| Abstract |
Strategies to successfully manage geothermal fields in the long term will optimize sustainability and promote beneficial environmental effects. Sustainable development may involve cyclic utilization. Factors to consider will include time-scales of depletion and recovery, and rates of mass and heat recharge. Practical environmental enhancement strategies may include: improved discharges from surface thermal features using targeted fluid injection or extraction, creation of enhanced thermal habitats, and treatment or injection of toxic chemicals or gases. International collaboration between IEA countries participating in the Geothermal Implementing Agreement (GIA) has facilitated valuable discussions with respect to these strategies. The optimum level of long-term sustainable production can be achieved by properly managing fluid production and injection rates and locations. Upon shutdown, practical replenishment (~95% recovery) will occur on time scales of the same order as the lifetime of the production cycle. The recovery factors that determine the long term response of these systems to energy extraction are dynamic. Recovery is influenced by an enhanced recharge driven by the strong pressure and temperature gradients created by the fluid and heat extraction. Because of this process, cyclic utilization of geothermal resources is a viable long-term strategy, and an economic and sustainable alternative to simply limiting extraction to maintain continuous steady-state reservoir conditions. The cycle durations can be tailored to meet demand cycles (daily or seasonal), or can be extended out to periods of the order of 100 years, with resource utilization alternating between geothermal systems in the same region. Regional allocation procedures will need to be sufficiently flexible to accommodate such a long term strategy. The key to achieving a successful outcome (without consuming all the cake at once) is adaptive and flexible resource management. |