Location of the pilot borehole for investigations of reservoir triggered seismicity at Koyna, India

Gupta, Harsh K.; Shashidhar, D.; Mahato, C. R.; Satyanarayana, H. V. S.; Rao, N. Purnachandra; Maity, B. S.; Navitha, K.

doi:10.1016/j.gr.2016.10.014

Cited by 22 publications

(10 citation statements)

References 29 publications

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“…They also suggested the association of these fissures with localized fault zones within the rock unit. Seismological studies including the analysis of seismograms recorded at a local network of 23 surface broadband stations and 6 borehole seismic stations show a distinct NNE-SSW trend of seismicity coinciding with the Donichawadi fault zone, indicating that the fault is still active [53,54]. This inference gains support from other studies carried out in the Koyna region.…”

Section: Geofluidssupporting

confidence: 71%

Chemical and Noble Gas Isotope Compositions of Formation Gases from a 3 km Deep Scientific Borehole in the Koyna Seismogenic Zone, Western India

et al. 2019

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A 3 km deep research borehole KFD1 was drilled in the Koyna reservoir-triggered seismicity region, Western India, between December 2016 and May 2017. The 1967 M 6.3 Koyna earthquake had generated a NNE-SSW trending surface fissure zone in the Nanel-Donichawadi-Kadoli sector. KFD1 is located ~5 km south of Kadoli along the trend of the Donichawadi fault zone. Online gas monitoring was carried out during drilling of KFD1 from 1315 m to 2831 m depth to sample and study the composition of crustal gases. Formation gases CO2, CH4, H2, and He were only observed during water flushing of ~100 m intervals following coring runs. Laboratory analyses of gas samples collected between 1737 m and 2831 m depth revealed concentrations of up to 1200 ppmv CO2, 186 ppmv CH4, 139 ppmv H2, and 12.8 ppmv He. Zones enriched in gases are mostly below the 2100 m depth with significant He enhancement ranging from 4.6 to 7.6 ppmv above the atmospheric value. The He-rich zones correlate well with the zones of anomalous physical and mechanical properties identified from geophysical logs and are characterized by high fracture density as revealed from borehole images, indicating that the borehole punctured multiple fracture zones. The helium concentrations are consistent with those previously observed over the surface fissures near Kadoli, suggesting a southward extension of the Donichawadi fault zone up to the KFD1 site and confirming that the fault zone is permeable even after 50 years of the 1967 Koyna earthquake. 3He/4He ratios of eleven gas samples fall between 0.426±0.022 and 0.912±0.059 Ra, with 4He/20Ne values between 0.3449±0.0091 and 0.751±0.020. Air-corrected helium isotope ratios indicate that helium is a mixture of atmospheric and crustal radiogenic components but no mantle contribution within 2σ analytical uncertainties.

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Section: Geofluidssupporting

confidence: 71%

Chemical and Noble Gas Isotope Compositions of Formation Gases from a 3 km Deep Scientific Borehole in the Koyna Seismogenic Zone, Western India

et al. 2019

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“…High helium concentrations in the range 1–7 ppm (above the atmospheric level of 5.24 ppm) coinciding with the surface fissures, relative to regional background value of 0.2 ppm at distance of 40–60 m on either side of the fissure zone, confirm that the fissures constitute the surface expression of a NNE‐SSW oriented seismically active fault and that the fault zone had not healed even 30 years after the 1967 earthquake. The borehole KFD1 is located ~5 km to the south of Kadoli along the trend of the Donichawadi fault zone, in a cluster of active seismicity as revealed by the analysis of seismological data from a local network of 23 surface broadband seismic stations and 6 borehole seismometers operational in the Koyna seismogenic zone over the past decade (Gupta et al, ; Shashidhar et al, , ). The strong NNE‐SSW trend of the seismic cluster coinciding with the trend of the Donachiwadi fault zone provides evidence that the fault zone is active (Gupta et al, ).…”

Section: Discussionmentioning

confidence: 99%

“…While these studies indicate the presence of heterogeneities in the upper crust, direct evidence for subsurface faults in the region is available from soil‐gas helium studies accompanied by shallow drilling carried out during 1995–1997 in the NNE‐SSW trending Donichawadi fissure zone associated with the 1967 Koyna earthquake (Gupta et al, ). Anomalous soil‐gas helium concentrations detected over the fissures near Kadoli village, about 6 km to the south of Koyna dam confirm that the fissures are an expression of a deeper, subsurface fault zone, a fact that is supported by clustering of earthquake epicenters along the trend of the Donichawadi fissure zone over the past decade (Gupta et al, ). Distribution of large number of low magnitude earthquakes (≤3) in the region (Figure ) indicates the possibility of a number of small‐scale faults in the subsurface, which could be subsidiaries of the main fault.…”

Section: Geologymentioning

confidence: 96%

Delineation of Damage Zones From 3 km Downhole Geophysical Logs in the Koyna Seismogenic Zone, Western India

2019

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Delineation of subsurface faults and damage zones is a major goal of scientific drilling projects in seismically active areas. Geophysical logs acquired in a 3‐km deep scientific borehole KFD1 in the Koyna seismogenic zone, a site of recurrent reservoir triggered seismicity over the past 55 years, provide an unprecedented opportunity to investigate the rock properties and delineate the fault zones. KFD1 passed through 1,247‐m thick Deccan traps and continued for 1,767 m into the underlying granitic basement rocks that host the seismic activity in the depth range 2–10 km. We have studied the physical properties and acoustic behavior of basement granitoids from the analysis of geophysical logs from 1,500 to 3,000 m. Salient results are as follows. (1) Seven anomalous zones are identified below 2,100‐m depth based on electrical resistivity, caliper, density, neutron porosity, self‐potential, and sonic data. (2) The anomalous zones are characterized by significant shear wave velocity anisotropy (up to 25%), as revealed by cross‐dipole sonic data. (3) Dispersion analysis of dipole flexural modes confirms that the anisotropy is primarily stress induced; fast polarized shear wave azimuth (FSA) therefore indicates the orientation of maximum horizontal compressive stress SHmax. (4) Comparison of FSA with independent estimates of SHmax orientations obtained from drilling induced tensile fractures and strike of inclined fractures in the anisotropic zones shows that FSA is controlled mainly by the stress regime. Therefore, the stress rotations inferred from anisotropy analyses in the anomalous zones indicate their association with subsurface fault damage zones.

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“…Anomalous high helium concentrations in the range 1–7 ppm over the atmospheric abundance of 5.24 ppm coinciding with the surface fissures, relative to regional background value of 0.2 ppm at distance of 40–60 m on either side of the fissure zone, confirmed that the fissures constitute the surface expression of a NNE‐SSW oriented fault zone that had not healed even 30 years after the 1967 earthquake (Gupta et al, ). Recent studies involving analyses of seismological data sets obtained from a local network of 23 surface stations and 6 borehole stations show that earthquakes in this area over the past decade are clustered along a NNE‐SSW alignment coinciding with the Donichawadi fault zone (Gupta et al, ; Shashidhar et al, ). Recent field investigations combined with microstructural studies on basement core samples confirm the near‐vertical dip of majority of the fractures and the extension of surface fissures to depth (Misra et al, ).…”

Section: Discussionmentioning

confidence: 99%

“…Seismological studies carried out during the past few decades provide important information about the spatial distribution of seismicity and the faulting mechanism(s) in the Koyna-Warna region (Gupta, 2002;Gupta et al, 2017;Rajendran & Harish, 2000;Shashidhar et al, 2011Shashidhar et al, , 2013Talwani, 1997a) (Figure 1). Although the studies reveal dominantly strike-slip faulting environment in the Koyna region and normal regime in the nearby Warna region, the tectonic setting of the region remains poorly constrained.…”

Section: Geologic and Tectonic Settingmentioning

confidence: 99%

In Situ Stress Orientation From 3 km Borehole Image Logs in the Koyna Seismogenic Zone, Western India: Implications for Transitional Faulting Environment

2020

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Knowledge of the in situ stress regime is critical to investigate the genesis of recurrent triggered seismicity over the past five decades in the Koyna seismogenic zone. Orientations of in situ horizontal stresses are determined for the first time from analyses of image logs in a 3 km deep scientific borehole KFD1 in the area. KFD1 passed through 1,247 m thick Deccan Traps and continued 1,767 m in the granitic basement. Stress-induced wellbore failures, breakouts and drilling-induced tensile fractures, are identified in the acoustic and microresistivity images of the granitic basement. Additionally, tightly constrained focal mechanisms of 50 earthquakes of M ≥ 3.6, reported in literature, are inverted to constrain the stress regime. Salient results are as follows: (i) wellbore breakouts and drilling-induced tensile fractures constrain N9°W ± 17°orientation for maximum horizontal principal stress (S Hmax ); (ii) consistency with the regional NNW-SSE orientation of S Hmax from inversion of earthquake focal mechanisms shows that the borehole data are representative for the Koyna region; (iii) breakout rotations at multiple depths below 2,100 m indicate that the borehole may have passed through localized fault damage zones; (iv) consistent strike azimuths of steeply dipping fractures with S Hmax orientation indicate favorable conditions for strike-slip to normal transitional faulting environment; and (v) stress inversion of 50 well-determined earthquake focal mechanisms supports transitional faulting environment in the Koyna seismogenic zone. Thus, stress orientation and fracture information from borehole data, together with stress regime constrained from inversion of earthquake focal mechanisms, shed new light on the faulting environment in the region.

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Location of the pilot borehole for investigations of reservoir triggered seismicity at Koyna, India

Cited by 22 publications

References 29 publications

Chemical and Noble Gas Isotope Compositions of Formation Gases from a 3 km Deep Scientific Borehole in the Koyna Seismogenic Zone, Western India

Chemical and Noble Gas Isotope Compositions of Formation Gases from a 3 km Deep Scientific Borehole in the Koyna Seismogenic Zone, Western India

Delineation of Damage Zones From 3 km Downhole Geophysical Logs in the Koyna Seismogenic Zone, Western India

In Situ Stress Orientation From 3 km Borehole Image Logs in the Koyna Seismogenic Zone, Western India: Implications for Transitional Faulting Environment

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