Diagenetic fabrics in some British Dinantian limestones

Bathurst, R. G. C.

doi:10.1002/gj.3350020103

Cited by 191 publications

(58 citation statements)

References 18 publications

(5 reference statements)

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“…Such microstructures are widely found in carbonate and sandstone rocks, often in association with evidence for grain scale microfracturing and cracking healing [Renard et al, 2000, Gratier et al, 2003. However, evidence for IPS and localized zones of pressure solution, such as stylolites, is perhaps most common in carbonate rocks [Bathurst, 1958;Tada and Siever, 1989;Renard et al, 2004]. About 60% of the world's oil and 40% of its gas reserves are found in carbonate reservoirs [Liteanu and Spiers, 2009; Schlumberger market analysis at http://www.slb.com/services/industry-challenges/ carbonates.aspx.].…”

Section: Introductionmentioning

confidence: 99%

Compaction creep of wet granular calcite by pressure solution at 28°C to 150°C

2010

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[1] Uniaxial compaction experiments have been carried out on wet calcite powders prepared from milled limestone, analytical grade calcite, and superpure calcite. The tests were performed at 28°C-150°C, effective stresses of 20-47 MPa, and a pore pressure of 20 MPa, using presaturated CaCO 3 solution as the pore fluid. Sample grain sizes ranged from 12 to 86 mm. The aim was to determine if creep occurs by intergranular pressure solution (IPS) under these conditions and to identify the rate-controlling process. The wet samples showed significant creep, while dry and oil-flooded samples did not. Wet samples were also characterized by microstructures such as sutured grain contacts, grain indentations, and overgrowths, suggesting the operation of IPS. The behavior of the wet samples at low strains (<4-5%) agreed well with the predictions of standard models for diffusion-controlled pressure solution. However, at higher strains (5-10%), creep slowed down compared with the model predictions. Transient flow-through tests performed in this regime led to an acceleration of creep, consistent with models for precipitation-controlled IPS, and demonstrated an increase in the impurity content of the pore fluid toward higher strains. Since some of these impurities (notably Mg 2+ ) retard precipitation in calcite, we suggest that creep occurred by diffusion-controlled IPS at low strain, giving way to precipitation control at larger strains as impurities accumulated. Fitting of the diffusion-controlled IPS model to the low strain data yielded values of the grain boundary diffusion product DS in calcite of ∼10 −19 m 3 s −1 at 150°C.

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Section: Introductionmentioning

confidence: 99%

Compaction creep of wet granular calcite by pressure solution at 28°C to 150°C

2010

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“…Failure of the neck region is then presumed to occur, either through brittle failure [Bathurst, 1958] or dislocation flow [Pharr and Ashby, 1983].…”

Section: Introductionmentioning

confidence: 99%

“…Alternatively, others have proposed that this boundary phase consists of loadbeating "islands" surrounded by an interconnected network of fluid-filled channels (i.e., an "island-channel" structure), wherein the fluid has properties close to those of bulk water [Raj and Chyuang, 1981;Lehner, 1990;]. Undercutting models do not require the presence of a high-diffusivity boundary between grains, but they do require either near-zero fluid wetting angles (i.e., the angle formed by the two solid-liquid interfaces where they intersect the grain boundary) [Pharr and Ashby, 1983] or enhanced solubility of the material at grain-to-grain contacts [Bathurst, 1958;Weyl, 1959].…”

Section: Introductionmentioning

confidence: 99%

Kinetics of pressure solution at halite‐silica interfaces and intergranular clay films

Hickman¹,

Evans²

1995

J. Geophys. Res.

172

126

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of pressure solution at halite-silica interfaces and intergranular clay films" (1995). by diffusion through an intergranular film with a very high diffusion coefficient (• 10 -5-10 -7 cm2/s). The data further suggest that the diffusion coefficient and/or thickness of this film increases with decreasing normal stresses, at least for normal stresses less than about 4 MPa. As no island-channel boundary structures were observed, we propose that this film consists of a continuous layer of strongly adsorbed (i.e., structured) water that is maintained between the halite and silica lenses during deformation. Convergence rates in similar experiments conducted at a constant load of 0.11 N but at 8.3 ø, 50.2 ø, and 90.2øC were approximately constant at a given normal stress and contact spot size. The cause of this temperature insensitivity is unknown but might result from changes in interphase boundary structure or thickness with increasing temperature that are sufficient to offset the expected thermal activation. An experiment was also conducted in which a halite lens was pressed against a fused silica fiat coated with an 0.8-/•m-thick film of Na-montmorillonite in brine. This clay film produced an approximately fivefold increase in convergence rates over those observed in a halite/ silica experiment conducted without clay at the same load and temperature. The strong sensitivity of IPS rates both to contact spot radius and to the presence of second phases along grain boundaries suggests that fine-grained, clay-rich fault gouges and multiphase granular aggregates should be particularly susceptible to pressure solution creep in the middle to upper crust.

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“…Le premier modèle (Weyl, 1959) suppose que les processus de dissolution et de diffusion permettent la réduction du volume des aspérités. Le deuxième modèle (Bathurst, 1958) suggère une dissolution localisée, en particulier dans les régions adjacentes aux points de contact, où il y a de plus fortes pressions, résultant en l'écrasement lorsque la zone de contact est réduite à une certaine dimension critique. Selon la prédominance de l'un ou l'autre de ces deux mécanismes de dissolution, il y a soit une diminution ou une augmentation de la perméabilité de la fracture.…”

Section: Processus Chimio-thermo-hydro-mécaniquesunclassified

Étude des processus chimio-hydro-mécaniques dans un massif rocheux fracturé perturbé par une exploitation minière :

Benlahcen¹

2003

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This study on the chemical, hydraulic and mechanical processes and their coupling, was conducted at the Bouchard-Hébert Mine, located in the Abitibi Mining District in Québec, Canada. In this mine environment, the acidic water migrating from the old mine workings to the new ones, in combination with the perturbed geomechanical stress field caused by the excavations, affect the rock mass permeability. Both field work and laboratory experiments were conducted in order to investigate these processes, particularly in the rock mass portion located between the two mine workings (drift at level 6A).Results of discontinuity mapping show that at the western part of the drift at level 6A (from 10600E to 10900E), the rock mass contains two sets of fractures: one set is subhorizontal (dip between 0° and 30°) with a trace length between 1 and 1.5 m, and the other set is subvertical (dip between 75° and 90°). This subvertical set is divided into two groups depending on their trace length: one group includes fractures with a trace length between 0.5 and 2 m, and the second group comprises fractures with a trace length between 3 and 3.5 m. The fracture density of these two sets of fractures varies from 1 to 6 m" 1 and their veins are 2 mm in width. At the eastern part of the drift at level 6A (from 10900E to 11200E), the rock mass contains the same two sets of fractures observed at the western part, plus a set of fractures with a moderate dip (between 15° and 45°) with NE trend. This later set of fractures is less frequent and has a variable trace length between 0.5 and 2.5 m; their veins have a width of 2 mm. The fracture density of all the fracture set is between 1 and 4 m' 1 . Although the rock mass at the eastern part of the drift at the level 6A contains three sets of fractures, it is less permeable than the one located at the western part considering its lower fracture density. Consequently, grounwater flow would be more intense in the rock mass at the western part of the drift at the level 6 A of the mine.The results of hydraulic testing in boreholes in the rock mass located immediately under the drift 6A and over a lengh of 48 m, have shown that in the eastern part of this excavation, the hydraulic conductivity of the rock mass is low and constant, between 1 xlO" 10 and 1 xlO " n ms"1 . In the central part of this drift, located just under the old excavations, the rock mass hydraulic conductivity is higher and increases with depth from 1 xlO" 11 and 1 xlO ' 6 ms" 1 , which is in accordance with the higher fracture density in this part of the drift.Hydrogeochemical results show that waters sampled from boreholes at the mine are of neutral pH and contain high concentrations in ions, such as Ca, SO4 and metals. Calcium originates from the dissolution of calcite which is in abundance in fractures. Sulfate and metals originate from sulfide mineral oxidation present in fractures as well as in the rock matrix. Waters at a bulkhead at the base of the old excavations and the mixing waters at the surface, pumped from all ...

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Diagenetic fabrics in some British Dinantian limestones

Cited by 191 publications

References 18 publications

Compaction creep of wet granular calcite by pressure solution at 28°C to 150°C

Compaction creep of wet granular calcite by pressure solution at 28°C to 150°C

Kinetics of pressure solution at halite‐silica interfaces and intergranular clay films

Étude des processus chimio-hydro-mécaniques dans un massif rocheux fracturé perturbé par une exploitation minière :

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