| Title | Three-Dimensional Heat Flow Model for Enhanced Geothermal Systems using Boundary Element Method |
|---|---|
| Authors | Dharmendra KUMAR, Marte GUTIERREZ |
| Year | 2013 |
| Conference | Stanford Geothermal Workshop |
| Keywords | Enhanced geothermal system, boundary element method, thermal energy extraction, heat circulation testn |
| Abstract | The paper presents a three-dimensional heat flow model for Enhanced Geothermal Systems (EGS) using the Boundary Element Method (BEM). The heat flow process in the EGS is combination of heat conduction and advection-diffusion. Injection of fracturing fluid during stimulation, with different temperature from the target rock temperature, will induce heat conduction in the surrounding rock mass. Inside the fracture, heat transfer will be mainly by advection-diffusion process due to fluid movement; however, heat process transfer will be a combination of conduction and convection due to fluid leak-off into reservoir. In general, the EGS reservoirs are impermeable or nearly permeable. Hence, zero fluid leak-off condition is assumed for modeling the heat flow. The BEM formulation depends on the fluid flow inside the fracture, which can be modeled either numerically or analytically. The BEM analysis results in a numerical procedure in which discretization of the reservoir geometry is eliminated; hence, only the fracture surface discretization is required. The fracture surface was discretized using 4-node rectangular elements. A point collocation technique with adaptive Gaussian quadrature was used for numerical implementation of boundary integral equation. The weak singularity of integral was removed using singularity transformation technique suggested by Lachat and Watson. Finally, the model was tested with two cases: one with pair of injection and production well and other for the EGS circulation test. Parametric studies were done to quantify the effects injection time on the temperature and on thermal energy extraction rate. |