Doctor of Philosophy (PhD)
Fractures are a source of extra compliance in the rock mass. Fracture compliance can estimate the fracture roughness and the type of fluid filling the fracture. The focus of this research study in chapter 2 is to illustrate how the compliance ratio of rough fractures can diverge from the compliance ratio of smooth fractures. The imperfect interface of the fracture is modeled with saw-tooth-like structures. The defined saw-tooth-like structures of contact asperities impose an in-plane asymmetry in the shear direction. The compliance ratio of the rough fracture is larger than the compliance ratio of the smooth fracture. Interlocking and riding up effects may explain our findings in chapter 2. Recovered core samples and extensive outcrops studies have proved the existence of natural fractures in many tight formations. These natural fractures are likely filled with digenetic materials such as clays, quartz or calcite. In chapter 3, this study suggests that small cemented natural fractures can be opened by the induced tensile stress due to the temperature difference between the cold fracturing fluid and hot formation. Cohesive zone model (CZM) is utilized here to simulate these natural fractures. Contribution of these micro natural fractures to cumulative gas production from a shale reservoir is investigated by modifying the transmissibility coefficient. Reservoir simulation results in chapter 3 suggest that reactivated natural fractures in the tight formations at early stages can improve gas production up to 25\%; however, their effect significantly reduces to 3\% in long term. Geothermal systems are identified as either open-loop systems (OLGS) or closed-loop systems (CLGS). The loss of working fluid, surface subsidence, formation compaction, and induced seismicity are major challenges in OLGS. To address the indicated challenges, CLGS can be considered as an alternative option. To improve the heat extraction from closed-loop wells, this research study in chapter 4 suggests highly conductive hydraulic fractures for CLGS to improve heat extraction rate. The results suggest that fractures significantly improve thermal power and cumulative extracted heat in CLGS. Thermal conductivity of the proppants is the key parameter enhancing heat extraction.
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Ahmadi, Milad, "Application of the Finite Element Method to Solve Coupled Multiphysics Problems for Subsurface Energy Extraction" (2016). LSU Doctoral Dissertations. 165.
Dahi Taleghani, Arash