- Home
- Conferences
- Conference Proceedings
- Conferences
3rd EAGE Shale Workshop - Shale Physics and Shale Chemistry
- Conference date: 23 Jan 2012 - 25 Jan 2012
- Location: Barcelona, Spain
- ISBN: 978-94-6282-062-3
- Published: 23 January 2012
1 - 20 of 40 results
-
-
Size Dependent Deformation of Nano-scale Pores during Consolidation
Authors S. Emmanuel and R.J. Day-StirratOne of the main challenges to effectively evaluating oil and gas reservoirs is determining the evolution of porosity and permeability during burial. During early diagenesis, consolidation is a critical process in all sedimentary rocks, reducing porosity, mean pore size, and subsequently permeability (Athy, 1930; Hedberg, 1936; Neuzil, 1994; Dewhurst et al., 1999). However, the evolution of all these parameters is ultimately determined by changes in pore size distributions within the sediment. Although experiments and field-based observations have provided crucial insight into the impact of consolidation on mud-rich sediments (e.g., Dewhurst et al., 1998; Yang and Aplin, 1998, 2007), a systematic approach that can predict the evolution of textural characteristics has yet to be fully achieved. Here, a mathematical model is presented that describes the evolution of pore size distributions during sediment consolidation. In addition, the model is tested by comparing numerical solutions with experimental data, providing a new quantitative tool with which to assess the mechanical behavior of sediments. Furthermore, we demonstrate that pore deformation decreases significantly with pore size and the magnitude of this effect is also calculated. Implications of the results for the behavior of other sedimentary rocks are also discussed.
-
-
-
Effects of Isotropic and Anisotropic Stresses on Elastic Properties of Shales
Authors M. Pervukhina, P. Golodoniuc, B. Gurevich and D.N. DewhurstUnderstanding seismic anisotropy in shales is important for quantitative interpretation of seismic data, 4D monitoring and pore pressure prediction. Along with intrinsic anisotropy caused by preferred mineral orientation that is common in shales, anisotropic stress is an important factor that affects shale elastic response. The effect of stress on elastic properties of shales is also important for understanding of depositional trends especially at the upper 2000-3000 meters where the compaction is mostly mechanical. Despite the importance of the effects of isotropic and especially anisotropic stress on elastic properties of shales, little work has been done on theoretical understanding and predicting such properties.
-
-
-
Ultrasonic Velocity Anomalies in the Draupne Formation Shales (Upper Jurassic, Norwegian Sea)
Authors M. Angeli, R.H. Gabrielsen and J.I. FaleideFluid migration through caprocks is a crucial process when it comes to evaluate their sealing capacity for underground CO2 storage. Migration mechanisms such as flow through fault systems or along wells are quite easily identified by their relatively large size and because these features can be monitored by the use of reflection seismic data or well logs. However, microcracks in rocks, which can allegedly cause fluid migration through tight rocks, are difficult to detect from large scale observations and can only be deduced from thorough investigation.
-
-
-
Experimental Study of Sealing Capacity of Clay Rock
By C.L. ZhangIn argillaceous rocks, self-sealing of fractures generated by the excavation of underground repositories can be expected due to combined impact of rock compression, backfill resistance, and clay swelling during the post-closure phase. The sealing process is determined by the deformability and swelling capacity of the host rock and the backfill as well as by the boundary conditions. As a crucial factor for the long-term safety of repositories, the sealing behaviour of fractures in claystone has been experimentally investigated by GRS on the Callovo-Oxfordian argillite (COX) at Bure in France and the Opalinus clay (OPA) at Mont-Terri in Switzerland under relevant repository conditions.
-
-
-
Recovery of Porosity and Permeability for High Plasticity Clays
Authors A. Krogsbøll and N. FogedStress history is normally evaluated based on an evaluation of geological history and if possible combined with oedometer tests where preconsolidation stress σp and compaction properties are measured. Often the constrained modulus M is used to define the stiffness, and the value will typically depend on the stress state of the sample. The stress state of a sample is typically defined by overconsolidation ratio OCR defined as the ratio between vertical preconsolidation stress and actual vertical stress (OCR = σp/σ0). Janbu (1963), Maine & Kulhawy (1982) and others have published typical relations that describe stress state and constrained modulus as functions of OCR, plasticity index and other quantities. They are all based on the assumption that the soil sample “remembers” previous load levels, and that stiffness of the sample is consequently increased due to the preloading. Definition and applicability of the reconsolidation stress is now questioned when high plasticity calys are considered. Even if it is known, that a clay layer has been exposed to a high stress level, for instance due to the weight of an ice shield, the actual stress level according to that preloading might not be the relevant parameter when estimating stiffness properties for use in basin modeling or other models.
-
-
-
Shale Swelling/Shrinkage - The Effects of Shale and Fluid Properties, Stress, and Water and Ion Transfer
By R.T. EwyTo study and understand shale swelling, a series of related lab tests was performed on samples obtained from nine different preserved shale cores. These cores came from wells located in various places around the world. All shale samples were kept fully preserved and were not contacted with any aqueous fluids prior to testing. The shales are all clay-rich (at least 60% clay) but represent a spectrum of different clay mineralogies and reactivity as well as different amounts of in situ burial and compaction.
-
-
-
Effects of Free and Bound Water on Stress Dependent Wave Velocities in Clays and Shales
By R.M. HoltWater has a profound control on wave velocities in clays and clay rich rocks like shale. Water exists as free pore water, but is also adsorbed on mineral surfaces and intercalated inside clay mineral sheets. The adsorbed or “bound” water is shown by various molecular dynamics simulations combined with Monte Carlo simulations (e.g. Leote de Carvalho and Skipper, 2001) to have an ordered crystal like structure. One may thus anticipate that bound water has properties different from bulk water, and in particular that it has shear stiffness. Even if bound water may be present only as one or a few layers of water molecules, it may fill a significant portion of the very small (nanometer size) pores in shale. Also, since it sits on mineral surfaces, it may control grain contact mechanics, which is known to be a major contributor to stress sensitivity of elastic properties in granular media.
-
-
-
In Situ Stress Path of a North-Sea Shale
Authors A. Bakk, J.F. Stenebraten and R.M. HoltThe main application of seismics was for many years tied to exploration. Currently however, seismics is more and more used for reservoir characterization. This has been made possible through development of AVO techniques, through the use of time lapse seismics to monitor e.g. injection fronts, and through the development of new detection techniques (such as seabed geophysics) permitting extensive use of S-wave data. These developments and the new applications have called for research on the link between observed wave signatures and rock characteristics; i.e. on rock physics. Rock physics may also point to new seismic attributes that may improve our ability to extract information from seismic data. Most likely, the development of improved rock physics methods to quantify effects of fluid substitution and pore pressure changes in 4D seismics may also prove fruitful for exploration applications of seismics.
-
-
-
Low-frequency Induced Anisotropy from a Sand-shale Sequence
By A. StovasA stack of thin sand-shale layers is typical example for vertically heterogeneous models in reservoir characterization. Reliable methods are required to predict the properties on a coarse scale that capture the influence of fine-scale structures. Most of these methods are based on the effective medium theory and require seismic upscaling. The upscaling results in induced seismic anisotropy which is an important property of effective medium. The standard Backus averaging technique (Backus, 1962) used for upscaling has to be applied for the total wavefield and provides the static (zero-frequency limit) properties of the effective medium. In my paper, I define the low-frequency effective medium and compute the frequency-dependent layer-induced anisotropy parameters from the sand-shale finely layers.
-
-
-
Borehole Breakouts in Black Shales - Experimental Investigations of a Transverse Isotropic Material
Authors T. Meier, E. Rybacki, A. Reinicke and G. DresenWithin this laboratory study we try to simulate a deviated drill path frequently used in the oil- and gas as well as geothermal industry. Especially the exploitation of unconventional resources, like oil and gas shale, requires deviated drilling techniques to increase the intersection of the borehole with the low permeable rock. The rock is therefore penetrated with different drillbit sizes and orientations creating a complicated stress concentration in the circumference of the borehole. In case the stress exceeds the strength of the rock borehole breakouts develop. These failures can lead to a loss in drilling fluid, stuck pipe, reaming and the necessity to side-track a lost hole as for example observed in high-angle wells drilled in a organic-rich shale formation in the North Sea by Økland and Cook (1998).
-
-
-
Shale Brittleness and Plasticity - Impacts on Borehole Fracturing and Collapse
By R.M. HoltIn oil industry jargon, terms like "brittleness" and "plasticity" are often used as qualitative descriptors of failure processes like those occurring during hydraulic fracturing or during borehole collapse. While plasticity is well-defined by the lack of strain reversibility upon stress reversal, brittleness lacks a unique definition.
-
-
-
Can Fracture Toughness be Used as a Proxi for Fracability?
Authors T. Backers and O. StephanssonFrom a fracture mechanical point of view, the fracture propagation in rock material and hence how easily rock can fracture is described by fracture toughness. Fracture toughness is a parameter that describes the resistance of the rock to the propagation of a fracture. In the theory of fracture mechanics, the stress intensity factor K is a measure of the amount of stress concentration at the tip of a crack as a function of applied load and fracture length. The fracture toughness KC is the critical value of the stress intensity factor at which an existing fracture extends. From this mathematical framework it derives that longer fractures are in general easier to propagate.
-
-
-
Evaluation of Mechanical Strength of a Barents Sea Shale by Applying the Most Common Failure Criteria
Authors M. Angeli, J. Naseryan Moghadam, N.H. Mondol and P. AagaardCaprock seals are formations that prevent the migration of hydrocarbon and storage CO2 to the surrounding formations. Shales and mudstones are most abundant formations in the sedimentary basin that can be found as caprock seals because of their low permeabilities. The most important mechanical parameter of the caprocks is the main principal stress that has crucial importance in exact determination of rock strength, fracture calculations and failure criteria. In this study, the most common failure criteria have been applied to analyze the triaxial test data that are obtained from geomechanical tests performed on the Hekkingen shales from the Barents Sea. The Hekkingen Formation consists of brownish-grey to very dark grey shale and claystone with occasional thin interbeds of limestone, dolomite, siltstone and sandstone. The core samples belonging to the Hekkingen Formation are selected from two depth intervals and are named as G1 and G2 (Table 1).
-
-
-
Improved Borehole Stability in Shales through Optimized Drilling Fluid Salt Concentration
Authors O.M. Nes, R. Bøe, E.F. Sønstebø, E. Fjær, K. Gran, S. Wold, A. Saasen and A. FjogstadSevere borehole instability problems may be encountered when drilling through shales, potentially representing a substantial cost to the operator. Such rock mechanical instabilities may have both physical and chemical origin. They are however generally influenced by time dependent mechanisms related to various diffusion processes, implying that even though a borehole is initially stable, it may turn unstable some days after drilling. In practice, the challenge is then to keep the borehole sufficiently stable until casing is set.
-
-
-
Impact of Saturation Change on Shale Properties
Authors D.N. Dewhurst, B. Maney, B. Clennell, C. Delle Piane, C. Madonna, E.H. Saenger and N. TisatoOver the last few years, interest in shales has sky-rocketed through their emergence as productive reservoirs in gas shale plays. Considerable interest in shale properties has also been generated through anomalous responses in shales, as opposed to in reservoirs, in highly expensive 4D seismic surveys. These issues have led to a surge in the amount of research being performed on shales and specifically, significant interest in shale properties, especially in the rock physics, petrophysics and geomechanics domains.
-
-
-
Attenuation Measurements in Fully and Partially Saturated Shales
Authors C. Delle Piane, C. Madonna, D.N. Dewhurst, M. Raven and E.H. SaengerThe study of wave attenuation in partially saturated porous rocks over a broad frequency range may provide valuable information about the fluids in such systems. In contrast with isotropic reservoir rock types like sandstone and carbonate, experiments aimed at measuring attenuation on shales in a wide frequency range are strikingly rare. The main goal of our work is to experimentally measure the seismic attenuation of well characterized shale samples, using an established workflow for the collection of mineralogical and physical properties and a novel experimental set-up for the measurements of attenuation as a function of frequency.
-
-
-
Pore Size and Permeability of Experimentally Compacted Smectire and Kaolinite Clay. Permeability and Elastic Moduli
More LessClay and shale sequences may constitute thick intervals with a gradual decrease in porosity and corresponding increase in velocity of elastic waves. This is seen also in intervals where clay and shale samples easily disintegrate in water, which would indicate that the porosity reduction is merely a consequence of mechanical compaction. Mondol et al. (2007, 2008) studied this phenomenon by laboratory experiments involving compaction of dry or sea-water saturated smectite and kaolonite powder. During these tests, velocity of elastic compressional waves and of elastic shear waves was measured; the volume of expelled water was monitored, and porosity () as well as bulk density, , could be calculated. From these data the authors could derive compressional modulus (M), shear modulus (G), and bulk modulus (K) as well as fluid permeability (k). From samples of the kaolinite and smectite used during these experiments, the specific surface could be measured by nitrogen adsorption (BET, Fabricius 2011). The BET data allow calculation of average pore radius. The present study addresses whether these data may be applied to derive a tool for estimating permeability from elastic moduli, bearing in mind that elastic moduli may be derived from logging data.
-
-
-
Pore Radius and Permeability Prediction from Sonic Velocity
Authors E.N. Mbia and I.L. FabriciusSeveral authors have predicted permeability of shales either through laboratory measurements and or from field data using various empirical relations. A critical literature review by Mondol et al., (2008) on available permeability models, concluded that none of the existing models is ideal and all need to be calibrated and validated through a much larger permeability database of well-characterized mudstones. His results on smectite and kaolinite aggregates suggest that the permeability of smectitic clays may be up to five orders of magnitude lower than that of kaolinitic clays with the same porosity, density, velocity or rock mechanical properties. Mari et al., (2011) described a methodology for obtaining a permeability log based on acoustic velocities Vp and Vs, porosity φ, P-wave attenuation and frequency, their calculation of the specific surface S of the formation was based on the relationship between porosity φ, Vp/Vs and S proposed by Fabricius et al. (2007). Fabricius (2011) indicate that pore radius and thus permeability of shale in the depth interval of mechanical compaction may be predicted from porosity and sonic velocity. In this work we are presenting the empirical equations developed from experimental data that can be used to predict pore radius and permeability of shale from sonic velocity data measured in the field.
-
-
-
Laboratory Analysis of Shale Permeability
Authors Q.J. Fisher, F. Kets, C. Grattoni, R. Buxton and P. LorincziUntil recently very few data were available on the permeability of shale samples. Those available were mainly obtained by those interested in top seal capacity, overpressure retention or radioactive waste disposal. The shale gas revolution, which has taken place in the USA over the last decade, has meant that the amount of data available on shale permeability has increased by several orders of magnitude; although it is important to note that “shale” gas reservoirs tend to have far less clay than shale seals to petroleum reservoirs and overpressured compartments. The experimental methods used by those involved in the shale gas industry differ significantly from those involved in seal analysis.
-
-
-
Hydrogen Gas Transfer Experiments within Callovo- Oxfordian Clayrock
Authors M. Didier, J. Talandier, P. Berne and L. CharletDuring the past few decades, clays have received more interest than other minerals [Bergaya et al., 2006]. This attention to clays is due to their common availability, their extraordinary properties and their heterogeneous composition. These materials present a wide range of porosities, principally micropores and mesopores and a laminated structure. No other group of inorganic materials shows such a wide range of reactivity and propensity for modification. This rock has been considered for many applications, for example the Callovo-Oxfordian (COx) clayrock [Gaucher et al., 2004] is investigated to be used as a host rock for French nuclear waste and alumina-pillared synthetic montmorillonites are studied for a new kind of hydrogen gas storage material for mobile applications [Gil et al., 2009]. Regarding nuclear waste storage, hydrogen gas is expected to develop from the corrosion processes of the waste containers.
-