Multi-fractal analysis for the AE energy dissipation of CO2 and CO2+ brine/water treated low-clay shales under uniaxial compressive tests

Tan, Jingqiang; Hu, Chenger; Lyu, Qiao; Dick, Jeffrey M.; Ranjith, P.G.; Li, Lei; Wang, Zhanghu

doi:10.1016/j.fuel.2019.03.008

Cited by 30 publications

(12 citation statements)

References 30 publications

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“…The multifractal method was used to further quantify the AE characteristics associated with the hydraulic fracturing experiments. It has been demonstrated that the time series of the AE parameters has multifractal characteristics [31]. The multifractal spectrum of the AE counts and energy time series throughout all stages is shown in Figure 6.…”

Section: Resultsmentioning

confidence: 96%

“…In addition, many studies have adopted multifractal theory to study the AE activity of rock fracturing [26,30]. In this study, the box-counting method was used to analyze the multifractal characteristics of the time series of the AE parameters [31,43]. The detailed calculation process of the multifractal spectrum of the AE time series is as follows [31]:…”

Section: Experimental System and Schemementioning

confidence: 99%

“…The results revealed that the time-varying multifractal characteristics could describe the AE mechanisms and the difference in strong and weak AE signals. Tan et al [31] studied the multifractal characteristics of shale acoustic emission energy in uniaxial experiments under different immersion conditions. The results showed that the multifractal spectrum of the AE parameters was influenced by soaking times, which was directly related to changes in the pores and cracks of the shale samples.…”

Section: Introductionmentioning

confidence: 99%

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Multifractal Analysis of Acoustic Emissions during Hydraulic Fracturing Experiments under Uniaxial Loading Conditions: A Niutitang Shale Example

Tan

Xie

et al. 2020

Geofluids

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Fracture characterization is essential for estimating the stimulated reservoir volume and guiding subsequent hydraulic fracturing stimulations in shale reservoirs. Laboratory fracturing experiments can help provide theoretical and technical guidance for field operations. In this study, hydraulic fracturing experiments on the shale samples from Niutitang Formation in Hunan Province (China) under a uniaxial loading condition are conducted. The multifractal method is used to analyze the acoustic emission (AE) signals and characterize fracture initiation and propagation. The hydraulic fracturing process can be divided into three stages based on the characteristics of AE signals: the initial stage, the quite stage, and the fracturing stage. The multifractal analysis results showed that: (1) the value of the spectrum width, Δα, continues to increase as the energy accumulates until the fracturing stage starts; and (2) the difference in the multifractal spectrum values, Δf, reflects the relationship between small and large signal frequencies and can quantify the fracture scale, i.e., the lower the Δf, the larger the fracture scale and vice versa. The results were further verified using a time-frequency analysis of the AE signals and micro-CT scanning of the samples. This study demonstrates that the multifractal method is feasible for quantitatively characterizing hydraulic fractures and can aid field hydraulic fracturing operations.

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Section: Resultsmentioning

confidence: 96%

Section: Experimental System and Schemementioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Multifractal Analysis of Acoustic Emissions during Hydraulic Fracturing Experiments under Uniaxial Loading Conditions: A Niutitang Shale Example

Tan

Xie

et al. 2020

Geofluids

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“…The process of N 2 adsorption is governed by Van der Waals force under low pressure (Raymond et al., 2010; Tan et al., 2019), corresponding to fractal dimension D 1 , which reflects the surface roughness of pore microstructure (Wang et al., 2016). Meanwhile, at higher pressure, adsorption increasingly depends on multilayer adsorption even capillary condensation, and corresponding to fractal dimension D 2 , which used to define the pore microstructure irregularity (Wang et al., 2016).…”

Section: Resultsmentioning

confidence: 99%

Characterization of pore microstructure and methane adsorption of organic-rich black shales in northwestern Hunan, South China

Huang

Dong

Hursthouse

et al. 2019

Energy Exploration & Exploitation

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The gas adsorption of shale is one of the most important factors influencing shale gas accumulation and production. Different from other shale gas fields, the shale in Northwestern Hunan province with strong structural deformation has especially high portion of adsorbed gas. The adsorption abilities of shale reservoir play a significant role in the success of exploration and production of shale gas in Northwestern Hunan. Therefore, based on many experiments including field emission scanning electron microscopy, N2/CO2 adsorption, excess CH4 adsorption with constant temperature and others, this paper found that: (1) the shale pores were identified with mineral matrix pores, organic-matter pores and fracture pores, and the pores can be further classified according to their shape features and forming mechanism; (2) after analyses of the distribution of the pore size, mesoporous is the largest contributor and widely distributed, and micropores provide more contribution on surface area but limited contribution to pore volume. Meanwhile, depth has little effect on the properties of shale reservoirs; (3) based on the fractal geometry theory, surface roughness is positively correlated to microstructure irregularity, which means the effects between the gas adsorption by Van der Waals force and by multilayer or capillary condensation in single pore system are consistent during the N2 adsorption process. (4) The abilities of gas storage are apparently sensitive to the surface roughness of shale pores and nonsensitive to microstructure irregularity. Total organic carbon has strong positive correlation with the surface roughness, specific surface area, total pore volume, and Langmuir volume, which means TOC can improve the adsorption of shale reservoir in many ways. Pyrite can offer much contribution to the ability of gas adsorption.

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“…Aplin et al (2006) reported that the microstructure and pore properties of Mexican mudstones changed due to mechanical compaction. Based on uniaxial and/or triaxial compression experiments, several studies have been conducted on the deformational behavior, microstructure and pore/fracture evolution of shale (Arora and Mishra, 2015;Mishra and Verma, 2015;Minaeian et al, 2017;Wang and Li, 2017;Wang et al, 2018;Bakhshian and Hosseini, 2019;Liu et al, 2019;Tan et al, 2019), with microstructure, pore properties and permeability all influenced by compression and deformation. Using artificial compaction to make pellets of Wyoming montmorillonite powder, (Kuila and Prasad, 2013) found that compaction could results in decrease in pore volume and reduction of macropores of the clays.…”

Section: Introductionmentioning

confidence: 99%

Preliminary Experimental Study of Methane Adsorption Capacity in Shale After Brittle Deformation Under Uniaxial Compression

et al. 2021

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This paper presents a preliminary experimental study on methane adsorption capacity in shales before and after artificial deformation. The experimental results are based on uniaxial compression and methane isothermal adsorption tests on different shale samples from the Silurian Longmaxi Formation, Daozhen County, South China. Two sets of similar cylindrical samples were drilled from the each same bulk sample, one set was subjected to a uniaxial compressive simulation test and then crushed as artificial deformed shale sample, the other set was directly crushed as the original undeformed shale sample. And then we conducted a comparative experimental study of the methane adsorption capacity of original undeformed and artificially deformed shales. The uniaxial compression simulation results show that the failure mode of all samples displayed brittle deformation. The methane isothermal adsorption results show that the organic matter content is the main controlling factor of shale methane adsorption capacity. However, the comparative results also show that the compression and deformation have an effect on methane adsorption capacity, with shale methane adsorption capacity decreasing by about 4.26–8.48% after uniaxial compression deformation for the all shale samples in this study.

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Multi-fractal analysis for the AE energy dissipation of CO2 and CO2+ brine/water treated low-clay shales under uniaxial compressive tests

Cited by 30 publications

References 30 publications

Multifractal Analysis of Acoustic Emissions during Hydraulic Fracturing Experiments under Uniaxial Loading Conditions: A Niutitang Shale Example

Multifractal Analysis of Acoustic Emissions during Hydraulic Fracturing Experiments under Uniaxial Loading Conditions: A Niutitang Shale Example

Characterization of pore microstructure and methane adsorption of organic-rich black shales in northwestern Hunan, South China

Preliminary Experimental Study of Methane Adsorption Capacity in Shale After Brittle Deformation Under Uniaxial Compression

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