Porosity Loss Research Articles

Hydrogen Evolution Reaction by Atomic Layer-Deposited MoNx on Porous Carbon Substrates: The Effects of Porosity and Annealing on Catalyst Activity and Stability.

Molybdenum-based compounds are considered as a potential replacement for expensive precious-metal electrocatalysts for the hydrogen evolution reaction (HER) in acid electrolytes. However, coating of thin films of molybdenum nitride or carbide on a large-area self-standing substrate with high precision is still challenging. Here, MoNx is uniformly coated on carbon cloth (CC) and nitrogen-doped carbon (NC)-modified CC (NCCC) substrates by atomic layer deposition (ALD). The as-deposited film has a nanocrystalline character close to amorphous and a composition of approximately Mo2 N with significant oxygen contamination, mainly at the surface. Among the as-prepared ALD-MoNx electrodes, the MoNx /NCCC has the highest HER activity (overpotential η≈236 mV to achieve 10 mA cm-2 ) owing to the high surface area and porosity of the NCCC substrate. However, the durability of the electrode is poor, owing to the poor adhesion of NC powder on CC. Annealing MoNx /NCCC in H2 atmosphere at 400 °C improves both the activity and durability of the electrode without significant change in the phase or porosity. Annealing at an elevated temperature of 600 °C results in formation of a Mo2 C phase that further enhances the activity (η≈196 mV to achieve 10 mA cm-2 ), although there is a huge reduction in the porosity of the electrode as a consequence of the annealing. The structure of the electrode is also systematically investigated by electrochemical impedance spectroscopy (EIS). A deviation in the conventional Warburg impedance is observed in EIS of the NCCC-based electrode and is ascribed to the change in the H+ ion diffusion characteristics, owing to the geometry of the pores. The change in porous nature with annealing and the loss in porosity are reflected in the EIS of H+ ion diffusion observed at high-frequency. The current work establishes a better understanding of the importance of various parameters for a highly active HER electrode and will help the development of a commercial electrode for HER using the ALD technique.

Compaction, rock physics and rock properties of sandstones of the Stø Formation: Case study of five wells from the south-western Barents Sea, Norway

Five wells containing Lower-Middle Jurassic sandstones of Stø Formation from the Hammerfest Basin (7120/9–1, 7121/7–1), the Ringvassøy-Loppa Fault Complex (7119/12–1, 7119/12–4) and the Troms-Finnmark Fault Complex (7019/1-1) in the Barents Sea area are considered in this study. The Stø Formation sandstones contain dominantly very fine-to medium-grained quartz arenites with occasional coarse-grained sandstone layers. Feldspathic and quartz wackes are also present. The effect of compaction and exhumation on reservoir properties (porosity and permeability) and seismic property (P-wave velocity) of these sandstones have been investigated. Source of quartz cement has also been investigated. Forty polished thin sections embedded in blue epoxy were studied using optical microscopy, scanning electron microscopy and cathodoluminiscence. Bulk mineralogy was also analysed using X-ray diffraction.The studied sandstones have experienced Cenozoic exhumation ranging between 820 and 1050 m. P-wave velocity is higher; porosities and permeabilities are lower in the western wells (7019/1-1, 7119/12–1 and 7119/12–4) compared to the eastern wells (7120/9–1 and 7121/7–1). Rock physics models and diagnostics show that the western wells are diagenetically more mature, stiffer, more compacted and more cemented than the eastern wells. These trends are attributed largely to difference in burial history from the east to the west and less to textural variations. Quartz cement is the most important authigenic mineral in these sandstones. Quartz cement in the western well (7119/12–1) is predominantly derived from clay-induced dissolution at macrostylolites whereas the eastern wells (7120/9–1 and 7121/7–1) are mostly sourced from clay-induced dissolution at grain contacts or microstylolites. While cementational porosity loss dominates in the western wells, compactional porosity loss dominates in the eastern wells. Compaction can reduce porosities down to 26% and this might be the reason for better porosity preservation and reservoir quality in the eastern wells than in the western wells.

What is diatomite?

AbstractDifferent types of biogenic remains, ranging from siliceous algae to carbonate precipitates, accumulate in the sediments of lakes and other aquatic ecosystems. Unicellular algae called diatoms, which form a siliceous test or frustule, are an ecologically and biogeochemically important group of organisms in aquatic environments and are often preserved in lake or marine sediments. When diatoms accumulate in large numbers in sediments, the fossilized remains can form diatomite. In sedimentological literature, “diatomite” is defined as a friable, light-coloured, sedimentary rock with a diatom content of at least 50%, however, in the Quaternary science literature diatomite is commonly used as a description of a sediment type that contains a “large” quantity of diatom frustules without a precise description of diatom abundance. Here we pose the question: What is diatomite? What quantity of diatoms define a sediment as diatomite? Is it an uncompacted sediment or a compacted sediment? We provide a short overview of prior practices and suggest that sediment with more than 50% of sediment weight comprised of diatom SiO2 and having high (>70%) porosity is diatomaceous ooze if unconsolidated and diatomite if consolidated. Greater burial depth and higher temperatures result in porosity loss and recrystallization into porcelanite, chert, and pure quartz.

Displacement-dependent microstructural and petrophysical properties of deformation bands and gouges in poorly lithified sandstone deformed at shallow burial depth (Crotone Basin, Italy)

We present the results of meso-and micro-structural analyses performed on fault-related soft-sediment deformation structures affecting poorly lithified, high-porosity siliciclastic sediments in the Crotone Basin, Southern Italy. The investigated extensional fault zone has a total displacement of ~90 m and juxtaposes marine clayish sediments in the hanging wall against arkosic to lithic arkosic sandstone in the footwall. In the footwall damage zone, deformation is achieved by a network of conjugate deformation bands, whereas the foliated fault core hosts cm-thick gouges. Deformation bands and black gouges accommodated displacement between 0.2 and 20 cm. Microstructural observations and quantitative image analysis pointed out that particulate flow operated during the early stages of faulting, followed by cataclasis after significant porosity loss. Mineralogy of clasts controlled grain-scale deformation mechanism: following this, feldspar experienced extensive intragranular crushing, while quartz grains were deformed mainly by splitting and abrasion. Permeability of pristine sandstone spans from 5.4 × 104 to 1.4 × 105 mD, while inside deformation bands is reduced by 1-2 orders of magnitude, reaching 3-4 orders of magnitude within fault gouges. Permeability drop inside the fault zone is related to the accommodated displacement along each deformation structure, potentially leading to hydraulic compartmentalization of high-porosity sandstone reservoir.

CO2‐Induced Spin‐State Switching at Room Temperature in a Monomeric Cobalt(II) Complex with the Porous Nature

AbstractCO2‐responsive spin‐state conversion between high‐spin (HS) and low‐spin (LS) states at room temperature was achieved in a monomeric cobalt(II) complex. A neutral cobalt(II) complex, [CoII(COO‐terpy)2]⋅4 H2O (1⋅4 H2O), stably formed cavities generated via π–π stacking motifs and hydrogen bond networks, resulting in the accommodation of four water molecules. Crystalline 1⋅4 H2O transformed to solvent‐free 1 without loss of porosity by heating to 420 K. Compound 1 exhibited a selective CO2 adsorption via a gate‐open type of the structural modification. Furthermore, the HS/LS transition temperature (T1/2) was able to be tuned by the CO2 pressure over a wide temperature range. Unlike 1 exhibits the HS state at 290 K, the CO2‐accomodated form 1⊃CO2 (P =110 kPa) was stabilized in the LS state at 290 K, probably caused by a chemical pressure effect by CO2 accommodation, which provides reversible spin‐state conversion by introducing/evacuating CO2 gas into/from 1.

Diagenetic evolution and its impact on reservoir quality of tight sandstones: A case study of the Triassic Chang 6 Member, Ordos Basin, northwest China

The Triassic Chang 6 Member sandstones are important oil reservoirs in the Ordos Basin of north-western China, and are actually considered to be typical tight sandstone reservoirs. Diagenetic alterations play a prominent role in considerably impacting the reservoir quality. In this study, an integrated approach of: thin sections, scanning electron microscopy (SEM), X-ray diffraction (XRD), cathodoluminescence (CL), fluid inclusions, laser Raman spectrographic analysis, and stable isotope analysis was applied to examine the diagenetic history recorded in the Chang 6 tight sandstones and investigate the influences of diagenesis on reservoir quality. The sandstones consist of fine-grained, moderated-to-well sorted arkoses (Q48.5F40.9R10.6) and lithic arkoses (Q54.3F29.1R16.6) with an average porosity and permeability of 9.10% and 0.39 mD, respectively. The sandstones have undergone complex diagenetic processes; dominant eogenetic features include: (ⅰ) mechanical compaction, (ⅱ) leaching of feldspar in meteoric water, (ⅲ) chlorite coats originating from the transformation of precursor clays and precipitating directly from interstitial water, (ⅳ) calcites filling intergranular pores as poikilotopic cements, and (ⅴ) quartz and albite overgrowths on surfaces of grains. Subsequent mesogenetic events include: (ⅰ) ankerite cements filling porosity and replacing framework grains, (ⅱ) extensive dissolution of feldspars and precipitation of kaolinites due to emplacement of organic acids, and (ⅲ) secondary quartz overgrowths in the late period of mesogenesis. Early calcite is characterized by 13C (δ13CPDB ranging from −3.45‰ to −0.30‰, mean = −2.00‰) and 18O (δ18OPDB varying from −16.70‰ to −5.80‰, mean = −10.50‰), while late ankerite is rich in 12C (δ13CPDB ranging from −10.71‰ to 0.80‰, mean = −3.58‰) and 16O (δ18OPDB varying from −24.30‰ to −15.80‰, mean = −19.93‰). Moreover, calcite hosts single liquid fluid inclusions, two-phase fluid inclusions are contained in ankerite cements (with mean homogenization temperature (Th) of 96.0 °C and salinity estimates from 11.47 to 18.96 eq. wt.% NaCl). These data indicate that the calcite originated from meteoric water and the ankerite was associated with organic matter and recrystallization of the early calcite cements. Furthermore, the metallic ions such as Fe2+, Mg2+, and Ca2+ required for ankerite precipitation were produced through alterations of volcanic fragments, feldspars, and biotites. In comparison, compaction has more important role than cementation in the loss of original porosity although cementation exerts enormous influence on reducing porosity. Quantitatively, the compactional porosity loss reaches 54.9%, while the cementation porosity loss accounts for up to 42.8%. Carbonate cements and the other authigenic products (quartz and albite overgrowth, and kaolinite) mostly fill intergranular pores, thus reduce porosity. Chlorite coats have effects in inhibiting compaction and restraining the development of quartz overgrowth, thereby protect the intergranular porosity to some extent. Early secondary porosity was enhanced by leaching and dissolution of feldspar in the eogenetic period. However, these processes did not increase the net porosity in the mesogenetic stage.

Influence of tectonic exhumation on porosity of Wufeng–Longmaxi shale in the Fuling gas field of the eastern Sichuan Basin, China

Thermal cracking of organic matter (OM) can enhance gas-shale porosity. However, thermally matured shales are generally characterized by low porosity with high OM content in tectonic exhumation settings. The Wufeng–Longmaxi shale in the Fuling gas field, China, was investigated via bulk analysis and scanning electron microscopy to reveal the influence of tectonic exhumation on the porosity of OM-rich shale. Thermal maturity and organic and mineralogical compositions are regionally homogeneous in the Fuling gas field. Shale porosity is positively correlated with total organic carbon (TOC) and clay mineral content in the gentle and open anticlines, respectively. The OM-hosted pores were preserved with spherical morphologies because of overpressure-associated overburden stress unloading in the gentle anticlines, whereas OM-hosted pores in the open anticlines are characterized by high aspect ratios and are regularly aligned perpendicular to lateral compression stress. A simple simulation confirmed that tectonic folding and compaction during exhumation caused the loss of porosity in the inner arcs of the open anticlines. Only pressure shadows formed by assemblages of clay mineral platelets and mechanically competent grains inhibited tectonic compaction of some OM-hosted pores in the open anticlines. Tectonic compaction of porosity generally increased the mean value of water saturation in the open anticlines. The extremely high water saturation (>60%) in the high-TOC interval (>2 wt. %) was generally associated with natural fractures, suggesting the occurrence of gas leakage.

Controls on Reservoirs Quality of the Upper Jurassic Mengyin Formation Sandstones in Dongying Depression, Bohai Bay Basin, Eastern China

The Upper Jurassic Mengyin Formation sandstones are important targets for petroleum exploration in Dongying Depression of Bohai Bay Basin, Eastern China. Although the current burial depth of the Upper Jurassic Mengyin Formation sandstones is shallow (900–2500 m), the reservoir rocks are characterized by low porosity and low permeability due to the complex diagenetic modifications after deposition. Experimental tests and statistical methods, such as thin section, scanning electron microscopy (SEM), cathodoluminescence (CL), high pressure mercury injection (HPMI) and fluid inclusion analysis are conducted to delineate the mineralogical, petrographic and petro-physical characteristics. Results show that physical and chemical processes, including burial depth, burial and thermal history and pore fluid evolution, are both important for the diagenetic modifications that result in a variety changes in pore system and reservoir quality. According to numerical simulation of porosity evolution during lengthy burial and thermal history, porosity loss due to the early deep burial process under the high paleo-geothermal gradient can reach about 20%. Moreover, the burial history (effective stress and temperature) has a better guidance to reservoir quality prediction compared with current burial depth. The extensive compaction in sandstones also resulted in extremely low pore fluid flow during subsequent diagenetic processes, thus, the reaction products of dissolution cannot be removed, which would be precipitated as carbonate cements during stable reburial phase. Dissolution resulted from uncomformity-related meteoric flushing have been the most important porosity-enhancing factor in Mengyin Formation sandstones in spite of low thin section porosity averaged out to 3.22%. Secondary pores derived from dissolution of unstable silicates are more likely to develop in sandstones near the regional unconformity. The oil source fault activities may enhance the heterogeneity of reservoir rocks and control the reservoir quality by inducing micro-fractures and providing the main pathways for hydrocarbon migration.

Diagenetic characteristics and quantitative evolution of porosity in tight gas sandstone reservoirs: A case study from the middle and lower Permian in the northwestern Ordos Basin, China

Tight sandstone gas is widespread in the middle and lower Permian Shan 1 and He 8 Members in the northwestern Ordos Basin. We have studied the diagenesis by means of many petrographic techniques and determined its important influence on reservoir quality. The quantitative characterization of porosity evolution is important when analyzing reservoir consolidation. We found that reservoir rock types are mainly sublitharenite, quartz arenite, and litharenite in the deltaic facies through petrological and mineralogical analyses. Metamorphic rock (quartzite), followed by volcanic rock, dominates the lithic fragment types. In the early diagenetic stage, the reservoirs mainly underwent intensive compaction, hydrolysis, and alteration of volcanic debris. Sandstones in the middle diagenesis stage were characterized by quartz overgrowth, volcanic debris dissolution, cementation, and calcite and kaolinite replacement. Based on the formula from Beard and Weyl, we calculated that the original porosity of tight gas sandstones was 38.61%. The porosity loss during compaction was 26.64%; by cementation, it was 11.46%; and carbonate, siliceous, and authigenic clay cements accounted for 1.31%, 3.61%, and 6.44% loss in porosity, respectively. Dissolution was relatively weak, with an average increase in porosity of 4.86%, whereas the present porosity is 7.47%. We observed that the pore types in the study area are composed of intragranular dissolution pores and kaolinite intercrystalline pores, followed by residual primary pores and intergranular dissolution pores. However, microcracks were not common. Based on the results of the rate-controlled mercury intrusion, the pore diameters in different samples are similar but there were clear differences in the throat diameters. Nuclear magnetic resonance results indicate that the cutoff value is 13 ms with the movable fluid mainly distributed in larger pores. As the pressure increased, fluid in the larger pores was discharged in large quantities but there was no discharge of nonmovable fluid in the small pores. We conclude that intensive diagenetic transformation was the main cause of reservoir consolidation and multistage cementation resulted in a complicated pore-throat network and reduced reservoir permeability.

New approach for the assessment of the contribution of adsorption, biodegradation and self-bioregeneration in the dynamic process of biologically active carbon functioning

This work developed an effective model of the cooperative removal process of organic compounds on biologically active carbon. This model involves the determination of the dynamics of adsorption efficiency and degradation of specific classes of target organic substances but also the dynamics of non-target filling of pores with products of vital microbial activity. It is possible to quantitatively assess the contributions of adsorption, biodegradation and self-bioregeneration in the process of biologically active carbon functioning and the changes in the activated carbon porous properties during the process.The model developed was applied to assess the efficiency of filtration of 2-nitrophenol through a biologically active carbon bed for 38 months. The activated carbon adsorption capacity for removing 2-nitrophenol was preserved after three years of the bed service due to the effective biodegradation that resulted in self-bioregeneration of the sorbent. Nontarget losses of porosity (filling with bioproducts) increased with increasing duration of system operation, and by the end of the experiment, these losses amounted to 61% of the pore volume of the fresh sorbent.

Thermal Ageing Effects in a Commercial Three-Way Catalyst: Physical Characterization of Washcoat and Active Metal Evolution

The main system to reduce engine emissions of gasoline-fueled vehicles is represented by the three-way catalyst (TWC). The main catalyst of this system usually works in extreme conditions which induce a phenomenon called thermal ageing, the major way of catalyst deactivation. Increasingly stringent emissions standards require not only high efficiency in emissions abatement, but also maintaining the performances at high vehicle mileage. Automotive manufacturers need to accelerate testing methods and that should be representative of the ageing on vehicle, at the minimum expense in terms or time and cost. In order to develop and validate such methods, a deep understanding of all the microscopic processes associated with ageing is necessary. In this work we discuss a methodology for the study of the static thermal ageing of a commercial TWC. A specific washcoat extraction method was developed, and the separated washcoat was analyzed using XRD, TEM microscopy, Raman Spectroscopy and BET. These techniques allow to follow the main morphological and chemical changes in the sample: the loss of porosity, the evolution of crystalline phases and metal particles sintering and oxidation. The potential of Raman spectroscopy for the spatially resolved analysis of ageing is also highlighted. The results allowed to understand the process that involve the washcoat at high temperature.

Deformation of Granular Aggregates: Static and Dynamic Bulk Moduli

AbstractSand and glass bead samples were monotonically loaded from 0 to 50 MPa and then monotonically unloaded, all under hydrostatic stress conditions. Sand deformed irreversibly and its porosity loss was permanent. In contrast, the glass bead deformation was almost fully reversible with the initial porosity recovered. During loading, the static bulk modulus in all sand samples increased from 0 to about 0.5 GPa between 0‐ and 15‐MPa stress and remained constant for the remainder of the loading. Such behavior, somewhat unexpected in a granular system, means that sand deforms as a linear elastic body during loading from 15 to 50 MPa. The unloading behavior was very different—the static bulk modulus almost linearly decreased from about 4 GPa at 50 MPa to zero as the stress was reduced. Once again, this behavior was very different from that observed in glass beads, where the static bulk modulus during loading was essentially the same as during unloading and appeared to be a unique function of stress, independent of the direction of its variation. Moreover, the static and dynamic bulk moduli in glass beads, the latter computed from Vp, Vs, and density measured during the loading/unloading cycle, were very close to each other. In contrast, the dynamic bulk modulus in dry sand exceeded the static modulus during unloading by a factor of 1.5 to 2.0. We used a quantitative theory based on contact mechanics and the concept of stress heterogeneity in particulates to analytically match the observed results.

Sustainable use of paper sludge from the Colombian paper industry

The paper industry is an important component in the Colombian economy, the need for the continuous use of paper and cardboard in different activities results in the generation of paper sludge, for this reason there is an imminent need to generate alternatives for the use of these industrial wastes. which have been on the rise in recent years. This study is divided into two stages, the first is the evaluation through experimental analysis of the demonstration of the effectiveness of paper mud as an important source of carbon in composting processes, the second is the life cycle analysis (LCA) of the Alternative replacement of Composting vs. Synthetic Fertilizers. The product obtained from the evaluation corresponds to a stabilized compost with chicken manure, which is an important source of Carbon, Nitrogen and Calcium Carbonate, resulting in an environmentally sustainable alternative compared to the use of synthetic fertilizers. In the future, an increase in the use of fertilizers is expected, due to the growth of the world population, which generates an expansion of food production and an imminent need to attend to it. The ALC provides a better understanding of the process and its environmental impacts, the results will allow us to conclude on the most appropriate management option by showing the advantages and disadvantages associated with the use of compost. Organic fertilizers, unlike synthetic fertilizers, improve the fertility, texture and structure of the soil in the long term, promoting good drainage, aeration, water retention and root penetration, in addition to contributing to the stabilization of pH in acidic soils. The main challenges in integrating composting from paper sludge and chicken manure is to balance the C / N ratio, making a balance of the nutrient mixture and thus improving composting times, the loss of humidity, temperature gain, microbiological control and porosity.

Comparative evaluation of physical properties of commercially available silicone-based soft denture liners and acrylic-based soft denture liners

Elastic materials used in dental prosthetics to line removable dentures should be characterized by biocompatibility toward oral tissues, shape, and color stability; resistance to abrasion; and durability of the junction between the lining and the denture. The resilient lining materials present problems during clinical use, such as weakening of bond between lining and denture loss of resiliency, color alterations, and porosity. This review was aimed to compare and evaluate the physical properties of soft denture liners acrylic and silicone based and to determine which denture liners would be best suited for clinical usage. A review protocol was structured on the basis of the guidelines proposed by the PRISMA statement and Centre for Reviews and Dissemination. Overall, the results indicated that silicone-based soft denture liners performed significantly better than acrylic-based soft denture liners when compared for color stability, surface hardness, tensile bond strength, water sorption, and solubility, concluding that silicone-based soft liners would be better for long-term clinical use.

Petrophysical Signatures and Water-Reservoir Potential of Southern Apennines Turbiditic Sandstones Suites

After the seismic event of Irpinia (Southern Apennines), occurred on November 23rd 1980, the Pavoncelli tunnel, that used to supply with water the Puglia Region, was seriously damaged. Because of the strategic importance of this civil engineering work, a new water tunnel named Pavoncelli-bis that should substitute the previous one, was built and finally tested during the end of the 2019. The geological features of the area, highlighted the presence of three main siliciclastic formations (Corleto, pre-Numidian/Numidian and Castelvetere formations), crossed by the tunnel trace, that were petrophysically analyzed through the mercury injection porosimetry for a better definition of their petrophysical signatures and related water-reservoir potential at regional scale as hydrocarbon-reservoir potential. Data highlighted the presence of two clusters: one represented by the Corleto and Pre-Numidian Fms. showing good permeability (respectively 181.70 mD and 122.25 mD in median) and low porosity (respectively 4.56 % and 3.94 % in median); the other, represented by the Castelvetere Fm. highlighting good porosity (9.58 % in median) and a very low permeability (4.84 mD in median). Permeability, more than porosity, affects the cluster differentiation, whereas the other variables (average pore diameter and nanopores volume) do not show any particular trend. All these petrophysical parameters were compared with the sandstone composition (Qm, F, Lt), highlighting that porosity results negatively correlated to monocrystalline quartz (Qm) and positively correlated with feldspars (F). The lithic fragments values (Lt) are sparse and do not show any specific trend. The variability of porosity is directly linked with the diagenetic processes that interested the clusters of the Corleto and pre-Numidian Fms. (rich of Qm) and the Castelvetere Fm. (rich of F). Particularly, where quartz is more abundant, quartz cementation and overgrowth are more efficient and widespread, resulting in a reduction of the porosity. On the contrary, where feldspars are abundant, during diagenesis their dissolution can create new pore spaces and also clay-minerals with a better porosity than the previous feldspars. Moreover, clay-minerals can coat the quartz grains present in the sandstones inhibit the porosity loss of the quartz cementation and overgrowth. However, despite an increase in porosity, permeability decreases because the authigenic clays is mainly formed by isolated and blind pores.

Chemical and textural relations of britholite- and apatite-group minerals from hydrothermal REE mineralization at the Rodeo de los Molles deposit, Central Argentina

AbstractBritholite group minerals (REE,Ca)5[(Si,P)O4]3(OH,F) are widespread rare-earth minerals in alkaline rocks and their associated metasomatic zones, where they usually are minor accessory phases. An exception is the REE deposit Rodeo de los Molles, Central Argentina, where fluorbritholite-(Ce) (FBri) is the main carrier of REE and is closely intergrown with fluorapatite (FAp). These minerals reach an abundance of locally up to 75 modal% (FBri) and 20 modal% (FAp) in the vein mineralizations. The Rodeo de los Molles deposit is hosted by a fenitized monzogranite of the Middle Devonian Las Chacras-Potrerillos batholith. The REE mineralization consists of fluorbritholite-(Ce), britholite-(Ce), fluorapatite, allanite-(Ce), and REE fluorcarbonates, and is associated with hydrothermal fluorite, quartz, albite, zircon, and titanite. The REE assemblage takes two forms: irregular patchy shaped REE-rich composites and discrete cross-cutting veins. The irregular composites are more common, but here fluorbritholite-(Ce) is mostly replaced by REE carbonates. The vein mineralization has more abundant and better-preserved britholite phases.The majority of britholite grains at Rodeo de los Molles are hydrothermally altered, and alteration is strongly enhanced by metamictization, which is indicated by darkening of the mineral, loss of birefringence, porosity, and volume changes leading to polygonal cracks in and around altered grains. A detailed electron microprobe study of apatite-britholite minerals from Rodeo de los Molles revealed compositional variations in fluorapatite and fluorbritholite-(Ce) consistent with the coupled substitution of REE3+ + Si4+ = Ca2+ + P5+ and a compositional gap of ~4 apfu between the two phases, which we interpret as a miscibility gap. Micrometer-scale intergrowths of fluorapatite in fluorbritholite-(Ce) minerals and vice versa are chemically characterized here for the first time and interpreted as exsolution textures that formed during cooling below the proposed solvus.

The Influence of Magmatic Intrusions on Diagenetic Processes and Stress Accumulation

Diagenetic changes in sedimentary basins may alter hydrocarbon reservoir quality with respect to porosity and permeability. Basins with magmatic intrusions have specific thermal histories that at time of emplacement and in the aftermath have the ability to enhance diagenetic processes. Through diagenesis the thermal conductivity of rocks may change significantly, and the transformations are able to create hydrocarbon traps. The present numerical study quantified the effect of magmatic intrusions on the transitions of opal A to opal CT to quartz, smectite to illite and quartz diagenesis. We also studied how these chemical alterations and the sills themselves have affected the way the subsurface responds to stresses. The modeling shows that the area in the vicinity of magmatic sills has enhanced porosity loss caused by diagenesis compared to remote areas not intruded. Particularly areas located between clusters of sills are prone to increased diagenetic changes. Furthermore, areas influenced by diagenesis have, due to altered physical properties, increased stress accumulations, which might lead to opening of fractures and activation/reactivation of faults, thus influencing the permeability and possible hydrocarbon migration in the subsurface. This study emphasizes the influence magmatic intrusions may have on the reservoir quality and illustrates how magmatic intrusions and diagenetic changes and their thermal and stress consequences can be included in basin models.

Detrimental effects of SO2 on gaseous mercury(II) adsorption and retention by CaO-based sorbent traps: Competition and heterogeneous reduction

Reliable gaseous Hg(II) measurement is crucial to mercury emissions control from coal-fired flue gas, but Hg(II) sampling under SO2 condition could probably increase the uncertainty of sorbent traps. CaO-AcS synthesized from calcium acetate and porous support were previously demonstrated to be effective for Hg(II) trapping under SO2-free condition. This work further evaluated SO2 influence on its Hg(II) retention ability via integrating experimental and DFT computational studies. Increased breakthrough rate of HgCl2 was found in a two-section CaO-AcS trap under SO2 conditions. Significant basicity and porosity loss of CaO-AcS were attributed to the formation of agglomerate CaSO3. Hg0 release from CaO-AcS samples suggested potential reactions between Hg(II) and SO2. The detected HgO and Hg2SO4 species by Hg-TPD in CaO-AcS further confirmed this speculation. Moreover, both competition and reduction effects of SO2 on surface-bound Hg(II) species were substantiated by DFT calculations. SO2 showed a stronger interaction with CaO than HgCl2 because SO2 has a lower LUMO level and can accept electrons easier. Reaction pathways indicated Hg(II) was partially reduced to Hg2SO4 under SO2-deficient condition, or directly reduced to Hg0 under SO2-rich condition. This work fully proposed the SO2 influence mechanisms and improvement countermeasures for practical gaseous Hg(II) sampling.

Thermal-hydro-chemical-mechanical alteration of coal pores in underground coal gasification

Underground coal gasification (UCG) is being considered an economically and environmentally sustainable clean coal technology which converts coal in-situ into combustible gases. It involves a number of complex physiochemical processes, e.g., drying and evaporation, thermal expansion, pyrolysis, compressional shrinkage, gasification and combustion. As a result, coal pores constantly undergo drastic changes in the course of UCG. This work aims to shed light upon the complex changes of coal structure in the context of UCG through modelling. A 3-D UCG model was constructed using very fine grids, and several important indicators regarding pore variations were studied, i.e., weight loss of coal, solid concentrations, porosity and permeability. The modelling results were comprehensively compared with experimental data, and a good agreement in trend was achieved. It shows that coal pores alteration is associated with the various phenomena occurred in UCG, and four distinct characteristics can be categorized in the indicator curves. Furthermore, coal pores variation with respect to coal gasification and combustion, not covered in the experimental works, was also revealed. The findings would serve as a helpful guide for process design and optimization.

Diagenetic Processes and Reservoir Heterogeneity in Salt-Encased Microbial Carbonate Reservoirs (Late Neoproterozoic, Oman)

A common problem in dolomite reservoirs is the heterogeneous distribution of porosity-reducing diagenetic phases. The intrasalt carbonates of the Ediacaran-Early Cambrian Ara Group in the South Oman Salt Basin represent a self-sourcing petroleum system. Depositional facies and carbonate/evaporite platform architecture are well understood, but original reservoir properties have been modified by diagenesis. Some of the carbonate reservoirs failed to produce hydrocarbons at acceptable rates, which triggered this study. The extent of primary porosity reduction by diagenetic phases was quantified using point counting. To visualize the distribution of diagenetic phases on a field scale, we constructed 2D interpolation diagenesis maps to identify patterns in cementation. The relative timing of diagenetic events was constrained based on thin-section observations and stable isotope analyses. Near-surface diagenesis is dominated by reflux-related processes, leading to porosity inversion in initial highly porous facies and a patchy distribution of early cements. This strong diagenetic overprint of primary and early diagenetic porosity by reflux-related cements leads to a reduction of stratigraphic and facies control on porosity. Calcite was identified as a burial-related cement phase that leads to an almost complete loss of intercrystalline porosity and permeability. Bitumen is an important pore-occluding phase and time marker of the deep-burial realm. The stratigraphic position of the dolomite reservoirs embedded at the base of a salt diapir had a strong impact on its diagenetic development. The salt isolated the dolomites from external fluids, leading to a closed system diagenesis and the buildup of near lithostatic fluid pressures. In combination, these processes decreased the impact of further burial diagenetic processes. The study highlights that cement distribution in salt-encased carbonate reservoirs is mainly related to early diagenetic processes but can be very heterogeneous on a field scale. Further work is needed to implement these heterogeneities in an integrated numerical reservoir model.