The Experts below are selected from a list of 2841 Experts worldwide ranked by ideXlab platform
Mathew Stevens - One of the best experts on this subject based on the ideXlab platform.
-
stress strain response and seismic signature analysis of phyllite reservoir rocks from blue mountain geothermal field
Geothermics, 2019Co-Authors: Arash Kamaliasl, Maziar Foroutan, Ehsan Ghazanfari, Trenton T Cladouhos, Mathew StevensAbstract:Abstract Geothermal energy is the heat contained in rock and fluid in the earth’s crust. In some areas the geothermal resource can be exploited by drilling wells to extract the heated fluids and piping the fluids to a power plant to generate renewable electricity. Geomechanical characterization of the rocks in geothermal reservoirs is necessary to (i) optimize a well stimulation program, (ii) reduce production decline, and (iii) build more accurate predictive models at reservoir scale. In this study, we present the results of a suite of experiments on mechanical characterization of phyllite rock specimens retrieved from DB-2 well (depth of 1260 m) at the Blue Mountain geothermal field in Nevada, United States. In order to investigate the effects of anisotropy on mechanical response of rock, one vertically-drilled and one horizontally-drilled sub-cores were extracted from the phyllite core. Multi-stage elastic, cyclic, creep, and multi-stage failure tests were performed to characterize the elastic, plastic, time-dependent, and failure properties as well as effects of anisotropy on the behavior of the phyllite specimens. The pressure-dependent static and dynamic moduli revealed that within the elastic region, the Young’s modulus increased with the increment of differential stress during the loading stage. While, 10% to 50% difference between the elastic moduli of the two specimens confirmed the anisotropic nature of the material. Negligible creep response was observed in both specimens, with a more pronounced change in P- and S-waves velocities during hydrostatic stage for vertically-drilled sub-core. The failure envelope, developed using the multi-stage failure test on the vertically-drilled specimen, indicated good agreement with both Linearized Mohr-Coulomb and Hoek-Brown failure criteria. On the other hand, significant changes were observed in the time-frequency maps of the transmitted seismic waves during multi-stage elastic test (i.e. change in confining level), however, slight changes in the time-frequency map were observed during creep test (i.e. application of differential stress for a relatively long period).
Nikolas I Christensen - One of the best experts on this subject based on the ideXlab platform.
-
split from slip and schist crustal anisotropy beneath northern cascadia from non volcanic tremor
Journal of Geophysical Research, 2012Co-Authors: M G Bostock, Nikolas I ChristensenAbstract:[1] Polarization and splitting analyses of minute-long windows of non-volcanic tremor at 3-component stations in the vicinity of southern Vancouver Island provide new evidence for the presence of anisotropy within the crustal portion of the North American plate beneath Cascadia. As reported previously, tremor particle motions are predominantly horizontal and inferred to manifest an upgoing wavefield composed primarily of S-waves. Under this assumption, estimates of incidence angle and back azimuth can be deduced from orientation of the smallest principle direction of motion. When subjected to standard S-wave splitting analysis, most stations yield systematic and reproducible fast polarization directions. Estimates of original polarization direction are more scattered and splitting times often exhibit multimodal distributions. Numerical simulations, wherein band-limited synthetic seismograms comprising contributions from multiple sources are analyzed for splitting, neatly reproduce these characteristics and thereby provide a framework for interpretation. A number of stations in our study sit astride the San Juan fault which, based on reflection studies, dips approximately 60 to 70° to the north. Underlying these stations is the Leech River Complex consisting of strongly foliated greenschist facies Phyllites with steeply dipping foliations striking parallel to fast polarization directions of split S-waves. Detailed laboratory velocity measurements at elevated pressures show that as little as 2 to 3 km of vertically dipping Leech River phyllite are required to produce the observed splitting. These Phyllites have some of the highest S-wave anisotropies measured to date and are part of a once continuous belt of anisotropic crust extending over 2000 km along the western North American coast from southern Vancouver Island to southwest Alaska.
-
the origin of reflections beneath the blue ridge piedmont allochthon a view through the grandfather mountain window
Tectonics, 1993Co-Authors: Daniel L Szymanski, Nikolas I ChristensenAbstract:A perplexing variety of crustal models have been proposed for the region beneath the southern Appalachian overthrust. Determining the true nature of crustal composition and structure in this region carries important scientific and economic implications. To evaluate the numerous models, compressional wave velocities and densities were measured on 30 rock samples collected within the Grandfather Mountain window in the Blue Ridge of North Carolina. The window breaches high-grade crystalline rocks, exposing Grenville gneisses, Late Proterozoic metasedimentary and metavolcanic rock, and Cambrian quartzite, phyllite, and dolostone that are likely to underlie the regional Blue Ridge-Piedmont thrust. Measured velocities range widely from 4.21 km s−1 for Cambrian phyllite to 7.47 km s−1 for tectonized Cambrian Shady Dolomite at 200 MPa. Velocity anisotropy is as great as 47% in the phyllite. The samples exhibit a broad range in densities as well: from 2500 kg m−3 in fractured quartzite to 3000 kg m−3 in metabasalts. Synthetic reflection seismograms were generated using these physical properties to consider the origin of subthrust reflection events. In addition to the much-publicized interpretation of Paleozoic sedimentary rocks residing beneath the crystalline sheet, modeling reveals that the reflections could also be explained by metamorphosed Paleozoic strata, by the regional Late Proterozoic metavolcanic and metaclastic rift sequence, and by pervasive shear zones (i.e., mylonites) within compositionally homogeneous gneisses. We interpret field data to strongly favor mylonitic gneisses as the subthrust reflectors. Still, surface data remain sufficiently ambiguous that the question will not be definitively settled without continental drilling.
Arash Kamaliasl - One of the best experts on this subject based on the ideXlab platform.
-
stress strain response and seismic signature analysis of phyllite reservoir rocks from blue mountain geothermal field
Geothermics, 2019Co-Authors: Arash Kamaliasl, Maziar Foroutan, Ehsan Ghazanfari, Trenton T Cladouhos, Mathew StevensAbstract:Abstract Geothermal energy is the heat contained in rock and fluid in the earth’s crust. In some areas the geothermal resource can be exploited by drilling wells to extract the heated fluids and piping the fluids to a power plant to generate renewable electricity. Geomechanical characterization of the rocks in geothermal reservoirs is necessary to (i) optimize a well stimulation program, (ii) reduce production decline, and (iii) build more accurate predictive models at reservoir scale. In this study, we present the results of a suite of experiments on mechanical characterization of phyllite rock specimens retrieved from DB-2 well (depth of 1260 m) at the Blue Mountain geothermal field in Nevada, United States. In order to investigate the effects of anisotropy on mechanical response of rock, one vertically-drilled and one horizontally-drilled sub-cores were extracted from the phyllite core. Multi-stage elastic, cyclic, creep, and multi-stage failure tests were performed to characterize the elastic, plastic, time-dependent, and failure properties as well as effects of anisotropy on the behavior of the phyllite specimens. The pressure-dependent static and dynamic moduli revealed that within the elastic region, the Young’s modulus increased with the increment of differential stress during the loading stage. While, 10% to 50% difference between the elastic moduli of the two specimens confirmed the anisotropic nature of the material. Negligible creep response was observed in both specimens, with a more pronounced change in P- and S-waves velocities during hydrostatic stage for vertically-drilled sub-core. The failure envelope, developed using the multi-stage failure test on the vertically-drilled specimen, indicated good agreement with both Linearized Mohr-Coulomb and Hoek-Brown failure criteria. On the other hand, significant changes were observed in the time-frequency maps of the transmitted seismic waves during multi-stage elastic test (i.e. change in confining level), however, slight changes in the time-frequency map were observed during creep test (i.e. application of differential stress for a relatively long period).
Pereira Zélia - One of the best experts on this subject based on the ideXlab platform.
-
New insights on the middle Givetian/middle Frasnian palynofloras from the Phyllite-Quartzite Formation in the Neves-Corvo mine region (Iberian Pyrite Belt, Portugal)
'Elsevier BV', 2024Co-Authors: Mendes Márcia, Pereira Zélia, Matos, João Xavier, Albardeiro Luís, Morais Igor, Solá, Ana Rita, Salgueiro Rute, Pacheco Nelson, Araújo Vítor, Inverno CarlosAbstract:ABSTRACT: A detailed palynostratigraphic study of two Somincor/Lundin Mining exploration drill holes intercepting the Phyllite-Quartzite (PQ) Formation in the geological basement of the Neves-Corvo mine region (Portuguese sector of the Iberian Pyrite Belt – IPB) allowed to first recognise the oldest ages for this formation in this region, ranging from midGivetian/midFrasnian (base unknown) to late Famennian. The TA Miospore Biozone (Cristatisporites triangulatus-Ancyrospora ancyrea) of middle Givetian age (Middle Devonian) was identified in NK30B-1 drill hole (Lombador North mine sector), whereas the BM Miospore Biozone (Verrucosisporites bulliferus-Lophozonotriletes media) and IV Miospore Biozone (based in the first occurrence of Rugospora bricei and Diducites cf. poljessicus) of middle Frasnian (Late Devonian) age were both recognised in drill hole SJ32 (Corvo-Semblana mine sector). The common presence of Early-Middle Devonian reworked spores, as well as similar inherited zircon ages may suggest that the lower PQ Formation age is not yet known. At Neves-Corvo mine, the Volcano-Sedimentary Complex is deposited directly above the PQ basement, spanning different ages, pointing out two major unconformities, a VSC/upper and/or lower PQ sequences and an upper PQ/lower PQ sequences. A palynostratigraphic correlation of the lowermost Phyllite-Quartzite Formation across the IPB is established. Phyllite-Quartzite Formation palynoassemblage of Neves-Corvo region is compared with lowermost PQ assemblages recovered in the NW sector of IPB (S. Francisco da Serra and Lousal-Caveira mine structures, Portugal) and in E sectors of the IPB in Spain (Gerena-El Garrobo section). The similar palynological record (also including the same reworked taxa signature) and ages obtained, suggests identical sedimentary provenance, close paleogeographic domain and temporal affinity throughout the lowermost IPB Phyllite-Quartzite Formation.info:eu-repo/semantics/publishedVersio
-
Preliminary dating of the Vale de Parreiras Formation of the late Famennian age, Iberian Pyrite Belt, Portugal, based on palynomorphs
LNEG - Laboratório Nacional de Energia e Geologia, 2020Co-Authors: Mendes Márcia, Pereira Zélia, Albardeiro Luís, Matos, João XavierAbstract:New palynostratigraphic data were obtained from Phyllites interbedded with quartzwackes of the Vale de Parreiras Formation, located to the south of the Grândola Fault in the Azinheira de Barros region, Portugal. The studied outcrops are located in the eastern bank of the Sado river. A mid-late Famennian age has been assigned based on significant presence of the key miospore species Grandispora cf. cornuta and Rugospora flexuosa, indicating a VCo Miospore Biozone for the Vale de Parreiras Formation. This age is older than previously considered for this formation, even despite the lack of palaeontological information and geochronological age determinations. This new attained palynological age provides helpful informations for the interpretation of regional tectonic structures. Also, its stratigraphic position could be reinterpreted and correlated to other late Famennian age units of Iberian Pyrite Belt, for instance, to the Phyllite-Quartzite Group. The new palynological age indicates that the Vale Parreiras Formation lithologies were deposited and belong to the same palaeogeographic realm as the former group during Late Devonian times. It may also suggest important post Variscan uplift of the Iberian Pyrite Belt in the area east of the Corona-Sado Fault and south of the Grândola Fault. These results also indicate a significant exposure of the mid-late Famennian basement wich can be considered a less favourable scenario to mineral exploration in this Iberian Pyrite Belt sectorDados palinoestratigráficos obtidos recentemente permitiram datar os filitos intercalados em quartzovaques da Formação Vale de Parreiras, situada na área noroeste da Faixa Piritosa Ibérica (FPI), em Portugal. Os afloramentos estudados localizam-se a sul da falha de Grândola, na margem este do rio Sado. A presença das espécies guia Grandispora cf. cornuta e Rugospora flexuosa, indicam a Biozona de Miosporos VCo, do Famenniano médio a superior, permitindo atribuir esta idade à Formação Vale de Parreiras. Esta datação pressupõe uma idade mais antiga que a previamente estimada para esta formação por correlação estratigráfica, mas sem dados paleontológicos de suporte. A nova idade palinológica alcançada fornece informações úteis para a interpretação das estruturas tectónicas regionais. A posição estratigráfica da Formação Vale de Parreiras pode ser reinterpretada e correlacionada com outras unidades do Famenniano superior da Faixa Piritosa Ibérica, nomeadamente com o Grupo Filito-Quartzito. Estes dados permitem inferir que a Formação Vale de Parreiras faria parte desta bacia paleogeográfica, durante o Devónico Superior. A nova idade palinológica da Formação Vale de Parreiras sugere um importante uplift pós-Varisco neste setor da FPI, localizado a este da falha de Corona-vale do rio Sado e a sul da falha de Grândola. Estes resultados sugerem ainda uma forte exposição do substrato Famenniano, sendo por isso, considerado um cenário menos favorável à exploração mineral nesta região da Faixa Piritosa Ibéricainfo:eu-repo/semantics/publishedVersio
-
New lower Givetian age miospores of the Phyllite-Quartzite Group, São Francisco da Serra Anticline, Iberian Pyrite Belt - Portugal
CIMA - University of the Algarve, 2014Co-Authors: Pereira Zélia, Matos, João Xavier, Fernandes Paulo, Jorge R. C. G. S., Oliveira, José TomásAbstract:Palynostratigraphical analysis of Phyllite Quartzite (PQ) Group shales recovered froma drill core and outcrops at the São Francisco da Serra anticline, in the westernmost area of the Iberian Pyrite Belt, yielded a moderately preserved miospore assemblage assigned to the upper part of AD miospore Biozone, subzone Lem, of lower Givetian age. This is the oldest age recognized, up to this date, for any rocks in the Iberian Pyrite Belt
-
A late Fammenian age storm-dominated succession at Berrocal (Iberian Pyrite Belt - Spain)
2014Co-Authors: Fernandes Paulo, Pereira Zélia, Oliveira, José Tomás, Jorge R. C. G. S., Relvas J.Abstract:The Berrocal area is situated in the northern limb of Valverde del Camino anticlinal in the Spanish sector the Iberian Belt and exposes the upper part of the Phyllite-Quartzite Group. Recent studies on palynostratigraphy and sedimentology of the Berocal section indicates that the stratigraphic succession is late Famennian age (VH miospore biozone) and was accumulated on the offshore zone of a siliciclastic shelf dominated by storm events
Giulio Morteani - One of the best experts on this subject based on the ideXlab platform.
-
partitioning of rare earth elements yttrium and some major elements among source rocks liquid and vapor of larderello travale geothermal field tuscany central italy
Geochimica et Cosmochimica Acta, 2003Co-Authors: P Moller, Peter Dulski, Giulio MorteaniAbstract:Rare earth elements (REE), yttrium and some major element concentrations have been measured in the high-enthalpy fluids (HEF) of several geothermal wells and the fluid′s source rocks in the Larderello-Travale area (Tuscany/Central Italy). The REE and Y abundances in the HEF range from 0.1 to about 10 pmol/kg and are slightly higher in the HEF originating from evaporite/carbonate sequences (Calcare Cavernoso) than in those from Phyllites. The resulting REY distribution factors between HEF and source rocks, appKdsource–rockHEF defined as the ratios of REY/Ca in both phases, range from <0.01 to 0.03 and 0.03 to 0.1 for Phyllites and evaporite-limestone sequences (Calcare Cavernoso), respectively. REE+Y are more retained by the source rocks than Ca. HEF show no inherited and, with exception of a small Y anomaly, no acquired anomalies. This indicates a static equilibrium between HEF and the source rocks. The absence of any Eu anomalies points to temperatures less than 250°C in the source region. The small negative Y anomalies are the result of Y depletion in the rock fractions taking part in the water-rock interaction. Due to depressurization of the HEF to about 120°C and 2 bars, a liquid and a vapor phase is produced, which were sampled for the determination of the REE+Y partitioning between the two phases. The apparent partition factors between vapor and liquid appDliquidvapor of REE+Y range between 0.05 to 0.2 and about 3 for HEF originating from the Phyllites and evaporites/carbonates, respectively. Among all ionic species determined, only NH4+ has an apparent partition factor appDliquidvapor above one. In general, REY partition more easily into the vapor phase than the earth alkaline and alkaline elements. No significant correlation of REE+Y in the vapor phase with any of the determined ionic species could be detected. This probably points to the dominant presence of ion pairing such as REY(OH)3o or REYO(OH)o.