| Abstract |
This talk covers optimisation of the cost of electric power from Hot Dry Rock (HDR) systems, otherwise known as Enhanced Geothermal Systems (EGS). These systems are hydraulically tight reservoirs whose permeability has been enhanced by hydraulic stimulation. An EGS “unit” in this talk refers to an injection well and the neighbouring production wells that derive fluid from it; for example, a doublet, triplet, five-spot, etc. The reservoir is assumed to be developed in the basement rock rather than in any sedimentary overburden. Most of the parameters in this exercise reflect the conditions encountered at the U.S.A. Desert Peak EGS project and the costs reflect 2006 U.S. dollars, but the conclusions reached here regarding optimisation should be applicable, at least qualitatively, to any EGS project today. Optimisation of geothermal resource economics calls for minimising the levelised cost of power (¢ per kilowatt-hour) over the project life. Minimising the levelised cost, in turn, requires minimising the capital cost of project development ($ per kilowatt-hour installed) as well as the operations-and-maintenance (O&M) cost (¢ per kilowatt-hour generated). The approach taken here is as follows: (a) using numerical simulation of an idealised reservoir to estimate power generation over time for various system configurations (number and spacing of wells, assumptions about stimulation effectiveness, etc.); (b) estimating the levelised power cost for each configuration, based on capital cost, O&M cost, cost of money and inflation rate; (c) determining the sensitivity of levelised cost to the cost components, interest and inflation rates, and resource characteristics (pumping rate, reservoir properties, depth to the reservoir, etc.); and (d) based on this sensitivity analysis and certain issues of site characteristics, identifying the practical steps that could be taken towards economic optimisation. |