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(a) Catalogued earthquakes for B084. Seismic energy density plotted as contours, with all earthquakes larger than 10⁻³ J m⁻³ plotted as larger markers. Red events represent main shocks that caused changes in permeability; black events are aftershocks from these events, while blue events caused no change in permeability. (b) Magnitude of events over time. Red events represent main shocks that caused changes in permeability; black events are aftershocks from these events, while blue events caused no change in permeability.
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Because of the influence pore pressures have on effective stress, understanding hydrogeologic properties that control fluid flow and pressure distribution is important in characterizing earthquake and deformation processes. Here, we utilize borehole pressure changes in response to earth tides to determine hydrogeologic properties and their time var...
Citations
... In addition to these hydrological effects, the elastic modulus (i.e., specific storage) also affects the amplitude and phase of tidal modulation. Simon et al. (2021) shows that the pressure tidal response to surface loading (both amplitude and phase) is heavily dependent on both permeability and specific storage. The Kuroko ore-cultivation apparatus deployed in Hole C9017 B at the Noho hydrothermal site, mid-Okinawa Trough. ...
We observed temperature variations over 10 months within a Kuroko ore (hydrothermal sulfide) cultivation apparatus installed atop a 50‐m‐deep borehole drilled in the Noho hydrothermal system in the mid‐Okinawa Trough, southwestern Japan, for monitoring of hydrothermal fluids and in situ mineral precipitation experiments. Temperature and pressure in the apparatus fluctuated with the tidal period immediately after its installation. Initially, the average temperature was 75–76°C and the amplitude of the semidiurnal tidal temperature modulation was ∼0.3°C. Four months later, the amplitude of tidal temperature modulation had gradually increased to 4°C in synchrony with an average temperature decrease to ∼40°C. Numerical modeling showed that both the increase in tidal amplitude and the decrease in average temperature were attributable to a gradual decrease in inflow to the apparatus, which promoted conductive cooling through the pipe wall. The reduced inflow was probably caused by clogging inside the apparatus, but we cannot rule out a natural cause, because the drilling would have significantly decreased the volume of hot fluid in the reservoir. The temperature fluctuation phase lagged the pressure fluctuation phase by ∼150°. Assuming that the fluctuations originated from inflow from the reservoir, we conducted 2D numerical hydrothermal modeling for a poroelastic medium. To generate the 150° phase lag, the permeability in the reservoir needed to exceed that in the ambient formation by ∼three orders of magnitude. The tidal variation phase can be a useful tool for assessing the hydrological state and response of a hydrothermal system.
Исследованию механизмов деформирования флюидонасыщенных коллекторов посвящено большое количество научных работ. Данные дистанционного прецизионного гидрогеологического мониторинга позволяют объективно оценивать фильтрационные свойства флюидонасыщенных коллекторов. Реакция системы «пласт - скважина» на атмосферное давление, земные приливы и прохождение сейсмических волн от землетрясений проявляется в виде осцилляций уровня подземных вод, косейсмических и постсейсмических эффектов. Гидрогеологические отклики на квазистационарные факторы соответствуют пороупругому деформированию массива горных пород. Эпизодическое сейсмическое воздействие может приводить как к пороупругой, так и к неупругой реакции флюидонасыщенного коллектора. В ближней зоне землетрясений, в области статических напряжений, установлено скачкообразное (ступенчатое) изменение проницаемости, которое может быть связано с различными механизмами. К ним относятся разжижение дисперсного грунта, дилатансия - трещинообразование на контакте пород с разными прочностными характеристиками и другие. В промежуточной и дальней зонах, области динамических напряжений, длиннопериодные колебания, вызванные прохождением поперечных и поверхностных волн, могут приводить к кольматации/декольматации микротрещин и вариациям проницаемости. Формирование целостного представления о режиме деформирования массива горных пород при сейсмическом воздействии направлено на прогнозную оценку возможных изменений фильтрационных свойств флюидонасыщенных коллекторов.
A large volume of scientific papers is devoted to the study of the deformation mechanisms of fluid-saturated reservoirs. Precision hydrogeological monitoring data allows to objectively assess filtration properties of fluid-saturated reservoirs. The reaction of the «reservoir-well» system to atmospheric pressure, Earth tides and the propagation of earthquakes seismic waves can occur in the form of the groundwater level oscillations, coseismic and postseismic effects. Hydrogeological responses to quasi-stationary factors are determined by poroelastic deformation of the rock mass. Episodic seismic impact can lead to both poroelastic and inelastic reaction of a fluid-saturated reservoir. In the near-field zone of earthquakes, in the area of static stresses, an abrupt (step-like) change of permeability has been established, which may be associated with various mechanisms. These include liquefaction of dispersed soil, dilatancy - crack formation at the contact zone of rocks with different strength characteristics, and others. In the intermediate and distant zones, areas of dynamic stresses, long-period oscillations caused by the passage of shear and surface waves can lead to microcracks clogging/unclogging and variations of permeability. The formation of a holistic view of the deformation regime of a rock mass under seismic impact is aimed to predictpossible changes of the fluid-saturated reservoirs filtration properties.
Subsurface tidal analysis requires only continuous pressure monitoring data and therefore can be a cost-effective technique for estimating aquifer properties. The tidal behavior of a well in a semiconfined aquifer can be described by a diffusion equation that includes a leakage term. This approach is valid for thin aquifers, as long as the overlying layer has low permeability relative to the main aquifer. However, in cases where the aquifer is not thin and the permeability of the overlying layer is not low, using the existing solutions based on these approximations may lead to unsatisfactory outcomes. Alternative solutions for both vertical and horizontal wells were obtained by solving the standard diffusion equation, with leakage expressed as a boundary condition. Furthermore, a nondimensional number was derived mathematically, which forms the basis for a quantitative criterion to assess the applicability of the existing solutions. In the case of a vertical well, the existing solution exhibits acceptable error only if the nondimensional number is less than 0.245. Our new solution extends this upper limitation to 0.475. However, when the number is greater than 0.475, both the existing solution and our new solution are invalid due to the invalid uniform flowrate assumption. For a horizontal well, when the number is less than 0.245, the existing solution is suitable with acceptable error. Our new solution effectively overcomes this limitation. Finally, the new solution was applied to the case of the Arbuckle aquifer to demonstrate the improved validity of the new solution compared to the existing one.
