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70th EAGE Conference and Exhibition incorporating SPE EUROPEC 2008
- Conference date: 09 Jun 2008 - 12 Jun 2008
- Location: Rome, Italy
- ISBN: 978-90-73781-53-5
- Published: 09 June 2008
81 - 100 of 556 results
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Evidence of Hydraulic Fracture Reorientation Across a Thrust Fault
Authors S. C. Maxwell, U. Zimmer, R. Gusek and D. QuirkMicroseismic imaging of a hydraulic fracture stimulation showed significant fracture reorientation across a thrust fault. Fracture orientations were identified through a combination of alignment of event locations, polarization of the seismic waves and injection details. Stimulation below the fault indicated a near horizontal fracture geometry. Above the fault, a near vertical fracture geometry was observed. This difference in fracture geometry was attributed to rotations in the direction of minimum principle stress, which is consistent with observed differences in the injection pressures. The fracture reorientation suggests a significant difference in the stimulated permeable pathways.
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Microseismic Features of Gel and Water Fracturing of Tight Gas Reservoirs
Authors C. Dinske and S. A. ShapiroWe analyse the spatio-temporal dynamics of hydraulic fracturing induced microseismicity. We present a model that describes the growth of a hydraulic fracture as a geometry and diffusion controlled process. This model contributes to estimate important parameters of the fractured area and to better understand underlying physical processes. We apply this model to well documented datasets from fracturing experiments in Cotton Valley tight gas reservoir. The treatments were performed with different parameters, e.g., type of fluid, injection rate, total volume of fluid and of proppant. In case of a gel-based fracturing, the r-t diagram of microseismicity shows signatures of fracture volume growth, fracturing fluid loss as well as a diffusion of the injection pressure. In contrast, in water-based fracturing a diffusion-like growth of microseismic event cloud is not clearly observable. However, for both the gel- as well as the water-based fracturing we obtain very similar estimates of fracture geometry and hydraulic parameters of the reservoir. The difference in permeability of the particular hydraulic fractures is probably caused by the different treatment parameters.
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Case Studies on 2D- and 3D-Time Reverse Modeling of Low-frequency Microtremors - Application to Reservoir Localization
Authors B. Steiner, E. H. Saenger and S. M. SchmalholzA fast and economically attractive procedure to detect hydrocarbon reservoirs is of main interest for the exploration and development of new oil or gas fields. Several studies at different oil and gas fields around the world have shown spectral anomalies with a high degree of correlation to the location and geometry of hydrocarbon reservoirs. It is reported that the narrow-band low frequency (1.5Hz-6Hz) tremor signals measured at the surface may originate from the reservoirs themselves. However, standard localization techniques fail to localize the signals for real data as one observes continuous tremors rather than single events. Time reverse modeling is a promising technique to reliably localize the so called hydrocarbon microtremors. We show with a numerical feasibility study and real data the potential of such an approach. By using a realistic geologic section we demonstrate with 2D- and 3D-Time reverse modeling that it is possible to localize the origin of tremor-signals.
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A Low Frequency, Passive Seismic Experiment over a Carbonate Reservoir in Abu Dhabi – Wavefront and Particle Motion Studi
Authors K. A. Berteussen, M. Y. A. Ali, J. S. Small and B. BarkatA low frequency passive seismic experiment conducted over an onshore carbonate oilfield in Abu Dhabi observed a narrow band of low frequency (2.5 – 2.8 Hz) signals over both the oil reservoir and the water saturated zone (Ali et al., 2007). The possible causes of this low frequency energy are not well understood and it has yet to be demonstrated what types of waves are being observed. In this paper we present results of an investigation carried out to determine the apparent velocities and the azimuth of the wave fronts as well as the particle motion of the recorded low frequency waves. This work is currently ongoing, but the results so far indicates that the observed waves are most likely some type of surface wave and the azimuth to the source is pointing towards the nearest coastline in the area (the Arabian Gulf).
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Seismic Spectroscopy Using Amplified 3C Geophones
Authors P. van Mastrigt and A. Al-Dulaijanion has now been integrated and used on a conventional seismic crew, representing the potential for large cost savings to record spectroscopy data. We believe that the latter is an industry first, initially reported on the I/O Middle East Technical Forum, Abu Dhabi, February 2007. Firm plans are now in place to take full advantage of this emerging technology by integrating spectroscopy recording on a survey-wide scale on the next seismic campaign. Should this materialize, then the resulting spectroscopy measurements will have a spatial redundancy that is really required assess this tool’ value as a reliable DHI.
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Location of and Monitoring with Induced Earthquakes in Oil and Gas Fields
Authors S. Sarkar and M. N. ToksozB048 Location of and Monitoring with Induced Earthquakes in Oil and Gas Fields S. Sarkar* (Massachusetts Institute of Technology) & M.N. Toksoz (Massachusetts Institute of Technology) SUMMARY We present some developments for location of induced seismic events and apply these to field data. Most commonly used earthquake location algorithms do not work for earthquakes in oil and gas fields. Induced earthquakes generally occur in sedimentary basins with alternating high and low velocity layers. Conventional algorithms based on either smooth velocity gradients or layers with increasing velocities cannot handle many thin layers with high and low velocities. In this paper we
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Three-dimensional Reflection Seismics Surfs the Crest of the Platinum Wave (Best of SAGA)
Authors J. Trickett, W. Düweke and S. KockDue to the highly favourable platinum market over the past decade, a substantial investment has gone into the customization of the 3D seismic reflection method for the unique requirements of the Bushveld Igneous Complex. All of the major South African platinum producers have capitalized on these technology advancements for the purposes of mine planning, risk reduction and development. Over and above their primary value as sources of excellent structural information, the high-resolution 3D seismic data volumes hold a tremendous amount of additional geological and geophysical information. Impulse Geophysical Consulting Services (Impulse) has been afforded the latitude to investigate a host of seismic attributes of the Impala Platinum Ltd. (Impala) 3D survey that was undertaken in 2000. Surface drainage patterns, subsurface weathering profiles, the middling distances between the UG2 and Merensky Reefs as well as the distribution and orientation of fault networks, dykes and iron-rich ultramafic pegmatite (IRUP) bodies were evaluated with particular reference to the root-mean square seismic energy values that were originally extracted by the Rock Deformation Research Group (Leeds University, U.K.). Until recently, very little was known about the seismic response of IRUP bodies. A detailed study including the forward modelling of these features (in the form of synthetic seismograms) yielded some useful results: IRUP bodies have high densities and reflect seismic energy where their thicknesses exceed ± 20m (owing to the seismic source bandwith). As a result, the underlying economic targets are relatively poorly imaged where they occur between thick intersections of these ultramafic bodies. Although more frequent in distribution, IRUP intersections that are thinner tend to be relatively transparent to seismic waves and do not result in significant energy losses.
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Geophysical Imaging of a "Blind" Zn-Pb-Ag Deposit
Authors B. Milkereit, W. Qian, H. Ugalde, E. Bongajum and M. GräberProperly constraining the shape and size of an ore body requires a comprehensive database of petrophysical, geophysical and geological information derived from both surface and borehole data. An integrated borehole and surface dc resistivity study enabled us to detect and delineate shallow Zn-Pb-Ag mineralization beneath thick overburden at the Nash Creek exploration area, New Brunswick, Canada. The 2D and 3D conductivity models are supported by downhole resistivity data and geochemical assay data from exploration boreholes.
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TDEM Method for Hydrothermal Water Prospection
Authors A. Menghini, G. Pagano, S. Floris and E. BerniniTDEM prospection allowed to reconstruct tectonic setting of a thermal basin, in Viterbo (Central Italy). A productive well was located at the intersection of two faults evidenced by geophysical data, reaching a depth of 127 m. and providing thermal water (58°C) with high productivity (spontaneous discharge 10 L/Sec). Interesting results were achieved by using offset-mode soundings, so minimizing costs of geophysical prospection. Also preliminary attempts with grounded system were promising.
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Statics in Magnetotellurics - Shift or Model?
Authors W. Soyer, S. Hallinan, R. L. Mackie and W. CummingMagnetotelluric data sets often show signs of significant local galvanic distortion - static shifts in its simplest form - complicating their quantitative analysis. Our accounting for this problem is two-fold. Co-located magnetic TDEM soundings provide representative resistivity estimates of an approximate 1 D near-surface structure, allowing for calibration of the MT apparent resistivity at the highest frequency limit. Remaining distortion that is unaccounted for can be addressed directly and automatically via 3D inversion: as galvanic effects occur equally in the synthetic simulation of the induction process whenever currents cross resistivity interfaces, the inversion algorithm generates shallow near-surface structure that can reproduce the observed statics. Today's increasing computer resources allow for the detailed meshes and small near surface cell sizes necessary for this approach. Constraints on model roughness prevent local statics solutions from affecting the deeper resistivity image in the minimum structure inversion. For some data sets and geological environments, direct inversion for static shift parameters in addition to the above structural approach may be preferred. Applicability of this two-fold approach is demonstrated on a combined MT data set from the geothermal prospect of Glass Mountain, California.
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The Development of a Multi-purpose Geothermal Site in an Urban Area
Authors K-H. A. A. Wolf, A. Willemsen, T. W. Bakker, A. K. T. Wever and D. T. GildingIn May 2007, students of Deft University, Department of Applied Earth Sciences, made for their 23rd lustrum an appraisal study regarding a combination of geothermal energy combined with CO2-injection. According to the pre-study, nine exploration wells in the Delft area show an anticline below the University grounds, which holds various sand bearing members at a depth of about 2 to 2.5 km. One member consists of highly permeable sands, which may produce about 120 m3/hr of water. The expected geothermal temperature of about 75C can be used for new and renovated buildings. In order to drill an injection and production well for geothermal use on a small foot print, a new light weight composite tubing is proposed. It is possible to drill almost weightless with an innovative mobile telescopic rig. The tubing of the injection and production wells also contain a thermoplastic inner wall, which is expected to be less corrosive and less expensive when compared to regular steel tubing. Hence, the option of CO2-injection into the returning water is considered. The two innovative aspects in this feasibility study, i.e. composite drilling and CO2-injection, got the attention of the industry, university and other (non-) governmental organizations.
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From Gas to Geothermal Exploration - A Case Study from the NE-German Basin
Authors I. Moeck, W. Brandt, G. Blöcher, H. G. Holl, G. Zimmermann, A. Saadat, T. Backers and E. HuengesThe sedimentary Lower Permian is a well known target for gas exploration in the North German Basin as part of the South Permian Basin System. In East Germany a huge quantity of well and 2D seismic data were generated from the 1960’s to 1990. We re-evaluated and re-processed some of these data to define potential geothermal reservoirs for power production. Since 2000, a non-productive gas exploration well, drilled in 1990 in the NE German Basin, is used as a geothermal in-situ laboratory for testing recovery strategies in terms if enhancing geothermal systems. After increasing the productivity of the well by several stimulation treatments, a second well was drilled from 2006-2007 to install a well doublet. The design of the new well differs considerably from gas well designs since geothermal wells need to satisfy some requirements like large diameters for housing the submersible pump, directional drilling to allow a set of parallel hydraulic fractures and drilling under near-balanced mud pressure conditions to minimize formation damage. Recently, a massive stimulation campaign increased the productivity of the new well considerably. This article shows the field development of a deep sedimentary reservoir as a integrated study from gas to geothermal exploration using latest technologies.
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Mapping Geothermal Reservoir Using Broadband 2-D MT Survey in Theistareykir, Iceland
Authors G. Yu, A. Gunnarsson, H. Tulinius, K. M. Strack, L. F. He and Z. X. HeThis initial 2-D MT survey has confirmed the finding of previous TEM survey in the Theistareykir field about the existence of a high temperature reservoir under the Theistareykja area, and also outlined better the boundaries of the reservoir along each long 2-D MT survey lines. This study establishes the relationship between resistivity, temperature and lithology. The geophysical exploration activities act as a very important role to help explore and characterize a geothermal reservoir among other geoscience methods for potential geothermal power plant construction project.
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Results of Stimulation Treatments at the Geothermal Research Wells in Groß Schönebeck, Germany
Authors G. Zimmermann, A. Reinicke, W. Brandt, G. Blöcher, H. Milsch, H. Holl, I. Moeck, T. Schulte, A. Saadat and E. HuengesThe aim of this work is to present results of previously performed fracture treatments in the geothermal research well GtGrSk4/05 at Groß Schönebeck. The fracture treatments included three hydraulic stimulations, two in the sandstone section of the Lower Permian and one in the volcanic section. In low permeable volcanic rocks we performed a cyclic waterfrac treatment over 6 days in conjunction with adding low sand concentrations. Flow rates of up to 150 l/s were realized with a total amount of injected water of 13170 m³. Monitoring water level in the offsetting well EGrSk3/90, which is 475 m apart at the final depth, showed a very rapidly water level increase due to the stimulation treatment. A possible explanation might be a fault zone in the volcanic rocks. It was known from previous treatments in the offsetting well that high permeable sandstones do not show a self propping effect, hence we performed two gel proppant treatments in these sandstones to maintain long-term access to the reservoir. A total amount of 100 to of high strength proppants with 500 m³ of cross-linked gel were injected during each treatment. The subsequent production test in conjunction with flowmeter logging showed the success of the treatments.
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Processing Techniques to Extract Surface Wave Dispersion Curve from 3D Seismic Acquisition
Authors L. V. Socco, D. Boiero, C. Comina, S. Foti and R. B. RegeThe wide diffusion of 3D seismic surveying introduces the need of processing techniques able to extract dispersion curves from data acquired with 2D arrays. In this work we evaluate two processing techniques: the multidimensional Fourier transform and the Frequency Domain Beamforming method. Synthetics and real data have been analysed with the two methods for this purpose. Synthetic data has been obtained with a finite elements modelling and the computed dispersion curves have been compared with the theoretical one. In the analysis of real data the obtained dispersion curves have been compared with the one achieved through a linear array acquisition. The two tested processing methods have been able to correctly identify the fundamental and higher modes of propagation. The curves obtained with the two techniques do not differentiates significantly one from the other and are in agreement with the one obtained by a linear array and theoretical one. So, no advantages in choosing a specific method emerges in terms of result quality. However Beamforming method is more expensive for what concerns the computation.
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Retrieving Lateral Variations from Surface Wave Data
Authors D. Boiero and L. V. SoccoThe task of this work is the evaluation of the possibility to identify lateral variation through Surface Wave dispersion analysis even if these techniques are mainly used to characterise 1D subsoil models. This is done exploiting the data redundancy of the ground roll contained in seismic reflection or refraction data through a fully automatic processing procedure that allows to stack dispersion curves obtained from different records and retrieve experimental uncertainties. Hence the dataset to be inverted will be an ensemble of dispersion curves associated to a series of spatial coordinates along the seismic line. In this contest the use of Laterally Constrained Inversion (LCI) algorithm allows to manage such 2D effects in spite of the 1D model assumed for the forward problem solution. Different test have been conducted on different dataset for two synthetic models to evaluate the effects of the processing parameters, of the presence of noise and of lacks of information on the inversion results. All these effects have been observed applying lateral constraints of different strength during the inversion process.
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Joint Inversion of Seismic Data by Means of Multi-objective Evolutionary Algorithms
Authors G. Dal Moro and M. PipanAny sort of data is able to cast light only onto a specific aspect of the investigated problem. The implementation of a joint inversion scheme is meant to proficiently integrate the information that can be extracted from one dataset with those coming from another one. If the two objectives depend upon the same variables we can obtain a better-focused solution, while if the two objectives pertain (even just partially) to different variables thus their joint use can lead to new considerations characterized by a higher so-to-speak added value. The proposed computational scheme allows the joint inversion of non-commensurable datasets by means of analysis of the Pareto front performed in the framework of a Multi-Objective Evolutionary Algorithm (MOEA). The adopted approach also allows the validation of the provisional interpretation. In fact, Pareto front symmetry proves to be a valuable tool to verify the coherency of the adopted interpretation as an incorrect number of layers, reflector/refractor attribution or assumed Poisson values determine non-symmetric Pareto front as well as a wider model distribution in the objective space.
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GPR Rock Mass Imaging and Characterization by Attenuation Analysis
More LessWe apply Ground Penetrating Radar (GPR) to evaluate rock characteristics of interest in geological, geomechanical, hydrogeological, engineering and environmental studies. Primary objective of the study is 3-D imaging and detailed reconstruction of the electromagnetic velocity and attenuation field to define rock volumes that can be considered homogeneous from the geological and geomechanical point of view. The study is based on a series of experiments carried out in two test sites: a limestone quarry (test site-1) and limestone/dolomite contacts (test site-2). Rock mass characterization is performed by linking rock mass properties that can be estimated from GPR data to petrophysical properties (e.g. porosity, fluid content, permeability) and to rock characteristics such as texture, density of fractures and filling materials.
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Audio- and Radiomagnetotelluric Investigations of the Area of Railway Tunnel Route
Authors A. K. Saraev, M. I. Pertel and O. M. ProkofjevResults of audiomagnetotelluric (AMT) and radiomagnetotelluric (RMT) methods at the area of construction of the San-Pedro tunnel of the high-speed railway Madrid - Vayadolid are considered. Estimations of possibilities of used methods at study of deep structure of the area and detail mapping of rocks at the top part of cross section are fulfilled. A comparison of obtained results with data of previous investigations and drilling is carried out.
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Multi-disciplinary Approach for the Instability Analisis of a Down-town Site - Case Study
Authors L. Orlando and E. OlivetiThe paper treats the multi-disciplinary approach for the evaluation of instability of a down-town site using topographic monitoring, geological data, boreholes, electrical tomography and seismic refraction and reflection surveys. The latter was performed acquiring P and SH components.
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