Shale softening: Observations, phenomenological behavior, and mechanisms

Du, Jianting; Hu, Liming; Meegoda, Jay N.; Zhang, Guoping

doi:10.1016/j.clay.2018.04.033

Cited by 62 publications

(26 citation statements)

References 50 publications

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“…Du et al [16,17] used deionized water for 48 hours without heating or applying pressure to soften the shale and degradation of mechanical properties after treatment. However, water-clay interaction will be different for actual natural gas reservoirs subjected to high temperature and pressure.…”

Section: Introductionmentioning

confidence: 99%

WITHDRAWN: Impact of Hydraulic fracturing on Mineralogy on Change in Micro and Nano Porosity and Permeability of Shales

Zhang

Meegoda

Silva

et al. 2021

Preprint

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Hydraulic fracturing is widely applied to economical gas production from shale reservoirs. Still, the gradual swelling of the clay micro/nanopores due to retained fluid from hydraulic fracturing causes a gradual reduction of gas production. Four different gas-bearing shale samples were investigated to quantify the expected shale swelling due to hydraulic fracturing. These shale samples were subject to heated deionized (DI) water at 100°C temperature and 1.2 MPa pressure in a laboratory reactor for 72 hours to simulate shale softening. The low-temperature nitrogen adsorption and density measurements were performed on the original and treated shale to determine the micro and nanopore structure change. The micro and nanopore structures changed during shale swelling, and the porosity decreased after shale treatment. The porosity decreased by 4% for clayey shale, while for well-cemented shale the porosity only decreased by 0.52%. The findings showed that the initial mineralogical composition of shale plays a significant role in the swelling of micro and nanopores and the pore structure alteration due to retained fluid from hydraulic fracturing. A pore network model was used to compare the permeability due to shale softening. The permeability results show a reduction from 3.76E-16 m2 to 2.62E-17 m2 after treatment based on the simulations.

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Section: Introductionmentioning

confidence: 99%

WITHDRAWN: Impact of Hydraulic fracturing on Mineralogy on Change in Micro and Nano Porosity and Permeability of Shales

Zhang

Meegoda

Silva

et al. 2021

Preprint

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“…The shape of the force-displacement curve after exposure to water-based fluids became less sharp indicating that the material after exposure changed from brittle to more ductile. Deterioration of shale hardness and strength upon exposure to water based fluids is a well-known phenomenon termed "shale softening" [20]. According to the literature, the main mechanisms responsible for "shale softening" are: (1) interaction of the foreign fluids with swelling clays present in shales that result in volumetric changes of the clay particles, (2) electrostatic repulsion between similarly charged clay particles, and (3) dissolution of cementation minerals [20].…”

Section: Resultsmentioning

confidence: 99%

“…Mixing of the shale pore fluid with the exposure fluid will thus cause the system to undergo changes toward a new equilibrium state. These changes may thus include: (1) ion exchange between clays and the new pore fluid followed by volumetric response of swelling clays (swelling, Energies 2021, 14, 2342 6 of 14 shrinkage), (2) changes in the interparticle interactions, (3) dissolution of some minerals due to contact with undersaturated solution [16,20]. minerals due to contact with undersaturated solution [16,20].…”

Section: Resultsmentioning

confidence: 99%

Acid Treatment as a Way to Reduce Shale Rock Mechanical Strength and to Create a Material Prone to the Formation of Permanent Well Barrier

et al. 2021

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Utilization of natural shale formations for the creation of annular barriers in oil and gas wells is currently discussed as a mean of simplifying cumbersome plugging and abandonment procedures. Shales that are likely to form annular barriers are shales with high content of swelling clays and relatively low content of cementation material (e.g., quartz, carbonates). Shales with large content of quartz and low content of swelling clays will be rather brittle and not easily deformable. In this paper we ask the question whether and to what extent it is possible to modify the mechanical properties of relatively brittle shales by chemically removing some cementation material. To answer this question, we have leached out carbonates from Pierre I shale matrix using hydrochloric acid and we have compared mechanical properties of shale before and after leaching. We have also followed leaching dynamics using X-ray tomography. The results show that removal of around 4–5 wt% of cementation material results in 43% reduction in Pierre I shale shear strength compared to the non-etched shale exposed to sodium chloride solution for the same time. The etching rate was shown to be strongly affected by the volume of fluid staying in direct contact with the shale sample.

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“…Ferrage [80] where Å refers to Ångström (1 Å = 0.1 nanometer). The exposure of shale to fluids with compositions even slightly different from those of in situ pore fluid induces a difference in chemical potential and changes the swelling pressure [81]. Under constant strain conditions, the increase of pressure due to adsorption-induced swelling can be as high as a hundred MPa up to a few GPa [82,83].…”

Section: Water Sensitivity Of Shale Rocksmentioning

confidence: 99%

Micro- and Macroscale Consequences of Interactions between CO2 and Shale Rocks

et al. 2020

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In carbon storage activities, and in shale oil and gas extraction (SOGE) with carbon dioxide (CO2) as stimulation fluid, CO2 comes into contact with shale rock and its pore fluid. As a reactive fluid, the injected CO2 displays a large potential to modify the shale’s chemical, physical, and mechanical properties, which need to be well studied and documented. The state of the art on shale–CO2 interactions published in several review articles does not exhaust all aspects of these interactions, such as changes in the mechanical, petrophysical, or petrochemical properties of shales. This review paper presents a characterization of shale rocks and reviews their possible interaction mechanisms with different phases of CO2. The effects of these interactions on petrophysical, chemical and mechanical properties are highlighted. In addition, a novel experimental approach is presented, developed and used by our team to investigate mechanical properties by exposing shale to different saturation fluids under controlled temperatures and pressures, without modifying the test exposure conditions prior to mechanical and acoustic measurements. This paper also underlines the major knowledge gaps that need to be filled in order to improve the safety and efficiency of SOGE and CO2 storage.

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Shale softening: Observations, phenomenological behavior, and mechanisms

Cited by 62 publications

References 50 publications

WITHDRAWN: Impact of Hydraulic fracturing on Mineralogy on Change in Micro and Nano Porosity and Permeability of Shales

WITHDRAWN: Impact of Hydraulic fracturing on Mineralogy on Change in Micro and Nano Porosity and Permeability of Shales

Acid Treatment as a Way to Reduce Shale Rock Mechanical Strength and to Create a Material Prone to the Formation of Permanent Well Barrier

Micro- and Macroscale Consequences of Interactions between CO2 and Shale Rocks

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