Modeling Studies of Single-Well EGS Configurations

Abstract

Single wellbore configurations show promise for Enhanced Geothermal Systems because they would reduce the number of wells that need to be drilled. We performed numerical modeling to investigate a variety of single wellbore configurations and compared them to a two-well injector/producer doublet. Wellbore and reservoir models were constructed separately and then coupled together using an iterative process. Some of the configurations included a downhole heat exchanger, which circulates a secondary working fluid through the wellbore. A separate loop brings heat to the well by circulating water through the reservoir and through a second annulus outside of the casing. The energy output of such a downhole heat exchanger system was found to be limited by the amount of fluid that could be induced to flow in the reservoir, although careful specification of the downhole tubulars resulted in worthwhile improvement. Appropriate choice of the circulating secondary fluid was also found to be important. In other configurations, fluid would be injected directly into the formation and produced back into the wellbore from a different interval in the same well. Fluid flow through the reservoir was assumed to occur either through an idealized single planar fracture, or through simple fracture networks.