An EGS Stimulation Experiment under Low Wellhead Pressures

Abstract

A stimulation experiment was conducted involving Coso injection well 34A-9óone of the stimulation targets within the Coso/EGS project. When the well was drilled, its measured temperatures were among the highest every recorded within the Coso field, but its permeability was poor. Steam condensate was then injected into the well, resulting in significant and immediate injectivity improvements. 34A-9 was subsequently used for several years as a steam condensate injector, but was shut in due to leaks in the shallow casing.

Upon repairing the liner, a second stimulation test was conducted in 34A-9, again resulting in injectivity improvements. Significant microseismicity was measured in the vicinity of the well during the early stages of injection. Tracer testing was conducted during a subsequent circulation test, revealing excellent communication with a neighboring production well. The injectivity of 34A-9 remains high, but is dependent on injection-fluid geochemistry. A geochemical fluid-mixing model was developed in order to explain injectivity trends.