Bodhisatwa Hazra, Debanjan Chandra, Vikram Vishal, Mehdi Ostadhassan, Chinmay Sethi, Binoy K. Saikia, Jai Krishna Pandey, Atul K. Varma
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In this study, thermally immature shales of contrasting organic richness from Rajmahal Basin of India were heated to different temperatures (pyrolysis at 350, 500 and 650 °C) to assess the temperature protocols necessary for hydrocarbon liberation and investigate the evolution of pore structural facets with implications for CO<sub>2</sub> sequestration in underground thermally treated shale horizons. Our results from low-pressure N<sub>2</sub> adsorption reveal reduced adsorption capacity in the shale splits treated at 350 and 500 ºC, which can be attributed to structural reworking of the organic matter within the samples leading to formation of complex pore structures that limits the access of nitrogen at low experimental temperatures. Consequently, for both the studied samples BET SSA decreased by ∼58% and 72% at 350 °C, and ∼67% and 68% at 500 °C, whereas average pore diameter increased by ∼45% and 91% at 350 °C, and ∼100% and 94% at 500 °C compared to their untreated counterparts. CO<sub>2</sub> adsorption results, unlike N<sub>2</sub>, revealed a pronounced rise in micropore properties (surface area and volume) at 500 and 650 ºC (∼30%–35% and ∼41%–63%, respectively for both samples), contradicting the N<sub>2</sub> adsorption outcomes. Scanning electron microscope (SEM) images complemented the findings, showing pore structures evolving from microcracks to collapsed pores with increasing thermal treatment. Analysis of the SEM images of both samples revealed a notable increase in average pore width (short axis): by ∼4 and 10 times at 350 °C, ∼5 and 12 times at 500 °C, and ∼10 and 28 times at 650 °C compared to the untreated samples. Rock-Eval analysis demonstrated the liberation of almost all pyrolyzable kerogen components in the shales heated to 650 °C. Additionally, the maximum micropore capacity, identified from CO<sub>2</sub> gas adsorption analysis, indicated 650 °C as the ideal temperature for in situ conversion and CO<sub>2</sub> sequestration. 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Our results from low-pressure N<sub>2</sub> adsorption reveal reduced adsorption capacity in the shale splits treated at 350 and 500 ºC, which can be attributed to structural reworking of the organic matter within the samples leading to formation of complex pore structures that limits the access of nitrogen at low experimental temperatures. Consequently, for both the studied samples BET SSA decreased by ∼58% and 72% at 350 °C, and ∼67% and 68% at 500 °C, whereas average pore diameter increased by ∼45% and 91% at 350 °C, and ∼100% and 94% at 500 °C compared to their untreated counterparts. CO<sub>2</sub> adsorption results, unlike N<sub>2</sub>, revealed a pronounced rise in micropore properties (surface area and volume) at 500 and 650 ºC (∼30%–35% and ∼41%–63%, respectively for both samples), contradicting the N<sub>2</sub> adsorption outcomes. 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引用次数: 0
摘要
从渗透率低的非常规页岩储层中提取天然气是一项挑战。为了克服这一难题,人们采用了水力压裂法(HF)。尽管可以提高页岩气产量,但水力压裂法也存在地下水污染和诱发地震等缺点。这些问题凸显了不断探索新型页岩气开采方法的必要性,例如通过燃烧或热解进行原位加热,以减轻操作和环境问题。在这项研究中,我们将印度拉杰马哈尔盆地有机质丰富程度不同的热未成熟页岩加热到不同的温度(350、500 和 650 °C 的热解温度),以评估碳氢化合物释放所需的温度协议,并研究孔隙结构面的演变对地下热处理页岩地层二氧化碳封存的影响。我们的低压 N2 吸附结果表明,在 350 ºC 和 500 ºC 温度下处理的页岩裂隙的吸附能力降低,这可能是由于样品中有机物的结构再加工导致形成复杂的孔隙结构,从而限制了氮气在低实验温度下的进入。因此,与未经处理的样品相比,所研究的两种样品的 BET SSA 在 350 °C 时分别降低了 58% 和 72%,在 500 °C 时分别降低了 67% 和 68%,而平均孔径在 350 °C 时分别增加了 45% 和 91%,在 500 °C 时分别增加了 100% 和 94%。与 N2 不同的是,CO2 的吸附结果表明,在 500 和 650 ºC 时,微孔特性(表面积和体积)明显增加(两种样品分别为 30% ∼ 35% 和 41% ∼ 63%),这与 N2 的吸附结果相矛盾。扫描电子显微镜(SEM)图像补充了这一发现,显示出孔隙结构随着热处理程度的增加而从微裂缝演变为塌陷孔隙。对两种样品的扫描电子显微镜图像进行分析后发现,与未经处理的样品相比,平均孔隙宽度(短轴)显著增加:350 °C时增加了4∼10倍,500 °C时增加了5∼12倍,650 °C时增加了10∼28倍。岩石评价分析表明,在加热至 650 °C 的页岩中,几乎所有可热解的角质成分都得到了释放。此外,通过二氧化碳气体吸附分析确定的最大微孔容量表明,650 °C是原地转化和二氧化碳封存的理想温度。不过,除了热处理之外,项目的可行性还取决于对页岩气开发的其他相关方面的评估,如地质力学稳定性和超临界二氧化碳的相互作用。
Experimental study on pore structure evolution of thermally treated shales: implications for CO2 storage in underground thermally treated shale horizons
Extracting gas from unconventional shale reservoirs with low permeability is challenging. To overcome this, hydraulic fracturing (HF) is employed. Despite enhancing shale gas production, HF has drawbacks like groundwater pollution and induced earthquakes. Such issues highlight the need for ongoing exploration of novel shale gas extraction methods such as in situ heating through combustion or pyrolysis to mitigate operational and environmental concerns. In this study, thermally immature shales of contrasting organic richness from Rajmahal Basin of India were heated to different temperatures (pyrolysis at 350, 500 and 650 °C) to assess the temperature protocols necessary for hydrocarbon liberation and investigate the evolution of pore structural facets with implications for CO2 sequestration in underground thermally treated shale horizons. Our results from low-pressure N2 adsorption reveal reduced adsorption capacity in the shale splits treated at 350 and 500 ºC, which can be attributed to structural reworking of the organic matter within the samples leading to formation of complex pore structures that limits the access of nitrogen at low experimental temperatures. Consequently, for both the studied samples BET SSA decreased by ∼58% and 72% at 350 °C, and ∼67% and 68% at 500 °C, whereas average pore diameter increased by ∼45% and 91% at 350 °C, and ∼100% and 94% at 500 °C compared to their untreated counterparts. CO2 adsorption results, unlike N2, revealed a pronounced rise in micropore properties (surface area and volume) at 500 and 650 ºC (∼30%–35% and ∼41%–63%, respectively for both samples), contradicting the N2 adsorption outcomes. Scanning electron microscope (SEM) images complemented the findings, showing pore structures evolving from microcracks to collapsed pores with increasing thermal treatment. Analysis of the SEM images of both samples revealed a notable increase in average pore width (short axis): by ∼4 and 10 times at 350 °C, ∼5 and 12 times at 500 °C, and ∼10 and 28 times at 650 °C compared to the untreated samples. Rock-Eval analysis demonstrated the liberation of almost all pyrolyzable kerogen components in the shales heated to 650 °C. Additionally, the maximum micropore capacity, identified from CO2 gas adsorption analysis, indicated 650 °C as the ideal temperature for in situ conversion and CO2 sequestration. Nevertheless, project viability hinges on assessing other relevant aspects of shale gas development such as geomechanical stability and supercritical CO2 interactions in addition to thermal treatment.
期刊介绍:
The International Journal of Coal Science & Technology is a peer-reviewed open access journal that focuses on key topics of coal scientific research and mining development. It serves as a forum for scientists to present research findings and discuss challenging issues in the field.
The journal covers a range of topics including coal geology, geochemistry, geophysics, mineralogy, and petrology. It also covers coal mining theory, technology, and engineering, as well as coal processing, utilization, and conversion. Additionally, the journal explores coal mining environment and reclamation, along with related aspects.
The International Journal of Coal Science & Technology is published with China Coal Society, who also cover the publication costs. This means that authors do not need to pay an article-processing charge.