Linking rock physics and basin history — Filling gaps between wells in frontier basins

A B S T R A C TRelationship between different geomechanical and acoustic properties measured from seven laboratory-tested unconsolidated natural sands with different mineralogical compositions and textures were presented. The samples were compacted in the uniaxial strain configuration from 0.5 to 30 MPa effective stress. Each sand sample was subjected to three loading-unloading cycles to study the influence of stress reduction. Geomechanical, elastic and acoustic parameters are different between normal compaction and overconsolidation (unloaded and reloaded). Stress path (K 0 ) data differ between normal consolidated and overconsolidated sediments. The K 0 value of approximately 0.5 is founded for most of the normal consolidated sands, but varies during unloading depending on mineral compositions and textural differences. The K 0 and overconsolidation ratio relation can be further simplified and can be influenced by the material compositions. K 0 can be used to estimate horizontal stress for drilling applications. The relationship between acoustic velocity and geomechanical is also found to be different between loading and unloading conditions. The static moduli of the overconsolidated sands are much higher than normal consolidated sands as the deformation is small (small strain). The correlation between dynamic and static elastic moduli is stronger for an overconsolidation stage than for a normal consolidation stage. The results of this study can contribute to geomechanical and acoustic dataset which can be applied for many seismic-geomechanics applications in shallow sands where mechanical compaction is the dominant mechanism.

Section: Introductionmentioning

confidence: 96%

Section: Introductionmentioning

confidence: 99%

Effects of stress reduction on geomechanical and acoustic relationship of overconsolidated sands

Narongsirikul

Mondol

Jahren

2019

“…Grude Landrø and Osdal ; Narongsirikul Mondol and Jahren –c; Draege et al . ; Avseth and Lehocki ) and experimental compaction studies (Nygård et al . ; Grande et al .…”

Section: Introductionmentioning

confidence: 99%

“…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 2013; Narongsirikul Mondol and Jahren 2013a-c;Draege et al 2014;Avseth and Lehocki 2016) and experimental compaction studies (Nygård et al 2004;Grande et al 2011). However, the understanding of the impact of stress unloading on rocks is still immature.…”

mentioning

confidence: 99%

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

Narongsirikul

Mondol

Jahren

2019

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.

“…This is important because pores with low aspect ratios have a major impact on rock physics properties by decreasing the compressional and shear stiffness of rocks (Kuster and Toksöz 1974;Berryman 1980a,b;Hudson 1981;Guéguen and Palciauskas 1994;Jakobsen, Hudson and Johansen 2003;Markov et al 2005). Hence, linking basin history with rock physics is key to get an insight in how reservoir properties and seismic velocities evolve through time (Helset et al 2004;Avseth et al 2005;Bjørlykke 2010;Draege et al 2014).…”

Section: Introductionmentioning

confidence: 99%

Rock physics modelling based on depositional and burial history of Barents Sea sandstones

Bredesen

Avseth

Johansen

et al. 2018

Understanding how physical properties and seismic signatures of present day rocks are related to ancient geological processes is important for enhanced reservoir characterization. In this paper, we have studied this relationship for the Kobbe Formation sandstone in the Barents Sea. These rocks show anomalous low shear velocities and high VP/VS ratios, which does not agree well with conventional rock physics models for moderately to well consolidated sandstones. These sandstones have been buried relatively deeply and subsequently uplifted 1–2 km. We compared well log data of the Kobbe sandstone with velocity–depth trends modelled by integrating basin modelling principles and rock physics. We found that more accurate velocity predictions were obtained when first honouring mechanical and chemical compaction during burial, followed by generation of micro‐cracks during uplift. We suspect that these micro‐cracks are formed as overburden is eroded, leading to changes in the subsurface stress‐field. Moreover, the Kobbe Formation is typically heterogeneous and characterized by structural clays and mica that can reduce the rigidity of grain contacts. By accounting for depositional and burial history, our velocity predictions become more consistent with geophysical observables. Our approach yields more robust velocity predictions, which are important in prospect risking and net erosion estimates.