TRANSIENT MULTI-LAYER MODELING WITHOUT A GRID AND TIME-STEPPING

An analytic approach is presented for modeling transient flow in multi-layer systems. As the approach is analytic, no grid or time-stepping is needed. The approach is based on the Laplace-transform analytic element method and is implemented in the free and open-source computer code TTim (pronounce: tee-tim). TTim may be applied to simulate transient flow in multi-layer systems consisting of an arbitrary number of layers. The current implementation allows for the modeling of wells, streams, and vertical fractures; well screens, streams, and fractures may be open to any number of layers. Features that may be modeled include: delayed response of the water table, wellbore storage, vertical anisotropy, and flow through abandoned wells. TTim (pronounce: tee-tim) is written in Python. The input for a simple TTim model consists of only a few lines of Python. For more complicated models, the input may be read from, for example, GIS shape files. TTim has many practical applications, including the design of riverbank filtration systems, analysis of aquifer tests near surface water bodies, design and evaluation of recirculation wells, and modeling of the transient pressure response of proposed carbon geologic sequestration projects. In addition, the short and simple input files and the absence of grids and time stepping make TTim well suited for education.