Investigation on the effect of tree-like bifurcation fracture networks properties on the EGS thermal recovery performance

Abstract

In order to truly describe the fracture network of the enhanced geothermal system (EGS), the tree-like fractal bifurcation theory is used to reflect the heterogeneity of the fracture network. The temperature-seepage coupling model is set up, the influences of bifurcation fracture networks and well layouts on thermal recovery performance are analyzed. The results show that the increase of bifurcation level, angle and length ratio all have positive effect on the thermal recovery performance. A higher bifurcation level produces a greater number of secondary fractures, a higher bifurcation angle and length ratio leads to a relatively spread fracture distribution, thereby improving thermal recovery performance. A higher aperture ratio is prone to premature thermal breakthrough, which limits the thermal recovery process. Under the conditions and scopes of our study, the optimal bifurcation level is 5, angle is 120°, length ratio is 0.55 and aperture ratio 0.4. This study provides some good guidance of efficient fracturing design for better thermal recovery performance.

Keywords

• Enhanced geothermal system
• Tree-like fractal bifurcation theory
• Temperature-seepage coupling
• Bifurcation fracture networks
• Well layouts