In-situ permeability from integrated poroelastic reflection coefficients.pdf

Chapter 8 In-Situ Permeability from Integrated Poroelastic Reflection Coefficients Abstract A reliable estimate of the in-situ permeability of a porous layer in the subsurface is extremely difficult to obtain. We have observed that at the field seismic frequency band the poroelastic behavior for different seismic wavemodes can differ in such a way that their combination gives unique estimates of in-situ permeability and porosity simultaneously. This is utilized in the integration of angle- and frequency- dependent poroelastic reflection coefficients in a cost function. Realistic numerical simulations show that the estimated values of permeability and porosity are robust against uncertainties in the employed poroelastic mechanism and in the data. Potential applications of this approach exist in hydrocarbon exploration, hydrogeology, and geotechnical engineering. 8.1 Introduction Reliable information of the distribution of the Darcy permeability (k0) in a porous layer in the subsurface is critically important in many disciplines, e.g., hydrocarbon exploration, hydrogeology and geotechnical engineering. Permeability can be highly variable, both vertically and horizontally. In general, in-situ k0 can hardly be assessed directly (e.g., Ratnam et al. 2005). The indirect methods are based on empirical rela- tions involving other measured parameters and have large uncertainties. For instance, with the Kozeny-Karman equation and an independent measurement of the porosity (φ), only an approximate estimate of k0 can be obtained. There have been attempts to estimate in-situ k0 from the attenuation of tube waves using poroelastic wave theory (e.g., Burns 1990). More recently, seismic body waves have been used for k0-estimation employing poroelasticity (De Barros This chapter has been published as a journal paper in Geophysical Research Letters 37, L12303 (van Dalen et al. 2010) and is reproduced with permission. Note that minor changes have been introduced to make the text consi