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DGG/EAGE Workshop - Geophysics for Unconventionals
- Conference date: 09 Mar 2012 - 09 Mar 2012
- Location: Hamburg, Germany
- ISBN: 978-94-6282-098-2
- Published: 09 March 2012
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The impact of converted wave data in unconventional reservoir evaluation
Authors Jacques P. Leveille, Santi Randazzo and Paul BrettwoodUnconventional resource plays involve the development of some unusual reservoirs, such as shales or other very tight formations with very low natural permeability. Reservoir development for these plays requires the identification of "sweet spots" for fracturing/production purposes, in what is usually a very inhomogeneous "reservoir". The nature of these sweet spots is somewhat elusive and we will choose to define the term as any portion of the reservoir that gives enhanced hydrocarbon production after optimization of the reservoir through some mechanical process such as hydraulic fracturing. The geophysical characterization of these sweet spots is highly dependent on the detailed rock properties of the shale, but most often takes the form of some highly optimized seismic attribute obtained after careful seismic processing and a seismic inversion. These seismic attributes may not be derived from p-wave data alone. In fact we will argue that the seismic attributes most often used in the identification of sweet spots in shale plays usually require a reasonably accurate determination of formation density which, in most circumstances, cannot be accurately estimated from p-wave data alone. We will then present the impact of converted waves and the additional information that they can bring to these developments when combined with other data.
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Borehole Geophysics for Unconventionals
By Mike LovellAttention has turned away from conventional gas reservoirs, characterised by a static density stratification and a hydrocarbon-water contact, to formations that act as both source and reservoir (shale gas and coal bed methane) or where gas is a solid component (gas hydrates). These unconventional resources may contain free or dissolved gas, augmented by adsorbed gas (shale and coal bed methane) or caged gas (gas hydrates). Compared with conventional reservoirs these unconventional resources often have large, ill-defined geographical areas (shale gas), constitute thin discontinuous seams that may vary locally (coal bed methane), or show scale variable concentrations (gas hydrates). These make for unusual physical reservoirs and their evaluation requires a reassessment of physical properties and a new approach to the interpretation of borehole geophysical responses. The focus of this paper is the role of borehole geophysics in respect of three different types of unconventional gas: shale gas, coal bed methane (CBM), and gas hydrates.
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Can Experiences with Passive Seismic Monitoring of CO2-Storage be Transferred to Shale-Gas Monitoring?
Authors Arie Verdel, Mei Zhang, Sjef Meekes and Rob ArtsThe application of (passive) seismic data as a tool for the monitoring of fracturing-induced shalegas production is widely known. Recently the various potential environmental risks associated with this man-induced fracturing have specifically received ample attention worldwide (see [1] for references). In The Netherlands, where an exploration drilling license near the town of Boxtel had been issued a vivid public debate took place.
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Geophysical methods to quantify gas hydrates and free gas in the shallow subsurface: Review and Outlook
More LessGas hydrates and free gas linked to gas hydrate systems account for 500 to 12000 Gt of carbon – most likely around 3500 Gt (Buffett und Archer, 2004; Kvenvolden, 1993; Milkov und Sassen, 2002). Gas hydrate is an ice-like compound consisting of water-captured gas molecules. Predominantly, natural gas hydrate contains methane that is produced by biological degradation of organic matter. With sufficient water- and of free gas-supply gas hydrate forms in sediment basins all over the world. As gas hydrate is stable only at high pressure and low temperature it occurs at water depth of more than 300 m. The exact depth depends on bottom water temperature and other environmental circumstances such as pore water salinity and the precise composition of the captured gas. Within the sediment the depth of the gas hydrate stability field is further controlled by the geothermal gradient.
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Fractal Behaviour of Fractures Derived from Seismic and FMI Data - A Case Study in a Tight Gas Area
Authors Heike Endres and Henning TrappeThe results of this study were obtained from an area in the North German Basin (NGB) located east of Bremen, Germany, where gas is produced from a deep Rotliegend sandstone reservoir. Faults and fractures play a major role in gas productivity. The deformations could have a negative influence on the productivity of the gas field as fractures are cemented and tight and may act as permeability barriers.
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Unconventionals in Seismic Monitoring
More LessPassive seismic monitoring gives essential information on reservoir dynamics, cap-rock integrity, propagation and extend of fracking activities, and eventual hazard scenarios by potential triggering of induced seismicity. Data analysis can either be performed by classical, seismological tools for determination of single-event properties like hypocenter, origin time, magnitude, and moment tensor to characterize the stress field and the related source mechanisms of relevant micro-earthquakes. Or one exploits innovative approaches to derive in-situ stress changes by statistical properties of large populations of small events (Grob and Baan, 2011). Both approaches apply equally well to standard and unconventional reservoirs; however, the more rapid changes in the latter make all kinds of time-lapse 4D monitoring even more attractive (Forgues et al., 2011).
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Logging and Interpretation Techniques in Gas Shales – a brief Overview
By Karl SchwabThis presentation will discuss basic log responses in hydrocarbon bearing shales and shall give an overview over basic and more advanced interpretation approaches to determine the key parameter TOC (Total Organic Carbon) content, as well as benefits and limitations of the approaches presented.
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Implications of the New Geophysics for Hydrocarbon Production
More LessAzimuthally varying seismic shear-wave splitting (SWS) (seismic birefringence) is widely observed above swarms of small earthquakes, in reflection and refraction surveys, and in local and teleseismic arrivals in almost all igneous, metamorphic, and sedimentary rocks throughout the Earth’s crust and uppermost ~400km of the mantle (Crampin 1994; Crampin and Peacock 2005, 2008). The splitting is caused by propagation through pervasive distributions of fluidsaturated stress-aligned vertical microcracks in almost all in situ crustal rocks, and intergranular films of hydrolysed melt in the mantle. Fig. 1 is a schematic illustration of SWS in stress-aligned microcracks. These fluid-saturated microcracks are the most compliant elements of in situ rock, so that changes of in situ stress in rock at depth modify microcrack geometry. These changes can be monitored by SWS (Crampin 1999, 2006; Crampin and Peacock 2008). The observed range of shear-wave velocity anisotropy (SWVA) is ~1.5% to ~4.5% in ostensibly-intact unfractured in situ rocks throughout the crust and mantle (Crampin 1994, 1999; Volti et al. 2003).
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CBM characterization based on seismic frequency spectral variations
By Yanghua WangIn this study, I propose to exploit the variational patterns of seismic frequency spectrum, for characterizing the spatial distribution of potential CBM reservoirs. Considering for example a 2-D seismic profile in the time-space domain, one can generate a vector of the instantaneous frequency spectrum at every point. Such frequency spectral vectors at different time-space positions have different variation patterns. If one uses different colours to present the time-space points with different variation patterns, one can create a colored 2D image. This colorful 2D picture may highlight the reservoir anomalies. I apply this technology to predict the spatial distribution of CBM reservoirs, which is an important unconventional energy resource (Shuck et al., 1996; Bachu and Michael, 2003; Peng et al., 2006).
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Geophysical characterization of black shales
Authors K. Bauer, R. Streich, F. Adao, M. Baumann-Wilke, O. Ritter, N.H. Schovsbo, E. Spangenberg and M. StillerBlack shales are dark, thinly bedded sedimentary rocks deposited under anaerobic conditions. They are rich in carbon, sulfides and organic matter, and potentially can serve as hydrocarbon source rocks. Black shales may also contain significant enrichments of gas or oil (gas shales, oil shales). Because of the continuous distribution of the natural gas or oil, they are considered to be unconventional reservoir types (Law and Curtis, 2002). During the last decades, increasing economic exploitation was triggered by the development of improved drilling and stimulation techniques, particularly in North America (e.g., Montgomery et al., 2005), but recently also in other regions such as Europe and Asia.
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Monitoring small amounts of CO2 injected into a thin reservoir structure - results from the Ketzin pilot site
By Stefan LüthIn the past decades, an increasing atmospheric concentration of carbon dioxide has been observed which is generally considered as the main cause of global warming and resulting climate change (IPCC 2005). Capture and geological storage of carbon dioxide (CCS) are discussed as one option to reduce greenhouse gas emissions while continuing the use of fossil fuels as long as they are available and as long as renewables and increased energy efficiency cannot replace fossils completely (Bachu 2003). Large scale storage projects which are currently in operation, such as, e.g. the Sleipner field offshore Norway (Arts et al. 2004) and the In Salah project in Algeria (Ringrose et al. 2009), are related to oil and gas production. Smaller scale projects covering different geological settings have been implemented worldwide, with a special focus on advancing monitoring technologies (e.g. Kikuta et al. 2005; Michael et al. 2010).
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