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First EAGE/ASGA Petroleum Exploration Workshop
- Conference date: 02 Oct 2017 - 04 Oct 2017
- Location: Luanda, Angola
- ISBN: 978-94-6282-230-6
- Published: 02 October 2017
1 - 20 of 24 results
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Recent Pre-salt Exploration of West Africa’s Salt Basins - Perhaps Less Successful than Hoped for, but Certainly Not Snsignificant
More LessThis study provides an overview of West African Pre-Salt exploration prior and post 1990. In addition to Post and Pre-Salt trends, some of the most recent exploratory successes and failures are discussed. The study focuses the on aforementioned Salt basins, but also makes reference to the Congo Fan which overlies the Lower Congo Basin and is pivotal in describing the exploration within the region.
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Using a West Africa Depositional Sequence Framework to Uncover Pre- & Post-salt Prospectivity in the Underexplored Deepwater Kwanza and Namibe Basins
By M. TyrrellIn this presentation the new datasets from the offshore Kwanza and Namibe Basins will be shown and the pre- and post-salt sequences, facies and plays that these illuminate will be explained. Examples will be shown of pre- and post-salt imaging, together with our understanding of the reservoir facies and reservoir properties in several intervals. Additionally, the results of a preliminary quantitative interpretation (QI) study, constrained by a depositional sequence model and using pre-stack seismic inversion will be shown, illustrating the reservoir and fluid property information that the seismic data reveals.
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Salt Tectonics in the Sivas Basin (Turkey) - Outstanding Seismic Analogues
Authors J.C. Ringenbach, J.P. Callot and Sivas GroupThe Sivas Basin in Anatolia is likely the world’s finest open-air museum of salt tectonic structures. It is an elongated Oligo-Miocene basin that developed in an orogenic context. From Late Eocene to Late Miocene salt deposition, salt tectonics and salt reworking occurred in a north-verging foreland fold-and-thrust belt setting north of the Taurus. The result is an intricate system of salt ridges, minibasins, salt sheets and successive canopies. Despite huge difference in content and evolution the Sivas basin provides outstanding outcrops of the classical geometries associated to the development of diapirs, i.e. halokinetic sequences along diapir walls, and associated stratal deformations. The Sivas Basin also presents more exotic structures such as 4-ways closed minibasins, megaflaps (thinned sedimentary sequences pinching out on top of diapirs and overturned during glaciers later development) and evaporites allochtonous sheets. Striking geometric analogies between these outcrops and seismic images from the classic petroleum province controlled by salt tectonics will illustrate the extraordinary quality of the Sivas basin as field analogue for the Atlantic Margin and chiefly Angola and the Gulf of Mexico. Some comparisons with analog models under scanner will also be shown.
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The South Angola Source-to-Sink Project - Characterization of the Cretaceous to Cenozoic Clastics Produced on the Onshore Erosion Surfaces
Authors M. Guiraud, Y. Dos Santos, C. Joly, G. Rimmele, M. Goyallon, O. Laurent, F. Despinois and J-M. ChampanhetThe source-to-sink (S2S) concept focuses on the quantification of the components of clastic sedimentary systems from initial sediment production in the source areas (i.e. onshore margin) through to their deposition within sedimentary sinks (i.e. offshore margin, Somme et al. 2016, Bhattacharya et al. 2016). Clastics provenance analysis provides fundamental information about source and catchment areas as well as the sedimentary budget marking the offshore margin domain. Clastics production on the margin is governed by the mechanical erosion and/or the chemical weathering of the onshore substrate. The intensity of the onshore erosion processes is mainly controlled by the lithology of the substrate, the rate of tectonic uplift, and the type of paleoclimate (hot humid climate favoring weathering versus cold dry climate favoring mechanical erosion). The main objective of the South Angola margin S2S project is to characterize (1) the factors controlling the intensity of the onshore erosional processes and (2) the volume and nature of the Cretaceous to Cenozoic clastics produced in the South Angola onshore domains and delivered to the offshore margin.
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West Africa Pre-salt Lacustine Carbonates
By P. RonchiDuring the Early Cretaceous rifting, the central segment of South Atlantic was characterized by a complex paleomorphology dominated by large lacustrine basins, that were filled by clastic and carbonate sediments and finally covered by restricted marine evaporites. These thick sequences constitute important hydrocarbon plays successfully explored in both eastern and western margins of South Atlantic. The carbonate bodies growth on paleo-highs constitutes giant fields in the Brasil offshore; in the African margin the success was lower, with good reservoirs in the Lower Congo Basin (Angola, Cabinda), and lower explorative results in the Kwanza Basin.
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Cost-effective Seismic Data Reprocessing for Sub-salt Imaging Enhancement.
Authors M.A.G. Mahgoub, B. Elias, M. Santos and W. LundungoFit-for-purpose seismic reprocessing workflow comprises improving the seismic bandwidth by spectral whitening and frequency shaping with longer gate amplitude scaling to recover the strong amplitude dimming laterally and vertically especially in the pre-salt seismic levels have been applied to the final migrated seismic volume of the legacy seismic data. To devise a cost-effective seismic data post-stack seismic processing for producing high-quality images in this complex geology subsalt basin.
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Dedicated Subsalt Imaging Reprocessing towards a Better Understanding of Seismic Signal Difference in Seismic Substacks
By D. KrueckAbstract In the West African ultra deep-offshore, complex subsalt reservoirs remain a challenge for seismic imaging and reservoir characterization. Advanced imaging technology is the key to better understanding seismic signals. This paper presents an integrated approach using well data, seismic interpretation data and reprocessing techniques to update the seismic offsets. A first subsalt development well was drilled based on general knowledge of the area and far-offset seismic substack. This well has shown good results that are not observed in the far-offset. The differences in seismic substacks (far vs. near) incurred a Reverse Time Migration (RTM) remigration study in order to obtain a more accurate comprehension of the area. This remigration generates an updated of 3D RTM gathers. When the remigrate images and a Norsar modeling study are correlated together; both data show good coherency in expected seismic signals on gathers from near to far offset. When the dips stay mild, near offset stacks deliver a reliable image. Far stacks are generally less reliable except when steep dips are expected. The results of the remigration study helped locating future development wells with greater confidence.
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Velocity Analysis of Multicomponent Seismic Data of a Model with Thin Salt Layer
More LessThe reservoirs of the pre-salt from Santos Basin have been a challenge to the offshore multicomponent seismic processing since they were discovered. However the challenge can become even greater when the reservoir presents a peculiarity as a thin salt layer what generate an even more complex reflection event. To perform the velocity analysis, we must use approximations that can control strong nonhyperbolicities, and treat the problem as an inversion due to the fact of the complex approximations have three parameters. Finishing the tests we can found which approximation presents the best results for this kind of model.
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3D Simultaneous Elastic Inversion from BroadSeis® Data - A Case Study from Angola
Authors L. Goncalves-Ferreira, Y. Arroub, F. Piriac, D. Pandolfi, J.-L. Formento, X. Carriere, J.-P. Coulon and T. Al-RomaniBroadband acquisition and dedicated processing can be regarded as one of the most recent innovations in Geophysics. The benefits of a new dataset acquired using broadband technology, BroadSeis®, and the 3D elastic inversion results are used to determine robust high-resolution estimates for P-impedance and Poisson’s Ratio volumes leading to a more reliable reservoir characterization. In this study we show the impact of broadband in key stages of the reservoir characterisation workflow (inversion and pseudo-Vclay estimation), for a more quantitative reservoir interpretation. The main challenges of the area, located deep offshore Angola in the Miocene interval, are the structural complexity associated to salt proximity and steep dips at the flanks of the structure. Key steps of this elastic inversion were the multi-well-driven deterministic wavelet extraction and the accurate velocity model derived from FWI that allowed enhancing the a-priori model building. This method enables better delineation of the sand bodies’ architecture, resulting in an updated geomodel structural grid and reliable litho-seismic attributes for future development well targeting. We conclude that pseudo-Vclay on BroadSeis® shows more lateral discontinuity (heterogeneity) than on conventional data, as confirmed by recent well analysis. The pseudo-Vclay on BroadSeis® has also confirmed sand quality, as proved by wells results.
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A Review of 4D Seismic at Greater Plutonio and PSVM
By M. RiviereThe deep-water developments of Greater Plutonio in Block 18 and PSVM (Plutao, Saturno, Venus and Marte) in Block 31 have each shown 4D seismic monitoring to be a very valuable surveillance tool in support of reservoir management. This paper describes the observations made from the 4D data across the two areas. Both areas have a mixture of channelised and sheet-like turbidite reservoirs: Greater Plutonio has a higher proportion of sheet-like reservoirs, with simple 4D anomalies. PSVM has a higher proportion of channelised reservoirs with more complex anomalies.
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Impact of Seismic Data on the PSVM Development
Authors C. Smith, I. de Lemos and A. MuondoThe PSVM ultra-deep water oil development started up in December 2012. The development, in the northern part of Block 31, comprises 9 segments in 4 main field areas – Plutao, Saturno, Venus and Marte. Oil recovery is mainly by waterflood, but three segments also have gas injection. Multiple seismic datasets have been acquired, processed and interpreted since block award and development drilling began. This presentation aims to look at the impact of key seismic data sets on development drill-out and reservoir management in the PSVM development.
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Cost-effective Seismic Data Reprocessing for Subsalt Imaging Enhancement
By M. MahgoubThe deep offshore is a challenge to seismic processing and imaging techniques, due to the complexity of the salt body structures and the omnipresence of mode conversions that mask the primary signal. Cost efficiency in the global recession because of the low oil price long standing issue could be motivated to look for another simple usable alternatives to the highly sophisticated techniques have been widely utilized in subsalt deep water imaging. Indeed Wide azimuth towed streamer WATS and even full azimuth single vessel coil shooting with high offset coverage and broad band seismic with extremely very low frequency less reaches 2.5 Hz was enables seismic energy penetrating the ultra-deep subsalt and brought a significant change in subsalt deep offshore imaging accordingly. The conventional offshore seismic data acquisition method known as Narrow-Azimuth Towed Streamer (NATS) and data collected this way, from just one direction (or azimuth), do not yield reliable images of the subsurface is not suited any longer for such a complex geology. Broadband seismic data has brought a new level of understanding to the mapping of these facies. Using the full spectrum of frequencies (from 2.5 Hz to 125 Hz). Pre stack depth imaging with advanced techniques such as the expensive and intensive computer CPU time such as RTM and FWI are proven technologies for high resolution velocity model with proper depth imaging techniques. They are the commonplace depth imaging techniques nowadays for complex subsalt geology seismic data type. However in this case studies to complying with cost optimization trend, another revisit of the subsalt legacy seismic survey deep offshore Angola was made to revoke if the seismic data quality could be improved and the residual seismic data concerns of those legacy seismic data sets could be overcommit.
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Opening up Ocean Bottom Seismic to the Exploration Market
Authors T. Bunting, J. Moses and J. KegginIt is generally accepted, by the industry, that seismic surveys acquired using seabed seismic receivers deliver the optimum measurement of subsurface reflectivity. However, historically seabed seismic surveys were not widely used due to the higher acquisition costs. In general, seabed surveys were only considered for the most challenging geophysical objectives such as production management projects where high repeatability is critical or complex geologies where full azimuth measurements are required. Recent technology advancements have delivered a step change in acquisition efficiency and cost with further improvements expected. The paper will review these improvements and make predictions on future survey efficiencies.
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Seismic Method Strategies on Kaombo Project Field Development
By C. GomesThis presentation aims to explain the Seismic method strategies which are employed by Kaombo Geosciences Team in order to: - Acquire the necessary seismic data where and when justified; - Obtain the best images possible by close collaboration with (in house) seismic imaging center; - Attain reservoir scale understanding for field development pattern optimization through seismic interpretation – a cross discipline exercise equally involving Asset geophysicists, geologists and reservoir engineers.
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Application of Sampling While Drilling to Improve Operations Efficiency without Compromising the Geological Well Objectives
Authors N. Gabriel, L. Magini and O. JoaquimThe X2 reservoir is placed in an extension faulted block without prior penetration, laterally adjacent to the chronologically older X1 reservoir, currently under production. The oil type and composition in X2 is unknown, therefore a representative fluid sample was required, along with formation pressure information, for proper fluid characterization and fluid gradient for pressure regime understanding. This information will define the future development strategy and if the extensional fault is conductive or represents a lateral barrier.
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Waterflood Performance Outcomes across a Set of Deep-water Turbidite Reservoirs
Authors E. Barber and P. CliffordMany Angola deep-water reservoirs now have a production history of at least a few years, and up to 15 years. In most cases, reservoir sweep has been tracked with one or more 4D seismic surveys, in addition to pressure and production data. The information has been integrated into reservoir simulation models. A set of waterflooded turbidite reservoirs is discussed, with deposition ranging from well-developed channel complexes to sheet-like sands. Some fields have significant quantities of thin-bedded pay, and there is varying influence from fault baffles. Aquifer strength is another important variable between reservoirs.
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Petrography and Diagenesis of Pre-salt Microbialite in the Kwanza Basin, Angola
Authors N. Rochelle-Bates, S. Schröder and R. DixonPetrographic and preliminary geochemical analyses have been conducted on a core from the pre-salt microbialite succession of the Kwanza Basin, Angola. The core is characterised by shrubby boundstones and spherulitic grainstones, with several intermediate facies. Magnesian clays are present in small amounts, this may be in part due to later diagenesis. The removal of Mg clays would make some facies classifications non-representative of the unit at the time of deposition. Scanning electron microscopy has also revealed the presence of microbial filaments within the shrubby calcite fabrics, but it is not certain if microbes contributed to calcite precipitation via organomineralization, or if they were merely a passive substrate. Chert preserves a variety of relict calcite textures. Some silica textures are similar Magadi Type microbial chert. Diagenesis was complex and multi-phase, with evidence of low and high temperature (possibly hydrothermal) fluids.
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Reservoir Analog Characterization Based on Outcrops and Darcy’s Methods
Authors B.P. Shidqi, M.A. As'ad, F. Fandrian and S.A. PricillaNowadays, research paradigm which occurs in the objectivity of academics and industrial landscape lead to a gap of judgment upon geological evolution, especially on outcrops analog on hydrocarbon exploration study and both perspectives can be combined in this study. The study is located on Walat Fm., Sukabumi. West Java. The data were collected from field mapping, measured section, and direct sampling. Processing data is done by using Darcy’s method and thin section analysis to define porosity and permeability and also qualitative interpretation to analyze the geometry of the reservoir itself. The stratigraphic column and the measured section of the area shows that Walat Fm. is considered as a good reservoir as the formation is laterally distributed around 5-6 km and vertically thickens to 150 ft. Also, the porosity and permeability of the sandstone qualified as the oil reservoir rocks. The geological section provides the information of petroleum elements such as traps, migration, and seal. Source rock geochemically tested and classified as moderate – good source rock. As a result of all the studies, Walat Fm. is concluded as a potentially good reservoir analog to be further analyzed to determine the hydrocarbon contain and prospect.
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Technical Screening of Enhanced Oil Recovery Methods - A Case Study of Block C in Offshore Angolan Oilfields
More LessThis paper presents a technical screening of enhanced oil recovery (EOR) methods by using an Artificial Intelligence (AI) model based on neuro-fuzzy (NF) algorithm. The presented NF approach will enable the user to select a suitable EOR method based on available worldwide successful EOR data and field under investigation. The NF approach presented in this study is a five layered feedforward-backpropagation neural networks where the knowledge pattern is extracted by combining both the searching potential of fuzzy-logic and the learning capability of neural network to make a priori decision. The extracted knowledge from the NF system can be expressed in the form of fuzzy rules by computing weights, number of rules and fuzzy set parameters and validated against reservoir properties data trained from worldwide successful EOR projects. The successfully trained and validated model is then tested on the Angolan oilfield data (Block C) where EOR application is yet to be fully established. The test results show that the NF presented in this study can be used for technical selection of suitable EOR techniques. Within the area investigated (Block C) polymer, hydrocarbon gas, and combustion were identified as the suitable techniques.
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Total Bi Wats Case Study- From Survey Design to Interpretation
Authors S. Tchikanha, K. Chikh and B. Santos-LuisBlock 32, deep offshore Angola, is located in an area of the Lower Congo Basin heavily affected by the salt tectonism: salt domes or canopies are extensive. As a consequence having a good seismic image is critical in terms of exploration but also development of discoveries. Over the past decade the focus has moved towards the sub-salt play and the use of conventional seismic has reached its limits. As a consequence, Total E&P Angola embarked in 2012 in a project to address complex subsalt challenges in the Central North East part of the Block 32, using innovative technologies: from survey design, to acquisition, processing and imaging. The objective was to deliver interpreters a state-of-the-art and fit for purpose solution in a timely and cost-effective manner. This project is known as the Block 32 CNE Bi WATS. This abstract aims to give a full overview of the project, from its genesis to its execution, and finally present some of the results
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