Optimal Control of Extraction/Injection Wells for Geothermal Circulation

One way to utilize geothermal energy is to produce hot water and re-inject the heat-depleted water back into the aquifer. This procedure maintains the reservoir pressure, prevents subsidence, and permits the recovery of heat contained in the permeable rock. As a result it creates low-temperature zones around injectors and these zones will grow with time and eventually reach the extraction wells. After breakthrough occurs, the water temperature is no longer constant at the extractors, and this may reduce drastically the efficiency of the geothermal circulation.

Heterogeneity of the aquifer significantly speeds up the breakthrough. Two types of doublets (extractor/injector pair) are investigated on a heterogeneous aquifer. A later breakthrough is observed in the well pattern which alternates injectors and extractors. It is not recommended to isolate each doublet from the influence of the others.

We develop an optimal control strategy of the extraction/injection wells to delay the breakthrough of low-temperature water in a heterogeneous aquifer. The objective function aims to improve the areal sweep by equalizing the temperature of producing water at the extractors. The approach significantly delays the breakthrough time in both types of doublets. In the more isolated type of doublet, the breakthrough is delayed from 18 years to 28 years; while in the more communicated type of doublet, the breakthrough is delayed from 31 years to 35 years.

AAPG Search and Discovery Article #90142 © 2012 AAPG Annual Convention and Exhibition, April 22-25, 2012, Long Beach, California