(A public domain version of linear equilibrium sorption) R C 3D, FV (alternate FE solver also provided) Y Gas is ‘air’ Non-gas sorption N Y Y Dynamic coupling R C 2D/3D, FE Y N N N Y Y Non-coupled, subreach scale MIKE SHE R C 1D/2D (surface), 3D (groundwater) N N N N Y N Dynamic coupling MODFLOW R P (C for many addon modules) 3D, FD With module (e.g. N N N With add-on module (e.g. SURFACT) With module (e.g. MT3D, or Non-coupled, regional scale MODHMS add-on provides coupled treatment
Appendix C - Examples of modelling for regional impact simulations Coal seam gas development project Modelling tool(s) adopted Modelling approach type adopted and processes included Simplifications and assumptions Uncertainty analysis Reference(s) Arrow Energy Surat Gas Project, Australia MODFLOW Regional groundwater model (120,000 km2 model domain) Well field represented by individual abstraction wells Cumulative impacts assessed (including CSG developments) Dual-phase and unsaturated flow, geomechanical effects, and dual porosity nature of coal all assumed insignificant Assessed to be limited groundwater–surface water interaction – simple (non-coupled) approach to groundwater–surface water interaction adopted Coal horizontal anisotropy not modelled Coal seams not modelled independently of coal measures Hydraulic connectivity of geologic structural features ignored (Hydraulic fracturing not proposed to be undertaken by Arrow, thus its potential impact was not required to be assessed) Deterministic uncertainty analysis only: Sensitivity analysis for specific aquifer parameters and multiple aquifers. Effect of sensitivity-adopted parameter values on calibration performance discussed Indicated significance of hydraulic parameters and range of drawdown magnitudes Arrow Energy Pty Ltd (2012c)
Australia Pacific LNG Project, Australia FEFLOW Regional groundwater (172,740 km2 model domain) Finite element method (FEFLOW) allows improved definition of complex geology Dual-phase flow implicitly accounted for by reducing coal seam permeability Cumulative impacts assessed (including other CSG developments) Geomechanical effects, and dual porosity nature of coal all assumed insignificant Simple (non-coupled) approach to groundwater–surface water interaction adopted Coal horizontal anisotropy not modelled Coal not modelled independently of coal measures CSG well represented by constant pressure head (rather than pumping flow rates) Hydraulic connectivity of geologic structural features ignored Discussion of hydraulic fracturing severely limited Hydraulic parameters assumed for most model layers due to limited data Simplified hydrogeological model, which may only reflect a partial understanding of the Surat Basin Connectivity between aquifers uncertain as geological structure poorly understood Upward propagation of depressurisation from coal deposits in the Basin not included Deterministic uncertainty analysis only: Sensitivity analysis (two extreme cases only) for aquifer, recharge and stream conductance parameters. Effect of sensitivity-adopted parameter values on calibration performance discussed Indicated significance of hydraulic parameters and range of drawdown magnitudes Australia Pacific LNG (2010), Geoscience Australia and Habermehl (2010)
Santos Gladstone LNG Project, Australia Analytical model (Roma field), MODFLOW (Comet Ridge field) Regional groundwater model Model domain limited to project area Time-varying constant head boundary condition used to represent well (rather than pumping/flow rates) for MODFLOW model; constant pumping rate used to represent well field in analytical model Model not calibrated Dual-phase flow, coal dual porosity and anisotropy, and geomechanical effects not included Coal seams not modelled independently of coal measures Vertical movement of groundwater not well constrained Aquifer confinement and interconnection simplified Effects of geological faults assumed insignificant Analytical modelling did not account for size of well Apparently no accounting of groundwater–surface water interaction Limited deterministic uncertainty analysis: Sensitivity analysis (four cases) for specific aquifer parameters and recharge for the MODFLOW model, and for storativity for the analytical model CSG well fields were modelled separately and cumulative impacts associated with other developments assessed on a qualitative basis Santos (2009a), Santos (2009b) Basin MODFLOW Regional groundwater model – CSG region divided into three subdomains (hydraulic compartmentalisation assumed) Time-varying constant head boundary condition Dual-phase flow, coal dual porosity and anisotropy, and geomechanical effects not included Coal not modelled independently of coal measures No consideration of rainfall recharge Simplified geology, homogeneous isotropic conditions Cumulative impacts not assessed None QGC (2009)
used to represent well field (rather than pumping/flow rates) Apparently no accounting of groundwater–surface water interaction Queensland Resources MODFLOW Regional groundwater model (300,000 km2 model domain) Modelling of historical CSG operation in Queensland (Surat and Bowen Basins) was undertaken Modelling included simulation of multiple CSG operations and was used to develop and assessment of cumulative impacts and aggregate groundwater extraction associated with CSG extraction Uncertainty analysis was carried out using multiple simulations incorporating changes to the model. The results of this analysis were used to assess uncertainty in the predicted impacts Queensland Water Commission (2012) Namoi Catchment MODFLOW Regional groundwater model (30,000 km2 model domain) CSG well fields modelled a specified extraction rate over each well field modelled Cumulative impacts (including existing and Separate of surface water system Multi-layered model to address future CSG and coal mine development. Modelling of existing, planned and possible development Cumulative effects assessed through multiple model analyses by comparing the results for a range of alternate development scenarios with a base case of limited development Groundwater impacts on surface water obtained using Sensitivity analyses carried out to assess uncertainty associated with rock permeability and recharge values adopted Schlumberger Water Services (2012)
proposed developments) nominated head boundaries to represent permanent water courses Powder Basin, Montana, US MODFLOW Regional groundwater model (1240 km2 domain) Subregional constant head boundary condition used to represent CSG well field Dual-phase flow, coal dual porosity and anisotropy not included. Geomechanical effects assumed to have no impact Coal not modelled independently of coal measures Cumulative impacts not assessed Implicit (uncoupled) groundwater–surface water interaction None Myers (2009)
interaction Most tools account for geomechanical processes, gas desorption and migration, dual phase flow and coal dual porosity, as well as complex geological conditions simplified way Regional groundwater impact assessment Tools practicable for regional scale impact assessment Capable of representing complex geology, assessing cumulative impacts and changes to groundwater quality Generally ignores geomechanical processes, gas desorption and migration, dual phase flow and coal dual porosity; this may create inaccuracies assessment of impacts, water quality, re-injection and cumulative impacts