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Second EAGE Workshop on Shales
- Conference date: 26 Apr 2010 - 28 Apr 2010
- Location: Nice, France
- ISBN: 978-94-6282-061-6
- Published: 26 April 2010
21 - 40 of 48 results
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Well Log and Seismically Derived Impedance of Clay-Rocks for Higher Resolution of Pore Pressure Prediction
Authors S.B. Nowak and P.D. HeppardIn this paper we discuss how acoustic impedance can be utilized for pore pressure prediction. Acoustic impedance, the product of velocity and density, of normally pressured shales behaves in a predictable manner of increasing impedance with increasing burial depth as shale compacts. Overpressure in clay rocks is noted by a deviation from the normal compaction trend to lower values. The minerology of clay rocks affects the impedance in a manner similar to other log responses of velocity, resistivity and density and must be considered when evaluating for pore pressure. Previous applications of seismically derived impedance for pore pressure have used it to modify migration-derived velocities to improve resolution. In this application we use a calibrated inversion of seismic data for shale impedance and directly convert to pore pressure. This process reduces the effects from other rock types, improving resolution and potentially accuracy. This is in contrast with seismic migration velocities which include an average property of all rocks over relatively thick sections. This negatively affects pore pressure predictions since almost all pore pressure calculations are based on the predictability of shale and clay rocks, not sandstone, siltstone, marl, limestone and other rock types.
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Experimental Simulation of 4D Overburden Effects Associated with Depletion of or Injection into a Subsurface Reservoir
Authors R.M. Holt and J.F. StenebråtenIn this presentation we show results of laboratory experiments on compacted brine-saturated clay specimens experiencing an initial stress state and stress changes representative of those occurring in situ during depletion of or injection into an underlying reservoir. The results can be used to assess expected 4D response in realistic field cases, to evaluate various 4D attributes, and also possibly to help quantify stress changes from 4D data.
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The Effect of Intra-Reservoir Shales on Effective Stress Sensitivity
Authors Y. HajNasser and C. MacBethIn most clastic reservoirs experiencing pressure depletion, the sands in the reservoir naturally compact. As a consequence, the much lower permeability reservoir shales may experience extension. This extension is counteracted to some degree by pressure equilibration of the shale. The effective seismic response of the reservoir interval may thus be a mix of both hardening and softening reservoir components, depending on the balance of these phenomena. This effect is predicted to alter the overall stress sensitivity of the seismic properties from that anticipated for a homogeneous, fully connected reservoir interval. However, the final resultant response depends on the time period over which this effect is observed. Numerical computation using simplified geological models indicates shales of 1m to 10m thickness should be taken into account when quantitatively assessing the 4D seismic signature from frequently shot time-lapse surveys with a periodicity of 3 to 12 months, whilst 5 to 10m thick shales could impact conventional 4D seismic surveys shot over 5 to 10 years. These conclusions are strongly affected by the mechanical and transport properties of the intra-reservoir shales, their thickness and distribution, and are hence also a function of the depositional environment.
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Ten Years of Microseismic Mapping of Shale Gas Completions: Lessons Learned
By R.J. ZinnoMicroseismic monitoring has played a critical role in the success of shale gas production in North America over the last ten years. Several surveys spanning that period, including the first survey in a shale gas field, describe the evolution of that success. These case histories illustrate important lessons learned about influence of fine geologic structures on the fracture behaviour of these reservoirs during stimulation. These stimulation mapping examples chronicle the evolution of modern completion techniques to address and exploit these reservoir complexities.
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Optimizing Drilling and Completions in a Gas Shale - Microseismic Monitoring in North America
By C. NealeCommercially driven development of oil and gas shale reservoirs usually requires hydraulic fracture stimulation to create induced fractures that connect naturally-occurring, hydrocarbon-filled fracture networks with the producing wellbore. The use of microseismic monitoring during hydraulic stimulation has become a standard practice in the development of most North American unconventional resource plays, providing rapid and significant improvements in completion efficiency. The reservoir parameters determined from monitoring include the local orientation of maximum stress, the volume of reservoir contacted by the induced fractures and reactivated natural fractures, and the dimensions of the induced fracture network on a stage by stage basis. This paper will discuss case histories from several US gas shale basins, presenting the development issues being addressed by the stimulation monitoring and how the microseismic monitoring provided direct answers to these problems. Also discussed is the use of temporary surface and permanent near-surface geophone arrays for data acquisition to expand the range of monitoring applications beyond those available from traditional borehole-located geophone array monitoring.
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Monitoring the Hydraulic Stimulation and Production of an Unconventional Reservoir Using 4D 3C Seismic
Authors J.W.G. Atkinson, J. Logel, E. Andersen, K. Wikel and D. GrayIn order to determine optimal well spacing, depletion radii, and vertical extent of the stimulated rock volume in an unconventional shale gas reservoir in the Western Canadian Sedimentary Basin, an advanced multicomponent, time-lapse survey was shot by Talisman Energy in 2008 along with microseismic (surface, water well, and downhole) surveys and a multicomponent VSP. Four seismic surveys were conducted before, during and after hydraulic fracturing of multiple horizontal wells. The purpose of the time-lapse data is to determine if unconventional production and hydraulic fracturing can be delineated using multicomponent seismic methods. Time-lapse work is relatively novel in the unconventional realm, and large amplitude/time changes of the magnitude seen in offshore conventional and many heavy oil reservoirs are not expected. This emphasizes the need for maintenance of quality control measures through the cross-equalization process. Preliminary results on the cross-equalized PP surveys indicate amplitude/time changes coincident with wellbore trajectory. Though clear evidence of time-lapse changes exists, work to understand these results continues.
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Microseismic Imaging of Hydraulic Fracture Complexity in Shale Gas Reservoirs
Authors S.C. Maxwell, C. Cipolla and M. MackMicroseismic imaging of shale gas hydraulic fracture treatments has shown that the stimulations are often complex, resulting from interaction of the injection with pre-existing natural fractures. In this paper, various case studies will be shown contrasting shale gas stimulations with tight gas hydraulic fracture treatments. Integration of microseismic images with reservoir characterization and geomechanical factors is important to understand the mechanisms controlling the complexity and their variation through the reservoir. Microseismic images are also valuable to characterize the success of the planned stimulation, which is important to understand the well performance and improve future stimulation designs and completion strategies.
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Innovative Modeling Techniques to Quantify Fracture Characteristics, Reservoir Properties, & Well Performance in Shales
Authors C.D. Jenkins, M.A. Miller, J.D. Walls and R.R. RaiIn order to characterize reservoir and hydraulic fracture properties using well performance data in shale gas reservoirs, it is essential to apply an appropriate workflow and advanced modeling techniques. The workflow should begin with a review of the well data followed by the use of analytical methods to identify different types of well behavior and to form hypotheses about the various production mechanisms at work. Numerical modeling can then proceed, first with scoping models and then with detailed numerical models to conduct production forecasting and completion optimization sensitivities. A useful tool for this detailed modeling is finite-element simulation which places a large number of closely-spaced nodes near the hydraulic fractures. This extremely fine-scale gridding captures high-resolution pressure transients that dominate well behavior during the first few years of production. The results of this work provide key insights into reservoir and fracture properties, and can be used to optimize production forecasts, well placements, lateral lengths, and completion techniques.
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Evaluation and Influence of Structural Trends from Magnetic and Gravity Data in the Texas-Louisiana Haynesville Play
Authors S.J. Campbell, G. Thompson, R. Inden, W. Pearson, T. Kerrane and J.D. FairheadA number of individual elements need to be present to produce a viable hydrocarbon system in both conventional and non-conventional shale plays. Key to this is the influence of both regional and localised fault and fracture patterns, and examples of these and their correlation with production from the Texas-Louisiana Haynesville area are presented. This paper demonstrates how powerful a tool high resolution gravity and magnetic data are in the identification of structural trends and fracture patterns in the Haynesville area. Analysis of these data helps define the trends that strongly influence the production, permeability and depositional trends in the Haynesville and other key stratigraphic units in the basin. Understanding of these trends, their inter-relationship and their influence on production can help focus an exploration programme.
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Limits to Hydrocarbon Stability in Deep Basins: Evidence from Stable Isotope Reversals and Noble Gas Geochemistry
Authors C.D. Laughrey and R.C. BurrussWe report reversals of both carbon and hydrogen isotopic compositions in natural gases in a deep sedimentary basin (Appalachian basin, eastern USA). The isotopic and molecular compositions together with unique geochemical properties of the source organic matter allow us to seperate mixing and source contributions to the gases so that we can identify trends due to Raleigh fractionation during hydrocarbon destruction by redox reactions. Data from noble gas geochemistry and the isotope geochemistry of carbon dioxide, nitrogen, and hydrogen sulfide in the gases support our arguements. Rapid development and exploitation of shale gas and other unconventional reservoirs has begun to encounter gases with partial to complete carbon isotope reversals. Our interpretation of the origin of reversals due to destruction of higher hydrocarbons at high thermal maturities in sedimentary basins may place constraints on the potential volume of resource from these types of gas accumulations.
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Application of Whole-Rock Elemental Data in Shale-Gas Development: An Example from the Jurassic Haynesville Formation
Authors D.R. Spain, M.C. Dix, J.L. Sano, K.T. Ratcliffe, S.N. Hughes, N.G. Casarta and D. BullerThe latest technologies for collection of elemental data from rocks are VERY BRIEFLY reviewed (and not emphasized). The applications of elemental data for shale gas development are then explained with reference to a large data base from eight North American shale gas formations. Finally, a specific example of how elemental data can be integrated with conventional data, and used throughout a drilling program, is given with the Jurassic Haynesville Formation as a case study.
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Experimentally-Derived Mechanical and Flow Properties of Mudstones
Authors J. Schneider, C.S. Peets, P.B. Flemings, R.J. Day-Stirrat and J.T. GermaineWe developed a systematic approach to predict mudstone compressibility and permeability as a function of composition. We prepared mixtures of natural Boston Blue Clay (BBC) and synthetic silt in four different proportions and resedimented these mixtures. From uniaxial consolidation tests we show that compressibility and permeability vary systematically with silt fraction. Compressibility linearly decreases with increasing silt fraction whereas permeability exponentially increases with increasing silt fraction. Normalizing the flow behavior by using effective void ratio allows the ability to predict permeability if porosity and composition are known.
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Metre-scale Effective Flow Properties of Heterogeneous Fine-Grained Sediments
Authors K.D. Kurtev, M. Drews, J. Ma and A.C. AplinThe evaluation of the effective flow properties of heterogeneous shales are key constraints for hydrocarbon and CO2 leakage evaluation, as well as for hydrocarbon migration through source rocks and tight reservoirs. Here, we demonstrate an approach to determine effective permeability and Capillary Enter Pressure based on capturing and stochastically simulating the natural variability of shale texture. It is shown that the shale texture or spatial variability of lithology is closely related to connectivity and thus to the anisotropy of effective flow properties. We believe that the proposed approach has additional potential for the estimation of the effective relative permeability of shale volumes 1m3 and upwards.
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Effects of Clay Content on Porosity Versus Depth Trends
Authors E. Fjær, A.E. Lothe and Ø. SyltaBased on a calibrated model for porosity versus depth in sedimentary basins, the impact of clay content is described. The model is based on rock mechanical principles, and describe porosity as a function of pore compaction and effective stress. The results show that local clay content affect both the initial (sea floor) porosity and the resistance against compaction while the average clay content in the overburden affects the effective stress. Such models may be applicable for pore pressure prediction as well as modelling of hydrocarbon migration, basin modelling and seismic velocity inversion.
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Empirical Approach for Evaluation of Compressive Strength of Shale
Authors M.R. Asef and M. FarrokhrouzA sound knowledge regarding the strength and stiffness properties of rock material could significantly improve engineering geological assessments. Shales are known as the most problematic rock material worldwide. Uniaxial compressive strength UCS is an essential input parameter for development of almost any engineering design. However, appropriate core specimen for measurement of UCS in the lab is often a real dilemma. Accordingly, extensive attempts have been made for strength estimation based on other parameters. In this research, an empirical equation is suggested for estimating UCS of shale based on Young’s modulus and porosity. This equation was achieved based on statistical analysis of lab experiments obtained over a wide range of geographical locations. A further attempt was made to describe mathematical meaning of the statistical results based on theory poroelasticity. Accordingly, at low porosity values both Young’s modulus and porosity significantly contribute in prediction of the UCS. This was attributed to poroelastic behavior of shale under these conditions. At high porosity values, however, E was the dominant parameter. One of the advantages of this research is that suggested equation is independent of the geographical location, while it is based on two input parameters Young’s modulus, and porosity.
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Bound Water in Shale: Molecular Scale Simulations and Experimental Indications
Authors M.I. Kolstø, D. Potyondy and R.M. HoltIn this paper we show through a molecular scale mechanics simulation that structural order of water near charged surfaces results in a finite shear stiffness of the water phase. This interpretation is supported with experimental data on compacted claystone. We illustrate how the results may be applied in a rock physics model for mudstone / shale.
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Effective Laboratory Measurements of Low Permeability of Shales
Authors P.F. Boulin, P. Bretonnier and E. BemerAssessing shale permeability is a key issue to ensure its efficiency as a reservoir cap rock or its relevancy as a geological barrier in radioactive waste disposals. Clay materials have such a low permeability that conventional experiments cannot be performed. Most of the authors dealing with the characterisation of shale use a transitional method called pulse decay. The experiment presented here is based on a steady state method. It appears to be faster and more reliable than any other permeability techniques. Permeabilities from 0.2 to 200 nD (2 10-22 to 2 10-19 m2) can be estimated in less than one day.
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Active and Passive Seismic Monitoring of Shales Under Triaxial Stress Conditions in the Laboratory
Authors J. Sarout, A. Ougier-Simonin, Y. Guéguen and A. SchubnelLaboratory experiments are reported that were aimed at estimating various rock physics parameters that are of importance in geophysics. Several triaxial deformation experiments on shale specimens from two offshore oil field reservoirs have been performed. Three main parameters were continuously monitored during the deformation process: (i) gas permeability; (ii) local strains in various directions; (iii) longitudinal and shear wave velocities for various directions of propagation; and (iv) micro-seismic events induced by the triaxial stress loading. The wave velocity surveys performed at various stages along the loading path allowed for the estimation and the update of the elastic wave velocity field. The strain data allowed for the update of the wave travel path length along the stress loading. This procedure ensured an accurate and reliable localization of the micro-seismic events that occurred between consecutive surveys. It also allowed for the estimation of the evolution of shale anisotropy under traixial stress loading.
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