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- Volume 37, Issue 2, 2019
First Break - Volume 37, Issue 2, 2019
Volume 37, Issue 2, 2019
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The role of thermal stress in near wellbore instabilities and its implications: a case study from the HTHP well, offshore East India
Authors Ajesh John, Manoj Gaur, Hari Krishna, V.R. Sunder and V. KothariAbstractDrilling through a narrow pore pressure-fracture pressure window, especially under HTHP (high temperature-high pressure) conditions, is one of the most challenging and costly operations in the oil and gas industry. In this case study, drilling results and thermal stress modelling emphasized the role of thermal stress in several borehole failures encountered at shallow depths and severe formation breakdown incidents at deeper depths. The thermal stress from cooling effects delayed the shear failure conditions by reducing the maximum tangential stress of the formation around the wellbore, but induced formation breakdown as the minimum tangential stress exceeded the tensile strength of the formation. The result from this study shows both the rock stiffness (Young’s Modulus, Poisson Ratio) and differential temperatures (ΔT) have a critical control on thermal stress-related instabilities. Thermal stress-based wellbore stability modelling shows that temperature fluctuations in the dynamic drilling environment can induce a stress change at the rate of 300–500 psi/10°C. Our study results show that the range of thermal stress magnitudes in stiff rocks can vary between 300–4000 psi for a ΔT range of 20–60°C.
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Seismic waveform classification based on Kohonen 3D neural networks with RGB visualization
Authors I.I. Priezzhev, P.C.H. Veeken, S.V. Egorov, A.N. Nikiforov and U. StreckerAbstractSeismic trace segments in a 3D volume over a reservoir interval are classified into seismic facies units via neural network trace analysis. Unsupervised classification is carried out in two stages: 1) Training, whereby typical (average) objects of each class are estimated and 2) Classification stage whereby all study objects are assigned to a certain class, based on a minimum similarity to a typical object of this class. Input parameters for the algorithm are: the number of classes, the size of the vertical segment, the investigated time window and the colour scheme applied. Unsupervised classification is fairly rapid and several software packages are available for this purpose. In contrast, a supervised workflow is more demanding yet facilitates interpretation of results. In addition, supervised classification and calibration permit probabilistic uncertainty analysis. An example of a non-supervised classification scheme is shown and the main advantages of supervised partitioning are discussed.
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S-Wave azimuthal anisotropy: an effective tool for stress monitoring
Authors Thomas L Davis and Steven L RocheAbstractReservoir monitoring is required in understanding reservoir behaviour under dynamic conditions associated with enhanced oil recovery processes related to carbon dioxide injection and shale reservoir development through multistage hydraulic fracturing. Geochemical and geomechanical changes associated with these processes may affect reservoir permeability both positively and negatively. These changes need to be monitored to understand the causative mechanism of these changes and to mitigate potential harmful effects including damage to our reservoirs.
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How big is a small earthquake? Challenges in determining microseismic magnitudes
AbstractEarthquake magnitudes are surprisingly difficult to estimate accurately. This is especially true when evaluating small earthquakes: for example, those caused by human activities such as shale gas stimulation, CO2 and waste water storage, and enhanced geothermal systems. Uncertainties are created by a range of issues including: which ‘magnitude’ scale is used; what type of instrument records the earthquake; how the instruments are deployed; and the heterogeneity of the Earth between the source and the receivers. Errors can be larger than an order of magnitude in scale. For very small earthquakes this is not usually of much concern. However, occasionally, larger earthquakes induced by human activity are felt at the surface. This has led to regulatory frameworks that require accurate assessment of earthquake magnitudes before they reach the point of being felt. Hence, to monitor and mitigate felt seismicity there is a need to calculate accurate earthquake magnitudes in real time. Regulatory monitoring of induced seismicity is becoming a key issue in the successful development of reservoir projects that involve stimulation or storage. Here, we discuss the challenges with implementing such reservoir monitoring, and provide a suggested monitoring strategy.
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Observed link between folded Seaward Dipping Reflectors (SDRs) and large-scale morphology and architecture of the Early Cretaceous carbonate build-up and platform in the Orange Basin
Authors Anongporn Intawong, Paolo Esestime and Karyna RodriguezAbstractThe Orange Basin is located in the volcanic-rifted margin of Namibia and South Africa and was formed during the break-up of Gondwana in the Late Jurassic to Early Cretaceous period (e.g. Nurnberg and Muller, 1991; Karner and Driscoll, 1999). Rifting and opening of the Orange Basin is believed to have occurred in an already extended and possibly inverted basement (Clemson et al., 2002). A general tectono-stratigraphic chart of the Orange Basin is presented in Figure 1.
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4D seismic opportunity: from feasibility to reservoir characterization – a case study offshore West Africa
AbstractTime-Lapse (4D) seismic data has shown to be a successful tool in monitoring a field and its production using two or more 3D seismic cubes spaced by months or by years.
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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)