Argon physisorption at 87 K is the new standard for texture analysis of microporous media recommended by the International Union of Pure and Applied Chemistry (IUPAC). However, geoscientists routinely use nitrogen (77 K) and carbon dioxide (273 K), both molecules with permanent polarization and the preference to interact with specific surface sites. In this work, N2, CO2, and Ar physisorption isotherms were measured and classical physisorption theories applied to investigate the suitability of Ar physisorption for the porosity assessment of mudrocks, clays, and (non)-porous analogs.

N2 and Ar physisorption isotherms are qualitatively similar with the most significant discrepancies in the submonolayer range. Textural parameters reveal linear relations but parameter ratios vary randomly, independent of the sorbent class. While N2 and CO2 (mostly) underestimate micropore volumes, nitrogen BET areas are consistently larger than argon BET areas. Those differences are probably associated with differences in polarization. But its effect on molecular orientation, for example, is presumably masked by microporosity and a narrow spacing of specific surface sites.

Mesopore size distributions and Gurvich (total) pore volumes agree well for N2 and Ar indicating similar pore size and pore volume access. Combining both parameters proves effective in identifying saturation pressure offsets which pose the largest uncertainty factor in the present study. Ar-based micropore size distributions reveal three distinct classes of mudrocks differing in organic matter maturity, and its contribution to microporosity. Empirical αs plots corroborate this classification underlining the discrepancies in the micropore range of mudrocks. Comparative hysteresis loop analysis indicated cavitation as one dominant evaporation mechanism in mudrocks and clays effecting a sample-specific compartmentalization of their pore networks.

Conventional oil drilling fluids often fail under extreme (high-pressure high-temperature, HPHT) conditions, leading to wellbore instability and formation damage, causing substantial economic losses in the drilling industry. The objective of this study was to evaluate the performance of Claytone-ER, a novel rheological additive for oil-based drilling fluids (OBDF), compared with a conventional organoclay (OC). Claytone-ER improved the drilling fluid performance significantly, including enhancement of the emulsion stability by 3% (863 V to 891 V), mitigation of sagging behavior, and substantial improvement in key rheological parameters such as plastic viscosity (PV) by 26.5%, yield point (YP) by 98%, and apparent viscosity (AV) by 36.5%. Additionally, Claytone-ER enhanced gel strength (GS) and improved filtration properties, reducing filtrate volume by 8% (5.0 cm3 to 4.6 cm3) and filter cake thickness by 6% (2.60 mm to 2.45 mm). These results demonstrated the potential of Claytone-ER to enhance the stability and performance of OBDFs under extreme HPHT conditions, leading to improved drilling efficiency, reduced non-productive time, and cost savings for drilling operations. Furthermore, the enhanced rheological properties, sag resistance, and filtration control contribute to better wellbore stability and minimize the risk of formation damage, ensuring long-term well productivity. This study represents a significant advancement in drilling fluid technology, paving the way for safer and more efficient drilling operations in challenging HPHT environments. Future research will focus on field trials to validate the efficacy of Claytone-ER in real-world HPHT drilling scenarios.

This study focused on a detailed mineralogical and crystal-chemical analysis of Mg-smectites from four bentonite samples from Turkey. Mg-rich smectites, mainly associated with alkaline and evaporitic depositional conditions, are formed in environments such as salt lakes, brine springs, and sabkhas, as well as in hydrothermal systems, in some cases by transformation from other phyllosilicates. Saponite has also been documented on the surface of Mars. The systems that produce Mg-smectites are less common than those that produce dioctahedral Al-smectites and consequently Mg-rich smectites are less abundant than dioctahedral smectites. For this reason, information on nanoscale mineralogy and crystal chemistry of Mg-smectites is relatively lacking. In this study, X-ray diffraction, thermal analysis and electron microscopy were used to study Mg-smectites. The crystal chemistry of single crystals determined with analytical electron microscopy in transmission electron microscopy (AEM-TEM) revealed that all samples had notable variability in the composition of individual crystals, such that no point analysis resulted in ideal structural formulae for saponite, stevensite, sepiolite, or palygorskite. They contain SiO2 content greater than that corresponding to a Mg-smectite, even stevensite, and often are intermediate to Mg-smectites and the sepiolite-palygorskite series. Meanwhile, the number of octahedral cations is small for fibrous clay minerals. Neither the point analysis of smectitic particles nor the mean structural formula fit properly for Mg-smectites showing crystallochemistry complexity. The results of these point analyses, in which no contamination has been observed, suggest that these smectites have intermediate compositions between trioctahedral smectites and sepiolite-palygorskite, indicating nanometer-scale intergrowths of these minerals in Mg-rich clay deposits.

Thermally activated palygorskite and sepiolite clays are commonly used for the bleaching of edible oils and fats. However, their bleaching capacity can vary depending on physicochemical clay characteristics. The present study focused on the impact of thermally treated palygorskite and palygorskite-smectite clays on bleaching performance and showed a correlation between bleaching performance and the physicochemical characteristics of the clays. The mineralogical and chemical composition, along with certain physicochemical characteristics of thermally treated (heated at 300°C) palygorskite and palygorskite-smectite clays, were assessed for their effect on bleaching performance. The samples were collected from exploratory boreholes from four currently exploited clay deposits, namely Knidi, Pilori, Harami, and Velanida of the Upper Pliocene-Lower Pleistocene Ventzia Basin, west Macedonia, Greece. Palygorskite was formed diagenetically from smectite precursors of lateritic origin and deposited in a fluvial-palustrine environment. Clay minerals were characterized by X-ray diffraction (XRD), near-infrared spectroscopy (NIR), inductively coupled plasma optical emission spectrometry (ICP-OES) analysis, and gas porosimetry. The bleaching ability of the samples was evaluated by measuring the absorption of visible light through standard bleached rapeseed oil. Results revealed that the bleaching performance was superior in mixed palygorskite-smectite clays and was directly proportional to the palygorskite content and to both the apparent bulk density and external surface area of the clays. By contrast, bleaching ability was inversely proportional to the amount of non-clay minerals, but independent of the small variance in Al, Fe, and Mg contents of the clays or the octahedral composition of palygorskite. The presence of smectite in smaller amounts promoted to a small extent the efficiency of the palygorskite-rich clays from the Ventzia Basin.