| Title | The Effects of Stimulation Process Conditions on the thermal Performance of an Engineered Geothermal Reservoir |
|---|---|
| Authors | Mohammed ALHASHIM, Thanh Tung LE, Donald KOCH |
| Year | 2018 |
| Conference | Stanford Geothermal Workshop |
| Keywords | Stimulation, Weak planes, Viscous pressure drop, Thermal Performance |
| Abstract | Engineered geothermal reservoirs are defined as low permeability hot dry rocks that are stimulated via the injection of a high pressure fluid. During the stimulation process, sealed weak planes are fractured forming a cluster of connected activated fractures. A weak plane is assumed to activate when the fluid pressure inside it reaches a critical value. The interconnectivity of the cluster of activated fractures varies depending on the importance of the viscous pressure drop when compared to the variability in the fracture’s critical pressures. A well-connected cluster can form when the viscous pressure drop dominates while a fractal network is formed when the viscous pressure drop is negligible. Assuming one-dimensional heat transfer into the rock adjacent to each fracture and neglecting the interference between neighboring activated fractures, the circulation process within clusters of activated fractures, formed at different stimulation conditions, is analyzed. It is found that for the same ratio of the separation between the circulating wells to the cluster’s radius, a well-connected cluster performs better than a fractal network. In the well-connected network, multiple flow paths connecting the two circulating wells are created while a fractal network provides a single flow path. For the well-connected network, the length of shortest path is on the order of magnitude of the Euclidean distance between the two wells providing a small surface area for thermal exchange. On the other hand, the shortest path of the formed fractal network is highly tortuous and its length is much larger than the separation distance between the two wells. Nevertheless, increasing the number of flow paths by a viscous-dominated fracturing process decreases the flow rate within each path leading to a net increase in the average residence time within the shortest path and better thermal performance. |