scholarly journals Comparative Porosity and Pore Structure Assessment in Shales: Measurement Techniques, Influencing Factors and Implications for Reservoir Characterization

Energies ◽  
2019 ◽  
Vol 12 (11) ◽  
pp. 2094 ◽  
Author(s):  
Yujie Yuan ◽  
Reza Rezaee
Keyword(s):  
Pore Structure ◽  
Gas Adsorption ◽  
Measurement Techniques ◽  
Bound Water ◽  
Total Porosity ◽  
Low Pressure ◽  
Effective Porosity ◽  
Shale Formations ◽  
Helium Expansion ◽  
The Impact

Porosity and pore size distribution (PSD) are essential petrophysical parameters controlling permeability and storage capacity in shale gas reservoirs. Various techniques to assess pore structure have been introduced; nevertheless, discrepancies and inconsistencies exist between each of them. This study compares the porosity and PSD in two different shale formations, i.e., the clay-rich Permian Carynginia Formation in the Perth Basin, Western Australia, and the clay-poor Monterey Formation in San Joaquin Basin, USA. Porosity and PSD have been interpreted based on nuclear magnetic resonance (NMR), low-pressure N2 gas adsorption (LP-N2-GA), mercury intrusion capillary pressure (MICP) and helium expansion porosimetry. The results highlight NMR with the advantage of detecting the full-scaled size of pores that are not accessible by MICP, and the ineffective/closed pores occupied by clay bound water (CBW) that are not approachable by other penetration techniques (e.g., helium expansion, low-pressure gas adsorption and MICP). The NMR porosity is largely discrepant with the helium porosity and the MICP porosity in clay-rich Carynginia shales, but a high consistency is displayed in clay-poor Monterey shales, implying the impact of clay contents on the distinction of shale pore structure interpretations between different measurements. Further, the CBW, which is calculated by subtracting the measured effective porosity from total porosity, presents a good linear correlation with the clay content (R2 = 0.76), implying that our correlated equation is adaptable to estimate the CBW in shale formations with the dominant clay type of illite.

scholarly journals Influence of Low-Pressure Treatment on the Morphological and Compositional Stability of Microscopic Ettringite

Materials ◽  
2021 ◽  
Vol 14 (11) ◽  
pp. 2720
Author(s):  
Patrick A. Kißling ◽  
Franziska Lübkemann ◽  
Tabea von Bronk ◽  
Dario Cotardo ◽  
Lei Lei ◽  
...  
Keyword(s):  
Chemical Composition ◽  
Environmental Scanning Electron Microscopy ◽  
Bound Water ◽  
Low Pressure ◽  
Environmental Scanning ◽  
Pressure Treatment ◽  
X Ray Diffraction ◽  
Compositional Stability ◽  
Drying Conditions ◽  
The Impact

The impact of low-pressure treatment on the crystal structure, morphology, and chemical composition of ettringite, due to their major importance with respect to processability (i.a., drying conditions) and to the analysis of ettringite-containing samples, is examined utilizing X-ray diffraction, thermogravimetric analysis, Raman spectroscopy, and environmental scanning electron microscopy. Synthetic ettringite was treated for various durations (5 min up to 72 h) and at two different levels of low-pressure (4.0 mbar and 60 µbar). Evaluation showed a correlation between the procedural parameters (time and pressure), the chemical composition, and the morphology of ettringite. The experiments reveal that, when exposed to 4 mbar pressure, nearly no changes occur in the ettringite’s morphology, whereas the crystals undergo swelling and slight deformations at very low pressures (60 µbar and 35.3 nbar), which is attributed to the loss of bound water and the partial transformation from ettringite to quicklime, anhydrite, and calcium aluminate. Furthermore, the strongly dehydrated ettringite shows the same morphology.

scholarly journals Experimental Study on Pore Structure and Gas Desorption Characteristics of a Low Rank Coal: Impact of Moisture

2021 ◽  
Author(s):  
Ming-yi Chen ◽  
Ya-pu Yang ◽  
Xiao-yun Chen ◽  
Fu-chao Tian ◽  
Wei-li Sun ◽  
...  
Keyword(s):  
Moisture Content ◽  
Pore Structure ◽  
Gas Adsorption ◽  
Negative Impact ◽  
Low Rank ◽  
Relative Pressure ◽  
Hill Model ◽  
Pore Size Distributions ◽  
Methane Desorption ◽  
The Impact

Abstract Coal and gas outburst is one of the most serious disasters for underground coal mining. The water adsorbed on coal can leads to that the pore structure of moist coal is different from that of dry coal, thereby affecting methane desorption characteristics of coal for the outburst risk prediction. In this paper, the impact of moisture on pore structure and methane desorption performance were investigated. The analysis on low-temperature nitrogen gas adsorption tests show that the micropores (pore diameter < 10 nm) are most affected by the adsorbed water. In particular, for water-equilibrated coal sample at 98% relatively humidity, the micropores less than 4 nm analyzed by DFT pore size distributions almost disappear probably due to the blocking effect of the formed water clusters and capillary water. In this case, the micropores can still contributes most sites for gas adsorption. Furthermore, the fractal dimension at relative pressure of 0–0.5 (D1) and 0.5–1 (D2) calculated by the Frenkel-Halsey-Hill model indicates that, when moisture content is less than 4.74%, D1 decreases rapidly while D2 shows a slight change; whereas, further increases in moisture content results in that D2 decreases significantly and D1 remains at about 2.32. Further investigation shows that, below the equilibrium moisture content, the ultimate desorption volume (A) and initial desorption rate (V0) are closely related to D1, while the desorption constant (Kt) mainly depends on D2. Therefore, the adsorbed moisture has significant negative impact on methane desorption performances by affecting characteristics of coal’s pores.

Sign in / Sign up

Export Citation Format

Share Document