In Situ Stress, Fracture, and Fluid Flow Analysis in Well 38C-9: an Enhanced Geothermal System in the Coso Geothermal Field

Abstract

Geoscientists from the Coso Operating Company,
EGI-Utah, GeoMechanics International, and the U.S.
Geological Survey are cooperating in a multi-year
study to develop an Enhanced Geothermal System
(EGS) in the Coso Geothermal Field. Key to the
creation of an EGS is an understanding of the
relationship among natural fracture distribution, fluid
flow, and the ambient tectonic stresses that exist
within the resource in order to design a hydraulic and
thermal stimulation of an east-flank injection well,
the first step in the creation of a heat exchanger at
depth. Well datasets from the east flank of the Coso
Geothermal Field are being analyzed to develop an
understanding of the relationships between natural
fracture distribution, fluid flow, and the ambient
tectonic stresses that exist within the resource.

During the second year of this project, wellbore logs
and stress data were acquired in a new production
well drilled in the Coso Geothermal Field, 38C-9.
The image analysis results include the discrimination
of natural from drilling induced fractures in wellbore
image data, natural fracture characterization, and
wellbore failure analysis. A hydraulic fracturing
stress test at 3,703 feet TVD was used to constrain a
normal faulting and strike-slip faulting stress tensor
for this reservoir. The shear and normal stresses
resolved on the fracture and fault planes were
calculated and used to identify the subset of critically
stressed planes that act to maintain permeability
within the Coso Geothermal Field.