ALBERT

Description: The building materials of the Theatre of Marcellus, 44–11 BCE, reflect Roman builders’ careful selections of tuff and travertine for dimension stone and volcanic aggregates for pozzolanic concretes. The vitric–lithic–crystal Tufo Lionato tuff dimension stone contains a high proportion of lava lithic fragments, which increase its compressive strength and decrease water sorption, enhancing durability. Sophisticated installations of travertine dimension stone reinforce the tuff masonry, which is integrated with durable concrete walls and barrel vaults. The pozzolanic mortars of the concretes contain harenae fossiciae mainly from the intermediate alteration facies of the mid-Pleistocene, scoriaceous Pozzolane Rosse pyroclastic flow. They have pervasive interpenetrating pozzolanic cements, including strätlingite, similar to highquality, imperial era mortars. Concrete walls are faced with refined Tufo Lionato opus reticulatum and tufelli, and opus testaceum of fired, greyish-yellow brick. The exploratory concrete masonry, which includes some of the earliest examples of brick facings and strätlingite cements in Rome, and the integration of these materials in complex architectural elements and internal spaces, reflect the highly skilled workmanship, rigorous work-site management and technical supervision of Roman builders trained in republican era methods and materials.

Description: Published

Description: 728–742

Description: JCR Journal

Description: restricted

Description: The rocks of Alban Hills and Monti Sabatini volcanoes (Central Italy) and their associated epiclastic deposits have been extensively used as building material in ancient Rome from about VIIIth century BCE to IVth century CE. However, the identification of the source areas of these rocks is difficult due to the lack of an integrated stratigraphic and geochemical analysis of the relationships between the two volcanic districts, and to the alteration affecting the primary products as consequence of weathering and pedogenetic processes. Here, a comprehensive, upgraded stratigraphic and geochronological review of the two volcanic districts, corroborated by new geochronological data for several eruptive units and altered deposits is presented, coupled to a complete geochemical background, achieved by means of newly determined major and trace element analyses for all the main eruptive units. A study of the alteration processes of the primary products is also presented, and the age of the main weathering and pedogenetic phases, associated to Quaternary climatic changes, are also investigated. The results are integrated with those from literature in order to construct discriminant diagrams based on selected trace elements, and allow us to characterize the primary and altered volcanic deposits in the Rome area, distinguish products of different volcanic districts, discuss the effects of different weathering processes on the mobility of some elements, and provide a reference frame for the provenance of the volcanic materials employed in ancient Roman masonry. The interdisciplinary data set and results presented here provide groundwork for volcanological, climate, pedological and archaeological provenance studies.

Description: Published

Description: 115–136

Description: JCR Journal

Description: restricted

Description: Ancient Roman syntheses of Al-tobermorite in a 2000-year-old concrete block submerged in the Bay of Pozzuoli ( Baianus Sinus ), near Naples, have unique aluminum-rich and silica-poor compositions relative to hydrothermal geological occurrences. In relict lime clasts, the crystals have calcium contents that are similar to ideal tobermorite, 33 to 35 wt%, but the low-silica contents, 39 to 40 wt%, reflect Al 3+ substitution for Si 4+ in Q 2 (1Al), Q 3 (1Al), and Q 3 (2 Al) tetrahedral chain and branching sites. The Al-tobermorite has a double silicate chain structure with long chain lengths in the b [020] crystallographic direction, and wide interlayer spacing, 11.49 Å. Na + and K + partially balance Al 3+ substitution for Si 4+ . Poorly crystalline calcium-aluminum-silicate-hydrate (C-A-S-H) cementitious binder in the dissolved perimeter of relict lime clasts has Ca/(Si+Al) = 0.79, nearly identical to the Al-tobermorite, but nanoscale heterogeneities with aluminum in both tetrahedral and octahedral coordination. The concrete is about 45 vol% glassy zeolitic tuff and 55 vol% hydrated lime-volcanic ash mortar; lime formed 〈10 wt% of the mix. Trace element studies confirm that the pyroclastic rock comes from Flegrean Fields volcanic district, as described in ancient Roman texts. An adiabatic thermal model of the 10 m 2 by 5.7 m thick Baianus Sinus breakwater from heat evolved through hydration of lime and formation of C-A-S-H suggests maximum temperatures of 85 to 97 ºC. Cooling to seawater temperatures occurred in two years. These elevated temperatures and the mineralizing effects of seawater and alkali- and alumina-rich volcanic ash appear to be critical to Al-tobermorite crystallization. The long-term stability of the Al-tobermorite provides a valuable context to improve future syntheses in innovative concretes with advanced properties using volcanic pozzolans.

Description: We have examined the behavior of the streaming potential under multiphase conditions, and under conditions of varying temperature and salinity, to evaluate the feasibility of using downhole streaming-potential measurements to determine fluid distributions in a reservoir. Using new insights into the pore-scale distribution of fluids and of electric charge, we found that the saturation dependence of the streaming potential coupling coefficient is important in determining the resulting streaming potential. Through examination of the four independent physical parameters which comprise the coupling coefficient, we developed an understanding of the behavior of the coupling coefficient under conditions of elevated temperature and brine salinity. We found that although increasing salinity substantially reduces the magnitude of the coupling coefficient, and therefore also the magnitude of the predicted streaming potential, increasing temperature has only a small effect, showing about a 10% change between 25°C and 75°C, depending on salinity.

Description: Multiple techniques are available to construct three-dimensional reservoir models. This study uses comparative analysis to test the impact of applying four commonly used stochastic modeling techniques to capture geologic heterogeneity and fluid-flow behavior in fluvial-dominated deltaic reservoirs of complex facies architecture: (1) sequential indicator simulation; (2) object-based modeling; (3) multiple-point statistics (MPS); and (4) spectral component geologic modeling. A reference for comparison is provided by a high-resolution model of an outcrop analog that captures facies architecture at the scale of parasequences, delta lobes, and facies-association belts. A sparse, pseudosubsurface data set extracted from the reference model is used to condition models constructed using each stochastic reservoir modeling technique. Models constructed using all four algorithms fail to match the facies-association proportions of the reference model because they are conditioned to well data that sample a small, unrepresentative volume of the reservoir. Simulated sweep efficiency is determined by the degree to which the modeling algorithms reproduce two aspects of facies architecture that control sand-body connectivity: (1) the abundance, continuity, and orientation of channelized fluvial sand bodies; and (2) the lateral continuity of barriers to vertical flow associated with flooding surfaces. The MPS algorithm performs best in this regard. However, the static and dynamic performance of the models (as measured against facies-association proportions, facies architecture, and recovery factor of the reference model) is more dependent on the quality and quantity of conditioning data and on the interpreted geologic scenario(s) implicit in the models than on the choice of modeling technique.

Description: We report the first measured values of the streaming potential coupling coefficient in chalk samples saturated with natural groundwater, and preliminary field measurements of the spontaneous potential (SP), at both ambient and pumped conditions, at a test site in the Berkshire Chalk aquifer in the southern UK. The ultimate aim of the work is to use measurements of SP, in conjunction with borehole data, to characterize groundwater flow and aquifer properties. Laboratory measurements yield a value of the streaming potential coupling coefficient of –60 ± 4 mV MPa –1 and a corresponding zeta potential of –13 ± 1 mV. A negative zeta potential contrasts with previous published open-system measurements on artificial calcite, and may reflect the presence of organic material in the natural chalk samples or HCO 3 and SO 4 ions in the groundwater. Field measurements at ambient conditions show temporal variations in SP consistent with flow processes within the aquifer, but no coherent spatial variations. Measurements during water abstraction demonstrate that voltages at the ground surface and in monitoring boreholes become more positive during pressure drawdown and more negative during pressure build-up, consistent with the negative values of streaming potential coupling coefficient and zeta potential observed in the laboratory. Moreover, the magnitude of the change in voltage is similar to that estimated using the laboratory value of the coupling coefficient. Our results suggest that measurements of SP may make a valuable contribution to characterizing groundwater flow in the UK Chalk aquifer.

Description: The pyroclastic aggregate concrete of Trajan’s Markets (110 CE), now Museo Fori Imperiali in Rome, has absorbed energy from seismic ground shaking and long-term foundation settlement for nearly two millenia while remaining largely intact at the structural scale. The scientific basis of this exceptional service record is explored through computed...

Description: Mantle-derived basaltic sills emplaced in the lower crust provide a mechanism for the generation of evolved magmas in deep crustal hot zones (DCHZ). This study uses numerical modelling to characterize the time required for evolved magma formation, the depth and temperature at which magma formation occurs, and the composition of the magma. The lower crust is assumed to comprise amphibolite. In an extension of previous DCHZ models, the new model couples heat transfer during the repetitive emplacement of sills with mass transfer via buoyancy-driven melt segregation along grain boundaries. The results shed light on the dynamics of DCHZ development and evolution. The DCHZ comprises a mush of crystals plus interstitial melt, except when a new influx of basaltic magma yields a short-lived (20–200 years) reservoir of melt plus suspended crystals (magma). Melt segregation and accumulation within the mush yields two contrasting modes of evolved magma formation, which operate over timescales of c . 10 kyr–1 Myr, depending upon emplacement rate and style. In one, favoured by emplacement via over-accretion, or emplacement at high rates, evolved magma forms in the crust overlying the intruded basalt sills, and is composed of crustal partial melt, and residual melt that has migrated upwards out of the crystallizing basalt. In the other, favoured by emplacement via under- or intra-accretion, or by emplacement at lower rates, evolved magma forms in the intruded basalt, and the resulting magma is composed primarily of residual melt. In all cases, the upward migration of buoyant melt yields cooler and more evolved magmas, which are broadly granitic in composition. Chemical differentiation is therefore driven by melt migration, because the melt migrates through, and chemically equilibrates with, partially molten rock at progressively lower temperatures. Crustal assimilation occurs during partial melting, and mixing of crustal and residual melt occurs when residual melt migrates into the partially molten crust, yielding chemical signatures indicative of a mixed crustal and mantle origin. However, residual melt is volumetrically more significant than crustal melt, except at the highest emplacement rates. Contamination of crustal melt by residual melt from basalt crystallization appears to be an inevitable consequence of melt segregation in DCHZ, and can explain the mixed crust–mantle origin of many granites.

Description: We present a surface-based approach to reservoir model construction in which all geological heterogeneity, whether structural, stratigraphic, sedimentological or diagenetic, that impacts on the spatial distribution of petrophysical properties is modelled as one or more discrete volumes bounded by surfaces. The modelled surfaces can be deterministically interpolated between control lines or points, or incorporate a stochastic element where control data are sparse. Models constructed from surfaces are not constrained by an underlying grid; indeed, the model is generated without reference to a grid. The only difference between ‘geological’ and ‘simulation’ models is that the latter incorporates a grid or mesh to allow numerical solution of the governing flow equations, the architecture of which is driven by the architecture of the modelled surfaces. This approach to gridding (or meshing) is directly compatible with the next generation of unstructured-mesh simulators, and allows the capabilities of the latter to be utilized fully in the modelling of complex reservoir architectures. A surface-based approach to model construction may facilitate a step change in reservoir modelling capabilities: once the requirement to upscale geological models to a structured simulation grid is removed, there is no need to build geological models that are restricted by grid resolution.

Description: It is well known that heterogeneities in carbonate reservoirs impact fluid flow during production. However, few studies have examined the impact of the same heterogeneities on flow behaviour with different fluid properties and production scenarios. We use integrated flow simulation and experimental design techniques to investigate the relative, first-order impact of stratigraphic and sedimentological heterogeneities on simulated recovery in carbonate ramp reservoirs. Two production strategies are compared, which promote dominance of either horizontal or vertical flow. We find that the modelled geology is more important than the simulated fluid properties and production scenarios over the ranges tested. Of the heterogeneities modelled here, rock properties and stratigraphic heterogeneities that control reservoir architecture and the spatial distribution of environment of deposition (EOD) belts are important controls on recovery regardless of the production strategy. The presence of cemented hardground surfaces becomes the key control on oil recovery in displacements dominated by vertical flow. Permeability anisotropy is of low importance for all production strategies. The impacts of stratigraphic heterogeneities on recovery factor and water breakthrough are more strongly influenced by fluid properties and well spacing in displacements dominated by vertical flow. These results help to streamline the reservoir modelling process, by identifying key heterogeneities, and to optimize production strategies.