Theoretical Model of the Hydrogeology of a Pull-Apart Basin

WHITE, PAMELA M., Fort Worth, TX

An accurate model of the hydrogeology of a basin is important in assessing the migration path of oil and its potential for remaining within a trap. Fluid flow in a basin is influenced by three driving forces: gravity, compaction, and density. The hydrogeology of most basins is affected by a combination of these three forces, but one is usually dominant.

The hydrogeology of a pull-apart basin, such as the Los Angeles basin, is controlled by a combination of gravity and compaction forces. Tectonic movement within the Los Angeles basin has produced a number of small mountain ranges. These elevated features produce a large hydraulic head, driving groundwater into the basin. At the same time, the basin is undergoing compaction driving groundwater out of the basin. The complex interaction of these two forces has influenced the hydrogeologic flow within the Los Angeles basin. Oilgen, a computer modeling program, was used to develop a theoretical model for fluid flow within the Los Angeles basin.

Extraction of oil in the early part of this century caused extensive subsidence in parts of the basin. To prevent further subsidence Long Beach established a water injection program in 1958. The water injection program has been successful in inhibiting subsidence and has even produced small, but measurable, amounts of rebound. Modeling was done both pre- and postinjection to allow the effects of the water injection on the hydrology of the basin to be evaluated.

AAPG Search and Discovery Article #91004 © 1991 AAPG Annual Convention Dallas, Texas, April 7-10, 1991 (2009)