| Title | Fault Tips as Favorable Drilling Targets for Geothermal Prospecting – a Fracture Mechanical Perspective |
|---|---|
| Authors | Tobias BACKERS, Inga MOECK |
| Year | 2015 |
| Conference | World Geothermal Congress |
| Keywords | hydraulic fracturing, fracture toughness, fracture growth, favorable drilling targets, fault controlled systems, geothermal reservoirs |
| Abstract | The productivity from geothermal systems is often strongly controlled by faults and fractures. Faults are known for their positive effects on fluid flow and heat transport, resulting in drilling targets at fault zones. It is, however, under debate which part of the fault might be the most favorable site for drilling. The catalog of geothermal systems in the Great Basin, Nevada, demonstrates that not the center of fault planes is the setting for high geothermal activity. Instead, step-over regions, fault intersections and fault tips belong to the favorable structural settings of geothermal fields in the Great Basin. Our attempt aims to explain from a fracture mechanical perspective the cause and effect why faults tips represent favorable settings for geothermal fields. Under shear load a fracture or fault tip shows a rather complex stress state compared to its trace. While the acting stress on the fault trace is uniform, at the fault tip the stresses range from increased compressional stresses on the one side of the fault to reduced stresses on the opposite side. This stress redistribution can be described mathematically. The specific altered stress state at the fault tip not only results in unique fracture patterns during the formation of the fault but also in magnified extensional stresses. This directly results in potentially increased fracture permeability with beneficial effects for geothermal applications. |