Investigation of microscopic pore structure variations of shale due to hydration effects through SEM fixed-point observation experiments

Sui, Weibo; Tian, Yingying; Yao, Chenhao

doi:10.1016/s1876-3804(18)30099-5

Cited by 28 publications

(7 citation statements)

References 14 publications

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“…Previous studies have indicated that the physical and chemical properties differ significantly according to mineral types and clay minerals are more active. For example, clay minerals mainly correlate with smaller pores; smectite and I/S are easier to hydrate and swell than illite and kaolinite (Zolfaghari et al, 2016;Al-Ameri et al, 2018;Sui et al, 2018), and their higher CEC will lead to stronger impacts on the chemical properties of flowback water (Greenland, 1971;Han et al, 2016;Saidian et al, 2016;Zolfaghari et al, 2016); along with burial evolution, smectite with large ISA will transfer to illite with no ISA by illitization, leading to the decreasing of ISA (Zhu et al, 2015;Wilson et al, 2016b;Singh et al, 2016) and the change of pore structure and BET-SSA (Wu et al, 2015;Wang and Guo, 2019). These differences will result in divergences in the interactions between pore walls and fluids and then affect the fluid flow significantly.…”

Section: Surfacesmentioning

confidence: 99%

“…These divergences will change the distribution, occlusion, and flow of fracturing fluid and oil. Furthermore, water is the main component in fracturing fluids, and it will interact with clay minerals (especially I/S) significantly during the pumping, flowback, and production stages (O'Brien and Chenevert, 1973;Makhanov et al, 2014;Xu and Dehghanpour, 2014;Sui et al, 2018;Shi et al, 2020) and might lead to the low flowback recovery, the changes of pore and surface properties, and the reduction of oil relative permeability. Therefore, characteristics and properties of pores and surfaces are the indispensable factors that need to be taken into the evaluation of shale oil potential.…”

Section: Significances and Prospectsmentioning

confidence: 99%

“…One of the key concerns of the exploitation of shale resources is the evaluation of the production performance after fracturing (Jarvie et al, 2007;Wang and Gale, 2009;Jin et al, 2014;Tang et al, 2019;Wei et al, 2020). Previous studies have observed that the fracturing fluids interact significantly with minerals and change their properties such as wettability, morphology, composition, water-bearing properties, and cation exchange capacity (CEC) (Chen et al, 2016;Chen et al, 2018a;Chen et al, 2018b;Lu et al, 2018;Sari et al, 2019;Zeng et al, 2019), leading to problems such as low flowback recovery of fracturing fluids, environment hazard, hydration, expansion, and rheology of clay minerals (O'Brien and Chenevert, 1973;Makhanov et al, 2014;Al-Ameri et al, 2018;Sui et al, 2018;Aadnøy and Looyeh, 2019;Zeng et al, 2019) and will impact seriously on the production progress. Therefore, to better understand the mechanisms of these problems and their potential effect on production performance, a detailed analysis of the characteristics of shale pores and surface structures and their potential interactions with the fracturing fluids and the confined fluids in shale formations is of great significance.…”

Section: Introductionmentioning

confidence: 99%

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Characteristics of Shale Pores and Surfaces and Their Potential Effects on the Fluid Flow From Shale Formation to Fractures

Cai

Gao

et al. 2021

Front. Earth Sci.

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Fluid flow is critical for the efficient exploitation of shale resources and can be split into two stages: the flow in the artificial fractures and, more importantly, the flow from shale formations to the artificial fractures. In this study, X-ray diffraction, N2 adsorption, mercury intrusion, and ethylene glycol monoethyl ether adsorption were conducted on the shales collected from Es3middle, Es3lower, and Es4upper sub-members in the Dongying Sag to reveal the potential effects of the characteristics and properties of pores and surfaces on the fluid flow in shale formations. The results are indicated as follows: 1) The shales from Es3middle and Es3lower contain more I/S and detrital minerals but less illite and carbonate minerals than those of Es4upper. 2) The shales from Es3middle and Es3lower are mainly composed of smaller pores present in larger surface areas and lead to the steeper slope between the BrunauerEmmettTeller specific surface area (BET-SSA) and pore volumes. 3) Clay minerals mainly contribute to pore development, and carbonate minerals inhibit pore development. All kinds of surface areas (especially the inner surface area) are sourced by clay minerals, while I/S and illite present opposite effects. 4) Pore size and surface properties affect significantly the fluid flow in shale formations. The shales from Es4upper are the favorable interval for shale oil accumulation and flow, especially for the shales with depth ranges of 3360∼3410 m, which possess high carbonates, illite and total organic carbon content, low clay mineral content, large pore volume, high large pore content, and small surface areas. Additionally, fluid composition needs to be paid more concern in the future.

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Section: Surfacesmentioning

confidence: 99%

Section: Significances and Prospectsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Characteristics of Shale Pores and Surfaces and Their Potential Effects on the Fluid Flow From Shale Formation to Fractures

Cai

Gao

et al. 2021

Front. Earth Sci.

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“…Identifying pore types is the basis for studying the microscopic pore structure of reservoirs. Some previous studies have pointed out that most pore systems in shale are micro pores, so they can not be seen by OM [31][32][33]. However, different types of pores can be revealed by high-precision scanning images.…”

Section: Pore Structure Typementioning

confidence: 99%

Research on Micro-Pore Structure and 3D Visual Characterization of Inter-Salt Shale Based on X-CT Imaging Digital Core Technology

Jie

Zhang

et al. 2022

Processes

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Pore structure is the key factor affecting reservoir accumulation and enrichment behavior. Due to the complex mineral components and pore structure of shale oil reservoirs and strong heterogeneity, it is necessary to explore the micro-pore structure characteristics of inter-salt shale. In this study, in order to qualitatively and quantitatively analyze the pore structure of inter-salt shale reservoirs, as well as evaluate the mineral composition and its spatial distribution characteristics, three shale samples from the 10th cyclothem of the Eq3 (Eq34–10 cyclothem) inter-salt shale were selected to acquire 2D and 3D grayscale images by modular automated processing system (MAPS) and X-ray micro-computed tomography (Micro-CT), respectively. The color map of the inlaid characteristics of mineral aggregates was established by Quantitative Evaluation of Minerals by Scanning Electron Microscopy (QEMSCAN), and different mineral types in the grayscale image were determined. After that, the digital core technology was used to reconstruct the core in 3D, and the maximum sphere method was used to extract the pore network model, so as to realize the quantification of micron pore throats and the 3D visualization of inter-shale samples. Meanwhile, in order to compare the fractal characteristics of the pores of the samples, the two-dimensional and three-dimensional fractal dimensions of the three cores were calculated by combining the digital core technique with fractal theory. The study yielded several notable results: the pore structure of inter-salt shale reservoirs is complex and multi-scale, and the CT scanning digital core technology can effectively realize 3D visualization of rock microstructure without damage. The pore types of rock samples are mainly intergranular pores, interparticle pores, and dissolved pores, and the minerals are mainly dolomite, calcite, and glauberite. The micron pore throat radius of the rock sample is 0.5–13.9 μm, the distribution of coordination number is mainly in the range of 1–4, and the shape of the pore throat is mainly triangular and square. The pore space of inter-salt shale has suitable fractal characteristics, and the three-dimensional fractal dimension of the three cores is in the range of 2.41–2.49. In sum, this work used digital core technology to study the microscopic pore structure of inter-salt shale oil, establishing a basis for further understanding of the seepage characteristics and exploration and development of shale oil.

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“…Qian et al (2017) used nuclear magnetic resonance and CT scanning technology carried out core hydration experiments under the condition of 10 MPa confining pressure and studied the effect of hydration on the pore fracture structure of shale. Sui et al (2018) based on the hydration experiment of 4 different types of shale outcrop rock samples and used the field emission scanning electron microscope to conduct fixedpoint observation and comparative analysis of the microscopic pore changes before and after the hydration of the experimental sample. Xue et al (2018) used field emission scanning electron microscopy (FESEM) to microscopically characterize shale samples before and after hydration and used the micro-CT scan, porosity, and permeability test experiments to study the difference between physical parameters and the microstructure of the original sample, saturated water.…”

Section: Introductionmentioning

confidence: 99%

Investigation on the influence of hydration on the elastic parameters of Longmaxi Formation shale

et al. 2021

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Through hydration experiments and ultrasonic transmission experiments, analyze the influence of hydration on the shale acoustic velocity, elastic parameters, and anisotropy parameters. The relationship between the elastic parameter C ij and the hydration time is given. The results show that: (1) The hydration of shale is a continuous and gradually stable process. (2) The qP wave velocity first significantly decreases with the hydration time and then tends to be flat, and the qSH wave velocity shows a decreasing trend with the hydration time. (3) The anisotropic strength parameter ε of the Longmaxi Formation shale increases first and then decreases, and tends to be stable with hydration time, and the magnitude of the change is relatively large, but the magnitude of γ the change is small. The results provide methods and ideas for accurately obtaining shale elastic parameters and studying the influence of hydration on shale wave speed, elastic parameters and anisotropy characteristics, and have important theoretical value and practical significance.

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Investigation of microscopic pore structure variations of shale due to hydration effects through SEM fixed-point observation experiments

Cited by 28 publications

References 14 publications

Characteristics of Shale Pores and Surfaces and Their Potential Effects on the Fluid Flow From Shale Formation to Fractures

Characteristics of Shale Pores and Surfaces and Their Potential Effects on the Fluid Flow From Shale Formation to Fractures

Research on Micro-Pore Structure and 3D Visual Characterization of Inter-Salt Shale Based on X-CT Imaging Digital Core Technology

Investigation on the influence of hydration on the elastic parameters of Longmaxi Formation shale

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