RELIABILITY OF EARLY MODELING STUDIES FOR HIGH-TEMPERATURE RESERVOIRS IN ICELAND AND THE PHILIPPINES

A 10-30 years long operation history of various geothermal steam fields in the Philippines shows that initial, simple model capacities are still being sustained. Volumetric heat reserve models therefore provide assurance that the resource in question can deliver necessary output to generate forecasted revenues. When applying the simple model approach to Icelandic resources, it appears that detailed numerical models conservatively estimate maximum generating capacities. Simple models, on the other hand, likely lead to aggressive production strategies. They also neglect risk of undesired resource behavior, such as cooler fluid invasion or fast pressure drawdown rates. Both can be mitigated at later stages in utilization history by make-up drilling and changed reinjection strategies. Initial costs are lower for aggressive power production but greater at later times, for maintaining steam flow rates. The reverse appears the case when intense green field development and detailed modeling are basis for conservative generating capacities. Interestingly, financial risks may be similar. Geothermal industries, which adopt aggressive production schemes, must prepare for higher steam field maintenance cost and should ensure that human and technical resources for the task are available. Detailed reservoir models should be preferred when it comes to address environmental issues like sustainable development and renewable power generation. Reason is that detailed models include boundary recharge; a reservoir property which allows successful utilization of a resource for generations.