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Hanspeter Harjes - One of the best experts on this subject based on the ideXlab platform.
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a model for fluid injection induced seismicity at the ktb germany
Geophysical Journal International, 2003Co-Authors: Stefan Baisch, Hanspeter HarjesAbstract:SUMMARY The 9.1 km deep KTB (Kontinentale Tiefbohrung, Germany) Drilling Hole is one of the best investigated deep-Drilling sites in the world. Among other parameters, in situ measurements revealed continuous profiles of principal stresses, pore fluid pressure and fracture geometry in the vicinity of the boreHole. The present study combines these parameters with hydraulic and seismicity data obtained during fluid-injection experiments conducted at the KTB to derive a conceptual model for fluid-injection-induced seismicity at the KTB. This model rests on the well constrained assumptions that (1) the crust is highly fractured with a permeable fracture network between 9 km depth and the Earth's surface and (2) the crust is in near-failure equilibrium, whereby a large number of fracture planes are under near-critical condition. During the injection experiment, the elevated pore fluid pressure remained well below the least principal stress and thus was too small to cause hydraulic opening of existing fractures. Consequently, the geometry of the fracture network was assumed to have not changed during fluid injection with induced seismicity occurring solely as a result of lowering of the effective normal stress, consistent with observed source mechanisms. The key parameter in the present model is the fracture permeability, which exhibits large spatial and directional variations. These variations are proposed to primarily control fluid migration paths and associated propagation of elevated fluid pressure during fluid injection. In contrast with common models based on isotropic fluid diffusion or spatially averaged permeability, highly permeable branches of the fracture network strongly affect the propagation of fluid pressure and prohibit the concept of a smooth ‘pressure front’. We find evidence that major fluid flow exists at comparatively low fluid pressure (below the critical pressure required to cause seismic failure) without being detected seismically. This might also explain the difference between 1011 J of hydraulic energy inserted into the system during fluid injection and ∼108 J of seismic energy: a major part of the hydraulic energy might be converted to potential energy of the ground water level caused by upward migrating fluid. From the fluid level response to changes of injection rate observed in a second boreHole we estimate fluid signal velocities to be as large as 300 m d−1. Importantly, the suggested model also accounts for the occurrence of repeating earthquakes (multiplets), a large number of which were observed during the injection experiment. The present model also suggests that coseismic changes of the stress field caused by tectonic shear stress release are very local and of small magnitude. This is consistent with the observation that none of the larger induced events is followed by aftershock series that would be expected if coseismic processes had noticeably perturbed the local stress field.
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probing the crust to 9 km depth fluid injection experiments and induced seismicity at the ktb superdeep Drilling Hole germany
Bulletin of the Seismological Society of America, 2002Co-Authors: Stefan Baisch, Marco Bohnhoff, Lars Ceranna, Yimin Tu, Hanspeter HarjesAbstract:A 60-day, long-term fluid-injection experiment was performed at the 9.1-km-deep Kontinentale Tiefbohrung, Germany (KTB), boreHole. About 4000 m3 of water were injected into the well head to induce seismicity near the open-Hole section at 9-km depth. Because of several leaks in the boreHole casing (unknown before), seismicity occurred at distinct depth levels between 3-km and 9-km depth. Two events occurred at 10-km and 15-km depth. The combination of a temporary, 40-element, three-component surface network of seismometers and a three-component downHole sonde at 3.8-km depth in the nearby pilot Hole enabled us to determine absolute hypocenter locations by using a velocity model that was calibrated from several downHole shots at depths of 5.4 km and 8.5 km. Of a total of 2799 induced events, hypocenter locations were obtained for 237 events having good signal-to-noise ratio at surface stations. The spatiotemporal distribution of hypocenters at each depth level exhibits complex structures extending several hundred meters from the injection points, with strong spatial and temporal clustering. Regions that were seismically active at a certain time often showed reduced or no activity at later times, indicating local shear-stress relaxation. A similar “memory” effect (Kaiser effect) is observed by comparing hypocenter locations of the present experiment with those obtained for a previous injection experiment at KTB. The limitation of hypocentral depths to 9.1 km for events near the boreHole suggests changes in rheological properties of the upper crust and thus supports a transition from the regime of brittle failure to ductile deformation at this depth. Large fluid-level changes observed in the nearby pilot Hole demonstrate that fluid flow occurs over distances greater than 1.5 km and that major flow zones are not mapped by the induced seismicity. This might also explain the occurence of isolated events at greater distances and depths. Brittle failure at depths greater than 10 km indicates the existence of critically stressed fractures even at temperature over 300°C.
Stefan Baisch - One of the best experts on this subject based on the ideXlab platform.
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a model for fluid injection induced seismicity at the ktb germany
Geophysical Journal International, 2003Co-Authors: Stefan Baisch, Hanspeter HarjesAbstract:SUMMARY The 9.1 km deep KTB (Kontinentale Tiefbohrung, Germany) Drilling Hole is one of the best investigated deep-Drilling sites in the world. Among other parameters, in situ measurements revealed continuous profiles of principal stresses, pore fluid pressure and fracture geometry in the vicinity of the boreHole. The present study combines these parameters with hydraulic and seismicity data obtained during fluid-injection experiments conducted at the KTB to derive a conceptual model for fluid-injection-induced seismicity at the KTB. This model rests on the well constrained assumptions that (1) the crust is highly fractured with a permeable fracture network between 9 km depth and the Earth's surface and (2) the crust is in near-failure equilibrium, whereby a large number of fracture planes are under near-critical condition. During the injection experiment, the elevated pore fluid pressure remained well below the least principal stress and thus was too small to cause hydraulic opening of existing fractures. Consequently, the geometry of the fracture network was assumed to have not changed during fluid injection with induced seismicity occurring solely as a result of lowering of the effective normal stress, consistent with observed source mechanisms. The key parameter in the present model is the fracture permeability, which exhibits large spatial and directional variations. These variations are proposed to primarily control fluid migration paths and associated propagation of elevated fluid pressure during fluid injection. In contrast with common models based on isotropic fluid diffusion or spatially averaged permeability, highly permeable branches of the fracture network strongly affect the propagation of fluid pressure and prohibit the concept of a smooth ‘pressure front’. We find evidence that major fluid flow exists at comparatively low fluid pressure (below the critical pressure required to cause seismic failure) without being detected seismically. This might also explain the difference between 1011 J of hydraulic energy inserted into the system during fluid injection and ∼108 J of seismic energy: a major part of the hydraulic energy might be converted to potential energy of the ground water level caused by upward migrating fluid. From the fluid level response to changes of injection rate observed in a second boreHole we estimate fluid signal velocities to be as large as 300 m d−1. Importantly, the suggested model also accounts for the occurrence of repeating earthquakes (multiplets), a large number of which were observed during the injection experiment. The present model also suggests that coseismic changes of the stress field caused by tectonic shear stress release are very local and of small magnitude. This is consistent with the observation that none of the larger induced events is followed by aftershock series that would be expected if coseismic processes had noticeably perturbed the local stress field.
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probing the crust to 9 km depth fluid injection experiments and induced seismicity at the ktb superdeep Drilling Hole germany
Bulletin of the Seismological Society of America, 2002Co-Authors: Stefan Baisch, Marco Bohnhoff, Lars Ceranna, Yimin Tu, Hanspeter HarjesAbstract:A 60-day, long-term fluid-injection experiment was performed at the 9.1-km-deep Kontinentale Tiefbohrung, Germany (KTB), boreHole. About 4000 m3 of water were injected into the well head to induce seismicity near the open-Hole section at 9-km depth. Because of several leaks in the boreHole casing (unknown before), seismicity occurred at distinct depth levels between 3-km and 9-km depth. Two events occurred at 10-km and 15-km depth. The combination of a temporary, 40-element, three-component surface network of seismometers and a three-component downHole sonde at 3.8-km depth in the nearby pilot Hole enabled us to determine absolute hypocenter locations by using a velocity model that was calibrated from several downHole shots at depths of 5.4 km and 8.5 km. Of a total of 2799 induced events, hypocenter locations were obtained for 237 events having good signal-to-noise ratio at surface stations. The spatiotemporal distribution of hypocenters at each depth level exhibits complex structures extending several hundred meters from the injection points, with strong spatial and temporal clustering. Regions that were seismically active at a certain time often showed reduced or no activity at later times, indicating local shear-stress relaxation. A similar “memory” effect (Kaiser effect) is observed by comparing hypocenter locations of the present experiment with those obtained for a previous injection experiment at KTB. The limitation of hypocentral depths to 9.1 km for events near the boreHole suggests changes in rheological properties of the upper crust and thus supports a transition from the regime of brittle failure to ductile deformation at this depth. Large fluid-level changes observed in the nearby pilot Hole demonstrate that fluid flow occurs over distances greater than 1.5 km and that major flow zones are not mapped by the induced seismicity. This might also explain the occurence of isolated events at greater distances and depths. Brittle failure at depths greater than 10 km indicates the existence of critically stressed fractures even at temperature over 300°C.
Shan Hongxian - One of the best experts on this subject based on the ideXlab platform.
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deep sea floor pore water pressure long term observation automatic laying system and deep sea floor pore water pressure long term observation automatic laying method
2015Co-Authors: Jia Yonggang, Guo Lei, Liu Xiaolei, Zhang Shaotong, Wang Zhenhao, Shan HongxianAbstract:The invention discloses a deep-sea floor pore water pressure long-term observation automatic laying system and a deep-sea floor pore water pressure long-term observation automatic laying method. The system comprises an automatic lifting pore pressure meter, a underwater acoustic/long wave communicator, a ship-borne controller and a laying apparatus; the automatic lifting pore pressure meter orderly comprises a lower drill, a balance weight, a master control cabin, a floating body material, an upper drill and a protective rest from bottom to top; the underwater acoustic/long wave communicator and the ship-borne controller are used for controlling the automatic lifting pore pressure meter. A laying bracket and the automatic lifting pore pressure are sent into the seabed surface through a hook while laying; the lower drill begins Drilling Hole to enter sediment, and the stops running after arriving a set depth; and then the hook is packed up through a cable to finish the laying. When the system is used for recycling, a releaser is started through the emission of a control signal, parts of the automatic lifting pore pressure meter except the lower drill and the balance weight thereof are separated so that the automatic lifting pore pressure meter is floated, and recycled. The repeated laying-recycling of a complex deep-sea instrument is avoided, the working efficiency is improved, the research cost is lowered, and the artificial disturbance on the field search environment in the laying-recycling process is avoided.
Marco Bohnhoff - One of the best experts on this subject based on the ideXlab platform.
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probing the crust to 9 km depth fluid injection experiments and induced seismicity at the ktb superdeep Drilling Hole germany
Bulletin of the Seismological Society of America, 2002Co-Authors: Stefan Baisch, Marco Bohnhoff, Lars Ceranna, Yimin Tu, Hanspeter HarjesAbstract:A 60-day, long-term fluid-injection experiment was performed at the 9.1-km-deep Kontinentale Tiefbohrung, Germany (KTB), boreHole. About 4000 m3 of water were injected into the well head to induce seismicity near the open-Hole section at 9-km depth. Because of several leaks in the boreHole casing (unknown before), seismicity occurred at distinct depth levels between 3-km and 9-km depth. Two events occurred at 10-km and 15-km depth. The combination of a temporary, 40-element, three-component surface network of seismometers and a three-component downHole sonde at 3.8-km depth in the nearby pilot Hole enabled us to determine absolute hypocenter locations by using a velocity model that was calibrated from several downHole shots at depths of 5.4 km and 8.5 km. Of a total of 2799 induced events, hypocenter locations were obtained for 237 events having good signal-to-noise ratio at surface stations. The spatiotemporal distribution of hypocenters at each depth level exhibits complex structures extending several hundred meters from the injection points, with strong spatial and temporal clustering. Regions that were seismically active at a certain time often showed reduced or no activity at later times, indicating local shear-stress relaxation. A similar “memory” effect (Kaiser effect) is observed by comparing hypocenter locations of the present experiment with those obtained for a previous injection experiment at KTB. The limitation of hypocentral depths to 9.1 km for events near the boreHole suggests changes in rheological properties of the upper crust and thus supports a transition from the regime of brittle failure to ductile deformation at this depth. Large fluid-level changes observed in the nearby pilot Hole demonstrate that fluid flow occurs over distances greater than 1.5 km and that major flow zones are not mapped by the induced seismicity. This might also explain the occurence of isolated events at greater distances and depths. Brittle failure at depths greater than 10 km indicates the existence of critically stressed fractures even at temperature over 300°C.
Lars Ceranna - One of the best experts on this subject based on the ideXlab platform.
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probing the crust to 9 km depth fluid injection experiments and induced seismicity at the ktb superdeep Drilling Hole germany
Bulletin of the Seismological Society of America, 2002Co-Authors: Stefan Baisch, Marco Bohnhoff, Lars Ceranna, Yimin Tu, Hanspeter HarjesAbstract:A 60-day, long-term fluid-injection experiment was performed at the 9.1-km-deep Kontinentale Tiefbohrung, Germany (KTB), boreHole. About 4000 m3 of water were injected into the well head to induce seismicity near the open-Hole section at 9-km depth. Because of several leaks in the boreHole casing (unknown before), seismicity occurred at distinct depth levels between 3-km and 9-km depth. Two events occurred at 10-km and 15-km depth. The combination of a temporary, 40-element, three-component surface network of seismometers and a three-component downHole sonde at 3.8-km depth in the nearby pilot Hole enabled us to determine absolute hypocenter locations by using a velocity model that was calibrated from several downHole shots at depths of 5.4 km and 8.5 km. Of a total of 2799 induced events, hypocenter locations were obtained for 237 events having good signal-to-noise ratio at surface stations. The spatiotemporal distribution of hypocenters at each depth level exhibits complex structures extending several hundred meters from the injection points, with strong spatial and temporal clustering. Regions that were seismically active at a certain time often showed reduced or no activity at later times, indicating local shear-stress relaxation. A similar “memory” effect (Kaiser effect) is observed by comparing hypocenter locations of the present experiment with those obtained for a previous injection experiment at KTB. The limitation of hypocentral depths to 9.1 km for events near the boreHole suggests changes in rheological properties of the upper crust and thus supports a transition from the regime of brittle failure to ductile deformation at this depth. Large fluid-level changes observed in the nearby pilot Hole demonstrate that fluid flow occurs over distances greater than 1.5 km and that major flow zones are not mapped by the induced seismicity. This might also explain the occurence of isolated events at greater distances and depths. Brittle failure at depths greater than 10 km indicates the existence of critically stressed fractures even at temperature over 300°C.
