Possible application of friable sand model for shallow mechanically compacted overconsolidated sands

Narongsirikul, Sirikarn; Mondol, Nazmul Haque; Jahren, Jens

doi:10.1190/segam2013-1303.1

Cited by 2 publications

(3 citation statements)

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“…While in a geological history, this can be associated with either a removal of overburden due to uplift/erosion or an increase in pore pressure. The experimental results reported in Narongsirikul, Mondol and Jahren (, ) show that overconsolidated sands affected by stress removal have steeper velocity–porosity trends compared to normally consolidated sands (Fig. ).…”

Section: Resultsmentioning

confidence: 87%

Acoustic and petrophysical properties of mechanically compacted overconsolidated sands: Part 2 – Rock physics modelling and applications

Narongsirikul

Mondol

Jahren

2018

Geophysical Prospecting

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Part one of this paper reported results from experimental compaction measurements of unconsolidated natural sand samples with different mineralogical compositions and textures. The experimental setup was designed with several cycles of stress loading and unloading applied to the samples. The setup was aimed to simulate a stress condition where sediments underwent episodes of compaction, uplift and erosion. P‐wave and S‐wave velocities and corresponding petrophysical (porosity and density) properties were reported. In this second part of the paper, rock physics modelling utilizing existing rock physics models to evaluate the model validity for measured data from part one were presented. The results show that a friable sand model, which was established for normally compacted sediments is also capable of describing overconsolidated sediments. The velocity–porosity data plotted along the friable sand lines not only describe sorting deterioration, as has been traditionally explained by other studies, but also variations in pre‐consolidation stress or degree of stress release. The deviation of the overconsolidated sands away from the normal compaction trend on the VP/VS and acoustic impedance space shows that various stress paths can be predicted on this domain when utilizing rock physics templates. Fluid saturation sensitivity is found to be lower in overconsolidated sands compared to normally consolidated sands. The sensitivity decreases with increasing pre‐consolidation stress. This means detectability for four‐dimensional fluid saturation changes can be affected if sediments were pre‐stressed and unloaded. Well log data from the Barents Sea show similar patterns to the experimental sand data. The findings allow the development of better rock physics diagnostics of unloaded sediments, and the understanding of expected 4D seismic response during time‐lapse seismic monitoring of uplifted basins. The studied outcomes also reveal an insight into the friable sand model that its diagnostic value is not only for describing sorting microtextures, but also pre‐consolidation stress history. The outcome extends the model application for pre‐consolidation stress estimation, for any unconsolidated sands experiencing similar unloading stress conditions to this study.

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Section: Resultsmentioning

confidence: 87%

Acoustic and petrophysical properties of mechanically compacted overconsolidated sands: Part 2 – Rock physics modelling and applications

Narongsirikul

Mondol

Jahren

2018

Geophysical Prospecting

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“…In addition, in the past few years, several experimental approaches have been developed with the aim of understanding the effects of complex burial histories or stress paths on rock properties, for example using rock physics modelling (e.g. Grude Landrø and Osdal ; Narongsirikul Mondol and Jahren –c; Draege et al . ; Avseth and Lehocki ) and experimental compaction studies (Nygård et al .…”

Section: Introductionmentioning

confidence: 99%

“…The resulting complex burial histories can influence the acoustic, petrophysical and mechanical properties differently compared to simple progressively buried sediments. This is seen on well logs where velocity and density of uplifted sediments are anomalously higher compared to normally compacted sediments at the given depth due to the pre-consolidation (Narongsirikul, Mondol and Jahren 2013a). In such cases, normal loading using conventional triaxial testing procedures will not appropriately describe the behaviour of decompacted rocks.…”

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confidence: 99%

Acoustic and petrophysical properties of mechanically compacted overconsolidated sands: part 1 – experimental results

Narongsirikul

Mondol

Jahren

2019

Geophysical Prospecting

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This paper part one is set out to lay primary observations of experimental compaction measurements to form the basis for rock physics modelling in paper part two. P‐ and S‐wave velocities and corresponding petrophysical (porosity and density) properties of seven unconsolidated natural sands with different mineralogical compositions and textures are reported. The samples were compacted in a uniaxial strain configuration from 0.5 up to 30 MPa effective stresses. Each sand sample was subjected to three loading cycles to study the influence of stress reduction on acoustic velocities and rock physical properties with the key focus on simulating a complex burial history with periods of uplift. Results show significant differences in rock physical properties between normal compaction and overconsolidation (unloaded and reloaded). The differences observed for total porosity, density, and P‐ and S‐wave velocities are attributed to irrecoverable permanent deformation. Microtextural differences affect petrophysical, acoustic, elastic and mechanical properties, mostly during normal consolidation but are less significant during unloading and reloading. Different pre‐consolidation stress magnitudes, stress conditions (isotropic or uniaxial) and mineral compositions do not significantly affect the change in porosity and velocities during unloading as a similar steep velocity–porosity gradient is observed. The magnitude of change in the total porosity is low compared to the associated change in P‐ and S‐wave velocities during stress release. This can be explained by the different sensitivity of the porosity and acoustic properties (velocities) to the change in stress. Stress reduction during unloading yields maximum changes in the total porosity, P‐ and S‐wave velocities of 5%, 25%, and 50%, respectively. These proportions constitute the basis for the following empirical (approximation) correlations: Δϕ ∼ ±5 ΔVP and ΔVP ∼ ±2ΔVS. The patterns observed in the experiments are similar to well log data from the Barents Sea. Applications to rock physics modelling and reservoir monitoring are reported in a companion paper.

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Possible application of friable sand model for shallow mechanically compacted overconsolidated sands

Cited by 2 publications

References 12 publications

Acoustic and petrophysical properties of mechanically compacted overconsolidated sands: Part 2 – Rock physics modelling and applications

Acoustic and petrophysical properties of mechanically compacted overconsolidated sands: Part 2 – Rock physics modelling and applications

Acoustic and petrophysical properties of mechanically compacted overconsolidated sands: part 1 – experimental results

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