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3rd EAGE North African/Mediterranean Petroleum and Geosciences Conference and Exhibition
- Conference date: 26 Feb 2007 - 28 Feb 2007
- Location: Tripoli, Libya
- ISBN: 978-90-73781-42-9
- Published: 26 February 2007
100 results
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Outcrop Investigation of the Lower Palaeozoic Succession of Kufra Basin, SE Libya - First Steps of Targeting Effective Hydrocarbon Plays
Authors K. Tawengi, Y. Ismail, S. Shabbo, A. Al-Madhuni, E. Abushaala, J.L. Tornero, M. Kresta, Y. Al-Shagruni and J. Hernan-GomezThe Kufra basin located in the southeastern part of Libya is an elongate SW-NE trending (?Hercynian) depression defining a zone of crustal weakness of the trans-Africa lineament (Turner, 1980; 1995). The basin covers an aerial extent of approximately 400,000 sq km extending into Chad, Sudan and Egypt. Two major tectonic elements are known to have significantly controlled the structural style of the basin and consequently affected lithology distribution namely the Hercynian and the Caledonian events of Early Carboniferous and Late Silurian age respectively (Bellini and Massa, 1980). The basin fill consisting of a clastic Mesozoic and essentially Palaeozoic sequence attains an approximate thickness of 4000 m in basin centre. Lower Palaeozoic strata are exposed in three major outcrops surrounding the basin; Jabal Dalma in the NE, Awaynat massif including Jabal Asba in SE and Jabal Eighe in the W-SW. The existence of these outcrops provided ideal opportunity to examine the Palaeozoic succession from within a sedimentological/stratigraphic framework. As the only non-producing basin of Libya, Kufra Basin has recently re-captured the intention of oil companies for a detailed work in a bid to solve uncertainties still surrounding the basin hydrocarbon potential. In the same context, Remsa has conducted a field campaign to the area with the aim of investigating the depositional packages of the Lower Palaeozoic sequence as the main possible hydrocarbon plays may have exist in the subsurface counterpart. Two separate campaigns have been carried out during March-April 2005/2006 in the NE of Kufra (Jabal Asba, Arkunu and Garda area) and in the NE of Kufra (Jabal Dalma area) during which more than 80 localities were visited. Lower Palaeozoic sequence is investigated including the InfraCambrian, Cambrain Hassawna Fm, Ordovician sequence of Hawaz, Melaz Shugran, and Mamuniyat Fms, Silurian Tanezzuft and Akakus Fms and the Devonian sequence of Tadrat/Oan Casa Fms and the Binem (Blitah Fm). Packages are dealt with in a large-scale architecture i.e. facies associations without considering details of facies scale. The aim is to predict depositional mode and palaeogeographic reconstruction within a sequence stratigraphic approach applying method of facies recognition, stacking pattern, palaeoflow data, surface logging and composite log reconstruction. The field campaign is augmented in some instances by geochemical, petrographic and petrophysical analysis for units of interest in addition to shallow hole drilling. The systematic and/or genetic evolution of the Lower Palaeozoic succession of the Kufra Basin seems to have been largely affected by the interaction of tectonics and sea level changes demonstrating a pronounced variation in facies architecture and stacking pattern as it varies from proximal in the SE “Awaynat Massif-Jabal Asba outcrops” into distal setting of the “Jabal Dalma outcrop” which provided the key of reconstructing the palaeogeography of individual time slices and their inferred depositional models.
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A Recipe for Exploration Success in the 21st Century - Exploration Ingredients that Led to BP’s Deep Raven Success Story
Authors T. Afifi and M.V. ShannThis oral presentation discusses a holistic set of ingredients used to deliver deep water gas exploration success in the Nile Delta of Egypt. An exemplary of BP's renown exploration method as applied in North Africa.
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An Early Miocene Play Fairway Opener in the Nile Delta, Egypt
More LessThis describes the technical background that led to the 2004 Raven deepwater exploration success in the offshore Nile Delta, Egypt. Presented by the lead explorer involved in the discovery. Pulls together regional synthesis, seismic imaging technology and an in depth set of exploration results from an important deep play opener that is critical in underpining the future exploration potential offshore North Africa.
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Hydrocarbon Prospectivity and Play Types of the Levantine Basin from Modern Seismic Data
Authors D. Rowlands, G. Roberts and D. PeaceThe paper describes the regional tectonic setting and evolution of the Levantine basin in the Eastern Mediterranean. Thereafter the majority of the paper focuses on the hydrocarbon prospectivity and play types in the basin derived from an interpretation of 20,000 km of modern, high quality seismic data.
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Structural Style Associated Structures on Occidental Saharan Atlas and Petroleum Implications (Algeria)
By H. BechiriThe study area is located at west of Algeria, straddling two different geological domains, the Saharan Platform in the south and the Alpine domain in the north. Two major Faults (South Mesitian Fault and South Atlasic Fault) subdivide the area in three geodynamically and tectonically distinct domains, High Plateaus, Occidental Saharan Atlas and Saharan Platform (or Bennoud Trough). Three stratigraphic columns are build to illustrate the stratigraphic series' nature and thickness variation of the geodynamic provinces. So as to set off the geometry of the Saharan Atlas associated structures, we've draw up dips domains sections perpendicular to the tectonic transport direction. The interpretation of these sections in depth, including wells and seismic data, permitted us to set up three regional equilibrated structural sections. These shows that the present structure of the Saharan Atlas is the result of regional NW-SE and N-S compressional direction which prevails since the Late Eocene and it illustrated by Fault-bend fold and Fault-propagation fold. Salt tectonic, in some cases, complicate structures. In Bennoud Trough, the two established regional transect evidencing two distinct zones; a calm zone in the south and a structured one in the north near the Saharan Atlas. The majors faults had an important role in the provinces' geodynamic evolution created during the distension stage (Trias-Upper Cretaceous). Each province had his own subsidence ratio and petroleum system. So, the discovery of hydrocarbons in the Occidental Saharan Atlas is possible if the structural style is taken into consideration. Structures geometry in depth must be defined before drilling, because the appearance and disappearance of traps depends on the evolution of the folds. Hydrocarbons accumulations can be trapped at the top of the major fold or in it's slices.
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Genetic Basin Analysis and Paleoenvironmental Reconstructions of the Mesozoic and Cenozoic Strata of the Libya Region
Authors K.M. Bohacs and W. HeinsOur analysis of the Libya region was built on foundation of previous proprietary and published studies and employed recent proprietary research on concepts and tools and newly available data and a new age model that included significant thicknesses of Mesozoic strata offshore. These allowed calibration of the seismic character of source and reservoir facies and their stratal packaging in proven onshore areas, and extrapolation to similar seismic facies & stratal packaging seen in offshore data. We concluded that the Libya region was in a favorable setting for accumulating source, reservoir, and seal-prone strata throughout the Mesozoic and Cenozoic, due to the: 1) common occurrence of shelfal water depths and paleogeographic restriction, 2) low-latitude setting, 3) warm, dry to sub humid paleoclimate, commonly with low seasonality, 4) some coastal upwelling, along with water mass mixing under ITCZ & tropical cyclones, 5) dominantly quartz-sand-prone provenance lithotypes, and 6) late development of shelf-bypass clastic dispersal systems. The incorporation of paleo-environmental reconstructions is a powerful tool in exploration, enabling evaluation of numerous frontier areas in less than 10 weeks of work by using our fundamental understanding of the dynamics of basin formation integrated with the regional paleo-environmental context.
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The Murzuq Basin, Libya - A Proven Petroleum System
Authors I. Sarkawi, G. Abeger, J.L. Tornero and E. AbushaalaThe Murzuq Basin is located to the southwest of Libya. The basin is a foreland intracratonic trough which was formed during the Pan-African orogeny. It has evolved through several tectonic events from Pan African to Alpinian. The complex glacial influence sedimentation and erosion have been recognized in the Ordovician Hawaz and Mamuniyat sediments. The Hawaz Fm. has been deeply eroded forming a spectacular terrain of escarpments and incised valleys where later filled by Melaz Shuqran and Mamuniyat Formations. Restricted basin during the early Silurian favored the deposition of organic rich Base Tanezzuft “Hot Shale”. A combination of both Ordovician Hawaz and Mamuniyat as reservoir with the Lower Silurian Tanezzuft Hot Shale creates the main play in the area. The presence of active petroleum system and hydrocarbon potential in the Murzuq Basin has been support by oil fields and discoveries. A total of 18 oil fields have been discovered with recoverable reserves exceeding 1.9 billion barrels.
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Mesozoic Tectonism in Northeast Africa
By W. BosworthMesozoic tectonism in NE Africa was locally, but significantly, impacted by older Neoproterozoic and Hercynian structures. During the Permo-Triassic to Neocomian, the dominant control on deformation was the newly formed Neotethyan margin to the north. From the late Aptian onward, stress fields represented the combined effects of distant plate boundaries, producing both extensional and compressional deformation.
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The Opening of the Eastern Mediterranean and its Impact on the Tectonics of North Africa
By J. HossackThe opening of the Eastern Mediterranean had a large impact on the structure of the North African passive margin. The first extension event that lead to the formation of the ocean can be traced back to the Permian. A Permian rift system is preserved in the subsurface of Tunisia, north of the Jefarra uplift. Renewed rifting occurred in the Triassic. Triassic rifts are preserved in the Atlas, Sicily, Sirt, and Levant margins. A phase of Jurassic rifting is observed in the Nile Delta and Sicily but a possible occurrence of rifting in the Sirt basin is obscured by younger Cretaceous rifting. Jurassic rift structures also occur in the Atlas. The North African margin rifted again in the Early Cretaceous when the Sirt Basin formed on the site of earlier Triassic rifts. The Sirt rift faults form a 3 armed system where the eastern faults trend E-W parallel to the earlier Triassic rift system. A southern arm trends SSW and a NW branch continues offshore across the passive margin. Early Cretacous rifts occur extensively in North Africa and are known to be related to South Atlantic spreading.
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Petroleum Geology in the NC41 Area (Western Libyan Offshore)
More LessThe NC41 area belongs to a polyphasic pull-apart basin in the western side of the Libyan offshore. The early stage of the basin was upper Cretaceous in age. The local troughs of the pull-apart were affected by restricted conditions that gave origin to the cretaceous source-rock (Kef Fm.). The deposition of the cretaceous source is a peculiar feature of the deepest part of the Sabratah-Misrata basin. The geochemical properties and evolution of the cretaceous source led to the generation of gas that largely contributed to most important accumulation of the area. The trap-forming processes started during the late Cretaceous transpressional phase. The early faults were reactivated later, sometime evolving into attractive exploration features. The present structural style, characterized by faulted anticlines, results in particular from late Cretaceous and Oligocene events. The two major exploration plays are the Eocene shallow-water carbonates and the Cretaceous carbonate platform. The former is the most successful play of the area. The latter is presently largely unexplored in spite of the close concurrence of effective source and reservoir units but it shall represent a challenging target for next future exploration.
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Regional Seismic Attribute Mapping for Nile Delta Deep Water Reservoir Imaging
Authors K.B. Halleland, J. Cotton and I. HanbalSixteen surfaces were mapped on a regional basin scale. The strategic focus for the mapping study was to identify the prospectivity in the Pre Pliocene section, so the horizons mapped were focused in this interval. Three areas of seismic mapping have been critical to completion of this phase of regional work : 1. Deep 2D seismic for basement structure as well as petroleum charge 2. Very large 3D mega merges for reservoir / seal definition & detailed lead mapping 3. Onshore & peripheral 2D mapping to extend the mapped key horizons both up dip & outward across the full project AOI. In addition several deeper surfaces were mapped carefully to calibrate the petroleum charge system.
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Pre-Screening Tectonic Heat Flows for Basin Modelling - Some Implications for Deep Water Exploration in the Mediterranean
Authors J.D. van Wees, G. Bertotti, P. David, F. van Bergen and S. CloetinghBasin modelling results can be very sensitive to (paleo-)temperature uncertainties. For frontier basins, in particular for deep water settings, the thermal signature of the basin is poorly constrained, as data from wells are lacking. This may lead to wrong heat flow assumptions if these are extrapolated from the shallow offshore or onshore. Furthermore large uncertainties can exist when dealing with constructing paleo-heat flow. The potential errors in spatial and temporal extrapolations are especially large in settings with strong spatial and temporal variations in tectonic regime. This is in particular true for the Mediterranean and North Africa. Heat flow modeling can be improved considerably through numerically modeling lithospheric processes underlying basin deformation. For this purpose we have developed a probabilistic tool which is capable of calculating tectonic heat flows calibrated to observed data and which can be used as input for maturation modelling. For various basin settings we will show the effect of adopting tectonic heat flows for improving spatial and temporal constraints on the temperature and maturation history in deep water exploration settings. Case studies include the Morrocan Atlantic margin and the Valencia Through (Spain).
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Crustal Structure and Early Opening of the Eastern Mediterranean Basin - Key Observations from Offshore Northern Egypt
Authors P.A. Bentham, I. Hanbal, J. Cotton, M.B. Longacre and R. EdwardsA significant body of literature has been published on the post-Paleozoic evolution of the Eastern Mediterranean Basin (EMB) however, many contrasting opinions are presented, and much is poorly understood about this particularly complex piece of the Tethyan system. Even the highest order aspects of the evolution of the continental margin of NE Africa are subject to debate and reinterpretation. Using recently-acquired industry data from the offshore Northern Egypt, we document results that address the fundamental questions concerning (1) the crustal structure underlying the EMB, and (2) the tectonic evolution associated with the early basin history. A synthesis of these results has been used to test existing plate tectonic models for the early Mesozoic evolution of the region and a preferred opening geometry is presented.
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The Petroleum System Knowledge Today and Tomorrow
Authors J.J. Biteau, G. Choppin de Janvry, J.J. Jarrige and F. ReverdyIn Basin and prospect evaluations we always deal with the assessment the Petroleum System elements. The Petroleum System is defined as the sequence of all the geological combined elements and processes which, from a source rock to one or several reservoir / seal pairs and using a common plumbing system leads to the formation of a genetically related family of hydrocarbon accumulations. We need to improve the seal efficiency studies: investigate the sealing sections as carefully as we do for reservoir intervals by a detailed mapping of their petrophysical parameters, thicknesses, the occurrence of hydrocarbon shows from mudlogs etc. We must also progress on hydrocarbon type predictions: We can use sophisticated simulators and calculators but only as sensitivity tools thanks to computers becoming more and more powerful, but we must not forget the geological and naturalist reasoning for helping to find new hydrocarbons! We need to come back to the geologic reflexion, following the key steps of the evaluation workflow and gather and integrate the knowledge and data even it becomes more and more complex to manage.
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Regional Hydrocarbon Charge in the Sirte Basin, Libya – Integration of Geochemistry, Basin Modeling and Regional Geology
Authors G.P.A. Muscio, N.D. Rodriguez and L. LiuA regional evaluation of hydrocarbon charge was undertaken in the Sirte Basin, Libya in order to improve the understanding of the general hydrocarbon charge system and to determine robustness of hydrocarbon charge in different areas in the basin. Geochemical data derived from crude oils and source rock extracts as well as source rock samples were integrated with regional map-based charge modeling and paleofacies mapping. Four main oil families and additional sub-families were identified, and correlated with the source rocks. Integration with maturity and lithofacies maps highlights that the Upper Cretaceous Rachmat Formation source rock appears to be the principal contributor to the resource-base (as opposed to the Sirte Shale). Moreover, this approach also reveals that the East Sirte Basin is more robust in terms of hydrocarbon charge than the West Sirte Basin.
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Looking for Hydrocarbons in Dry Holes - Application of Fluid Inclusion Chemistry in North Africa/Mediterranean
Authors P.J.R. Nederlof, A. Bell and D. HallFluid inclusions can provide hard evidence for the presence of hydrocarbons in a ‘dry’ hole and fluid inclusion screening of cuttings forms a routine part of a dry hole analysis in many oil companies. Subsequent microscopic and chemical analyses provide additional compositional information via cryo-optical and quantitative fluorescence techniques, constrain the timing of migration or reservoir filling (from paired analyses of coeval petroleum and aqueous inclusions) and can identify the source of the hydrocarbons via GCMS and/or isotopic methods. A particularly useful technique is compound specific isotope analyses (CSIA) of the gas components of the fluid inclusions. For instance, in many basins in North Africa and the Mediterranean, there is uncertainty about the presence of the Silurian Tannezuft (Qusaiba) source rock. This source rock was deposited after the Silurian deglaciation and source rock quality depends on the anoxia and stratification of the water column, which varied regionally with the topography at that time of deposition. With CSIA analyses of fluid inclusions, the presence of Silurian generated gas is easily recognized from the carbon isotopes that are characteristic for the Silurian generated gases. In this presentation, we describe recent applications of the fluid inclusion geochemistry from Libya, Syria and Oman.
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An Overview of North African Petroleum Systems as Revealed by Petroleum Geochemistry
More LessPredictions of source rock type, geologic age, and thermal maturity can be made based on biomarkers from migrated crude oils whilst natural gas origin and maturity can be deduced from stable isotopic compositions. Various petroleum systems are mapped across northern Africa, based upon the predicted source rock type and age. The solid component of petroleum, asphaltenes, can be used as source rock kerogen surrogates to determine generation kinetic characteristics.
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Geochemical Evaluation of Source Rocks in Block NC98, and the Relationship between Petroleum Habitat in Block NC98
More LessIdentifying of source rocks is essential for the evaluation of the petroleum potential of the sediments dominated by terrestrial organic matter in exploration areas. This will improve the modeling of the generation history of the source rock sediments.The knowledge of the petroleum generation and the characteristics of the source rock sediments is one of the main factors in the exploration success of an area. Geochemical data were used to examine the amount, type, and maturation of organic matter and Hydrocarbon potentials of source rocks within the Block NC98. Block NC98 source rock intervals have been identified in Lower and Upper Cretaceous group. The source rocks have been determined by identification of various organic Geochemical and palyonologyical methods and techniques. The data obtained indicates that both petroleum systems have a very good source section with high potential for oil and gas generation. Both petroleum systems have organic facies derived from marine and terrestrial organic input. This was confirmed by the optical examination, and organically rich TOC. The Geochemical analysis including carbon isotope, GC, and GC - MS indicates that the Hydrocarbon extracted from Lower Cretaceous group have a positive correlation with Hydrocarbon found in the Upper Nubian sandstone.
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Global Neoproterozoic Petroleum Systems - Snowballs, Source Rocks and the search for “Old Oil” in North Africa and Middle East
By J. CraigThe Neoproterozoic eon, stretching from 1000 Ma to the base of the Cambrian at 542 Ma, is relatively poorly known from a petroleum perspective despite the existence of proven plays in many parts of the world including Oman, Mauritania, Siberia, India, Pakistan, Australia and the United States. Many of the proven “Infracambrian” (Neoproterozoic to Early Cambrian) hydrocarbon plays around the world depend on the presence of prolific “Infracambrian” source rocks. There is increasing evidence that deposition of many of these organic-rich units was triggered by strong post-glacial sea level rises, on a global scale, following the “Snowball Earth” type glaciations, coupled, in some areas at least, with basin development and rifting on a more local scale. Neoproterozoic to Early Cambrian organic-rich strata were deposited in both high latitudes (e.g. Mauritania) and low latitudes (e.g. Oman) along the North Gondwana Margin. Some of the black shales encountered on the West African Craton may be as old as 1000 Ma and clearly predate the Pan-African orogenic event. These are substantially older than the majority of the Infracambrian organic-rich units that occur across much of North Africa and the Middle East (including those in Oman) which predominantly range from c. 850 - c. 540 Ma in age.
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The Eocene Ramp Complex of Al Jabal al Akhdar, Cyrenaica, NE Libya - A Surface Analogue for Nummulite Reservoirs
Authors A.S. El-Hawat, S. Jorry, O. Hammuda, A. Obeidi, H. Barghathi and B. CalineForty eight high resolution stratigraphic sections and more than 850 thin sections were used to study the Eocene of Cyrenaica. Sections are located on the northern limb of Al Jabal al Akhdar inversion anticlinorium that formed a series of submerged Cretaceous structural highs and islands. These played an important role in the development of the Eocene nummulitic ramp complex. Evolved regionally parallel facies belts consisted of outer ramp mudstone clinoforms and mass transported facies, mid-ramp nummulite facies and inner ramp miliolid-orbitolites, coral-coralgal and skeletal facies respectively. Progradation of these belts led to an upward shallowing mega-sequence constituting Apollonia and Dernah Formations. It consisted of three correlatable nummulite dominated sequences in Ras al Hilal area. The top two of which pass eastward into structurally controlled reefal-coralgal-discocyclinid dominated facies. Reworking of nummulite bodies by waves and currents over structural highs led to improvement of primary porosity. Syndepositional reactivation of the structures not only triggered mass transport of the mid-ramp deposits, but also controlled nummulite body geometry, internal heterogeneities and diagenesis by spatially shifting high-energy and subaerial exposure zones through time. There no single nummulite ramp model that would characterize this active inversion setting, as depositional parameters changes in space and time.
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Large-Scale Physiography of the Murzuq Basin Shelf during Hirnantian Ice-Sheet Final Retreat and Silurian Transgression
Authors J. Moreau, L. Degermann, J.F. Ghienne and J.L. RubinoThe Hirnantian glaciation strongly affected the lower Palaeozoic sedimentary succession of the Murzuq Basin (Libya). After final deglaciation, the remnant topography displays imprints of most of the ice-sheet retreat evolution. One large ice stream pathway, in the form of a wide erosional trough including surbordinate higher areas, has been recognized. Several ice-fronts and related proglacial fan-deltas are localized at basin scale. These architectural elements are closely associated with the position of the Ordovician reservoir relative to the Silurian “Hot Shale”.
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The Upper Miocene Melquart Fm.- A Reefal Barrier South of the Gabes Gulf (Libya)
Authors J.L. Rubino, J. Camy-Peyret and P. LapointeBase on 3D seismic analysis an outcrops occurence an extensive reefal barrier is described in the Gabes Gulf including all the morphological elements that are known in the modern complexes.
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The Numidian Flysch Complex of Onshore Tunisia (Southern Kroumirie Range) - Facies Analysis and Stratigraphic Review
Authors S. Riahi, K. Bou Khalfa, M. Soussi and K. Ben Ismail-LattracheSedimentological analysis and biostratigraphic review of the Oligo-Miocene deposits of northern Tunisia provide new data allowing new stratigraphic and paleogeographic reconstruction. The Kroumirie and Zouza member have the same age and correspond to sand/mud and mud/sand rich systems of a deep sea fan system with a detrital influx supplied from the North. Structural analysis demonstrate that the Numidian flysch has been displaced by a major thrust fault.
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Coastal Plain Depositional Systems of the “Trias Carbonate” in the Berkine Basin, Algeria
By N. SabaouThe Trias Carbonaté overlying the TAGI is present in the Berkine Basin and comprises mainly dolomitic shales, with interbedded dolomite layers. The interval is essentially non-reservoir, although thin channel sandstones (often oil stained) are occasionally encountered. Some fluvial terrigenous input is still important at this stage, with the influence of sea level fluctuations and probably regional tectonic events. Sandstones are fine to medium-grained and very thin in the central part of Berkine Basin (where marine conditions are dominant), but they may become thicker to the south of the basin (Turner et al., 2001). Based on core analysis, these sands are interpreted as high sinuosity fluvial/estuarine channels cutting a coastal plain. The purpose of this study is to identify vertical changes in facies, depositional environments and their distribution, sequence stratigraphy and relative sea level controls (Sabaou, 2003). Correlation of the stratigraphic successions with the regional sequence stratigraphic framework, based on 120 wells (Turner et al., 2001), shows that the vertical change in coastal plain character can be related to relatively high-frequency base level cycles that are expressed as transgressive-regressive marine cycles in downdip areas.
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Sedimentary Evolution of Late Ordovician Sequence in El-Feel Field – An Example of Integrated Sedimentologic, Stratigraphic and 3D Seismic Data
Authors G. Serafini and E. TrinciantiNew data concerning the Mamuniyat and Melaz Shugran Fms. in El-Feel Field. are presented. Integrating palynological analyses with sedimentological and 3D seismic data, the physical stratigraphic framework and the vertical sedimentary evolution of the Cambro-Ordovician sequence were defined. The regionally recognised paleohighs-lows model in Mamuniyat Fm. seems not to be supported at the field scale. What was previously defined as Hawaz Fm. in some wells is now ascribed to Mamuniyat Fm. and, as a consequence, it wouldn’t represent the infilling of the morphological lows among the Hawaz paleohighs. Mamuniyat Fm. might represent the infilling of a large scale physiographic element whose edges are not recognisable within the 3D seismic grid. The Melaz Shugran Fm. is quite organised in terms of vertical stacking pattern showing some differences with respect to the classic shaly sequence found in the Murzuk Basin. The regional map of the Melaz Shugran Fm. facies distribution would suggest the occurrence of an extensive fluvio-deltaic depositional system sourced from the South possibly originated by the melting of the ice front during the Ordovician glaciation.
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El Feel Field – An Innovative Approach to Control Prior Model & PetroAcoustic Data for Seismic Reservoir Characterization
Authors A.I. Marini, E.L. Della Rossa and F. OwainaEl Feel reservoir is characterized by high impedance fluvio-glacial Ordovician sandstone sealed by soft shales. Recognition of seismic responses at Top reservoir cannot provide information on reservoir quality due to simultaneous changes of reservoir and sealing acoustic properties. Acoustic inversion, integrating well and seismic data was therefore a crucial step to derive a 3D seismic reservoir characterization and a robust prior model is required. A limited number of the utilized wells are vertical and the rest are mostly slanted (borehole dips >40°), therefore acquired velocity measurements are mostly biased by shale anisotropy. Also input seismic data fidelity is an issue; it was managed by adopting CRS-stack volume, superior for interpretative and quantitative uses. A geostatistical-based proprietary methodology was developed to integrate seismic and well impedance trends, horizons interpretation, and conditioning wells. Thomsen’s anisotropy parameters estimates from well data were used to reduce velocity measures to vertical wells conditions. The followed approach improved data reliability for Petro-Acoustic analysis, well-seismic tie, prior model generation, and inversion. Impedance-Porosity analyses suggested inversion results calibration feasibility by linear or non-linear (Neural Network) approaches. Output Porosity cube, useful for reservoir modelling, captured sedimentary features highlighted by visualization techniques.
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New Concepts in Stratigraphy for Near-Synchronous Correlation of the Paleocene-Eocene Interval of the Se Sirte Basin
Authors M.G.G. de Jong and S.D. NioThe new method of climate stratigraphy has been used to generate a well-to-well near-synchronous correlation framework with a unifying stratigraphic scheme for the interval from the uppermost Cretaceous to Eocene in the southeastern Sirte Basin of Libya. Climate stratigraphy combines the principles of global cyclostratigraphy with spectral (frequency) analysis of facies-sensitive wireline logs such as GR to identify near-synchronous bounding surfaces. The so-called spectral trend attribute curve (INPEFA_GR) has been developed to show the breaks and trends which are used for correlation. Seventeen regionally important near-synchronous bounding surfaces have been systematically identified in wells. Lateral facies variations between these bounding surfaces as well as regional differences in facies development through time become apparent – a framework for systematic evaluation of potential reservoir-seal pairs has been generated. Problems and uncertainties inherent to lithostratigraphic correlations are largely overcome. Details of the method and of its application to well correlation in the SE Sirte Basin will be given in the presentation.
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Comparative Anatomy of Cretaceous Carbonate Ramps - An Outcrop-Driven Interpretation for a Sirte Basin Field
By J. RushThe use of outcrop analogs for constraining stratigraphic interpretations has often been presented for mature fields with seemingly inexhaustible data and tight well spacing. In contrast, a viable fourth-order stratigraphic interpretation of a mixed carbonate siliciclastic system is proposed for a Sirte Basin field with only twenty wells on 640-acre spacing. The objective was to squeeze as much information regarding the depositional environments from scarce well data, integrate observations within an outcrop analog, and develop a play concept to prioritize a potential field acquisition candidate. The result is an outcrop-driven depositional model and stratigraphic framework that honors observations made from core, thin sections, accommodation trends, and paleogeographic setting. A “best fit” analog was identified from Albian outcrops along the Lower Canyons of the Rio Grande in the Big Bend region of Texas. Lithofacies, fossil assemblages, and accommodation trends were analyzed for comparison and were found to be remarkably similar. Actual and comparative evidence suggests this field was situated atop a shallow, current-swept, intrabasin platform, characterized by localized ramps onlapping basement highs. Clastic-rich, radiolitid buildups and associated grainstones developed along the inner ramp, onlapping basement highs, and grade offstructure into chalky Inoceramus-globigerinid wackestones and shales.
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Chemostratigraphy of Cambro-Ordovician to Silurian Sequences from Block NC186 in the Murzuq Basin, Western Libya
Authors O. Kaabar, J.L. Algibez, T. Pearce and A. KhojaThe characterization and correlation of sedimentary sequences based on changes in inorganic geochemical data. The bulk geochemistry of sediments changes in response to subtle changes in mineralogy caused by source composition, facies, weathering or diagenesis. The analytical techniques employed are highly sensitive and the technique can often see correlative features that cannot be detected using E-log data. In some instances, this enables apparently uniform successions to be correlated with confidence.
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Climate Sequence Stratygraphy Unraveled by the Analysis of the Clay Content Evolution
More LessCase Study - The Triassic Formation of the Hassi R’mel Field (Algeria). In the sedimentary recordings, clays, if inherited can give a fundamental a reliable and fundamental indication on the continental contributions. The examples studied come from central sahara wells of various basins. The triassic shale sandstone formation of the central sahara is about 200 meters thick, made of two series of the shale sandstone separated by volcanic rocks. The clay fraction was studied by using diffractometer and the following results were obtained: - from the point of view of the clay fraction constitution a) in oued mya basin the principal minerals are illite, chlorite and mixed layers; b) on the other hand in the berkine basin, there is an association of illite, chlorite mixed layers and kaolinite -from the point of view of the characteristic of clay: during the interpretation of the diffractogramms and by superimposing them we remark that: the intensity of illite peak (I001) and chlorite peak (I002) vary considerably with the depth. The peak variation does not occur at the random. In fact, as observed the intensity of the illite peak (I001) decrease from the bottom to the top in a metric level or profile. Thus, it was observed that at the bottom of the profile, illite shows a high intensity (I001) peak, with a good cristallinity, and as one goes up in the profile(i.e.a decrease in the depth) the peak intensity becomes weaker and sometimes, nothing can be noticed on the diffractogramm. The explanation of the loss of the intensity is not due to the reduction in the partiules but to the worse cristalline organisation of the crystalline system. Indeed the climate which characterized the triassic period is arid or semi arid, he is marked by alternation of wet and dry period. The state of the clay fraction, which depends of the source of the sedimentary material that is homogenous in the sedimentary environment system. In period of dryness, the evaporation is intense, concentrates the solutions which become more agressive and start to initially deteriorate the sedimentary unit with the contatc water sediment then penetrates in the sedimentary unit according to its permeability. This proves that the substance analysed is amorphous by XRD, revealing thus a high weathering of the clay fraction. This decrease in the intensity of the I001 peak of illite from the bottom to the top of the level is spectacular. This phenomenon is observed both in the clay fraction content in the sand and shale samples. The repetition of this phenomenon in the space et time and at the regional scale shows the regularity of the climate.This evolution of the clay fraction is similar to the present day pedogenetic one. Thus, degradations or tranformations by degradations seem to be an overall mechanism in the meteoric alteration and pedogenetic process. This permits us to define sections in the sequence called genetic sequences.
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Stratigraphic Architecture of the Devonian Succession in Awaynat Wanin Area - Ghadamis Basin, Western Libya
Authors M.M. Rahuma, J.N. Proust and R. EschardDuring Palaeozoic times, the structuration of North Gondwana induced the formation of sub-basins separated by tectonic arches on the N orth African platforms. The slowly subsiding sub-basins were fed by periodically emerging and eroded arches (uplift vs eustatic sea-level drops) that control sediment distribution in space and time. The Devonian successions, located at the boundary between the Qarqaf arch and the subsiding Ghadamis basins in western Libya, represent a good record of this evolution and then an opportunity to discuss the relative influences of parameters that control the sequence architecture and reservoir distribution. The Devonian formations (Tadrart, Ouan Kasa, Awaynat Wanin, and Tahara Formations) in western Libya consist of more than 1000m of siliciclastic sediments. The succession is Pragian (Early Devonian) to Strunian (Late Devonian) in age and lies on Llandoverian (Early Silurian) shales along the Caledonian unconformity. These rocks are among the largest oil reservoirs in N orthern Africa. Most them are stratigraphic rather than structural traps and require detailed sedimentologic and stratigraphic works to improve the results of the exploration activities.This study based on outcrop and subsurface data respectively collected along the arch in Awaynat Wanin area and into the Ghadamis basin can provide some guidelines to fulfil this perspective.
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High-Resolution Chronostratigraphy of Varied Biostratigraphic Data from Sirt Basin Wells - An Example of Graphic Correlation and Discussion of Other Methodologies
Authors T.D. Demchuk and W.N. KrebsThe use of high-resolution bio- and chronostratigraphy to delineate and subdivide the strata of the Sirt Basin. Investigations utilizing varied microfossil data and unique biostratigraphic software techniques to construct chronostratigraphic frameworks for use in exploration and exploitation in the Sirt Basin. Identification of depositional sequences and correlation and calibration to other sedimentological and stratigraphic interpretations.
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OBC Systems for Imaging in Challanged Environments - Results and Remaining Challanges
Authors M.L. Johnson and M.W. NorrisA suite of tests were preformed in the Gulf of Mexico to evaluate the ability of conventional air gun arrays to generate low frequency energy. The tests utilized a MEMS OBC system to record the data generated by various air gun configurations. This presentation reports on the acoustic blanket configuration used with a deep air gun array.
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Azimuthal Seismic Fracture Detection in a Carbonate Reservoir - Integrated Seismic P-Wave Study
Authors J.M. DeGraff, M.K. Johns, D.Y. Wang, C.P. Lu, S.Z. Sun, S. Xu and D. ZhouUnderstanding the distribution of fractures in carbonate reservoirs can greatly improve modeling of production rate and flow anisotropy. Seismic anisotropy may be a cost-effective technique sensitive to open fractures affecting flow, and can provide volumetric information on fracture properties. This talk focuses on azimuthal AVO effects at interfaces between fractured and unfractured rocks. We calculate AzAVO attributes for a Cretaceous limestone reservoir in East Texas. The workflow integrates inversion results with rock physics, forward seismic modeling, dipole sonic and image logs, and core to interpret azimuthal attributes relative to geology and production data. AzAVO inversion results for the field show anomalies that broadly tie to fracture indicators and are geologically reasonable. Anisotropy magnitude aligns with many NE-trending faults, which is consistent with fault-related fracturing. AzAVO orientations generally parallel ENE-trending fractures in core, maximum horizontal stress from image logs, and fast-velocity direction from a dipole sonic log. However, moderate to poor seismic data quality and sparse geologic well control limit our confidence in quantitative fracture prediction. Overburden effects manifested by amplitude dimming degrade AzAVO inversion quality over the structural crest and highlight the sensitivity of the inversion algorithm to amplitude artifacts.
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Predicting Fractures Using Wide Azimuth Seismic Data in Tiguentourine Field, Algeria
Authors S.R. Tod, D. Sawyer, B. Taylor, R.G. Johnston, T.J. Allen, D. Buddery, A. Hutchison, A.M. Malik and D. AbdelouafiA small pilot area wide azimuth P-wave seismic survey was acquired over a part of the Tiguentourine gas condensate field in 2004 to test the ability of surface seismic data to accurately predict the P-wave anisotropy resulting from the preferential orientation of open fractures within the Cambro-Ordivician reservoir. Comparison of velocity anisotropy attribute estimation from the seismic data with image log data recorded in a number of wells shows an encouraging positive correlation that provides confidence in the use of the seismic attributes to assist in the locating of wells to target areas of high oriented fracturing in the believe that these can provide a considerable permeability assist and thus provide a significant boost to well productivity rates.
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Multi Azimuth 3D Bringing Clarity to Pre-Messinian Reservoir Imaging
Authors J. Keggin, M. Benson, W. Rietveld, T. Manning, B. Barley, P. Cook, E. Jones, C. Page and M. WidmaierA thin but complex layer of partially eroded anhydrite and other facies lie at a depth of around 3km across large areas of the Nile Delta, offshore Egypt. Wavefield distortion, attenuation and the generation of complex multiple diffraction noise cause the quality of the underlying seismic image to be highly variable. In this paper we describe the problem and then demonstrate how multi-azimuth seismic is able to improve the Pre-Messinian image
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Velocity Model Building for Pre-Stack Depth Migration - An Onshore Libya Case Study
Authors L. Auchterlonie, V. Vinje and R. TaylorTypically, velocity models for land datasets are built using a traditional “blocky” layer-based velocity model. Here we use a dataset from the Masrab field in the Sirte basin south-east of Tripoli, Libya, to compare this traditional way of building depth models with a “smooth”, volumetric velocity model building approach. We show that the volumetric approach provides improved image quality whilst decreasing the turnarund time.
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A Fast-Cycle Volumetric Approach for PSDM Velocity Model Building Applied to a Major Fault in Western Desert - Egypt
Authors M. Emile, A. Ramadan, S. Zimine, C. Pinson, P. Mitouard, V. Vinje, R. Saba, A. El-Fiki and G. BakryThe case history presented here is for a desert environment and contains a strong lateral velocity variation (up to 1500 m/s) across a major fault with a throw reaching 3 km. The results from this study show that the new velocity model buiding approach improved imaging in the shadow zone of the fault where traditional methods failed.
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Petrophysical Seismic Inversion Applied to the Troll Field
Authors A.J. van Wijngaarden, T. Couleou, A.N. Haaland, J.L. Formento and R. OnaWe present an application of petrophysical seismic inversion, a method driven by petro-elastic models, updating a fine-scale geological model in depth to make it fully compatible with pre-stack seismic measurements on a part of the Troll Field Central province, in the North Sea. The results are being evaluated for infill drilling and for a future 4D inversion to determine the remaining oil in the thin oil leg.
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EM Seabed Logging on the Troll Field
Authors S. Johnstad, B.A. Farrelly and C. RingstadA seabed logging R&D study was conducted on the Troll Field in December 2003 – January 2004. Different EM waveforms and frequencies were tested to optimize the hydrocarbon response from this shallow water gas and oil field. The survey consists of 41 receivers, deployed along a line crossing the Oil Province, the Western Gas Province and the Eastern Gas Province of the Troll Field. All receivers recorded two orthogonal components of the horizontal electric field, and 12 receivers measured in addition two orthogonal components of the horizontal magnetic field. The R&D study was carried out as an attempt to qualify seabed logging for shallow waters (less than 500 m) and optimize acquisition parameters for such cases. Up until now the marine controlled source EM method has been qualified for use in deep waters (more than 1000 m water depth) mainly because of the disturbing influence from the air wave in shallower water areas. The Troll Field seabed logging data is of excellent quality and helps in solving problems related to shallow water applications of this method.
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Mapping Offshore Facies and Structures Using CSEM
Authors L.J. Srnka and L.A. WahrmundMarine controlled-source electromagnetics (CSEM) has grown into a useful method for oil and gas exploration, with many surveys acquired worldwide since 2000 by industry including ExxonMobil. Pre-drill prediction success rates are encouraging. The technology is geophysically sound, but needs more development to be useful across the full Upstream. CSEM data interpretation is improved significantly by integration with other data including seismic. An example from deepwater Brazil shows the ability of CSEM to map facies. Extension of the technology to offshore deepwater Libya poses new challenges, including resistive non-reservoir facies and deep targets.
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Gravity and Magnetic Data Interpretation in the Sirte Basin
More Lesshas been created from the available well, seismic and published map data, the gravity effect has been forward modeled and subtracted from the observed gravity. The remaining gravity field has been inverted to derive a first basement depth map. The results of this work will be used in basin-SR charge modeling which should further our understanding of the Sirte basin’s petroleum system.
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HFVS Optimzation for Land Operations - Shake and Go
Authors M.L. Johnson and C.E. KrohnA new vibroseis acquisition technique, which uses HFVS (High Fidelity Vibrator Seismic) separation with continuous sweeping, results in unsurpassed production rates and at the same time excellent data quality. With Continuous HFVS, there is no waiting for between sweep listening times or for between vibrator slip times. All vibrators sweep simultaneously using a long segmented sweep and then move to the next shot points. Calculated production rates are as great or greater than other high productivity methods, particularly with multi-fleet flip-flop operations. In processing, each long data record is parsed into individual segments and separated with the HFVS technique. Separation with C-HFVS is as good as standard HFVS separation. Cross contamination of signal from the vibrator points being acquired simultaneously is not observable in the output records. As long as the sweep segment length is greater than 1.5 times the listening time, the noise quality is comparable to that of HFVS, since harmonic interference noise from sweeping during the listening time is limited to times near the end of the sweep segment.
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“Sparse 3D” Acquisition – An Efficient Exploration Technique
Authors C. Webb, M. Millington, H. Crook and R. HeathWith the seismic and rig markets being very tight in Libya, and in light of the 5 year EPSA-IV licence period, any chance to fast-track the work programme should be examined. For BG Libya, the ‘sparse’ 3D acquisition design discussed in this paper should allow acquisition of high quality 3D data, whilst retaining an efficient survey acquisition schedule and pricing. Use of the existing 2D data and acquisition of a test line ahead of the survey design was a great advantage in the design optimisation, and should be considered as best practice in ‘sparse’ 3D design.
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Desert Sparse 3D as an Alternative to 2D Exploration
Authors B. Pagliccia and P.L. PichonClassically, the first step in exploration corresponds to shooting of 2D seismic, in order to obtain a preliminary image of the subsurface. Through interpretation of these initial data, sub-areas are defined with good exploration potential. Thereof the most prospective areas are then covered with 2D infill layouts. This classical strategy is now challenged by recent acquisition systems with high-channel capacities which, with an adapted sparse design, allow to acquire 3D seismic in a cost effective way compared to 2D. Furthermore, this “Sparse 3D” approach gives a better definition of the prospective areas. A sparse 3D has been acquired by Total E&P Libya on the NC192 concession, with a design optimization derived from decimation test performed on conventional 3D. This sparse 3D has documented a major progress in imagery compared to pre-existing 2D acquired in 1992 by previous operators. Based on the new images, major elements of the structural framework had to be revised, which in term resulted in an optimized definition of new prospects. When surface and subsurface conditions are favourable for sparse 3D acquisition, it has to be considered as a serious alternative to conventional 2D. Then this method may improve significantly the geological understanding of the subsurface under reasonable costs.
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Fit-for-Purpose Seismic Technology - A Case Study in the Use of Point-Receiver Recording for Exploration in the Western Desert of Egypt
Authors P.V. Baaren and J. QuigleySeismic survey design balances the complex interaction of many factors against the objective of delivering a cost-effective and fit-for-purpose dataset, on time, to the seismic interpreter. The availability of new technology allows reevaluation of this balance of factors to best realize the value the technology can provide. Traditional assumptions in terms of fold requirements and source and receiver effort can be revisited. A case history is presented from a 2000-km2 3D Vibroseis survey in the Western Desert of Egypt. Availability of a high-channel-count point-receiver acquisition system and associated source and processing technology allowed a significant rebalancing of the field acquisition parameterization relative to an existing, successful, conventional technique. The resulting dataset, though acquired with a reduced field effort, compares favorably with the existing data both geophysically and economically.
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Environmental Impact Limitation during Exploration Activities in a Highly Sensitive Environment
More LessLimitation of the environmental footprint caused by exploration activities is achievable, especially through applying control measures at the time the operations take place. The current GIS project is an example of the additional benefits that can be created, as a by-product of the implementation of operational procedures.
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Enhanced Understanding of the Krechba Field, Algeria by Using Modern Processing and Depth Conversion Techniques
Authors C. Reiser, J. Sinden, A. Castoro, H. Sognnes, S. Omri, S. Brown, A.M. Malik, D. Abdelouafi and M. FrenchKrechba is one of eight fields in the In Salah Gas Development in Central Algeria, operated jointly by BP, Sonatrach and Statoil. The field is in the northern part of the acreage retained for development, and consists of reservoirs in the Carboniferous and Devonian. The Carboniferous, Tournasian C10.2 sands are the main contributor to the gas production to date, being developed for first gas in 2004. The original field discovery made in 1957 was based on 2D seismic. Due to uncertainty on the top reservoir and the thin reservoir, a 3D seismic dataset of approximately 600 km2 was acquired in 1997. Seismic amplitudes were used to define accurately the presence and quality of the estuarine sands very well developed over the field. This reservoir consists of several stacked thinner sands, at depths ranging from 2800 m to 3400 m. With this challenging task, to improve the seismic resolution and the seismic quality lead to reprocessing of the 3D volume which was finalized in 2006. This paper reviews the main steps of the seismic depth conversion process with the use of seismic velocity on this field using the reprocessed seismic, and draws some conclusions regarding the future development of the field.
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Formation Evaluation and Reservoir Monitoring behind Dual Casings - A First Libya’s Case Study
Authors R.G. Gauchet, C.R. Robert, M.A. Attayeb and L.W. WihardjoThe success of Formation Evaluation and Reservoir with modern tools, provided proper planning & Monitoring behind dual casings can be achieved logging preparation. The casing ex-centralization and well deviation are key factors that provide tool orientation and make it possible to record a stronger formation signal. The quantitative water saturation comparison (between open and cased hole evaluation) has indicated significant remaining oil left at the Dahra formation. The current oil water contact has been positively identified.
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Opportunities and Challenges for Improved Oil Recovery
Authors G.F. Teletzke, J.R. Wilkinson and K.C. KingA worldwide look at long-term trends reveals that new discoveries of conventional oil fields are declining while demand for oil is estimated to increase approximately 1.5% per year from the current levels of approximately 85 million bopd. A portion of the increased demand will be met by increasing supplies from non-conventional deposits but the majority will need to come from improved rates and recovery in conventional oil fields. Industry experience and performance to date indicates that while considerable opportunities exist, there will also be fundamental challenges facing our ability to increase light oil recovery. This means increasing attention on fundamental parameters driving increased field offtake rates and recovery factors. This paper will discuss both basic technical parameters that need to be addressed and the IOR/EOR technologies that can be deployed (or developed) to meet this challenge. It also covers the pros and cons of various types of enhanced oil recovery injection fluids. Attributes of enhanced recovery cost elements that need to be considered in fiscal regimes that are mutually beneficial to both host governments and the international partners will also be summarized.
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IOR/EOR in Hydro
Authors H. Tonne and R. NygaardIn this paper Hydro’s historic IOR achievements are reviewed. Key technologies for future IOR opportunities are identified. Improved reservoir control and well technology will continue to add new reserves to our portfolio of fields. Seismic monitoring, integrated operations, wired drill pipe, expandable metal and autonomous down-hole inflow valves will be important elements of our future IOR effort.
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Integrated Processing and F3 Reservoir Sand Interpretation Study, Wafa Field, Onshore Libya
Authors A.N. Fogg, T.H. Larsen, D.R. Sallis, H. Fares, F. Ghrouda, H. Zbeda, C. Pazzi and J. MartinThis paper describes the interpretation, seismic inversion and associated petrophysical analysis of an 868km2 full fold (1100km2 total) 3D seismic dataset over the Wafa field in Concession Block NC 169A, Ghadames Basin, Libya. The data was acquired for EniGAS BV. Seismic processing was carried out by Veritas DGC Limited during 2005 and the interpretation and seismic inversion was carried out in Veritas’ Crawley (UK) office from February 2005 to November 2005 by the VHR (Veritas Hampson-Russell) division.
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Characterization and Modelling of a Reservoir with Multiple Scales of Fracturing
Authors F. Gouth, A. Toublanc and M. MresahAn integrated fracture study from characterization to modelling on a carbonate field is described. This oil and gas accumulation is produced through 6 horizontal wells. Outcrop data allowed us to understand the spatial organisation of fractures seen on well imagery and to identify the main fractures scales: bed confined (BCF) in tight layers, highly persistent (HPF) and conductive faults. Two orientations have been identified at both BCF and HPF scales: axial N70 fractures related to the folding and N150 fractures uniformly distributed throughout the reservoir. Mud losses have been used to rank the conductivity of the different scales encountered at the well and PLTs have shown a clear relationship between fractures and productivity. A correlation between KH from PBU and N70 FF has emphasized the key dynamic impact of the HPFs. The fracture modelling has been performed using a DFN and has focused on HPFs. A fracture permeability grid data has been processed by the DFN and was used as an input for a double porosity model. The shape factor derived from well imagery data was lowered to match the historical GOR. This is thought to be due to the heterogeneity in dynamic properties of the HPF set.
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Well Test Analysis and Modeling of a Multi-Scale Fractured Reservoir – The in Amenas Field, Algeria
Authors R. Basquet, O.P. Wennberg, H.H. Veire, P. Ingsøy and A. DraouThe In Amenas in East Algeria is operated by a joint venture between Statoil, BP and Sonatrach. In this study we focus on the gas condensate production of the Cambrian and Ordovician reservoir Units of Tiguentourine field. A study to develop a methodology for a fracture model has been based on the available static data, i.e. borehole images, cores and seismic. The objectives are 1) to validate the structural image proposed by the geological and geophysical analysis, and 2) to characterize the hydrodynamical properties of this complex multi-scale fractured reservoir from dynamic data such as well test measurement. One well with both FMI interpretation and well test data have been analyzed. Firstly, a conventional well test interpretation was used. However, such a tool does not capture all the heterogeneities of the fracture system. Therefore, analyze was completed using a methodology based on fluid flow simulation within the actual fracture system. The applied FRACA model preserves the fracture distribution along the wellbore according the FMI interpretation. Despite the number of unknown parameters and the large uncertainties on the other characteristics, it was possible to match the well test signature fixing all the parameters with realistic values.
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Fracture Network Modeling and Dual Permeability Simulation of Carbonate Reservoirs
Authors J.M. DeGraff, M.E. Meurer, L.H. Landis and S. Lyonselement models to compute effective matrix permeability; 3) analysis of fracture data from core, image logs, and outcrop; and 4) integration of field performance, structure, stratigraphy, and lithology. Directional equivalent fracture permeability, porosity, and matrix block dimensions are estimated using discrete fracture network (DFN) and 3D geologic models, while effective matrix permeability is derived using proprietary technology (patent pending). Fracture analysis consists of identifying structural and stratigraphic controls on fracture data from available sources, and then using this knowledge to derive a set of rules to populate a DFN model. Dual-porosity / permeability reservoir simulation models are built in EMpower™ using a similar grid geometry and cell size, effective matrix properties, and DFN-generated fracture properties. Simulation results show a better history match with less iteration than previous models when compared with multiphase production history. In test cases, dual-porosity / permeability models more accurately capture the impact of fractures on fluid flow than do single-medium models.
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Rock-Fabric Facies and Diagenetic Controls on Carbonate Reservoirs
More LessA Case Study from the Early Eocene El Garia Formation, Tunisia.
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Effective Simulation of Thick Carbonate Reservoirs
Authors C.E. Shuchart and I.S. Abou-SayedWorldwide, substantial oil and gas resources are contained in low permeability sandstone reservoirs and variable permeability carbonate reservoirs. Matrix or fracture stimulation treatments are typically required to effectively and optimally produce these resources. Many of the larger resources are characterized by thick intervals and/or multiple reservoir targets. ExxonMobil has undertaken multi-disciplinary approaches to the development and integration of technologies for design, implementation, and evaluation of acid and fracture stimulation treatments for these reservoirs. Specifically for matrix stimulation of thick carbonate reservoirs, acid placement and diversion are extremely important and challenging. Additional challenges associated with stimulating thick reservoirs include increased rock heterogeneity, development of differential reservoir pressures, and impact of the hydrostatic pressure of the fluid in the wellbore. Successful stimulation of moderate thickness intervals (100-500 ft) has been achieved through a combination of high-rate injection, viscous diversion, and selective perforating. However, for thicker reservoirs these methods may not be sufficient. ExxonMobil continues to advance the development of mechanical, chemical, and engineering methods to improve acid placement in very thick reservoirs (500+ ft).
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Physics Limit Drilling
Authors S.R. Keller and F.E. DupriestThis extended abstract describes the use of a physics-based approach to well construction. First, physics-based drilling models and limit states are integrated in a quantitative risk analysis framework to help plan the well. Then, during drillng operations, a physics-based, energy approach is used to maximize penetration rates.
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Acid's Behavior and Performance on the Matrix with Time - Hassi R'mel Field, Algeria
Authors M. Boussa, D. Bencherif and M. KhodjaSandstone matrix stimulation has been the subject of extensive investigations for over 40 years and extensive experimental work has been conducted to investigate the reactions of various mud acid systems with damaging and formation materials[1-2-3]. Theoretical analysis and modelling of the stimulation process have also been studied by some investigators[4-5-6]. Another experiment of acidizing was realised in Hassi-R'Mel field with 3 types of acid. This field is a gas condensate reservoir with a superposition of three layers having very good petrophysic characteristics. A decrease in production of the wells was observed in the various zones. Build up tests realised on those wells showed significant skin, which is due primarily to the excessive invasion of the mud used during drilling and Work Overs. For that, a stimulation by acidizing was decided to optimise and to improve the potential of these wells which is less than that hoped within sight of their petrophysic characteristics. In order to study the effects of stimulation, PLT’s were realised before and after the acidizing. Before stimulation, studies were undertaken to see and analyze each acid's behavior on the matrix and to draw the conclusions on the capacities and disadvantages of each one of them on the reservoir. The analyses carried out before, during the acidizing and several years after us made it possible to make a technical and economic study which will enable to see and to understand acid's behavior with time and its impacts on the reservoir , on the wells's equipment and investment costs. The purpose of this presentation is to show: -various methods of acidizing used and the concentrations used. -acid's behavior and performance on matrix with time -the advantages and disadvantages from this stimulation campaign. -the ratio of the profit on the capital costs after the operation of acidizing
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Porosity and Permeability from Drill Cuttings
Authors R. Lenormand, P. Egermann and J. BouillotThe early determination of rock petrophysical properties is one of the main concerns during the reservoir characterization process because it impacts directly the reserves (porosity, saturation) and also the well deliverability (permeability). Logs generally provide a good estimate of porosity and saturations along the well, but permeability is more difficult to obtain especially in carbonates. Drill cuttings can provide additional information on the petrophysical properties of the reservoir. In this paper, we have described a method for measuring permeability on drill cuttings with the following capabilities: size of cuttings down to 1 mm diameter,volume of cuttings around 1 cm3 (2-3 grams of dry cuttings),permeability from the microDarcy to around 100 mDarcy. The main constrain of the method is to need consolidated cuttings with a porosity larger than 4% in order to have a minimum volume of air trapped during the spontaneous imbibition. Porosity is difficult to measure on small cuttings. The more accurate method is based on NMR relaxometry with an apparatus dedicated to the measurement of small volumes.
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Determining Reservoir Connectivity in Producing Fields – Examples from Eastern Canada and the Gulf of Mexico
Authors M.L. Sweet, P. Vrolijk, L.T. Sumpter, J.W. Snedden, R. Myers, B. James, E. Meurer and A. MosolaMaximizing recovery from oil and gas fields requires an understanding of the initial distribution of fluid contacts that may vary between segments of the field. It also requires an understanding of which geologic elements affect connections between wells as the field is produced. We have developed a technique, Reservoir Connectivity Analysis (RCA), for rigorously defining differences in fluid contact elevation and relating these contact differences to geologic elements with the goal of identifying pre-production, reservoir compartments. This technique has been applied to more than a dozen ExxonMobil fields in depositional environments ranging from aeolian to deepwater and in structures that range from simple folds to complexly folded and faulted structures. Some of these studies have led to successful predictions of contacts in previously undrilled compartments of mature fields. In other cases, we have found that as the field is produced these geologic features affect production by limiting drainage area and pressure support. In addition to geologic features that control contact elevation over geologic timescales, we have observed other features that may be transmissible over geologic time, but that affect connectivity as the field is produced.
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3D Seismic Data Attribute Analysis for Predicting Wara Reservoir Qualities in the Al-Khafji Field, Middle East
Authors K. Chakraborty, S.L Nimmagadda and M. Al-HajeriReservoir property such as porosity, its lateral variations and areal extensions can be predicted from seismic attribute data, if they are appropriately calibrated and integrated by vertical seismic profiling (VSP) and petrophysical data. Objectives of the present study are to explore Wara reservoir qualities and their spatial distribution and examine its stratigraphic trapping mechanism by 3D seismic imaging. Gross porosities and sand volumes have been computed and mapped at well locations and seismic crossings. Seismic attributes calibrated at well locations, have been mapped all along and across the seismic grid covering the entire Al-Khafji field area. Cross plotting between seismic attribute values and well driven-porosities has facilitated to derive a correlation function and estimate of porosity attributes. Porosity estimation using seismic attributes of their seismic locations provide good confidence and its confidence is better improved at well locations thus describing reservoir properties between wells and away from wells. Porosity maps derived from well-data combined with calibrated seismic amplitudes and computed sand volume maps, predict sand bodies and their lateral extensions, particularly in the eastern part of Al-Khafji oil field, which open up additional exploration areas for Wara reserve accretion in the Gulf of Kuwait.
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Constraining Reservoir Models by their Diagenetic Overprints - Impact on Reservoir Connectivity
Authors R. Labourdette, A. Meyer, M. Sudrie, F. Walgenwitz and C. JavauxDolomitic formations constitute one of the most important reservoirs in the Middle East Region. The complex diagenetic history which prevails in these reservoirs impacts on the final static and dynamic reservoir properties. Therefore in order to optimise the current production of reservoirs and future field development plans, it is mandatory to: •understand the type, impact and timing of the main diagenetic phases at all scales from regional understanding to the fine-scale reservoir heterogeneities in order to constrain geometry, •and develop approaches to effectively incorporate the most significant ones into the static reservoir model. Dolomitization is one of the most crucial diagenetic phases since it strongly constrains the permeability architecture of the field. Detailed diagenetic studies suggest that various types of genetic dolomite types exist, including evaporative, mixed evolved sea-water - freshwater and late thermobaric dolomites. The modelling approach is geologically-driven and based on the relationships between dolomite type, stratigraphic position, palaeogeographic position, depositional facies, and proximity to fault/fracture zones. The results are then quality controlled to ensure coherency with the conceptual models. The outcome of this modelling workflow is fed into a dynamic simulator to assess the potential impact on field behaviour, production profiles and well productivities.
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Geologic Modeling and History Matching of Production Fields Using an Integrated Geologic/Engineering Approach (RETR)
Authors L.H. Landis, B.A. Proett, J.J. Lawrence and C.J. LyttleThe Reservoir Evaluation Time Reduction (RETR) methodology was developed to improve the process of building reservoir simulation models and reduce the time required to establish the technical basis for business decisions. This integrated history matching process was tested on four producing fields of varying stratigraphic complexity, number of wells, and depositional environment. These tests demonstrated that using the RETR process offers several advantages over the traditional approach.
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Optimal Reservoir Management and Field Rejuvenation – Key Geoscience Technologies and Trends
By K. RudolphThe objective of this discussion is to provide a broad overview of Integrated Reservoir Management, using examples from fields around the world. Reservoir management can be viewed as a three component learning system. The first component is reservoir characterization based on the analysis and interpretation of fundamental geoscience and engineering data. The second is quantification of the subsurface via a geologic model, reservoir simulation, and facility model, providing the basis for future depletion plans. The third stage of learning follows production start up as we collect production surveillance data to evaluate the accuracy of the geologic interpretation and development plan. This repeated cycle of interpretation, modeling, and production feedback drives continuous improvement of the subsurface model and depletion plan, maximizing value from both new and mature fields, and cost-effectively recovering more oil and gas
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Qualitative Characterization of Silurian
Authors R. Perona, J. Dessay, J.L. Algibez, J.M. Gonzalez Muñoz, M. Sweed and J.J. MartinIn most prospects drilled the Upper Ordovician Mamuniyat formation is the main target, being the Tanezzuft formation the covering seal of the petroleum system. In this case a prompt identification from Mudlogging data of its basal member (“Hot Shale”) would be helpful for: - Correlation while drilling. - Anticipate the top of possible reservoir for opearional purposes.
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A New Workflow for Better 4D Seismic Interpretation
More Less4D seismic images are often replete with artifacts of the time-lapse methodology, unrelated to actual changes in properties within the reservoir. These artifacts introduce uncertainty into the interpretation of flow fronts and pressurization and can greatly diminish the value of the 4D data. In many cases the artifacts originate from seismic signal and noise which cannot be, but, ideally should be exactly repeated from one survey to the next. Practical limitations of seismic acquisition and processing technology inherently limit data repeatability. Current 4D workflows rely heavily upon seismic repeatability. Current workflows utilize subtraction of data (or images) from repeated surveys to localize changes in properties to the time interval between surveys. These subtraction-based methodologies therefore assume that repeated signal and noise will subtract to zero provided subsurface properties have not changed over time. One can relax repeatability requirements by direct inversion for the changes in properties between two surveys. This new 4D workflow avoids subtraction altogether and can greatly reduce artifacts and uncertainty in the resulting images. Improvement is particularly evident for time-lapse relative to the pre-production conditions of the reservoir. These pre-production properties have frequently been recorded through a legacy seismic survey with particularly poor repeatability.
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Contributions of the Seismic 3D in the Interpretation and Comprehension of Geometry of the Paleovallees of the Ordovician
By S.S. SaibMany studies treat of deposits and processes of Ordovician paléovallées within the Illizi basin. Their limits and their extensions remain difficult to understind. These deposits are characterized by a short and glacial episode, which are responsible on the formation of irregular incisions in Ordovician. This results in depressions filled by the deposits of the various units of the upper Ordovician (IV-3/IV2/IV-1). They can reach 300m depths and rest on the various units under unclaimed of Ordovician, or on Cambrian unit II, even directly on the Précambrien base. Their widths are variable 1 with 3Km. Two types of orientations have summers met NW SE and WNW - ESE in the Illizi basin. The acquisition of 3D seismic in the study area, not only makes it possible to include/understand their geometry, their orientation but also to delimit them with precision. The seismic interpretations, combined with the geological data (ground, well, cores etc....) allow to have another design of these paléovalées, as well as the oil potential which is associated.
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Imaging Vertical Boundaries Using Duplex Wave Migration
By B.H. LinkConventional 3D anisotropic prestack depth migration provides accurate structural boundary information for events with dips from 0 to about 70 degrees. For vertical or near vertical events conventional methods rely on turning wave technology that will only be accurate if the recording aperture is very large and the depth model is known to a very high degree of accuracy. Also, the energy to perform this imaging methodology will only be recorded if the velocity depth model is characterized by significant vertical velocity heterogeneity. Duplex Wave Migration is a newly developed technology that is capable of imaging only vertical events (plus or minus 20 degrees) and it does not require either a large recording aperture or any specific a velocity model that must have strong vertical velocity heterogeneity. It is planned that this paper will provide the first examples of the use of this technology on North African data.
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Palaeozoic Sequence Development and Stacking Patterns - A Tale of Moving Continents and Changing Climates
Authors P. Spaak, D. Middleton and S. MurfittSeveral prolific Palaeozoic petroleum systems are present in North Africa and the Middle East. The stacking patterns and trends of the Palaeozoic hydrocarbon-bearing successions of this vast area show trends and similarities that can be contributed to climatic and tectonic events. Several of these events and their impact on the sedimentary record will be discussed.
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Review of Recent Satellite Image Analyses of the Ghadames Basin (Libya) and the Tassili Region of S Algeria
Authors R.N. Diggens and J.N. DiggensThe Ghadames Basin is a prolific hydrocarbon province with a complex and long petroleum geology history. An integrated approach to understanding its regional structure is essential for exploration success in the region. The remote sensing analysis of Earth Observation (EO) data for the surface expression of sub surface structures is a very cost-effective method for a refinement of the interpretation of sub-surface data for the geometry, interaction, timing and distribution of structures, lithologies and sedimentary features. This study is based on new work carried out on several different types of satellite imagery at different resolutions. A major analysis of the EO data was also undertaken in order to better understand the Late Ordovician glaciogenic deposits in the region with a view to using them as direct analogues to assist in the interpretation of the equivalent horizons in the subsurface data. The Late Ordovician sediments appear to be a channelised, reworked, sheet complex containing associated sedimentary features, which are consistent with having been deposited in a fluvial to marine regime coeval within a glaciation environment. The outcrops show evidence for multiple phases of glaciation, with older sediments being eroded and reworked by subsequent glacial forces.
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Hydrodynamism Implication in Exploration: Triassic Sandstones Reservoirs (Tagi Fm.)in Southern Tunisia
By A. MaazaouiThe main purpose of this technique was to help understand the complex flow patterns synthesis of Triassic sandstones reservoirs, main hydrocarbon producer in Southern Tunisia. Compilation and mapping of chemical analysis of available formation water, static pressure, total dissolved solids with possible classification and potential level distribution at top TAGI formation was accomplished. The obtained results provide the basic information to understanding the relationship between recharge and discharge zones, origin and causes of variation in chemical composition and genetic water types of these subsurface waters. Therefore for better assessment of possible and additional hydrocarbon accumulation It was essential to integrate the above results with facies distribution, tectonic events, fluids attributes and their hydrodynamic effects on entrapments and highlight the most likely trends of additional hydrocarbon accumulation (exploration leads). This study can assist moreover to understand and to may explain why we have inefficiently drilled wells, by using fluids migration paths in respect to hydrocarbon draining area and perhaps to allow outlining the remaining prospective plays for accurate drilling. In other hand, this method may increase the successful ratio of drilling if we have regular and sufficient chemical formation water analyses.
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Maturity Modelling and Hydrocarbon Charge In South-Western Berkine Basin, Eastern Algeria
Authors M. Arab and R. SoulaliThe South-western Berkine basin is a depression bordered by two structural trends (Rhoure- Nouss and Gassi- Touil- Nezla) associated to important gas and oil fields whose Triassic and upper Silurian reservoirs are sourced from Silurian hot shale. These radioactive shales, at the base of the Silurian formation, are dated Llandovery. They are 10-60m thick in the structural zones and up to 80m in the Marfeg trough. The organic matter is marine type II. The organic richness is fair to good, the TOC values range from 2 to 8%. The maturity level decreased from the Marfeg trough (dry gas window) to the flanks (Rhourde-Nouss- Hassi-Touareg) (oil window).
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Trap and Petroleum Models of Gara Gara South Fields Illizi Basin South East Sahara, Algeria
By M.D. MebbaniThe Illizi basin is one of the most potential and mature basins in Algeria where many oil and gas were discovered since 1950s. Among these, Gara Gara South Fields located in the center of Illizi basin. Several oil and gas accumulations of various sizes have been found within the F6 reservoir of Silurian-Lower Devonian age and Ordovician in the Illizi basin. Lithologically, the F6 reservoir consists of interbedded sandstones and shales and is subdivided into M, A, B and C units. These reservoirs, which were deposited in offshore coastal bars and tidal channels, show a high degree of lateral and vertical facies variation. The Ordovician reservoir is known by the rapid variation of facies due to the glacial environnement. There are units which produce in some area but does not exist in others. This paper describes the petroleum geology of F6, which contains a gas cap and a rim of oil, and Ordovician reservoirs. In this area, Ordovician does not produce. Also, the purpose of this study is to determine the trap and petroleum models of Gara Gara South Fields, to compare the 2D and 3D interpretations and to explain the wells results.
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Production Optimization of Gas Wells - Problem of Water Influx
By M. BoussaThe field of Hassi R' mel is a gas condensate reservoir with a superposition of three layers A - B - C having very good petrophysic characteristics and a rather significant oil rim in the Eastern and Southern peripheries. Producing wells were drilled in
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Evolution of Glaciogenic Stratigraphic Interpretation with Improved Seismic Data in Tiguentourine Field, Algeria
Authors A.R. Hutchison, D.E. Sawyer, S.R. Tod, B. Taylor, D. Buddery, I. Alstadsaeter and D. AbdelouafiThe application of modern full azimuth seismic technology in the Cambro-Ordovician of the Tiguentourine Field, Algeria, has allowed stratigraphic interpretation of the sub-surface at an unusual level of detail. Careful use of analogues has given a high level of confidence in tunnel valley interpretations. Sub-division of the reservoir has also improved very significantly, backed up by improving well to seismic ties. The tool will be extremely valuable in well planning, understanding reservoir surveillance data, and in reservoir modelling. Principal contacts regarding this project are D.Buddery (BP; acquisition), B.Taylor (BP; instigator of the project, planning, processing).
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FMI Characterisation of Late Ordovician Facies & Surfaces (Murzuq Basin)
Authors J. Joubert, J. Moreau, J.L. Ghienne and J.B. RosThe imager analysis is justified by a sedimentological purpose - a detailed evaluation of the reservoir intervals to include sedimentary feature analysis, manual dip picking and small-scale structural features.
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Rock Physics Analysis of an Anisotropic Tight Gas Reservoir - A Field Case
Authors P.O. Lys and J. MarrauldIn this paper, we present the methodology we used to build a Rock Physics Model adapted to fractured Tight Gas Reservoirs. Azimuthal anisotropy is modelled in order to evaluate a 3D azimuthal seismic added value.
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Optimizing Production Gas Wells by Using a Dual Completion Hassi R’mel Field, Algeria
More LessDual completion was for a long time used to produce wells perforated on several zones. This type of completion concerns especially the oil wells, but few or not used on the gas wells. In order to improve the production in the upper zone of gas wells, a study was carried out on production gas wells with 2 layers and 3 layers in Hassi-Rmel's field. This field is located 500 km southward from Algiers in the Algerian Sahara and is one of the largest wet gas reservoirs in the world. The gas-producing Hassi R’Mel field has three distinct reservoir horizons, zones A,B and C. The zone A sandstones are composed of very fine grained sandstones which are locally clay-rich with anhydritic cementing in some places. The zones B and C have very good reservoir quality with permeabilities to gas ranging from 300 to 1200 mD. Zone A also has very good reservoir quality for gas , however, it has lower permeability of generally less than 300 mD. PLT recorded on these wells showed that the lower Zones B and C contribute to the majority of the gas production with the upper Zone A providing a lower contribution to the total production, in spite of an acidification of this layer. The isolated zone C of some wells due to the water influx generated an increase in the flow of zone A. This result pushes us to take in consideration the completion and to suggest to carry out a dual completion for the producing wells with several zones in order to improve the production of the zone A which is obstructed by the good potential of the zone C. This study will make it possible to show the necessity to use a dual completion on the producing gas wells with several layers, in order to improve the production of the upper zone and for avoiding having a cross-flow from this one towards the lower depleted zone. The results carried us made it possible to make a technical and economic study which will enable to see the impacts on the reservoir, on the well's equipment and investment costs. The purpose of this presentation is to show: -the advantages and disadvantages from this completion on gas wells. -the ratio of the profit on the capital costs after these completion.
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Survey Performances of the Polymers in the Water Based Systems Used to Drill Deep Wells
More LessA laboratory study has been undertaken to elucidate the influence of structural parameters of polymer/electrolyte systems commonly used for the formulation of water-based drilling fluids on their performances as filtrate reducers or viscosifiers.High temperatures and salt conditions encountered in the well may modify the rheological properties and this makes the use of polymers necessary. High molecular weight polymers (XC, gums, polyacrylamides), have been used in the formulation of water-based drilling fluids for reducing filtration, facilitating clay stabilisation, improving débris suspension capacity and drillstring lubrication in the drilling operation. The rheological behaviour has been modelised. The modele describe structural changes under shear or at rest as well as the associated stress growth makes it an attractive tool to use in order to improuve hydraulic predictions in deep well drilling.
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New Rigorous Method to Characterize and Modelize the Rheological Behaviour for Complex Fluids Used to Drill Deep Wells
More LessThe success of the drilling operations mainly depends on rheological parameters of fluids (muds), the choice of an adequate mud to the specific particularities of a crossed formations and to a geological conditions permits therefore, not only to increase the efficiency of drilling apparatus, but also to avoid the damage (plugging) of producer layers allowing a better productivity of a drilled well. The aim of this first part of this work is to study the influence of the pressure and the temperature on rheological behavior of drilling fluids used to drill the reservoir.
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Biostratigraphic and Sedimentological Analysis of Al Abraq Formation, Al Jabala Al Akhdar Arae, NE Libya
Authors A. Muftah, A. El Mehaghag and A. AddaloushSurface samples from different exposures of Al Abraq Formation at Al jabal Al Akhdar were subjected to micropaleontological (Calcareous nannofossisl and gforaminifers)investigation. It is restricted to calcareous nannofossils biozones NP24-NP25 (Late Oligocene).
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Optimization of a Portfolio of Exploration- Production (E&P) Projects
By S. GaciThe purpose of all companies is to create wealth; they are held to ensure a profitability at least equal to the average cost of their capital to be enough with refunding to the loans and remuneration to the shareholders. Those are sometimes faced to a whole of profitable projects where the decision to invest or give up depends closely on the limitation of the financial availabilities. According to their resources, these companies seek to constitute a portfolio of projects which maximizes their incomes. In order to avoid the disadvantages relating to the traditional methods, we apply the modern theory of the wallet. This theory, developped by Harry Mr. Markowitz and intended initially for the financial markets, propose to the company an optimal portfolio ensuring a good combination “value –risk” (maximal value – minimal risk) under specified constraints. This new approach takes account of the risk. As application, we used this theory to constitute an optimal portfolio of 16 E&P projects. And we propose the use of this technique to the projects of exploration of Sonatrach, and in particular to the gas projects of the South-west of Algeria considering their characteristic.
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Production Optimization of Oil Wells - Problem of Salt Deposit
Authors M. Boussa, D. Bencherif and M. KhodjaThe field of Hassi R' Mel is a gas condensate reservoir with a rather significant oil rim in the Eastern and Southern peripheries. Producing wells were drilled to develop the oil zone, unfortunately these wells are confronted to a severe salt deposit problem more or less related to exploitation regime perturbing oil rim production or shut in the well totally. The presence of sodium chloride inorganic precipitate is undoubtedly influenced by: -the type and quantity of water influx -operating procedures -reservoir characteristics such as temperature and pressure. A permanent fresh water injection under packer does not give improvement for these wells. A large volume is required for particular wells; the rapid salt deposition needs then a daily Coil tubing intervention. The treatment becomes a cost factor and these wells are then shut in. A study was undertaken in collaboration with the research and development center ( CRD ) to solve the salt deposit problem in the column of production due to temperature change effect. It consists to analyse a sample of the formation water in order to understand the phenomenon of the salt deposit, to test the anti-deposition product efficiency and to optimise its concentration under surface and bottom conditions; keeping in mind the reduction of the amount of the injection water. Laboratory testing was first of all undertaken, in order to assess chemical water injection compatibility with formation water to ensure that the two fluids will not produce precipitates. It has shown that the alkyl amide aqueous solution is used to prevent precipitation of sodium chloride crystals from high chloride brines from bottom of the hole, changing crystals growth from symmetrical cubic orientation to non-symmetrical dentritic type. Independently of the temperature, its efficiency will also depends on the presence of other salts in the brine and the pH. The purpose of this presentation is to show: Problem of sodium chlorite salt deposit which penalizes the good performance of a well. Solutions to adopt to improve the Index of productivity, by using chemicals to reduce deposit of salt.
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3D Modelling of (Upper Triassic) Continental Mixed Fluvial Systems Integrating “Lidar” Digital Outcrop Images with High-
Authors I. Fabuel-Perez, J. Redfern and D. HodgettsThe Oukaimeden Sandstones Formation is an Upper Triassic fluvial/aeolian formation located in the High Atlas Range of Morocco. The study area offers extensive outcrops in excess of 200 m high and extending for many kilometres. The formation is composed of stacked lenticular shaped sand bodies often containing cross-bedding and current ripples, interbedded with more tabular shape fluvial bars showing erosional bases with conglomeratic lags containing rounded pebbles of quartz, chert and felsic volcanics. Minor amounts of interbedded siltstones and mudstones are also present showing bioturbation and some lamination. The application of high resolution 3D laser mapping (LIDAR) to these outcrops combined with Differential Global Positioning System (DGPS) mapping and traditional sedimentological data have provided a very powerful and detailed dataset from which several ‘close to deterministic’ reservoir models have been produced. 31 separate LIDAR scan positions containing over a billion points has been collected covering a total area of 5 km long by 250 m high, along with a high resolution field dataset consisting of 12 sedimentary logs 3 gamma ray sections and analyses of the different geo-objects. New approaches and methodologies have been developed in order to integrate the different data into a 3D georeferenced framework.
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Kufra, Murzuq and Eastern Sirte Basins a Comparison of the Cambro-Ordovician Sediments and Silurian Source Rock
More LessMurzuq basin, Kufra basin and the eastern Sirte basin influenced by almost similar geological events. The three regions in many cases share different geological and geophysical limitations therefore it is logical to make some comparison between the three regions to resolve and identify some of the geological and geophysical problems. Murzuq and Kufra basins remarkably went through similar tectonic events and Eastern Sirte basin share similar source rock distribution, maturation and migration paths problems, which are possibly effected by the same tectonic events of the Paleozoic time. Also the three reigns (Kufra, Murzuq, and Eastern Sirte Basin) having the primary reservoir as clastic sediments of mostly unidentified Cambro-Ordovician units. The seismic resolution is highly influenced by the facies distribution and digenesis in the light of the lack of age determination where sand is setting on different sand of probably of different age and origin similarly in the three regions. Recent studies in Eastern Sirte basin chemostratigraphy analysis results shows an encouraging findings which can be applied to both Murzuq and Kufra basins. Source rocks analysis and hypothesis can be extended from both areas in Easter Sirte basin and Murzuq basin to better enhance our understanding of the source rock presence, maturation and migration time to the Kufra basin.
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Keynote; Sedimentology and Depositional Environments from Image Logs and Cores. Examples from the Gargaf Gp. and the Sarir Sandstone of the Eastern Sirte Basin
Deciphering the depositional settings of a reservoir is a crucial step in predicting its characteristics, which are necessary for an optimal field development. In this sense, integrated core and image log studies led to the sedimentological and depositional interpretation of several reservoirs. Examples are provided for two reservoirs from the Wintershall concessions in the Eastern Sirte Basin. The Early Paleozoic Gargaf reservoir shows a transition from deltaic environments to fluvial systems with varying density of channel stacking patterns. The major part of the reservoir consists of units sedimented by northerly-directed braided river systems. The top of the reservoir includes units deposited by braid deltas within a shallow water embayment. The Early Cretaceous Sarir series represents a complex interfingering of fluvial systems, shoreface/deltaic systems, and a lacustrine environment. The deposition was controlled by palaeogeography and variations of the base-level. These integrated studies improved the understanding of the reservoirs at different scales: depositional facies and facies associations, sediment geometries, palaeogeographical context (palaeocurrent directions and sediment fairways, areas of non-deposition, possible flooding surfaces, etc.). The image logs, once calibrated with cores, provided a powerful tool for interpretation of facies and palaeocurrents. Regional changes in palaeocurrents identified in wells also provided markers, which could support the well correlations.
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Synthesis of the Stratigraphic Architecture of the Siluro-Devonian Succession in Algeria and Libya
Authors R. Eschard, K. Boumendjel and M. Ben RahumaThe stratigraphic architecture of the Siluro-Devonian succession was studied in Algeria and Libya from outcrop sections, logs and sesimic data. A regional transect between the Libyan basins and the western Algerian basins is proposed, using also a new stratigraphic chart. The role of the sub-basins and arches are highlighted in these paleogeographic reconstructions.
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Keynote; Wide Azimuth Seismic in BP – Off the Shelf Business Solutions
Authors Richard Hollingsworth, B. Barley and T.P. SummersWe present four unique seismic acquisition methods pioneered inside BP between 2003 and 2006, taking them from concepts to field trials and to large scale implementation: 1) Multi-azimuth (MAZ) Streamer, acquiring 6 conventional surveys at 30 degree azimuth increments and stacking (Offshore Nile Delta example); 2) Wide Azimuth Towed Streamer (WATS), using a recording vessel plus two source vessels to obtain azimuthally diverse data in one pass (GOM example), 3) A regular grid of Autonomous Recording units (Nodes) placed on the seabed using a Remote Operating Vehicle (GOM example) 4) Permanent Seismic Surveillance Systems, trenched ocean bottom cables with continuous recording via fibre optic links to shore (Valhall, Norway example). The operational advantages and disadvantages and performance in practice are compared and contrasted. MAZ is simple and robust to apply in 70m+ deep water uncluttered by platforms. WATS is more complex to plan and process, but can be highly optimised given a velocity model and high end 3D acoustic modelling, and represents the premier solution for subsalt severe velocity anomalies. Nodes fill the wide azimuth niche when platforms and very deepwater are present which obstruct streamer access. Densely sampled Permanent Surveillance systems probably represent the reachable technical limit for seismic quality today, offering high fold, wide azimuth, excellent S/N and low frequency content at very low repeat costs and cycle times.
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Keynote; Exploring the Subsurface Using Marin Electromagnetic Seabed Logging Technology
Authors Erik Gundersen, Tage Røsten, Ketil Hokstad and Andreas BrechtSeismic imaging techniques can readily detect potential hydrocarbon traps, however discriminating between presence of water or hydrocarbons in such traps is a challenge. Detection of subsurface hydrocarbons by a marine controlled-source electromagnetic (MCSEM) surveying application, also known as seabed logging (SBL), shows very promising results as a complementary tool to seismic data. Oil and gas have high electrical resistivity compared to brine-filled sandstones. The major challenge is to analyse the MCSEM data, and to improve understanding of the subsurface to help make the right exploration decisions. Resistivity determination is hardly a fool-proof method for hydrocarbon identification, since many geologic facies are electrically resistive relative to their surroundings. We have developed advanced imaging techniques to reduce the uncertainty of misinterpreting the MSCEM data.
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Architecture and Petrophysics of Active Faults in Platform Carbonates, Italy
More LessWe illustrate two case studies of active normal and strike-slip faults in platform carbonates.The architecture of both normal and strike-slip faults were characterized in detail in the field, and the porosity, permeability, and capillary pressure of samples collected from both core and damage zones measured in the laboratory. The host rocks are Mesozoic platform carbonates with low porosity and permeability. In general, the results of our analyses showed that the fractured carbonate host rocks of the damage zones have a higher secondary porosity relative to the fault rocks of the cores.
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Development and Petrophysical Properties of Faults in Carbonate Grainstones (San Vito Lo Capo Peninsula, Sicily)
Authors E. Tondi, F. Agosta and M. AlessandroniDetailed field mapping and microstructural and textural analyses carried out in the San Vito Lo Capo peninsula (in north-western Sicily) allowed us to document failure modes and fault development in porous carbonate grainstones. We show that individual compactive shear bands represent the simplest fundamental shear structures, and that pressure solution processes often localize within previously developed compactive shear bands. In the Lower-Pleistocene carbonate grainstones of San Vito Lo Capo peninsula, composed of eroded carbonate and marl fragments, pressure solution processes localize mostly grain-to-grain, hence leading to the formation of zones of weakness which facilitate slip and the development of larger displacement. Finally, laboratory analyses of representative fault rock samples, also show that the structures described above have sealing capacity with respect to the host rock, and may compartmentalize any geofluid reservoir.
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Field Study - Microseismic Rendering of Hydraulic Fracture Geometry from Data Recorded in the Treated Well
Authors K.D. Mahrer, R.J. Zinno and J.R. Baileydata in the injection well. To deploy in the treatment well, we used the TriAxial Borehole Seismic (TABS*) tool on a standard, 7-conductor wireline. TABS is a single, ~21 m by ~0.06 m tool carrying three, 8-m-spaced, 3-component geophones packages; pressure and temperature sensors; and an orientation gyro. During the treatment, TABS was turned off and locked at depth in the injection well. Because it’s narrow and robust, TABS easily withstood the battering from in-well placement during injection. TABS began recording and telemetering data immediately following injection. In the next 1 ½ hours, TABS recorded ~400 microseismic events. Because the on-board gyro enables in-hole movement and re-orientation, we repositioned TABS twice to compare and, thus, find optimal recording perspectives. On analysis, the microseismic data yielded an in situ picture of complex fracture geometry, delineating an asymmetric fracture network with substantial near-wellbore upward growth and possible breakdown of the cement-casing bond or cement-formation bond. As an added benefit, the TABS deployment minimally intruded or obstructed treatment and field operations. (*Licensed from ExxonMobil Upstream Research Company).
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