A method to evaluate long-term rheology of Zechstein salt in the Tertiary

Shi-yan, LI; Urai, János; Strozyk, Frank; Abe, Steffen; Kukla, Peter A.; Gent, Heijnderik Willem van

doi:10.1201/b12041-31

Cited by 19 publications

(14 citation statements)

References 3 publications

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“…So, even if rock salt core gets recovered successfully, the bulk of the rock salt behavior would still remain unknown as spatial heterogeneities in rock salt can be very large. In many cases, geological arguments as to the possible composition of salt at a specific location as affected by its deposition environment and subsequent deformation or diapirism [see, e.g., Geluk , ; Geluk et al , ; Urai et al , ], in conjunction with back‐calculation of the material response from field situations where rock salt flow is important (e.g., Breunese et al [] or Li et al []), can also be very informative. Note that geophysical exploration data can also help better understand the internal structure of salt bodies [see, e.g., van Gent et al , ], as the presence of other evaporites can significantly affect the creep response of a salt body.…”

Section: Discussion Implications For Modeling and Conclusionmentioning

confidence: 99%

“…A further argument suggesting that pressure solution may not operate at low stresses, and that flow may be ubiquitously dominated by dislocation creep, stems from the theoretical possibility that at sufficiently low‐stress intergrain boundary healing could disconnect the grain boundary fluid pathway through which ionic diffusion from high‐ to low‐stress grain contacts occurs and so block pressure solution [ van Noort et al , ]. This might be to some extent supported by numerical calculations reported by Li et al [] that show that dense anhydrite stringers present in naturally deformed rock salt bodies do not sink through the salt, which seem to imply that viscosities are much higher than what were calculated for pressure solution. However, there could be other explanations for the observations of Li et al, notably the presence of sufficient anhydrite inside the rock salt body in question, which could slow down the sinking of these stringers.…”

Section: The Creep Behavior Of Rock Saltmentioning

confidence: 97%

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Impact of rock salt creep law choice on subsidence calculations for hydrocarbon reservoirs overlain by evaporite caprocks

2016

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Accurate forward modeling of surface subsidence above producing hydrocarbons reservoirs requires an understanding of the mechanisms determining how ground deformation and subsidence evolve. Here we focus entirely on rock salt, which overlies a large number of reservoirs worldwide, and specifically on the role of creep of rock salt caprocks in response to production‐induced differential stresses. We start by discussing available rock salt creep flow laws. We then present the subsidence evolution above an axisymmetric finite element representation of a generic reservoir that extends over a few kilometers and explore the effects of rock salt flow law choice on the subsidence response. We find that if rock salt creep is linear, as appropriate for steady state flow by pressure solution, the subsidence response to any pressure reduction history contains two distinct components, one that leads to the subsidence bowl becoming narrower and deeper and one that leads to subsidence rebound and becomes dominant at later stages. This subsidence rebound becomes inhibited if rock salt deforms purely through steady state power law creep at low stresses. We also show that an approximate representation of transient creep leads to relatively small differences in subsidence predictions. Most importantly, the results confirm that rock salt flow must be modeled accurately if good subsidence predictions are required. However, in practice, large uncertainties exist in the creep behavior of rock salt, especially at low stresses. These are a consequence of the spatial variability of rock salt physical properties, which is practically impossible to constrain. A conclusion therefore is that modelers can only resort to calculating bounds for the subsidence evolution above producing rock salt‐capped reservoirs.

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Section: Discussion Implications For Modeling and Conclusionmentioning

confidence: 99%

Section: The Creep Behavior Of Rock Saltmentioning

confidence: 97%

Impact of rock salt creep law choice on subsidence calculations for hydrocarbon reservoirs overlain by evaporite caprocks

2016

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“…Breunese et al (2003) have commented on the applicability of certain rocksalt flow laws based on how well models using them fit the evolution of subsidence above a solution-mined rocksalt cavity. Li et al (2012) have studied the gravitational sinking of inclusion of different density (stringers) within rocksalt to come to the conclusion that rocksalt viscosity needs to be non-linear over geological time scales. Our problem however involves deformation over different timescales over which linear salt creep seems equally relevant on the basis of experimental observations.…”

Section: O D E L S E T U Pmentioning

confidence: 99%

Ground motions induced by a producing hydrocarbon reservoir that is overlain by a viscoelastic rocksalt layer: a numerical model

Marketos¹,

Govers²,

Spiers³

2015

Geophys. J. Int.

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S U M M A R YHydrocarbon reservoir pressure depletion leads to stress changes inside the reservoir and ground deformation which is registered at the surface as subsidence. As reservoirs are often overlain by layers of rocksalt (or other evaporites), which are materials that flow so as to relax stresses inside them, there is the potential for time-varying surface subsidence. This work focuses on understanding the macroscopic mechanisms that lead to rocksalt flow-induced ground displacements. A Finite Element Model is used for this purpose in which the rocksalt layer is represented by a viscoelastic Maxwell material. Two distinct mechanisms that lead to displacement are observed. These are active during different stages of the deformation and have different timescales associated with them. An important observation is that the timescale for deformation that is measured at the ground surface is not equal to the timescale for deformation of a viscoelastic material element, but can be many times larger than that. The sensitivity of the response to the thickness and location of the rocksalt layer is also presented. Conclusions are drawn which allow for the relative importance of the presence of the rocksalt layer to be assessed and for a framework for understanding time-dependent subsidence above producing hydrocarbon reservoirs to be developed. Finally the changes in stress distribution around a producing reservoir are also briefly discussed.

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“…In this paper, through the introduction of deformation mechanisms of rock salt and reading previous references about salt creep in laboratories, we have summarized the experimental results and built a database about the strain rate and differential stress relationships. However, direct measurements of rheology at these low rates are not possible, and the rheology of rock salt during long-term deformation in nature is controversial (Li et al 2012b). …”

Section: Introductionmentioning

confidence: 99%

Rheology of rock salt for salt tectonics modeling

Urai

2016

Pet. Sci.

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Numerical modeling of salt tectonics is a rapidly evolving field; however, the constitutive equations to model long-term rock salt rheology in nature still remain controversial. Firstly, we built a database about the strain rate versus the differential stress through collecting the data from salt creep experiments at a range of temperatures (20-200°C) in laboratories. The aim is to collect data about salt deformation in nature, and the flow properties can be extracted from the data in laboratory experiments. Moreover, as an important preparation for salt tectonics modeling, a numerical model based on creep experiments of rock salt was developed in order to verify the specific model using the Abaqus package. Finally, under the condition of low differential stresses, the deformation mechanism would be extrapolated and discussed according to microstructure research. Since the studies of salt deformation in nature are the reliable extrapolation of laboratory data, we simplified the rock salt rheology to dislocation creep corresponding to power law creep (n = 5) with the appropriate material parameters in the salt tectonic modeling.

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A method to evaluate long-term rheology of Zechstein salt in the Tertiary

Cited by 19 publications

References 3 publications

Impact of rock salt creep law choice on subsidence calculations for hydrocarbon reservoirs overlain by evaporite caprocks

Impact of rock salt creep law choice on subsidence calculations for hydrocarbon reservoirs overlain by evaporite caprocks

Ground motions induced by a producing hydrocarbon reservoir that is overlain by a viscoelastic rocksalt layer: a numerical model

Rheology of rock salt for salt tectonics modeling

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