- 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
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.
-
-
-
Air Injection Laboratory Experiments on Opalinus Clay. Experimental techniques, Results and Analyses
Authors E. Romero, R. Senger and P. MarschallUnderstanding gas transport processes is one of the key issues in the assessment of radioactive waste repository performance and is the focus of this research. If the gas production rate (generated by the anaerobic corrosion of the ferrous metal and microbial degradation of organic material) exceeds the rate of diffusion of gas in the host rock pore-water, a free gas phase will develop, pressure will increase and gas will migrate through the engineered barrier system (EBS) and into the surrounding host rock. The actual gas migration mechanisms may entail standard two-phase flow or more complex mechanisms involving coupled two-phase geomechanical and possibly geochemical phenomena.
-
-
-
The Thermal Volume Change of Opalinus Clay
Authors M. Monfared, J. Sulem, M. Mohajerani and P. DelageDeep geological storage of high activity radioactivity waste is an option considered in many countries. In Belgium, France and Switzerland, clays and claystones are considered as possible geological barriers. In this context, the NAGRA agency of Switzerland is operating an Underground Research Laboratory (URL) of Mont Terri excavated in the Opalinus Claystone.
-
-
-
Basement Configuration and its Impact on Permo- Triassic Prospectivity in Kuwait
Authors M. Monfared, J. Sulem, P. Delage and M. MohajeraniTo better assess the performance of deep geological storage of high activity radioactivity waste under the temperature changes due to the heat emitted by exothermic wastes, an investigation of the thermal pressurization in the Opalinus claystone has been conducted. Thermal pressurization is a pore pressure increase that occurs in low permeability rocks submitted to temperature elevation. It is due to the significant difference between the thermal dilation coefficient of water (w) and that of the solid phase ( s), with w >> s. Since water is not free to expand in undrained (or poorly drained in-situ conditions in low permeability rocks), temperature elevation results in the build up of a thermal pore pressure and of a decrease of the effective stress in the rock mass. These effects may have some negative consequence on the rock permeability properties, in particular due to possible induced fractures and rock damage. This problem was one of the main concerns of the European TIMODAZ project (2006 – 2010), devoted to thermal damage in shales in the framework of radioactive waste disposal.
-
-
-
Thermal Rock Physics of Shales - Laboratory Measurements under Drained and Undrained Conditions
Authors A. Bauer, A. van der Linden and F. KorndorfferCap rocks of oil and gas reservoirs, or reservoirs used for CO2 storage in carbon-capture-and-storage (CCS) projects, are often low-permeability shales. If the temperature of the reservoir or some wells is changed, e.g. by steam injection in thermal EOR or injection of CO2 with a lower temperature than the subsurface rock formations, heat will diffuse from the reservoir into the overlying cap rock or from the wells into the surrounding rock formations and may cause some damage. Especially for CCS projects, a thorough assessment of caprock integrity is a licence-to-operate requirement.
-
-
-
In Situ Behaviour of Opalinus Clay under Thermal Loading
Authors A. Gens, B. Garitte and J. VaunatIf an argillaceous rock is selected as the geological host medium to house a repository of high level radioactive waste, it is necessary to examine the rock under very generalised loading conditions. The rock will be subjected to drying from tunnel ventilation and, possibly, from the suction of the engineered barrier surrounding the waste. This drying will be in turn compensated, at least partially, by water inflow from the outer reaches of the rock mass. High level radioactive waste is heat emitting, so a significant thermal loading will also be applied to the rock. Those hydraulic and thermal changes will in turn bring about mechanical and chemical changes.
-
-
-
Testing the Thermo-Hydro-Mechanical Behaviour of a Shale
Authors L. Laloui, A. Ferrari and S. SalagerHighly overconsolidated clayey materials are found in numerous geotechnical applications, such as the design of nuclear waste repositories, petroleum exploitation or gas shale extraction. Stress history, diagenesis and cementation may cause these materials to have a high preconsolidation pressure (usually greater than 10 MPa). Moreover, it is well known that the mechanical response of clayey materials depends on thermal and hydraulic changes. Temperature changes affect the swelling pressure, the thermal dilatation and contraction behavior, the stiffness, the yielding limit and the time dependent behavior (e.g. Hueckel and Baldi, 1990; Cekerevac and Laloui, 2009).
-
-
-
Pore-water Chemistry in Clays and Shales - Methods and Applications
By M. MazurekOwing to their ultra-low permeability, solute transport in clays and shales is generally dominated by diffusion. Because diffusion is a slow process on the formation scale, the chemical composition of pore waters constitutes a geochemical archive suited to study past events and processes whose signatures have long been obliterated in the embedding aquifers. Changes of the ground-water composition in these aquifers lead to diffusive adjustment of the pore-water chemistry to the new boundary condition. The spatial distribution of pore-water composition across shale formations frequently shows curved profiles, indicative of a transient state of exchange with the boundaries. The characteristic transport times in clays and shales depend on the formation thickness and on the solutespecific diffusion coefficient.
-
-
-
Two-phase Matrix Transport Experiments on Lowpermeable Mudstones and Shales within the CO2 SEALS Project
Authors A. Amann-Hildenbrand, A. Ghanizadeh and B.M. KroossWithin the CO2SEALS project funded by the German ministry an experimental procedure for quantifying fluid transport properties of nano-permeable lithotypes was set up. The observed range in matrix permeability could be related to mineral composition and maturity of the lithotypes. The mineralogically mature shales, as well as immature mudstones and marly limestones, studied have sufficiently low permeabilities to be considered adequate seals for CO2 storage. For the shales no CO2 breakthrough could be achieved experimentally at differential pressures relevant for CO2 storage. For the mudstones CO2 breakthrough occurred at differential pressures above 6 MPa. These lithotypes can consequently be considered as excellent capillary seals. The marly limestones had lesser sealing efficiency with a minimum He breakthrough pressure of 1.3 MPa. Experimental exposure of cap rock samples to CO2-charged brine at conditions typical of CO2 storage for up to 50 days did not result in any detectable mineral alterations. However, slight changes in transport properties were observed, which, however are considered too small to jeopardise seal integrity.
-
-
-
Pressure Transmission Test for Evaluating Sealing Capacity of Shale Caprocks
Authors S. da Fontoura and V.M.A. MelendezDisposal of CO2 into deep aquifers or depleted oil reservoirs is increasingly being studied as a strategy for limiting the anthropogenic CO2 emissions (Fischer et al., 2005; Nelms et al., 2004; USDOE, 2002). Clayey rocks (siltstones, claystones, shales, mudrocks,) represent major constituents of sedimentary basins and act as potential flow barriers and seals for subsurface fluid transport due to their low permeability and high capillary entry pressure. During gas accumulation or storage in the subsurface, gas leakage may occur through the clayey rocks once the minimum capillary entry pressure (threshold capillary pressure) is exceeded and the gas phase forms an interconnected pathway through the pore system of the rock.
-
-
-
CO2 Entry Pressure into Shale - Scoping Test
By R.T. Ewyorganizing committee desires). What did we do right? What did we do wrong? How can this method be improved? Can any aspects of this method be adopted as ‘best practice’ for measurement of CO2 entry into shales? What other best practices should we add to this method?
-
-
-
Clay/CO2 Interactions in the Context of Geological Storage of Carbon Dioxide
Authors A. Busch, P. Bertier, Y. Gensterblum, P. Giesting, S. Guggenheim, A. Koster van Groos and P. WenigerA major concern when storing CO2 in geological formations is the sealing efficiency of lowpermeable sequences overlying potential storage reservoirs. The long-term integrity of these sealing layers (caprocks) is a prerequisite to maintain CO2 in place and avoid dissipative loss to the atmosphere. Such leakage will occur either by capillary leakage, via diffusion or through existing or induced faults and fractures The assessment of leakage risks and leakage rates, considering different potential mechanisms, is therefore an important issue for site approval and public acceptance.
-
-
-
On the Use of Imaging Methods in Characterizing the Pore Space of Clay Rocks in 3D
By L.M. KellerIn the context of the disposal of radioactive waste, the production of shale gas and CO2 sequestration gas transport along the intergranular pore space in clay rock formations is an important issue. In order to validate the isolation potential of a host rock for radioactive waste or in order to better understand the deliverability of gas of shale gas reservoirs, the gas transport pathways and their connectivity have to be comprehend very well. It is well known that the intergranular pore system is dominated by pores with radii on the nanoscale; whereas it is proposed that gas flow is controlled by the geometry of those pores that corresponds to comparable larger pores (i.e. > 10nm). Thus, information on larger pore connectivity, geometry and distribution are important. In addition, and in the case of gas shales, micron-scale carbonaceous particles are associated with an increased nanoporosity and it is assumed that this organic material forms pathways for locally enhanced gas transport. In addition to organic material, silty-sandy layers in different sizes are potential pathways for enhanced transport through an otherwise largely impermeable matrix of fine grained clay grains of which a majority of pores have radii < 10 nm.
-
-
-
Preferred Orientation, Microstructures, and Porosity Analysis of Posidonia Shales
Authors F. Kets, W. Kanitpanyacharoen, H.R. Wenk and R. WirthSynchrotron X-ray diffraction technique was used to characterize composition, microstructure, and texture of four source rock samples of Lower Jurassic Toarcian Posidonia shales retrieved from the Hils Syncline in northern Germany. The samples were obtained from similar depth from boreholes drilled with a lateral distance of roughly 10-20 km from each other. However, the total organic content (TOC) of the samples varies in thermal maturity, with vitrinite reflectance varying over a wide range from 0.68% to 1.45% (Littke et al., 1988). This variation indicates differences in local temperature history due to either a local igneous intrusion or a complex burial history (e.g. Leythaeuser et al., 1980; Rullkötter et al., 1988; Petmecky et al., 1999). The porosity of shales from the four wells is generally low and ranging from 4% to 10%, inferred from the mercury injection (MICP) (Mann, 1987). Mann (1987) reports pore throat sizes between <2.2 nm (estimate) to 60 nm, with most pores being in the order of nanometers. The objective of this work is to investigate whether the thermal history has affected the preferred orientation patterns of Posidonia shales and whether clay minerals may have been diagenetically altered, with consequent changes in preferred orientation. Furthermore, synchrotron X-ray microtomography was used to investigate the three-dimensional (3D) distribution of porosity and constituent phases and to compare the obtained porosity with previous measurements (Mann et al., 1986; Mann, 1987). Microstructures at the nanoscale were studied by transmission electron microscopy (TEM).
-
-
-
Shale Reservoir Properties from Digital Rock Physics
More LessDRP merges three key technologies that have evolved rapidly over the last decade. One is high resolution diagnostic imaging methods that permit detailed examination of the internal structure of rock samples over a wide range of scales. The second is advanced numerical methods for simulating complex physical phenomenon and the third is high speed, massively parallel computation using powerful graphical processing units (GPU’s) that were originally developed for computer gaming and animation. Based on pore-scale images from a wide range of organic shales, it can be seen that organic material is present in a variety of forms. Three primary forms, non-porous, spongy, and pendular are commonly observed. Non-porous organic components fill all of the available non-mineral space leaving virtually no porosity or fluid flow path. Porous or “spongy” organic material is commonly encountered in thermally mature gas shales. Pendular organic material appears to fill the small intergranular and grain contact regions, leaving open pore space in the larger voids. These pore types are largely controlled by kerogen type and thermal maturity, and they exert large influence on the porosity, permeability, and overall shale reservoir quality.
-
-
-
New Insights into Gas Shale Fabrics Using Chemical Degradation Combined with STXM
Authors C. Glombitza, S. Bernard, K. Mangelsdorf, A. Schreiber, I. Kögel-Knabner, M. Steffens and B. HorsfieldThe generation of oil and gas from shales during thermal maturation is accompanied by structural and chemical evolution of the original kerogen of the shales. During hydrocarbon generation the organic material becomes increasingly recalcitrant due to the degradation of functional groups and labile bonds in the kerogen matrix. Thus, the hydrocarbon generation potential of shales is not only related to the amount of aliphatic moieties in the kerogen structure but also to the distribution of functional units and the linkage properties inside the kerogen network.
-
-
-
Seismic Stratigraphic Analysis of the Barnett Shale and Ellenburger Unconformity Southwest of the Newark East Field
Authors E.T. Baruch, R.M. Slatt and K.J. MarfurtThe sequence stratigraphic framework established for the subsurface Barnett Shale in the northern part of the Fort Worth Basin is helping to resolve the age, nature and fill of karst features under the Barnett in the southwestern part of the basin. The southwestern Fort Worth Basin is characterized by absence of the Upper Ordovician Viola Limestone and Simpson Group, which separate the Lower Barnett Shale from the underlying Ordovician Ellenburger Group, as well as the Forestburg Limestone, which separates the Upper and Lower Barnett Shale to the north (Montgomery, 2005). Consequently, the undifferentiated Barnett Shale unconformably overlies the water-bearing Ellenburger Group, and results in a higher risk of water encroachment during stimulation and production of Barnett gas wells.
-
-
-
Application of Inorganic Whole Rock Geochemistry to Shale Resource Plays - An Example from the Eagle Ford Shale Formation
By T. PearceOver the few past years shale resource plays have become increasingly important hydrocarbon plays. In the USA, formations such as the Barnett Formation, the Haynesville Formation and the Eagle Ford Shale Formation have become major hydrocarbon exploration targets. However, understanding the controls on reservoir quality in these shale formations is still in its infancy, despite thousands of well penetrations. In this paper, the Eagle Ford Shale Formation is used to demonstrate how inorganic whole rock geochemical data that are primarily obtained to provide stratigraphic correlations can be used to help understand mineralogy, organic content and rock brittleness.
-
-
-
Form and Distribution of Organic Matter-Hosted Pores, Marcellus Formation (Devonian), Pennsylvania, USA
Authors K.L. Milliken, M.D. Rudnicki and D.N. AwwillerPore systems hosted dominantly within organic matter (OM) are widely documented in gas shales (e.g., Ambrose et al., 2010; Curtis et al., 2011a; Curtis et al., 2011b; Loucks et al., 2009; Passey et al., 2010; Sondergeld et al., 2010) and siliciclastic mudrocks of the Marcellus Formation in northern Pennsylvania, USA provide an excellent example.
-
-
-
Origin of High Salinities in Hydraulic Fracture Flow Back Fluids - An Example from the Haynesville Shale Gas Play, USA
More LessEconomic development of shale gas resources requires successful hydraulic fracture stimulation of the gas-bearing shale utilizing significant volumes of water. The availability, treatment and disposal of this water are significant non-technical risks and can be important factors impacting the viability of shale gas opportunities. A typical Haynesville hydraulic fracturing job requires ~11,000 barrels of water and a total of ~350,000 lbs of proppant. The water initially injected into the subsurface is fresh, typically with a TDS content of 1 to 5 kppm (TDS = Total Dissolved Solids). However, clean up and recovery of the fracture fluids prior to bringing gas on stream typically recovers only ~5 to 10% of the originally injected volume of water. This water tends to be highly saline, often with TDS contents of ~200 kppm. Similar observations have been reported from other shale gas plays such as the Barnett and Marcellus. This begs the obvious question “Where did all the water go?”.
-
-
-
The Methane Storage Capacity of Black Shales
Authors M. Gasparik, A. Ghanizadeh, Y. Gensterblum, B. Krooss and R. LittkeEstimations of gas storage capacities (GIP) are crucial in evaluation of gas shale plays, yet they are affected by a great deal of uncertainty owing to strong heterogeneity of shale rocks, scarcity of available data and our incomplete knowledge of storage mechanisms in gas shales and their dependence on reservoir conditions. Storage capacity of gas shales comprises compressed (“free”) gas in the pore volume as well as sorbed gas associated mainly with organic matter and clay minerals. The relative significance of free vs. sorbed gas remains to be established for a broader range of samples and experimental conditions. Some authors suggest that at high temperatures the total storage capacity of gas shale play is controlled primarily by total effective porosity with only a negligible contribution from sorbed gas (e.g. [1]).
-