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78th EAGE Conference and Exhibition 2016
- Conference date: May 30, 2016 - June 2, 2016
- Location: Online
- Published: 30 May 2016
51 - 100 of 1034 results
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Integrated Structural Reconstruction and History Matching Using Ensemble Filter and Low-frequency Electromagnetic Data
Authors C. Etienam, R. Villegas and M. BabaeiSummaryIn this work, we describe a new integrated structural reconstruction approach based on the level set technique and ensemble Kalman filter-based history matching1 using water saturation distribution from low-frequency electromagnetic techniques (Maxwell’s equations) 2 and initial stochastic realisations of permeability distribution. In this work, we discuss the use of the ensemble Kalman filter combined with the Level Set method3 to solve the severely ill-posed problem of parameter and shape reconstruction in history matching of 3D reservoirs. The developed algorithm utilizes Sequential Gaussian Simulation for the creation of the initial geostatistical guesses for permeability which will then be utilized in the ensemble Kalman filter for honoring dynamic production data. The production data here includes water and oil production rates and water saturation distribution from low frequency EM reconstruction. This integrated methodology allows to obtain a better match of the produtcion data honouring the water monitoring obtained from low frequency EM data and also considering the initial model uncertatinty based on geostatistical techniques. The methodology is applied to a 3D syntethic oil reservoir model, the simulator (Schlumberger’s ECLIPSE E100) has been employed for the forward modelling and our in house Fortran and matlab codes has been employed for the History Matching and Electromagnetic reconstruction.
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Geostatistical History Matching with Ensemble Updating
Authors M.J. Quintão, A. Soares and L. AzevedoSummaryIn this work we propose a new history matching methodology that couples within the same framework the benefits of using geostatistical sequential simulation and the principles of ensemble Kalman filters, denominated as history matching based on ensemble updating. The main idea is to use simultaneously the relationship between petrophysical properties and the dynamical results in this process, to update the static properties at each iteration and to define the areas of influence of each well. This relation is established through the experimental non-stationary covariances, simply computed in the several forms of the Ensemble Kalman Filters (EnKF) for history matching of hydrocarbon reservoirs. The proposed iterative history matching procedure was applied to a 2D synthetic reservoir, built to mimic a classical 5-spot configuration with 4 producers located near the corners of the model and an injector well in the center of the grid. In order to assess the performance of the proposed approach, comparison tests were carried out in order to distinguish the advantages of the two main enhancements proposed: the use of areas of influence and the ensemble updating.
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Different approaches for prediction of reservoir volume in slope channel complexes (Miocene, offshore Nile Delta, Egypt)
Authors S. Lang, G. von Halem, A.H. Hassan Soliman and U. LorangSummaryTurbidite channel complexes are important reservoirs. Due to their heterogeneous architecture it is difficult to quantify the gross reservoir volume. Three methods were tested at a prospect case study. Seismic data quality allowed the detailed mapping of four sets of amalgamated channels inside the channel complex. The reservoir volume was calculated by multiplying the horizon area by thickness. Afterwards, it was tried to obtain the reservoir volume by applying an amplitude cutoff to the seismic and multiplying the cumulative amplitude area with a thickness. In a third approach, an acoustic inversion has been carried out and calibrated at a nearby well. Sand bodies have been extracted as geobodies based on an impedance cutoff. All three gross reservoir volumes were divided by the channel complex volume in order to compare the resulting net/gross ratios and they vary from 5%–20%. These net/gross ratios are lower than the net/ gross encountered in a well in a nearby channel complex, which is in-line with an observed higher sand content on seismic at that well location. Therefore, estimating gross rock volume from seismic could reduce the uncertainty compared to using offset well data only.
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Stratigraphic Compartmentalization of the Alvheim Field
Authors A. Hjellbakk, A. Bang, A. Kotwicki, K. Langaas, M.A. Leonthin and K.L. StuartSummaryThe reservoir of the Alvheim Field is the upper part of the deep-marine deposited Palaeocene Heimdal Formation. It is located in the Northern part of the Norwegian North Sea with a small portion extending into the UK sector. Despite the reservoir’s high net to gross ratio of more than 85%, a 1.5–5 meter thick continuous mudstones exists and is in places causing reservoir compartmentalization, even resulting in multiple hydrocarbon columns. A tripartite subdivision of the reservoir was originally made based on log correlation, biostratigraphy and seismic interpretation. This reservoir subdivision was used as input to the reservoir models, which together with a new 4D seismic data set built a good basis for the 2015 infill-well planning. During the infill drilling of pilot wells with single, dual and trilateral producers, new and important information became available, including data from deep resistivity tools which were run in all horizontal branches. The well results were interesting and partly surprising, leading to a significant adjustment of the stratigraphic model. The incorporation of the persistent claystone units into static and dynamic 4D supported models is essential to get a realistic simulation of the reservoir behavior, and to locate undrained targets for future infill drilling.
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Mid-late Miocene Sea Level Falls, Gas Hydrates Decay, Submarine Sliding, and Tsunamites in the Black Sea Basin
Authors A.A. Kitchka, A.P. Tyshchenko and V.I. LysenkoSummaryFull range of structural settings and related features of extensional, translation and compressive domains of the submarine mass transport complexes (MTCs) has been recognized by thematic interpreting of the regional 2D seismic data covering Ukrainian deepwater area in the Black Sea. At the same the time the synchronous to deepwater MTCs the Sarmatian tempestites or even tsunamites known under local name heraclites as well as seismites are described and studied in the SW Crimea in the rock cliffs of the Heraclean Plateau south of Sevastopol. This study links the rapid pulses of the Black sea level fall in the Middle to Late Miocene epoch accompanied by erosion of the shelf break areas and formation of submarine incision valleys, dissociation of gas hydrates, slope failures and large scale rock downslides triggering tsunamis (that imprinted the shore sequences outcropping around the basin) as precursors and characteristic features of the Messinian crisis s.l. manifestation in the Paratethys sea belt further evolved during the Meotian to culminate in mid-Pontian time.
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Deep Water Depositional Architecture, Evolution and Reservoir Potential in the Rakhine Basin, Offshore Myanmar
More LessSummaryFrom 2004 to 2006, 3 biogenic gas fields (Shwe, Shwe Phyu, and Mya) were discovered in Rakhine Basin. Since then, the Rakhine Basin has been the focus of deep water exploration. In our research, industrial and high-resolution 2D and 3D seismic and well data were analyzed to study deepwater architectural elements, depositional evolution and hydrocarbon reservoir potential of the Rakhine.
Six different types of architectural elements are recognized in the Rakhine basin: submarine canyons, confined slope channel complexes, aggradational channel-levee complexes, frontal splays, isolated slope channels, and mass-transport complexes.
Deepwater depositional system showed continuous progradation, and the extent and scope strengthened and widened gradually from the Late Eocene to Pleistocene. The Oligocene mainly comprised confined slope channel complexes. The Miocene was dominated mainly by confined channel complexes and levee-overbank sediments. The Pliocene mainly consisted of confined slope channel complexes, frontal splays. The Pleistocene mainly developed aggradational channel-levee complexes, frontal splays, and mass transport complexes.
Controlled by structural and depositional evolution, the Pliocene confined slope channel complexes and frontal splays have the best reservoir potential in the study area. In gentle fold belt, there are numerous frontal splays and various types of slope channels that remain untested.
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Sequence Stratigraphy of the Middle Jurassic Dhruma Formation in the Oman Mountains (Sultanate of Oman)
Authors M. Schlaich and T. AignerSummaryThis outcrop analog study focuses on a genetic understanding of the reservoir/seal potential and architecture of the Jurassic Dhruma Formation in Oman. As a joint project of the University of Tübingen (Germany) and Petroleum Development Oman (PDO) outcrop logging in nine sections in the Oman Mountains was carried out, supplemented by thin section analyses and spectral gamma-ray measurements. Observed facies types range from peritidal sandstones and microbial laminites to low-energy lagoonal deposits and high-energy, peloid and ooid dominated, shoal associated deposits. Cores and cuttings of the Dhruma, Tuwaiq Mountain and Hanifa/Jubaila Formations were logged over central and northern Oman. A sequence stratigraphic framework and 2D correlations were established based on litho-, chemo- and biostratigraphy. They reveal a clear decrease in thickness of the Dhruma Formation from west to east, which is due to (1) a small unconformity at the bottom and (2) a large Tithonian unconformity, which cuts down into Jurassic strata, eroding the whole Hanifa/Jubaila and Tuwaiq Mountain Formations as well as the top of the Dhruma Formation in outcrops. A 3D geo-cellular facies model was created with Petrel for the Dhruma, Tuwaiq Mountain and Hanifa/Jubaila Formations in central and northern Oman which has implications for the regional prospectivity.
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Sequence Stratigraphic Analysis of the Lower Cretaceous of South Pakistan
By S. MahmoudSummarySedimentological, chronostratigraphic, and sequence stratigraphic interpretations were integrated in order to predict four types of systems tracts, which were used as the building blocks of each interpreted sequence, which, in turn, were used in prediction the chronostratigraphic framework and depositional history of the Lower Indus Basin within the Jati Block. The study highlighted the importance of forced regressive sands of the Falling Stage systems Tract, as high-quality reservoirs encased in shelf mudstones, forming favorable targets for hydrocarbons due to the effective lateral and vertical seals and the expected maturity of intra-formational source rocks. Several lines of evidence support the frequent presence of these forced regressive sands as indicated from seismic attributes, well log sedimentology and sequence stratigraphy, well to well correlation, and from the established sequence models.
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Hydrocarbon Occurrences and Deformation Styles in the Zagros - A Focus on the Kurdistan and Lorestan HC Provinces
Authors R. Di Cuia, P. Pace, R. Bitonte and A. RivaSummaryThe Zagros Thrust Belt is a prolific hydrocarbon province. Intense exploration has been mainly focused on the productive Fars Zone and Dezful Embayement regions of Iran in the central sector of the Zagros thrust belt. During the last years, the NE-SW-trending northwestern sector of the Zagros, extending over the Kurdistan region of northeast Iraq and the Lorestan province of Iran has increasingly received attention related to a renewed interest for hydrocarbon exploration. In this study, compressional features over the Kurdistan and Lorestan regions were characterized from regional to local-scale by integrating various data and methodologies in order to contribute in a better understanding of the compressional deformation styles, mechanisms and evolution of the trap-forming structures and their impact on hydrocarbon occurrences.
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Detachment Folding in the Polar Urals Foreland -Structural Geology and Hidden Petroleum Potential
Authors K. Sobornov, V. Danilov, P. Prijmak and N. NikinovSummaryRegional interpretation of vintage and recently acquired geological and geophysical data provided new insight into structure and petroleum habitat of the Polar Urals foldbelt. The study shows that the deformations observed in the Polar Urals foreland are mainly related to the thrusting and detachment faulting. The principal detachment in the sedimentary cover is provided by the Upper Ordovician evaporates which is pinching out if the area of the Chernyshov swell. The updated structural model permits the identification of the new large exploration opportunities. Bulk of the new gas reserves is predicted in the folded zone in front of the Urals involving large thrust-related closures. Significant oil discoveries are expected in the transition zone between the Chernyshov swell and the Kosyu Rogov foredeep which is a focus of regional hydrocarbon migration. New seismic data provide evidence for the considerable development of the hypogenic karst and dolomitization of the Serpukhovian sulphates and carbonates capable increasing porosity of the reservoirs.
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Sparse Ocean Bottom Node on the Alwyn Field - From Acquisition to Joint PP-PS Imaging
Authors J. Brunelliere, S. Sioni, A. Mitra, X. Lu and A. KaragulSummaryThis case study presents the first ocean bottom node (OBN) survey acquisition and processing over the Alwyn field. The objectives of this sparse acquisition were the enhancement of lateral and vertical resolution of Triassic reservoir. Vintage seismic data consists of three conventional towed streamer surveys acquired in 1981, 1995, and 2000, suffering from limited illumination and none are repeat surveys. This new OBN survey, full azimuth, long offset seismic provided both P and PS-waves datasets for imaging and pre-stack AVO joint inversion.
The objective of this paper is to present the acquisition and processing of both P and PS-wave. Early P-wave output, obtained three months after start of processing, showed the potential of OBN data. This volume confirmed the step change in imaging over existing vintage data. PS-wave intermediate images could only be compared with P-wave due to lack of legacy PS data; structural imaging using PS data remained a challenge, however results are expected to bring value at the joint pre-stack PP-PS inversion stage.
This project demonstrated the ability of sparse OBN data to provide improved P-wave imaging at reservoir levels. Parallel P & PS-wave processing allowed a reduced turnaround time for an early PP & PS joint AVO inversion.
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Sparse Nodes and Shallow Water - PS Imaging Challenges on the Alwyn North Field
Authors J. Holden, D. Fritz, O. Bukola, J. McLeman, R. Refaat, C. Page, J. Brunelliere, S. Sioni, A. Mitra and X. LuSummaryImaging PS-wave data acquired in the shallow water at Alwyn North with ROV-deployed ocean-bottom nodes presented particular challenges due to the sparsity of the receivers. Having ensured vector fidelity of all recorded wavefields, the processing flow made simultaneous use of the PP and PS wavefields at several junctures, including construction of the imaging velocity-depth model, requiring all wavefields to be processed in parallel and in a consistent manner. Shear-wave splitting corrections and PS demultiple were addressed to improve PS data resolution and achieve data consistency. Constructing an anisotropic velocity model based on residual move-out analysis alone was not feasible as the sparse receiver sampling resulted in poor near-offset coverage. To mitigate this full waveform inversion was used to update the P-leg velocity, and surface wave inversion for the S-leg in the crucial near-seabed interval most affected by the slowest shear velocities. Joint PP-PS non-linear tomography was used to refine this velocity model. PS-wave controlled-beam pre-stack depth migration was used extensively to assess the pre-processing as well as to validate updates to the velocity model. The resultant PS-wave data, imaged with a depth model consistent with that used for the P-wave imaging, were thus suitable for joint PP-PS elastic inversion.
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Benefit of OBS PP and PS Data for Structural Interpretation on Snøhvit and Albatross Fields
Authors B. Osdal, H. M. Zadeh, M. S. Guttormsen, H. A. Aronsen, D. C. Cannavo and G. O. ØxnevadSummaryIn this case study from Snøhvit and Albatross we show how Ocean Bottom Seismic (OBS) PP and PS data is used to improve the structural interpretation of reservoirs below overburden shallow gas anomalies. Comprehensive processing, velocity model building and data integration were crucial to achieve good results. The OBS PS has a good quality below the shallow gas anomaly on both Albatross and Snøhvit. On Snøhvit, OBS PP data shows better quality compare to streamer data. This clearly reduces uncertainties related to structural interpretation compare to streamer data alone.
However, on Albatross the quality of both OBS PP and streamer data are poor, and high quality OBS PS data has given largest impact on structural interpretation. Updated structural interpretation greatly improved our geological understanding and may change the reservoir management of the field.
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Full-azimuth Ocean Bottom Seismic for Imaging Beneath Complex Overburden at Johan Sverdrup
Authors B. King, S. Winterstø, J. Nilssen, D. Underwood, D. Brager, S. Mitchell and J. AvilesSummaryStructural interpretation of reservoir events at the Johan Sverdrup field in the North Sea can be challenging in areas with complex overburden. Re-mobilised sands (injectites) with very high velocity relative to surrounding sediments cause strongly localized pull-up of deeper reflections. In addition, shallow channels less than 200m below sea bed filled with low velocity sediments cause pull-down effects. Both pull-up and pull-down effects can leave imprints in the interpretation of reservoir events.
We will show how Ocean Bottom Seismic (OBS) data with long offset and rich azimuth can help resolve such problems, by either under-shooting the injectities completely, or by providing high quality data to enable better processing and velocity model building, including FWI.
The survey was acquired at a reduced cost by using a system with multi-component nodes connected by passive cables. We will show that good data quality was achieved using this system, and we will discuss the additional processing steps required.
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Efficient Wave Mode Separation in Anisotropic Media - Part I-Separation Operators
More LessSummaryIn this paper we present efficient wave mode separation operators in anisotropic media. These operators are constructed by local rotation of wave vector to direction where qP-wave is polarized. The deviation angle between wave normal and qP-wave’s polarization direction is spatially estimated using poynting vector. The proposed operators provide comparable results with those generated by classical space domain convolution operators in anisotropic media. In the meantime, the added computational cost by applying new operators is small when compared to divergence and curl operators as used in isotropic case. Synthetic results validate the effectiveness of the present operators.
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Efficient Wave Mode Separation in Anisotropic Media - Part II-Phase and Amplitude Corrections
More LessSummaryIn this paper we present two improved wave mode separation methods in anisotropic media. The proposed methods aim to efficiently implement wave mode separation while preserving properties of decomposed physical quantities from original elastic wavefields. The first approach is using vector decomposition which output decomposed wave modes with same amplitude, phase as the input wavfields. The second method is introducing amplitude and phase corrections to divergence-like and curl-like operators, then wavefields energy can be conserved in wave mode separation. Synthetic results verify the effectiveness of the proposed methods.
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A New Scalar Imaging Condition for Vector-based Elastic Reverse Time Migration
More LessSummaryScalar images (i.e. PP-, PS-, SP- and SS-wave images) of elastic reverse time migration (RTM) can generated by applying an imaging condition to pure wave modes. Decoupled P- and S-wave equation provides an alternative way to separate P- and S-wavefields in elastic RTM. However, the output separated wavefields are both vectorial. To obtain the scalar images, we propose a new imaging condition in which the scalar product of two vector wavefields is exploited to produce scalar images in elastic RTM. For this scalar-product-based source-normalized elastic crosscorrelation condition needs, no additional prior information is required, except for the P- and S-wave velocities. And additional polarity reversal correction methods are not required to correct polarity changes in converted-wave images for the output separated wavefields have consistent amplitude polarity. Numerical example on Marmosui2 is used to test the effectiveness and robustness of our new imaging condition.
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Elastic Reverse Time Migration Based on Decoupled Wave Equation and Inner Product Imaging Condition
More LessSummaryIn conventional elastic reverse time migration, Helmholtz Decomposition is applied for wavefield separation, which leads to polarity reversal in converted wave imaging. In this paper, we introduce a vector wavefields separation method with amplitude preserved based on decoupled elastic wave equation and illuminate the specific physical meaning of the vector P- and S-wave. In addition, the inner product imaging condition is utilized to obtain image results form the vector P- and S-wavefield. Analysis of imaging kernel indicates that the presented method can effectively circumvent polarity reversal in ground seismic exploration. Migration results have demonstrated the feasibility and effectiveness of this imaging method.
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A Single-sided Representation for Virtual Sources and Virtual Receivers
Authors K. Wapenaar, J.W. Thorbecke, J.R. van der Neut, S. Singh, E.C. Slob and R. SniederSummaryVirtual sources can be created in several ways. In seismic interferometry, a virtual source is created by crosscorrelating responses at different receivers, which are illuminated from all directions. Seismic interferometry can be mathematically described by the homogeneous Green’s function representation, which is a closed boundary integral.
Virtual sources can also be created with the Marchenko method. For the Marchenko method it is sufficient that the position of the virtual source is illuminated from one side. We derive a single-sided homogeneous Green’s function representation, which is an open boundary integral along reflection measurements at the surface. Applying this representation, we obtain virtual sources and virtual receivers in the subsurface from real sources and receivers at the surface (note that in our earlier work on the Marchenko method the response to the virtual source was only obtained for receivers at the surface). The retrieved virtual data show the entire evolution of the response to a virtual source in the subsurface, including primary and multiple scattering at unknown interfaces.
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Full-wavefield Redatuming of Perturbed Fields with the Marchenko Method
Authors I. Vasconcelos and J. van der NeutSummaryWavefield extrapolation, or redatuming, is a critical step for imaging. It is particularly challenging in areas such as subsalt or under complex overburdens. The framework of Marchenko redatuming allows for the retrieval of up- and downgoing fields at chosen locations in the subsurface that contain primary arrivals and internal multiples, while requiring relatively little knowledge of the subsurface model. In this paper, we present a new form of the Marchenko system for perturbed fields. Based on this system, we present a new iterative scheme that explicitly reconstructs only the unknown perturbations to the Marchenko focusing functions, and by consequence only the perturbed/scattered up- and downgoing Green’s functions. This new scheme departs from previous versions of the method in that it requires additional inputs, which include an extra initial focusing operator and perturbations to the surface reflection data. We validate our method with numerical tests, showing that it is particularly well-suited to properly handle complex models with large/sharp constrasts such as salt boundaries. We foresee this new approach to be of use not only in general imaging applications, but also for time-lapse studies as it can directly redatum time-lapse changes.
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Constructing Only the Primary Reflections in Seismic Data - Without Multiple Removal
Authors G.A. Meles, K. Wapenaar, A. Curtis and C. da Costa FilhoSummaryState of the art methods to image the Earth’s subsurface using active-source seismic reflection data involve reverse-time migration (RTM). This, and other standard seismic processing methods such as velocity analysis, provide best results only when all waves in the data set are primaries (waves reflected only once). A variety of methods are therefore deployed as pre-processing to predict multiples (waves reflected several times); however, accurate removal of those predicted multiples from recorded data using adaptive subtraction techniques proves challenging, even in cases where they can be predicted with reasonable accuracy. We describe a new, alternative strategy: we construct a parallel data set consisting of only primaries, which is calculated directly from recorded data. This obviates the need for both multiple prediction and removal methods. Primaries are constructed using convolutional interferometry to combine first arriving events of up-going and direct-wave down-going Green’s functions to virtual receivers in the subsurface. The required up-going wavefields to virtual receivers are constructed by Marchenko redatuming. Crucially, this is possible without detailed models of the Earth’s subsurface velocity structure. The method is shown both to be particularly robust against errors in the reference velocity model used, and to improve migrated images substantially.
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Coupled Seismo-Electromagnetic Interferometry for 2D Homogeneous SH-TE Scenarios
Authors N. Grobbe, E.C. Slob and C.P.A. WapenaarSummaryWe here explore the application of interferometric principles to the coupled seismo-electromagnetic system. We consider 2D homogeneous space scenarios, and focus on one of the two seismo-electromagnetic propagation modes, the SH-TE mode, where horizontally polarized shear-waves are coupled to the transverse electric mode.
We start by presenting the theory for retrieving seismo-electromagnetic Green’s function responses via interferometry by cross-correlation.
Using explicit homogeneous space solutions, we numerically investigate the interferometric retrieval of an electric field response and a magnetic field response due to a seismic source. We first study the theoretically desirable circular source configuration, providing illumination from all sides, followed by a more realistic line source configuration, exploiting the interferometric far-field approximation. These two numerical examples prove for the selected source-receiver type combinations, that we can indeed retrieve correct dynamic seismo-electromagnetic 2D SH-TE responses using seismic boundary sources only. This is a promising result for the next step: applying 3D seismo-electromagnetic interferometry in the field.
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Anisotropic Seismic Noise Gradiometry by Elliptically-anisotropic Wave Equation Inversion - An Example Ekofisk
Authors S.A.L. de Ridder and A. CurtisSummaryWe propose an anisotropic wavefield gradiometry technique to extract azimuthally anisotropic phase velocities from seismic noise that is dominated by a single surface wave mode. The method relies on a two-dimensional elliptical-anisotropic wave equation. This wave equation equates the spatial derivatives of the wavefield amplitudes with the temporal derivatives through the elements of a two-by-two matrix characterizing the medium parameters. The derivatives are evaluated using finite differences, and the system is inverted with a smoothness constraint. We test the procedure on ambient seismic noise recorded in a large and dense array installed over Ekofisk field. Because the station spacing is much larger cross-line then inline, the approximation error of the spatial finite difference results in an apparent anisotropy. From an experiment with synthetic isotropic plane waves, we define a Jacobian to correct the finite difference stencils. With the corrected finite difference stencils, we extracted anisotropic phase velocities at Ekofisk from as little as 10 minutes of seismic noise recordings. The azimuthal anisotropy forms a circular geometry around the production induced subsidence bowl. The methodology is a promising technique for studying changes in the subsurface geomechanical stress-state resulting from time-dependent phenomena operating at a short time-scales.
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Use of Ambient Noise to Enhance Low Frequencies Seismic Migration Images
Authors B. De Cacqueray, J. Cotton, F. Duret, C. Berron and E. ForguesSummaryIn this study, we propose an example of body wave retrieval using ambient noise correlation. The correlated data are migrated using a Kirchhoff pre-stack time migration (PSTM) and then with the migration obtained with conventional active data. It allows to considerably broaden the final image spectrum toward the low frequencies.
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Shallow Rayleigh-wave Tomography Using Traffic Noise From Long Beach, California, USA
Authors J.P. Chang, S.A.L. de Ridder and B.L. BiondiSummaryUsing recordings from a dense seismic array in Long Beach, California, USA, we demonstrate the effectiveness of using traffic noise for shallow subsurface imaging. Using the ambient-noise cross-correlation technique at frequencies greater than 3 Hz, we extract fundamental- and first-order-mode Rayleigh waves generated by Interstate 405 and local roads. We use group travel times associated with the fundamental mode in a weighted straight-ray tomography procedure to produce group velocity maps at 3.0 Hz and 3.5 Hz. The velocity trends in our results correspond to shallow depths and coincide well with lithologies outlined in a geologic map of the survey area. The most prominent features resolved in our velocity maps are the low velocities in the north corresponding to less-consolidated materials, high velocities in the south corresponding to more-consolidated materials, a low-velocity zone corresponding to artificial fill in Alamitos Bay, and a low-velocity linear feature in the Newport-Inglewood Fault Zone.
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Locating Scatterers Ahead of a Tunnel Boring Machine Using Noise Correlation
Authors U. Harmankaya, A. Kaslilar, K. Wapenaar and D. DraganovSummaryThe investigation and detection of faults, fractures, karst zones, cavities, etc., is important to reduce hazardous risks, in particular during excavation with tunnel boring machines. To locate such scatterers, we propose a method based on seismic interferometry that uses the noise signals generated by a TBM. Using finite-difference modelling of TBM noise in a homogeneous half-space, we model noise recordings. We then correlate the noise to obtain non-physical scattered arrivals for various scatterer locations. We use both non-physical scattered P- and S-wave arrival times to successfully estimate the location of scatterers.
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3D Modeling of the Regional Basement Structure Off- and Onshore Congo Based on Inversion of Satellite-derived Gravity Da
More LessSummaryThe regional geology of the African equatorial west coast is complex and not well understood since the seismic coverage of deeper crustal features is sparse. The intricate structural settings are also reflected in potential field anomalies, and in particular in gravity data. The presented study primarily aims at estimating basement depths from satellite-derived gravity anomalies in a 400 km by 300 km wide area off-and onshore the territories of Congo, Cabinda, and the Democratic Republic of Congo. Where available, well and seismic data are used to constrain the inversion. The final 3D density model indicates a lateral division in 3 zones (oceanic crust, transition zone, continental crust) and maximum sediment thicknesses of 2.5 / 7.5 km on- / offshore. Although non-uniqueness and ambiguity of potential field data still pose challenges, it is concluded that public-domain gravity data can add useful information for regional modeling.
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Applying Magnetic Magnitude Transforms to Aid Structural Mapping in Areas Where the RTP Calculation Is Unreliable
Authors S. Cheyney, C.M. Green, S.J. Campbell and D. de LermaSummaryA common use for magnetic data is to locate the edges of subsurface bodies. Numerous transformations have been developed in order to obtain more easily interpretable maps, however many initially require the data to be reduced to the pole (RTP) if they are to be used for edge detection. The RTP operation is unstable at low magnetic latitudes, which affects significant areas of equatorial regions currently of interest to the oil and gas industry. In addition, any remanent magnetisation will often lead to anomalous results.
We demonstrate the advantages and disadvantages of using magnitude transformations, focusing on the scenarios where they are likely to be the most useful: at low latitudes and in the presence of remanent magnetisation. Based on synthetic modelling, magnitude transforms equivalent to 1st or 2nd order derivatives of the magnetic field appear most suitable, however when applied to real data the effects of enhancing the noise level limits the usefulness. The Total Amplitude, which is of the same order as the observed TMI data, has higher centricity than the TMI allowing lineament interpretation, without biasing the result to shorter-wavelength features and accentuating the noise level in the data.
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Noise Rejection in Processing of Magnetic Data - 2D Fourier Transformation Treated as an Inverse Problem
Authors H. Szegedi, A. Kiss, M. Dobroka and Á. GyulaiSummaryIn this paper, a new, robust and resistant, inversion based 2D Fourier transformation is presented where the spectrum is discretized by series expansion (S-IRLS-FT). The series expansion coefficients as model parameters are given by the solution of the inverse problem. Since it is advantageous to use squared-integrable, full, orthogonal and normed basis functions, Hermite-functions are chosen as basis functions of the inversion based Fourier transformation. Taking advantage of the beneficial properties of Hermite polynomials, that they are the eigenfunctions of the inverse Fourier transformation, the elements of the Jacobian matrix can be calculated fast and easily, without integration. The procedure can be robustified using Iteratively Reweighted Least Squares (IRLS) method with Steiner weights. The advantage of the Steiner weights is that the scale parameters ( 2) can be determined from the statistic of the measured data set in an inner iteration process. Thus, a very effective robust and resistant inversion procedure can be defined. Its applicability using magnetic data calculated above a square and “L”-shape object is proved.
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Approximate CRUST1.0 Model-based and Space-domain Calculated Gravitational Effect of the Earth Crust
Authors J. Mikuška, I. Marušiak, P. Zahorec, J. Papčo and R. PaštekaSummaryRecent deep seismic studies support the existing isostatic systems only to a limited extent and, in some areas, considerable disagreements have been pointed at. This implies that we should attempt to replace the classic isostatic corrections by quantities calculated from a-priori information which should be as independent of the gravity data themselves as possible. We believe that CRUST1.0 model provides applicable material for such an attempt. In our contribution we demonstrate that to calculate gravitational effects of the CRUST1.0 model layers taking the model densities into consideration is in fact a viable option. We have used two different methods of calculation, more or less independent of each other, both of them working in space domain. We believe that space-domain calculations are suitable for employing the results in gravimetrical practice since they not only are synoptic, i.e. offering a general view of the whole, but also enable us to analyze their elementary and differential properties.
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Applications of the Fractional Order Analytic Signal amplitude and Local Wavenumber
More LessSummaryAnalytic expressions for the fractional order anomaly, analytic signal amplitude, and local wavenumber of different magnetic models are derived. These expressions can be integrated with existing source-distance methods and used as part of the semi-automatic interpretation of magnetic anomalies. The order of the fractional order derivatives can be chosen based on the noise levels of the data.
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3D Inversion of Gravity Gradient Data Based on Cokriging to Identify the Dip Angle of a Dipping Dike Model
More LessSummaryWhen we invert gravity gradient data to recover 3D density distributions by cokriging, the dip angle of a dike directly influence the recovered results. Where there is a lack of the prior information about the dip angle, to obtain the reasonable results we present a method to identify the angle. Firstly, keeping the parameters same in cokriging inversion but we introduce some different dip angles by angle scan approach, then according to the prior information, only zero and positive density contrast are chosen. The standard deviations of the residuals between the observed and predicted data change with the angle. And the estimated dip angle of this method is the scan angle corresponding to the minimum standard deviation. In this paper, we choose four typical dipping dike model with the dip angle of 0o, 45o, 90o, 135o. Tzz data was inverted to test the validity of the mothed. All these four dip angles can be estimated correctly. This result make cokriging can be applied in more cases in which even the dip angle is unavailable.
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Identification the Basin Structure Using FHD and SVD - The Case Study in North East Java Basin
Authors F.H. Hisyam, Q.D.T.F. Fiandani and Z.F. Zuhrotul FirdausSummaryResearch has been done in North East Java Basin using gravity method. The data which be processed on this research are obtained from Bureau Gravimétrique International (International Gravimetric Bureau). Initial data processing yields Complete Bouguer Anomaly map which is filtered using Upward Continuation to separate regional and residual anomaly. The residual anomaly data was processed using derivative analysis include First Horizontal Derivative (FHD) and Second Vertical Derivative (SVD). The angle which used in FHD is 135o. Result from this analysis show six fault structures which has NE - SW orientation. The structures are normal fault which associated with half graben. The high area (ridge zone) is shown with high value Residual Bouguer Anomaly (RBA) ranged 6 until 11 mGal. The low area (trough zone) is shown with low value RBA ranged -16 until -8 mGal. These results appropriate with geological data of the research area.
Keyword: FHD, SVD, Geology Structure, North East Java Basin
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Robust Time-domain Migration Velocity Analysis Methods for Initial-model Building in a Full Waveform Tomography Workflow
Authors H.B. Santos, J. Schleicher, A. Novais, A. Kurzmann and T. BohlenSummaryFull-waveform tomography (FWT) is notorious for its strong dependence on the initial model. We present a workflow for the construction of initial velocity-models for FWT methods consisting of automatic time-migration velocity analysis by means of double multi-stack migration, followed by time-to-depth conversion by image-ray wavefront propagation. Evaluation of the converted velocity model as an initial velocity model in an acoustic FWT process indicates the potential of using a combination of these methods to achieve a fully automatic tool for initial-model building in a FWT workflow. Our tests on a modified version of the Marmousi-2 model have shown that correct background velocity information can be successfully extracted from automatic time-domain migration velocity analysis even in media where time-migration cannot provide satisfactory seismic images.
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Hybrid Super Memory Gradient Method Full Waveform Inversion
Authors Y Hu, L.G. Han, v Zhang, L. Bai and T.Z. ZhangSummaryIn this paper, we discussed the Hybrid Super Memory Gradient (HSPM) method for FWI, whereby the Super Memory Gradient (SPM) method and Unconstrained Super Memory Gradient (USPM) method are used for FWI iterations. SPM method uses many gradients information to correct current descent direction, so we can obtain more accurate descent direction. USPM method without Wolfe linear search which can save a lot of computational time. Firstly, at low frequencies, we use USPM method , and then use SPM method to inverse high frequencies information. The numerical examples show that HSPM delivers similar results as those expected with the SPM method, and improved computational efficiency over Conjugate Gradient method.
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Frequency Domain FWI with Angle Domain Wavenumber Filter Using Local Slant Stacking
More LessSummaryThe scale length of velocity perturbations is closely related to the scattering angels of the wave. In the full waveform inversion, waves with different scattering angles can retrieve model parameters of different scale length. We introduce an angle-domain wavenumber filter for frequency domain full waveform inversion. Both source- and receiver-side waves are decomposed into local plane waves using slant-stack method. At each grid point, the scattering angles between the incident and scattering directions are used as the constraint to determine the wavenumber components to be retrieved. Large scattering angles are related to large-scale model perturbations, so by filtering out small scattering angles in the inversion, we can get the large-scale background model. Numerical examples show that when the initial model has large velocity errors and the low-frequency information is missing in the data, the angle-domain filter can largely improve the convergence in the initial iteration stage.
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Multi-scale Frequency-domain Elastic Full Waveform Inversion Based on Dual-level Parallelism
More LessSummaryThe complexity of the elastic wavefield increases the nonlinearity of inversion. To some extent, multi-scale inversion decreases the nonlinearity of inversion and prevents it from falling into local extremes. A multi-scale strategy based on the simultaneous use of frequency groups and layer stripping method based on damped wave field improves the stability of inversion. A dual-level parallel algorithm is then used to decrease the computational cost and improve practicability. The seismic wave modeling of a single frequency and inversion in a frequency group are computed in parallel by multiple nodes based on MUMPS and MPI. Numerical tests using an overthrust model show that the proposed inversion algorithm can effectively improve the stability and accuracy of inversion by selecting the appropriate inversion frequency and damping factor in low-frequency seismic data.
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An Optimized Correlation-based Full Waveform Inversion
Authors Y. Choi and T. AlkhalifahSummaryThe conventional correlation-based objective function for FWI has a limitation: the desired (accurate) solution is not exactly located at the global minimum (or maximum) since the auto-correlation of the observed wavefield has some energy at non-zero time-lags. We propose two optimized correlation-based objective functions incorporating the auto-correlation term. Including this term in the new objective functions as a reference for the cross-correlation to fit locates the desired solution at the global minimum (or maximum). We derive the gradient expressions of the new objective functions using the adjoint-state method, where only two modelling steps are needed to calculate the gradients. The numerical examples show that FWI based on the new objective functions generate good convergent results, whereas the conventional correlation-based FWI does not.
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Wavelet Filter Based Low-frequency Data Reconstruction for Time Domain Full Waveform Inversion
Authors P. Zhang, L.G. Han, F.J. Zhang and Y. ZhouSummaryThe conventional full waveform inversion (FWI) often uses local optimization algorithm to update velocity model. So the initial model we provide should be good enough to avoid local minimum. Abundant low-frequency information can compensate for the inaccuracy of the initial model and help to avoid cycle-skipping. In this paper, we proposed a wavelet filter based low-frequency data reconstruction method. We extracted the subsurface impulse responses using Fast Iterative Shrinkage-Thresholding Algorithm (FISTA), and convolved the broad-band impulse responses with band-limited low-frequency source wavelets to obtain low-frequency data. The convolution process is equivalent to filtering using low-frequency source wavelets. The accuracy analysis demonstrated that the reconstructed data can meet the requirement of FWI. We proposed a new strategy for multiscale time domain full waveform inversion (TDFWI), which using a series of low-frequency reconstructed data as observed data. One distinct advantage is that the wavelet is accurately known for the reconstructed data, which reduces the uncertainty of FWI. This strategy avoids the effect of source wavelets uncertainty on inversion results, and avoids the simultaneously pre-process of data and wavelets. Numerical example shows that our strategy can avoid cycle-skipping effectively and can converge on a bad initial model.
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Hybrid Frequency Domain Full Waveform Inversion Using Born Sensitivity Kernels
Authors R. Djebbi and T. AlkhalifahSummaryFull Waveform inversion (FWI) using the scattering integral (SI) approach is an explicit formulation of the inversion optimization problem. The inversion equations are straightforward and the dependence on the data residuals and model parameters is clear. However, the biggest limitation with this approach is the huge computational cost for exploration seismology applications. To deal with this issue, we propose a hybrid implementation of the frequency domain FWI using the Born sensitivity kernels. Specifically, we use the sensitivity kernels computed from dynamic ray-tracing to build the gradient. We compute also the truncated Gauss-Newton update direction using the kernels without extra wavefield modeling steps. Considering that in FWI long-to-intermediate wavelengths are updated during the first iterations, using a transmission experiment
we obtain accurate inverted models. The inversion managed to develop the anomaly embedded in the homogeneous background medium. The truncated Gauss-Newton updates helped in the fast convergence. With this approach we managed to reduce the computational cost and the memory requirements. For more complex models, the hybrid inversion method help improving the initial model with little cost compared to conventional SI inversion.
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Multiscale Adaptive Full Waveform Inversion Based on the Wavelet Transform
Authors L. Bai, L.G. Han, F.J. Zhang, P. Zhang and Y. HuSummaryThe conventional full waveform inversion (FWI) is often suffered from the cycle skipping problem. In order to solve this problem, we introduced the wavelet transform to the FWI, and combined with the least squares filter in the wavelet domain. It can effectively reduce the influence of the cycle skipping problem in the inversion procedure, and improve the stability of the FWI. The least square filter has the higher accuracy in the wavelet domain than in the time domain. By using this feature we can narrow the phase difference between the predicted data and observed data, and construct a new objective function to make the inversion procedure steadily converge to the global minimum. Meanwhile, due to the multiscale characteristic of the wavelet transform, the data can be divided into different frequency bands. We could run the FWI in a multiscale way. The results from the synthetic example demonstrates that the multiscale adaptive FWI based on the wavelet transform is much less dependent on the initial model and low-frequency data. The method can also effectively reduce the cycle skipping problem and more robust than the conventional FWI.
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The Comparison between Full-stack Data and Pure P-wave Data on Deeply Buried Ordovician Paleokarst Reservoir Prediction
More LessSummaryThe present burial depth of the paleokarst reservoirs in the Tarim Basin is greater than 5000m, which premises rigorous demands for the data quality for accurate predictions. Although routinely used for reservoir prediction, the conventional full-stack data are often contaminated by the AV O (amplitude versus offset) effects no matter how much signal to noise ratio degree can be enhanced via stacking. This contamination usually changes with different geological deposits, and could reach an inappropriate and unacceptable level for the deeply buried carbonate reservoir in the Tarim Basin. In this paper, the pure P-wave data theoretically inverted through AVO effects removal are employed to improve the reservoir prediction, which are illustrated by the comparisons with that of the conventional full-stack data for the four classical AVO models and the field data in the ZG8 area, Tarim Basin. The dominant frequency has been improved for 8 Hz from 15 to 23 Hz in the target Yingshan formation, Ordovician through AVO effects removal, and the reflection events of the pure P-wave data are obviously more continuous comparing with that of the full-stack data. The fake potential reservoir caused by AVO effects in the northeast area has been removed, while the integral delineation of paleokarst reservoirs have been significantly improved with a higher fitness with the oil-testing results, which are more beneficial for later on exploration. The pure P-wave data inversion is in essence an important complement to current processing strategy.
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Flow Detection Using Well Seismic Data
Authors J.L.O. Mari and G. PorelSummaryThe aquifer studied, 20 to 130 m in depth, consists of tight karstic carbonates. 3D seismic survey revealed three high-porosity, presumably-water-productive, layers. Ambient seismic noise and VSP data have been recorded in 11 wells in order to evaluate the potential of the well seismic method to detect karstic bodies and flows, the results being compared with full waveform acoustic data, BHTV logs and flow measurements.
The paper describes the methodology developed to detect flow using both ambient noise measurement and conversion of P-wave into Stoneley waves, observed on VSP data recorded with hydrophone sensor. An attribute, named VSP flow index, has been calculated to detect both karstic levels and flows. Concerning the karstic level detection, the results obtained on 11 wells are compared with full waveform acoustic data and confirmed by BHTV logging data and at a large scale by seismic data (3D seismic). The results obtained are consistent. The VSP data have also been compared with PLT data. An attempt to obtain a VSP flow detector has been done. The conclusions of the study show that ambient noise analysis and conversion of P- body waves into Stoneley waves can be fruitfully used to detect productive levels and flow circulation.
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Well Controlling Multi-trace Seismic Deconvolution Technology
More LessSummaryConventional deconvolution methods in reducing band-limited wavelet interference often cause lateral instability of the estimated reflectivity or impedance. In addition, conventional deconvolution processing ignores the spatial relationship between traces. Spatial regularization technique can solve the problems to some extent, but there is still lack of recovery of low frequency and high frequency and ill posed problems. In this paper, based on spatial regularization, we induced logging data and proposed wells controlling multi-trace deconvolution method. A synthetic data example and a field data example are adopted to illustrate the method effectively. After processing, the seismic data resolution is improved significantly and its spatial continuity keeps well. The result has good match with low-pass filtering of logging data. The method can provide high resolution seismic data for thin reservoir prediction.
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Multi-scale Fracture Prediction Using P-wave Data - A Case Study
More LessSummaryFracture prediction is very difficult when characterizing unconventional hydrocarbon reservoirs, especially for reservoirs with different fracture scale sizes. Here, we present an integrated workflow combined with poststack and prestack seismic attributes to distinguish between fractures of different scale, which is used in a case study from a basin in China. We classify fracture scales into three categories: macro-scale, meso-scale and micro-scale. In this case study, we used poststack seismic attributes to predict the macro-scale fractures, and utilized prestack seismic inversion to determine the meso-scale fractures. Micro-scale fracture prediction is out of the range of this study. We combined the prediction results with the superimposed images of faults, verified the corresponding relation between meso-scale fractures and faults, and finally comprehensively analyzed the fracture development of the target horizon. The integrated prediction result indicates that the structure of the target horizon is mainly controlled by several major faults and meso-scale fractures are distributed along the fault zones.
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Karst Carbonate Reservoir Identification Using Frequency-dependent AVO Inversion in Tarim Basin, China
More LessSummaryThe dominate storage spaces of karst carbonate reservoir in Hadexun area, Tarim basin are dissolved pores and cavities. The influence of multi-stage structure movement makes the fluid discrimination difficult. Therefore, how to further recognise the fluid type in such reservoir is the key point. Unlike conventional post-stack methods have difficulties in fluid identification, AVOF inversion algorithm utilize P-wave dispersion property reflected by fluid to discriminate its type. Thus greatly improve the accuracy of oil exploration. In this paper, the AVOF inversion method is applied on 3D field seismic data in Hadexun area to solve the problem of fluid discrimination in karst reservoir. Field data application demonstrates that reservoirs filled up with water and hydrocarbon can be effectively separated by inverted P-wave dispersion. To be more important, by analyzing the inversion result and fault distribution, we successfully divided the faults into two groups, which are water-contained and hydrocarbon filled. In sum, the encouraging result of AVOF inversion provided robust information in karst reservoir characterization and fluid distribution, which directly offer key data for well optimization and deployment.
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Seismic Facies Characterization of the Realgrunnen Subgroup in the Wider Hoop Area, Barents Sea
Authors W. Athmer, M. Etchebes, E. Stueland, S.C. Robertson, H.G. Borgos, B.A. Tjostheim, L. Sonneland and J.R. GranliSummaryA seismic facies characterization of the Late Triassic Fruholmen Formation and the Jurassic Stø Formation —both hydrocarbon-bearing reservoir units within the Realgrunnen Subgroup in the Barents Sea—was performed to better understand reservoir facies distributions and variations in the wider Hoop area. Depositional features such as fluvial channels and associated elements were highlighted using (1) RMS amplitude maps draped onto stratal slices, and (2) colour-blended images obtained from partial reconstructions of the seismic volume reflection spectrum (VRS). Depositional thickness variations were investigated using isochore maps, and information obtained from regional well data was considered for the analysis. The study indicates a fluvial-dominated depositional system for the mid- to upper-Fruholmen Formation, and a shallow-marine environment for the overlying Stø Formation. Differences in facies thickness distributions are attributed to morphological changes that constrain the depositional environment and are related to paleo-topography, and fault activity before and during deposition of the reservoir section.
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High Precise Time-frequency Analysis Technology in Hydrocarbon Detection of the Ultra-deep Carbonate Rocks in Tarimbasin
By Q.N. DangSummaryWe present results from a case study being performed in the Ordovician ultra-deep(6500m-8100m) carbonate rocks of TB area in Tarim basin that utilizes the high precise WVD (Wigner Ville distribution) time-frequency technology to detect hydrocarbon of Ordovician carbonate rocks. Through suppressing the cross-term of WVD based on the technique of two weight window function, we obtain the high quality frequency spectrum imaging which preserves low frequency. This technology can not only characterize the boundary of the “string” of carbonate cave-fracture, but also detect the hydrocarbon in the “string”. Two sets of hydrocarbon detection criterion have been built about karst reservoir in buried hill and in interlayer. The results of hydrocarbon detection are compared with several drilled wells to confirm the validity of this technology.
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Influence of Seismic and Velocity Uncertainties on Reservoir Volume
Authors D.T. Odinsson, N. Cardozo and L. SchulteSummaryUncertainty estimation is a well-known concept in geology that can lead to re-evaluation of important development decisions if properly assessed. This study evaluates structural uncertainty through the set-up of “scenarios”. For each parameter of the structural model a low case, base case and high case are defined. The combination of these cases results in numerous structural models that deliver a distribution of the bulk volume. A generally acknowledged way of handling the large number of models coming from the different combinations of the model parameters is experimental design.
This study shows that uncertainties in seismic picks and consequently in reservoir thickness have a large impact on the gross-volume. The reservoir structural geometry controls the influence of fault uncertainty on the reservoir volume. The well velocities used for domain conversion are quite accurate but sparsely sampled and therefore also subject to uncertainty. In addition, the geologic complexity may have a dramatic influence on the uncertainty of the depth conversion. The assessment of seismic and velocity uncertainties was applied to the structural model to estimate the reservoir volume uncertainty. The results confirm that structural uncertainty is a major contributor to the hydrocarbon volume uncertainty.
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Altering the Relaxation Modulus of Crude Oil Using Pulsated Magnetic Field
By D. PandeySummaryThe aim of this technical paper is to present the idea through an experiment that magnetic field can be used as an alternative tool to change the relaxation modulus of crude oil and thus improving its transportation efficiency. During the experiment, it was found that the contact angle between crude oil and sensor probe was influenced by magnetic treatment which resulted in the prevention of wax sticking on the sensor probe. From the experiment it was confirmed that the field can also be used to prevent the wax accumulation.
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