Pore-Scale Modeling of Fluid–Rock Chemical Interactions in Shale during Hydraulic Fracturing

Fazeli, Hossein; Vandeginste, Veerle; Rabbani, Arash; Babaei, Masoud; Muljadi, Bagus Putra

doi:10.1021/acs.energyfuels.0c02975

Cited by 11 publications

(9 citation statements)

References 51 publications

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“…These species mostly react with other ions in solution to form precipitates, which may be responsible for occlusion of fractures. Though many researchers believe that salinity of fracturing fluids has an impact on pyrite dissolution, they consider this impact insignificant …”

Section: Discussionmentioning

confidence: 99%

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Integrated Experimental and Modeling Study of Geochemical Reactions of Simple Fracturing Fluids with Caney Shale

et al. 2022

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Interactions between rock minerals and hydraulic fracturing fluids directly impact the geochemical and geomechanical properties of shale formations. However, the mechanisms of geochemical reactions in shale unconventional reservoirs remain poorly understood. To investigate the geochemical reactions between shale and hydraulic fracturing fluids, a series of batch reactor experiments were undertaken. Three rock samples with different mineralogical compositions and three fluid samples of different compositions [deionized water, deionized water + 2% potassium chloride (KCl), and deionized water + 0.5% choline chloride (C5H14ClNO)] were used. Experiments were undertaken at reservoir temperature and atmospheric pressure. Elemental compositions of effluents after 1, 3, 7, 14, and 28 days were analyzed using inductively coupled plasma mass spectrometry. Medical computed tomography scanning and X-ray fluorescence spectroscopy were conducted on the entire core to help upscale results obtained from rock–fluid interaction experiments. Geochemical modeling using a reactive simulator, TOUGHREACT, was undertaken to corroborate experimental results. Results show that a lower pH triggered high dissolution rates in the rock samples, especially the carbonate components. As the pH increased, the rate of dissolution declined significantly, though for most cases dissolution still continued. The observed dissolved silica concentrations were much higher than the quartz solubility, suggesting that much of the silica originated from more soluble silica polymorphs and possibly desorption from clay mineral exchange sites. The concentration of most elemental species in solution increased, but aluminum (Al) and magnesium (Mg) concentrations declined rapidly following initial entry into solution. Geochemical modeling corroborated the conclusions regarding mineral dissolution and precipitation observed from experiments, notably the dissolution of calcite and pyrite in the reacted shale samples, the likely presence of silica polymorphs such as opal, chalcedony, or amorphous silica in these samples, and the reduction of Al and Mg concentrations in solution by precipitation of secondary aluminosilicate phases. The de-flocculation of clay minerals during reaction implies fines migration after hydraulic fracturing. This is detrimental to reservoir productivity as clay fines are displaced and lodged within the micro- and nanofractures created during fracturing. The immediate consumption of Al and Mg also has implications on blockage of hydrocarbon pathways due to precipitation of new minerals in these locations.

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Section: Discussionmentioning

confidence: 99%

“…Though many researchers believe that salinity of fracturing fluids has an impact on pyrite dissolution, they consider this impact insignificant. 37 4.6. Quartz and Silica Interactions with Hydraulic Fracturing Fluids.…”

Section: Pyrite Interactions With Hydraulic Fracturingmentioning

confidence: 99%

Integrated Experimental and Modeling Study of Geochemical Reactions of Simple Fracturing Fluids with Caney Shale

et al. 2022

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“…Flow is initiated by injecting neutral brine (pump E) at a flow rate of 0.01 mL/min at ambient pressure and temperature with no confining pressure applied on the core. The flow rate was chosen to ensure laminar flow ( Re = 1.02) with high Péclet number ( Pe = 845; fracture width (L frac width ) = 650 μm; self-diffusion coefficient of water ( D water–water ) = 2.3 × 10 –9 m 2 /s, A frac = 6 × 10 –8 m 2 ), which is consistent with the flow characteristics at the fracture/matrix interface during hydraulic fracturing operations. , After the fracture and near fracture pore space is saturated, the three-way valve is flipped and pump R is activated, thereby initiating reactive brine injection.…”

Section: Methodsmentioning

confidence: 99%

“…This stimulation, which is spearheaded by highly oxic acidic fluid, generates both conductive fractures and a more permeable matrix/fracture interface, allowing the release of hydrocarbons from the shale interior into the propped advective conduits. , A cascade of physicochemical interactions subsequently unfold between low-pH HFF and shale rock, creating coupled mineral dissolution and precipitation reactions, along with wettability alteration, shale softening, and fines migration . These effects ultimately dictate fracture conductivity and the lifespan of productivity for a given well. , Multiple studies have focused on the chemical reactions occurring at the shale/HFF interface, − with the general consensus that pyrite readily oxidizes − and carbonates are dissolved creating pore space on the fracture surface. − The reactions that occur are highly dependent on the shale mineralogy, specifically the carbonate and clay content, and the HFF composition. , Most of these experiments involve immersion-type batch reaction systems, ,,, where reactive brine is allowed to interact with a shale sample subject to diffusive solute transport in an enclosed chamber for an extended period of time, mimicking the shut-in period during the hydraulic fracturing operation. A limited number of studies have been conducted under advective flow conditions.…”

Section: Introductionmentioning

confidence: 99%

Impact of Concurrent Solubilization and Fines Migration on Fracture Aperture Growth in Shales during Acidized Brine Injection

2022

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Acidic hydraulic fracturing fluid chemically and physically alters shale rock fabric during injection and shut-in, creating a “reaction-altered zone” along the fracture faces. To better characterize the variable thickness and composition of this reaction-altered zone under advective flow, we take a coupled experimental and modeling approach. A fluidic cell, with six fiducial markers, is first fabricated to keep the rock sample in place during the core floods and to allow image alignment of acquired images. Then, we conduct a series of reactive core floods in a clay-rich siliceous Wolfcamp shale sample with 10 wt % carbonate, using a synthetic fracturing fluid under no confining stress and at room temperature. High-resolution computed tomography (CT) scans are periodically conducted to observe the spatial alteration of the fracture network. We then perform scanning electron microscopy (SEM-EDS) on the two orthogonal surfaces (fracture surface and freshly cut profile face) to generate high-resolution elemental maps that show the change in mineralogy, both with distance along a given flow path along a fracture surface and with depth from the fracture surface into the shale matrix. These results are contrasted against a two-dimensional (2D) advection-diffusion reaction model developed previously for batch reactions between shale and synthetic fracturing fluids. The model simulates the geochemical interaction occurring at the fracture/matrix interface and penetrating into the shale matrix during the reactive core flood. Both model and experimental results show that the acidic brine is neutralized during the core flood, corresponding to an increase in fracture aperture as a function of fluid volume injected with the greatest change near the inlet. SEM-EDS scans reveal significant dissolution of carbonates on the fracture surface without pyrite oxidation. The reactive transport model indicates that carbonate depletion into the shale interior should be observable, yet SEM-EDS shows no discernible loss of carbonate in the orthogonal profile face. The combination of these observations suggests an additional fracture evolution mechanism in the reactive system, i.e., fines migration. We show that fines migration enhances the access of fracturing fluid to the matrix resulting in a more pronounced fracture widening. We conclude that coupled mineral dissolution and fines migration govern fracture aperture growth during acidized brine injection. In this work, we effectively show the underlying risk of relying solely on models that do not include an important (transport) process that can alter the system significantly and propose a combined chemomechanical mechanism for fracture evolution appropriate for this shale mineralogy.

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“…Even for substantial mineral precipitation in fractures, permeability can remain almost unchanged up to two months duration if the deposition is mainly located behind contact asperities with respect to the flow direction [30]. Interestingly, limestone permeability can even increase with time if flowing DI produces "wormholes" that develop due to dissolution and mass transfer [16].These findings suggest that mineral dissolution/precipitation effects on fracture permeability evolution are closely related to the fluid/rock compositions, the reaction kinetics, and how the reactive components reshape the flow channel patterns [40][41][42].…”

Section: Introductionmentioning

confidence: 98%

Long-Term Evolution of Fracture Permeability in Slate: An Experimental Study with Implications for Enhanced Geothermal Systems (EGS)

et al. 2021

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The long-term sustainability of fractures within rocks determines whether it is reasonable to utilize such formations as potential EGS reservoirs. Representative for reservoirs in Variscan metamorphic rocks, three long-term (one month each) fracture permeability experiments on saw-cut slate core samples from the Hahnenklee well (Harz Mountains, Germany) were performed. The purpose was to investigate fracture permeability evolution at temperatures up to 90 °C using both deionized water (DI) and a 0.5 M NaCl solution as the pore fluid. Flow with DI resulted in a fracture permeability decline that is more pronounced at 90 °C, but permeability slightly increased with the NaCl fluid. Microstructural observations and analyses of the effluent composition suggest that fracture permeability evolution is governed by an interplay of free-face dissolution and pressure solution. It is concluded that newly introduced fractures may be subject to a certain permeability reduction due to pressure solution that is unlikely to be mitigated. However, long-term fracture permeability may be sustainable or even increase by free-face dissolution when the injection fluid possesses a certain (NaCl) salinity.

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Pore-Scale Modeling of Fluid–Rock Chemical Interactions in Shale during Hydraulic Fracturing

Cited by 11 publications

References 51 publications

Integrated Experimental and Modeling Study of Geochemical Reactions of Simple Fracturing Fluids with Caney Shale

Integrated Experimental and Modeling Study of Geochemical Reactions of Simple Fracturing Fluids with Caney Shale

Impact of Concurrent Solubilization and Fines Migration on Fracture Aperture Growth in Shales during Acidized Brine Injection

Long-Term Evolution of Fracture Permeability in Slate: An Experimental Study with Implications for Enhanced Geothermal Systems (EGS)

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