Quantitative Formation Permeability Evaluation from Stoneley Waves

Abstract

Summary The borehole Stoneley wave has been shown to be sensitive to fluid mobility, the ratio of permeability, and viscosity. The phenomenon is well described using the Biot theory and the effect of the mudcake was modeled as an elastic membrane. An inversion technique, which uses both slowness and attenuation of the Stoneley wave over a range of frequency to evaluate mobility, was proposed. This paper describes the implementation of an interpretation methodology based on this technique. The error analysis shows that an accurate determination of the fluid mobility requires that some critical parameters, such as the mud slowness, mud attenuation, and the pore-fluid modulus, be precisely determined. An interpretation procedure is proposed to determine these parameters with good accuracy. The fluid mobility can then be determined without the need for external calibration with another measurement. The intrinsic permeability of the rock can then be derived, knowing the various fluid components, their relative permeabilities, and their respective viscosity. When using the proposed methodology within the applicable limits, the Stoneley wave can provide a continuous estimation of the formation permeability along the well. Core measurements are not required for calibration although they can be used for verification. This technique will find applications in reservoir engineering optimization of well production through better placement of the perforated intervals.