Use of convolution and geotechnical rock properties to analyze free flowing discharge test

Abstract

Discharge tests are conducted in order to determine aquifers transmissivity (T) and storage coefficient (S). However the interpretation of test data is not unique and the results may vary depending on adopted hypothesis. In this work, the convolution technique is applied for the reconstruction of observed drawdown curves aiming for the reduction of uncertainty. The interference between a flowing well and an observation well is evaluated in order to determine the hydrogeological parameters of the confined Guarani Aquifer

Flowing Well—Time‐Domain Solution and Inverse Problem Revisited

“…The T value obtained by fitting the flowrate observations only is practically the same while S is 50% lower. The results for fitting flow data only are similar to Wendland's (2014) results, but with a smaller difference in S . The T and S from fitting flowrate data only were strongly correlated (−0.99) while the correlation was much weaker for the results from fitting both drawdown and flowrate data (−0.75).…”

“…The results for simultaneous fitting to flowrate and drawdown observations with (Figure 2) and without smoothing of the flowing well drawdown replicated Wendland's (2014) results with small differences in T and S that can be attributed to the different methodologies used in the analysis (Table 1). Piece-wise linear representation (e.g., Mishra et al 2013) of drawdown at the flowing well was also used as a more accurate alternative to the step-wise representation while utilizing a smaller number of t-s w points, with similar results.…”

“…Wendland (2008) corrected the drawdown at the flowing well for frictional losses; the corrected drawdown at the well screen increases with time. Wendland (2014) analyzed the flowrate observations after 25 min using the Jacob and Lohman (1952) straightline method and validated the results by calculating the time-drawdown data and also by computing S using the compressibility and porosity values from samples of the aquifer material. The results were T = 411 m 2 /d and S = 2.75 × 10 −4 .…”

“…The flowing well test published by Wendland (2008Wendland ( , 2014 includes flowrate records from the flowing well and drawdown records from an observation well at a distance of 832 m. The aquifer thickness is 200 m and the wells are over 1000 m deep. The observation well registered drawdown at 90 min.…”

“…The time-domain solution allows transforming measurements of flowrate from a flowing well and drawdown at an observation well into an equivalent constant rate test data set that can be analyzed using the Theis 1935 function. Flowrate and drawdown observations from a flowing well test (Wendland 2008(Wendland , 2014 are re-analyzed first by fitting the Theis function to the ratio of drawdown to flowrate and then by simultaneous fitting to measured flowrate from the test well and drawdown recorded at an observation well. Using both flow and drawdown observations results in a better posed inverse problem for estimating aquifer hydraulic properties than using flow observations alone.…”