TOUGH-UDEC SIMULATOR FOR THE COUPLED MULTIPHASE FLUID FLOW, HEAT
TRANSFER, AND DEFORMATION IN FRACTURED POROUS MEDIA
ABSTRACT
Shear slip of fractures in fractured rock masses is a critical issue for many geological engineering
applications, such as the design of underground nuclear waste repositories, enhanced geothermal systems
(EGS), and geosequestration of CO2. This paper presents new development of the TOUGH-UDEC
simulator for analysis of coupled thermal-hydraulic-mechanical (THM) processes in fractured porous
media. As an alternative to developing a single coupled THM code in discontinuum, two existing wellestablished codes, namely TOUGH2 and UDEC, are coupled to cover coupled THM analysis of multiphase
fluid flow, heat transfer, and deformation in fractured porous media. TOUGH2 is widely used for modeling
heat transfer and multiphase, multicomponent fluid flow, and UDEC is a well-known discrete element code
for rock mechanics, which have been verified and used by many groups all over the world. Although a
sequential coupling of two codes is less efficient than having a single code in principal, a big advantage
with coupling of TOUGH2 and UDEC is that both codes are well tested and widely applied in their
respective fields. When linking two codes, the coupled equations cannot be solved simultaneously; they
should be solved sequentially, with coupling parameters passed to each equation at specific intervals. After
solving thermal-hydraulic equations through the TOUGH2 model, pressure (P) and temperature (T)
information is delivered to UDEC model. Pressure information is directly stored at the center of each
UDEC zone and domain, however, temperature information is interpolated from zone-centers to the
corners nodes. After solving the mechanical equation through the UDEC model—considering new pressure
and temperature—calculated fracture apertures are converted to equivalent permeability for TOUGH2 flow
analysis. The solution was calculated by iteratively following an explicit sequence for numerical efficiency.
Verification examples are presented to demonstrate the capabilities of the coupled TOUGH-UDEC
simulator.
Figure 1 – Schematic view of code-linking logic and information conversion for TOUGH-UDEC
KEYWORDS
TOUGH-UDEC, THM coupling, fractured porous media