Fluid induced seismicity guided by a continental fault: Injection experiment of 2004/2005 at the German Deep Drilling Site (KTB)

Abstract

[1] Recent hydraulic experiments at the KTB site have shown that seismicity induced by long-term fluid injection directly into a continental crustal fault remains guided by this fault. The seismicity is triggered by pressure perturbations as low as 0.01 -1 bars at the hypocenters. A combination of sequential one-year fluid extraction (2002/ 2003) and one-year fluid injection (2004/2005) experiments has shown that only positive pore pressure perturbation (i.e., injections) was able to induce the seismicity. Moreover, the onset of seismicity roughly coincides with the time of compensation of the extracted fluid volume by the following injection. This confirms that the pressure diffusion is a dominant mechanism of seismicity triggering by fluid injections. The probed fault shows a significant anisotropy and non-linearity of its hydraulic behaviour. Its hydraulic diffusivity is up to one order of magnitude larger than that of surrounding rocks.

Static behaviour of induced seismicity

“…In fact, the approach could be applied to more problematic data sets that involve anisotropy and other heterogeneities. The most common example of anisotropy is the case of induced seismicity being spatially guided by a fault structure, such as during the 2004-2005 German Continental Deep Drilling Programme (KTB) injection (Shapiro et al, 2006) or the 2013 St Gallen, Switzerland stimulation (Edwards et al, 2015). Figure 5 illustrates how such heterogeneity can be implemented in the geometrical approach, by adding the historical static stress field that is associated with an active tectonic fault.…”

“…This led to the addition of an arbitrary non-zero starting time t 0 in previous works (e.g. Shapiro et al, 2006), including the Basel case (Shapiro and Dinske, 2009), and finally to the consideration of non-linear poroelasticity (ibid.). The proposal in the present article of a more parsimonious and transparent approach obviously does not mean that it is superior to poroelasticity.…”

Two Massive Hydraulic Tests Completed in Deep KTB Pilot Hole

“…3). Analysis of those data has revealed that seismicity induced by injecting fluid directly into a crustal fault remains guided by this fault and is triggered by porepressure perturbations as low as 0.01-1.00 bar at hypocenters (Shapiro et al, 2006). Most notable was the observation that seismicity started only after injecting a fluid volume approximately equivalent to the amount previously extracted by the pump test into the incompletely saturated formations.…”

Horizontal respect distance for hydraulic fracturing in the vicinity of existing faults in deep geological reservoirs: a review and modelling study

“…Any faults that are present in the Coal Measures of the Carboniferous Fracture Intensity: 0.35 Fig. 7 The results relating to each stress threshold value [0.001 MPa (Kilb et al 2002;Shapiro et al 2006), 0.1 MPa (Stein 1999;Kilb et al 2002;Freed 2005;Shapiro et al 2006), 0.3 MPa (Freed 2005 and 0.5 MPa (Kilb et al 2002)] are calculated for the three P32 intensity values (shaded grey dark 0.15, mid 0.25 and light 0.35) and three source mechanism weightings (from left to right 50% inflation, 25% strike-slip, 25% reverse; 25% inflation, 50% strike-slip, 25% reverse; 25% inflation, 25% strike-slip, 50% reverse). The tails indicate the maximum and minimum values of the data set, the box ends the mean plus/minus 1 standard deviation, the star is the mean and the horizontal line the median must also be in the shale.…”