The aim of this project was to integrate analysis of hydrochemical, geophysical, hydraulic and structural geology to develop methodologies to improve characterisation of faults using a case study of the Gloucester Basin, NSW and incorporate the knowledge into a regional groundwater model. This paper presents the hydraulic and groundwater hydrochemical characterisation of the Gloucester Basin, with a focus on an area where CSG exploration occurred.
Hierarchical Cluster Analysis and Principal Components Analysis were performed on water quality data from all bores, as well as subsets of the data including data from grouped layers 1-6, 8, and 8-12 of the geological model, and within the focus area. Hydraulic head contours for layers 1-6, 8, 10 and 11-14 were combined with fault interpretation from seismic data and TDS contours to estimate flow orientations.
No distinct pattern in groundwater chemistry across the basin, or within the area of interest was evident. Water from layer 6 was consistently grouped together in the different analyses, indicating less hydrochemical variation. HCA and PCA also showed that TCMB04 had a relatively distinct hydrochemical composition, mainly driven by pH.
Hydraulic head analysis showed an east-west flow, with discontinuity across certain fault segments. Vertical flow was evident in shallow layers at particular fault segment locations. WK11 showed an up forward flow, opposite to WK12 and WK14, inferring a chimney of permeability enhancement. In the Stratford area, hydraulic head contours and TDS distribution showed a significant discontinuity, suggesting a lack of across fault flow but indicating vertical flow in a damaged zone.
In this case, hydraulic analysis was more useful for elucidating flow orientation and fault characteristics than multivariate statistical methods applied to groundwater chemistry data; which is mostly descriptive in nature. However, TDS was a strong indicator of up-welling along fault damage zones.