Integrating hydraulic profiling tool pressure logs and hydraulic tomography for improved high-resolution characterization of subsurface heterogeneity

Hydraulic tomography (HT) has been developed as a robust technique in characterizing subsurface heterogeneity over the last two decades. Hydraulic conductivity (K) and specific storage (Ss) estimated by geostatistically-based HT inversion approaches are typically smooth and lack geological features when observation data density is sparse. Although integrating geological information can be helpful in adding structural features into parameter fields, costly efforts are required to obtain borehole logging through conventional coring and sampling. Also, identification of geological features such as layer boundaries from sampled materials can be a subjective process. In this study, corrected pressure (P-c) logs collected during hydraulic profiling tool (HPT) surveys are utilized to derive the local hydrostratigraphic layers of the glaciofluvial deposit at the North Campus Research Site (NCRS) in Waterloo, Ontario, Canada. Site-specific geological models representing aquifer and aquitard layers are developed and calibrated to drawdown data of multiple pumping tests. Results show that estimated K fields correctly reflect the variation features of permeameter-estimated K profiles, as well as the spatial distribution of high and low K sediments. The calibrated geological models performed better than the geostatistically-based inversion approach in predicting independent pumping tests used for model validation. Moreover, by including K estimates of geological models as prior means, the estimated K fields reveal both intra- and interlayer heterogeneity, and the performances of drawdown prediction are further improved for the geostatistical inversion approach. Overall, our study suggests that, integration of stratigraphic information derived from HPT P-c logs is useful for HT to capture the sharp boundaries in K fields, especially when the pumping test data is sparse.

Automated summary

Hydraulic tomography has been developed as a robust technique for characterizing subsurface heterogeneity, but geostatistically-based inversion approaches may lack geological features when observation data is sparse. In this study, local hydrostratigraphic layers of glaciofluvial deposits were derived from corrected pressure logs collected during HPT surveys, and site-specific geological models were developed and calibrated to predict drawdown data of multiple pumping tests. The calibrated geological models outperformed geostatistical inversion approaches in predicting independent pumping tests, demonstrating the usefulness of integrating stratigraphic information derived from HPT logs for capturing sharp boundaries in hydraulic conductivity fields.