Thermal Alteration Research Articles

Crust occurrence on a Galatian rock‐cut dwelling in central Anatolia, Turkey

AbstractMahkemağcin Underground City (MUC) is a four‐floored rock‐cut dwelling complex carved into ignimbrite tuffs of the Early‐Middle Miocene age in central Anatolia. The whole interior of the complex is covered by a 1–5 cm thick alteration crust that is not detected in any cave or outcrop in the region. This crust is investigated using microscopy, scanning electron microscopy, X‐ray diffraction and X‐ray fluorescence analyses, and the results are discussed from the geomechanical point of view. The colour of the outer surface of the crust is black, which turns red inside and grades into pale yellow above the white parent rock. The compaction and solidity of the crust are relatively high, as much as double that of the parent rock. The crust seems to have prevented and/or significantly decreased the erosion of the surfaces of the room walls. Mineralogical and chemical analyses together with experimental studies on selected samples suggest that such a crust could have formed because of thermal alteration at high temperatures ca. 600–950°C. On examination of the heated samples, the main geochemical changes within heated rocks were (i) an increase in silica concentration by ca. 2%–3% and (ii) the disappearance of zeolites and sericites. Thermoluminescence dating of the crust revealed thermal resetting of quartz crystals within the ignimbrite tuff at 243 ± 260 CE. All the analytical methods applied to the site indicate that the crust was obtained intentionally, possibly by burning woods indoors, aiming to harden the wall surfaces, mainly by Galatian people of the early Medieval time.

A Review on Drug Penetration Enhancer

Drug penetration induced by penetration enhancers has been widely used in dermatological drug delivery, such as treatment of skin carcinoma, anti angina drug delivery and similar therapies. Absorption rate depends on different factors such as hydrophobicity of skin, skin moisture content, molecular size of Drug, pore size and drug penetration. The poor penetration of many drugs with topical application is limited and restrains the optimum drug release into blood stream, which could restrict desired outcomes. Treatment of skin with chemical and physical methods helps in enhancing skin penetration. Chemical methods include modification in formulation, alternative enhancers, blood flow enhancers etc. Physical methods include skin hydration, drug diffusion, iontophoresis and thermal alteration. This review was focused to all the latest issues related to skin penetration enhancers and their use in drug therapy. Also focus on advantages, and drawbacks of drug penetration on human skin. The objective of this review is to evaluate and summarize all recent studies done in the deild of drug penetration enhancers.

No effect of thermal maturity on the Mo, U, Cd, and Zn isotope compositions of Lower Jurassic organic-rich sediments

AbstractThe isotope ratios of redox-sensitive metals in organic-rich rocks are critical tools for quantifying the timing and severity of deoxygenation and nutrient cycling in Earth's past. The resilience of isotopic data to thermal alteration of the host sediments over millions of years of burial is, however, largely unknown. We present molybdenum, uranium, cadmium, and zinc stable-isotope data from two stratigraphic successions of the same Lower Jurassic Posidonienschiefer unit in the Lower Saxony Basin of northern Germany that were affected by different burial histories. We show that thermal maturity had no effect on the isotopic compositions of these elements but does appear to have increased their concentrations in the rock. The data corroborate the results of laboratory-based maturation studies and provide constraints on the Mo, U, Cd, and Zn isotopic compositions of ca. 182 Ma seawater in the Lower Saxony Basin.

Simulations and global sensitivity analysis of the thermo-hydraulic-mechanical processes in a fractured geothermal reservoir

A fractured reservoir can support and sustain long-term geothermal energy extraction operations. The process of injecting cold water to extract hot water from a fractured reservoir result in thermal and poroelastic stress alteration in the rock matrix and the fracture. The thermo-hydro-mechanical (THM) processes govern the efficiency of an enhanced geothermal system (EGS) operation. The THM processes are controlled by various rock and fluid parameters and the initial and boundary conditions of the model set-up. In this paper, we have identified and analyzed 22 parameters. Due to this large number of involved parameters, it is a rigorous process to accurately estimate the relative importance of individual parameters. Thermal breakthrough time, mass flux and overall energy recovery are the three key aspects of operating a geothermal reservoir efficiently and economically. We have performed an extensive sensitivity analysis using the design of the experiments method (Plackett-Burman) and identified key parameters influencing these three key aspects. For a given discrete fracture network, the fracture aperture, the rock matrix permeability, and the wellbore radius are the most influential parameters controlling the thermal breakthrough time, production well mass flux, and overall energy recovery. Accurate estimation of these influencing parameters is important before a field investigation.

Mithraism under the microscope: new revelations about rituals through micromorphology, histotaphonomy and zooarchaeology

This paper is the first to use an innovative multi-proxy approach to obtain insights into hitherto unknown Mithraic cult practices. Using soil micromorphology, zooarchaeology and histotaphonomy, we investigated two mithraea (Biesheim FR, Kempraten CH) and one cult cave (Zillis CH). This was also the first study to include micromorphological and histotaphonomic approaches within the context of Mithraic research. The systematic evaluation of thermal alteration and bioerosion (in particular bacterial attack) on the animal bones, in combination with zooarchaeological results, allows a differentiation between various (cult) practices involving animals. Thanks to the micromorphological investigations, it was possible to demonstrate that repeatedly spreading combustion residues and renewing the floor were important parts of the cult practices of Mithraism. Our results suggest that a cult practice consisting of several stages was carried out on all three sites. Our study highlights that multiple floor constructions as well as the related sediments and (micro-) artefacts of cultic indoor features are important sources of information.

Active structures and thermal state of the Piton de la Fournaise summit revealed by combined UAV magnetic and thermal infrared measurements

In this study, we demonstrate the strong potential of combining Unmanned Aerial Vehicle (UAV)-based thermal infrared (IR) and magnetic measurements to image the thermal state of volcanic edifices, as well as the distribution of active volcano-tectonic features at depth. Since magnetization is strongly dependent on temperature and alteration, thermally active structures are also associated with a decrease in magnetization. Based on the analysis of recent combined magnetic and infrared acquisitions, we focus on the recent evolution of the summit activity at Piton de la Fournaise. The comparison clearly highlights zones of major thermal activity, alteration and high permeability, and potentially areas of low mechanical resistance. Those observations provide information on preferential pathways for future activity, and also provide constraints on fluid transfer, diffusion, and cooling processes occurring within the volcano subsurface. Through reiterations, such combined UAV measurements are therefore particularly relevant in monitoring volcanic hazards before, during and after eruptions.

Active structures and thermal state of the Piton de la Fournaise summit revealed by combined UAV magnetic and thermal infrared measurements

In this study, we demonstrate the strong potential of combining Unmanned Aerial Vehicle (UAV)-based thermal infrared (IR) and magnetic measurements to image the thermal state of volcanic edifices, as well as the distribution of active volcano-tectonic features at depth. Since magnetization is strongly dependent on temperature and alteration, thermally active structures are also associated with a decrease in magnetization. Based on the analysis of recent combined magnetic and infrared acquisitions, we focus on the recent evolution of the summit activity at Piton de la Fournaise. The comparison clearly highlights zones of major thermal activity, alteration and high permeability, and potentially areas of low mechanical resistance. Those observations provide information on preferential pathways for future activity, and also provide constraints on fluid transfer, diffusion, and cooling processes occurring within the volcano subsurface. Through reiterations, such combined UAV measurements are therefore particularly relevant in monitoring volcanic hazards before, during and after eruptions.

Effects of various temperature and pressure initial conditions to predict the thermal conductivity and phase alteration duration of water based carbon hybrid nanofluids via MD approach

Due to the presence of fluid flow inside channels in many natural and artificial systems and their widespread applications in recent years, attention to the issue of improving heat transfer is growing at an increasing rate. On the other hand, poor fluid heat transfer properties like water are a major obstacle to increasing heat transfer and making heat exchangers more efficient. At present work, hydrodynamic and thermal performances of liquid water in the attendance of two carbon structures (nanosheets of graphene and nanotubes of carbon) were examined by molecular dynamics simulation (MDS). At first, the atomic behavior of hybrid nanofluids was investigated by velocity and density profiles. Then, by studing the coefficient of conductivity (k) and duration of phase alteration in different initial conditions (different initial temperatures (t) and pressures (p)), the hydrodynamic and thermal performances of this mixture were presented. The results revealed with increasing initial t, the thermal conductivity and phase change duration changed from 0.68 W/m.K and 1.29 ns to 0.80 W/m.K and 1.05 ns. This change was due to the increase in the oscillation amplitude and the mobility of the particles in the box of simulation. Moreover, With increasing pressure in the structures, the amount of oscillation amplitude and the mobility of atomic structures decreased.

Study of the elastic properties and thermal shock behavior of Al–SiC-graphite hybrid composites fabricated by spark plasma sintering

Al–SiC and hybrid Al–SiC-graphite MMCs with up to 70 vol% SiC and 10 vol% graphite were fabricated using spark plasma sintering. Detailed studies of the microstructure, Vickers hardness, longitudinal elastic constant C 11 , as well as thermal shock resistance of the MMC samples were carried out. Non-destructive ultrasound phase spectroscopy was used to measure the C 11 elastic constant of the MMCs, and the measured values were compared with different micromechanical models for particle reinforced composites. For both two- and three-component MMCs, the Hashin Shtrikman lower bound fitted best to the experimental results in the absence of any porosity. Thermal shock resistance of the MMCs was carried out by heating in air to 500 °C and subsequently quenching in water for ten times. The extent of thermal shock-induced structural alteration was determined via a systematic study of the change in density, hardness, and C 11 of the samples. It is observed that the thermal shock resistance of the MMCs depends upon multiple factors such as SiC content, graphite content, and the amount of residual porosity. While the reduction in mechanical properties of the Al–SiC MMCs due to graphite addition is according to the expected line, the present study shows that graphite addition also reduces the thermal shock resistance of the MMC.

Integrated Magnetotelluric (MT), Gravity and Seismic Study of Lower Kutai Basin Configuration

This work describes a subsurface basin configuration of the Lower Kutai Basin (hereinafter LKB) in East Kalimantan, Indonesia, as inferred from combination of magnetotelluric (MT), seismic, and gravity data. LKB is structurally controlled mainly by the Samarinda Anticlinorium extending in a NNE-SSW direction and is one of the most prolific hydrocarbon basins in Indonesia. The phase tensor analysis of MT data from most stations and frequencies exhibited a 2D character with a relatively low skew (-3° < β < 3°). The geo-electrical strike direction was estimated at N30°E, which is in good agreement with the regional geological strike with a NNE-SSW direction. 2D MT inversion modeling was performed to infer the subsurface resistivity distribution associated with LKB’s configuration. From the integration of MT, seismic and gravity models it was shown that LKB’s configuration is composed mainly of sandstone, black shale, claystone, and basement rocks. The conductive zones of the MT models are associated with thermal alteration of black shale, which changes its mineralization, leading to lower resistivity. Hence, the black shale may be interpreted as potential hydrocarbon source rock in LKB.

Diamondoids and thiadiamondoids generated from hydrothermal pyrolysis of crude oil and TSR experiments

Diamondoid compounds are widely used to reflect thermal maturation of high mature source rocks or oils and oil cracking extents. However, diamondoids and thiadiamondoids were demonstrated to have newly been generated and decomposed in our hydrothermal pyrolysis of crude oil and TSR experiments. Our results show that adamantanes and diamantanes are generated primarily within the maturity range 0.48–2.1% and 1.2–3.0% EasyRo, respectively. Their formation is enhanced and the decomposition of diamantanes obviously lags at elevated temperatures compared with anhydrous experiments. MDI, EAI, DMAI-1, DMDI-2 may serve as reliable maturity proxies at > ca.1.0% EasyRo, and other isomerization indices (TMAI-1, TMAI-2 and DMAI-2) are effective for the highly mature organic matter at EasyRo > 2.0%. The extent of oil cracking (EOC) calculated from the broadly used (3- + 4-) MD method (Dahl et al. in Nature 399:54–56, 1999) is proven to overestimate, especially for highly cracked samples due to the new generation of (3- + 4-) MD. Still, it can be corrected using a new formula at < 3.0% EasyRo. Other diamondoid-related indices (e.g., EAI, DMDI-2, As/Ds, MAs/MDs, DMAs/DMDs, and DMAs/MDs) can also be used to estimate EOC. However, these indices cannot be applied to TSR-altered petroleum. TSR is experimentally confirmed to generate diamantanes and thiaadmantanes at 1.81% EasyRo likely via direct reactions of reduced S species with hydrocarbons and accelerate the decomposition of diamantanes at > 2.62% EasyRo compared with thermal chemical alteration (TCA). More studies are needed to assess specific mechanisms for the formation of thiadiamondoids under natural conditions.

Nano-scale physicochemical attributes and their impact on pore heterogeneity in shale

Heterogeneity in shale due to distribution of mineral and organic matter controls the disposition of pores in them. While the effect of vertical anisotropy is accounted for most cases of porosity estimation, the effect of bedding parallel heterogeneity is often ignored. This study dives deep into the shale fabric using bedding parallel sections, and the pore volume distribution is estimated in shales of varying thermal maturity and organic carbon content (2.6% − 38.2 %). Three among the five shales used in this study are early mature (Tmax: 439–444 °C), whereas the remaining two are over-mature, signified by very high S4Tpeak (670–685 °C). The higher thermal maturity indicates thermal alteration induced by igneous intrusion. The pore volume, functional groups, and organic matter distribution are systematically derived in different positions of the bedding parallel section using a combination of 3D imaging, spectroscopy, small-angle scattering and low-pressure gas adsorption techniques. These spot-specific properties are further compared with bulk properties to quantify the extent of heterogeneity. It is observed that the over-mature shales with higher aromaticity contain 150–200% more bulk accessible pore volume than the lesser-mature shales. It is also evident that the smaller mesopores (∼10 nm pore width) are more inaccessible compared to their coarser (∼20 nm pore width) counterparts. Higher matured shales show increased inaccessibility of mesopores up to 228 % due to bitumen deposition in pores during thermal maturation, resulting in a sharp decline in mesopore surface fractal dimension. The uniformity of the functional group and organic matter distribution in different parts of the shale depends on the maturity, and reflects the extent of variation in pore volume across the specimen. The 3D tomography-derived spatial abundance of organic matter in over-mature shales show higher deviation (±15-20%) from the average than lesser-mature shales (5–10%). This study proposes a multiscale methodology which can evolve and develop as a protocol for systematic, reservoir-scale maturity-dependent heterogeneity quantification in gas-shales.

Discovery of the Lower-Middle Jurassic high potential source rocks based on the geochemical investigation from the Indus Basin, Pakistan

The Lower to Middle Jurassic sedimentary succession of the Indus Basin, Pakistan represents thick strata of shale, siliciclastic and carbonate rocks. The shale is subjected to the experimental methods of total organic carbon contents (TOC), rock-eval™, vitrinite reflectance, and x-ray diffraction with clay mineralogy for identification of high potential source rock. This set of black shale having well-defined kerogen types I and II, an abundance of organic matter ≥2%, HI ≥ 150 or 200 mg HC/g TOC, Tmax ≤ 465 °C, good maturity such as 1.3–2.0 Ro%, thermal alteration index ≥2, and spore color index ≥5, and illite-smectite clay is strong enough (60–80%) to produce hydrocarbon. Furthermore, the stratigraphic thickness is ≤ 100 m in studied strata in a depth of 3500–4500 m in the Indus Basin feasible for future exploration. The chemical composition of black shale is siliceous mudstone, calcareous mudstone, argillaceous mudstone, and siliceous marlstone. The cross plot of OI versus HI and Tmax versus HI shows mature types II and I kerogen while the cross plots of TOC versus S1 + S2 with TOC versus generative potentials (GP) showing good to high potentials of indigenous hydrocarbons. The plotting of the Tmax versus productive index (PI) exhibits that the kerogen mostly lies in the mature zone, having the capacity of oil generation. Besides the geochemical properties, the studied rock is thick and widely disturbed across the Indus Basin deposited under the dysoxic-anoxic setting. Moreover, the Lower to Middle Jurassic strata are correlated with the equivalent stratigraphic formations in India and China for their importance in the regional context.

Evaluation of Thermal Maturation of Hydrocarbon Potential Source Rocks From Kombe-Kompina-Missole Areas of the Douala Sub- Basin Using Spore Color Variation Technique

The Douala sub-Basin is well-known as a highly prospective basin for petroleum generation. The depletion of some oil Wells originally discovered in Cameroon calls for further investigation on the maturity of potential source rocks so as to discover more oil fields. The current methods used by many researchers for evaluating the thermal maturity of potential source rocks are mostly the geochemical techniques which are pretty expensive. Thus, this study was set out to evaluate thermal maturation of potential source rocks exposed in the Kombe-Kompina-Missole areas of the Douala Sub-Basin through the use of spore color variation as an alternative cheaper method of determination with a higher precision than the former. This work had three specific objectives; to carry out loggings, to obtain and identify sporomorphs, to determine the extent of thermal alteration of sporomorphs present in the samples through microscopic examination of spore and pollen color variation. A total number of fifteen samples obtained from the sedimentary sequences encountered in the studied area were sent for laboratory analysis. The results obtained from palynological analysis showed that color index of organic matter at Kombe and Kompina ranges from 2 to 2/3 which are immature to early mature source rocks with kerogen type II, III and IV. While for Missole, color index ranges from 2/3 to 3 indicating early maturity to mature source rocks with kerogen type II. Facies identified from lithofacies analysis included: sandstones, shales, mudstones, siltstones, conglomerates. Therefore, palynological methods based on spore color variationis an efficient and cheaper method of determining thermal maturity.

Macroinvertebrate and diatom community responses to thermal alterations below water supply reservoirs

AbstractRiver impoundments have transformed river ecosystems globally due to the modification of various abiotic and biotic factors. This study provides rare evidence quantifying how water supply reservoirs alter water temperature regimes and its effects on macroinvertebrate and diatom communities over a 4‐year period. We obtained near‐continuous water temperature measurements upstream and downstream of three reservoirs and analysed thermal variables in association with macroinvertebrate and diatom community indices (including taxonomic richness, proportion of Ephemeroptera, Plecoptera and Trichoptera taxa [%EPT] and diatom ecological guilds). Reservoirs typically decreased downstream thermal variability, with reduced summer temperatures and increased winter temperatures, and a delayed timing of annual temperature extremes. Marked differences in thermal regime modifications between reservoirs were observed, including evidence of inter‐annual variation associated with inter‐basin water transfers downstream of one reservoir. Biomonitoring indices showed associations with thermal indices that differed between site types (regulated versus non‐regulated) and seasons (spring vs. autumn). Various macroinvertebrate and diatom indices capturing community diversity elements and sensitivities to different environmental pressures were associated with higher maximum summer temperatures and lower minimum winter temperatures, suggesting ecological effects of reduced thermal variation downstream of reservoirs. Different ecological responses to thermal indices were observed between seasons, likely due to organism life‐cycle effects and intra‐annual thermal variations. Contrasting macroinvertebrate and diatom communities were observed between regulated and non‐regulated sites, which may be driven by differences in the thermal regime and other abiotic factors at regulated sites, including nutrient, sediment and flow regimes. Long‐term continuous water temperature monitoring of both multiple regulated and non‐regulated river systems is necessary to better understand the environmental and ecological effects of river impoundments. Given the extent to which river impoundment has modified stream temperatures globally, the inclusion of thermal regime data in environmental flow studies alongside hydrological information may guide the implementation of mitigation measures on impounded waterbodies.

Petrologic Characteristics and Chemical Structures of Macerals in a Suite of Thermally Altered Coals by Confocal Raman.

Thermally altered coals affect the safety and efficiency of coal mining and utilization, but most studies of thermally altered coal have only focused on the whole coal instead of on different macerals. Thermally altered coals have complex and special maceral components; not only intrinsic macerals but also newly formed macerals such as pyrolytic carbon can be observed. The shape and texture of intrinsic macerals also change significantly after thermal alteration, especially for vitrinite. Therefore, employing an in situ testing method to study the macerals in thermally altered coals is necessary. Herein, a confocal Raman imaging microscope was used. Results show that macerals become coked in samples adjacent to the sill, and circular mosaic texture is the most common texture observed in this series of samples. In samples away from the sill, inertinite is isotropic, while in samples closest to the sill, anisotropic inertinite can be found. The Raman spectra of inertinite and vitrinite (mosaic texture) are significantly different. For vitrinite, the D and G peaks are closer, and the height of D is lower than for inertinite. The Raman spectra of thermally altered coal include 13 bands after curve fitting. Curved-fitted results show that for vitrinite, polycondensation provides the nucleation of mesophase spheres, and newly formed aromatics take part in the growth of mesophase spheres. However, for inertinite, excessive amorphous carbon and substituents, such as aromatic alkyl and aryl–alkyl ether, form cross-linked structures and hinder the anisotropic development of inertinite.

Influence of surface integrity induced by multiple machining processes upon the fatigue performance of a nickel based superalloy

Machining operations are of key importance to the fatigue performance of nickel based superalloys due to the high thermal/mechanical loadings yielded on the machined workpiece which can significantly alter the surface integrity of the components. Therefore, understanding the influence mechanisms of machining induced surface integrity upon fatigue response is vital to determine their manufacturing processes and applications. In this respect, this paper investigates the surface integrity of nickel based superalloy subject to different mechanical and thermal loadings induced by various machining processes including conventional machining (e.g. finish and rough milling) and nonconventional machining (e.g. laser assisted milling and abrasive waterjet cutting) methods, as well as their influences upon fatigue performance and failure mechanisms. In-depth surface metallurgical and crystallographic analysis has been conducted to reveal the surface damage mechanisms, which allows the description of the machining induced mechanical and thermal alterations on the machined workpiece. Furthermore, the examination of the fractography from the fatigue specimen has been conducted, which enables the understanding of the influence mechanism of the corresponding surface defects on the fatigue crack initiation and propagation, subject to a four points bending fatigue test. While the resulted S-N curves indicate that the high cycle fatigue of machined nickel based superalloy is mainly dominated by the machining induced residual stress conditions, the surface defects from different machining processes can particularly influence fatigue crack initiation and propagation mechanisms in both the low and high cycle regimes.

Source Rocks’ Potentiality of the Sargelu Formation (Middle Jurassic) in the Taq Taq Oilfield, Kurdistan Region, Iraq

Thirty rock samples were selected from the well Tq-1 that penetrated the Jurassic beds in the Taq Taq Oilfield to be studied the source rock potentiality of the Sargelu Formation. The formation is characterized by three types of microfacies, namely, foraminiferal packstone, grainstone microfacies, fossiliferous packstone microfacies, and foraminiferal wackestone which were deposited in an environment extending from middle to outer carbonate ramp. An average of 3.03 wt.% of total organic carbon was obtained from a Rock Eval pyrolysis analysis carried out on 24 selected rock samples. The petrographic analysis for such organic matters revealed that they are of kerogen types III and IV and they are currently in a post-mature state. Pyrolysis parameters showed that limited generation potential was remained for these sources to expel generated hydrocarbons. The palynological study showed that Amorphous Organic Matter forms the highest percentage of organic matter components with more than 70%, followed by phytoclasts with 10 – 25 % and palynomorphs of less than 10%. The organic matters within the Sargelu Formation are deposited at the distal part of the basin under suboxic to anoxic condition. The color of the organic matter components, examined under transmitted light, showed Thermal Alteration Index values between 3+ and 4-. Such values may indicate that these organic matters are thermally at the end of the liquid oil generation zone and beginning of condensate-wet gas generation zone. The thermal maturity of the Sargelu Formation depending on the calculated VRo% revealed that the formation in the studied oilfield is currently at the peak of the oil generation zone. The Sargelu Formation in the studied field is considered as an effective source rock, as it has already generated and expelled hydrocarbons.

Carbon isotopes, ammonites and earthquakes: Key Triassic-Jurassic boundary events in the coastal sections of south-east County Antrim, Northern Ireland, UK

A continuous succession of marine and marginal-marine sediments of Rhaetian (Late Triassic) and Hettangian (Early Jurassic) age is present in the Larne Basin in Northern Ireland. These strata cover a period in Earth's history that included the emplacement of the Central Atlantic Magmatic Province (CAMP), the End Triassic Mass extinction (ETE), the Triassic–Jurassic Boundary (TJB), and major perturbations in the global carbon cycle. The Waterloo Bay section in the Larne Basin offers a well exposed sedimentary succession that spans this interval, and it has previously been proposed as a candidate GSSP for the base of the Jurassic System. A high-resolution δ13Corg and organic carbon record for this locality is presented here, with these new data tied to previous stratigraphic descriptions, ammonite biostratigraphy, atmospheric carbon dioxide concentration (pCO2) estimates, and nearby borehole sections that do not suffer from the thermal alteration that has affected the Waterloo Bay section. Several new exposures, unaffected by thermal metamorphism, are described that could provide future palynological and micropalaentological studies across this important boundary interval. Correlation is established between the well-studied sections in north Somerset and the likely position of the TJB in the Larne Basin, and records of soft sediment deformation, synsedimentary fault movement, relative sea-level change and their likely causes are discussed.

The impact of porous medium heterogeneity on the thermal feedback of open-loop shallow geothermal systems

Groundwater has been increasingly used to provide low-carbon heating and cooling of buildings with open-loop shallow geothermal systems. Water is generally reinjected into the same aquifer after the heat exchange in order to avoid the aquifer depletion. However, this can result in the return of part of the injected water to the production well(s), causing a gradual thermal alteration known as thermal feedback. Thermal feedback is a major design issue of open-loop shallow systems but, so far, it has been mainly addressed neglecting the heterogeneity of the aquifer properties. This study investigates the impact of aquifer heterogeneity on two main metrics that characterize thermal feedback: thermal breakthrough time (i.e., the first arrival time of the thermal plume) and recirculating ratio (i.e., the fraction of water coming back to production well). A stochastic approach was adopted performing a large number of numerical simulations that cover a wide range of possible scenarios. The results highlight that conductivity heterogeneity plays a major influence on the temperature evolution at the production well. The breakthrough time alone might lead to misleading evaluations of the system efficiency, given that a few particles can reach the production well by traveling in the highly-conductive layers. Conversely, both the heterogeneity and the thermal dispersivity have a negligible impact on the recirculating ratio, which quantifies the long-term evolution of thermal feedback. As a consequence, the available approaches based on advection-only and homogeneous medium are a robust tool to predict the long-term behavior of shallow open-loop geothermal systems.