Beschreibung
Our proposal focuses on 4D present-day stress field investigation in a cratonic area. We have already observed that continuous formation and development of stress-induced
borehole enlargements is still ongoing in a tectonically very stable and almost aseismic area. That is unforeseen and raises questions of worldwide relevance. Theoretically, the continuous growth of the deformations in time and space should not occur and the failures approaching a steady-state within a short time period. The Outokumpu deformation data already acquired in 2006 and 2011 show that a slow but continued deformation, albeit unexpected, is still present. To repeat the downhole measurement and check the progression of damage in time is one of the main objectives of this proposal. Outokumpu borehole represents a unique and extraordinary opportunity to measure and investigate the time-dependent deformation in an aseismic area directly in-situ inside the 2500 m open borehole in eastern Finland. Usually an estimation of the growth of breakouts is mainly based on laboratory experiments or numerical models because the access to the hole after drilling completion is not possible anymore as the wellbore is cased and/or abandoned. We will use acoustic image data from 2006 to calculate the deformation (time-to-failure) by means of numerical simulations using the finite element method. The modelling result will be compared with the actual deformation data observed in reality in 2011 in the well by the televiewer log.
The method is repeated using real borehole data from 2011 to calculate and predict future breakout development (time-to-failure) and compare again these theoretical results with the actual results we will achieve in 2019. As since 2005 the Outokumpu borehole is still open, the well represents the ideal site to repeat in-situ measurements for investigation and estimation of the time-dependent stress-induced deformation over a period of 13 years in a cratonic shield.