Compaction creep of quartz sand at 400–600°C: experimental evidence for dissolution-controlled pressure solution
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Pressure solution
Overburden pressure
Deformation mechanism
Diffusion creep
Deformation mechanism
Pressure solution
Superplasticity
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During compaction band formation, various mechanisms can be involved at different scales. Mechanical and chemical degradation of the solid skeleton and grain damage are important factors that may trigger instabilities in the form of compaction bands. Here we explore the conditions of compaction band formation in quartz- and carbonate-based geomaterials by considering the effect of chemical dissolution and grain breakage. As the stresses/deformations evolve, the grains of the material break, leading to an increase of their specific surface. Consequently, their dissolution is accelerated and chemical softening is triggered. By accounting for (a) the mass diffusion of the system, (b) a macroscopic failure criterion with dissolution softening, and (c) the reaction kinetics at the microlevel, a model is proposed and the conditions for compaction instabilities are investigated. Distinguishing the microscale (grain level) from the macrolevel (representative elementary volume) and considering the heterogeneous microstructure of the representative elementary volume, it is possible to discuss the thickness and periodicity of compaction bands. Two case studies are investigated. The first one concerns a sandstone rock reservoir which is water flooded and the second one a carbonate rock in which CO2 is injected for storage. It is shown that compaction band instabilities are possible in both cases.
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Compaction of sedimentary porous rock by dissolution and precipitation is a complex deformation mechanism, that is often localized on stylolites and pressure solution seams. We consider a one‐dimensional model of compaction near a thin clay‐rich stylolite embedded in a porous rock. Under the assumption that the clay enhances solubility, the model predicts a reactive transport away from the clay layer followed by pore cementation. The evolution of the porosity, reactant transport, and compaction rate are studied as functions of model parameters and shown to reach a stationary state. We find good agreement between the porosity distribution predicted by the model and previously reported field measurements. The model provides quantitative estimates for compaction rates on stylolitic surfaces.
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Overburden pressure
Overburden
Hydrostatic pressure
Pressure solution
Hydrostatic equilibrium
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Cataclastic rock
Deformation bands
Stylolite
Deformation mechanism
Cementation (geology)
Pressure solution
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Abstract The deformation behavior of fine grained limestones from the Monte Sirino area (Lucania region) of the southern Apennines has been analysed by constraining microstructural observations and crystallographic fabrics with data on the metamorphic conditions of deformation. X-ray and infrared analysis of clay minerals, together with illite ‘crystallinity’ data, suggest that the studied rocks underwent very low grade metamorphism in the deep diagenetic zone. The limestones consist of very fine grained ( 20 μm) crystalline fillings, provide common strain markers. Optical microstructures and strain analysis indicate heterogeneous intracrystalline strain in the coarser (>50 μm) calcite. On the other hand, SEM and TEM observations, and crystallographic fabrics determined by X-ray texture goniometry, indicate a deformation involving not only intracrystalline slip, but also an important component of grain boundary sliding in the fine grained matrix. The inferred microscopic deformation mechanisms are compared with constitutive flow laws derived from experimental studies. For the maximum inferred temperature of deformation of 250 °C and geologic strain rates of 10 –13 –10 –15 s –1 , deformation mechanism maps for calcite suggest twinning and other glide mechanisms to be active in grains larger than about 5–10 μm. Smaller grains would be mostly deformed by grain size sensitive creep mechanisms, which include both diffusion mass transfer processes and grain boundary sliding. Deformation features observed in the study limestones are compatible with the prediction of such temperature-dependent mechanism maps.
Deformation mechanism
Strain partitioning
Grain Boundary Sliding
Pressure solution
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