A comparison of nano-scale pore attributes of Barakar Formation gas shales from Raniganj and Wardha Basin, India using low pressure sorption and FEG-SEM analysis

Chandra, Debanjan; Vishal, Vikram

doi:10.1016/j.jngse.2020.103453

Cited by 30 publications

(14 citation statements)

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“…This means that smaller pores which were earlier accessible by N 2 were now rendered inaccessible when degassed at 200 °C. Similar behavior for oil window shales was reported by Chandra et al 28 Considering the thermal behavior of the shales (Section 3.4), we can interpret that the lower detection of smaller pores (<13 nm diameter) is caused by bitumen generation and the blockage of porous structures to N 2 when degassed at 200 °C. Similar features were observed for the <1 mm crush size BS sample when degassed at 110 and 200 °C.…”

Section: Resultssupporting

confidence: 87%

“…Shales, previously looked upon as “source rocks”, have received unprecedented research focus since their development as “unconventional petroleum systems”. − Further, the fact that shales are also being studied to be one of the preferred options for CO 2 sequestration has warranted more efforts for characterizing their fundamental attributes, viz., gas storage capacity, nature of porous structures, kinetics of hydrocarbon generation, etc. − The primary factor that controls the petroleum generation and/or gas storage in shales is the nature of the organic matter present within them. ,− Although clay minerals have also been identified as the other significant component in shale reservoirs, their complete role in storage and transport still presents certain ambiguity. Several researchers have extensively used the low-pressure gas adsorption (LPGA) technique using N 2 and CO 2 to comprehend the complexity of pore attributes of shales. − …”

Section: Introductionmentioning

confidence: 99%

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Impact of Degassing Time and Temperature on the Estimation of Pore Attributes in Shale

et al. 2021

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The influence of degassing time and temperature on low-pressure gas adsorption (LPGA) behavior of shales was examined in this study. Two organic-rich shales of contrasting maturity, reactivity and organic matter type, were crushed to <1 mm and <212 μm grain-sizes and degassed at 110, 200, and 300 °C for 3 and 12 h, respectively. Our results indicate that degassing duration has a minimal influence on pore-character interpretations from LPGA experiments, while the degassing temperature shows a strong influence on the pore attributes. For both shales, reliable porosity estimates were obtained when the samples were degassed at 110 °C. When the degassing temperature was increased to 200 and further to 300 °C, distinct changes in adsorption isotherms and other pore structural features were observed. For the mesoporous low-mature shale (collected from a lignite mine) when the degassing temperature was kept at 200 °C, a macroporous character was induced with a manifold increase in pore diameter. Results from thermogravimetry and Rock-Eval indicate abundance of reactive kerogen, which undergoes alteration when degassed at higher temperatures. When the degassing temperature was kept at 300 °C, the organic matter underwent further alteration and showed an isotherm similar to the shales degassed at 110 °C. Similarly, for the oil-window mature shale sample, a transition towards macroporous structure was observed when the sample was degassed at 200 and 300 °C, compared to a mesoporous structure observed when degassed at 110 °C. The results from fractal dimensions also support the above inferences, indicating the presence of simpler structures at higher degassing temperatures. Reduction in pore volume (110–200 °C) and its further rise (200–300 °C) are also evident in the micropore domain, more distinctly in the oil window mature shale. Our results strongly indicate that degassing temperature should be kept at around 110 °C for reliable shale pore character estimation.

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Section: Resultssupporting

confidence: 87%

Section: Introductionmentioning

confidence: 99%

Impact of Degassing Time and Temperature on the Estimation of Pore Attributes in Shale

et al. 2021

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“…Organic-hosted porosity is one of the most critical elements in successful shale plays. Different techniques viz., imaging (e.g., broad ion beam-scanning electron microscopy, and focused ion beam-scanning electron microscopy), gas adsorption (low pressure and high pressure gas adsorption techniques), mercury intrusion porosimetry, neutron scattering (e.g., ultrasmall/small angle neutron scattering), etc., are used to assess shale porosity. ,,,− In addition to several factors, such as the presence of surface functional groups, the mesopores and micropores, and the specific surface area, etc., thermal maturity levels have been identified to strongly control the development of organic porosity and, hence, the gas adsorption capacity of shales and carbonaceous matter. − Loucks et al observed organic nanopore development to be strongly dependent on the thermal maturity levels of the samples and inferred that this is essentially caused by the conversion of kerogen to hydrocarbons and the formation of pores within the organic matter in the process.…”

Section: Co2 Adsorption Versus Ch4 Desorption: Vis-à-vis Co2 Sequest...mentioning

confidence: 99%

Impact of Supercritical CO₂ on Shale Reservoirs and Its Implication for CO₂ Sequestration

et al. 2022

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Hydraulic fracturing has transformed the international energy landscape by becoming the go-to method for the exploitation of natural gas from unconventional shale reservoirs. However, in the recent years, the search for an alternative method of shale-gas exploration has intensified, because of various problems (e.g., contamination of ground and surface water, overexploitation of precious water resources, air pollution, etc.) associated with the usage of water-based fracturing techniques. The use of CO2 for shale gas exploitation has emerged as a better alternative to aqueous-based gas exploration techniques. CO2 when injected into deep shale reservoirs, transitions into supercritical CO2 (SC-CO2) when temperature and pressure condition exceeds the critical point, i.e., 31.1 °C and 7.38 MPa. In this paper, we comprehensively review the impact of SC-CO2 on shale gas reservoirs during the different stages of shale-gas exploration, i.e., (i) drilling, which involves the superiority of SC-CO2 over water-based drilling fluids, in terms of achieving under-balanced well condition, higher rates of penetration, and resistance to formation damage; (ii) fracturing, which involves factors affecting the tortuosity of fractures created by SC-CO2 fracturing, breakdown pressure, and proppant-carrying capacity; and (iii) injection, which involves the twin-headed benefit of enhanced recovery due to CO2/CH4 competitive adsorption and geological sequestration, CO2 vs CH4 excess sorption as a function of pressure, etc. Several research works have indicated discrepancies on how SC-CO2 impacts different shale properties. Some studies show low-pressure N2-gas-adsorption-derived surface area and total pore volume to be increasing with SC-CO2 imbibition, while others show a decreasing trend for the same. Similarly, for some shales, the quartz content, along with the clay mineral contents, decreased as the exposure to SC-CO2 increased, while in some other studies, with similar long-term exposure to SC-CO2, the quartz content was observed to increase along with the decrease in clay content and vice versa. Essentially, the increased exposure to SC-CO2 results in the dissolution of primary porous structures and fractures, and reformation of newer porous structure and conduits in shales. Nonetheless, these changes in the mineralogy weaken the microstructure of the rock bringing significant changes in the mechanical properties of the shales with implications on the wellbore stability and fracturing efficiency. The mechanical properties such as uniaxial compressive strength (UCS), Young’s modulus, and tensile strength decrease as the SC-CO2 saturation period increases. However, some studies have shown factors like bedding angle and phase-state of CO2 having varying effect on the strength behavior of the shales. Moreover, changes in the structure of shales caused by the creation of fractures and the reduction of their strength can also pose major risks, because of potential leakage of CO2 through these created pathways. How these processes would i...

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“…A detailed comparison of the stratigraphic succession in the Damodar and Wardha valleys has been discussed in Chandra et al Coal samples belonging to these two basins are predominantly of sub-bituminous rank, and majority of the coal volume in the Wardha valley is found up to a depth of 300 m, whereas bulk of the coal volume in the Damodar valley is found up to a depth of 600 m . Petrographic and maceral compositions of coal samples from both of these basins have been reported in detail previously. , The Chandrapur region falls close to the Majri colliery, and a detailed study of coal organic microconstituents in this region indicates significant abundance of inertinite (>50%) followed by vitrinite and exinite .…”

Section: Samples and Methodologymentioning

confidence: 99%

A Comparative Analysis of Pore Attributes of Sub-Bituminous Gondwana Coal from the Damodar and Wardha Valleys: Implication for Enhanced Coalbed Methane Recovery

Chandra

Vishal

2022

Energy Fuels

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With the increasing drive for geological CO2 sequestration, unconventional resources like shale gas and coalbed methane have gained massive popularity. With a vast resource of bituminous Gondwana coal, India has a good potential for enhanced coalbed methane recovery through CO2 sequestration. Pore attributes and their interconnectivity play a significant role in determining the gas storage capacity and ease of injection/production. In this study, samples from both opencast and underground measures were collected for a thorough comparison between coal samples of the Damodar and Wardha valleys belonging to the same Gondwana coal measure. Quantitative pore attributes determined using CO2 and N2 low-pressure gas adsorption suggests that the coal samples from Wardha are more adsorptive and thus have more gas storage capacity. The total mesopore volume in Wardha coals determined using the density functional theory model (low-pressure N2 adsorption branch) is higher with coals from opencast mines showing the highest pore volume. Two distinct Frenkel–Halsey–Hill fractal dimensions were observed in the mesopore range. Here, larger mesopores demonstrated higher fractal dimensions, indicating that surface roughness is higher for larger mesopores. The total micropore volume determined using CO2-density functional theory (DFT) (on low-pressure CO2 adsorption isotherm) is higher in the Wardha coals, showcasing a positive correlation with increasing depth and organic matter composition. The adsorption-derived pore attributes were validated using high-resolution microscopic imaging and subsequent image analysis. Elemental analysis of the isolated kerogen indicates an escalation of organic carbon with depth, whereas clay content (primarily kaolinite) shows an opposite trend. This study has elucidated the entire spectrum of micro- to mesopore attributes for these two significant coal basins, illustrating their distinguishing characteristics caused by different depositional settings and diagenesis, despite belonging to the same Gondwana measure.

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A comparison of nano-scale pore attributes of Barakar Formation gas shales from Raniganj and Wardha Basin, India using low pressure sorption and FEG-SEM analysis

Cited by 30 publications

References 62 publications

Impact of Degassing Time and Temperature on the Estimation of Pore Attributes in Shale

Impact of Degassing Time and Temperature on the Estimation of Pore Attributes in Shale

Impact of Supercritical CO₂ on Shale Reservoirs and Its Implication for CO₂ Sequestration

A Comparative Analysis of Pore Attributes of Sub-Bituminous Gondwana Coal from the Damodar and Wardha Valleys: Implication for Enhanced Coalbed Methane Recovery

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A comparison of nano-scale pore attributes of Barakar Formation gas shales from Raniganj and Wardha Basin, India using low pressure sorption and FEG-SEM analysis

Cited by 30 publications

References 62 publications

Impact of Degassing Time and Temperature on the Estimation of Pore Attributes in Shale

Impact of Degassing Time and Temperature on the Estimation of Pore Attributes in Shale

Impact of Supercritical CO2 on Shale Reservoirs and Its Implication for CO2 Sequestration

A Comparative Analysis of Pore Attributes of Sub-Bituminous Gondwana Coal from the Damodar and Wardha Valleys: Implication for Enhanced Coalbed Methane Recovery

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Impact of Supercritical CO₂ on Shale Reservoirs and Its Implication for CO₂ Sequestration