The impact of flow connectivity on the interpretation of pumping test data

Abstract

The spatial variability of subsurface flow parameters, such as the transmissivity or storativity, is a common feature of all geologic systems. Traditional geostatistical techniques expressed this heterogeneity in terms of two-point correlations. Recent research suggests that such characterization technique may not be adequate to fully represent the complex patterns of flow and transport in heterogeneous subsurface systems. The concept of flow connectivity has been introduced to describe how different regions of the aquifer relate to each other. In this study, the impact of point-to-point flow connectivity on radially convergent flow towards a well is investigated numerically. A Monte Carlo approach is adopted whereby a large number of heterogeneous aquifer systems with different levels of connectivity are synthetically generated and then used to simulate pumping tests. Two pumping test methods, the Cooper-Jacob Method and the Continuous Derivation Method, are used to estimate the flow parameters from the time-drawdown curves, and examine how the estimated parameters relate to the underlying heterogeneous aquifer systems. Results indicate that the estimated transmissivity value approaches to the geometric mean of the full transmissivity field as the time-drawdown derivative dataset is included in the interpretation. On the other hand, the estimated storativity is strongly influenced by the spatial distribution of the transmissivity, the aquifer point-to-point flow connectivity and the relative locations of the observation and pumping wells. The relations between the estimated storage coefficient and a static measure of connectivity are also examined.