A hydrogeologic study to optimize steamflood performance in a giant oilfield: Kern River field, California

Abstract

The stratigraphic interval above the Round Mountain formation in the Kern River field contains four confined aquifers. Two of these confined aquifers are composed of sandstones in the main and transition zones of the Santa Margarita formation, and the remaining two are composed of sandstones in the lower and middle zones of the Chanac Formation. Above the confined aquifers is one regional, mainly unconfined aquifer in sandstones of the upper Chanac Formation and lower zones (U-lower K2) of the Kern River Formation. This unconfined aquifer is overlain by several perched aquifers in sandstones of the upper zones (upper K2-C) of the Kern River Formation. Oil production in the Kern River field is from sandstones comprising the unconfined and perched aquifers in the Kern River Formation and is greatly facilitated by steamflood operations. Flow between the various zones of the Kern River Formation and from underlying formations used for water disposal may provide unwanted pressure support for the steamed intervals, resulting in poor steamflood performance. Results of our study suggest that a water management program designed to remove and dispose of excess water from the producing zones will increase steamflood efficiency. The overall dip of the potentiometric surface in the regional unconfined aquifer and the smaller perched aquifers is westward and parallels the structural dip of the beds. Widespread fluid depletion in zones along the updip edge of the field, and the absence of a potentiometric gradient showing flow outward from the Kern River, suggest minimal groundwater recharge from natural sources. These observations suggest that fluids move downdip by gravity drainage from a closed volume, with significant removal of fluids by producing operations causing an overall decline in pressure in the unconfined aquifer. These findings are highly favorable for the implementation of a water management program designed to pump out and dispose of water from the producing zones.