Optimum Geothermal Well Diameters

Abstract

Geothermal well diameters have been a hot topic and been debated in geothermal industry since 1960’s. Since geothermal wells are produced through casings instead of tubings in oil and gas wells, casing diameter designs have always been a discussing issue. As known, early geothermal wells have been cased with standard 9 5/8” and non standard 8 5/8” production pipes. In geothermal steam fields like Larderello larger diameter pipes (133/8”) have been utilized with the aim of controlling of frictional losses during the fluid flow and consequent increase in production. In Turkey, different diameters are used without any scientific and technological basis. These large diameters might sometimes cause serious cost overruns in some geothermal fields. On the other hand, sometimes large diameter wells create disapointments due to highly exagerated expectations when the limited permeability is found. This study is conducted to define the optimum well diameters for geothermal wells depending upon the depths. With this aim, deterministic and stochastic studies are carried out trying to find optimum diameters. Moreover, in order to assess better the underground uncertainty a risk analysis study is conducted, and the results for different depths are presented. Moreover, some recommendations are given for selection of most suitable well diameters.