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Suppressing non-repeatable noise and enhancing 4D signal is a key challenge in time-lapse seismic processing, especially when we expect the 4D signal to be weak. With the assumption that multiple vintage migration volumes contain similar primary and varying noise, we can cooperatively detect and attenuate noise in the complex wavelet transform domain for individual volumes simultaneously. Data examples on a simulated 4D survey with a 3D dataset in deep-water Gulf of Mexico show that this method can effectively attenuate non-repeatable noise (e.g., random noise and migration swings) and significantly increase the 4D signal-to-noise ratio.
Elebiju, Bunmi (BP America) | Ariston, Pierre-Olivier (BP America) | van Gestel, Jean-Paul (BP America) | Murphy, Rachel (BP America) | Chakraborty, Samarjit (BP America) | Jansen, Kjetil (BP America) | Rodenberger, Douglas (Shell America) | White, Roy C. (Shell America) | Chen, Yongping (CGG) | Hren, David (CGG) | Hu, Lingli (CGG) | Huang, Yan (CGG)
Using the Kepler and Ariel Fields as a case study, this paper discusses the processing challenges and solutions applied to a 4D co-processing of Wide Azimuth Towed Streamer (WATS) on Narrow Azimuth Towed Streamer (NATS) data. Unlike a dedicated 4D acquisition, WATS on NATS 4D has relatively low repeatability in terms of acquisition geometry and bandwidth differences. All these factors can negatively impact the extraction of a meaningful 4D signal. In this paper, we demonstrate how processing techniques can help to increase repeatability and enhance 4D signal. We focus on the following 4D processing procedures: 4D co-binning, data matching, and post-migration co-denoise. Due largely to these techniques, the final co-processed volumes show an optimized 4D seismic signal with a median Normalized Root Mean Square (NRMS, which measures the repeatability between base and monitor. Details refer to Kragh and Christie, 2002) of 0.10 along the water bottom and 0.28 above the reservoir.
Atlantis Field is a large field in the Gulf of Mexico that has significant imaging challenges due to a complicated overlying salt body. In 2005-2006 the world’s first deepwater Ocean Bottom Nodes (OBN) survey was acquired over this field to improve imaging and to serve as a base line for future time lapse (4D) surveys. In 2009, which was two years after production started, the world’s first OBN repeat survey was acquired. The results from this time lapse survey are presented in this abstract. Due to excellent repeatability of both sources and receivers, extremely low 4D noise has been achieved with an average Normalized Root Mean Square (NRMS) value as low as 5.3% after post stack processing. Unfortunately due to the imaging challenges the area with good data quality is limited. The most valuable time lapse observations are the time shift response in the part of the reservoir that has undergone the strongest pressure depletion. This time shift response can be related to reservoir compaction and confirms other observations seen in production data. The amplitude difference response occurs in a similar area as the time shift response, but is weaker than and opposite to predictions. Sensitivity to pressure response remains the main uncertainty as the observations in the amplitude data do not match observations from laboratory measurements on core data.
Kepler Field is located in Mississippi Canyon block 383 in deep water GoM. With production to the Nakika host which began in 2004, Kepler has historically out-performed its production forecasts over time. As nameplate life expectancy of the Nakika platform nears, it is important to have accurate expectations of dynamic reservoir behavior in order to invest wisely in upgrades & opportunities to extend hub life. Dedicated 4D co-processing of legacy seismic datasets was conducted in 2013 in order to understand the dynamic behavior of the main Kepler reservoir designated K1. We observed clear 4D amplitude changes, robust overburden time shifts, and time shifts of a slightly lower quality within the reservoir. Separating signals caused by aquifer sweep, compaction, and gas break out proved difficult with the available 4D data. In some areas we achieved a match between actual and modeled 4D signals, enabling a reasonably coherent interpretation of the dynamic reservoir behavior of the K1 reservoir at Kepler.
Kepler field consists of a single commercial oil reservoir, the K1. The majority of the K1 is located in OCS block MC-383 in approximately 5700 feet of water. The block is currently held via SOP with Shell and BP each having a 50% working interest. The K1 reservoir is one of the largest single reservoirs in the NaKika development. The Kepler K1 reservoir is stratigraphically trapped, at least in part, on the east flank by a large south-plunging anticlinal nose. The up-dip west-southwest flank of the trap is clearly defined by a channel cut that abruptly truncates the reservoir. The Shell MC- 383 no.1 well, the first well drilled in the NaKika area, reached total depth in August 1987, finding excellent reservoir properties and oil quality. The K1 sand was subsequently developed by two high rate horizontal wells. History matching of 3 years of dynamic production data and 2 shut-in episodes due to hurricane activity indicates that still greater reservoir energy exists (Schott et al, 2005). Figure 1 shows the K1 amplitude map with the two producing wells K-1 and K-2.
Abstract For more than a decade, BP has been deploying a growing range of 4-D seismic technologies, and applying these to a variety of reservoir situations. This paper reviews the "macro" view of BP's 4-D experience and offers insights into possible emerging future trends, giving a wider context to complement other IPTC papers on specific 4-D technologies. BP has experience in about 80 operated and 30 non-operated surveys* around the world, concentrated in the North Sea and Gulf-of-Mexico (GOM). Reservoir types surveyed include clastic, carbonate and fractured under different recovery schemes, including depletion, secondary water-floods and tertiary EOR schemes. The main historical "mode" of 4-D data acquisition for BP has been with marine surface-tow streamer operations, acquired every 2–5 years. However, by the time of this presentation, BP will have installed and be operating its third permanent ocean bottom cable (OBC) seismic monitoring system. The bulk of successful track-record to date has been in oil reservoirs under water-flood, using streamer data. Significant value has been generated through improved targeting of infill and development wells, and increasingly through improved reservoir management and reducing drilling hazards. Permanent seabed cable systems are now providing high quality wide-azimuth 3D seismic images and 'on demand' reservoir surveillance to meet the development challenges of the most complex reservoirs. Other emerging technologies include land 4-D, permanent in-well 4-D VSPs, passive seismic monitoring, and development of quantitative integration of 4-D data into reservoir models. With 4-D now being increasingly accepted as a valuable and maturing reservoir management tool, and with many fields and projects around the world moving into the production phase, a global expansion in 4-D activity, certainly within BP, is now emerging. This will require careful deployment of the most appropriate technologies from an ever-expanding 4-D toolkit, as considered in this paper. Introduction Over the course of the last 10–15 years, BP has helped lead the testing, development and widespread deployment of 4-D seismic technologies that are now used around a significant proportion of its worldwide asset portfolio (Figure 1). From initial investigations in the early-mid-1990's using legacy repeat 3-D surveys to investigate the possibility of detecting 4-D effects over established oil-fields, 4-D application is now considered routine in many areas with proven business value, and very often a fully integral part of field management. Early testing and deployment was dominated by the North Sea "4-D laboratory", rapidly followed by the deepwater Gulf of Mexico and now an ever-increasing expansion towards more global application to both existing (e.g. Alaska) and new and emerging production (e.g. Azerbaijan, Angola). Technologies have developed and diversified from simple marine streamer operations to now include high-spec overlapping and steerable streamers, permanent ocean bottom cable (OBC) systems, of which BP now has the world's first three systems, and the early testing of permanent in-well VSP monitoring. Processing, interpretation and integration technologies continue to evolve to ensure maximum value from the acquired data. However, despite the major strides in the maturity and acceptance of the 4-D monitoring method, some big challenges and questions remain. Why is 4-D not used on many more fields and on different types of reservoir? Why hasn't every operator and region decided to use 4-D technology yet? What are the appropriate technologies to use? What will be the future role of 4-D monitoring in ever more efficient field exploitation and in the drive towards ultimate recovery?