ABSTRACT: Sedimentologic Controls on Movement of Contaminants through Aquifers: Lessons Learned from Petroleum Geology

Lee F. Kystinik, Dan J. Wyatt

Most predictive hydrologic models for contaminant transport in unfractured sandstone aquifers assume sheet-like, uniform flow down a potentiometric gradient and ignore sedimentary heterogeneities. In contrast, petroleum exploitation efforts document depositionally induced heterogeneities that control fluid movement through sandstone deposits.

Sandstone deposits from many depositional environments contain heterogeneities capable of diverting contaminants outside the path predicted by potentiometric theory. Fluvial deposits can be linear sandstone bodies encased within impermeable mudstone, often oriented at high angles to the potentiometric gradient. Internally, fluvial sandstone bodies can be highly compartmentalized, resulting in complex but predictable flow paths.

Similarly, predictable permeability relationships occur in other depositional environments. The internal stratification of eolianites causes directionally preferred flow of fluids and layered behavior. Eolianites have maximum preferred permeabilities, perpendicular to paleowind, that can exceed intermediate (parallel to paleowind) and vertical permeabilities by 2 to 3 orders of magnitude. Even sheet-like strandline deposits contain internal flow barriers that can isolate or divert contaminants. These predictable permeability relationships can have a dramatic impact upon fluid flow through aquifers, as well as hydrocarbon reservoirs.

Prediction of heterogeneity requires a detailed understanding of the deposit in question. Core, well logs, and outcrop studies, rarely used in hydrogeology, are necessary to accurately predict flow characteristics. Although core and well logs are expensive, predictive sedimentology can offset these expenses by eliminating unnecessary monitor wells drilled large distances from the compartmentalized path of contaminant transport.

AAPG Search and Discovery Article #91003©1990 AAPG Annual Convention, San Francisco, California, June 3-6, 1990