Figure 5
From: Inferring the in situ stress regime in deep sediments: an example from the Bruchsal geothermal site
Uncertainty analysis of the determined S hmin gradients derived from LOT-2023 and LOT-2245. According to the critical stress concept, the effective stress ratio σ1/σ3 should not exceed a factor of 4.68 (gray shaded area). Assuming a Sv gradient of 23.8 MPa km−1 and a NF regime, the σ1/σ3 ratio for LOT-2023 is within this range whereas LOT-2245 shows inconsistent ratios between 6 and 7. The slight increase of Shmin from 12.3 to 13.2 MPa km−1 (blue shaded area) indicates the minimum necessary variation to keep the σ1/σ3 ratio of LOT-2245 within the predicted threshold of σ1/σ3 ≤ 4.68. Uncertainty range of Shmin magnitudes is estimated following observations of Valley ([2007]) for deep well injection tests in Soultz.