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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
41 - 48 of 48 results
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Control of Geomechanical instability of Shale based on Optimized Well Engineering Decision
Authors M Farrokhrouz and M.R. AsefShale instability is essentially driven by changes in stress and/or chemical alteration. However, sometimes less attention may be paid to geochemical processes. In addition, some well engineering approaches may inevitably facilitate geochemical alterations. An appropriate decision may be more difficult if shale is observed as interbred layers in a carbonate reservoir (rather than as a cap rock). In this research an exceptional approach was chosen to identify geochemical processes that induced geomechanical instability in a gas reservoir with shale interbeds in the South of Iran. Nevertheless, the problem and potential solutions were worked out corresponding to the conceptual engineering geological skills. The results showed that excessive water and HCL acid (traditionally used for well stimulation) in contact with shale interbeds could have significantly contributed in plugging of the well. Site investigations revealed that the amount of excessive (unwanted) water, to a large extent depends on the gas production rate. A systematic analysis of geochemical processes at different production rates was conducted. Mineral precipitation/dissolution of shale formation was simulated accordingly. Corresponding geomechanical interpretations were considered as key points to make an appropriate decision based on economic production rate and the likely well engineering problems.
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An Alternative to Hydrofracture
By G.D. CouplesHydrofracturing is an inprobable process in basins. Instead, dilational, shear-related deformations are predicted under the conditions that can normally be achieved. Such dilational responses explain the observed pressure profiles and the outcrop-based observations.
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Numerical Study of Consolidation Effect on Time Delayed Borehole Stability During Underbalanced Drilling in Shale
More LessTime delayed mechanical borehole stability is mostly depending on the pore pressure consolidation process. Establishment of pore pressure equilibrium in shale is a time dependent process which is characterized by shale intrinsic properties. In shale, water movement is greatly restricted by the low permeability of shale which may cause pore pressure storage and lead to redistribution of borehole stresses. To prevent wellbore instability problems, accurate predictions of stresses and deformations around the wellbore are essential, particularly when drilling in underbalance in shale. Using an adequate constitutive model for shale is crucial in obtaining accurate predictions of the stress changes and deformations. Recent research shows that several mechanisms contribute to shale instability, including swelling, pressure diffusion, plasticity, anisotropy, capillary effects, osmosis and physcio- chemical alteration. It is clear that it may be impossible to consider all features of shales in one model. However, an improved understanding of the behaviour of shales during UBD will enable the main features to be included and facilitate more rational predictions. This study was developed numerical material model. The model is enabled to predict borehole collapse risk with the impact of time delayed consolidation effect. The generality of this study is to enhance knowledge of downhole
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Overpressure Prediction based on a Rock Physics Model for Shales
By A. NogeitzigThe stress sensitivity of seismic velocities is used for overpressure prediction. A software code calibrates sonic data with predicted velocities and returns an estimation of pressure, smectite illitisation (in mineral fraction), temperature, conductivity and porosity with depth. The results show good agree of predictions with measured data, as long as geological/lithological input information is reliable.
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Passive Seismic Monitoring to Optimize Hydraulic Fracturing Treatments: Lessons Learned from our American Cousins
Authors J. Le Calvez, S. Maxwell and A. MartinezNorth American shale-gas recovery efforts are quite large, while the extent of such unconventional gas reserves in Europe is largely unknown. Some tests of gas shale formations have recently been carried out with good success in various basins (e.g., Germany’s Lower Saxony, Vienna Basin, southern Sweden, etc.) The development of Europe’s gas resources will take years and may benefit from lessons learned in North America. Firstly production from unconventional shale formations (e.g., Barnett, Fayetteville, Marcellus, Woodford, etc.) has been enabled by modern well log evaluation techniques and completion methods. These are particularly important since stress anisotropy strongly influences fracture system development. Secondly, it is critical to monitor the initiation and evolution of hydraulically-induced fracture systems. Currently almost all predictive models used by reservoir and production engineers to estimate recovery in stimulated wells are based on assumptions that naturally lead to oversimplified fracture geometry. Microseismic monitoring enables reservoir engineers and geoscientists to understand the development of hydraulically-induced fracture systems as well as naturally pre-existing fracture networks in four dimensions.
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