Hasil untuk "Petrology"

Xiaodong Zhao, Xiao Zhang, Qingwen Zhong et al.

Abstract The compressive torsion (C-T) fractures are widely distributed in water-saturated, clay-poor, and cementation-weak Cretaceous sandstones in Western China due to asymmetric tectonic convergence. The formation of these fractures significantly depends on the characteristics of sandstones, particularly the dynamics of sandstone physics induced by water entry and its timing. This study prepared synthetic sandstones possessing main hydro-mechanical characteristics of natural sandstones by establishing dual intergranular cementation while retaining free grains, overcoming the challenges of natural core sampling and single-variable test implementing. Furthermore, a mode with passive control of principal stresses was proposed to simulate the load boundaries for fracture formation. Through a series of tests under various water conditions, C-T paths and pressure levels, combined with real-time X-ray CT observations, it was found that a selection of low pressures and C-T paths capable of achieving low peak normalized generalized shear stress facilitates the reproduction of penetrated C-T fractures within synthetic specimens. The C-T path influences strength characteristics before fracture penetration by governing microcrack evolution derived from principal stress axis rotation, where the maximum rotation angle determines the inclination angle of the penetrated fracture. Whereas timing of pore water pressure enhances the complexity of the C-T fracture system by altering the specimen’s pore structure. These findings provide insights for clarifying the physical mechanisms of C-T fracture formation.

Kokorina, Tatyana A., Gon, Ruslan T.

This study presents, for the first time, a comprehensive typological classification and mapping of the littoral landscapes in the eastern part of Salmon Bay (Aniva Bay, the Sea of Okhotsk, southern coast of Sakhalin Island), using methods of underwater landscape (bentema) typology developed for the Sea of Japan (according B.V. Preobrazhensky et al.). The research utilized data collected in the intertidal zone, which provided a representative sampling of relief forms, substrate types and skeletal content, as well as the state of the macrobenthos. Seven main types of bentema are described: metagest, skatebra, fractum, segetium, arenoid, peltium, and saxosium. For each landscape type, key morphological, granulometric, and biotic parameters are provided, as well as the main edificators and characteristic species. The study found that traces of organism activity (vestigial features) contribute to a more accurate determination of landscape boundaries. The results demonstrate the possibility of adapting the sublittoral bentema typology to the littoral zone and confirm its effectiveness for the recognition and structurally mapping of the dynamic coastal ecosystems. The classification system, which integrates physicogeographical and biotic parameters, can be used to monitor the state of coastal ecosystems and conduct comparative studies in coastal waters, as well as to objectively map the landscapes of the littoral.

Martin Bizzarro, Martin Schiller, Jesper Holst et al.

Abstract Planetary materials show systematic variations in their nucleosynthetic isotope compositions that resonate with orbital distance. The origin of this pattern remains debated, limiting how these isotopic signatures can be used to trace the precursors of terrestrial planets. Here we test the hypothesis that interstellar ices carried supernova-produced nuclides by searching for a supernova nucleosynthetic fingerprint in aqueous alteration minerals from carbonaceous and non-carbonaceous chondrite meteorites. We focus on zirconium, a refractory element that includes the neutron-rich isotope 96Zr formed in core-collapse supernovae. Leaching experiments reveal extreme 96Zr enrichments in alteration minerals, showing that they incorporated supernova material hosted in interstellar ices. We show that the Solar System’s zirconium isotope variability reflects mixing between these ices and an ice-free rocky component. Finally, the presence of supernova nuclides in a volatile carrier supports models where the Solar System’s nucleosynthetic variability was imparted by thermal processing of material in the protoplanetary disk and during planetary accretion.

Yajie Zhao, Xin Deng, Wenzhong Wang et al.

Abstract Seismological studies have previously detected abundant scatterers in the lower mantle, potentially linked to long-term slab subduction, and petrology studies suggest carbonates can be sequestrated within the oceanic crust and transported into the lower mantle via subduction. Here, we report ab initio calculations of elastic properties of calcium carbonate within various structures at lower-mantle conditions, as well as phase boundary between different calcium carbonate phases. Combining our results with previous data, we derived the density and wave velocities of carbonated oceanic crust, considering the possible reactions between carbonates and silicates. Our results suggest calcium carbonate high-pressure phases exhibit much lower density and wave velocities than other lower-mantle minerals. However, the moderately carbonated oceanic crust still displays positive wave velocity anomalies in the lower mantle, except at mid-mantle depths. Besides, the carbonated oceanic crust reaches similar shear wave velocity to the surrounding mantle at ~1100 km depth, which could explain the scarcity of seismic scatterers at this depth.

Guangyong SONG, Zhanguo LIU, Yanqing WANG et al.

The saline lacustrine hybrid sedimentary rocks are complex in lithology and unknown for their sedimentary mechanisms. The hybrid sedimentary rocks samples from the Neogene upper Ganchaigou Formation to lower Youshashan Formation (N1–N21) in the Fengxi area Qaidam Basin, were investigated through core-log and petrology-geochemistry cross-analysis by using the core, casting thin section, scanning electron microscope, X-ray diffraction, logging, and carbon/oxygen isotopic data. The hybrid sedimentary rocks in the Fengxi area, including terrigenous clastic rock and lacustrine carbonate rock, were deposited in a shallow lake environment far from the source, or occasionally in a semi-deep lake environment, with 5 lithofacies types and 6 microfacies types recognized. Stable carbon and oxygen isotopic compositions reveal that the formation of sedimentary cycles is controlled by a climate-driven compensation-undercompensation cyclic mechanism. A sedimentary cycle model of hybrid sedimentary rocks in an arid and saline setting is proposed. According to this model, in the compensation period, the lake level rises sharply, and microfacies such as mud flat, sand-mud flat and beach are developed, with physical subsidence as the dominant sedimentary mechanism; in the undercompensation period, the lake level falls slowly, and microfacies such as lime-mud flat, lime-dolomite flat and algal mound/mat are developed, with chemical-biological process as the dominant sedimentary mechanism. In the saline lacustrine sedimentary system, lacustrine carbonate rock is mainly formed along with regression, the facies change is not interpreted by the accommodation believed traditionally, but controlled by the temporary fluctuation of lake water chemistry caused by climate change. The research results update the interpreted high-resolution sequence model and genesis of hybrid sedimentary rocks in the saline lacustrine basin and provide a valuable guidance for exploring unconventional hydrocarbons of saline lacustrine facies.

Geoffrey A Lerner, Claus Siebe, Israel Ramírez-Uribe et al.

The Holocene La Taza andesitic volcano is one of over 1000 volcanic centers located within the Michoacán-Guanajuato Volcanic Field (MGVF) in central-western Mexico. La Taza (~8500–8200 yr BP) represents one possible eruption style within the field, with deposits indicating Strombolian activity followed by a series of lava flows. In our study, we reconstruct the eruption of La Taza through a combination of LiDAR mapping and petrological and geochemical analyses. LiDAR mapping combined with ground- truthing in the field allowed us to differentiate and determine the sequence of the volcano’s lava flows, revealing seven lava flows with a volume of ~0.6 km3. This morphological information was paired with geothermobarometers to estimate lava flow viscosities, mean effusion rates, and emplacement times, showing a likely duration of 1.1–4.3 years. Recreating this eruption contributes to the understanding of potential durations and lava flow rheology of future MGVF eruptions, crucial characteristics for hazard planning and mitigation.

S.G. Dhanil Dev, E. Shaji, M. Santosh et al.

Charnockites constitute the major rock type in the crustal blocks of Southern Granulite Terrain (SGT) in India. Here we present petrology, mineral chemistry, and geochemistry of the oldest charnockites in the SGT from the Coorg Block. The charnockites from this block are dominantly composed of orthopyroxene, clinopyroxene, hornblende, biotite, K-feldspar, plagioclase, ilmenite, and minor garnet. Geochemical features of the charnockites indicate granitic to granodioritic protolith. In terms of aluminum saturation index, these rocks are metaluminous and represent magnesian, calc-alkaline to calcic series similar to fractionated I-type granites. They are characterized by high Mg#, enrichment of L.I.L.E. (Rb, Ba, Th, and K) and LREE (La, Ce, Nd), depletion of HFSE (Nb, Ta, Zr, Sr, P, and Ti), typical of volcanic arc granitoid. Their geochemical characteristics are consistent with crystal fractionation of the parental magma and chemically evolved magma. Mineral chemistry of orthopyroxene shows the trend of igneous pyroxene. The rocks were subjected to granulite facies metamorphism with estimated pressure-temperature conditions of 760–800 °C and 7.1–8.4 kbar. The Coorg charnockites represent vestiges of Mesoarchean arc magmatism and crust building.

D. Basualto, D. Basualto, A. Tassara et al.

<p>High-silica explosive eruptions are one of the most dangerous natural phenomena, yet it is unclear which processes are involved in this infrequent kind of event. We present the first systematic characterization of near-field seismicity associated with a large high-silica eruption analyzing data recorded before, during and after the 4 June 2011 rhyolitic eruption of Puyehue–Cordón Caulle Volcanic Complex (PCCVC). Results of a first-level data processing, developed by the Southern Andean Volcano Observatory (OVDAS) to monitor unrest and the evolution of the eruption, are complemented here with the relocation of hypocenters into a local 1D velocity model, the time series of the <span class="inline-formula"><i>b</i></span> value and the computation of the focal mechanism. This information allows us to define several phases before and after the onset of the eruption, describing details of the space–time evolution of seismicity, defining and characterizing the seismic sources, and identifying the structural control of the magmatic intrusion and stress variations during the eruption. Our results illuminate several underlying processes, with emphasis on the possible role that basement structures had on the storage, transport and evacuation of magma. Integrating our results with previous findings based on satellite geodesy and petrology of erupted materials, we discuss general conceptual models regarding destabilization of structurally controlled acidic magmatic systems, the pass from unrest to eruption, and changes in eruptive style and waning phases of eruptions, with broader implications for monitoring and forecast of violent silicic eruptions.</p>

C. P. B. Fernandes, W. P. Coutinho, J. W. L. Silva et al.

Abstract Over the past decades, directional drilling has continuously advanced to increase hydrocarbon recovery by effectively targeting high-productivity reservoirs. However, many existing approaches primarily focus on heuristic optimization algorithms. Moreover, existing models often neglect the incorporation of petrophysical attributes that can significantly impact the selection of production targets, such as the reservoir quality indicator. This article introduces a novel application of mixed-integer programming to define directional drilling paths, considering practical aspects of interest. The paths are subject to drift angle constraints and reference coordinates that align with the optimal reservoir targets. Such targets are identified using the authors’ proposed technique of maximum closeness centrality and the geologic model of hydraulic flow units. In order to evaluate the effectiveness of this approach, a realistic model of the Campos Basin in Brazil is studied. The results reveal that the highest recovery factors obtained with the proposed methodology (17%) exceed the historical average recovery factor of the studied reservoir (15.66%). We believe this study can contribute to the ongoing efforts to enhance directional drilling and maximize the production potential of offshore oil and gas reservoirs.

Mahjoub Himi, Mickel Anton, Alex Sendrós et al.

Geophysical surveys are a noninvasive reliable tool to improve geological models without requiring extensive in situ borehole campaigns. The usage of seismic refraction tomography (SRT), electrical resistivity tomography (ERT) and borehole data for calibrating is very appropriate to define landslide body geometries; however, it is still only used occasionally. We present here the case of a Spanish Pyrenees slow-moving landslide, where ERT, SRT and lithological log data were integrated to obtain a geological three-dimensional model. The high contrasts of P-wave velocity and electrical resistivity values of the upper materials (colluvial debris and clayey siltstone) provided accurate information on the geometry of the materials involved in the landslide body, as well as the sliding surface. Geophysical prospecting allowed us to identify the critical sliding surface over a large area and at a reduced cost and, therefore, gives the geophysical method an advantage over borehole data. The three-dimensional model was used to carry out stability analyses of a landslide in 2D and 3D, which, coherently with previous studies, reveal that the lower part is more unstable than the upper units.

Oluwasanmi Olabode, Sunday Isehunwa, Oyinkepreye Orodu et al.

Abstract Thin oil rim reservoirs are predominantly those with pay thickness of less than 100 ft. Oil production challenges arise due to the nature of the gas cap and aquifer in such reservoirs and well placement with respect to the fluid contacts. Case studies of oil rim reservoir and operational properties from the Niger-Delta region are used to build classic synthetic oil rim models with different reservoir parameters using a design of experiment. The black oil simulation model of the ECLIPSE software is activated with additional reservoir properties and subsequently initialized to estimate initial oil and gas in place. To optimize hydrocarbon production, 2 horizontal wells are initiated, each to concurrently produce oil and gas. Well placements of (0.5 ft., 0.25 ft. and 0.75 ft.) are made with respect to the pay thickness and then to the fluid contacts. The results show that for oil rim with bigger aquifers, an oil recovery of 8.3% is expected when horizontal wells are placed at 0.75 ft. of the pay thickness away from the gas oil contact, 8.1% oil recovery in oil rims with larger gas caps with completions at 0.75 ft. of the pay zone from the gas oil contacts, 6% oil recovery with relatively small gas caps and aquifer and 9.3% from oil rims with large gas caps and aquifers, with completions at mid-stream of the pay zone.

Shakhawat Hossain

Abstract Seismic attributes can be important predictors, either qualitative or quantitative, of reservoir geometries when they are correctly used in reservoir characterization studies. This paper discusses seismic attribute analyses and their usefulness in seismic geomorphology study of Moragot field of Pattani Basin, Gulf of Thailand. Early to Middle Miocene fluvial channel and overbank sands are the reservoirs in Pattani Basin. Due to their limited horizontal and vertical distribution, it is not always possible to predict the geometry and distribution of these sands based on the conventional seismic interpretation. This study utilized various seismic attributes, e.g., RMS amplitude analysis, spectral decomposition, semblance and dip-steered similarity, RGB blending to image the geometry and the spatial distribution of sand bodies in horizon and stratal slices at different stratigraphic intervals. Attribute analyses reveal, at shallow stratigraphic levels, RMS and semblance can successfully identify channel-shaped sand bodies and mud-filled channels associated with channel belts. On the other hand in deeper stratigraphic intervals, sand distribution can be imaged more effectively by using spectral decomposition and dip-steered similarity volumes. High-frequency spectral decomposition slices can image thin sands, and low-frequency slices can image thick sands quite effectively in deeper intervals. RGB blending of different frequency slices is particularly useful in delineating channel systems of various dimensions at deeper intervals. These images show the distribution of sands and mud-filled channels at various stratigraphic levels. The width of channel belts varies from 200 m to 3 km. These channel belts are N–S or NW–SE oriented. From the channel pattern and their dimensions, depositional environments can be predicted. Mud-filled channels identified in the horizon slices will act as a connectivity barrier between sand bodies at either side of the channel. They can also act as lateral and up-dip seal to form stratigraphic traps. The seismic attribute analyses clearly show the geometry and spatial distribution of sand bodies. Hence, this method for predicting sand body geometry might help in field development planning as well as in reducing exploration risk.

Csibri Tamás, Rybár Samuel, Šarinová Katarína et al.

The Blatné Depression located in the NW part of the Danube Basin represents the northernmost sub-basins of the Pannonian Basin System. Its subsidence is associated with oblique collision of the Central Western Carpathians with the European platform, followed by the back-arc basin rifting stage in the Pannonian domain. The conglomerates recognized in the Cífer-2 well document the latest Burdigalian–early Langhian deposition in fan delta lobes situated above the footwall and hanging wall of a WSW–ENE trending fault system, the activity of which preceded the opening of the late Langhian–Serravallian accommodation space with a NE–SW direction. The provenance area of the “Cífer conglomerate” was linked to the Tatric Super-unit complexes. Similar rocks crop out in the southern part of the Malé Karpaty Mts. and are also present in the pre-Cenozoic basement of the Danube Basin. Documented extensive erosion of the crystalline basement and its sedimentary cover lasted until the early/middle Miocene boundary. The “Cífer conglomerate” has distinct clast composition. The basal part consists of poorly sorted conglomerate with sub-angular clasts of metamorphic rocks. Toward the overlying strata, the clasts consist of poorly sorted conglomerates with sub-rounded to well-rounded carbonates and granitoids. The uppermost part consists of poorly sorted conglomerates with sub-rounded to rounded clasts of carbonate, granitoid and metamorphic rock. Within the studied samples a transition from clast to matrix supported conglomerates was observed.

Yusef Vesali, Darush Esmaeili, Fatemeh Sepidbar et al.

The Jalal Abad region lies within the southern sector of Posht Badam block near to Jalal Abad, Najaf Abad iron deposits. In this region, several mafic intrusions and associated dyke and sills were intruded within the volcano-sedimentary unit of Rizu series and magnetite veins producing a narrow contact metamorphic aureole and overlain by Desu Series dolomites. These intrusion massives include irregular coarse- grained gabbro- diorites stocks and several NW-SE-trending basaltic dykes and sills. Petrographical and geochemical studies on the Jalal Abad mafic units reveal that they are alkaline in nature and based on the tectonic discrimination diagrams are grouped in alkaline basalts field of the intra-continental rift setting. They display LREE enrichment and HREE depletion, and significant enrichment in LILE in comparison to HFSE and HREE. Compositionally, they resemble modern OIB and the Hawaiian alkaline basalts. Magmas of these OIB-type and alkaline rock associations formed from partial melting of garnet- lherzolite facieses in the plume source, during the rift-drift and seafloor spreading evolution of the Proto-Tethys oceanic lithosphere during the Ordovician through Silurian periods.

Abdullah S. Sultan

Abstract Emulsification has been widely used in the oil industry. The thermal stability of emulsified systems, such as emulsified gels or acids, is critical for the placement success of the emulsified system. Early separation of the system in a tubular well leads to corrosion. In the present study, the stability of emulsified polyacrylamide/polyethylenimine (PAM/PEI) gels is investigated in high-temperature and high-salinity (HTHS) environments. The influences of different parameters such as surfactant concentration, water–oil ratio, salinity, intensity of mixing and temperature on the droplet size and the emulsion thermal stability are studied. The droplet size of the PAM/PEI system, which is emulsified in diesel, decreases, and the separation time increases with increasing mixing speed, surfactant concentration, and salinity. The emulsions with smaller droplets are thermally stable compared with large droplets since the rate of droplet coalescence is low. The effect of emulsion stability on gelation kinetics and gel strength is investigated. The emulsification reduces both the gel strength and the gelation rate. The cross-linking (gelation) rate in the unemulsified PAM/PEI is almost ten times higher than that in the emulsified gels. This gelation process is slow in the case of stable emulsified PAM/PEI solution and is believed to be the result of limited heat and mass transfer. The emulsion stability achieved in this work adds to the current understanding of how to control emulsion stability through different parameters to withstand HTHS environments and how this stability influences the gelation process.

E. M. Ruidiaz, A. Winter, O. V. Trevisan

Abstract Enhanced oil recovery in carbonates due to wettability alteration has received much attention recently. In contrast to sandstones reservoirs, carbonates are neutral-wet or preferentially oil-wet. The use of CO2 dissolved into water has emerged as an alternative method for EOR operations in carbonates reservoirs. In the present paper, oil recovery from two carbonate outcrop rocks was evaluated with different brines containing CO2. The evaluation included a qualitative approach by spontaneous imbibition tests and a quantitative assessment by the Amott–Harvey index. The rocks tested were limestone and dolomite samples known as analogous to Brazilian pre-salt reservoirs. The testing fluids were a medium gravity crude oil, seawater concentration brine, formation equivalent brine and the carbonated version of these brines. Results shown additional oil recovery directly associated with wettability alteration driven by brine concentration switches. Oil recovery increases were observed independently if the brine concentration decreased or increased over the water replacement process. Wettability alteration took place in both carbonate types starting at oil-wet to neutral-wet conditions. Similar tests carried out with equivalent carbonated brines showed similar alterations in the wetting properties, trending no dependence on salt concentration. However, CO2 and its derived ions dissolved in the brines seem to inhibit the wettability alteration mechanism.

Barbara Grillo, Carla Braitenberg, Roberto Devoti et al.

We propose an interdisciplinary study of karstic aquifers using tiltmeters and GPS observations. The study region is located in northeastern Italy, in the seismic area of the Cansiglio Plateau. The Zöllner type Marussi tiltmeters are installed in a natural cavity (Bus de la Genziana) that is part of an interesting karstic area of particular hydrogeologic importance. The Livenza river forms from a number of springs at the foothills of the karstic massif and flows throughthe Friuli-Veneto plain into the Adriatic Sea. Comparing the tiltmeter signal recorded at the Genziana station withthe local pluviometrical series and the hydrometric series of the Livenza river, a clear correlation is recognized. Moreover, the data of a permanent GPS station located on the southern slopes of the Cansiglio Massif (CANV) show also a clear correspondence withthe water runoff. Here we present the hydrologic induced deformations as observed by tiltmeter and GPS. After heavy rain events we record rapid deformations bothby tiltmeters and GPS corresponding to the rainfall duration. In the following days a slow geodetic motion recovers the accumulated deformation witha distinctive pattern bothin tilt and GPS data, whichcorrelates withthe runoff of the karstic aquifer. The purpose of this researchis to open a new multidisciplinary frontier between geodetic and karstic systems studies to improve the knowledge of the underground fluid flow circulation in karstic areas. Furthermore a better characterization of the hydrologic effects on GPS and tilt observations will have the benefit that these signals can be corrected when the focus of the study is to recover the tectonic deformation.

Franci Gabrovšek

Vin Davis, Rob Ixer

The Wong Tei Tung archaeological site was discovered in 2003. Two periods have been proposed: an earlier period dating to around 40,000 years bp, and a later period dating to around 7000 years bp, but these dates should be treated cautiously. Initially, reported research found a few traits of the Wong Tei Tung assemblage to be similar to South-east Asia lithics, especially the short axe and Sumatralith cores. It has been reported that the Wong Tei Tung assemblage is a lithic cluster of certain 'techno-complex' implements rather than an archaeological culture; it offers a glimpse of lithic manufacturing in adaptation to its particular coastal environment. The published evidence points to a production of stone tools that considerably exceeded anticipated immediate local need. It is likely, therefore, that products from the site were distributed widely across the Zhujiang Estuary (Pearl River) area and beyond (Fig. 1: map). This article presents the results of initial investigations into the geological setting of the site; provides new petrographic descriptions using data obtained from thin sections and geochemical analyses; and makes tentative comparisons with similar archaeological stone tool manufacturing sites in Britain.

Stanislav Južnič

Karel Dežman’s research of the karst phenomena was examined. Among his works the cave research, description of Proteus, other cave animals and plants were found. A special concern was put on Dežman’s sources dealing with Proteus research. As the custodian of the Land Museum of Ljubljana, Dežman promoted the Ljubljanian natural history research of his time. His scientific works are not very well known because he did not follow the political line of the official Slovenian national representatives.