Modeling Studies of Sibayak Geothermal Reservoir, Northern Sumatra, Indonesia

Abstract

The Sibayak geothermal field is located in the Singkut caldera. Exploration surveys conducted at the field since 1989 indicated at least 4.5 km2 of prospective reservoir area. Geologically, the field consists of altered volcanic rocks in the shallow zone from the surface down to about 1150 m depth and meta-sedimentary rocks in the deeper zone. Main water loss zones of high temperature are present at the boundary of these zones and extend along fault systems. A conceptual reservoir model of Sibayak is proposed using data from ten exploration wells; high temperature fluid flows up in a zone beneath Mt. Sibayak and flows laterally southeast toward the caldera rim. A numerical simulation of the natural state of Sibayak was carried out. The simulated results successfully explained both the fluid flow pattern of the conceptual model and measured temperatures in wells.