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Fourth EAGE Shale Workshop
- Conference date: April 6-9, 2014
- Location: Porto, Portugal
- Published: 06 April 2014
21 - 32 of 32 results
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Permeability and Compressibility of Resedimented Gulf of Mexico Mudrocks
Authors P.B. Flemings and W. BettsSummaryWe used resedimentation and constant rate of strain (CRS) compression tests to study the compaction and permeability evolution of material derived from Plio-Pleistocene aged mudrock from the Eugene Island Block 330 oilfield, offshore Louisiana. We compare our results to previously published in-situ data derived from well logs and to previous tests of intact core. We find remarkable agreement in both compression and permeability behaviour between our resedimentation experiments and intact measurements. Resedimentation provides a systematic approach to understanding mudrock behaviour at high effective stresses. The correlation between in-situ measurements and resedimented results allows us to derived characteristic compression and permability behaviour for Gulf of Mexico mudrocks. These results suggest that there has been little diagenesis or other ageing processes that have occurred in these mudrocks even though they have been buried to more than 3,000 m.
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On the Elastic Anisotropy of Shales
By L. DurantiSummaryThe elastic properties of shales, and their anisotropic character, have been tested more extensively with the introduction of the large group of lithologies which are collectively named gas shales. With respect to a traditional view of “shales = claystones”, gas shales have certainly introduced a more complex compositional mix, with a strong presence of carbonate material and, more limitedly organic matter. The direct impact is a distinct new trend in the relationship between elastic anisotropy and clay content, with probable implications on the constitutive equation of shales, as well as on the interplay between stiffness tensor and particle alignment. It is certainly noteworthy the fact that introducing isotropically (i.e. randomly) carbonate material in the architecture of an anisotropic composite has increased anisotropy significantly. In addition, we currently do not observe a direct relationship between the amount of organic material and elastic anisotropy. The implication is that the key to a general anisotropic “hardening” in gas shales relies in an additional parameter which is currently not understood.
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Mechanical Anisotropy of Gas Shales and Claystones
By R.T. EwySummaryThis abstract/presentation explores mechanical anisotropy of gas shales and claystones and compares the two. The types of anisotropy addressed are 1) static Young’s Modulus anisotropy, 2) static Poisson’s Ratio anisotropy and 3) compressive strength anisotropy. Claystones are found in many ways to be an ‘end member’ of the gas shale universe, and preliminary data suggest that carbonates might represent another logical end member. The dataset consists of mechanical property measurements on fifty different core intervals spread across six different shale gas plays, plus several different clay-rich mudstones. Gas shales mostly have Young’s Moduli values much higher than claystones, and often more anisotropic. Most gas shales have horizontal:vertical modulus ratios of ∼1.4:1 to 2.5:1 or higher. While modulus correlates with bulk density, anisotropy does not. Poisson’s Ratio is also anisotropic, with the vertical Poisson’s Ratio being less than the horizontal. Gas shales also have significant strength anisotropy, more so than most mudstones, due to a low relative shear strength of the bedding planes. Implications of the observed mechanical anisotropy for horizontal stress estimation and for wellbore stability are discussed.
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Thermal Well Stimulation in Gas Shales Through Oxygen Injection and Combustion
Authors G.C. Chapiro and J. BruiningSummaryThe amount of extracted natural gas from low permeable organic rich shale has increased rapidly over the past decade. The technologies used to improve the permeability of a shale gas reservoir are horizontal drilling and hydraulic fracturing. The potential environmental impact of hydraulic fracturing motivates research aiming at alternative permeability enhancement methods.
In this paper we investigate the possibility of in-situ combustion to improve permeability. We consider two possibilities for the in-situ fuel source, viz., methane or kerogen.
A one dimensional model is considered. Under simplifying hypotheses a quasi-analytical solution for the corresponding Riemann problem is obtained using advanced mathematical techniques. The solution was analysed with parameters that correspond to resonance conditions, i.e., conditions for which the speeds of the heat wave and the combustion wave are equal. We conclude that methane combustion cannot generate enough heat to enhance the permeability. However kerogen, if present in sufficient quantities, makes this possible. We present the set of parameters for which the combustion reaches the optimal temperature to improve the permeability.
Finally we validate the analytical approximation with direct numerical simulations. With the numerical model we can calculate the pressure distribution in the reservoir and the production improvement by the thermal treatment.
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On the Water Retention Behaviour of Shales
Authors V. Favero, A. Ferrari and L. LalouiSummaryThe involvement of shales in engineering fields such as the extraction of shale gas or the nuclear waste geological disposal is mainly driven by the low permeability and the high retention properties of these geomaterials. The high capillary forces developed in the matrix of the shales allow the fluid trapping with the consequence that the material remains saturated until significant values of suction. However, in the context of several engineering applications, the shale formations are exposed to relative humidity values which might induce changes in the degree of saturation. As a consequence, the investigation of the air entry value and of the retention behaviour of the material is of primary significance.The following paper presents an investigation on the water retention properties of shales. The experimental technique developed for such analysis is described in detail and selected results are presented. The testing methodology is based on the control of the water content and on the subsequent measurement of the total suction at equilibrium.The volumetric behaviour of the material is monitored in order to compute the retention curve in terms of degree of saturation. The results allow to identify a relationship between the air entry values and the porosity for Swiss shales.
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Hydraulic and Gas Transport Testing of Brauner Dogger and Opalinus Clay
Authors C.C. Graham, J.F. Harrington and R.J. CussSummaryWe present results from fluid flow experiments on samples of Brown Dogger and Opalinus Clay (OPA). Hydraulic testing was carried out on both samples, with flow perpendicular to bedding. Fitting numerical model outputs with the resulting laboratory data provides hydraulic permeabilities similar to those previously reported for Opalinus Clay. However, both samples exhibited slightly lower values, as might be expected given their burial history, whilst the Brown Dogger sample displayed a relatively higher value for specific storage than the OPA. We also present findings from gas injection testing of the OPA sample. Gas entry pressure is non-trivial to determine, but findings suggest that entry occurred close to a gas pressure of 4MPa above applied pore-water pressure. However, outflow was observed to be minimal until much higher excess gas pressures ∼10–11MPa. These findings indicate that, within the pressure window examined, the gas entry characteristics of OPA may be relatively insensitive to the applied boundary conditions and provide additional information on the hydraulic and gas transport properties of the Opalinus Clay/Brown Dogger formations.
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Experimental Observations of the Flow of Water and Gas along Fractures in Opalinus Clay
Authors R.J. Cuss and J.F. HarringtonSummaryThis study introduces experimental results of the flow of water and gas along fractures in Opalinus clay (OPA). The flow characteristics are far from simple. Initial swelling of the fractures reduced fracture flow by one order of magnitude. Shear reduced flow by a further order of magnitude and was an effective self-sealing mechanism. However, continued shear increased flow by over four orders of magnitude. The injection of gas had no detrimental effect on the hydraulic properties of the fracture. The gas entry pressure of OPA appeared to remain unchanged by shearing and this suggests shear was not an effective mechanism to reduce fracture gas transmissivity. The characteristics of gas pressure response post entry was nonrepeatable and suggests that the physics governing gas entry are reproducible, but the flow, which is dictated by the number and spatial distribution of dilatant pathways, was not consistent due to variation in the number of formed pathways.
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Gas Breakthrough and Flow Tests on Opalinus Clay - Ambiguities in the Interpretation of Experimental Data
Authors S. Amann-Hildenbrand, A. Busch and B.M. KroossSummaryWe present and discuss the results of a comparative study of two laboratory procedures for the determination of the capillary gas breakthrough pressures of low-permeable lithotypes with intrinsic permeability coefficients below 10–20 m2. Well-characterized and mineralogical homogeneous core section of the Opalinus Clay (Mont Terri) were used in this study. The experimental conditions corresponded to a depth of approximately 1500 m depth, representative of a typical CO2 storage scenario (30 MPa confining pressure, 45°C).
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Hydraulic Conductance of the EDZ around Underground Structures of a Geological Repository for Radioactive Waste
Authors A. Alcolea Rodriguez and U KuhlmannSummaryThe present study focuses on the temporal evolution of hydraulic parameters of the Excavation Damage Zone (EDZ hereinafter). To that end, a hybrid finite/discrete element method (FEMDEM) was first used to simulate the geometry and geomechanical conditions of discrete fracture networks forming the EDZ, which develop in response to the excavation process in the rock mass around the underground structures of a radioactive waste repository ( NAGRA, 2013 ). The simulated geometry and geomechanical properties are mapped onto a finite element mesh, which allows us to solve the fluid motion equations at the near-field.
The resaturation of the EDZ causes a pore pressure increase at that zone. This leads to a decrease of the normal effective stress and, correspondingly, to the progressive closure of the fracture. This closure causes fracture hydraulic conductivity to drop in time, while matrix conductivity increases due to swelling.
The objectives of this study are:
- To quantify the temporal evolution of hydraulic properties in response to pressure variations caused by
- To quantify the temporal evolution of the specific axial flux through the EDZ.
- To quantify the total time required for a full resaturation of the EDZ.
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Modeling the Hydraulic and Two-phase Flow Behaviour of the Heterogeneous, Fractured EDZ in the Opalinus Clay During the HG-A Experiment at the Mont Terri URL
Authors R.K. Senger, G.W. Lanyon and P. MarschallSummaryThe characterization of gas migration through low-permeability clay formations has been a focus of R&D programs for radioactive waste disposal. Nagra has developed a comprehensive program to characterize gas flow in the Opalinus Clay including the excavation disturbed zone (EDZ) around the underground openings of the repository. The experiment (“Gas path through host rock and along seal sections / HG-A“) as part of the Mont Terri research programme was designed as a long-term water & gas injection experiment in a backfilled microtunnel, to investigate both water/gas leak-off rates and gas release paths from a sealed tunnel section in a low permeability host rock. The experiment combines field investigations with extensive hydro-mechanical instrumentation in and around the HG-A microtunnel with geotechnical laboratory studies on core samples and extensive modelling activities for the validation of coupled hydromechanical models. For the numerical modeling of the HG-A experiment, a 3D model was developed, taking into account the heterogeneity associated with the fractured EDZ. In addition, the relevant coupled hydro-mechanical phenomena were implemented which include (a) the gradual sealing of the fractures in the EDZ during resaturation, and (b) a pressure-dependent permeability associated the water- and gas injection tests.
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Geomechanical Characterization and Numerical Parametrization of Opalinus Clay with Application to Underground Structures
Authors S.B. Giger, P. Marschall, P. Nater, W. Shiu and D. BillauxSummaryResults of a new geomechanical testing program of Opalinus Clay core samples from a deep geothermal well in northeast Switzerland are presented. The experimental findings are in qualitative agreement with previously reported characteristics of the mechanical behaviour of Opalinus Clay. These characteristics comprise of a distinct strain softening irrespective of the degree of overconsolidation, anisotropy in elastic and strength properties, complex non-saturated and moderate swelling behaviour. Based on the relatively strong localization of deformation and pronounced brittleness, a bi-linear Mohr-Coulomb model with a tension cut-off was chosen to represent failure behaviour. Undrained triaxial deformation tests were then reproduced numerically using FLAC 3D software and a bilinear, strain softening ubiquitous joint constitutive model, capable of accounting for anisotropic strength but neither anisotropic nor stressdependent elastic properties. Comparison between laboratory and numerical results highlights that adequate reproduction of strength evolution can be achieved either parallel or perpendicular to the plane of anisotropy assuming isotropic elasticity, but not in both directions. Given this limitation the appropriate choice of modelling input parameters is discussed for application to cavern stability assessment for potential repositories in Opalinus Clay at a depth of 600m.
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