| Project Detail |
This project aims at investigating the physical mechanism for attenuation and dispersion of seismic waves which is referred to as squirt flow. A wave propagating in subsurface causes small deformations to a porous rock, but flat pores such as cracks and grain contacts are drastically deformed. The fluid pressure in these pores is then largely increased, so fluid flows into other pores. This flow of a viscous fluid is dissipative and results in frequency-dependent attenuation peaking at seismic or higher frequencies. The importance of understanding well the seismic attenuation/dispersion signature of squirt flow lies on the strong necessity of remotely characterizing fluid-saturated rocks in subsurface using geophysical methods. Knowledge of pore and fracture characteristics and their interconnectivity is of enormous significance, for example, to the development and production of geo-thermal resources as well as for the geological sequestration of CO2. Squirt flow has been studied analytically since 1977, but the frequency-dependent attenuation and stiffness dispersion caused by this mechanism was only measured in laboratory in the last 10 years. A first order interpretation of these measurements has been done using analytical solutions based on simple rock pore geometries and related characteristics such as the pore aspect ratio. For effective development in this research field, two important aspects need to be addressed. First, accurate interpretation of such laboratory measurements requires numerical simulation of squirt flow in models that can precisely describe the rock pore geometry. These models can be derived from X-ray micro-CT images and improved with other accessory laboratory measurements. Second, accurate analytical solutions based on more adequate representations of rock pore geometries need to be developed for more accurate planning and first order interpretation of laboratory measurements. We plan to make laboratory measurements of frequency-dependent attenuation and stiffness dispersion on rock samples saturated with a viscous fluid. Numerical simulations based on models of the precise rock pore geometry will be used to plan and mainly to interpret those measurements. Using such numerical and laboratory tools, fundamental aspects of squirt flow will be re-visited and analytical solutions will be tested and improved. The main goals are (i) to achieve a deeper understanding of the squirt flow mechanism causing seismic attenuation and dispersion and (ii) to re-set important methodological and conceptual starting points for future research by the scientific community. |
