Groundwater Flow in Low‐Permeability Environments

Abstract

Certain geologic media are known to have small permeability; subsurface environments composed of these media and lacking well developed secondary permeability have groundwater flow sytems with many distinctive characteristics. Moreover, groundwater flow in these environments appears to influence the evolution of certain hydrologic, geologic, and geochemical systems, may affect the accumulation of pertroleum and ores, and probably has a role in the structural evolution of parts of the crust. Such environments are also important in the context of waste disposal. This review attempts to synthesize the diverse contributions of various disciplines to the problem of flow in low‐permeability environments. Problems hindering analysis are enumerated together with suggested approaches to overcoming them. A common thread running through the discussion is the significance of size‐ and time‐scale limitations of the ability to directly observe flow behavior and make measurements of parameters. These limitations have resulted in rather distinct small‐ and large‐scale approaches to the problem. The first part of the review considers experimental investigations of low‐permeability flow, including in situ testing; these are generally conducted on temporal and spatial scales which are relatively small compared with those of interest. Results from this work have provided increasingly detailed information about many aspects of the flow but leave certain questions unanswered. Recent advances in laboratory and in situ testing techniques have permitted measurements of permeability and storage properties in progressively “tighter” media and investigation of transient flow under these conditions. However, very large hydraulic gradients are still required for the tests; an observational gap exists for typical in situ gradients. The applicability of Darcy's law in this range is therefore untested, although claims of observed non‐Darcian behavior appear flawed. Two important nonhydraulic flow phenomena, osmosis and ultrafiltration, are experimentally well established in prepared clays but have been incompletely investigated, particularly in undisturbed geologic media. Small‐scale experimental results form much of the basis for analyses of flow in low‐permeability environments which occurs on scales of time and size too large to permit direct observation. Such large‐scale flow behavior is the focus of the second part of the review. Extrapolation of small‐scale experimental experience becomes an important and sometimes controversial problem in this context. In large flow systems under steady state conditions the regional permeability can sometimes be determined, but systems with transient flow are more difficult to analyze. The complexity of the problem is enhanced by the sensitivity of large‐scale flow to the effects of slow geologic processes. One‐dimensional studies have begun to elucidate how simple burial or exhumation can generate transient flow conditions by changing the state of stress and temperature and by burial metamorphism. Invest...

Geological processes and the management of groundwater resources in coastal areas

“…Combining Darcy's Law with the continuity principle leads to the well known diffusion equation for head or fluid pressure. From this equation, the response time, x p , of the fluid pressure/head and the flow field of a groundwater system can be readily derived (e.g., Neuzil, 1986). It is controlled by the hydraulic diffusivity, D h , of the sediments and a measure of the spatial scale, L, of the system, where hydraulic diffusivity is defined as…”

“…For multidimensional flow the exact response depends on the domain geometry and boundary conditions, but (2) still provides a useful measure of the approximate behaviour (Neuzil, 1986). For non-uniform hydraulic properties, x p is controlled by weighted averages of the hydraulic diffusivities.…”

Land Subsidence Along the Texas Gulf Coast Due to Oil and Gas Withdrawal

“…Causes of depressurization include hydrocarbon or groundwater extraction, downward flow through low-permeability strata, and expansion of low permeability rocks upon erosion (Neuzil, 1986). Although the Gulf Coast Basin contains many low permeability rocks, depressurization by the latter two processes would not have produced pressures as low as was found within these fields .…”

Generic Argillite/Shale Disposal Reference Case

“…1.3e-6 to 1.2e-4 Ordovician Ontario Sykes et al (2008) 8.0e-7 Pierre Shale South Dakota Neuzil (1986) 2.69e-5 to 3.60e-5 Pierre Shale South Dakota Bredehoeft et al (1983) 1.1e-5 to 2.4 e-5 Pierre Shale Saskatchewan Smith et al (2013) 1.2e-6 to 1. …”

“…In the Great Plains Province, most of the data analyzed refers to the Pierre Shale (Neuzil 1986;1993;Bredehoeft et al 1983;Olgaard et al 1995;Smith et al 2013). …”