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AbstractThe Olorgesailie Formation (1.2–0.49 Ma) consists of fluvial and lacustrine rift sediments that have yielded abundant Acheulean artifacts and a fossil hominin (Homo cf. erectus). In testing prior understandings of the paleoenvironmental context, we define nine new geochemical zones. A Chemical Index of Alteration suggests increased catchment weathering during deposition of Members 1, 2, 7, 11, and 13. Biophile elements (Br, S) peak in M8–9 and lower M13 possibly reflecting increased input from soil erosion. REE data show that the Magadi Trachytes supplied most siliciclastic grains. Sixteen diatom stages indicate conductivities of 200–16,000 μS cm− 1 and pH of 7.5–9.5 for five deep-water lakes, ten shallow lakes and sixteen wetlands. These results are compared with diatom data from other sections in the basin and show aquatic spatial variability over km-scale distances. Similar floras are traceable over several kilometers for M2, M3 and M9, indicating broadly homogeneous lacustrine conditions during these times, but diatoms in other members imply variable conditions, some related to local tectonic controls. This lateral and temporal variability emphasizes the importance of carrying out stratigraphic sampling at multiple sites within a basin in efforts to define the environmental context relevant to human evolution.

Abstract Thermal-Solvent Assisted Gravity Drainage processes are heavy oil recovery processes in which the stimulation mechanism for bitumen viscosity reduction is by heating and dilution. The range of the injected solvent concentration with steam may be low such as in Solvent Assisted-SAGD or very high such as in Heated Vapour Extraction. The performance behaviour of these processes is significantly driven by the complex thermodynamic interaction of steam and solvent, heat transfer, multiphase fluid equilibrium and flow in the porous medium. ExxonMobil and its affiliate Imperial have been optimizing the existing recovery processes and developing new technologies to improve the efficiencies and environmental performance of the heavy oil production operations. Recent focus has been on developing thermal-solvent based recovery processes through an integrated research program that includes fundamental laboratory work, advanced numerical simulation studies, laboratory scaled physical modeling, and field piloting. The research program aims at in-depth investigation and understanding of process physics and mechanisms, and evaluating process performance and behaviour to enable development of new recovery methods and to enhance the performance. This paper focuses on the fundamental concepts of Azeotropic Heated Vapour Extraction, a new thermal solvent recovery technology developed by ExxonMobil-Imperial. This technology takes the combined advantages of the solvent dilution mechanism for enhanced oil production rate with the minimum required energy (GHG emission), as well as the effectiveness of energy transport of steam to minimize the required solvent in circulation for the extraction process. In this paper, the complex solvent-steam phase behaviour and reservoir fluid flow and their interaction under operating conditions are investigated. The analysis of experimental and modeling data shows that the injection of solvent-steam mixture at its azeotropic condition results in significant improvement in process key performance indicators (KPI's). At these conditions, the reservoir is heated to the minimum boiling temperature of the solvent-steam mixture compared to a Heated VAPEX or Solvent Assisted-SAGD process resulting in the reduction of the required energy thereby minimizing the solvent-to-oil ratio. Also, due to phase equilibrium, the vaporization of in-situ water is prevented resulting in the reduction of retained solvent in the depleted zone of the reservoir. It is found that an improvement in the process KPI's is dependent on the volatility of the selected solvent. The process KPI's also vary with operational conditions. The recovery process is optimized for certain reservoir constraints through the selection of the solvent boiling range and consequently the azeotropic steam content in the injected mixture.

article i nfo This study utilizes geomorphology, marine sediment data, environmental reconstructions and the Gorham's Cave occupational record during the Middle to Upper Paleolithic transition to illustrate the impacts of climate changes on human population dynamics in the Western Mediterranean. Geomorphologic evolution has been dated and appears to be driven primarily by coastal dune systems, sea-level changes and seismo-tectonic evolution. Continental and marine records are well correlated and used to interpret the Gorham's Cave sequence. Specific focus is given to the three hiatus sections found in Gorham's Cave during Heinrich periods 4, 3 and 2. These time intervals are compared with a wide range of regional geomorphologic, climatic, paleoseismic, faunal and archeological records. Our data compilations indicate that climatic and local geo- morphologic changes explain the Homo sapiens spp. occupational hiatuses during Heinrich periods 4 and 3. The last hiatus corresponds to the replacement of Homo neanderthalensis by H. sapiens. Records of dated cave openings, slope breccias and stalactite falls suggest that marked geomorphologic changes, seismic activ- ity and ecological perturbations occurred during the period when Homo replacement took place.

The complete set of 21 elastic stiffnesses of a composite material are found from ultrasonic measurements of the phase velocity anisotropy. Quasi‐P and quasi‐S wave phase speeds at a variety of incident angles within a number of differing planes through the material are obtained using the τ‐p plane wave decomposition technique. The 779 individual phase velocities were inverted, under no a priori presumptions about the symmetry or orientation of the material, to provide all the stiffnesses. These show that the material has nearly orthorhombic symmetry, as is expected from its texture. This orthorhombic character was further apparent in a number of bootstrap tests of the inversion that assumed differing levels of symmetry from triclinic to orthorhombic and using various subsets of the measured phase velocities. However, the present analysis does not account for the effects of wave speed dispersion evident in the observed waveforms. This dispersion is particularly severe for the in‐plane q‐S polarization and is possibly a consequence of the fine‐layered structure of the material.

Abstract Performance predictions made by reservoir simulators are highly dependent on experimentally-determined relative permeability data assigned to simulation grid cells. There is often no apparent relationship between this type of data and a quantifiable property of cells, meaning that samples within a group of neighboring relative permeability curves do not have similar values of a common characterization property. On the other hand, it is easier to correlate primary drainage capillary pressure data to cell properties and create a petrophysical static rock type (PSRT) from a group of similar capillary pressure data. The common approach is to average the relative permeability data corresponding to each PSRT and input that into a simulator. In practice, relative permeability curves corresponding to a given PSRT would exhibit a significant scatter, especially in carbonate formations. This will cause the resulting average relative permeability data to be highly uncertain and poorly representative of true dynamic behavior of the cells. In this study, a new technique is proposed to reduce uncertainties associated with classical methods of assigning relative permeability data to grid cells of a simulation model. The idea is based on a robust and universal criterion for characterization of dynamic characteristics of rocks from laboratory-derived flow data to define a petrophysical dynamic rock type (PDRT). A PDRT is defined as a collection of rocks with similar True Effective Mobility (TEM) behavior. A TEM-function for analysis of relative permeability is defined as a product of relative mobility by the square of a mean pore radius, and is analogous to the well-known J-function for scaling capillary pressure curves. For a given PDRT, a special weighted average of corresponding relative permeability data, or average TEM data should be used as input to a simulator. In the latter case, the simulator should have the capability to back-calculate cells’ quasi-relative permeabilities using the inputted average TEM data. Moreover, we show that factors such as wettability and pore-scale heterogeneity can cause phase-dependent dynamic characteristics (i.e., different dynamics with respect to each fluid phase). Hence, different dynamic rock typing schemes should be applied to the flow of each fluid in system. A structured methodology is presented to identify PDRTs using TEM-function and prepare input parameters to simulators by analyzing relative permeabilities using the universal criterion developed in this work. Ultimately, special core analysis data from the Asmari Formation, a carbonate reservoir from one of the Iranian Fields, is used to verify and demonstrate the applicability of the presented technique.

Abstract Grenvillian (1.2 to 1.0 Ga) plutonic rocks in northern Virginia preserve evidence of episodic, mostly granitic magmatism that spanned more than 150 million years (m.y.) of crustal reworking. Crystallization ages determined by sensitive high resolution ion microprobe (SHRIMP) U–Pb isotopic analyses of zircon and monazite, combined with results from previous studies, define three periods of magmatic activity at 1183–1144 Ma (Magmatic Interval I), 1120–1111 Ma (Magmatic Interval II), and 1078–1028 Ma (Magmatic Interval III). Magmatic activity produced dominantly tholeiitic plutons composed of (1) low-silica charnockite, (2) leucogranite, (3) non-leucocratic granitoid (with or without orthopyroxene (opx)), and (4) intermediate biotite-rich granitoid. Field, petrologic, geochemical, and geochronologic data indicate that charnockite and non-charnockitic granitoids were closely associated in both space and time, indicating that presence of opx is related to magmatic conditions, not metamorphic grade. Geochemical and Nd isotopic data, combined with results from experimental studies, indicate that leucogranites (Magmatic Intervals I and III) and non-leucocratic granitoids (Magmatic Intervals I and II) were derived from parental magmas produced by either a high degree of partial melting of isotopically evolved tonalitic sources or less advanced partial melting of dominantly tonalitic sources that also included a more mafic component. Post-orogenic, circa 1050 Ma low-silica charnockite is characterized by A-type compositional affinity including high FeOt/(FeOt + MgO), Ga/Al, Zr, Nb, Y, and Zn, and was derived from parental magmas produced by partial melting of potassic mafic sources in the lower crust. Linear geochemical trends defined by leucogranites, low-silica charnockite, and biotite-rich monzogranite emplaced during Magmatic Interval III reflect differences in source-related characteristics; these features do not represent an igneous fractionation sequence. A compositional gap between circa 1160 Ma magnesian low-silica charnockite and penecontemporaneous higher silica lithologies likewise precludes a fractionation relationship among plutons intruded during Magmatic Interval I. Correspondence in timing of magmatic activity between the Blue Ridge and neighboring Mesoproterozoic terranes underscores the widespread nature of Grenvillian processes in the region.

AbstractHolocene paleosea-level data for Fiji, represented by 77 dates and emergence magnitudes, are presented, screened, and adjusted. Most data are from coral microatolls, potentially the most precise paleosea-level indicators in this region. Holocene sea-level changes are reconstructed for five areas within Fiji known to have had different late Quaternary tectonic histories. Resulting analysis suggests that postglacial sea level in Fiji reached its present level more than 6900 14C yr B.P. It also suggests either that a single maximum 5650–3200 14C yr B.P. (perhaps +2.19 m but more likely +1.35–1.50 m) occurred or that two maxima occurred 6100–4550 14C yr B.P. (+0.75–1.85 m) and 3590–2800 14C yr B.P. (+0.90–2.46 m). Broad agreement exists between these empirical sea-level reconstructions and those derived theoretically using the ICE-4G model (predicted maximum ∼4000 14C yr B.P.; ∼+2.1 m). This suggests that both methods of reconstructing Holocene sea-level changes are valid, as are the assumptions underpinning the ICE-4G model. The most important of these, that eustatic sea level had effectively stopped rising by late middle-Holocene time (5000–4000 yr B.P.), is confirmed by observations from Fiji.

ABSTRACTElectrical resistivity imaging has been successfully used to monitor near‐surface hydrologic processes but use of standard measurement arrays may not provide the greatest data sensitivity to the imaged region. We present a method of experimental design based on the concept of informed imaging for creating an electrical resistivity imaging experiment to monitor flow beneath a recharge pond. Informed imaging is the integration of all available data about a site into the acquisition, inversion and interpretation of electrical resistivity data. Informed experimental design uses all available information to develop an a priori model of the subsurface conductivity structure that guides the selection of measurement arrays for an electrical resistivity imaging experiment given spatial and temporal constraints on the acquisition. Selection of arrays focuses on maximizing the amount of unique information acquired with each source pair. We apply the method to the selection of arrays for imaging the top 5 m of the subsurface beneath a recharge pond in Northern California, which is part of an aquifer storage and recovery project. Decreasing infiltration rates over time reduce the effectiveness of the recharge pond. We seek to monitor infiltration processes at the contact between a fines‐rich sand layer and coarser sand layer in an effort to understand the hydrologic controls on infiltration. The performance of the arrays selected using informed experimental design relative to two standard arrays (Wenner and dipole‐dipole) is validated on two synthetic subsurface conductivity models, which are representative of conductivity structures that may arise during an infiltration event. Performance is evaluated in terms of a singular value decomposition of the sensitivity matrix produced by the three types of arrays, as well as a measure of the region of investigation. Results demonstrate that arrays selected using informed experimental design provide independent information about the imaged region and are robust in the presence of noise, improving the ability to image changes in a conductivity structure that result from infiltration processes.

Abstract North American basement and cover rocks of the Monashee complex (MC) are exposed through a tectonic window within the hinterland of the southeastern Canadian Cordillera. The complex records a history of Late Cretaceous to early Tertiary crustal thickening (F1/F2) related to emplacement of the Selkirk allochthon (SA). Part of the MC and overlying SA then formed a mid-crustal wedge that was extruded towards the foreland from the overthickened hinterland (F3, F4). Finally, the complex was exhumed by Eocene ductile and brittle extensional deformation (D5). Rocks along the studied west flank of the MC are thoroughly transposed by F1/F2 (into S2). The extent of the transposition, and a well-developed northeast-trending L2 lineation, indicate intense strain during F1/F2 throughout the studied portion of the MC (4–5 km thickness exposed) and overlying SA. Ductile flow continued, resulting in northeast-verging F3 folds in the MC, west-southwest-verging F3 folds in the SA and broad F4 warps in the MC and SA. A shear zone records significant reactivated slip on S2 during D5. Rapid exhumation of the MC is attributed to ductile flow during extrusion and extensional deformation; this ductile flow is correlated with foreland thrusting, which ended in the Early Eocene.