Experimental investigation of surface energy and subcritical crack growth in calcite

Røyne, Anja; Bisschop, Jan; Dysthe, Dag Kristian

doi:10.1029/2010jb008033

Cited by 104 publications

(115 citation statements)

References 39 publications

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“…Taking this correction into account, the effective stress leading to failure should be of the order [Lawn, 1993] of s eff = (1 − ') ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi E=r max p ∼16-22 MPa, where g = 0.2 J m −2 is the interfacial energy of calcite [Røyne et al, 2011], E = 12.9-24 GPa is the Young's modulus for ' = 0.25 [Gommesen et al, 2007]. Here, ' = 0.25 and r max = 5.5 mm are the porosity and maximum pore size at the onset of compaction (from Figure 4).…”

Section: Compaction Front Modelmentioning

confidence: 99%

A compaction front in North Sea chalk

et al. 2011

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[1] North Sea chalk from 18 wells shows a pronounced porosity drop, from ∼20% to less than 10% over a compaction front of less than 300 m. The position of the compaction front is independent of stratigraphic position, temperature, and actual depth, but closely tied to an effective stress (load stress minus fluid pressure) of ∼17 MPa. These observations require a strongly nonlinear rheology with a marked increase in compaction rate at a specific effective stress. Grain-scale observations demonstrate that the compaction front coincides with marked grain coarsening and recrystallization of fossils and fossil fragments. We propose that this nonlinear rheology is caused by stress-driven failure of the larger pores and the associated generation of reactive surface area by subcritical crack propagation away from these pores. Before the onset of this instability, compaction by pressure solution is slowed down by the inhibitory effect of organic compounds associated with the fossils. Although the compaction mechanism is mainly by pressure solution, the rheological response to burial may still be dominantly plastic and controlled by the (fracturing controlled) rate of exposure of reactive surface area. The nonlinear compaction of chalk has significant implications for the evolution of petroleum systems in the central North Sea, both with respect to sea-floor subsidence above hydrocarbon-producing chalk reservoirs and for the formation of low-porosity pressure seals within the chalk.

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Section: Compaction Front Modelmentioning

confidence: 99%

A compaction front in North Sea chalk

et al. 2011

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“…A number of studies linking pH to crack growth have, however, been done on quartz [Atkinson and Meredith, 1981] and glass [Wiederhorn and Johnson, 1972]. In the present study we expand the testing conditions of Røyne et al [2011] and Rostom et al [2013] to investigate the effect of (1) the fluid pH and (2) the fluid composition and salinity on the crack propagation and healing of cracks in calcite single crystals.…”

Section: Introductionmentioning

confidence: 99%

The effect of fluid composition, salinity, and acidity on subcritical crack growth in calcite crystals

et al. 2016

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Chemically activated processes of subcritical cracking in calcite control the time‐dependent strength of this mineral, which is a major constituent of the Earth's brittle upper crust. Here experimental data on subcritical crack growth are acquired with a double torsion apparatus to characterize the influence of fluid pH (range 5–7.5) and ionic strength and species (Na2SO4, NaCl, MgSO4, and MgCl2) on the propagation of microcracks in calcite single crystals. The effect of different ions on crack healing has also been investigated by decreasing the load on the crack for durations up to 30 min and allowing it to relax and close. All solutions were saturated with CaCO3. The crack velocities reached during the experiments are in the range 10−9–10−2 m/s and cover the range of subcritical to close to dynamic rupture propagation velocities. Results show that for calcite saturated solutions, the energy necessary to fracture calcite is independent of pH. As a consequence, the effects of fluid salinity, measured through its ionic strength, or the variation of water activity have stronger effects on subcritical crack propagation in calcite than pH. Consequently, when considering the geological sequestration of CO2 into carbonate reservoirs, the decrease of pH within the range of 5–7.5 due to CO2 dissolution into water should not significantly alter the rate of fracturing of calcite. Increase in salinity caused by drying may lead to further reduction in cracking and consequently a decrease in brittle creep. The healing of cracks is found to vary with the specific ions present.

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“…The primary result from the experiments is that the produced Ca-concentration is higher for the high-stress experiments than the low-stress experiments. In order to capture this observation we may simplify the physics described in Equation (25). In the high stress experiments, grain re-organization leads to reduction in the pore volume, and hence increased reaction rate, compared to the low-stress experiments.…”

Section: Changes To the Produced Solute Concentrationmentioning

confidence: 99%

“…Under the assumption that differences in, A 0 , m/m 0 , n, and g(C) are small compared to the pore volume changes, we may re-scale Equation (25) to obtain the ratio of produced Ca-concentrations of the 12.3 MPa experiment to the concentrations in the 0.5 MPa experiment: Please note that here we only address the effect of solute pore volume reduction and omit any differences in, e.g., n (which depends on the integrated concentrations). The comparison between the 0.5 and 12.3 MPa experiment is shown in Figure 10.…”

Section: Changes To the Produced Solute Concentrationmentioning

confidence: 99%

“…Sub-critical crack growth, where cracks propagate at imposed stresses below a critical level due to the chemical interplay between the fluids and rock surface close to the crack tip [25], may also be an effective driver of deformation and grain re-organization. In addition, the adsorption of sulfate in the diffusive double layer sets up a disjoining pressure at the grain contacts that leads to a reduction in the attractive van der Waals forces.…”

Section: Introductionmentioning

confidence: 99%

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How Stress and Temperature Conditions Affect Rock-Fluid Chemistry and Mechanical Deformation

et al. 2016

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We report the results from a series of chalk flow-through-compaction experiments performed at three effective stresses (0.5, 3.5, and 12.3 MPa) and two temperatures (92 and 130 • C). The results show that both stress and temperature are important to both chemical alteration and mechanical deformation. The experiments were conducted on cores drilled from the same block of outcrop chalks from the Obourg quarry within the Saint Vast formation (Mons, Belgium). The pore pressure was kept at 0.7 MPa for all experiments with a continuous flow of 0.219 M MgCl 2 brine at a constant flow rate; 1 original pore volume (PV) per day. The experiments have been performed in tri-axial cells with independent control of the external stress (hydraulic pressure in the confining oil), pore pressure, temperature, and the injected flow rate. Each experiment consists of two phases; a loading phase where stress-strain dependencies are investigated (approximately 2 days), and a creep phase that lasts for 150-160 days. During creep, the axial deformation was logged, and the effluent samples were collected for ion chromatography analyses. Any difference between the injected and produced water chemistry gives insight into the rock-fluid interactions that occur during flow through the core. The observed effluent concentration shows a reduction in Mg 2+ , while the Ca 2+ concentration is increased. This, together with SEM-EDS analysis, indicates that magnesium-bearing mineral phases are precipitated leading to dissolution of calcite. This is in-line with other flow-through experiments reported earlier. The observed dissolution and precipitation are sensitive to the effective stress and test temperature. Higher stress and temperature lead to increased Mg 2+ and Ca 2+ concentration changes. The observed strain can be partitioned additively into a mechanical and chemical driven component.

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Experimental investigation of surface energy and subcritical crack growth in calcite

Cited by 104 publications

References 39 publications

A compaction front in North Sea chalk

A compaction front in North Sea chalk

The effect of fluid composition, salinity, and acidity on subcritical crack growth in calcite crystals

How Stress and Temperature Conditions Affect Rock-Fluid Chemistry and Mechanical Deformation

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