Basin‐scale hydrogeologic modeling

Abstract

Mathematical modeling of coupled groundwater flow, heat transfer, and chemical mass transport at the sedimentary basin scale has been increasingly used by Earth scientists studying a wide range of geologic processes including the formation of excess pore pressures, infiltration‐driven metamorphism, heat flow anomalies, nuclear waste isolation, hydrothermal ore genesis, sediment diagenesis, basin tectonics, and petroleum generation and migration. These models have provided important insights into the rates and pathways of groundwater migration through basins, the relative importance of different driving mechanisms for fluid flow, and the nature of coupling between the hydraulic, thermal, chemical, and stress regimes. The mathematical descriptions of basin transport processes, the analytical and numerical solution methods employed, and the application of modeling to sedimentary basins around the world are the subject of this review paper. The special considerations made to represent coupled transport processes at the basin scale are emphasized. Future modeling efforts will probably utilize three‐dimensional descriptions of transport processes, incorporate greater information regarding natural geological heterogeneity, further explore coupled processes, and involve greater field applications.

Fluid flow in accretionary prisms: Evidence for focused, time‐variable discharge

“…Important considerations in interpreting data from downhole cores include the following: (1) recovery is incomplete, and more coherent, less fractured material may be preferentially recovered so that core data may be more useful for delineating matrix properties than the hydrogeologic properties of fault zones; (2) core sample tests generally test vertical flow properties, whereas in situ tests evaluate horizontal flow properties; and (3) measured permeabilities are dependent on effective stress conditions, which may be very complex in accretionary complexes. As noted in section 3, the •1og of clastic sediment permeability has been observed to vary with the porosity [Neuzil, 1994;Person et al, 1996]. Porosity in sedimentary basins decreases with depth because of increasing effective stress.…”

Permeability of shaly sands

“…However, this should be checked by additional tests of our model. Regarding the second question, we think that our model is applicable to the evaluation of water resources and subsurface water circulation because it is particularly suitable for determining permeability profiles from downhole measurement analysis (these permeability profiles can be integrated in basin simulators which begin to be widely used to understand subsurface hydrological circulations [e.g., Person et al, 1996]). The information required to determine permeability profiles from downhole measurement analysis are the following: (1) the clay mineralogy and the shale content which both can be determined from the inversion of natural radioactivity logs, (2) the grain distribution of the sand fraction which can be obtained from core samples or from downhole measurements, (3) the porosity (obtained from a lithodensity log) and a compac- [Baker, 1975].…”

“…Permeability must be known to understand many natural phenomena including basin-scale hydrogeologic circulation [e.g., Person et al, 1996], fault dynamics [e.g., Wintsch et al, 1995], the safety of waste repositories [e.g., Moore et al, 1982], and many other problems related to subsurface hydrology. Many permeability models have been proposed [e.g., Walsh and Brace, 1984;Bethke, 1989;Berryman, 1992;Nelson, 1994].…”

Faults as conduit‐barrier systems to fluid flow in siliciclastic sedimentary aquifers

“…Note that we do not consider the impact of an increasing temperature with depth, due to geothermal heat flow, on fluid viscosity (m) and density (r f ). This assumption is reasonable as we consider a relatively shallow groundwater flow system (<1000 m) where these temperature effects will be of minor importance [Person et al, 1996].…”