ESSO - Indian National Centre for Ocean Information Services

(An Autonomous Body under the Ministry of Earth Sciences, Govt. of India)

Determination of in-situ stress regime in the Koyna seismogenic zone, India from hydrofrac tests in a 3 km deep scientific borehole: implications for reservoir triggered seismicity

Vyasulu V Akkiraju1, Deepjyoti Goswami1, Jochem Kueck2, Gerd Klee3, Brijesh K. Bansal4 and Sukanta Roy1

1Ministry of Earth Sciences, Borehole Geophysics Research Laboratory, Karad 415 114, India

2ICDP, GFZ German Research Centre for Geosciences, Telegrafenberg, 14473 Potsdam, Germany

3Solexperts GmbH, Branch MeSy, Meesmannstr. 49, 44807 Bochum, Germany

4Ministry of Earth Sciences, Borehole Geophysics Research Laboratory, Karad 415114, India

Abstract : A critical gap in the understanding of the recurrent reservoir triggered seismicity over more than five decades in the Koyna region is the lack of complete information on the stress regime. To constrain the magnitudes and orientations of the principal horizontal stresses in the seismogenic zone, hydraulic fracturing (HF) tests were conducted at 9 levels in the crystalline basement between 1600 m and 2400 m depth in a 3 km deep scientific borehole. A conventional wireline double straddle packer assembly was used to carry out HF tests at the selected depth intervals. The results are as follows. (1) The stress-depth profiles for the depth range 1607-2374 m are given by: SHmin [MPa] = (22.4 +- 1.7) + (0.016 +- 0.003) * (TVD [m] - 1607); SHmax [MPa] = (44.3 +- 2.8) + (0.031 +- 0.006) * (TVD [m] - 1607), TVD being true vertical depth. (2) The mean orientation of SHmax is N-S+-17°, consistent with both breakout data down to 3 km depth as well as focal mechanism data of the region. (3) These stress magnitudes indicate a dominantly strike-slip to normal transitional faulting environment. (4) The crust beneath the Koyna region is critically stressed for hydraulically conductive fractures whereas differential stress in the dry, intact crystalline rock is not sufficient to cause faulting. This study supports the role of water in triggering earthquakes in the region, either by percolation from surface to the hypocentral depth through interconnected fractures or by diffusion of water pressure to the fault zone.

Keypoints :
  • 1.Stress magnitudes are determined for the first time in Koyna seismic zone from hydrofrac tests in deep crystalline basement.
  • 2.Stress magnitudes confirm strike-slip to normal transitional faulting environment and offer new insights to understand triggered seismicity.
  • 3.Only hydraulically conductive faults/fractures are critically stressed for failure as per Coulomb frictional-failure theory.
Data utilized for this study

Please contact Dr. Sukanta Roy (sukanta.roy@nic.in; sukantaroy@yahoo.com) for further detail if any.





Data & Information