Mechanical and physical behavior of high-porosity chalks exposed to chemical perturbation

Megawati, M.; Madland, Merete Vadla; Hiorth, A.

doi:10.1016/j.petrol.2015.06.026

Cited by 35 publications

(23 citation statements)

References 36 publications

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“…More information about mineralogy, petrography, and rheological characteristics of these chalk successions can be found in literature [12,33,35,38,39]. Onshore chalk successions are used as analogues for North Sea reservoir chalk in several studies [8,17,20,21,35].…”

Section: Samplesmentioning

confidence: 99%

“…It is important to understand how fluids interact with rocks, because textural and chemical/mineralogical changes in the pore space affect the way water will adsorb and expel oil from the rock [3,8,[11][12][13][14][15][16][17]. Previous research on fluid injection has been carried out [5,8,[17][18][19][20][21], and three ions have been proven to play important roles when chalk is exposed to seawater at elevated temperatures: Ca 2+ , Mg 2+ , and SO 4 2− . The injected seawater triggers several mechanisms such as precipitation, dissolution, ion exchange, adsorption, and desorption, to interplay at the same time, with different relative significance depending on the position in the reservoir (nearby to the injector or to the producer).…”

Section: Introductionmentioning

confidence: 99%

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Quick, Easy, and Economic Mineralogical Studies of Flooded Chalk for EOR Experiments Using Raman Spectroscopy

et al. 2018

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Understanding the chalk-fluid interactions and the associated mineralogical and mechanical alterations on a sub-micron scale are major goals in Enhanced Oil Recovery. Mechanical strength, porosity, and permeability of chalk are linked to mineral dissolution that occurs during brine injections, and affect the reservoir potential. This paper presents a novel "single grain" methodology to recognize the varieties of carbonates in rocks and loose sediments: Raman spectroscopy is a non-destructive, quick, and user-friendly technique representing a powerful tool to identify minerals down to 1 µm. An innovative working technique for oil exploration is proposed, as the mineralogy of micron-sized crystals grown in two flooded chalk samples (Liége, Belgium) was successfully investigated by Raman spectroscopy. The drilled chalk cores were flooded with MgCl 2 for ca. 1.5 (Long Term Test) and 3 years (Ultra Long Term Test) under North Sea reservoir conditions (Long Term Test: 130 • C, 1 PV/day, 9.3 MPa effective stress; Ultra Long Term Test: 130 • C, varying between 1-3 PV/day, 10.4 MPa effective stress). Raman spectroscopy was able to identify the presence of recrystallized magnesite along the core of the Long Term Test up to 4 cm from the injection surface, down to the crystal size of 1-2 µm. In the Ultra Long Term Test core, the growth of MgCO 3 affected nearly the entire core (7 cm). In both samples, no dolomite or high-magnesium calcite secondary growth could be detected when analysing 557 and 90 Raman spectra on the Long and Ultra Long Term Test, respectively. This study can offer Raman spectroscopy as a breakthrough tool in petroleum exploration of unconventional reservoirs, due to its quickness, spatial resolution, and non-destructive acquisition of data. These characteristics would encourage its use coupled with electron microscopes and energy dispersive systems or even electron microprobe studies.

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Section: Samplesmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Quick, Easy, and Economic Mineralogical Studies of Flooded Chalk for EOR Experiments Using Raman Spectroscopy

et al. 2018

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show abstract

“…More information about mineralogy, petrography, and rheological characteristics of these chalk successions can be found in literature [35,39,[40][41][42]. Onshore chalk successions are used as analogues for North Sea reservoir chalk in several studies [8,17,20,21,35].…”

Section: Samplesmentioning

confidence: 99%

Quick, Easy and Economic Mineralogical Studies of Flooded Chalk for EOR Experiments Using Raman Spectroscopy

Borromeo¹,

Egeland²,

Minde³

et al. 2018

Preprint

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Understanding the chalk-fluid interactions and the associated mineralogical and mechanical alteration at sub-micron scale are major goals in Enhanced Oil Recovery. Mechanical strength, porosity, and permeability of chalk are linked to mineral dissolution that occurs during brine injections, and affect the reservoir potential. This paper presents a novel "single grain" methodology to recognize the varieties of carbonates in rocks and loose sediments: Raman spectroscopy is a non-destructive, quick, and user-friendly technique representing a powerful tool to identify minerals down to 1 µm. An innovative working technique for oil exploration is proposed, as the mineralogy of micron-sized crystals grown in two flooded chalk samples (Liége, Belgium) was successfully investigated by Raman spectroscopy. The drilled chalk cores were flooded with MgCl2 for c. 1.5 (Long Term Test) and 3 years (Ultra Long Term Test) under North Sea reservoir conditions (Long Term Test: 130°C, 1 PV/day, 9.3 MPa effective stress; Ultra Long Term Test: 130°C, varying between 1-3 PV/day, 10.4 MPa effective stress). Raman spectroscopy was able to identify the presence of recrystallized magnesite along the core of the Long Term Test up to 4 cm from the injection surface, down to the crystal size of 1-2 µm. In the Ultra Long Term Test core the growth of MgCO3 affected nearly the entire core (7 cm). In both samples, no dolomite or high-magnesium calcite secondary growth could be detected when analysing 557 and 90 Raman spectra on the Long and Ultra Long Term Test, respectively. This study can offer Raman spectroscopy as a breakthrough tool in petroleum exploration of unconventional reservoirs, due to its quickness, spatial resolution, and non-destructive acquisition of data. These characteristics would encourage its use coupled with electron microscopes and energy dispersive systems or even electron microprobe studies.

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“…At high temperatures, sulfate and magnesium ions are particularly important to trigger accelerated creep strain rates during continuous flow-through and compaction, although the way that these two ions dictate overall compaction rates differ (e.g., Nermoen et al, 2014Nermoen et al, , 2015. Experiments indicate that the ion exchange on available surface sites as well as the dissolution of calcite and formation of secondary minerals can play a role in dictating the observed mechanical response (Madland et al, 2011); (5) Within the elastic domain, water softening of chalk at elevated temperatures has been observed, in triaxial cell experiments (e.g., Madland et al, 2011;Megawati et al, 2013Megawati et al, , 2015 and in elastic moduli derived from ultrasonic velocities (Japsen et al, 2004;Katika et al, 2015).…”

Section: Introductionmentioning

confidence: 99%

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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Mechanical and physical behavior of high-porosity chalks exposed to chemical perturbation

Cited by 35 publications

References 36 publications

Quick, Easy, and Economic Mineralogical Studies of Flooded Chalk for EOR Experiments Using Raman Spectroscopy

Quick, Easy, and Economic Mineralogical Studies of Flooded Chalk for EOR Experiments Using Raman Spectroscopy

Quick, Easy and Economic Mineralogical Studies of Flooded Chalk for EOR Experiments Using Raman Spectroscopy

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

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