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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
81 - 100 of 462 results
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Structural Evolution and Hydrocarbon Accumulation in Central Iran, Qum Region
Authors J. Letouzey, D. Baghbani, J.L. Rudkiewicz, L. Cuilhe and K. KazemiThe study area covered a segment of eastern Pomerania close to the Gdansk Bay. The region is regarded as prospective for hybrocarbon exploration. The main objective of gravity and seismic survey was to support interpretation of reflection seismic data. The problem of seismic survey in the area includes a highly reflective complex of Zechstein evaporates, which screen the propagation of seismic waves, and locally thick complex of unconsolidated sediments of Pleistocene, which severely attenuates seismic energy. As a result, poor quality data especially from sub-Zechstein complexes were often obtained. Magnetotelluric and gravity measurements were made mainly along seismic profiles. A part of gravity sites were scattered between profiles. Magnetotelluric surwey was made in two ways: as isolated soundings located at crossings of seismic profiles, and continuous profiling covering selected parts of profiles. Results of integrated gravity and magnetotelluric interpretation supplement results of seismic survey in relation to Paleozoic and Precambrian formations screened by very elastic complexes of Zechstein evaporates. A great diversity of density and resistivity in thick Silurian measures was found. Major tectonic zones in Paleozoic and Precambrian rocks were reconstructed. Results of gravity and magnetotelluric data interpretation are generally in agreement.
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Accurate and Verifiable Interwellbore Fracture Attribute Predictions
Authors P. Eichhubl, S.E. Laubach, J.E. Olson and R.H. LanderThe continuity of fracture porosity is of fundamental importance for fluid flow in tight formations. Some authors emphasize the role of in situ stress on determining which fractures are conductive and which are not, where the maximum permeability direction in fractured media is expected to align with the maximum compressive stress for opening mode fractures or with the strike orientation of critically stressed faults. Other work has focused on the role of diagenesis that occurs contemporaneous with or after natural fracturing events. Precipitation of cements in a fracture can prop it open, occlude the porosity, or otherwise affect the stress sensitivity of fracture permeability. In this paper, we examine the potential consequences of the interplay between diagenesis and mechanics in the development of a natural fracture network using diagenetic models that incorporate fracture, geomechanical models of fracture population growth that incorporate diagenesis, and extensive observations of fracture populations in core and in outcrop reservoir analogs. We report patterns of fracture growth and decay that are generally applicable to fractured siliciclastic and carbonate rocks.
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Determination of Permeability Zones and Traps by Means of the Proni Filtration Method
Authors S. Smolin, G. Mitrofanov and L. SlepokurovaPresent investigations concern to processing and interpretation of surface seismic data. It is the new method using for oil-field tasks solution. In particular the Proni filtration method can be applied to a solution of the task of zones detecting with high permeability and fractured which can be conductive to fluids reservoirs and traps of unstructured forms. Possibilities of this approach are demonstrated on the basis of real seismic data processing obtained in Western Siberia.
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Fractured Reservoir Characterization Using Post-Stack Seismic Attributes - Application to a Hungarian Reservoir
Authors A.M. Zellou, T. Royer, G.C. Robinson, P. Zahuczki and A. KiralyEfficient development of fractured reservoirs has been notoriously difficult. This inefficiency arises from the difficulty in locating the fractures in the reservoir. By synergistically combining seismic data, containing the interwell information, with geologic and engineering data at the wells, we develop a fracture model that honors the various datasets and successfully predicts the location of fractures within the reservoir.
The reservoir consists of fractured metamorphic basement, with a hereogeneous distribution of both porosity and fractures. Thirteen wells exist in the field, 5 of which were used in building the reservoir model. Seismic inversion and spectral decomposition were applied to a 3D seismic survey covering the field in order to generate attributes used in the fracture characterization. In addition to the 4 post-stack seismic attributes, gamma ray, porosity, and resistivity models and 9 geomechanical attributes were generated for the fracture modeling. Using these 16 attributes and the fracture intensity at the control wells, a fracture model was built for the reservoir using the continuous fracture modeling (CFM) approach. Validation using the blind wells indicates that the fracture model was able to successfully predict both the highly fractured zones and the relatively unfractured zones within the reservoir.
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Fracture Characterization at Clair - Analysis of P-Wave Azimuthal Anisotropy in 2D & 3D Ocean-Bottom Data
More LessOver the past ten years, there has been a continuous increase in the use of 3D P-wave data for fracture characterization. In this study, we analyze P-wave azimuthal anisotropy in three 2D OBC (Ocean-Bottom-Cable) lines combined with a patch of 3D OBC data from the Clair Field, in the UK continental shelf (UKCS), in order to assess how seismic anisotropy can help improving fracture characterization in this field. The three 2D OBC lines are at 45-degree angle with each other, intersecting at a well position, and overlaps with the 3D survey. Analysis of the P-wave amplitude and velocity at the intersecting point shows significant azimuthal variation. P-wave interval velocities show about 10% variation in azimuth and the orientation is at N94oE, agreeing with previous studies. The 2D and 3D results are consistent at the intersecting point, and the joint analysis of 2D and 3D data increases the spatial coverage and improves the accuracy, further confirming the potential for using azimuthal variations of P-wave attributes for fracture detection.
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Dynamic Characterization of a Karstic Reservoir - A Field Case Study
By F. GouthWell tests are commonly recognized as a valuable source of information for the large scale characterization of the dynamic behaviour of a reservoir. However, when the level of heterogeneity is high, the interpretation becomes complex as the data convolute multi-scale responses. A key to resolving the complexity may be to isolate the wells evidencing a specific flow mechanism.
This paper focuses on a karst reservoir where both emersion & hydrothermal circulation occurred. The static model has been discussed in a previous paper (1) and more specifically the way fractures control karst development. In the present work, we focus on the dynamic data and show how the main features of the karst can be characterized by the use of well test and pressure build up data.
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Detection of Out-Of-Zone Growth in Multi-Stage Hydraulic Fracturing by Microseismic Monitoring
Authors L. Eisner, T. Fischer and J. Le CalvezOut-of-zone growth in multi-stage hydraulic fracture treatments can be detected by analysis of microseismic multiplets. This novel technique allows detection of the out-of-zone growth when we observe a repeated hydraulic fracturing of the part of the reservoir which has been fractured in a previous stage (i.e. cross-stage fracturing). The cross-stage fracturing is detected by automated identification of multiplets, i.e. microseismic events with similar source mechanisms and nearly identical locations. We applied multiplet identification to detect the cross-stage fracturing on two hydraulic fracture monitoring datasets (Canyon Sand and Barnett Shale Formations) one of which is described in this paper. We verified this detection method with the initial microseismic events locations. The cross-stage fracturing was detected only a few minutes after the first microseismic events were detected.
The computation cost of this new multiplet identification method is a fraction of a second per detected microseismic event, thus making this application suitable for real-time monitoring. The identification of the multiplets provides additional information to the locations of microseismic events and can be used to verify or justify change during hydraulic fracturing treatment. The early detection of the cross-stage fracturing could lead to real-time adjustments of the hydraulic fracturing.
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Dynamics of Microseismicity by Hydraulic Fracturing - An Approach to Interpretation
Authors S.A. Shapiro, C. Dinske and E. RothertSeveral basic dynamic processes related to propagation of hydraulic fracturing modify the effective stress in rocks and, therefore, are relevant for triggering of microseismicity. For instance, these are the creation of the new fracture volume, fracturing fluid loss and its infiltration into reservoir rocks as well as diffusion of the injection pressure into the surrounding rocks and inside the fracture.
Here, using real data we show that some of these processes can be seen from features of the spatio-temporal distributions of the induced microseismicity. Especially, the back front of the induced seismicity starting to propagate after termination of the fluid injection seems to be characteristic and informative for the aims of reservoir engineering.
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Statistical Characterization of Rock Strength Using Fluid-Induced Seismicity
Authors E. Rothert and S.A. ShapiroWe estimate the strength of fractured rocks in-situy by analysing fluid-induced microseismicity. Such an analysis is able to provide us with a completely new feature of naturally fractured rocks. The strength corresponds to the value of critical pressure in the pore space that must be exceeded in order to trigger earthquakes. We assume that during hydraulic injection experiments in boreholes, microseismicity is mainly triggered by a diffusive process of pore pressure perturbation. An analytical solution can be applied to find time-dependent pore pressure perturbations in rocks. Characteristics of the spatio-temporal evolution of microseismic clouds can be then used to estimate minimum and maximum pressures necessary to trigger earthquakes as well as the full spectrum of rock strength. We verify the approach using numerical data and apply it to real data of injection-induced microseismicity from Hot-Dry-Rock tests in crystal
line rocks and a hydro-fracturing experiment in sediments. We find that quite low critical pressures are characterising the strength of pre-existing cracks for all data sets analysed. The strength of the rock at sedimentary environment is found to be at least one order of magnitude smaller than for crystalline rocks.
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Multiwave Seismic Survey under Conditions of Salt-Dome Tectonics of the South of Cis-Ural Trough
Considered are results of applying the multiwave seismic technologies based on the use of different types of seismic waves: reflected, scattered waves and waves of infrasonic seismic emission of hydrocarbon beds to solution of basic problems of prospecting HC reservoirs under complicated conditions of salt-dome tectonics. The use of multiwave seismic technologies allows solve such problems as building a detail structural plan, mapping fractured zones and identifying oil and gas saturation of reservoirs. By way of example considered is solution of these problems for the south of Cis-Ural Trough, particularly for the Akobinsk area.
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The Use of X-Ray Tomography in Complex Research of Rock-Collectors of Oil and Gas in Residual Soil of Carbonates
Authors E.A. Zhukovskaya and Y.M. LopushnyakThe use of X-ray tomography by complex research of full-size core sample of oil-filled pre-Jurassic bauxite-like and strongly sideritised rocks of Urmansk oilfield (Western Siberia) allows to explain the absence of dependence between their physical and collector properties, and also between the structure of rocks
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Relocation of AE Events from a Compression Test of a Rock Salt Specimen by Coherence Collapsing Method
Authors H. Asanuma, A. Hotta, G. Manthei and H. NiitsumaThe authors combined the concept of the Collapsing method and multiplet analysis, and derived an algorithm that is a variation of the collapsing method (Coherence Collapsing method). In the Coherence Collapsing method, the absolute locations of the multiplets are selectively located to the simplest structure, and the whole AE/MS cloud is optimized in the same manner as in the Collapsing method. Because the multiplets are related to the multiple slip of a fracture/fault, their locations are of importance to interpret the physical phenomenon. In this paper, we describe an application of the Coherence Collapsing method to the AE events from a compression test of a salt rock specimen and compare the locations with the distribution of the fractures in the specimen.
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Use of Reflected and Scattered Seismic Waves to Build Geologic Model of Riphean Reservoirs of East Siberia
Considered are results of applying Side-View Seismic Location method (SVSL), designed for mapping open fracturing based on scattered seismic waves, and structural 2D seismic based on Focusing Transformation of seismic wavefield for refining a geological model of the Riphean complex of East Siberia (Kuyumba oil field) and identifying fractured zones which are promising drilling targets. Proposed is a technique for identifying organogenic reef structures in the interval of Riphean complex. This technique allows materially improve the reliability of geological recommendations for selecting optimal exploratory drilling sites and produce oil at a maximum flow rate. Based on the use of information about a distribution of subvertical tectonic fracturing and location of organogenic structures submitted are recommendations for drilling exploratory wells
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Integrated Study Of Fracture Characterization Using 3D P-Wave Seismic Data in Southwest China
More LessHere, we present a case study of fracture detection using 3D P-wave seismic data from the Sichuan Basin in Southwest China. A major aspect of this study is the integration of outcrop, core and wireline logs with seismic data for reducing the uncertainties in the seismic results. The target is a gas reservoir buried at about 1700m in depth, and the reservoir rocks are tight sandstones with an average porosity about 2% only, and fractures are the main fluid pathways. Analysis of core and log data from 21 boreholes reveals that there are two major sets of fractures in the study area striking northeast and northwest, respectively, with an average linear fracture density about one fracture every two metres. We have processed and analyzed 50 square kilometres of 3D P-wave seismic data in order to evaluate the fracture characteristics between the boreholes. The seismic data is of average quality. Nevertheless with carefully-calibrated processing, the final fracture orientation and intensity maps estimated from the amplitude attributes compare reasonably well with the regional pattern in the area, and the seismic results at the well locations are consistent with the borehole results.
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Spectral Attenuation Analysis in a Mexican Mature Oil Field
Authors L.C. Ramirez, L.C. Ramirez and R. del ValleSeismic attenuation analysis is used to distinguish changes in the spectral and amplitude characteristics of the seismic signal with the purpose of identifying the presence of fluid and fractures within the rock system. The analysis of such chances can be used as a tool for characterizing rock properties and for understanding the behaviour of wave propagation in a complex environment composed by pores and cracks containing fluids. The study is carried out using high-resolution reflection data obtained from a mature fractured carbonate reservoir near the northeast coast of Mexico. Production from this reservoir is declining considerably. For that reason, a horizontally drilling program is considered. The result obtained from in situ measurements indicates that the spectral changes and attenuation anomalies are related to the presence of hydrocarbons on the fractured reservoir rocks; however, such anomalies are also related to the highly fractured areas due to wave scattering. The seismic attenuation patterns associated to productive zones helped to identify new potential areas and in assisting for horizontal drilling targets.
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Benefits of Full-Waveform Modelling and Inversion. A Case Study from the Polish Basin
Authors M. Malinowski and S. OpertoIn this study we present the workflow and results of modelling the 3D wide-offset data acquired in central Poland during the GRUNDY 2003 seismic experiment. Previously those data were modeled using more "conventional" approach, like reflection processing and the traveltime tomography. Here we focus on the application of the frequency-domain full-waveform tomography for the interpretation of such kind of seismic data. We consider this method as a tool for obtaining both the structural image and a detailed velocity field in single step without the need for performing prestack migration or forward ray-tracing modelling. The validity of our results was tested by the comparison with well velocity survey.
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Elastic Parameter Estimation from the 2D Waveform Inversion of a Look-Ahead Walk-Away VSP Survey
Authors M.A. Roberts and S.C. SinghPore pressure in sediments beneath salt in the Gulf of Mexico varies widely creating a potentially dangerous and difficult drilling challenge. The elastic parameters are key to identifying many attributes, but in this paper the elastic parameters are being estimated with the aim of predicting the pore pressure in the sedimentary layer immediately below the salt. The elastic parameters have previously been estimated using an AVO type approach. In this paper we investigate the ability of full waveform inversion to estimate the P-wave and S-wave velocity models from a walk-away VSP in the context of a salt dome. Results demonstrate the ability to further localize the position of the bottom of the salt and extract velocity information beneath the salt.
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Comparison of Regularization Techniques for Waveform Inversion
More LessWe compare different regularization techniques of the steepest-descent directions appearing in waveform inversion using a backpropagation technique. In the waveform inversion using the steepest-descent method, we can have better convergence to a true velocity model by regularizing the steepest-descent directions properly. The regularization can be done by using the diagonal of pseudo Hessian matrix instead of using the approximate Hessian matrix that appears in Gauss-Newton method but is too expensive to calculate. We can apply the regularization to inversion algorithms in two different ways. One is to regularize the steepest-descent direction at each frequency independently. The other is to regularize the steepest-descent direction summed over entire frequency band. The former plays a role of equally distributing a weight to the steepest-descent direction at each frequency. For the conventional waveform inversion, the former gives better results than the latter. We also applied the two regularization methods for the logarithmic waveform inversion, which gives better results than the conventional waveform inversion for the original Marmousi data. Numerical examples showed that the logarithmic waveform inversion is not sensitive to the regularization, because the logarithm makes the steepest-descent direction at each frequency commensurate with each other.
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Conventional vx. Cepstral Full Waveform Inversion
Authors J.B. Bednar and C. ShinConventional vs full wavform inversion is usually a least squares process. In this paper we investigate the use of a logarithm or cepstrum style objective function and show that this approach is vastly superior to the more traditional method.
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Distant Relief Effect and Its Possible Impact on Large-Scale Gravity Interpretations
Authors J. Mikuska, R. Pasteka, I. Marusiak, M. Bielik and M. HajachIn gravimetry, the topography and bathymetry beyond the angular distance of approximately 1.5 degree from the point of calculation (we call it distant relief) is conventionally not accounted for. However, the availability of powerful personal computers as well as satellite digital elevation models, allows us to estimate the effects of those features on the measured gravity and thus also on the values of Bouguer anomalies. Using an approximate spherical Earth model, we have calculated distant relief effect as well as its vertical gradient within the territory of Central Europe. We show that although distant relief effect varies relatively slowly in the study area, it can occasionally be considered in the framework of large-scale gravity studies. On the other hand, vertical gradient of the distant relief effect is practically negligible.
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