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- Volume 36, Issue 10, 2018
First Break - Volume 36, Issue 10, 2018
Volume 36, Issue 10, 2018
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Characterization of a cave by means of microgravity and electrical resistivity 3D-inversions: Zé de Braga cave (Mira de Aire, Portugal)
AbstractUsing geophysical methods to locate unknown caves is a common practice. Here, we present a new code for cave modelling from the residual gravity anomaly. To test its effectiveness, the code has been applied to the well-known Zé de Braga cave, located in Mira de Aire-Santo Antonio Range within the Maciço Calcareo Estremeho (Portugal). This cave has a vertical entry (sinkhole) and develops in an L-form shape at 10–15 m depth within the Jurassic limestones of the massif. A 2D grid of resistivity and microgravity data were acquired over the cave. The cavity is highlighted by high resistivity values (∼7500 ohm·m) and minimal values surrounded by maxima on the residual gravity map. The new gravity modelling code divides the sub-surface into blocks with densities of 0 g/cm3 (hole) to represent the cave, and 2.67 g/cm3 for the environment (limestones). The calculated 3D model of the cave is very close to the real morphology, dimensions and position, and is comparable to the inverted resistivities.
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Present and future contribution of geophysics to the prevention through design and quality management approaches for tunneling operations
Authors E. De Cillis, P. Fargione, L. Maida and L. SambuelliAbstractTunnels should be constructed, maintained and used without neglecting the basic principal of occupational health and safety, environmental protection and economic efficiency. This involves a prevention through design approach from the very first steps of the project, and a careful risk management during the tunneling operations, both based on the identification and evaluation of a number of input parameters. However, owing to the peculiarities of tunneling operations, many of these parameters are difficult to forecast and assess with sufficient detail. This problem can dramatically affect the quality of the result, and can cause accidents, environmental pollution and work stoppages, with consequent economic losses. The paper stresses the advantages of further implementation of near surface geophysics in tunneling design, construction and maintenance from an economic point of view. Moreover, it provides a comparison data on the economic losses owing to a not exhaustive knowledge of the rock characteristics vs the investments in the up-to-date geophysical investigations necessary to ensure a better quality of the design input data.
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Measuring gravity gradient in rugged terrain: HeliFalcon survey in Aso-Oguni, Japan
Authors Tianyou Chen and Mark DransfieldAbstractSince the first Falcon AGG survey in 1999 (van Leuwen et al., 2000), fixed-wing airborne gravity gradiometry (AGG) has proved to be a valuable tool for mining and oil and gas exploration (Dransfield, 2007). The more compact digital Falcon AGG allowed the system to be installed in a helicopter and helicopter AGG surveys began in 2006 (Boggs et al., 2007). Compared with fixed-wing aircraft, the helicopter platform can fly surveys low and slow, offering superior spatial resolution as well as an improved signal-to-noise ratio (Dransfield, 2007). The superior spatial resolution and improved signal-to-noise ratio provided by helicopter AGG enhances its capability to detect smaller targets and better delineate subtler features. Dransfield and Christensen (2013) reported a HeliFalcon performance of 6 Eö RMS at 45 m resolution in vertical gravity gradient, by far the finest spatial resolution of any airborne AGG system.
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Inversion of TEM responses to create a near surface velocity stucture
Authors I. Shelokhov, I. Buddo, A. Smirnov, M. Sharlov and Y. AgafonovAbstractPermafrost in Russia occupies about 5 × 106 km2 (Brown et al., 1997), and many known mineral deposits and oil and gas fields fall within this zone. Seismic data from northern petroleum provinces, including West Siberia, may be of low quality because of permafrost effects. Permafrost is localized in a relatively thin near-surface layer of variable thickness and produces velocity anomalies, which have to be taken into account in interpretations. Neglect of the permafrost influence on the geometry of reflectors may cause significant errors in modelling and yield low-quality wave patterns over the entire time range (Figure 1).
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Water resources detection at Santiago Island, Cape Verde using electromagnetic methods
AbstractFreshwater availability is a growing problem all over the world. This is especially true in drier regions with marked population growth. That is the case at the Cape Verde archipelago off the coast of West Africa. The problem of water availability has been part of the archipelago’s history since the 15th century, when these uninhabited islands were discovered by Portuguese navigators. The inconstancy and shortage of drinking water has always been related to low rainfall and prolonged drought. Most of the islands do not have high elevations, which does not favour orographic precipitation. Population and agricultural activity have always been limited by the use of existing water; either stored from the rainy season or from wells excavated in the valley’s riverbanks. To overcame this condition many boreholes have been drilled since the 1950s and 1960s at the known aquifiers. This was done under the scope of geologic and hydrogeological data and methods. The present study is an electromagnetic geophysical survey at Santiago Island, the biggest and most populated of the archipelago. Beginning in 2005, there was at least one campaign a year until 2009. The surveyed regions are the most important valleys and agricultural areas, where the water needs are bigger. The problem of groundwater is not just its amount and availability but also its quality. The problem of sea or salty water intrusion into the near sea groundwater aquifers was detected at many boreholes and by the wells’ hydrochemistry data. The aim of this EM survey was to image the groundwater condition; location and quality throughout the studied areas. To fulfill this, transient electroMagnetic (TEM) soundings have been done. In addition some very low frequency (VLF) profiles and magnetoteluric (MT) soundings have been carried on to confirm and cross-check TEM data.
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Mapping seafloor massive sulfides with the Golden Eye frequency-domain EM profiler
AbstractSince the early discovery of a black-smoker complex in 1978 on the East Pacific Rise at 21°N, speculations and expectations have been driven about the potential and perspectives of mining seafloor massive sulfide (SMS) deposits in the deep-ocean. With a worldwide accelerating industrialization, emerging markets, increased commodity prices and metal demand, and advancements in deep-water mining and extraction technologies, mining of SMS may become economically feasible in the near future (Kowalczyk, 2008). However, we still know little about the resource potential of SMS deposits, and the development of geophysical methods for an assessment of their spatial extent, composition, and inner structure is crucial to derive a proper assessment of their economic value. Novel geophysical mapping techniques and exploration strategies are required to locate extinct and buried clusters of SMS deposits, away from the active vent fields and of larger economic potential, but are difficult to find and sample by conventional methods.
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Cloud computing for large-scale controlled-source electromagnetic inversions, Barents Sea, Norway
AbstractSince the late 1990s, the continuous development and application of the Controlled-Source Electromagnetic (CSEM) technology have vastly improved its usage in exploration (e.g., Constable, 2010; Løseth et al., 2015; Zach et al., 2009). CSEM inversion results are the main input for interpretation of resistivity data, especially potential fluid anomalies. Complementary to other geophysical methods, e.g. Amplitude versus Offset (AVO), it can therefore be a valuable tool in hydrocarbon exploration.
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Advances in electromagnetic techniques for exploration, prospecting, and monitoring of hydrocarbon deposits
More LessAbstractTraditional exploration and prospecting for hydrocarbons (HC) has traditionally been carried out using seismic techniques. At the same time, it is well known that seismic techniques are inefficient in the presence of high-velocity layers (which reduce resolution at great depth), igneous rocks, thrusts within the crystalline basement, and tight limestone. Being sensitive to geological structure, seismic techniques are characterized by low resolution at the level of micro-parameters such as fluid type, porosity/ fracture, and degree of pores HC-saturation. Moreover, technical complications, e.g., highly rugged topography, dense vegetation and object remoteness may make seismic surveys difficult, expensive, or even impossible.
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Can oil and gas exploration deliver on prediction?
AbstractThe age old problem of underperformance in petroleum exploration is directly related to over-optimistic evaluations of the size of undrilled prospects. Although the assessment of geological risk in proven plays is usually not a problem, the chance of economic success is generally much lower than predicted by companies as a consequence of the deficit in expected volumes. An EAGE workshop held in Copenhagen in June 2018 addressed this issue and one of the outcomes was the recommendation that prospect evaluations are more closely linked to historical data, particularly on the downside size of discoveries.
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Volumes & issues
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Volume 42 (2024)
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Volume 41 (2023)
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Volume 40 (2022)
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Volume 39 (2021)
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Volume 38 (2020)
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Volume 37 (2019)
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Volume 36 (2018)
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Volume 35 (2017)
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Volume 34 (2016)
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Volume 33 (2015)
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Volume 32 (2014)
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Volume 31 (2013)
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Volume 30 (2012)
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Volume 29 (2011)
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Volume 28 (2010)
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Volume 27 (2009)
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Volume 26 (2008)
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Volume 25 (2007)
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Volume 24 (2006)
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Volume 23 (2005)
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Volume 22 (2004)
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Volume 21 (2003)
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Volume 20 (2002)
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Volume 19 (2001)
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Volume 18 (2000)
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Volume 17 (1999)
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Volume 16 (1998)
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Volume 15 (1997)
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Volume 14 (1996)
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Volume 13 (1995)
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Volume 12 (1994)
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Volume 11 (1993)
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Volume 10 (1992)
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Volume 9 (1991)
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Volume 8 (1990)
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Volume 7 (1989)
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Volume 6 (1988)
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Volume 5 (1987)
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Volume 4 (1986)
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Volume 3 (1985)
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Volume 2 (1984)
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Volume 1 (1983)