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- Volume 9, Issue 1, 2003
Petroleum Geoscience - Volume 9, Issue 1, 2003
Volume 9, Issue 1, 2003
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Overview of global 4D seismic implementation strategy
Authors Hans de Waal and Rodney CalvertFor many Shell-operated fields around the world, time-lapse reservoir monitoring (4D) is now an integral part of field management and some 25 dedicated 4D surveys were acquired for this purpose by the end of 2002. This widespread application is the result of a focused implementation effort aimed at global deployment to maximize the value extracted from the surveys in terms of saved costs, increased production, increased recovery and improved HSE management, where effective implementation is achieved through a combination of global operatorship and technology capability.
Apart from ensuring global deployment, there is the challenge to extend the range of 4D applicability. To achieve this the project has three application portfolios:
- today's‘ proven’ 4D technology portfolio, which is about monitoring fluid movements in thick clastic oil reservoirs offshore. Results come largely from comparing reservoir simulator output with difference maps derived from repeat 4D streamer surveys;
- a‘ stretch’ portfolio where the technology is applied to gas reservoirs, land data, stacked reservoirs, carbonate fields and to the monitoring of pressure changes;
- a‘ tomorrow's technology’ portfolio, which has the potential to increase the application base even further. The new technologies are about the use of permanent arrays, downhole acquisition, passive listening and ‘smart fields’ where semi-continuous 4D monitoring provides eyes and ears between the wells.
More and more value is realized as 4D becomes fully integrated with subsurface work flows and modelling tools. Benefits from 4D technology for individual fields can be in the tens or hundreds of millions of dollars. A large fraction of these come from 4D surprises, illustrating that we tend to underestimate our uncertainties and suggesting different approaches to field management.
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BP's increasing systematic use of time-lapse seismic technology
Authors J. Marcus Marsh, David N. Whitcombe, Sue A. Raikes, Ronnie S. Parr and Tim NashFollowing experimental success in the application of 4D technology in the Magnus and Foinaven fields and the delivery of commercial value from the application of time-lapse seismic (4D) studies in the Forties and West of Shetland fields and in the Pompano Field in the Gulf of Mexico, BP has embarked on the systematic use of 4D monitoring in its NW Europe operations to enhance value in the light of an increasing production challenge. Within the past two years, 12 datasets have been acquired over 19 fields of varied reservoir age, type and property. Although specific questions differ from field to field, in all cases a major objective is to influence the location and design of infill wells.
Useful time-lapse information has been gained from post-stack matched ‘legacy’ surveys of varying data quality. However, it is clear that more value is added by custom-designed 4D surveys: seismic quality and repeatability are critical to the successful delivery of reliable time-lapse seismic monitoring. Integration of seismic data with dynamic data is still relatively ‘low-tech’ and further benefits will be gained by improvement in this area.
The paradigm is shifting to a position where 4D monitoring in the North Sea is the rule rather than the exception. Now that there is clear evidence of added value in the most obvious target reservoirs, surveys are being carried out in areas that are technically more challenging – and the early results indicate that these too will be of real commercial benefit. Use of 4D data is also being progressed in other regions, including the Gulf of Mexico, and application in other basins around the world is being planned. On the technology development front, BP is seeking continuous improvements in acquisition and processing, both in quality and turnaround time, and richer integration with production and conventional well-based surveillance data. The ultimate goal is for effective reservoir management based on a range of surveillance methods.
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4D using legacy seismic data on the Alwyn North Oil Field
Authors C. Hubans, M. Rapin, J.F. Ottlé, M. Manin, S.D. Harker, G Richardson and R. CooperThis paper presents the results of 4D (time-lapse) seismic analysis of the westerly dipping Brent Group fault blocks of Alwyn North, a TotalFinaElf oil field located in the northern North Sea. Two legacy 3D surveys were used; one shot in 1980–1981, the second in 1996 with different sources, shooting directions and other acquisition and processing parameters. The Brent reservoir is of Middle Jurassic age, Alwyn North burial depths are in excess of 3000 m and oil production commenced in 1987. Careful processing and imaging of the amplitudes from the two surveys produced a visual qualitative comparison with hydrocarbon production, water injection and fluid movement within the reservoir. The 4D results show a close correspondence to the sweep determined by reservoir simulation after nine years of production and confirmed by well results. A third 3D survey was acquired in 2001, following commencement of miscible gas injection, and further 4D work is planned to follow on from the encouraging results of the present study.
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Successful application of time-lapse seismic data in Shell Expro's Gannet Fields, Central North Sea, UKCS
Authors H. J. Kloosterman, R. S. Kelly, J. Stammeijer, M. Hartung, J. van Waarde and C. ChajeckiThe Central North Sea contains a large variety of oil and gas fields at different stages of maturity within the life cycle of an asset, at varying depths, in varied geology and at widely differing pressure and temperature conditions. Over the last three years Shell UK Exploration and Production (Shell Expro) has acquired new 3D surveys over many of these fields which, following careful attention to detail in acquisition and processing, have been quantitatively compared to pre-production surveys. Differences between these time-lapse seismic datasets have then been interpreted in terms of changes in reservoir fluid movement and changed pressure/temperature conditions. These interpretations have proven useful for reservoir management by identifying swept versus unswept zones, sealing versus non-sealing faults, efficiency of drive mechanisms and connected volumes to specific wells
Four case studies from the Gannet Development illustrate how these observations have impacted reservoir management and show how application of this relatively new, yet rapidly maturing technology has had a positive impact on the remaining value of these fields. Importantly, the detectability of changes in the reservoir has been seen to be greater than predicted prior to data acquisition. Indeed, 4D seismic data have become an established part of the long-term plans for all of Shell Expro's subsurface assets. With these successes have come fresh challenges and future efforts will focus on reducing costs in proven 4D technology whilst pushing to introduce new techniques for data gathering and for interpretation of large volumes of new information.
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Time-lapse seismic programme at Gullfaks: value and the road ahead
Authors Nazih F. Najjar, Lars Kristian Strønen and Trine AlsosImproved hydrocarbon recovery through the identification of unswept oil regions has been the primary objective of the time-lapse seismic programme at the Gullfaks Field in the North Sea. Three time-lapse seismic surveys covering the entire field have been acquired, a pre-production survey in 1985 followed by two surveys in 1996 and 1999. Input from qualitative time-lapse interpretations has resulted in the drilling of a number of successful wells, and has improved the understanding of drainage patterns. Recently, a quantitative time-lapse study was launched. The objective of the study was two-fold: to link flow simulation predictions directly to the 4D seismic response and to map changes in oil saturation and quantify associated uncertainties.
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Integrated time-lapse reservoir monitoring and characterization of the Cervia Field: a case study
Authors Luciano Kovacic and Elio PoggiagliomiSeismic time-lapse reservoir monitoring (4D) was used to assess the performance of a gas field (Cervia), located offshore Italy, in the central part ofthe gas-producing area of the Adriatic Sea. The chief objective of this work was the characterization of the field producing intervals by applying an innovative methodology based on a high level of integration of seismic data with borehole data. The work, carried out on two ‘legacy’ 3D seismic surveys and all available borehole data, consisted of three main steps.
- Characterization of the physical properties of the main reservoir, by extensive measurement and analysis of the core samples. This was in order to implement a petroacoustic model for calibration of seismic acoustic impedance volumes to reservoir description parameters. In addition all borehole data were employed during the implementation, calibration and testing of the petroacoustic model.
- Integrated time-lapse processing of the two seismic volumes to achieve high repeatability. Seismic processing parameters were determined independently and objectively for each of the two surveys using well data. Spectral equalization of wavelets in the seismic traces was performed to further improve repeatability.
- Integrated Multidimensional Petroacoustic Calibration (IMPAC) of the two seismic volumes. Here the microscopic properties of the reservoir rocks, obtained from the petroacoustic model outlined in step 1 above, were used, together with log data, to derive the main reservoir description parameters (i.e. lithology, porosity, saturation and pressure).
This approach produced good repeatability between the two processed seismic volumes. In addition, time-lapse analysis of the acoustic impedance volumes, calibrated to reservoir description parameters, enabled the visualization of fluid movement within the main reservoirs. This, in turn, led to the identification of areas where the gas may only have been partially depleted. These significant results will provide an important contribution for an improved and more efficient gas production from the field.
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New tools for 4D seismic analysis in compacting reservoirs
Authors M. Nickel, J. Schlaf and L. SønnelandIn order to successfully use time-lapse seismic data to monitor dynamic effects occurring in carbonate reservoirs, the development and adaptation of tools for seismic attribute analysis are necessary. In particular, since carbonate reservoirs tend to compact and subside under production, it is desirable to estimate this effect from the time-lapse seismic data and to separate this response from fluid effects that influence the seismic response. Furthermore, it is very important to identify and classify the fault network of carbonate reservoirs in detail due to its strong influence on the fluid flow. New tools are presented that address these problems. These tools are applied to seismic time-lapse data from the Ekofisk Field to demonstrate how compaction distributions can be quantified in 3D and how migration paths of injected water along fault and fracture zones can be identified.
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Improved reservoir modelling with time-lapse seismic data in a Gulf of Mexico gas condensate reservoir
Authors J. R. Waggoner, A. Cominelli, R. H. Seymour and A. StradiottiTime-lapse 3D – or 4D – seismic data have been tried in several fields to date, with some good case studies published to demonstrate the utility of the 4D seismic information. While another 4D case study would be useful, this paper describes two novel aspects of a recent application in the Gulf of Mexico. First, the target reservoir contains a gas condensate fluid under primary depletion, so pressure, rather than saturation, changes create the observed 4D acoustic response. Further, the primary impact of the pressure change is to the fluid composition as the initially dense gas phase lightens as condensate drops out below the dew point. The result was a 2.8% change in acoustic impedance predicted in the feasibility study.
Second, the 4D seismic result was used to constrain an optimized history-matching procedure, along with the production data. After describing the method used, the paper will discuss the changes to the reservoir model that resulted. While the results should not be considered unique, they do give some insight intothe structure of the reservoir that should be considered for optimal reservoir management.
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4D integrated technologies for deep-water turbidite reservoirs:from petrophysics to fluid flow simulation
Petrobras has been developing its 4D seismic technological programme since 1998, focused on the Brazilian deep-water fields in the Campos Basin, and considering the technical, operational and economic challenges involved in the development plan and reservoir management in this environment.
The first step was to align the objectives of the project with the company goals for the following 15 years, in terms of earnings growth, production growth and reserves replacement. This information guided how the 4D reservoir management should be employed: as hedging technology to ensure that production targets would be achieved in several key fields at once, or as a direct technology investment to increase the production of individual, independent fields. The mission of reservoir management for each field involved was understood and new deep-water seismic technologies were developed to face the global operational and economic targets.
3D seismic reservoir monitoring, or 4D seismic study, was defined as an ‘integration of multidisciplinary technologies that includes the time-lapse monitoring of the drainage efficiency, using cores, well logs, seismic data, production history and pressure management’.
Water injection is the preferable recovery method for the deep-water reservoirs in Brazil. Therefore, seismic monitoring should be able to distinguish contrasts of both fluids – injected water and remaining oil – that normally produce small seismic impedance values. This characteristic has brought the first technical challenge: the use of the 3D P-wave surface legacy data from the 1980s and 1990s, when the major fields started production, as 4D base-volumes to be correlated with future recommended 3D seismic data (surface or ocean bottom systems) as 4D monitor-volumes.
In addition to all developed seismic technologies for data processing, a general 4D work flow was designed and the concept of the integrated reservoir model was adapted to relate all such technologies to the reservoir engineering needs and to the field economics, generating reliable 4D images for each reservoir study.
This paper summarizes the multidisciplinary technical integration, including geological and seismic modelling, petrophysical simulations, seismic processing and interpretation, and reservoir simulation. A 4D methodology was implemented to integrate all such technical development and economic analysis, identifying where, when and how seismic monitoring can contribute to the reservoir management. This methodology has been applied to the Campos Basin deep-water reservoir, Rio de Janeiro State, Brazil.
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A method for performing history matching of reservoir flow models using 4D seismic data
Authors M. Lygren, K. Fagervik, T.S. Valen, A. Hetlelid, G. Berge, G.V. Dahl, L. Sønneland, H.E. Lie and I. MagnusA generic method for performing history matching of reservoir flow models using 4D seismic data is described. Several key technology components are used in the procedure, including seismic attribute analysis and classification, reservoir simulator technologies, domain transformation algorithms, as well as the optimization algorithms that guide the history-matching process. The novel 4D history-matching procedure was applied to the Tordis Field in the North Sea. As a result the transmissibilities of the fault network in the reservoir model were modified. In addition a production well was successfully side-tracked using results of the analysis from the time-lapse data.
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Optimizing 4D fluid imaging
Authors A. T. McInally, T. Redondo-López, J. Garnham, J. Kunka, A. D. Brooks, L. Stenstrup Hansen, F. Barclay and D. DaviesIntegrated analysis of 4D seismic data and petrophysical data is used to produce probabilistic fluid and lithology volumes for monitoring reservoir performance on the Nelson Field. Petrophysical analysis of log data shows distinct fields for oil sand, water sand, shale and heterolithic‘ lithologies’ in acoustic impedance – Poisson's ratio space. Elastic inversion techniques applied to conventional 4D AVO datasets convert the reflectivity data to acoustic impedance, shear impedance, Poisson's ratio and angle impedances. The elastic inversion datasets are used to quantify oil–water contact movements through volume sculpting techniques. Well-derived relationships are used to predict 3D volumes of oil sand probability from three different seismic survey vintages: 1990, 1997 and 2000. Changes in oil sand probability due to production are verified by comparison with repeat production logs. Integrated volume interpretation of 4D far offset inversion difference (oil–water contact (OWC) movement) and oil sand probability shows areas of unswept oil, highlighting infill opportunities. Early results from infill drilling have validated the method, realizing the potential economic benefits of 4D seismic technologies.
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Analysis of time-lapse data from the Alba Field 4C/4D seismic survey
Authors R. Hanson, P. Condon, R. Behrens, S. Groves and M. MacLeodThe 1998 Alba 3D Ocean Bottom Cable (OBC) survey was designed to accomplish multiple objectives. The primary goal was to image low impedance reservoir sands with converted wave (PS) reflections; one important secondary goal was to image fluid movement by comparing the OBC data with a 1989 streamer survey. Modelling shows that a strong original oil–water contact reflector should be visible throughout much of the field and that water saturation changes should be observable by analysing the time-lapse differences between the 1989 streamer data and 1998 OBC survey. Differences between the 1989 and 1998 seismic field data confirm that fluid changes are clearly visible near several producing and injector wells. However, extracting additional quantitative saturation information from the seismic data has proven difficult, possibly because of: (a) complex interaction between the fluids, sands and shales within the Alba reservoir; (b) moderate to poor repeatability of the seismic response to reservoir fluids.
The focus of this paper is the acquisition and analysis of Alba time-lapse data. We show that production- and injection-related effects are predicted by modelling and observed in the data and then we make an attempt to relate these effects quantitatively to oil production and water injection. Despite the challenges in using the Alba time-lapse data quantitatively, the data have been successfully used qualitatively for well planning risk assessment and for guiding reservoir simulation efforts. Lessons from this work will be used in any future time-lapse surveys at Alba.
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Volumes & issues
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Volume 30 (2024)
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Volume 29 (2023)
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Volume 28 (2022)
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Volume 27 (2021)
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Volume 26 (2020)
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Volume 25 (2019)
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Volume 24 (2018)
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Volume 23 (2017)
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Volume 22 (2016)
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Volume 21 (2015)
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Volume 20 (2014)
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Volume 19 (2013)
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Volume 18 (2012)
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Volume 17 (2011)
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Volume 16 (2010)
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Volume 15 (2009)
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Volume 14 (2008)
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Volume 13 (2007)
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Volume 12 (2006)
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Volume 11 (2005)
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Volume 10 (2004)
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Volume 9 (2003)
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Volume 8 (2002)
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Volume 7 (2001)
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Volume 6 (2000)
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Volume 5 (1999)
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Volume 4 (1998)
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Volume 3 (1997)
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Volume 2 (1996)
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Volume 1 (1995)