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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
61 - 80 of 462 results
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First Gas after 40 Years - The Geophysical Challenges of the Saturn Gas Complex
By S.D. ElamConocoPhillips has held Block 48/10b in the UK southern North Sea for some 40 years. The first gas production from the Saturn field in this block was achieved in September 2005. The main geophysical challenge of this block is to understand the sub-salt wall structure of the Rotliegendes reservoir. A variety of geophysical techniques have been applied, some of the earlier methods are briefly reviewed. The main emphasis of this presentation is the interpretation of the pre-stack depth migrated data and its subsequent depth conversion, including a subjective method of removing the artefact created under the salt wall overhangs. The results of the recent horizontal wells, together with the pre and post drilling interpretations are used to show the limitations of the seismic reflection data to predict the details of the reservoir structure beneath this salt wall. Finally, a brief review will be made of the two previously stranded gas fields that will be developed using these new Saturn facilities.
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Surface Seismic Techniques for the Recovery of Heavy Oil
Authors J.M. Garrity, M. Rajab, I. Al-Hakim, A.S. Smart, A. Shabrawi, A. Laake, W. Gamal El-Din, P.M. van Baaren, D.L. Barge and S.D. GriestThis paper shows the results from a number of experiments conducted using single-sensor and single-vibrator techniques to image heavy-oil sands at a depth of 300 m to 600 m in an existing oilfield in the Partitioned Neutral Zone between Kuwait and the Kingdom of Saudi Arabia. The aim of the experiments was to investigate whether surface seismic techniques can obtain the bandwidth required to be able to image the thick heavy-oil layers in the near surface in the presence of high-amplitude coherent noise that masks most of the reflected energy from the target. Further complications are introduced by the presence of high acoustic impedance layers above and below the heavy oil deposits and the presence of high ambient noise levels from the oilfield infrastructure.
An 800-m x 800-m 3D seismic grid was acquired over an area that will be the site of pilot long-term steam-flood in 200X. This heavy oil (18 API) reservoir currently produces 78,000 barrels of oil per day. For efficient steam injection, knowledge of the heavy oil reservoir is essential.
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Petrophysically-Constrained Simultaneous Inversion and Interpretation of a Deepwater Gulf of Mexico Field
More LessIn an effort to extract reliable density data from pre-stack seismic data, a new seismic inversion process has been developed that simultaneously solves for density (ρ), P impedance (Ip), and S-impedance (Is). Because all three parameters are linked and solved for simultaneously in this process, this type of inversion is referred to as a dependent inversion; that is, each term is consistent with the other two terms. Conventional inversion techniques independently solve for these three parameters, and the resultant density may or may not be internally consistent.
In addition to a better inversion algorithm, this process also utilizes petrophysical data to put constraints on the relationship(s) between velocities and density. The petrophysical data is also used to better constrain the porosity, allowing a more robust estimation of water saturations from the inverted density volume.
This new technique is applied to a deepwater Gulf of Mexico field, where conventional analysis of both pre- and post-stack seismic data proved to be problematic. This analysis allowed for reservoir fluids to be more accurately predicted. However, evaluation of the seismic data also shows the reservoir to be more discontinuous and complex than previously thought.
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Mapping Thin Sandstone Reservoirs - Application of 3D Visualization and Spectral Decomposition Techniques
Authors H. Lal, C.G. Rao, R.C.P. Saxena, J.L. Nangia, A. Sood and S.K. GuptaThe 3-D data of C-37 of Tapti-Daman sub-basin of Mumbai offshore Basin, India, have been evaluated for delineation and mapping of Oligocene Mahuva
pay sands. Post drill analysis of log and seismic data show that low impedance pay sands, embedded in high impedance shales, are separated in thin beds by limestone and/or shale streaks. Delineation of these sands by conventional interpretation methods is difficult because of thin and discontinuous occurrences, abundance of limestone streaks and limited bandwidth of seismic data.
3-D visualization of surfaces and volume attributes, neural network based seismic trace shape classification and spectral decomposition techniques have been applied with integration of well and log data. Amplitude attributes based on full bandwidth data were found more contaminated by thin limestone streaks. Spectral decomposition based iso-frequency sections and slices mapped areal extent and temporal thickness of pay zone. 3-D visualization of selected frequencies from instantaneous frequency volumes and seismic trace shape classification maps provided comparable image of the reservoir sands.
Marine sands near shore-zone areas during continued sea level fall are envisaged depositional system for the pay sands. The sandstones are spread over 90 km2 area in isolated sand bodies.
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Migration Velocity Analysis and Inverse-Ray Imaging of 3D Sedimentary Structures
By T.K. WangMajor horizons from stacked sections and velocity analysis of the time migrated sections along eighteen oblique profiles in the southernmost Ryukyu forearc region are integrated based on the inverse-ray method. Inverse-ray imaging starts from shooting three inverse rays at three non-collinear sources/receivers, propagating through structural layers and arriving at a planar reflector. All possible triangulations of the picked reflection times between neighboring profiles are applied for 3-D inverse-ray imaging of the Ryukyu forearc structures and in a layer-stripping approach. The results show that the top of the oceanic crust subducts deepest near the Nanao forearc basin and the maximum thickness of the accretionary prism south of the Nanao forearc basin is greater than 9 km whereas that south of the East Nanao forearc basin is only greater than 5 km. These may imply the most active subduction in the southernmost Ryukyu forearc region is probably along the Nanao forearc basin which is also supported by the active earthquakes below the Nanao forearc basin.
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Dense, High-Resolution Velocity Model Building Onshore; Application to a Major Fault System in Western Desert - Egypt
Authors M. Emile, R. Saba, A. El-Fiky, G. Bakry, S. Zimine, C. Pinson, P. Mitouard and V. VinjeThe long turnaround of the velocity model building phase in the past has been the main drawback of the depth migration when compared to the time migration. To compensate for this, CGG has recently developed alternative methods to the time consuming layer stripping approach. The method described here is based on dense, volumetric picking of the residual move-out followed by non-linear finite-offset tomographic update. One single layer is updated.
Earlier published cases on similar methodology have been mostly in marine environment. The case test in this paper is onshore, in desert environment and contains a strong lateral velocity variation (up to 1500 m/s) across a major fault induced by a throw reaching 3 km. An important question is whether the new volumetric, tomographic approach is able to represent the complexity of the velocity model needed for pre-stack depth migration. Land data is also typically noisier, which may cause problems for the automated, dense volumetric picking approach described here.
The results from this study show that the new VMB approach may also be feasible onshore. In addition to giving an improved imaging in the vicinity of the problematic fault zone, it is also considerably less work-intensive.
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Time Migration Tomography
By R.J. LeggottThe tomography algorithm presented will generate an optimum velocity model for time migration. The velocity model is computed to flatten every sample on every common image gather, whilst being constrained to be smooth and bounded, and using the correct relationship between residual curvature and velocity update. This avoids the inconsistency of vertical updating which updates the velocity differently from how the velocity is used for imaging. The resulting interval velocity model satisfies all available information and is shown to contain valid high resolution features. Consequently the updated velocity model gives an improved seismic image.
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Gravity and Magnetotelluric Survey of Sub-Zechstein Structures in Northern Poland
Authors M. Stefaniuk, C. Ostrowski, T. Wolnowski, A. Mickholz, P. Targosz, M. Wojdyla and I. KosobudzkaAn integrated geological model was built for the strongly tectonized belt of the Balaton-lineament in the Zala Basin, SW Hungary, to help further exploration and exploitation in this mature hydrocarbon sub-province. Investigation of core samples and interpretation of recently acquired 3D seismic surveys showed that the most important events of the tectonic evolution were Neogene strike-slip movements and a Pliocene/Quaternary basin inversion. Application of the geological model made it possible 1) to explain the peculiar behaviour of reservoirs; 2) to specify the rock volume and the reserves of known reservoirs; 3) to recognize and exclude a non-perspective sub-region from exploration; 4) and to discover a new hydrocarbon accumulation.
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Integrated Geological Model of Balaton-lineament as a Key to Success of Exploration and Exploitation
Authors A. Németh, J. Jósvai, I. Czeller and A. Szuromi-KoreczIn the Transylvanian Basin have been discovered more than ninety gas fields. The gases consist only of biogenic methane reservoired in the Upper Badenian, Sarmatian and Lower Pliocene rocks. The almost all gas structures are dome-shaped and most of them are controlled by salt diapirism of different intensities that suggest more mechanisms of the salt movement. To study the salt flow and the formation of the gas structures we used a simple model considering an elastic plate overlying a viscous fluid. In this model the viscous fluid is the layer of Badenian salt and the elastic plate is represented by the overburden composed of Upper Miocene and Pliocene deposits. The model shows that the early stages of salt movement have been due to folding of the overburden during compression in the Uppermost Sarmatian and Pliocene compressive regime and dragged by the Sarmatian deltaic deposits. The salt buoyancy was the main mechanism in the later stage of diapirism. The results are in agreement with the geological evolution of the basin, gas generation and accumulation.
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Relationships between Gas Accumulation and Salt Diapirism in the Transylvanian Basin
More LessThe Transcarpathian gas-prone sub-basin of the Carpathian and Pannonian petroleum provinces embraces the territory of West Ukraine bordering with Slovak Republic, Hungary, Romania, and the East Carpathians Mts. In terms of geology it is a depression of 20-48 km in width and 147 km in length. Only 3% of the region’s hydrocarbon potential are discovered to the date. Probable reserves of the basin are estimated at 112.3 Bcm of natural gas with specific density of probable reserves varying from 7-8 to 12-13 toe per 1 sq.km for different sedimentary complexes. Proven gas reserves of 4 discovered fields are 2.3 Bcm. According to exploration works there are more than 10 prospects and leads here with probable gas reserves of 23.5 Bcm that requires further seismic exploration and drilling. An economic advantage of this highly immature exploration area is a possibility to use abandoned wells drilled to the pre-Neogene basement as hot water producers to utilize hydrothermal energy and conversion of depleted fields into gas storages on the way of Russian gas to the West.
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Shallow Gas of the Ukrainian Transcarpathian - Its Status Quo and Exploration Perspectives
Authors L.F. Hafych, A.A. Kitchka and O.I. GafychSeismic data interpretation in geologically complex areas suffers from the shortcomings of out-of-date 2D data acquisition technique and time-domain processing, both of which are still predominant in Ukraine. With numerous examples from a variety of structural settings in onshore and offshore Ukraine, we demonstrate that prestack depth migration yields great improvements in seismic imaging and structural positioning as compared to poststack time migration. Because of the absence of any 3D survey in the majority of prospective arias in Ukraine, we are not able to take advantage of this data acquisition technique and have to use a 2.5D migration procedure. With examples from onshore Ukraine, we demonstrate that even such an out-of-data process allows out-of-plane reflection events to be greatly diminished, which favors more confident seismic data interpretation. This study is aimed to justify that a great improvement in exploration success in Ukraine may be achieved in the future by using a combination of 3D seismic acquisition technique and high-quality depth processing.
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Seismic Depth Imaging in Onshore and Offshore Ukraine - Case Studies
Authors A.N. Tiapkina, Z.Y. Voitsytski and R.S. KhomaEmissions of coalbed methane released by mining and related underground hazards are major problems for safe and efficient coal exploitation in the Donets Basin, which mines are among the gasiest in the world. There is a proved potential for coal bed methane capture and utilization as an emerging energy resource. Almost the all coal fields of the Donets Basin excluding most eastern superanthracite regions are characterised by high coalbed methane content in situ (from 8-10 to 25-37 m³/t). Some seams during underground coal mining demonstrate more than 100 m³ per ton of mined coal. In this paper, the catalogues of coal properties and methane content and outburst danger of coal seams in the Donbas were used to establish maps of vitrinite reflectance, methane generation, methane adsorption, and actually observed methane content of coals. These maps allow to understand migration of methane in the basin and to determine the areas that present a high potential for coal mine methane projects and industrial coalbed methane exploitation.
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Seismic Imaging of Imbricate Structures in Southwest China: A Case Study
More LessThe hydrocarbon prospects of the Western China Thrust Belt require solving a most challenging problem in seismic imaging --- irregular topography associated with a rugged terrain, complexity of the near-surface that includes high-velocity layers and outcrops with significant lateral velocity variations, complexity of the overburden, and the complexity of the target imbricate structures themselves. We present a case study that demonstrates a workflow to solve this challenging problem: (1) The near-surface model is estimated by nonlinear traveltime tomography that accounts for topography, and resolves lateral and vertical velocity variations. The near-surface corrections are based on wavefield datuming rather than shot-receiver statics. (2) The subsurface overburden model is estimated by prestack time migration combined with powerful interactive tools to pick rms velocities that are structurally consistent and laterally consistent, and the substratum model is estimated by half-space velocity analysis. (3) The subsurface image is obtained by prestack depth migration of shot gathers from topography.
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Comprehensive Application of Geophysical Techniques to Igneous Rock Study
By D.C. LiPresently, the igneous reservoir has become a new exploration target for hydrocarbon reserves and increased more and more attention from worldwide petroleum and geology experts. The concept of comprehensive application of different geophysical techniques can provide a new and effective approach for igneous reservoir detection and delimitation since it advocates the principle of solving problem by combining multi-technique and comprehensive interpretation.
Comprehensive application of gravity and magnetic data, electric data and seismic data provides a platform for jointed data processing and interpretation, consequently, reduces the interpretation ambiguity, and enhances the ability for special geological body study such as igneous rock distribution and lithology identification. The concept made the research on igneous rock in several large basins in west China extremely successful
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Fe-Chlorite Coating Evolution in Sandstones during Late Diagenesis - Is Temperature a Key Parameter?
Authors A. Ortenzi and E. Previde MassaraIn this paper, we describe a geometrical algorithm to solve the problem of the kinematics at basin scale. Two elementary models of geological deformation are considered: flexural slip and vertical shear. The combination of these models enable us to properly describe mechanical stratigraphy of a sedimentary basin sequence.
The methodology presented is 3D, reversible, simple to implement and fast. Validations are presented on two different examples: one synthetic to validate the algorithm, and a structurally complex model.
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Reversible 3D Structural Deformation for Basin Modelling
Authors M. Thibaut, N. Gibergues, J.P. Gratier and W. SassiWe use seismic tomography at time delays of first-arrival waves in order to solve this problem. Special 2D time fields t(õ,l) of reference waves are used for velocity inversion. It allows us to combine wave-arrival times into a unified system when observed with different details, and also when isolated travel-time curves are not correlated.
The developed technology of seismic tomography is common in different problem-solving in oil and ore geology and in studying deep Earth’s crust of Siberia. These problems are as follows:
- Interpretation of first waves recorded by CDP method in ore regions makes it possible to study the uppermost heterogeneous layer of the Earth’s crust and to forecast new ore knots and investigate their structures;
- Problem-solving in prospecting for oil and gas in West Siberia allows studying structures and compositions (in combination with drilling logs) of the oil-and-gas Paleozoic, which is rather difficult to do by CDP method;
- Illumination of the inner structure of the deep Earth’s crust and disclosure of wave guides, zones of disintegration, deep faults.
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First Wave Seismic Tomography in Ore and Oil Problem-Solving and Studying the Earth's Crust of Siberia
Authors A. Salnikov, V. Kuznetsov, V. Markov and V. TitarenkoAvailable surface and industrial subsurface data provide the basis for a general balanced cross-section from the Sahara platform to the Mediterranean Sea in Central Algeria. This section gives an overview of the whole Maghrebian orogen comprising from south to north: the intra-continental Atlas system; the External Tell system, the Flyschs domain and the Kabylides domain of European affinities. Restoration of the southern segment of the section, comprising the Atlas and External Tell systems, yields a minimum value of 40 km (20%) of horizontal shortening. For this part of the section, a four-step kinematic scenario, illustrates the main stages of the deformation history: 1. late Eocene "Atlas" deformation pulse, 2. early Miocene deposition of a thick flexural sequence, 3. middle-late Miocene emplacement of the Tell nappes and 4. late Miocene to present out-of-sequence thrusting. On this basis, a conceptual geodynamic model is proposed for the Maghrebian orogen. After the Atlas event, which just preceded the roll-back of the Tethyan slab, the model emphasises the role of subduction responsible for: flexuration of the subducting plate (slab pull effect); development of both accretionary prism and back-arc basin and late uplift linked to slab break-off.
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Post Cretaceous Deformation in the Tell-Atlas System in Central Algeria
Authors N. Benaouali-Mebarek, D. Frizon de Lamotte and F. RoureA seismic line is shot over a relatively flat area in North-East India that has a thrust fault in the subsurface. The quality of the seismic data does not allow adequate imaging of the thrust. Also, the surface expression of the thrust is too subtle to be used as a key for interpretation. To aid the interpretation, first arrival times have been inverted using a well-established regularized inversion algorithm and a shallow (~1.5 km deep) velocity-depth model has been developed. The thrust has been interpreted on the velocity-depth model based on the variations of the velocity contours. This interpretation can be converted in time and used to interpret deeper parts of the thrust in the seismic data.
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Velocity Modeling of Naga Thrust, North-East India
Authors P. Jaiswal, C.A. Zelt, A.W. Bally and R. DasguptaThe sedimentary basins of the Alpine-Carpathian mountain belt extend from France to Romania. These basins, some being known hydrocarbon provinces since the mid-XIX century, form important exploration areas in several countries. Although mature, the basins attract considerable interest, following the political changes of the early 1990s and application of new petroleum technologies. During the 2000-2005 period, new concessions were granted, 2D/3D seismic programs recorded, and over 250 exploratory wells drilled, resulting in some 145 successful operations. Bulk of the action was reported from Austria (51 wells), Poland (87 wells) and Romania (about 100 wells). Significant new discoveries of the period are Erdpress, Strasshof Tief (Austria), Jasionka, Terliczka, Trzebownisko, Stobierna (Poland), two Bilca wells and Fratauti (Romania). History of reserves additions (creaming curves) shows that new gas discoveries are generally small and new oil discoveries have been scarce since the mid-1970s. Apart from Poland, the arrival of a diachronous gas plateau is observed for majority of the basins since mid-1980s. The remaining hydrocarbon potential is believed to be principally associated with the prospects at greater depths, sub-thrust plays and stratigraphic traps. Application of 3D seismic is expected to help resolve internal flysch structures.
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Recent Exploration Developments in the Alpine-Carpathian Mountain Belt - Review of Successes and Potential
Authors H.D. Dobrova, P. Gawenda and E. KollyCentral Iran is a tectonically complex and under explored region. Recent seismic, gravity, magnetic and geological field studies allow to understand the tectonic style and the structural evolution of this region during the tertiary. Petroleum system and trapping potential are discussed.
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