A Study of the strength, compressibility, and density trends within the chalk of South East England

Carter, Paul G.; Mallard, D. J.

doi:10.1144/gsl.qjeg.1974.007.01.03

Cited by 31 publications

(13 citation statements)

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“…Carter & Mallard 1974;Bell 1977;Clayton 1983;Bell et al 1999). This distinction has been borne out by this study: the mean porosity of 11 chalk samples collected from Pegwell Bay is 43.2%, while three samples collected from Flamborough Head have porosities ranging from 8 to 17% -although Bell et al (1999) suggested that porosity in the NE chalks can be up to approximately 25%.…”

Section: Outcrop Analysis Of Fractures In Chalkmentioning

confidence: 66%

“…This distinction has been borne out by this study: the mean porosity of 11 chalk samples collected from Pegwell Bay is 43.2%, while three samples collected from Flamborough Head have porosities ranging from 8 to 17% -although Bell et al (1999) suggested that porosity in the NE chalks can be up to approximately 25%. Carter & Mallard (1974) suggested that this distinction is due to a greater maximum depth of burial for the NE chalks; comparison of the measured porosities against porosity-depth trends for normally compacted chalk from the North Sea (Mallon & Swarbrick 2002) suggest a maximum depth of burial of the Pegwell Bay chalk of around 500 m, compared with approximately 2 km for the Flamborough Head chalk (Fig. 2).…”

Section: Outcrop Analysis Of Fractures In Chalkmentioning

confidence: 99%

“…This may be related to different burial histories (Carter & Mallard 1974) or to different diagenetic processes (Clayton 1983). † It may result from different regional structure and tectonic history.…”

Section: Flamborough Head Ne Englandmentioning

confidence: 99%

“…There is an extensive body of literature detailing the results of laboratory measurements of different mechanical properties on samples of chalk taken from outcrop or boreholes, including Carter & Mallard (1974), Bell (1977), Mortimore (1979), Jones et al (1984), Clayton (1990), Clayton & Saffari-Shooshtari (1990), Flexer et al (1990), Kronieger (1990), Mimram & Michaeli (1990), Mortimore & Fielding (1990), Bell et al (1999), Katz et al (2000), Gommesen & Fabricius (2001), Bowden et al (2002) and Mortimore et al (2004). These studies all show that the key control on mechanical properties of chalk is the porosity: as this decreases with burial and compaction, the tensile strength, UCS and Young's modulus of chalk will all increase (the relationship between porosity and Poisson's ratio is less clear so we have used a constant value for Poisson's ratio in this study).…”

Section: Mechanical Propertiesmentioning

confidence: 99%

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Using mechanical models to investigate the controls on fracture geometry and distribution in chalk

Welch¹,

Souque

Davies³

et al. 2014

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Chalk is an important reservoir rock. However, owing to its low permeability, fractures are key to producing hydrocarbons from chalk reservoirs. Fractures in chalk usually form one of three geometric patterns: localized fractures (commonly concentric rings) developed around tips, bends and splays in larger faults; regularly spaced regional fracture sets; and fracture corridors comprising narrow zones of closely spaced parallel fractures. Localized fracture patterns are likely to give only local permeability enhancement; regional fracture sets and, especially, fracture corridors may provide long, high-permeability flow pathways through the chalk. Field mapping shows that both localized fracture patterns and fracture corridors often nucleate around larger faults; however, the fracture corridors rapidly propagate away from the faults following the regional stress orientation. It is therefore not necessary to know the detailed fault geometry to predict the geometry of the fracture corridors, although the fault density can help to predict the spacing of the fracture corridors. Mechanical modelling shows that while localized fracture patterns can form under normal fluid pressure conditions as a result of local stress anomalies around fault bends, tips and splays, fracture corridors can only form under conditions of fluid overpressure. Once they nucleate, they will continue to propagate until they either intersect another fault or the fluid pressure in them is dissipated.Gold Open Access: This article is published under the terms of the CC-BY 3.0 license.Cretaceous chalk is an important reservoir unit in the North Sea, and hosts a number of large fields in the Norwegian, Danish and UK sectors. However, the matrix permeability of chalk is generally very low (typically ,1 mD), and, hence, fractures are often important in controlling fluid flow in the subsurface and are key to producing these fields economically ( Aims and objectivesIn this study we use mechanical modelling techniques to examine the controls on fracture development and resulting geometry in chalk, and compare these results with fracture patterns observed in two chalk outcrops from southern and NE England. In particular, we will examine the relationship between fractures, fracture corridors and larger scale faults, and the impact of fluid pressure on fracture development. We will use elastic dislocation and finite-element models to investigate the in situ stress patterns developed around larger faults under different conditions of deformation and compare these with the observed fracture patterns. The elastic dislocation models simply assume the chalk to be a continuum elastic material, and take no account of fluid pressure. However, the finite-element models allow us to incorporate the effects of fluid overpressure, leading to dilation of the faults and fractures. We model two end-member cases of overpressured chalk: a case with a permeable host rock, in which the fluid overpressure results in a decrease in the effective horizontal stress; and a...

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Section: Outcrop Analysis Of Fractures In Chalkmentioning

confidence: 66%

Section: Outcrop Analysis Of Fractures In Chalkmentioning

confidence: 99%

Section: Flamborough Head Ne Englandmentioning

confidence: 99%

Section: Mechanical Propertiesmentioning

confidence: 99%

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Using mechanical models to investigate the controls on fracture geometry and distribution in chalk

Welch¹,

Souque

Davies³

et al. 2014

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“…The Chalk aquifer is highly compressible (Carter & Mallard 1974;Price et al 1993) hence the high estimates of specific storage by Lewis et al (1993) and the corresponding high values of storage coefficient measured from confined pumping tests. In unconfined situations, the specific yield is limited by the small proportion of Chalk pores that can drain under gravity -less than 1% of the Chalk bulk volume (Price et al 1976;Price 1987) and the limited volume of groundwater stored in fractures.…”

Section: Confined and Unconfined Conditionsmentioning

confidence: 99%

Aquifer properties of the Chalk of England

MacDonald

Allen²

2001

QJEGH

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Aquifer properties data from 2100 pumping tests carried out in the Chalk aquifer have been collated as part of a joint British Geological Survey / Environment Agency project. The dataset is highly biased: most pumping tests have been undertaken in valley areas where the yield of the Chalk is highest.Transmissivity values from measured sites give the appearance of log-normality, but are not truly log- The data indicate several trends and relationships in Chalk aquifer properties. Transmissivity is highest in the harder Chalk of Yorkshire and Lincolnshire (median 1800 m²/d). Throughout much of the Chalk aquifer a direct relation is observed between transmissivity and storage coefficient, reflecting the importance of fractures in governing both storage and transmissivity. Pumping tests undertaken in unconfined conditions give consistently higher measurements of transmissivity than in confined areas, probably as a result of increased dissolution enhancement of fractures in unconfined areas. At a catchment scale the data illustrate a relation between transmissivity and winter flowing streams. Word Count 7500QJEGH 34:371-384Alan MacDonaldPage 2 of 26 submitted QJEGHThe Chalk is the most important aquifer within the UK. It accounts for 60% of the groundwater used inEngland and Wales and 20% of the total water used in England and Wales (UK Groundwater Forum 1998). To protect and manage this unique resource it is essential to know and understand the variations of aquifer properties throughout the Chalk.Against this background a three-year collaborative project between the British Geological Survey (BGS) and the Environment Agency (EA) was devised. The aim of the study was to collect, collate and present information concerning the physical properties of the major aquifers in England and Wales (Allen et al. 1997). This included creating a database of available pumping tests for the major aquifers. This paper presents an analysis and interpretation of all available Chalk data in the Aquifer Properties Database. OVERVIEW OF THE DEVELOPMENT OF CHALK AQUIFER PROPERTIESThe presence and development of fractures gives the Chalk the properties of an aquifer. Without fractures, the permeability and specific yield of the Chalk would be negligible. Furthermore, without solution enhancement of the fractures, the high transmissivity of the Chalk would be impossible, and without further concentration of groundwater flow and dissolution of chalk, conduits and karstic features would not be observed. The Chalk is often referred to as possessing dual porosity (Price 1987;Barker 1991;Price et al. 1993). In a classic dual porosity aquifer, the matrix pores provide the storage, and the fractures provide the permeable pathways to permit groundwater flow. Groundwater movement within the Chalk is more complex: the high porosity (produced by the coccoliths) is not readily drained, due to the very small pore throats (Price et al. 1976), therefore effective groundwater storage is primarily within the fracture network and the larger pores....

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

Hickman

Gutierrez

Gennaro

et al. 2008

Num Anal Meth Geomechanics

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SUMMARYChalk and other porous rocks are known to behave differently when saturated with different pore fluids. The behavior of these rocks varies with different pore fluids and additional deformation occurs when the pore fluid composition changes. In this article, we review the evidence that behavior in porous rocks is pore-fluid-dependent, present a constitutive model for pore-fluid-dependent porous rocks, and present a compilation of previously published data to develop quantitative relationships between various pore fluids and mechanical behavior. The model proposed here is based on a state parameter approach for weathering and has similarities to models previously proposed for weathering-sensitive rocks in that the values for parameters that characterize material behavior vary as a function of weathering. Comparisons with published experimental data indicate that the model is capable of reproducing observed behavior of chalk under a variety of loading conditions and changes in pore fluid composition.

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A Study of the strength, compressibility, and density trends within the chalk of South East England

Cited by 31 publications

References 1 publication

Using mechanical models to investigate the controls on fracture geometry and distribution in chalk

Using mechanical models to investigate the controls on fracture geometry and distribution in chalk

Aquifer properties of the Chalk of England

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

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