Local groundwater flow systems

Two types of local groundwater flow systems may develop in sedimentary basins at depth ranges of interest for studies of hydrocarbon migration and accumulation flow systems driven by buoyancy (Section 2.4.1) and those driven by osmosis (Section 2.4.2). 

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The main large-scale groundwater flow systems that may develop during the different stages of evolution of a sedimentary basin are described in Sections 2.1 to 2.3. These sections also present some examples of the relation between a basin type and type of groundwater flow system. Section 2.4 gives an overview of local groundwater flow systems of interest in petroleum-related studies. 

Figure 1 Illustration of the development of increasingly complex flow systems as topography becomes more complex. Contours of hydraulic head are indicated by dashed lines and groundwater flow lines by solid arrows. Scale is arbitrary, but might correspond to 100 km in the horizontal direction. In (a), smooth topography produces a regional-scale flow system. In (b) and (c) increasing local topography creates a mixture of intermediate and local-scale flow systems superimposed on the regional one (Freeze and Witherspoon, 1967) (reproduced by permission of American Geophysical Union from Water Resour. Res. 1967, 3, 623-634).

Lateral variations in permeability, caused by e.g. facies changes unconformities, faults, can profoundly affect the gravity-induced groundwater flow system (Figure 2.24), which in some cases can lead to the creation of local flow systems (Garven and Freeze, 1984b). 

Beginning in the late 1980s, a number of groups have worked to develop reactive transport models of geochemical reaction in systems open to groundwater flow. As models of this class have become more sophisticated, reliable, and accessible, they have assumed increased importance in the geosciences (e.g., Steefel et al., 2005). The models are a natural marriage (Rubin, 1983 Bahr and Rubin, 1987) of the local equilibrium and kinetic models already discussed with the mass transport... 

The local through-flow groundwater system is well drained to the sea. 

The groundwater systems of the planned area and its immediate surroundings have to be identified in terms of through-flow systems (the area may belong to several local drainage basins) and stagnant systems (unconfined and confined). 

Local flow systems dominate groundwater circulation at shallow depths (down to as much as 100 m) in humid regions (i.e., having significant diffuse areal recharge), unless the topography is very flat (Toth, 1963). Such systems vary from —100 m to several kilometers in horizontal scale. It is the discharge from such systems that supports surface-water flow in streams and rivers under all but storm conditions. The primary control on... 

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