Sedimentary basin

Summary

Sedimentary basins are region-scale depressions of the Earth's crust where subsidence has occurred and a thick sequence of sediments have accumulated to form a large three-dimensional body of sedimentary rock. They form when long-term subsidence creates a regional depression that provides accommodation space for accumulation of sediments. Over millions or tens or hundreds of millions of years the deposition of sediment, primarily gravity-driven transportation of water-borne eroded material, acts to fill the depression. As the sediments are buried, they are subject to increasing pressure and begin the processes of compaction and lithification that transform them into sedimentary rock. Sedimentary basins are created by deformation of Earth's lithosphere in diverse geological settings, usually as a result of plate tectonic activity. Mechanisms of crustal deformation that lead to subsidence and sedimentary basin formation include the thinning of underlying crust; depression of the crust

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https://en.wikipedia.org/wiki/Sedimentary_basin

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The seismic history of the Mosha fault, the largest and most active fault of Eastern Tehran metropolis, and its relation to the Damavand active volcano, the highest mountain in the Middle East, is investigated. We deduce that the central Mosha, near the Damavand, has a higher seismicity than either its western or eastern segments. On 7 May 2020, an Mw 5.1 earthquake occurred on the central Mosha, about 40 km east of Tehran and 10 km southwest of the Damavand crest, and it was felt intensely in Tehran. Its rupture is imaged and located in a region that presented a relative seismic quiescence compared to its eastern and western parts, during the last 14 years, suggesting its partial locking and heterogeneous distribution of fault frictional strength on this segment of Mosha. Its significant directivity to the west is confirmed by the mainshock rupture model, its PGA distribution, and distribution of early aftershocks. The rupture model suggests a relatively small stress drop of 2.6 bar, which is consistent with the comparatively high rupture dimension of 9 km for a Mw 5.1 earthquake, and indicates the easy rupture expansion on the central Mosha near the Damavand Volcano. The central Mosha experienced earthquakes in 1930, 1955, and 1983, as well as high microseismic activity and the 2020 seismic sequence, all of which strongly point to a possible influence of the Damavand Volcano on the seismicity of the central Mosha. This is corroborated by the observation of hydrothermal zones on the Mosha fault and the extension of a sill-like Damavand young magma chamber until central Mosha in tomography studies. We propose that the existing heat may increase the pore pressure on the fault, which lowers the effective normal stress, facilitates the nucleation-expansion of the rupture, and unclamps the fault. Damavand could act as a fuse and nucleate earthquakes, and if the rupture extends toward the west, it could have a significant directivity effect on low-frequency seismic waves that reach Tehran without attenuation and affect tall structures. In addition, high site amplification for frequencies up to 16 Hz due to the deep sedimentary basin, mainly in the mid-city of Tehran, will be remarkable for short buildings.

2022

Impact of the anisotropy of fracture toughness on the propagation of planar 3D hydraulic fracture

Brice Tanguy Alphonse Lecampion, Weihan Zhang, Haseeb Zia

Sedimentary rocks often exhibit a transverse isotropy due to fine scale layering. We investigate the effect of the anisotropy of fracture toughness on the propagation of a planar 3D hydraulic fracture perpendicular to the isotropy plane: a configuration commonly encountered in sedimentary basins. We extend a fully implicit level set scheme for the simulation of hydraulic fracture growth to the case of anisotropic fracture toughness. We derive an analytical solution for the propagation of an elliptical hydraulic fracture in the toughness dominated regime—a shape which results from a particular form of toughness anisotropy. The developed numerical solver closely matches this solution as well as classical benchmarks for hydraulic fracture growth with isotropic toughness. We then quantify numerically the transition between the viscosity dominated propagation regime at early time—where the fracture grows radially—to the toughness dominated regime at large time where the fracture reaches an elliptical shape in the case of an elliptical anisotropy. The time scale at which the fracture starts to deviate from the radial shape and gets more elongated in the direction of lower toughness is in accordance with the viscosity to toughness transition time-scale for a radial fracture defined with the largest value of fracture toughness. Similarly, the toughness dominated regime is fully reached along the whole fracture front when the time gets significantly larger than the same transition time-scale defined with the lowest value of toughness. Using different toughness anisotropy functions, we also illustrate how the details of the complete variation of fracture toughness with propagation direction governs the final hydraulic fracture shape at large time. Our results highlight toughness anisotropy as a possible hydraulic fracture height containment mechanism as well as the need for its careful characterization beyond measurements in the sole material axes (divider and arrester) directions.

2018

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Hydraulic fracturing is a widespread technology used to enhance reservoir production but also to measure the in-situ stress field. It consists of growing a tensile (mode I) fracture via the injection of a viscous fluid (usually at a constant rate) from a wellbore. Hydraulic fracturing treatments vary widely in scales, rates and volumes injected. For example, a well stimulation operation typically consists in injecting up to 100’000 liters at a rate of about 20-50 liters per second, while only ~5 liters are injected over the two-three minutes of the duration of an injection cycle of a micro-hydraulic fracturing stress measurement. The main risk associated with hydraulic fracturing treatment relates to vertical fracture growth above the desired formation of interest, toward environmentally sensitive layers. In sedimentary basins, characterised by rock strata at different scales, hydraulic fractures are typically observed to be contained at depth and propagate horizontally in a “finger-like” geometry (Economides & Nolte 2000, Bunger & Lecampion 2017). Such containment is usually explained by the increase of the horizontal confining stress in the layers above and below the stimulated reservoir. Of course, variation of material properties such as elastic modulus, permeability, fracture toughness can also contribute to containment (Simonson et al. 1978, Thiercelin et al. 1989). In this work, we consider the symmetric scenario where the injection point is located at the center of a layer of height H bounded by two layers of similar properties. We investigate the case where the material fracture toughness in the central layer is lower than in the bounding layers, assuming the other properties to be uniform (see Fig. 1). We focus on the so-called toughness dominated regime, where the fluid viscous energy is negligible compared to the energy spent in creating new fracture surfaces. By means of numerical simulations and scaling analysis, we establish whether, or not, a fluid-driven fracture can remain confined between the two tough layers. We show that a ratio of fracture toughness between the layers larger than √2 is sufficient to contain indefinitely the growing hydraulic fracture. For toughness ratios lower than that limit, we estimate the amount of time the propagating fracture remains contained before breaking through. Finally, we discuss how a finite amount of fluid viscous energy affects containment in that configuration.

2021

2022

Impact of the anisotropy of fracture toughness on the propagation of planar 3D hydraulic fracture

Brice Tanguy Alphonse Lecampion, Weihan Zhang, Haseeb Zia

2018

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2021