operations, and customers to address formation challenges with effective and efficient tools.