| Abstract |
For integrity and induced seismicity hazards associated with both injection and cooling in geothermal projects, the in-situ stress conditions are vitally important. In geothermal projects in sedimentary systems in the Netherlands, the largest hazard is usually from potential fault reactivation from cooling. The existing measurements of in-situ (horizontal) stress have come mostly from oil and gas projects, which are in a different geological situation, i.e. usually at geological highs, and do not include the impact of cooling. Therefore, a research program (Geo4All) was launched to measure in-situ stresses and, in addition, take valuable and scarce direct measurements of in-situ horizontal stresses in cooled geothermal reservoirs. Two operational geothermal projects were used, with the plans taking into account the project specific characteristics. In one project, a doublet was being redrilled – allowing downhole openhole stress measurements (mini-frac) in both cooled and initial temperature reservoir locations within a short time interval. Another project, undertook cased hole (minifrac) measurements prior to any operation, with a plan to test exactly the same location after cooling for a number of years. The combination of these tests will give direct insights both into the initial stress conditions in geothermal plays in the Netherlands and the impact of cooling on the stresses in sedimentary geothermal systems, allowed better calculations of seismic risk and allowable injection pressures. |