A novel numerical modelling of well-aquifer response induced by seismic waves

Water level in an open well usually fluctuates in response to seismic waves. This fluctuation process reflects the characteristic parameters of the well-aquifer system such as hydraulic transmissivity, aquifer thickness, etc. through the amplification factor. Cooper (1965) presented an amplification factor theory to explain the dynamic response behavior of the well water level. Based on this theory, researchers used and further developed an amplification curve to determine the relationship between the amplification factor and well-aquifer parameters. However, redundancy problems, as well as the many theoretical assumptions limit its application prospects.

In this work, we firstly established an idealized fluid model to simplify the complex solid-fluid coupling process, aiming to discuss the influence of different well structural parameters on the amplification factor separately, such as the diameter, height of the water column and the length of the well screen. Subsequently, we established a novel three-dimensional numerical model to study the well-aquifer response induced by seismic waves based on the finite element method. Under certain hypothetical conditions, this model can be utilized to discuss more specific scenarios, such as the response of the water level due to different wave periods, different aquifer hydraulic parameters, etc. Preliminary results show that, even in an idealized fluid model, the maximum amplification factor is much less than the theoretical value. Based on parameters of the Wali well which was established in Liu et al. (1989), we find that the period of peak gain is around 20s and relatively insensitive to the thickness of the aquifer, which is basically in agreement with the analysis by Liu et al. (1989). Up to the work we did, the 'resonant frequency' of the well plays an important role for the amplification factor. Furthermore, based on the existing numerical model, we will discuss a more reasonable relationship between the amplification factor and well-aquifer parameters.

References Cooper, H.H., J.D. Bredhoeft, I.S. Papdopulos, and R.R. Bennett, (1965), The response of aquifer-well systems to seismic waves, J, Geophys. Res., 70, 3915-3926. Liu, L.B., E. Roeloffs, and X.Y. Zheng, (1989), Seismically induced water level oscillations in the Wali well, Beijing, China, J. Geophys. Res., 94, 9453-9462.