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68th EAGE Conference and Exhibition incorporating SPE EUROPEC 2006
- Conference date: 12 Jun 2006 - 15 Jun 2006
- Location: Vienna, Austria
- ISBN: 978-90-73781-00-9
- Published: 12 June 2006
101 - 120 of 462 results
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Edge Enhancement Using the Tilt Angle
More LessMeasures of the local phase of potential fields can be a useful aid to their interpretation. There are several variations in use, such as the tilt angle, tilt derivative and the Theta map. This paper introduces some new phase based filters which show improved performance as edge detectors in different ways. The filters are demonstrated on aeromagnetic data from South Africa and Australia.
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Wavelet Based Semblance Analysis
More LessSemblance filtering compares the phases of two datasets as a function of frequency. Because it is based on the Fourier transform its application suffers from all the problems associated with that transform, in particular its assumption that the frequency content of the data does not change with time. Semblance is here extended in two ways, using the continuous and the discrete wavelet transforms. When calculated using the continuous wavelet transform, semblance analysis allows the local phase relationships between the two datasets to be studied as a function of scale (or wavelength). Additionally, the efficient inverse transform of the discrete wavelet transform allows datasets to be filtered based on their local semblance, which offers considerable advantages over previous Fourier methods.
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Using Gravity Gradiometry to find Gold Deposits in Weathered Terrains
More LessAirborne gravity gradiometry (AGG) is a new geophysical tool that has been limited in its ability to find many mineral deposists in weathered terrains due to regolith variations swamping the signals from subtle changes in basement rock density. Previous approaches to adress this issue have tried and failed to compensate for the regolith. We have simulated (in 3-D)the response of a number of gold deposits as examples of using gravity gradiometry to find mineral deposits indirectly. The result is that most near-surface deposists in weathered terrains have a detectable negative gravity gradient anomaly due to preferential weathering. Thus, we demonstrate a new way of interpreting AGG data to find gold deposits in areas normally considered unsuitable for AGG.
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Interpretation of Electrical Properties for Humid and Saturated Hematitic Sandstone Sample
More LessEffects of water saturation on electrical properties, of humid, partially, and satrurated hematitic sandstone sample, were investigated experimentally. These data were discussed theoretically using models that account for the electrical polarization. We change the saturation of a hematitic sandstone sample from normal relative humidity (~50 RH) to fully saturated. Complex impedance measurements were performed in the frequency range from 1 Hz to 100 KHz. Experimental data indicates that the electrical properties vary strongly with water saturations. As the frequency increases the rate of dielectric constant change decreases and the change is nearly constant at high frequencies. The rate of decrease of the dielectric constant with frequency decreases as the water saturation decrease. The changes of the electrical properties due to saturation were attributed to the ionic surface charge at grain interface. The interaction between the matrix of a porous material and a small quantity of water located in its pore space induces polarization phenomena and enhances the charge transport. The results can be explained as proton conduction in the humid case and low saturations and electrolytic conduction along with protonic transport in the fully saturated case.
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SP Monitoring of an Acid Stimulation of the Soultz Geothermal Reservoir
Authors G. Marquis and A. GerardSP monitoring of a sequence of water-acid-water injections over a span of three weeks in the Soultz geothermal reservoir shows a decrease of the surface electric potential during the acid stimulation. This requires a negative electrokinetic coupling coefficient, which is predicted by the theory for fluids with very low pH. Post-acid injections also yielded negative signals that are likely caused by electrochemical processes during the increase in ionic content of the injected water. These results have some importance when considering using acid stimulations for geothermal reservoirs in a production phase.
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Potential Field Continuation between Irregular Surfaces - Problems and Applications
Authors B. Meurers and A. AhlThe field continuation procedure by Ivan (1994) providing potential field continuation between arbitrary surfaces has been implemented for use of unevenly scattered rather than gridded data. Errors induced by under-sampling are investigated by synthetic case studies. The basic assumption of dipole magnitudes linearly varying on the triangle facets of the polyhedral topography approximation turns out to limit the accuracy of Ivan’s algorithm. The method is applied to combine aeromagnetic data acquired by different partly overlapping surveys in order to remove unknown biases and to refer all data to a common surface with constant topography clearance.
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Predictive Environmental Geophysics in Israel
By M. RybakovThis paper presents the unpublished early data with an analysis of the new sinkholes opened after the surveys. That confirms predicting power of the microgravity and micromagnetic methods for sinkhole hazard assesement.
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Preliminary Research of Possibility Gravity Monitoring Use at Gas Deposits
More LessThe researches consisting in numerical modeling of gravitational effects of operation of a gas deposit are carried out.
The modeling with use of parameters of a real deposit allows to estimate close to true size of possible variations of a gravitational field and to estimate a degree of influence of a number of major parameters. The measurement of variations of gravity (gravity monitoring) is represented to one of most reliable and cheapest way of the control behind moving, gas or injection of water at operation of deposits. The carried out experimental accounts have shown a basic opportunity of the gravimetric control of gas withdrawal.
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Analytical Continuation of Geophysical Fields into the Area of Anomaly Sources by the Continued Fraction Method (CFCM)
More LessMany works of the leading geophysicists are devoted to the method of analytical continuation of geophysical field from the measuring profile to the lower half-space. But promising results in this area are practically absent. Linear presentation of the field in the form of polynomials, Taylor or Fourier series leads to essential ill position of the inverse problem. Field description, close to reality, is the construction of the fractional-rational type. In this case the presence of function poles in the lower half-space corresponds adequately to the zeros in denominator. Method proposed below is based on the Pade approximants and its particular but important case - continued fractions. The proposed method is called - Continued Fraction Continuation Method.
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Nature of Gravitational Anomaly in the South Caspian Basin
More LessThe South Caspian Basin (SCB) at present attracts increased attention of researchers in connection with its exceptionally rich oil and gas resources.
This paper presents an evaluation for predicted gravity anomaly in the SCB, that may have formed as a result of the continental plate subsidence at its central part. The gravity anomaly formed as a result of subsidence of plate has been appraised through its comparison with Earth crust of the Russian Craton.
This anomaly has been revealed to be equal to -193 mGal and strongly differs from those observed in the SCB. In fact these 193 mGal appear to be possible compensated due to an action of the strata located beneath the Moho partition with considerably higher density than that of mantle material.
The gravitational action of the excessive masses located in the upper mantle was considered as an action of the horizontal cylinder shaped body and depth interval of the consolidated part of the upper mantle has been evaluated. On creating the geodynamic evolution model for the SCB one needs to take into account an astenospheric projection which is predicted to occur at 36-87 km interval.
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Analysis of Crustal Seismic Data in a Geothermal Field (Southern Tuscany)
Authors U. Tinivella, F. Accaino, R. Nicolich and G. RossiSouthern Tuscany is characterised by an extensional regime, crustal thinning and magmatic intrusions. Important geothermal reservoirs and anomalous pore fluids are associated with an intricate geological setting.
The area was investigated by applying integrated methodologies to deep crustal seismic reflection data: amplitude versus offset inversion, and theoretical approaches to model overpressure conditions. The seismic transect CROP-18, split into two lines (18-A and 18-B), has imaged the exceptionally high reflectivity of some markers within the metamorphic crystalline basement units and of the medium-lower crust in this region. Joint analysis of the available data enabled us to distinguish between the lithological reflectors and the reflections caused by a predominant fluids, such as overpressure conditions. We detected the presence of vertical conduits, responsible for magmatic intrusions rising from the crust-mantle transition to the near-surface layers, as well as overpressured reservoirs. Theoretical models are used to quantify the effect of overpressure in terms of porosity increase, and the consequent density decrease in the area where the main marker characterizing the geothermal fields, the K-horizon, becomes shallow.
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An Integrated Geophysical Approach to Investigate the Ancient Copper Mine of Kalwang/Austria
Authors R. Scholger and E. NiesnerThe chalcopyrite deposit Teichgraben is situated 15 km W of Leoben in Austria. There is evidence for first exploitation activity during bronze-age, systematic mining started in the 15th century. The investigated orebody occurs in the Greywacke Zone of the Upper Austro-Alpine nappe. The mineralisations are bound to weekly metamorphic greenschists in the tectonically highest segment of the Greywacke Zone, the Noric Nappe.
Only few information is available on the extension of the mineralised zone to deeper layers. We investigated the extension of this mineralised zone in an integrated geophysical approach ranging from magnetic, electromagnetic, electric, self potential to spectral gamma ray measurements.
The interpretation was done using an electrofacies approach. The lithologies could be specified using the geological mapping and documentations available from the mining activity. A thrust fault between nappes of the greywacke zone intersects the area. The mineralised zone itself is interrupted by small faults. All mentioned features can be recognized on the measured geophysical data and the extension of the mineralised zone has been interpreted based on the integration of all results. The depth extend of the mineralised zone is limited to a maximum depth of about 50 m below the ancient base gallery.
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Thermal Effect of Magma Intrusion on Electrical Properties of Magnetic Rocks from Hamamat Sediments, NE Desert, Egypt
Authors M. M. M. S. Gomaa and R. A. M. ElsayedThermal effects of magmatic intrusion on electrical properties, of magnetic rocks from Hamamat sediments, NE desert, Egypt, were investigated experimentally. An intrusion of granitic magma was intruded in the Hamamat sediments, which is a mixture (mainly magnetite with sandstone) and due to the thermal effect the area around it was altered, with different degrees and magnetite was transformed into hematite with different degrees according to its location. Complex impedance measurements were performed in the frequency range from 10 Hz to 100 KHz. Experimental data indicates that the electrical properties vary strongly with distance. The conductivity of hematite is higher than that of magnetite. As we move from magnetite to hematite it is supposed that the conductivity will decrease, but it was found that the conductivity increases. The increase of conductivity as we move from magnetite to hematite were argued to the heating that make partial or complete melting of the samples, then the porosity of the samples were decreased and accordingly the conductivity and dielectric constant increase. Also, it was supposed that the grains of the conductor in the samples are coated completely or isolated with insulator material.
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From Scarcity to Plenty – Who Shapes the Energy Mix of the Future and What Might It Be?
More LessThe global pattern of primary energy sources will change profoundly during the 21st century. Consumers, businesses and governments together will shape the new energy mix. They all share three strong desires, which will deeply influence their energy decisions: · Sustained strong economic growth · Security of energy supply · A clean and safe environment. Consumer preferences, business solutions, and government demands will drive the change – not the depletion of any energy source. Global demand for commercially traded primary energy might grow from 10.8 billion tOE in 2004 to around 35 billion tOE in 2100. ‘Renewable’ primary energy sources could provide at least 35% of global demand in the year 2100; the solar portion of that might be 15%. Distributed power generation from ‘renewable’ energy sources such as solar, wind, water, and geothermal, is expected to become significant. New ways will have to be found to correctly measure the usage of distributed primary energy since a substantial part will be produced and consumed without ever being commercially traded. Fossil fuels - so dominant in 2004 with 83% - should still be important in absolute terms in 2100 (about 10 billion tOE), but with a much smaller relative share (about 28%). Natural gas and coal are expected to replace oil for many purposes. Nuclear could provide about 20% of the global primary energy demand in the year 2100. Fuel on fuel competition will be strong in the second half of the 21st century. Consumers will be able to choose from many options. This should lead to lower energy prices and to continuous improvements in energy conversion efficiencies. There is plenty of energy in the universe. It is a noble goal to capture enough of this energy so that all may prosper in a clean and safe environment. A lot needs to happen, if we want to get there by 2100. We need to seize the moment.
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Gas Supply in Europe, Gas Demand, Resources and Deliveries to European Consumers in the Upcoming Decades
By J. GallistlAt the beginning of the first decade of this century natural gas primary demand in the European Union with about 470 bcm accounted for more than 20 % of its total primary energy demand (World Energy Outlook 2004, IEA). According to the last “Reference Scenario” of the IEA the European Union is projected to have a natural gas average growth of 1.8 % per year during the period 2000 - 2030. This projected development leads to the total gas demand of more than 780 bcm in the European Union in 2030. The steady increase in gas demand requires an expansion of exploration and production. There is a positive phenomenon in this respect: proven reserves of natural gas have outpaced production by a wide margin since 1970. The world proven reserves account for 180 tcm as of 1 January 2004 (Cedigaz statistics). Russia and the former Soviet republics hold almost a third of global reserves, but its share has decreased steadily over the past decade. The Middle East holds 40% of all reserves and its share is growing. In 2030 the Middle East will be the world’s largest exporting region. Natural gas reserves in Europe come not even to 4% of world total and its share is decreasing. However, natural gas resources which could be imported to the European Union can easily meet the projected increase in gas demand of that region provided we take into account that higher oil prices will stimulate exploration and production of new more remote and challenging reserves. Another precondition is that long term contracts are allowed which will continue to play a decisive role in investment into production and infrastructure. The excellent track record of the European gas industry in the course of last few decades has helped to create a picture of secure natural gas supply to Europe. However, security of supply means not only the physical existence of sufficient and reliable resources, but also the existence of an adequate and reliable infrastructure to bring those resources to the market. At present there are three main corridors for supplying Europe with piped natural gas: from Russia to Central and Western Europe, from North Africa to Italy and Spain and from Norway to UK and Western Europe. To open up a forth corridor to connect the European markets with the world’s second biggest resources in the Caspian region and the Middle East is one of the big challenges of the future to further guarantee security of supply. In addition LNG will also play an increasing role regarding future gas imports to the European Union. All this shows that the European gas industry is facing big challenges to meet future gas demands of European gas consumers.
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Oil resources – Estimates and Uncertainties
More LessOil reserves are reasonably well known, but they are not a reliable indicator of long-term supply. Future oil availability will depend upon reserve additions, which are highly uncertain. New reserves will come from three sources: 1) new field discoveries, 2) growth of reserves in existing fields, and 3) development of unconventional resources. U.S. Geological Survey estimates of global undiscovered conventional oil have a mean value of about 650 billion barrels, but the estimates range from a few hundred billion barrels to 1100 billion and more if the possibility of successful exploration in remote, untested basins is included. Reserve growth in existing fields, which has added more than 250 billion barrels to reserves in the last two decades, is equally uncertain; global estimates of future growth range from tens of billions to 1000 billion barrels or more. Unconventional resources, particularly heavy oil and tar, may also add many hundreds of billions of barrels to reserves, but at unknown rates and costs. Thus estimated future additions to oil reserves range over an order of magnitude, from a few hundred to a few thousand billion barrels. Given the importance of oil to human activity, planners might want to retain the flexibility to adapt to a range of possible scenarios of future oil supply.
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Managing a Field with 24yrs of Production History and More Than 40 Years Still to Go
By G. SundThe Valhall chalk Field, located in the Southern North Sea, is unique in it’s production history, reserves growth linked to technology and expected long future ahead. It was discovered in 1979 and put on production in 1982. Starting with estimated reserves of 250 mm bo, the field today has 2 billion barrels as its ambition and potential. Being a soft, high porosity and essentially uncemented and high pressure chalk, the reservoir has been on primary depletion producing from a strong compaction drive for more than 20 yrs. The crest, hidden under a gas cloud, was the primary target area. Due to drilling problems through the compacting and subsiding, soft overburden and unsuccessful extended-reach drilling two flank platforms were put in place in 2002 and 2003. This has significantly contributed to reserves growth and the reservoir limits are pushed deeper and outwards as we drill on the flanks. In the crest, a water injection program was sanctioned, to build up pressure and increase production through matrix sweep and pressure support. The IP platform was in place in 2003 and water injection started through two converted wells first in the northwest area of the field in 2004. Today a crestal monitoring well (measuring pressure and water induced rock compaction underneath crest installations) and a first crestal water injector are in place as the first parts of a planned water injection programme with a line drive patterns consisting of injectors and producers. A key element in the water injection programme is surveillance. An advanced surveillance program allowing for steering and detecting the pattern of water flow is planned and about to be implemented. Equally important perhaps even more, is the Life of Field Seismic (LoFS) installed at Valhall. Kilometres of cables are covering the field allowing for regular acquisition of seismic data across the field. Primarily installed for following the 4D changes in the field associated with the water injection programme, LoFS has shown to have impact on essentially the entire reservoir management: Well planning, Wells management and for 4D effect in the reservoir. There are challenges to overcome in that details are still hidden underneath the gas cloud and details are still to be unlocked I the images resulting from the successive surveys. However, we are unlocking more and more of the story of the chalk reservoir, changing essentially every day as oil is produced and water is injected.
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Understanding Underground Coal Fires for Utilization
Authors K. H. A. A. Wolf, J. Bruining and R. MeeuwisUnderground coal fires are difficult to extinguish. As an alternative they might be used for heat production. Hence, their controlling factors have to be investigated. Experimental work on in-situ coal gasification and geological surveys on underground coal fires are used to develop a model to understand the combustion process and subsidence behavior. Coal fires are divided in five thermal zones with different thermo-mechanical characteristics. The three zones in and above the seam are used in a convection model. In experiments temperatures, ranging from surface temperature to 1200°C, are applied to claystones, shales and sandstones. Changing mineralogy, thermal expansion, shrinkage, bulk moduli and permeability of grain aggregates are established under defined in-situ T,P-conditions. The results are implemented in finite difference- and creep models to calculate subsidence. Volume changes are converted to permeability fields for a convection model. In this model, seam-, rubble- and overburden thicknesses, their depths and fault densities, are other input parameters. The model calculates the temperature-, convection- and oxygen distribution in the sub-surface. For shallow coal fires (15 m), the overburden, faults and collapsed rubble zone are used for oxygen supply and thermal convection. Deep coal fires (40 m) use the rubble zone and faults for the process.
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Seismic Monitoring the Variations of Open Fracturing of Reservoir Rocks due to Lunisolar Tides
Studied is the dynamics of natural variation of open fracturing of petroleum reservoirs caused by lunisolar tides. Experimental seismic studies were performed by monitoring the fracturing using Side-View Seismic Location (SVSL) and Seismic Location of Emission Centers (SLEC) - active and passive seismic methods, respectively. A periodic variation of open fracturing intensity is established with maximums of open fracturing correlating with maximums of gravity gradients. It is found that the largest variations are predominantly characteristic for subvertical fractures and the role of fracturing variation is crucial for deep-seated reservoirs. The effect of natural time variations of open fracturing should be taken into account when performing reservoir stimulation and during oil recovery and water injection to provide the high efficiency of production especially for mature oil fields where such operations are common.
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Hydrocarbon Microtremors Interpreted as Oscillations Driven by Oceanic Background Waves
Authors R. Holzner, P. Eschle, M. Frehner, S. Schmalholz and Y. PodlachikovHydrocarbon Microtremor Analysis (HyMAS) is an innovative technology for identifying the presence of hydrocarbon containing geological structures by analyzing low frequency background wave signals. A possible interpretation of this reproducibly observable phenomenon is the excitation of hydrocarbon related resonances. Synthetic spectra produced by basic linear and non-linear one-dimensional models of an oscillating liquid filled porous medium show characteristic features of measured HyMAS spectra when oceanic background waves around 0.1-0.2Hz are assumed to be the external driving force.
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