| Title | An Assessment of the Economic Feasibility of Electricity Generation from Pumped Wells Tapping Lateral Outflows of Liquid Dominated Geothermal Systems |
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| Authors | Aaron Hochwimmer, Greg Ussher, Luis Urzua and Cameron Parker |
| Year | 2013 |
| Conference | New Zealand Geothermal Workshop |
| Keywords | Power Generation, Liquid Dominated Geothermal, Pumped Production, Organic Rankine Cycle, Numerical Modeling, Economic Assessment |
| Abstract | Conventional liquid dominated geothermal systems can be considered as undergoing idealised convective processes. Hot fluid up flows from depth and boils into a liquid and steam mixture as it rises and the pressure reduces. The liquid is cooled by boiling and often some mixing with cooler in-situ water. Near surface topography and the presence of high permeability geological layers in the upper 1000m of many systems can enable the development of productive moderate temperature reservoirs above and partly isolated from deeper high temperature reservoirs. Lateral outflow zones of hot liquid water, often with temperature reversals beneath are found in many fields and in some fields these outflows are extensive and have prolific flow rates. Line shaft or electrical submersible pumps can be used to pump fluid from relatively shallow depths (< 1000m) tapping these lateral outflows which provide the high permeability required to achieve high well productivity without excessive power lost in pumping. Electricity can be produced from energy extracted from the pumped brine using the Organic Rankine Cycle (ORC) process in a binary geothermal power plant. It is envisaged that 100% of geothermal brine is reinjected further down gradient along the outflow and at depth providing an option for power generation that has minimal environmental impact. Numerical models representing engineering processes of pumped well flow, fluid flow in pipework, and electrical power generation have been developed and applied to the typical conditions encountered in outflow type systems. These models are presented and are used to establish net power, and annualised power generation as a function of geothermal resource conditions. Considering indicative costs for capital plant and project development the Return on Investment (ROI) has been evaluated using a financial project development model. The ROI for a pumped outflow development is compared to conventional geothermal generation (deep self discharging wells to condensing steam turbine, binary, or combined cycle power plant) options. The sensitivities of outflow temperature, depth of drilling, flow rates, and well productivity to project economics are then discussed. |