Acid demineralization with pyrite removal and critical point drying for kerogen microstructural analysis

Sun, Tao; Bake, Kyle D.; Craddock, Paul R.; Gunawan, Bryan; Darnell, L. M.; Bissada, K. K.; Pomerantz, Andrew E.

doi:10.1016/j.fuel.2019.05.024

Cited by 10 publications

(11 citation statements)

References 34 publications

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“…Effective isolation of kerogen from bulk mudrocks is the basis for the analysis of organic matter free of mineral contamination. The demonstrable best practice for kerogen isolation is now a conservative, closed-system chemical demineralization for chemical analyses, followed by critical point drying for surface area and pore volume. − For effective isolation, rock samples must first be crushed to powder to increase the available surface area for chemical treatments. Soluble organic phases (e.g., soluble bitumens and oils) must be extracted (dissolved) using organic solvents, prior to acid demineralization of minerals.…”

Section: Preparation Of Bulk Kerogen Isolatesmentioning

confidence: 99%

“…A typical hold time for each acid treatment is 2–6 h. At the end of the isolation procedure, the kerogen isolate is collected from the surface of the membrane filter on the reaction cell outlet. The conservative, closed-system isolation process has been repeatedly shown to yield a kerogen isolate with a recovery factor exceeding 80% and a residual mineral impurity less than 3% by mass. − Note that strong oxidizing acids, such as HNO 3 and HClO 4 , must never be used for mineral dissolution because these are shown to alter the native characteristics of the organic matter.…”

Section: Preparation Of Bulk Kerogen Isolatesmentioning

confidence: 99%

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Critical Practices for the Preparation and Analysis of Kerogen

et al. 2022

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Knowledge of the chemical and structural properties of kerogen is needed for accurate volumetric and economic appraisal of petroleum-bearing unconventional resources. Unfortunately, research concerning kerogen does not always follow demonstrated best practices for laboratory isolation and analysis. Here, we outline critical procedures for studies of bulk kerogen. Analyses of kerogen isolates require the dissolution of all nonkerogen components in the rock. Soluble hydrocarbons are removed first, using solvent extraction techniques. The mineral matrix is effectively removed using concentrated acids inside a closed-system, flow-through reaction cell. The acidization sequence includes HCl and HF for dissolution of carbonates and silicates, respectively, and acidified CrCl 2 for dissolution of pyrite. This closed-system procedure consistently achieves recovery efficiencies exceeding 80−85% and kerogen purities exceeding 95− 97%. Removal of pyrite by density-gradient centrifugation, common in traditional isolation workflows, is discouraged because of its limited efficacy. Following isolation, kerogen must be dried appropriately, using critical point drying for pore structural characterization. Oven drying should be avoided because it can collapse pores, destroying the native pore characteristics. Minimum methods for validating the purity of isolated kerogen include elemental and ash quantification by flash combustion and pyrolysis. Elemental analysis is further required for computing petrophysical properties of kerogen, guiding molecular dynamics simulations, and for correcting mineral contamination in laboratory measurements. Skeletal density is critical for organic-rich shale petrophysics and should be determined using helium pycnometry. Density-gradient centrifugation for density determinations should be avoided. Molecular structures can be assessed using several solid-state spectroscopies, including nuclear magnetic resonance (NMR), X-ray, infrared, and Raman. Using NMR as one example, it is shown how proper spectral acquisition and interpretation are both critical for quantifying basic molecular characteristics of kerogen. The practices presented here serve as a foundation for the geochemistry community for future kerogen studies.

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Section: Preparation Of Bulk Kerogen Isolatesmentioning

confidence: 99%

Section: Preparation Of Bulk Kerogen Isolatesmentioning

confidence: 99%

Critical Practices for the Preparation and Analysis of Kerogen

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“…92 Recent development of critical point drying methods to remove residual solvents without thermal evaporation now enable microstructural preservation and characterization of isolated kerogen. 92,93 Reproducible methods for the effective and non-destructive isolation of kerogen are essential for the characterization of kerogen properties free of soluble OM and inorganic minerals.…”

Section: Synthesis Sample Set and Preparationmentioning

confidence: 99%

“…Routine methods of oven-drying kerogen to remove residual liquid solvents from the isolation process can result in microstructural alteration of the kerogen, including collapse of its internal pore network . Recent development of critical point drying methods to remove residual solvents without thermal evaporation now enable microstructural preservation and characterization of isolated kerogen. , …”

Section: Synthesis Sample Set and Preparationmentioning

confidence: 99%

“…Recent advances in the isolation of kerogen combining acid demineralization and critical point drying now permit the structural preservation of kerogen in its isolated form, making it amenable to representative microstructural analysis free of the mineral matrix. , Multi-stage nitrogen absorption provides a quantitative determination of the specific surface area (area per mass, m 2 /g) of porous media and has been applied to the analysis of both bulk shale − and microstructurally preserved kerogen isolates. ,, The measurement is based on the Brunauer–Emmett–Teller (BET) theory of non-interacting multi-layer gas adsorption on solid surfaces, which measures the adsorbate quantity (in volume or mass units) as a function of the pressure . The specific surface area (SSA) is calculated from the resulting BET adsorption isotherm.…”

Section: Universal Curves Describing Evolution Of Type II Kerogen Pro...mentioning

confidence: 99%

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Universal Curves Describing the Chemical and Physical Evolution of Type II Kerogen during Thermal Maturation

et al. 2020

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This paper synthesizes and interprets literature data relating to the chemical and physical characteristics of kerogen (solid, insoluble sedimentary organic matter) representing more than a dozen petroliferous sedimentary basins across four continents, 400 million years of sedimentation, and burial histories ranging from thermally immature to overmature. The studied kerogen properties include chemical composition (elemental composition and carbon and heteroatom speciation), physical properties (skeletal density), nuclear responses (petrophysical properties), and microstructure (surface area). As occurs in the vast majority of economically significant conventional and unconventional petroliferous sedimentary basins, the kerogens are observed to be predominantly or entirely paleo-marine (derived from marine plankton and algae) and classified as so-called type II kerogen. The analysis described here reveals that that the wide range of chemical and physical properties of type II kerogen is explained nearly entirely by its extent of thermal maturation and is independent of basin location, age, and other basin-specific characteristics, such as formation lithology. The analysis results in a series of universal curves relating many type II kerogen properties to thermal maturity, with correlation coefficients typically of 0.85−0.90. The indistinguishable property−maturity relationships among type II kerogen in petroleum-bearing formations globally make it possible to infer its relevant chemical and physical characteristics only from knowledge of the thermal maturity of the organic matter. As shown by example, this presents substantial practical benefit for unconventional shale exploration and appraisal because chemical, physical, and petrophysical properties of kerogen are critical in such workflows but are nearly always unknown and otherwise impractical to measure in typical industrial projects.

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