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Core Data (core + data)
Selected AbstractsThe Geysers geothermal field: results from shear-wave splitting analysis in a fractured reservoirGEOPHYSICAL JOURNAL INTERNATIONAL, Issue 3 2005Maya Elkibbi SUMMARY Clear shear-wave splitting (SWS) is observed in 1757 high signal-to-noise ratio microearthquake seismograms recorded by two high density seismic arrays in the NW and the SE Geysers geothermal fields in California. The Geysers reservoir rocks within the study area are largely composed of lithic, low-grade metamorphism, well-fractured metagraywackes which commonly lack schistosity, warranting the general assumption that shear-wave splitting here is induced solely by stress-aligned fracturing in an otherwise isotropic medium. The high quality of observed shear-wave splitting parameters (fast shear-wave polarization directions and time delays) and the generally good data spatial coverage provide an unprecedented opportunity to demonstrate the applicability and limitations of the shear-wave splitting approach to successfully detect fracture systems in the shallow crust based on SWS field observations from a geothermal reservoir. Results from borehole stations in the NW Geysers indicate that polarization orientations range between N and N60E; while in the SE Geysers, ground surface stations show polarization directions that are generally N5E, N35E-to-N60E, N75E-to-N85E, and N20W-to-N55W. Crack orientations obtained from observed polarization orientations are in good agreement with independent field evidence, such as cracks in geological core data, tracer tests, locally mapped fractures, and the regional tectonic setting. Time delays range typically between 8 and 40 ms km,1, indicating crack densities well within the norm of fractured reservoirs. The sizeable collection of high resolution shear-wave splitting parameters shows evidence of prevalent vertical to nearly vertical fracture patterns in The Geysers field. At some locations, however, strong variations of SWS parameters with ray azimuth and incident angle within the shear-wave window of seismic stations indicate the presence of more complex fracture patterns in the subsurface. [source] The future role of the Scandinavian anaesthesiologist: a web-based surveyACTA ANAESTHESIOLOGICA SCANDINAVICA, Issue 9 2010A. ÅNEMAN Background: The Board of the Scandinavian Society for Anaesthesiology and Intensive Care Medicine (SSAI) decided in 2008 to undertake a survey among members of the SSAI aiming at exploring some key points of training, professional activities and definitions of the specialty. Methods: A web-based questionnaire was used to capture core data on workforce demographics and working patterns together with opinions on definitions for practice/practitioners in the four areas of anaesthesia, intensive care medicine, emergency medicine and pain medicine. Results: One thousand seven hundred and four responses were lodged, representing close to half of the total SSAI membership. The majority of participants reported in excess of 10 years of professional experience in general anaesthesia and intensive care medicine as well as emergency and pain medicine. While no support for separate or secondary specialities in the four areas was reported, a majority of respondents favoured sub-specialisation or recognition of particular medical competencies, notably so for intensive care medicine. Seventy-five percent or more of the respondents supported a common framework of employment within all four areas irrespective of further specialisation. Conclusions: The future of Scandinavian anaesthesiology is likely to involve further specialisation towards particular medical competencies. With such diversification of the workforce, the majority of the respondents still acknowledge the importance of belonging to one organisational body. [source] Late Cretaceous blueschist facies metamorphism in southern Thrace (Turkey) and its geodynamic implicationsJOURNAL OF METAMORPHIC GEOLOGY, Issue 9 2008G. TOPUZ Abstract A blueschist facies tectonic sliver, 9 km long and 1 km wide, crops out within the Miocene clastic rocks bounded by the strands of the North Anatolian Fault zone in southern Thrace, NW Turkey. Two types of blueschist facies rock assemblages occur in the sliver: (i) A serpentinite body with numerous dykes of incipient blueschist facies metadiabase (ii) a well-foliated and thoroughly recrystallized rock assemblage consisting of blueschist, marble and metachert. Both are partially enveloped by an Upper Eocene wildflysch, which includes olistoliths of serpentinite,metadiabase, Upper Cretaceous and Palaeogene pelagic limestone, Upper Eocene reefal limestone, radiolarian chert, quartzite and minor greenschist. Field relations in combination with the bore core data suggest that the tectonic sliver forms a positive flower structure within the Miocene clastic rocks in a transpressional strike,slip setting, and represents an uplifted part of the pre-Eocene basement. The blueschists are represented by lawsonite,glaucophane-bearing assemblages equilibrated at 270,310 °C and ,0.8 GPa. The metadiabase dykes in the serpentinite, on the other hand, are represented by pumpellyite,glaucophane,lawsonite-assemblages that most probably equilibrated below 290 °C and at 0.75 GPa. One metadiabase olistolith in the Upper Eocene flysch sequence contains the mineral assemblage epidote + pumpellyite + glaucophane, recording P,T conditions of 290,350 °C and 0.65,0.78 GPa, indicative of slightly lower depths and different thermal setting. Timing of the blueschist facies metamorphism is constrained to c. 86 Ma (Coniacian/Santonian) by Rb,Sr phengite,whole rock and incremental 40Ar,39Ar phengite dating on blueschists. The activity of the strike,slip fault post-dates the blueschist facies metamorphism and exhumation, and is only responsible for the present outcrop pattern and post-Miocene exhumation (,2 km). The high- P/T metamorphic rocks of southern Thrace and the Biga Peninsula are located to the southeast of the Circum Rhodope Belt and indicate Late Cretaceous subduction and accretion under the northern continent, i.e. the Rhodope Massif, enveloped by the Circum Rhodope Belt. The Late Cretaceous is therefore a time of continued accretionary growth of this continental domain. [source] A FUZZY LOGIC APPROACH TO ESTIMATING HYDRAULIC FLOW UNITS FROM WELL LOG DATA: A CASE STUDY FROM THE AHWAZ OILFIELD, SOUTH IRANJOURNAL OF PETROLEUM GEOLOGY, Issue 1 2009A. Kadkhodaie-Ilkhchi Porosity-permeability relationships in the framework of hydraulic flow units can be used to characterize heterogeneous reservoir rocks. Porosity is a volumetric parameter whereas permeability is a measure of a rock's flow properties and depends on pore distribution and connectivity. Thus zonation of a reservoir using flow zone indicators and the identification of flow units can be used to evaluate reservoir quality based on porosity-permeability relationships. In the present study, we attempt to make a quantitative correlation between flow units and well log responses using fuzzy logic in the mixed carbonate-clastic Asmari Formation at the Ahwaz oilfield, South Iran. A hybrid neuro-fuzzy approach was used to verify the results of fuzzy modelling. For this purpose, well log and core data from three wells at Ahwaz were used to make an intelligent formulation between core-derived flow units and well log responses. Data from a separate well was used for evaluation and validation of the results. The results of this study demonstrate that there is a good agreement between core-derived and fuzzy-logic derived flow units. Fuzzy logic was successful in modelling flow units from well logs at well locations for which no core data was available. [source] PERMEABILITY ANISOTROPY DISTRIBUTIONS IN AN UPPER JURASSIC CARBONATE RESERVOIR, EASTERN SAUDI ARABIAJOURNAL OF PETROLEUM GEOLOGY, Issue 2 2007A. Sahin Most classical reservoir engineering concepts are based on homogeneous reservoirs despite the fact that homogeneous reservoirs are the exception rather than the rule. This is especially true of carbonate reservoirs in the Middle East which are known to be highly heterogeneous. The realistic petrophysical characterization of these kinds of reservoirs is not an easy task and must include the study of directional variations of permeability. Such variation can be incorporated into engineering calculations as the square root of the ratio of horizontal to vertical permeability, a parameter known as the anisotropy ratio. This paper addresses the distribution of anisotropy ratio values in an Upper Jurassic carbonate reservoir in the Eastern Province of Saudi Arabia. Based on whole core data from a number of vertical wells, statistical distributions of horizontal and vertical permeability measurements as well as anisotropy ratios were determined. The distributions of both permeability measurements and anisotropy ratios have similar patterns characterized by considerable positive skewness. The coefficients of variation for these distributions are relatively high, indicating their very heterogeneous nature. Comparison of plots of anisotropy ratios against depth for the wells and the corresponding core permeability values indicate that reservoir intervals with lower vertical permeability yield consistently higher ratios with considerable fluctuations. These intervals are represented by lower porosity mud-rich and/or mud-rich/granular facies. Granular facies, on the other hand, yielded considerably lower ratios without significant fluctuations. [source] NEURAL NETWORK PREDICTION OF PERMEABILITY IN THE EL GARIA FORMATION, ASHTART OILFIELD, OFFSHORE TUNISIAJOURNAL OF PETROLEUM GEOLOGY, Issue 4 2001J.H. Ligtenberg The Lower Eocene El Garia Formation forms the reservoir rock at the Ashtart oilfield, offshore Tunisia. It comprises a thick package of mainly nummulitic packstones and grainstones with variable reservoir quality. Although porosity is moderate to high, permeability is often poor to fair with some high permeability streaks. The aim of this study was to establish relationships between log-derived data and core data, and to apply these relationships in a predictive sense to uncored intervals. An initial objective was to predict from measured logs and core data the limestone depositional texture (as indicated by the Dunham classification), as well as porosity and permeability. A total of nine wells with complete logging suites, multiple cored intervals with core plug measurements together with detailed core interpretations were available. We used a fully-connected Multi-Layer-Perceptron network (a type of neural network) to establish possible non-linear relationships. Detailed analyses revealed that no relationship exists between log response and limestone texture (Dunham class). The initial idea to predict Dunham class, and subsequently to use the classification results to predict permeability, could not therefore be pursued. However, further analyses revealed that it was feasible to predict permeability without using the depositional fabric, but using a combination of wireline logs and measured core porosity. Careful preparation of the training set for the neural network proved to be very important. Early experiments showed that low to fair permeability (1,35 mD) could be predicted with confidence, but that the network failed to predict the high permeability streaks. "Balancing " the data set solved this problem. Balancing is a technique in which the training set is increased by adding more examples to the under-sampled part of the data space. Examples are created by random selection from the training set and white noise is added. After balancing, the neural network's performance improved significantly. Testing the neural network on two wells indicated that this method is capable of predicting the entire range of permeability with confidence. [source] Holocene sedimentation in the Skagerrak interpreted from chirp sonar and core data,JOURNAL OF QUATERNARY SCIENCE, Issue 1 2005Richard Gyllencreutz Abstract High-resolution chirp sonar profiling in the northeastern Skagerrak shows acoustically stratified sediments draping a rough-surfaced substratum. A 32 metre long sediment core retrieved from the survey area encompasses the entire Holocene and latest Pleistocene. The uppermost seismo-acoustic units in the chirp profiles represent Holocene marine sediments. The lowermost unit is interpreted as ice-proximal glacial-marine sediments rapidly deposited during the last deglaciation. The end of ice-proximal sedimentation is marked by a strong reflector, interpreted to have been formed during latest Pleistocene time as a consequence of rapid ice retreat and drastically lowered sedimentation rate. The subsequent distal glacial-marine sediments were deposited with initially high sedimentation rates caused by an isostatic rebound-associated sea-level fall. Based on correlation between the core and the chirp sonar profiles using measured sediment physical properties and AMS 14C dating, we propose a revised position for the Pleistocene/Holocene boundary in the seismo-acoustic stratigraphy of the investigated area. Copyright © 2005 John Wiley & Sons, Ltd. [source] Geophysical evidence for Holocene lake-level change in southern California (Dry Lake)BOREAS, Issue 1 2010BROXTON W. BIRD Bird, B. W., Kirby, M. E., Howat, I. M. & Tulaczyk, S. 2009: Geophysical evidence for Holocene lake-level change in southern California (Dry Lake). Boreas, 10.1111/j.1502-3885.2009.00114.x. ISSN 0300-9483. Ground penetrating radar (GPR) data are used in combination with previously published sediment cores to develop a Holocene history of basin sedimentation in a small, alpine lake in southern California (Dry Lake). The GPR data identify three depositional sequences spanning the past 9000 calendar years before present (cal. yr BP). Sequence I represents the first phase of an early Holocene highstand. A regression between <8320 and >8120 cal. yr BP separates Sequence I from Sequence II, perhaps associated with the 8200 cal. yr BP cold event. Sequence II represents the second phase of the early-to-mid Holocene highstand. Sequence IIIa represents a permanent shift to predominantly low lake stands beginning ,5550 cal. yr BP. This mid-Holocene shift was accompanied by a dramatic decrease in sedimentation rate as well as a contraction of the basin's area of sedimentation. By ,1860 cal. yr BP (Sequence IIIb), the lake was restricted to the modern, central basin. Taken together, the GPR and core data indicate a wet early Holocene followed by a long-term Holocene drying trend. The similarity in ages of the early Holocene highstand across the greater southern California region suggests a common external forcing , perhaps modulation of early Holocene storm activity by insolation. However, regional lake level records are less congruous following the initial early Holocene highstand, which may indicate a change in the spatial domain of climate forcing(s) throughout the Holocene in western North America. [source] Holocene denudation of the northwest sector of Iceland as determined from accumulation of sediments on the continental marginBOREAS, Issue 3 2007JOHN T. ANDREWSArticle first published online: 28 JUN 200 Radiocarbon-dated marine cores, measurements of sediment density and seismic surveys were used to estimate the sediment and mass accumulation rates (m/kyr and kg/m2/kyr) in the troughs from the southwest to north-central Iceland shelf (i.e. northwest sector of Iceland). The 3.5-kHz seismic survey showed varying thicknesses of acoustically transparent sediment in the troughs, whereas the inter-trough banks were largely devoid of sediment. The survey showed a pervasive reflector 1 to , 60 m below the sea floor, which turned out to be Saksunarvatn tephra, dated at 10 180 ± 60 cal. yr BP. The 3.5-kHz analogue data were digitized at 1-min intervals and provided 1645 estimates of maximum sediment thickness and 979 estimates of sediment accumulation over the last 10200 cal. yr BP. Maximum sediment accumulation occurred in the mid-troughs and not, as expected, in the fjords. The median sediment accumulation rate (SAR) based on the core data was 0.23 m/kyr, but was 0.77 m/kyr based on the seismic data: the difference is attributed to coring limitations. Based on the volume of offshore sediment and the contributing terrestrial drainage area, the Holocene denudation of northern Iceland (c. 50 000 km2) is calculated to have been between 0.02 to 0.05 m/kyr, substantially lower that the 1,3 m/kyr derived from the suspended sediment load of rivers from southern Iceland but in agreement with the rate of accumulation of Holocene glacial lacustrine sediments in central Iceland. [source] | ||||||||||