Performance influences of a deep high temperature fractured geothermal system

Abstract

To assess the influences of various parameters in ultra deep (>4km), high temperature, fractured geothermal systems, the system's NPV was evaluated as these parameters were varied. The examined fracture network had multiple fractures leading between the wells in a single doublet. The tested input parameters concern rock matrix parameters (permeability, porosity, thermal conductivity and heat capacity), apertures in the fracture network and cold-water injection rates. After simulation of flow, the resulting data has been used for the calculation of NPV, which provided an indication for the performance. Larger values for matrix parameters and higher fracture apertures amplified each other's positive effect they had on the NPV of the system, as they both prevented bottlenecked flow of injected water from injector to producer wells and kept the system lifetime longer by allowing injected water more time to absorb heat before reaching the production well. An optimum exists when selecting injection rate with regards to system NPV. Lower injection rates lead to lower energy production, while higher injection rates lead to shorter lifetimes. A balanced injection rate lead to a maximum NPV. More investigation into optimization of injection rate over system lifetime will prove valuable for maximizing performance.