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- Volume 34, Issue 5, 2016
First Break - Volume 34, Issue 5, 2016
Volume 34, Issue 5, 2016
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Integrated application of a high-resolution LIDAR outcrop survey of an unconventional Niobrara Reservoir, Denver Basin, Colorado
More LessThe Niobrara Shale is a major reservoir in the Denver Basin. To understand the importance of natural fractures in this reservoir a dataset comprised of fracture plane orientations and fracture intensity variations using a ground-based LIDAR (Light Detection and Ranging) and photogrammetry was acquired. The purpose was to use an outcrop as an analog to the subsurface reservoir for improved reservoir characterization. Listric faults associated with negative flower structures show increased fracture intensity near the faults. Fracture sets remain consistent throughout the interbedded chalks, marls, and limestones. However, there is an apparent variability of fracture spacing associated with changes in lithology. Mapping the fracture orientation and intensity into the subsurface using the outcrop analog should give rise to better geomechanical and fluid flow modelling.
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The influence of pore pressure in assessing hydrocarbon prospectivity: a review
Authors Sam Green, Stephen O'Connor and Alexander EdwardsAssessing the prospectivity of a basin or a play is a complex process that combines a multitude of geological, geomechanical and geophysical analyses with the aim to de-risk whether a particular basin/play should be explored further. However, it is possible to group the analyses under five simple terms: source, charge, reservoir, trap, and seal. In basic terms, if a basin/play can be demonstrated to have a source of hydrocarbons, a reservoir to accept the charge and a trap and seal to limit the migration of the hydrocarbons any further then the ‘opportunity’ has been shown to be prospective for hydrocarbon exploration, i.e. de-risking has occurred. Typical elements of this de-risking process would include assessing the presence and quality of the source rock or building a structural and stratigraphic model from seismic amplitude data. Other components would be modelling porosity for instance. However, the particular focus of this paper is that many of the other components that need to be understood and modelled as part of the assessment of prospectivity are related to the pressure regime within a basin/acreage block in which a prospect is located. The focus of this paper is, therefore, to highlight and review those aspects of hydrocarbon prospectivity that pertain to reservoir quality, migration, maturation, prospect identification and hydrocarbon retention that are demonstrably influenced by pore pressure (Figure 1). It is important to note that whilst understanding the reservoir forms a key focus within such studies of prospectivity, the pore pressure within the bounding shales (relative to the reservoir) is also important to understand aside from the implications for well planning.
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2(3)D convolution modelling of complex geological targets beyond – 1D convolution
Seismic modelling is necessary to understand elasticwave propagation in the subsurface. Modelling is costeffective and insightful, as long as adequate methods are used. An ideal seismic-modelling strategy is to generate complete synthetic seismograms for realistic earth models, then process them as performed with real seismic data. These complete seismograms are best obtained by full-wavefield (FW) approaches. FW methods are therefore used in extensive benchmarking studies, which may require the joint effort of several institutions owing to high resource costs. Though computer power continues to increase, we are still a long way from applying ideal modelling to all cases where synthetic data is necessary to constrain results. This is especially true in interpretation and sensitivity analysis, where the influence of multiple parameters must be assessed. In many situations, ray-based (RB) methods are suitable alternatives, especially when rays, traveltimes, etc., are useful information for the problem at hand (Gjøystdal et al., 2007). However, standard RB methods do not allow modelling of detailed target structures owing to smoothness requirements. Geoscientists needing seismic modelling of such targets will then often resort to 1D convolution (Lecomte et al., 2015). 1D convolution has been successfully used for decades, and is still the method behind most standard well calibration, seismic inversion, etc. However, its conceptual validity is in reality very limited.
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Efficient development of unconventional reservoirs using 3G workflows – Breaking the silos to achieve true integration with multi-disciplinary software
Authors A. Ouenes, Y. Kiche, L. Ouhib, R. Smaoui, M. Paryani, S. Poludasu, A. Bachir and D. BaloghThe Shale 1.0 revolution achieved a geopolitical goal, reducing US dependence on foreign petroleum, which partially contributed to the current low commodity price environment. When setting aside the financial and geopolitical factors, the shale revolution was and is still in many minds a manufacturing process, where multiple wells equally spaced are hydraulically fractured with a similar number of regularly spaced stages, also called geometric completions. Ignoring the complex geologic nature of shale reservoirs created a very inefficient manufacturing process. Jacobs (2016) summarized these inefficiencies by stating that ‘Widely cited studies show that as a result of these geometric completions, 40% to 60% of stages produce little or no hydrocarbons, while 30% of the stages represent 80% of a well’s entire production. Baker Hughes estimates that ineffective stages have come at an annual cost upwards of $40 billion.’
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Fault geometric and seismic attributes – an integrated study with focus on the Barents Sea
Authors A. Torabi, B. Alaei, D. Kolyukhin, R.H. Libak, R.H. Gabrielsen and A. BraathenA full fault analysis assessing the influences of faults on (hydrocarbon) prospects and fluid communication includes analysis of the fault geometry, the fault architecture and segment linkage, assessment of petrophysical properties as well as establishment of the time-related geological development. It is also crucial to realize that faults are three-dimensional rock bodies, rather than surfaces (Chester and Logan, 1986; Caine et al., 1996; Gabrielsen and Braathen, 2014; Gabrielsen et al., 2016a). Basic data for such study are commonly derived from seismic interpretation and drilling, although studies that combine dedicated fault imaging (Lindanger et al., 2004; Botter et al., 2014) and field data (e.g. Walsh and Watterson, 1991; Childs et al., 2009; Davatzes and Aydin, 2005; Bastesen et al., 2013; Gabrielsen et al., 2016a) has lately become feasible. It is therefore necessary to enhance the tools and capacity for utilizing reflection seismic data in fault analysis, particularly because inaccurate interpretation and mapping of faults could cause incorrect trap definition, leading to the drilling of dry wells and causing misinterpretation of influence of faults on fluid transport. Research efforts by the seismic community have focused much on the use of advanced algorithms (e.g. Chopra and Marfurt, 2007), but has to a lesser extent utilized results from outcrop studies of faults carried out by structural geologists.
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Seismic efficiency on a vast scale – a case study from offshore Gabon
Authors Luke Twigger, Rob Schouten, Guy James and Jo FirthSeismic surveys come in all shapes and sizes, depending on factors such as objectives, geographical area, geological environment, local licence requirements, and budget. Small surveys over a focused area can make sense individually, though there may be inefficiencies, such as many vessel turns when recording short lines. When several such surveys are located near by there can be both gaps in coverage and redundancy of the aperture needed to ensure that areas of interest are fully imaged. Moreover, velocity models may seem fine-tuned for each individual survey but frequently do not connect together smoothly when examined on a regional scale. At some point, it makes more sense to acquire and process one large survey rather than several smaller pieces. Multi-client surveys provide a cost-effective route to large, high-quality datasets. Costs are shared, so larger surveys can be acquired, for a better overall view of the prospectivity than is generally the case with smaller, proprietary surveys. Access to large surveys, in both mature and frontier areas, allows companies to reduce their exploration risk. It can also help to cut the time between the award of a licence and the drilling of the first well.
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Passive seismic techniques are developing in many directions
Yasin C. El-Taha, Petroleum Development Oman, reports on the 6th EAGE Passive Seismic Workshop held on 1-3 February in Muscat with the theme ‘From Data to Decisions’. Attended by approximately 50 participants, the workshop was well received both in discussions during the event and in excellent feedback submitted since. Strongly supported by various operators and service companies, the industry showed renewed commitment to the technology and its development worldwide. After an opening address from keynote speaker Salim Rawahi, geosolutions manager, Petroleum Development Oman (PDO), the workshop continued with a regional focus. From a European perspective, projects were shown with a link to strong drivers or requirements from regulatory bodies. This situation is currently under heavy scrutiny amongst industry and media alike with high profile projects such as the Groningen gas field. An overview was given of hydraulic fracture monitoring (HFM) in China showcasing a rapid rise in uptake of this technology. Monitoring of fracking completions in China has progressed to an advanced stage and is now being regularly used for field development decisions, well placement optimisation and fracking design improvement.
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Building more robust low-frequency models for seismic impedance inversion
Authors Amit Kumar Ray and Satinder ChopraSeismic impedance inversion is an important tool for estimating rock and reservoir properties from the seismic data. Seismic data is band-limited in nature and lacks the low-frequency component. As the low-frequency component holds the basic information on geological structure, the lack of low-frequency information degrades the quantitative prediction based on seismic inversion. It is therefore essential to build an accurate low-frequency model to have confidence in seismic inversion and in turn on the quantitative predictions made therefrom. In this paper, we develop a novel workflow of predicting the low-frequency impedance model that uses a single-well lowfrequency model apart from other relevant seismic attributes in the multi-attribute regression analysis. The workflow was successfully applied to a number of impedance inversion exercises out of which two cases are discussed here. Our inversion exercises were carried out on datasets from northeastern British Columbia and Alberta, in Canada. The inversion results using this approach have been validated at blind well locations and an excellent match between well logs and inversion results has been observed.
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Interpretation of complex faulted deposits in the North Sea using the relative geological time model
Authors Nicolas Daynac, Sébastien Lacaze and Fabien PaugetThis paper shows how a novel method, which consists of building a relative geological time (RGT) model from seismic data, was applied to a large-scale volume located on the offshore block K05 in the North Sea.
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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)