A model for pore‐fluid‐sensitive rock behavior using a weathering state parameter

Hickman, R.J.; Gutierrez, Marte; Gennaro, Vincenzo De; Delage, Pierre

doi:10.1002/nag.703

Cited by 13 publications

(7 citation statements)

References 42 publications

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“…Since the effects of capillarity were deemed to be negligible for the long-term behaviour of calcarenite, chalk and other porous rocks (Ciantia et al, 2014;Papamichos, Brignoli, & Santarelli, 1997;Risnes & Flaageng, 1999;Risnes, Madland, Hole, & Kwabiah, 2005), following Hickman, Gutierrez, De Gennaro, and Delage (2008), the model here illustrated is developed in terms of conventional effective stress that neglects the effects of matrix suction from partial saturation on effective stresses. In the following, the standard apex notation identifying the effective stress has been omitted.…”

Section: General Formulation In Rate Formmentioning

confidence: 99%

Modelling weathering effects on the mechanical behaviour of rocks

Ciantia

Castellanza

2015

European Journal of Environmental and Civil Engineering

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The paper presents an experimental, theoretical and numerical approach in order to describe the effects of rock weathering on bonded geomaterials. The term rock weathering is used to refer to a number of chemical and physical phenomena that continuously transform a rock mass into granular soil. From an engineering point of view, rock weathering can be interpreted as a generalised decay of the mechanical properties of the original material. It acts at a constitutive level essentially by reducing the strength of the bonds joining the grains together. Such a material degradation can occur in a time scale which is comparable to the average life of engineering structures. Weathering can be crucial for what concerns the stability of slopes, cliffs and abandoned underground caves. In the experimental part of the paper micro and macro experimental investigations performed on calcarenite, a natural soft rock, are shown; short-and long-term debonding processes are identified as characterising rock weathering. A large set of hydro-chemo-mechanical data are recovered to properly characterise debonding processes by means of specific weathering tests. In particular, to reproduce long-term rock weathering in laboratory time, the progressive chemical debonding has been induced through the exposition of the rock to a uniform flow of an acid solution. In the theoretical part, it is shown how the progressive deterioration of the intergranular bonds due to weathering has been modelled satisfactorily by extending a strain hardening elastoplastic model by means of multiscale approach coupling hydro-chemo-mechanical processes. Such a model has been corroborated by simulating some tests of the previous part. Finally, in the numerical part of the work, some boundary value problems are presented, in which weathering effects cannot be neglected.

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Section: General Formulation In Rate Formmentioning

confidence: 99%

Modelling weathering effects on the mechanical behaviour of rocks

Ciantia

Castellanza

2015

European Journal of Environmental and Civil Engineering

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“…It is well known that capillarity effects scarcely affect the mechanical behavior of calcarenites, chalks, and other carbonate porous rocks as the apparent cohesion induced by capillary bridges can be neglected with respect to the natural cementation of the material. Therefore, following , the model here illustrated is developed in terms of conventional effective stresses neglecting the role of matric suction when the material behaves under partially saturated conditions. In other words, in the following, according to the previous assumption

σ_{i j}^{'} = σ_{i j} - u^{*} δ_{i j}

where

u^{*} = ({, \begin{array}{l} left & 0 & 0 \leq S_{r} < 1 \\ left & u_{w} & S_{r} = 1 \end{array})

and u w is the water pressure.…”

Section: The Constitutive Relationshipmentioning

confidence: 99%

Extension of plasticity theory to debonding, grain dissolution, and chemical damage of calcarenites

Ciantia¹,

Prisco

2015

Num Anal Meth Geomechanics

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The mechanical properties of calcarenites are known to be significantly affected by water saturation: both stiffness and strength decrease for wetting in the short term and for chemical dissolution in the long term. Both processes mainly affect bonds among grains: immediately after inundation depositional bonds fall in suspension whereas diagenetic bonds dissolve more slowly. In this paper, the authors started from the micro-structural analysis of the weathering processes to conceive a strain hardening hydro -chemo -mechanical coupled elasto-plastic constitutive model. The concept of extended hardening rules is here enriched: weathering functions have been determined by employing a micro to macro simple upscaling procedure.Chemical damage is incorporated in the formulation by means of a scalar damage function. Its evolution is also described by using a multiscale approach. A new term is added to the strain rate tensor in order to incorporate the dissolution induced chemical deformations developing once the soft rock is turned into a granular material. A calibration procedure for the constitutive parameters is suggested and the model is validated by using both coupled and uncoupled chemo mechanical experimental test results.2

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“…Studies of chalk reservoirs have shown that replacement of oil with water during enhanced oil recovery by water flooding results in collapse of the overlying rock column (De Gennaro et al 2004;Hickman et al 2008). The collapse is not due to overpressure release since it occurs even when fluid pressure was maintained (De Gennaro et al 2004).…”

Section: Introductionmentioning

confidence: 98%

The Effect of Oil Saturation On the Mechanism of Compaction In Granular Materials: Higher Oil Saturations Lead To More Grain Fracturing and Less Pressure Solution

Sathar

Worden

Faulkner

et al. 2012

Journal of Sedimentary Research

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Whether addition of oil to sandstones slows, stops, or has no influence upon pressure solution and quartz cementation has long been disputed, despite having major implications for petroleum exploration and appraisal strategies. To elucidate the effect of addition of oil to compaction, pressure solution, and cementation processes, this study utilizes an experimental approach simulating isochemical, volumetric compaction using granular halite in the presence of variable brineoil mixtures. Each experiment, at 500 kPa effective stress, lasted 48 hours and involved repeated measurements of volumetric strain. The lithified products of experiments were examined using SEM techniques. After 30 hours, approximately 4% volumetric strain occurs when the brine-oil ratio is 100:0 (pure brine). Fractures are rare in samples from experiments undertaken with pure brine so that pressure solution, and concomitant cementation, must be the compaction mechanism. When the brine-oil ratio is decreased from 100:0 to 40:60, the volumetric strain remains about 4% but there are more fractures, as quantified from SEM image analysis. These observations suggest that, although pressure solution has occurred, some of the volumetric strain is the result of fracturing, implying that pressure solution has been less effective in the presence of some oil than it is in the presence of pure brine. When the brine-oil ratio is decreased further from 40:60 to 5:95, the volumetric strain increases up to 7.3%; SEM image analysis reveals that the strain is predominantly due to grain fracturing. This change from pressure solution to grain fracturing is likely due to heterogeneous pressure solution resulting from heterogeneous distribution of stresses. Brine-coated grain contacts undergo pressure solution but oil-coated grain contacts experience increasing stress up to the point of failure, as the surrounding grain pack compacts. When the brine-oil ratio is decreased to less than 5:95, volumetric strain decreased to about 1% with few induced fractures and little pressure solution. Compaction is negligible when the brine-oil ratio is 0:100 (only oil in the pores) and fractures are negligible. Halite is more water-soluble and more hygroscopic than quartz so that water will cling to halite surfaces more tenaciously than to quartz. Since even halite has its mechanism of volumetric strain affected when the brine-oil ratio is less than 40:60, quartz pressure solution and subsequent cementation is even more likely to be affected by oil filling. This experimental study suggests that the mechanism and extent of compaction and subsequent cementation in sandstones is strongly affected by the addition of oil.

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A model for pore‐fluid‐sensitive rock behavior using a weathering state parameter

Cited by 13 publications

References 42 publications

Modelling weathering effects on the mechanical behaviour of rocks

Modelling weathering effects on the mechanical behaviour of rocks

Extension of plasticity theory to debonding, grain dissolution, and chemical damage of calcarenites

The Effect of Oil Saturation On the Mechanism of Compaction In Granular Materials: Higher Oil Saturations Lead To More Grain Fracturing and Less Pressure Solution

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