Maximizing Recovery Rates in Unconfined Aquifers

Technical Category:
Modeling and Groundwater Hydraulics

Author:
Rolf Herrmann, Schlumberger Water Services, Abu Dhabi, United Arab
Emirates, rherrmann@slb.com

Abstract:

The main objective of a strategic aquifer storage is to recovery the maximum
extraction rate possible during an emergency event. The high hydraulic stresses
applied need to be fully understood in order to prevent any damages to the ASR
system performance. The paper will evaluate and compare the performance of ASR
systems in unconfined conditions where recharge was carried out through injection
wells or surface infiltration. Due to density differences of the native groundwater and
the injected water, a density stratification will develop with heavier saline water
increasing towards the bottom of the aquifer. During recovery in an emergency
situation, extreme hydrodynamic pumping conditions may result in coning or saline
water breakthrough, where undesired more saline aquifer water will be produced to
surface. A shift of the density stratification can seriously impact the fluid distribution
in the aquifer, damage the buffer water necessary to protect the injected freshwater
from mixing with saline water and therefore have considerable negative impact on
the recovery efficiency of an ASR system.

The selection of the recharge method, well field optimization, withdrawal rate and
screen length and depth optimization, will result in a considerable improvement of
producing high recovery rates after long term storage during an emergency event
without impairment of the ASR system for subsequent storage cycles.