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- Volume 35, Issue 11, 2017
First Break - Volume 35, Issue 11, 2017
Volume 35, Issue 11, 2017
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Using Big Loop and ensemble-based methods for more reliable reservoir predictions: applications on fractured reservoirs
Authors Jarlie Frette and Julie VonnetPredicting the future and generating information on future oil and gas field behaviour is key to present and future reservoir management decision-making. The traditional approach to predicting oil and gas field behaviour and updating reservoir models relies on a small number of scenarios (base, high and low cases) and introduces deterministic steps that do not always fit with modern reservoir management guidelines. It also means the lack of an automated workflow, making model updates time consuming. It is with these critical aspects in mind that Emerson has developed the Big Loop workflow. A cornerstone of Emerson’s reservoir characterization and modelling workflow, the software tightly integrates static and dynamic domains and offers the propagation of uncertainties from seismic characterization through to geological modelling and simulation. Big Loop also includes modern, ensemble-based approaches, using results from a large set of models to analyse the uncertainty in the predicted values and enabling workflow automation for easier model updates. To effectively manage oil and gas related risks, it is essential to have uncertainty information. The evaluation of risk means having a set of possibilities each with quantified probabilities and quantified losses/gains. The oil and gas industry has also now reached a stage where a large fraction of producing fields can provide several years of operational and production history. This includes not only production data (well data) but also seismic data that should be shared through the same models. Models that capture the reservoir uncertainties and integrate the acquired data will build more accurate predictions of the future. Through an ensemble-based history matching workflow, uncertain inputs are identified and characterized in order to parameterize the reservoir model and give reservoir engineers the chance to constrain those parameters with the observed ‘real’ measurements. How to estimate the probability of a hypothesis? That is the challenge reservoir engineers’ face in their daily work. For example, if we observe the cumulative produced volumes of fields after ten years of production, what is the likelihood that the production was driven by, for instance, the aquifer’s strength?
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Application of blended sources offshore Abu Dhabi
Authors C.D.T. Walker, G. Ajlani, M. Hall, S. Al Masaabi, A. Al Kobaisi, G. Casson and H. HagiwaraSimultaneous or blended sources were initially developed for onshore applications using vibratory sources with dramatic improvements in both data quality and operational performance (Foster et al., 2010; Al-Ghamdi et al., 2010; Al-Mahrooqi et al., 2012). Offshore, there have been a number of both towed streamer and ocean bottom surveys acquired (Moore et al., 2012; Moldovaneau et al., 2013; Walker et al., 2013; Abma, 2014) where both data quality – through higher fold and improved survey efficiency – have again been amply demonstrated. The improvement in survey efficiency arising from simultaneous sources is clearly illustrated in Figure 1 (Etgen et al., 2015) where the combination of improved seabed receiver deployment rates and multiple simultaneous sources reduces the time needed to acquire a 400 km2 survey from 108 days to 21 days – a staggering 80% reduction in survey duration. There have been a number of approaches applied in these marine cases to ease the task of separating the desired shots from the unwanted ones – dithering the sources by small differences in firing time, distance separating the shooting vessels, firing each shot at pseudo-randomly distributed shot-point locations and operating the source vessels completely independently. In this article, we will focus on the application of the pseudo- random shot-point interval method offshore Abu Dhabi, where the very high amplitude levels of shot-generated low velocity Scholte wave noise (mud roll) represent a particular challenge given the long offsets cross-spread geometries needed to image the deep zone(s) of interest.
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Source and streamer towing strategies for improved efficiency, spatial sampling and near offset coverage
By Andrew LongSeveral towing concepts have arisen in recent years that break the convention of towing two source arrays between the innermost two streamers in a multi-streamer 3D configuration (‘dualsource shooting’). Three ‘arrays’ of one or more sub-arrays were towed more than 20 years ago to improve cross-line spatial sampling, but inline spatial sampling and fold were compromised by inefficient recycling times on air gun compressors and limited recording lengths. Modern acquisition systems enable continuous recording, very short physical shot intervals, and up to six source arrays being deployed between the innermost two streamers; always with the ambition of improving cross-line spatial sampling. I discuss two newer variations to these scenarios using either dual-source or triple-source shooting, although the principles may be expanded to more sources distributed in the cross-line direction: 1. Towing source arrays outside the innermost two streamers such that survey efficiency is improved courtesy of the nominal sail-line separation being increased. It is demonstrated that cross-line fold becomes irregular as source separation increases in the cross-line direction, so complementary processing methods may be required to reduce imaging artifacts. 2. Alternatively, if the sail-line separation is based on a conventional source towing scenario, some flexibility may be created in terms of near offset sampling.
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Cutting-edge marine seismic technologies — some novel approaches to acquiring 3D seismic data in a complex marine environment
Authors Azizur Rahman Khan, Turki M. Al-Ghamdi and Fuad A. Al-SomaliThe use of streamer or Ocean Bottom Cable (OBC) techniques for a seismic survey in a complex marine environment present major operational challenges owing to islands, large variations in water depth within a few kilometres from the shore and a complex sea floor because of canyons, pinnacles, steep reef flanks, rugose sea floor, and corals. Salt-dominated provinces, too, present a complicated geological setting — deep targets below salt layers of variable thickness, salt mounds, massive halite and anhydrite layers in the overburden, a highly rotated post-salt section, steep geological dips at the target level, and a complex fault system. Complexity of the survey area requires novel approaches and customized seismic data acquisition technologies for a cost-effective imaging solution. We present four innovative marine seismic technologies, tested to assess their efficacy in acquiring long offset wide azimuth data, in a logistically complex marine environment.
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MASS — taking OBN acquisition to new heights
More LessOcean bottom seismic (OBS) has been gaining market share over high-end streamer acquisition and more operators are turning to nodes to address long-standing challenges in seismic imaging. Novel cost-effective systems that provide step-changing efficiencies on the receiver side show that OBS acquisition is on the path to equal productivity with high-end towed marine acquisition. One such technology is Magseis’ Marine Autonomous Seismic System (MASS). Until recently, 90% of the seismic acquired for the oil and gas industry has been through traditional streamer surveys. Only 10% was obtained through Ocean Bottom Seismic (OBS), which has been struggling with inefficient technologies, static acquisitions and limited marketplace, all leading to higher cost, which historically has been the greatest barrier to a wider adaptation of the technology. In contrast, the quality of OBS data in comparison to other seismic technologies are undisputed, and demand for full azimuth seismic is increasing, owing to its improved imaging in areas with reservoir complexity, gas clouds, in pre- and sub-salt basins and for infrastructure and monitoring purposes. With major technological enhancements now being developed to overcome the traditional barriers, OBS is slowly gaining market share. Since late 2013 Magseis has operated its MASS technology on 12 projects. The first survey was acquired with 75 km of cable and 3000 nodes on the Snøhvit and Albatross fields in the Barents Sea in very rough weather conditions. In the next years Magseis has significantly increased its capacity with more equipment deployed on the seabed, enabling larger surveys to be acquired at a reduced cost. In addition to the company’s in-house knowledge and R&D, Magseis has steadily developed and manufactured its automated handling system with its partner Robot Norge as well as Siemens and Berget regarding the manufacturing of the nodes.
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The Midwater Stationary Cable (FreeCable) to solve today’s offshore seismic acquisition paradox
By Luc HaumontéThe world economy is demanding an increasing volume of oil and according to oil market specialists this trend is not expected to decrease in the next decades. The easy oil is gone and oil companies currently seek either increasing the existing production, which will last for some limited period of time, or continuing exploration for new discoveries. The fact that the easy oil has already been found practically means that the new exploration challenge is to look for complex reservoirs such as deep target, complicated geological environments, subsalt imaging, or hardly accessible sites. Generally speaking, solving this problem requires a high-end seismic acquisition technique able to provide full offset full azimuth coverage, broadband data and deep penetration. Indeed, zero offset traces are needed to build a reliable structural model and estimate velocity for deep imaging. Long offsets are required to illuminate salt body flanks and subsalt reservoirs. The low frequency content is necessary to image layer boundaries and obtain good penetration. The high frequency content is used for obtaining interface details and resolving thinner beds. Deep penetration is also obtained through low measurement noise and high fold leading to a great post-stack signal-to-noise ratio. Finally, full azimuth and full offset maximizes the target reservoir illumination and minimized the probability of shadow areas. Such a qualitative acquisition method is generally perceived to be very expensive. On the other hand, the economic downturn in the oil and gas industry and especially in the exploration market puts high pressure on expenditures and places traditional acquisition technologies in difficulty. Lots of seismic vessels are placed in cold stack and the ocean bottom cable time seems to be over. To solve this paradox the seismic industry is looking for new solutions providing better, cheaper, and faster acquisitions. Nodes are gaining momentum but do not completely respond to the three criteria. Robotic projects tend to flourish, but most of them are not yet industrial. In this article a field proven unmanned solution able to address the new industry challenges is presented. The patented technology developed by Kietta consists of controlling unmanned midwater stationary cables (MSCs).
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Argentine Basin: the new search for oil in one of the least explored basins on planet Earth
Authors Neil Hodgson, Steve De Vito, Karyna Rodriguez and Mike SaundersA remarkable property of the Argentine Basin, located in the Atlantic west of Argentina, is that within its 450,000 km2 of extent – not one exploration well has been drilled. Compared to the world’s other continental passive margins, this makes it the most unexplored high potential basin on Earth. Partly this is owing to a lack of modern seismic data in this basin, with exploration previously focused on rifts that lie on the continental shelf. Yet also it is unexplored because of the lack of industry access to the area in the last 10-15 years since deep water drilling technologies have become widely available. However, this is all about to change. The Argentine government is opening the area to international exploration investment, at the same time as a new 35,000 km 2D seismic programme is being acquired by Spectrum in 2017 (Figure 1). This survey aims to reveal the fundamentals of multiple oil-prone hydrocarbon systems in the basin, which include Pre-Atlantic rift plays, syn-rift and post rift plays in upper and lower slope settings, in addition to a base of slope/basin floor play that has the potential for ‘super-basin’ resource.
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Regional Focus: United Kingdom
This month we are pleased to introduce a new regular feature in First Break called Regional Focus. The section will give our readers an insight into the exploration activities of a particular region and this month we are starting with the UK, which launched the 30th Oil and Gas licensing round on 25 July with 852 blocks on offer.
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Practical synthetic well ties: an example
Authors Rob Simm and John ChamberlainThis paper highlights the process of tying well synthetics to seismic data for the purposes of seismic interpretation. There are three stages to the well tie process namely a) phase estimation, b) seismic data zero phasing and c) zero phase well tie. As a consequence, it is useful to draw a distinction between a ‘phase match’ tie and a ‘zero phase’ tie particularly when the original seismic is not zero phase. A practical example is presented using the RokDoc software.
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Volumes & issues
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Volume 42 (2024)
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Volume 41 (2023)
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Volume 40 (2022)
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Volume 39 (2021)
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Volume 38 (2020)
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Volume 37 (2019)
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Volume 36 (2018)
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Volume 35 (2017)
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Volume 34 (2016)
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Volume 33 (2015)
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Volume 32 (2014)
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Volume 31 (2013)
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Volume 30 (2012)
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Volume 29 (2011)
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Volume 28 (2010)
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Volume 27 (2009)
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Volume 26 (2008)
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Volume 25 (2007)
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Volume 24 (2006)
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Volume 23 (2005)
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Volume 22 (2004)
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Volume 21 (2003)
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Volume 20 (2002)
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Volume 19 (2001)
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Volume 18 (2000)
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Volume 17 (1999)
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Volume 16 (1998)
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Volume 15 (1997)
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Volume 14 (1996)
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Volume 13 (1995)
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Volume 12 (1994)
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Volume 11 (1993)
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Volume 10 (1992)
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Volume 9 (1991)
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Volume 8 (1990)
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Volume 7 (1989)
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Volume 6 (1988)
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Volume 5 (1987)
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Volume 4 (1986)
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Volume 3 (1985)
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Volume 2 (1984)
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Volume 1 (1983)