Spatial heterogeneity analyses of pore structure and mineral composition of Barnett Shale using X-ray scattering techniques

Cheng

2023

Energy Fuels

The microscopic structure of the pore system in fine-grained mudrocks provides spaces for hydrocarbon percolation, migration, and occurrence. It exhibits strong heterogeneity due to the intimate mingling of organic matter (OM) and inorganic minerals and the intricate architecture of the internal network and dynamic changes along the diagenetic pathway and OM thermal maturation. The present review critically summarizes the advances in structure characterization, geological controlling factors, and heterogeneity of the pore system in mudrocks. The pore system in mudrocks can be divided into micro-, meso-, and macropores by diameters, OM-hosted, interparticles, and intraparticle pores by origin and distribution and connected and nonconnected pores according to whether they are connected. The commonly used pore structure characterization techniques can be classified into three categories: i.e., imaging, fluid invasion, and ray-related techniques. Their principles, experimental conditions, applicability, required sample sizes, detectable pore types and diameter ranges, advantages, and disadvantages have been comparatively summarized. To obtain more precise and comprehensive structural properties, multiple techniques are highly recommended to validate and complement each other. The depositional environment, diagenetic events, and OM thermal maturation jointly control the formation and evolution of the pore system. Differences in provenance and depositional background affect primary grain assemblages and thus changes in physical properties during burial depth. Diagenetic transformations mainly change the morphology and structure of mineral-related pores, while OM thermal maturation mainly controls that of OM-hosted pores. Furthermore, the pore structure of mudrocks generally shows strong heterogeneity, which can be effectively assessed by a point-counting porosity quantification and multifractal theory. Finally, we propose the challenges and prospects of microscopic pore structure characterization of mudrocks. More attention needs to be paid to quantifying OM-hosted and mineral-related pore volume fractions, effectively distinguishing connected and nonconnected pores, and comprehensively quantifying the coupled effect of diagenesis and hydrocarbon generation on pore network evolution. In conclusion, the most important aspect of this review is to summarize modern characterization methods and geological controls on pore structure development and propose prospects for unconventional reservoir characterization, with the hope of providing the ultimate knowledge to researchers engaged in unconventional shale oil and gas resources.

Section: Pore Structure Heterogeneitymentioning

confidence: 99%

Section: Pore Structure Heterogeneitymentioning

confidence: 99%

Advances in Microscopic Pore Structure Characterization of Fine-Grained Mudrocks

Cheng

2023

Energy Fuels

“…The detectable pore diameter range is ~1 Å-6 μm, and the range of scattering vector Q is 8×10 -5 < Q < 6 A −1 . Each sampling spot was scanned by ultra-SAXS for 90 s and by (U)SAXS for 10 s with an X-ray energy of 21 keV, yielding the combined (U)SAXS data (Wang et al, 2021b). Calibration and background subtraction were needed during (U)SAXS experiments for consequent data reduction.…”

Section: (Ultra) Small Angle X-ray Scatteringmentioning

confidence: 99%

Multiple experimental studies of pore structure and mineral grain sizes of the Woodford shale in southern Oklahoma, USA

Zhao

Hu²,

et al. 2022

Front. Earth Sci.

Self Cite

Pore structure study is an important part of unconventional shale reservoir characterization, since the pore system provides the primary petroleum storage space and fluid flow pathways. Previous studies have suggested that the pore structure is related to the total organic carbon (TOC) content, mineral compositions, and the maturity of the organic matter (OM). However, few studies have focused on the mineral grains, the primary grains being deposited but before cementation, which are the building blocks of shale. Eight Woodford Shale outcrop samples from southern Oklahoma were chosen to study the effects of mineral grain size on the pore structure characterization, using multiple and complementary experimental approaches, including laser diffraction, mineralogy, TOC, pyrolysis, liquid immersion porosimetry, mercury intrusion porosimetry, gas physisorption, (ultra) small angle X-ray scattering, scanning electron microscopy, and spontaneous imbibition. The results from different experiments of eight samples show that the Woodford Shale has the mean mineral grain diameters at 3–6 μm, a wide range of porosity at 3–40% and pore diameters at 50–1,000 nm, and various pore connectivity. Grain size variation was probably caused by the sea-level fluctuation during its deposition, which affect the porosity, pore size distribution, and pore connectivity. With decreasing mineral grain sizes, the porosity tends to increase while the pore connectivity worsens. The results also indicate that OM and carbonates in this low-maturity Woodford Shale could block the pores and decrease the porosity. Coupling with the grain size analyses, the control of depositional environment on grain sizes and subsequent effects on pore structure is identified. The pore structure characteristics over a wide pore-diameter range provided by multiple experiments could improve the understanding of storage space and fluid flow in the Woodford Shale to further increase its petroleum production.

“…USAXS/SAXS/WAXS analyses were conducted at 9-ID beamline of Advanced Photo Source (APS) at Argonne National Laboratory. The detailed beamline parameters, fundamental principles, analyses procedure, and data processing follow the work of , , and Wang et al (2021b). For the C sample, a total of 37 positions were scanned (Fig.…”

Section: X-ray Scatteringmentioning

confidence: 99%

Micro- to nano-scale areal heterogeneity in pore structure and mineral compositions of a sub-decimeter-sized Eagle Ford Shale

Zhao

et al. 2022

Preprint

To improve the understanding of spatial heterogeneity in fine-grained shale, methods of microscale X-ray fluorescence (μ-XRF) mapping, (ultra-) small-angle x-ray scattering [(U)SAXS] and wide-angle X-ray scattering were used to determine elemental and pore structure variations in sizes up to ˜10 cm on two samples prepared at circular (8 cm×8 cm×0.8 mm in width×length×thickness) and rectangular (5 cm×8 cm×0.8 mm) orientations from a piece of Eagle Ford Shale outcrop in South Texas. Thin section petrography and field emission-scanning electron microscopy, X-ray diffraction (XRD), total organic carbon, and pyrolysis were also utilized to investigate the potential spatial heterogeneity of pore types, mineral and organic matter compositions for both samples. Overall, the siliceous-carbonate mineral contents in these carbonate-rich Eagle Ford Shale vary between laminations at mm scales. For the circular sample, porosity and surface area variations range from 0.82 to 3.04% and 1.51 to 14.1 m 2 /g, respectively. For the rectangular sample, values for porosity and surface area vary from 0.93 to 2.50% and 3.95 to 10.8 m 2 /g. By analyzing six selected sub-samples on each of two samples with X-ray scattering and XRD techniques, nm-sized pores are mainly interparticle ones in the higher calcite regions, where the porosity is also relatively lower, while the lower calcite regions consist of both interparticle and intraparticle pore types with higher porosity. Finally, the μ-XRF and (U)SAXS are combined to generate porosity distribution maps to provide more insights about its heterogeneity related to the laminations and fractures at our observational scales.