Simulation of Horizontal Well Depressurization - MODFLOW versus FEFLOW
Karl P. Lawrence1, Ph.D., Willy Zawadzki2, Ashley Mathai3, Jeff Randall1
1
Golder Associates Ltd, Guelph, ON, Canada
Golder Associates Ltd, Vancouver, BC, Canada
3
Golder Associates Ltd, Mississauga, ON, Canada
2
ABSTRACT
Vertical wells have been historically used for depressurizing confined aquifers in mining and oil and gas
applications. Advanced drilling technologies, however, permit well field optimization by efficient
installation of horizontal wells lined by a pre-packed screen. This can enhance water extraction rates due
to increased aquifer-well contact provided that the aquifer has sufficient yield and the well design and
placement is adequate. The potential advantage of horizontal wells is the focus of several ongoing oil and
gas projects in Western Canada where detailed hydrogeological modelling is required in support of mine
planning.
Large scale mining and oil and gas operations usually relay on three-dimensional groundwater flow model
to provide forecasting of hydrogeological conditions at various stages of mining. Representing horizontal
wells in these models to assess effectiveness of horizontal wells, however, is performed less regularly
due to the high degree of grid/mesh refinement required. Groundwater abstraction from horizontal wells
also produces a lateral flow field in the aquifer (as opposed to a radial flow field for a vertical well) which
is generally more difficult to interpret and necessitates the use of three-dimensional models to adequately
represent the response. This paper assesses the implementation of horizontal wells in two most
commonly used groundwater flow models – MODFLOW and FEFLOW. Several approaches for
implementing these wells, including refined grid discretization, discrete features, and multi-node wells, in
multiple groundwater flow packages are compared to benchmark analytical solutions as well as semianalytical solutions from Saphir. Based upon the results, recommendations are provided for representing
horizontal wells in complex flow models. The limitations associated with each of the different approaches
are also discussed.