Experimental investigation on the effects of different fracturing fluids on shale surface morphology

Tan, Jingqiang; Hu, Chenger; Lyu, Qiao; Gui, Feng; Chen, Shefa

doi:10.1016/j.petrol.2022.110356

Cited by 20 publications

(12 citation statements)

References 50 publications

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“…It can confirm the oxidation reaction of pyrite. ,, The OH – ions prevalent in neutral and alkaline fracturing fluids combine with Fe 3+ ions to form ferric hydroxide precipitates (Eqs. , ), , which may block the pores and microfracture spaces inside the shale . With an increase in immersion time, the surface coating formed by the secondary mineral precipitation leads to the passivation of the pyrite surface and the reaction is not complete. , …”

Section: Discussionmentioning

confidence: 90%

“…The process of shale deformation can be divided into three periods according to the soaking time, as mentioned above. In the early soaking period (the first 15 days of soaking), fluids enter fractures and macropore spaces and react intensely with shale minerals . The physical properties of shale change significantly, as reflected in the obvious variations of the AE characteristics.…”

Section: Discussionmentioning

confidence: 99%

“…In the early soaking period (the first 15 days of soaking), fluids enter fractures and macropore spaces and react intensely with shale minerals. 75 The physical properties of shale change significantly, as reflected in the obvious variations of the AE characteristics. In the middle period of soaking (1−6 months), the fluids gradually penetrate into the micro-and nanoscale pore space and further react with other minerals in shale.…”

Section: Fluid−rock Reactions Under Various Soakingmentioning

confidence: 99%

“…11, 12), 78,79 which may block the pores and microfracture spaces inside the shale. 75 With an increase in immersion time, the surface coating formed by the secondary mineral precipitation leads to the passivation of the pyrite surface and the reaction is not complete. 76 As quartz has an ultralow solubility, it does not react significantly in low pH solutions.…”

Section: Fluid−rock Reactions Under Various Soakingmentioning

confidence: 99%

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Multifractal Analysis for the Acoustic Emission Energy Dissipation of Shale after Long-Term Immersion in Fracturing Fluids with Various pH

Xie,

Tan,

Lyu

et al. 2023

Energy Fuels

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The interaction between shale and fracturing fluids will change the internal pore structure and adsorption capacity of shale, which have an important impact on shale gas productivity. This study aims to investigate the variations in acoustic emission (AE) energy and multifractal characteristics of shale under different pH values of fracturing fluids with implications for shale gas productivity. A series of immersion experiments were carried out on shale with fracturing fluids, with pH values of 6, 7, and 8, respectively. The uniaxial compression tests and AE tests were conducted on shale under fracturing fluid immersion with pH values of 6, 7, and 8. The multifractal theory is applied to analyze the evolution of fracture closure and propagation during uniaxial compression based on AE signals. The study also examines the deformation and crack evolution of shale after long-term fracturing fluid immersion, with particular emphasis on fluid−rock reactions. The results show that the maximum cumulative AE energy of shale after immersion is higher than that of intact shale. The focus is on understanding the fracture evolution process of shale during uniaxial compression at different stages. The fluid−rock reactions determine the deformation and crack evolution of shale after longterm fracturing fluid immersion. The increase of shale spectrum width Δα after immersion indicates that the distribution of AE signals is more uneven after immersion. The Δf value of shale after acid fracturing fluid soaking changes more significantly than those of neutral or alkaline fracturing fluids. All the fractal spectra of shale samples generally show a left-skewed distribution. The values of spectrum parameters are affected by soaking fluid, soaking time, and compression stages, resulting in the variation of multifractal characteristics. Hydration expansion of clay minerals is dominant in the middle and late period of immersion. The research results have a certain guidance for understanding the deformation and crack evolution and the influence of rock−fluid reactions on the failure process of shale samples.

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Section: Discussionmentioning

confidence: 90%

Section: Discussionmentioning

confidence: 99%

Section: Fluid−rock Reactions Under Various Soakingmentioning

confidence: 99%

Section: Fluid−rock Reactions Under Various Soakingmentioning

confidence: 99%

See 2 more Smart Citations

Multifractal Analysis for the Acoustic Emission Energy Dissipation of Shale after Long-Term Immersion in Fracturing Fluids with Various pH

Xie,

Tan,

Lyu

et al. 2023

Energy Fuels

Self Cite

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“…The main damage caused by hydration is the result of clay mineral swelling, dissolution, and the shedding of clastic particles. − Variations in the pore structure resulting from hydration mainly result from the dissolution of minerals and result in the dislodging of mineral particles and the concomitant enlargement of pores. , However, higher clay mineral contents may lead to pore blockage due to clast swelling and the concomitant pore shrinkage. , In addition, hydration reduces the strength of shale, which may exacerbate wellbore collapse or aid hydraulic fracturing. − Hydration may even generate micro-fractures and form complex fracture networks connecting micro- or nano-pores. − With the progress of hydration, micro-fractures will extend and connect, ultimately developing transmissive fracture systems. , Thus, hydration promotes changes in the pore structure and the physical characteristics of shales, manifest as changes in the porosity and permeability, with clay mineral type, hydration time, pH, and ionic composition of the water (i.e., different fracturing fluids) all impacting the response. − However, the detailed imbibition process and hydration damage on transitional shale has not been fully revealed.…”

Section: Introductionmentioning

confidence: 99%

Hydration of Transitional Shale and Evolution of Physical Properties Constrained by Concurrent NMR and Acoustic Observations

Chen³

et al. 2023

Energy Fuels

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Hydration state is a key factor affecting the pore structure and mechanical properties of shale that directly impacts the migration and then production of geofluids. We quantify the impact of the hydration state on physical properties through spontaneous imbibition experiments constrained by concurrent nuclear magnetic resonance (NMR) and acoustic observations as diagnostics of response. The long-duration experiments (24 days) are on samples from the Permian Shanxi Formation of the Ordos Basin, complemented by measurements of composition and physical properties. These shales primarily comprise quartz and clay minerals with intraparticle pores present within the clay minerals. The NMR T 2 spectra indicate that mesopores (2–50 nm) comprise ∼80% of the total pore space. The imbibition rate decreases by a factor of 3 from 0.08 g/h to a stable rate of 0.03 g/h from the 1st to the 24th hour. This is accompanied by a 10% decrease in the deformation modulus from 44 to 40.3 GPa over 24 days. The reduction in the modulus is consistent with observations of the shedding and spalling of hydrophilic quartz particles from the unconstrained surface and the generation of fractures. Reduction in the imbibition rate is consistent with the swelling followed by squeezing of clay minerals and the corresponding reduction in pore diameters in the confined core of the sample, together with the reduction in saturation gradients with the progress of imbibition. Understanding the mechanisms and effects of hydration on the pore structure and mechanical properties is important in understanding the shale hydration process and defining diagnostic (acoustic and NMR) signatures that may be used in reservoir surveillance.

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Experimental Study on the Mechanical Properties of Shale After Long-term of Immersion in Fracturing Fluids with Different pH

Lyu

Wang

et al. 2022

Rock Mech Rock Eng

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Experimental investigation on the effects of different fracturing fluids on shale surface morphology

Cited by 20 publications

References 50 publications

Multifractal Analysis for the Acoustic Emission Energy Dissipation of Shale after Long-Term Immersion in Fracturing Fluids with Various pH

Multifractal Analysis for the Acoustic Emission Energy Dissipation of Shale after Long-Term Immersion in Fracturing Fluids with Various pH

Hydration of Transitional Shale and Evolution of Physical Properties Constrained by Concurrent NMR and Acoustic Observations

Experimental Study on the Mechanical Properties of Shale After Long-term of Immersion in Fracturing Fluids with Different pH

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