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- Volume 16, Issue 5, 1998
First Break - Volume 16, Issue 5, 1998
Volume 16, Issue 5, 1998
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Dedicated to the depth domain: the evolution of Oz Yilmaz
By A. McBarnetOne of the leading names in geophysics theory, Oz Yilmaz, tells Andrew McBarnet about his unusual path to guru status in the industry and how he has come to be promoting the value of the depth domain in seismic analysis.
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Reserves uncertainty: some historical trends and wider implications
By F. DemirmenIt is a well-known fact that the petroleum industry generally does a poor job in estimating hydrocarbon reserves. Judging from the comparison of pre-drill estimates and post-drill outcomes, reserves from exploration discoveries in USA, for example, tend to be grossly overestimated (P.R. Rose, pers. comm.; Capen 1992). A similar message comes from the Shell Group (Sluijk & Parker 1986). Post-discovery reserves estimates do not fare any better. According to a recent study by Dromgoole & Speers (1997), field reserves on the UKCS, from the time of Government sanction (of development plan) to 4 years after production, were over- or underestimated by 10±20% depending on reservoir complexity. There is little doubt that had the period covered been longer, the error would have been larger. In the Norwegian sector of the North Sea, also, field reserves after discovery show considerable fluctuation through time, with initial estimates being generally on the conservative side (Hermanrud et al. 1996). Ble¬haut (1991) reported similar conservatism from East Malaysia. Early conservatism in reserves estimates was also the hallmark of many giant oil fields, e.g. East Texas, USA (Arps 1956). Unpublished studies tell a similar story. A review of field data by a major oil company several years ago revealed significant underestimation of reserves after discovery: over a period of 9 years, the reserves had increased by 60%. The aforementioned statistics refer to the `best' or `representative' estimate of reserves, e.g. the expectation value, which is a single-value estimate. Reserves estimation, however, should encompass not only the best estimate, but also the uncertainty surrounding the best estimate. Unfortunately, few companies seem to pay attention to how reserves uncertainty changes through time. As it will be noted later, reserves uncertainty has a significant impact on upstream economics. The focus of this paper is to investigate historical trends in reserves uncertainty for a number of fields, interpret the results, and discuss ramifications. The analysis is confined to the preproduction phase, when reserves estimates are based on well data and seismic (and perhaps analogue cases), to the exclusion of well performance data. The historical trends therefore reflect primarily the impact of seismic and appraisal on reserves uncertainty. The pre-production phase is also the phase when all the major investment decisions (facilities and infrastructure) for field development are made.
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Evaluation of the timedip, correlation and coherence maps for structural interpretation of seismic data
More LessIn recent years, seismic attribute maps have become important tools in the structural interpretation of seismic data (e.g. Buchanan et al. 1988; Flint et al. 1988; Dalley et al. 1989; Voggenreiter 1991, 1993; Hoetz & Watters 1992; Rye-Larsen 1994; Dorn et al. 1995; Eggink et al. 1996; Jones & Knipe 1996, Hesthammer & Fossen 1997a,b). The attribute maps have proven especially valuable for identifying minor structures such as faults close to or below seismic resolution. Such faults may have a dramatic effect on reservoir performance (e.g. Antonellini & Aydin 1994), particularly for thin reservoir units separated by impermeable shales, but also for thicker sandstone units where deformation structures may drastically decrease permeability. The importance of being able to identify minor faults has led to a marked increase in the focus on seismic attribute maps as the interpreter is challenged to provide more accurate and detailed structure maps. But the increased attention also contains pitfalls that may lead to erroneous interpretation unless the seismic interpreter is aware of the dangers and knows how to quality control the seismic observations (Hesthammer, in press). This paper will focus on the use of the timedip, coherence and correlation maps for structural interpretation of seismic data. Special focus is paid to the problem of seismic noise and how well data may help separate noise features from real structures. A direct comparison of the different attribute maps will help to critically evaluate some of the new, and increasingly popular, methods of attribute analysis for structural interpretation.
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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)