Biot's coefficient as an indicator of strength and porosity reduction: Calcareous sediments from Kerguelen Plateau

Alam, Mohammad Monzurul; Borre, Mai K.; Fabricius, Ida Lykke; Hedegaard, Kathrine; Røgen, Birte; Hossain, Zakir; Krogsbøll, Anette

doi:10.1016/j.petrol.2009.11.021

Cited by 56 publications

(35 citation statements)

References 8 publications

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“…A 20% porosity chalk may have a α ranging between 0.60 and 0.92, depending on the cementation, whereas for 40% porosity chalk, the variation may be less than 0.1 (Figure 8). This observation is in accordance with Alam et al (2010): they show that during the diagenesis process of deep sea carbonate ooze, α does not decrease with porosity unless cementation between the grain contacts starts to develop.…”

Section: Behavior Of αsupporting

confidence: 91%

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Static and dynamic effective stress coefficient of chalk

2012

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Deformation of a hydrocarbon reservoir can ideally be used to estimate the effective stress acting on it. The effective stress in the subsurface is the difference between the stress due to the weight of the sediment and a fraction (effective stress coefficient) of the pore pressure. The effective stress coefficient is thus relevant for studying reservoir deformation and for evaluating 4D seismic for the correct pore pressure prediction. The static effective stress coefficient [Formula: see text] is estimated from mechanical tests and is highly relevant for effective stress prediction because it is directly related to mechanical strain in the elastic stress regime. The corresponding dynamic effective stress coefficient [Formula: see text] is easy to estimate from density and velocity of acoustic (elastic) waves. We studied [Formula: see text] and [Formula: see text] of chalk from the reservoir zone of the Valhall field, North Sea, and found that [Formula: see text] and [Formula: see text] vary with differential stress (overburden stress-pore pressure). For Valhall reservoir chalk with 40% porosity, [Formula: see text] ranges between 0.98 and 0.85 and decreases by 10% if the differential stress is increased by 25 MPa. In contrast, for chalk with 15% porosity from the same reservoir, [Formula: see text] ranges between 0.85 and 0.70 and decreases by 5% due to a similar increase in differential stress. Our data indicate that [Formula: see text] measured from sonic velocity data falls in the same range as for [Formula: see text], and that [Formula: see text] is always below unity. Stress-dependent behavior of [Formula: see text] is similar (decrease with increasing differential stress) to that of [Formula: see text] during elastic deformation caused by pore pressure buildup, for example, during waterflooding. By contrast, during the increase in differential stress, as in the case of pore pressure depletion due to production, [Formula: see text] increases with stress while [Formula: see text] decreases.

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Section: Behavior Of αsupporting

confidence: 91%

“…Contact cement precipitation between the grains depends on the diagenetic process of the chalk which in turn impacts on the value of the effective stress coefficient (Alam et al, 2010). Presence of fine clay may reduce the calcite-to-calcite grain contacts and consequently, the contact cement.…”

Section: Behavior Of αmentioning

confidence: 99%

Static and dynamic effective stress coefficient of chalk

2012

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“…We show that Biot's coefficient is correlated to the water saturation of the Kraka reservoir and is partly controlled by its stratigraphic sub-units. While a direct causal relationship cannot be established between Biot's coefficient and porosity, a correlation is also identified between the two, implying that some degree of pore filling cementation occurred in Kraka (Alam, 2010). Lack of correlation between Biot's coefficient and Gamma Ray (GR) indicates that the small amount of clay present is generally located in the pore space, thus not contributing to frame stiffness.…”

Section: Introductionmentioning

confidence: 99%

“…The coefficient α is inversely proportional to the degree of cementation in a sedimentary rock and for a given mineralogy, and has been found to correlate with strength and stiffness parameters such as compressional and shear modulus, yield strength and creep (Alam et al, 2010).…”

Section: Introductionmentioning

confidence: 99%

Controls on Cementation in a Chalk Reservoir

Meireles¹,

Hussain

Welch

et al. 2017

Proceedings

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SummaryIn this study, we identify different controls on cementation in a chalk reservoir. Biot's coefficient, a measure of cementation, stiffness and strength in porous rocks, is calculated from logging data (bulk density and sonic Pwave velocity). We show that Biot's coefficient is correlated to the water saturation of the Kraka reservoir and is partly controlled by its stratigraphic sub-units. While the direct causal relationship between Biot's coefficient and water saturation cannot be extended for Biot's coefficient and porosity, a correlation is also identified between the two, implying that some degree of pore filling cementation occurred in Kraka (Alam, 2010). Lack of correlation between Biot's coefficient and Gamma Ray (GR) indicates that the small amount of clay present is generally located in the pore space, thus not contributing to frame stiffness. While there was no compositional control on cementation via clay, we could infer that stratigraphy impacts on the diagenetic process.

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“…The determination of effective stress is an important aspect of stability analysis, and has a number of engineering applications especially in geotechnical and petroleum engineering, including underground and surface rock structures, oil and gas production, and sequestration of carbon dioxide (Alam et al, 2009;Alam et al, 2010;Hu et al, 2010). Failure criteria are represented using the effective stress, the concept of which was first introduced by Terzaghi (1936) for soil, and is commonly known as Terzaghi's effective stress principle.…”

Section: Introductionmentioning

confidence: 99%

A new approach to evaluate effective stress coefficient for strength in Kimachi sandstone

Dassanayake

Fujii

Fukuda

et al. 2015

Journal of Petroleum Science and Engineering

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This paper is devoted to experimental investigation of effective stress coefficient for peak and residual strengths of saturated Kimachi sandstone. Authors have described the Modified Failure Envelope Method (MFEM), which can be used to obtain the effective stress coefficients for peak and residual strengths (α -Peak and α -Residual). The effective stress coefficients for intact and fractured Kimachi sandstone (α -Biot's and α -Fractured) were also evaluated using conventional methods, and the data were compared with the coefficient values obtained by MFEM for the peak and residual strengths. The effective stress coefficient for intact rock, α -Biot's decreased with increasing confining pressure, and was in the range 1 > α -Biot's > 0.8. The effective stress coefficient for fractured rock, α-Fractured was larger than that for intact rock, and was close to unity. The effective stress coefficient calculated for peak strengths, α -Peak using both the single and multistage MFEMs decreased with increasing effective confining pressure and was in the range 0.8 > α -Peak > 0.4. For residual strength states, effective stress coefficient, α -Residual was between the peak strength value and that for intact rock. Based on the results, multistage MFEM is suitable for obtaining an effective stress coefficient for the peak strength, α -Peak . An equation to obtain the effective stress coefficient from total confining pressure and pore pressure, and a method to choose the coefficients for elastic stress analyses and failure evaluations for intact rock structures or structures in rock mass were proposed.

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Biot's coefficient as an indicator of strength and porosity reduction: Calcareous sediments from Kerguelen Plateau

Cited by 56 publications

References 8 publications

Static and dynamic effective stress coefficient of chalk

Static and dynamic effective stress coefficient of chalk

Controls on Cementation in a Chalk Reservoir

A new approach to evaluate effective stress coefficient for strength in Kimachi sandstone

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