Modeling Thermo-Mechanical Effects On Flow Channeling In Fractures

Fractures are ubiquitous in the Earth’s crust and play a key role in the transport of mass and heat in the subsurface. It is highly valuable to understand how fluid flows within these high-permeability features, as they often focus and facilitate flow in reservoirs. Natural heterogeneities of fractures make them difficult to model and give rise to further focusing of flow into channels of particularly high permeability within each fracture. This flow channeling has an adverse effect on the conformance (sweep efficiency) of injected fluid in the fracture, reducing the amount of oil or heat extracted from petroleum or geothermal reservoirs, respectively. We investigate the effects of thermo-mechanics on single-phase flow channeling behavior in a fracture. Cold water injected into a fracture causes the host rock to thermally contract, decreasing normal stress in much of the fracture, but also creating regions of increased stress. Consequently, non-uniform patterns of permeability enhancement and reduction form throughout the fracture. Using the Barton-Bandis model, we investigate this “stress-ring,” focusing on where it occurs and its effects on the severity and evolution of flow channeling. We show that thermo-mechanics enhances flow channeling in both homogeneous and heterogeneous fractures, while the stress-ring accounts for 5-30% of this enhancement. Using the Complex Systems Modeling Platform, CSMP , we present a 3D thermo-mechanical model using a mixed Finite Element and Finite Volume, operator-split method. We model fractures as discrete, lower-dimensional planes; temperature and pressure dependent, realistic water properties are used. By first understanding the evolution of flow channeling in a single fracture, behavior of flow in complex fracture networks can be better discerned, benefiting both the petroleum and geothermal industries.