Variational Phase-field modeling of hydraulic fracture interaction with
natural fractures and application to Enhanced Geothermal Systems
Abstract
In every tight formation reservoir, natural fractures play an important
role for mass and energy transport and stress distribution. Enhanced
Geothermal Systems (EGS) make no exception and stimulation aims at
increasing the reservoir permeability to enhance fluid circulation and
heat transport. EGS development relies upon the complex task of
predicting accurate hydraulic fracture propagation pathway by taking
into account reservoir heterogeneities and natural or pre-existing
fractures. In this contribution, we employ the variational phase-field
method which handles hydraulic fracture initiation, propagation and
interaction with natural fractures and is tested under varying
conditions of rock mechanical properties and natural fractures
distributions. We run bi-dimensional finite element simulations
employing the open-source software OpenGeoSys and apply the model to
simulate realistic stimulation scenarios, each one built from field data
and considering complex natural fracture geometries in the order of a
thousand of fractures. Key mechanical properties are derived from
laboratory measurements on samples obtained in the field. Simulations
results confirm the fundamental role played by natural fractures in
stimulation’s predictions, which is essential for developing successful
EGS projects.