Comparative Study of Five Outcrop Chalks Flooded at Reservoir Conditions: Chemo-mechanical Behaviour and Profiles of Compositional Alteration

Andersen, Pål Østebø; Wang, W.; Madland, Merete Vadla; Zimmermann, Udo; Korsnes, Reidar Inge; Bertolino, S.; Minde, Mona Wetrhus; Schulz, Bernhard; Gilbricht, Sabine

doi:10.1007/s11242-017-0953-6

Cited by 40 publications

(59 citation statements)

References 45 publications

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“…An injecting rate of 0.05 ml∕ min corresponds to a loading rate from 1.2 to 10.0 MPa during 2 h, which is a trade-off to avoid pore pressure build-up inside the sample and sufficiently fast to minimize the effect of time-dependent plastic compaction. The brine permeability of Liège chalk was reported by Andersen et al (2017) to be 1.8 and 1.9 mD, whereas Nermoen et al 2015report it to be 1.1 mD.…”

Section: Loading Experimentsmentioning

confidence: 97%

Incorporating electrostatic effects into the effective stress relation — Insights from chalk experiments

et al. 2018

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Which forces are responsible for holding highly porous chalks together? We use the effective stress to quantify the electrostatic effects around particle contacts originating from the adsorption of ions onto charged mineral surfaces. The induration of chalk indicates that it is held together by contact cement, where planar crystal contacts allow the action of short-ranged adhesive Van der Waals forces. At particle distances exceeding a few nanometers, recent studies have indicated electrostatic repulsion between water-embedded adjacent particles. The magnitude of the repelling force depends, among other parameters, upon temperature and brine composition. Our premise is that by perturbing the electrostatic forces at the particle level, we can control the mechanical behavior of chalk samples tested in triaxial cells. We report the results of an experimental series, investigating how the mechanical strength and stiffness varied among samples saturated with four different brines, tested at two temperatures, and tested directly or after aging for three weeks at high temperature. We associate stiffness with bulk modulus and strength with the stress at yield. Systematic softening and weakening is observed, especially when the pore fluid is sulfate bearing, as well as for some high-temperature experiments and for aged samples. However, softening and weakening are not totally correlated, and neither brine composition, temperature, nor aging can alone dictate the mechanical behavior of the chalk — a combination is required to predict the chalk stiffness and strength. To obtain a coherent description of our experimental results, we estimated the electrostatic stress arising from ion adsorption and found it unnecessary for these experiments to postulate significant dissolution or precipitation-related changes to the rock frame.

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Section: Loading Experimentsmentioning

confidence: 97%

Incorporating electrostatic effects into the effective stress relation — Insights from chalk experiments

et al. 2018

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“…The yield point can be considered a measure of the "strength" or "compaction strength" of the core, while the time-dependent creep that occurs after the yield point has been exceeded might be considered as a kind of "viscosity". Figure 1 shows an example where a chalk core from the Aalborg outcrop was heated to 130 • C, loaded up to 12 MPa, and then left to creep for 61 days at a constant stress of 12 MPa, while a solution of 0.657M NaCl was passed through at a flooding rate of 1PV (Pore Volume) per day [6]. As can be seen from Figure 1a, the axial strain is proportional to the axial stress (e.g., the core deformation is elastic) up to the yield point at~8.2 MPa (the solid black line).…”

Section: Interpreting Triaxial Core Deformation Experiments In Terms mentioning

confidence: 99%

“…The dashed line is the de Waal model (text equation 1) with parameters .ε V (0) = 0.012%/hour and B = 0.43%. Data are from[6].…”

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confidence: 99%

Compaction and Fluid—Rock Interaction in Chalk Insight from Modelling and Data at Pore-, Core-, and Field-Scale

Minde

Hiorth

2019

Geosciences

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Water weakening is a phenomenon that is observed in high porosity chalk formations. The rock interacts with ions in injected water and additional deformation occurs. This important effect needs to be taken into account when modelling the water flooding of these reservoirs. The models used on field scale are simple and only model the effect as a change in water saturation. In this paper, we argue that the water weakening effect can to a large extend be understood as a combination of changes in water activity, surface charge and chemical dissolution. We apply the de Waal model to analyse compaction experiments, and to extract the additional deformation induced by the chemical interaction between the injected water and the rock. The chemical changes are studied on a field scale using potential flow models. On a field scale, we show that the dissolution/precipitation mechanisms studied in the lab will propagate at a much lower speed and mainly affect compaction near the well region and close to the temperature front. Changes in surface charge travel much faster in the reservoir and might be an important contributor to the observed water weakening effect. We also discuss how mineralogical variations impacts compaction.

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“…Triaxial tests on intact chalk specimens demonstrated the expansion (i.e., hardening) of the yield surface with decreasing porosity and higher rate of deformation, and its shrinkage (i.e., softening) with increasing water saturation (S w ) and temperature (M. A. Andersen et al, 1992;P. Ø. Andersen et al, 2018;Collin et al, 2002;Havmøller & Foged, 1996;Hickman, 2004;Homand & Shao, 2000;Johnsen et al, 2011;Korsnes et al, 2008;Megawati et al, 2013;Minde et al, 2018;Papamichos et al, 1997;Risnes & Flaageng, 1999;Risnes et al, 1998Risnes et al, , 2005Schroeder et al, 1998).…”

Section: Introductionmentioning

confidence: 99%

“…Considering clean chalk lithology with a negligible amount of clay and quartz, the yield surface is not static and changes locus depending on four key parameters: porosity, saturating fluid, temperature and rate of deformation. Triaxial tests on intact chalk specimens demonstrated the expansion (i.e., hardening) of the yield surface with decreasing porosity and higher rate of deformation, and its shrinkage (i.e., softening) with increasing water saturation (S w ) and temperature (M. A. Andersen et al., 1992; P. Ø. Andersen et al., 2018; Collin et al., 2002; Havmøller & Foged, 1996; Hickman, 2004; Homand & Shao, 2000; Johnsen et al., 2011; Korsnes et al., 2008; Megawati et al., 2013; Minde et al., 2018; Papamichos et al., 1997; Risnes & Flaageng, 1999; Risnes et al., 1998, 2005; Schroeder et al., 1998). The large majority of previous studies were conducted on outcrop chalk, thereby limiting applicability of the results to the deep subsurface chalks.…”

Section: Introductionmentioning

confidence: 99%

Effects of Porosity and Water Saturation on the Yield Surface of Upper Cretaceous Reservoir Chalks From the Danish North Sea

et al. 2021

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Comparative Study of Five Outcrop Chalks Flooded at Reservoir Conditions: Chemo-mechanical Behaviour and Profiles of Compositional Alteration

Cited by 40 publications

References 45 publications

Incorporating electrostatic effects into the effective stress relation — Insights from chalk experiments

Incorporating electrostatic effects into the effective stress relation — Insights from chalk experiments

Compaction and Fluid—Rock Interaction in Chalk Insight from Modelling and Data at Pore-, Core-, and Field-Scale

Effects of Porosity and Water Saturation on the Yield Surface of Upper Cretaceous Reservoir Chalks From the Danish North Sea

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