A novel numerical modelling of well-aquifer response induced by pressure disturbance

Under hydrostatic conditions, the water level observed in a well is often supposed to be equivalent to the pressure head in the surrounding aquifer. When the aquifer is subject to disturbing processes and activities, fluctuations of water level can be observed. Generally, the measured water level in the well is often considered to be less than the pressure head in the aquifer due to wellbore storage and skin effects (Ramey et al., 1972). In fact, there is another factor that can suppress or enhance the oscillating water level, which is termed the amplification effect (Cooper et al., 1965). Related studies point out that this effect is affected by well geometry (e.g. well diameter, water column height and well screen length), aquifer properties (e.g. transmissivity and storativity) and the period of the disturbed pressure head (Kipp, 1985; Liu, 1989). However, previous studies have obvious divergences in quantifying the amplification effect.

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 geometry parameters on the amplification factor separately, such as the well diameter, water column height and well screen length. Subsequently, we built a well-aquifer coupling numerical model to study the well-aquifer response induced by disturbed pressure based on the finite element method. Simulations of 125 scenarios showed that the amplification factor gradually increased until it reached a peak, and then decreased to 1 as the period of disturbed pressure became larger. The corresponding period of an amplification factor peak was significantly influenced by the water column height, which controlled the position of an “optimal period”. Aquifer properties can also affect the amplification factor, especially its peak value. In further numerical studies, more complicated scenarios will be investigated, considering different types of wells and aquifers.