A note on induced stress changes in hydrocarbon and geothermal reservoirs

Segall, P.; Fitzgerald, Shaun

doi:10.1016/s0040-1951(97)00311-9

Cited by 348 publications

(234 citation statements)

References 19 publications

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“…LOFGREN (1981) and DENLINGER and BUFE (1982) analyzed local geodetic data at The Geysers and found a negative strain in horizontal directions and subsidence in the vertical direction. SEGALL (1997, 1999) and SEGALL and FITZGERALD (1998) analyzed GPS and leveling data that confirmed earlier estimates of subsidence within the reservoir, with rates as high as 0.047 ± 0.002 m/year during the period 1977-1996. They also estimated volume strain, temperature change, pressure change, and bulk modulus in the producing part of the reservoir. PRESCOTT and YU (1986) used regional geodetic data to show that regional strain in The Geysers was primarily a shear with extension oriented N79°W and contraction oriented N11°E.…”

Section: Previous Studiessupporting

confidence: 61%

Source Mechanisms of Induced Earthquakes at The Geysers Geothermal Reservoir

Johnson

2014

Pure Appl. Geophys.

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Abstract-At The Geysers geothermal reservoir in northern California, evidence strongly suggests that activities associated with production of electric power cause an increase in the number of small earthquakes. First-degree dynamic moment tensors are used to investigate the relationship between induced earthquakes and injection of water into a well as part of a controlled experiment in the northwest Geysers. The estimation of dynamic moment tensors in the complex shallow crust at The Geysers is challenging, so the method is described in detail with particular attention given to the uncertainty in the results. For seismic events in the moment magnitude range of 0.9-2.8, spectral moduli of dynamic moment tensors are reliably recovered in the frequency range of 1-100 Hz, but uncertainty in the associated spectral phases limits their use to a few simple results. A number of different static moment tensors are investigated, with the preferred one obtained from parameters of a model fitted to the spectral modulus of the dynamic moment tensor. Moment tensors estimated for a group of 20 earthquakes exhibit a range of source mechanisms, with over half having significant isotropic parts of either positive or negative sign. Corner frequencies of the isotropic part of the moment tensor are about 40 % larger than the average of the deviatoric moment tensor. Some spatial patterns are present in source mechanisms, with earthquakes closely related in space tending to have similar mechanisms, but at the same time, some nearby earthquakes have very different mechanisms. Tensional axes of displacement in the source regions are primarily horizontal, while the pressure axes range from near horizontal to vertical. Injection of water into the well in the center of the study area clearly causes an increase in the number of earthquakes per day, but an effect upon source mechanisms is not evident.

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Section: Previous Studiessupporting

confidence: 61%

Source Mechanisms of Induced Earthquakes at The Geysers Geothermal Reservoir

Johnson

2014

Pure Appl. Geophys.

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“…The role of fluids modifying the stress field and the faulting regime has been already pointed out in earlier studies [e.g., Hardebeck and Hauksson, 1999;Kato et al, 2011]. In particular, Segall and Fitzgerald [1998] related a potential vertical variation of the stress state within the reservoir, above and below it to poroelastic effects related to reservoir depletion, i.e., on a time scale of decades. Specifically, the authors suggest that the horizontal stresses immediately above and below a reservoir are more compressive than within the reservoir.…”

Section: Discussionmentioning

confidence: 72%

Stress Tensor Changes Related to Fluid Injection at The Geysers Geothermal Field, California

et al. 2014

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[1] Studying variations of the stress field in reservoirs caused by massive fluid injection is important toward an improved understanding of geomechanical processes involved. We report on spatio-temporal variations of the local stress tensor orientation at The Geysers geothermal field, California. We apply two stress inversion methods with detailed uncertainty assessments using a selection of events recorded between 2007 and 2012. Our results clearly indicate variations in the orientation of the principal stress axes for the reservoir as a whole showing a normal faulting regime at the reservoir depth between 2 and 3.7 km bounded by a strike-slip regime above and below. Analyzing the temporal evolution of the stress tensor orientation for a prominent seismicity cluster we observe a clear correlation of changes in orientation for s 1-3 with the highest injection rates. These results suggest that temporal changes in the stress tensor orientation could contribute to characterize reservoirs during stimulation.

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“…Around producing fractures, where strong temperature and pressure gradients are expected, thermoelastic effects may dominate over poroelastic effects and alter the stress state within the reservoir [Segall and Fitzgerald , 1998]. …”

Section: Double-couple Earthquakesmentioning

confidence: 99%

Focal mechanisms and size distribution of earthquakes beneath the Krafla central volcano, NE Iceland

et al. 2016

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Seismicity was monitored beneath the Krafla central volcano, NE Iceland, between 2009 and 2012 during a period of volcanic quiescence, when most earthquakes occurred within the shallow geothermal field. The highest concentration of earthquakes is located close to the rock‐melt transition zone as the Iceland Deep Drilling Project‐1 (IDDP‐1) wellbore suggests and decays quickly at greater depths. We recorded multiple swarms of microearthquakes, which coincide often with periods of changes in geothermal field operations, and found that about one third of the total number of earthquakes are repeating events. The event size distribution, evaluated within the central caldera, indicates average crustal values with b = 0.79 ± 0.04. No significant spatial b value contrasts are resolved within the geothermal field nor in the vicinity of the drilled melt. Besides the seismicity analysis, focal mechanisms are calculated for 342 events. Most of these short‐period events have source radiation patterns consistent with double‐couple (DC) mechanisms. A few events are attributed to non‐shear‐faulting mechanisms with geothermal fluids likely playing an important role in their source processes. Diverse faulting styles are inferred from DC events, but normal faulting prevails in the central caldera. The best fitting compressional and tensional axes of DC mechanisms are interpreted in terms of the principal stress or deformation rate orientations across the plate boundary rift. Maximum compressive stress directions are near‐vertically aligned in different study volumes, as expected in an extensional tectonic setting. Beneath the natural geothermal fields, the least compressive stress axis is found to align with the regional spreading direction. In the main geothermal field both horizontal stresses appear to have similar magnitudes causing a diversity of focal mechanisms.

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A note on induced stress changes in hydrocarbon and geothermal reservoirs

Cited by 348 publications

References 19 publications

Source Mechanisms of Induced Earthquakes at The Geysers Geothermal Reservoir

Source Mechanisms of Induced Earthquakes at The Geysers Geothermal Reservoir

Stress Tensor Changes Related to Fluid Injection at The Geysers Geothermal Field, California

Focal mechanisms and size distribution of earthquakes beneath the Krafla central volcano, NE Iceland

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