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Understanding Seismic Anisotropy in Exploration and Exploitation (second edition) by Leon Thomsen is designed to show you how to recognize the effects of anisotropy in your data and to provide you with the intuitive concepts that you will need to analyze it. Since its original publication in 2002, seismic anisotropy has become a mainstream topic in exploration geophysics. With the emergence of the shale resource play, the issues of seismic anisotropy have become central, because all shales are seismically anisotropic, whether fractured or not. With the advent of wide-azimuth surveying, it has become apparent that most rocks are azimuthally anisotropic, with P-wave velocities and P-AVO gradients varying with source-receiver azimuth. What this means is that analysis of such data with narrow-azimuth algorithms and concepts will necessarily fail to get the most out of this expensively acquired data. The issues include not only seismic wave propagation, but also seismic rock physics. Isotropic concepts including velocity, Young’s modulus, and Poisson’s ratio have no place in the discussion of anisotropic rocks, unless qualified in some directional way (e.g., vertical Young’s modulus). Likewise, fluid substitution in anisotropic rocks, using the isotropic Biot/Gassmann formula, leads to formal errors, because the bulk modulus does not appear, in a natural way, within the anisotropic P-wave velocity. This updated edition is now current as of 2014.
A comprehensive overview of the key geologic, geomechanical and engineering principles that govern the development of unconventional oil and gas reservoirs. Covering hydrocarbon-bearing formations, horizontal drilling, reservoir seismology and environmental impacts, this is an invaluable resource for geologists, geophysicists and reservoir engineers.
Following the breakthrough in the last decade in identifying the key parameters for time and depth imaging in anisotropic media and developing practical methodologies for estimating them from seismic data, Seismic Signatures and Analysis of Reflection Data in Anisotropic Media primarily focuses on the far reaching exploration benefits of anisotropic processing. This volume provides the first comprehensive description of reflection seismic signatures and processing methods in anisotropic media. It identifies the key parameters for time and depth imaging in transversely isotropic media and describes practical methodologies for estimating them from seismic data. Also, it contains a thorough discussion of the important issues of uniqueness and stability of seismic velocity analysis in the presence of anisotropy. The book contains a complete description of anisotropic imaging methods, from the theoretical background to algorithms to implementation issues. Numerous applications to synthetic and field data illustrate the improvements achieved by the anisotropic processing and the possibility of using the estimated anisotropic parameters in lithology discrimination. Focuses on the far reaching exploration benefits of anisotropic processing First comprehensive description of reflection seismic signatures and processing methods in anisotropic media
The Woodford Shale formation is currently an important unconventional gas resource that extends across parts of the mid-continent of the United States. A resource shale acts as source, seal, and reservoir, and its characterization is vital to successful exploitation and production of hydrocarbons. This work is a surface seismic observation and investigation of the seismic anisotropy present in the Woodford Shale formation in the Anadarko Basin, Oklahoma. One of the main causes of anisotropy here is commonly believed to be vertical natural fractures (HTI) and horizontal alignment of clay minerals (VTI). Understanding the natural fracture orientation and density, as well as regional stress orientation, is important to the development of hydraulic fracturing programs in shales, such as the Woodford, producing natural gas. Dipole sonic log measurements in vertical boreholes suggest that the Woodford does possess vertical transverse isotropy (VTI), due possibly to horizontal layering or aligned clay minerals. Further, the borehole logs do not indicate horizontal transverse isotropy (HTI) associated with fracturing in the Woodford interval. An amplitude varying with angle and azimuth (AVAZ) analysis was applied to 3-D surface seismic data in the Anadarko Basin and shows the dipole sonic logs may not be completely characterizing the anisotropy observed in the Woodford. Once this apparent contradiction was discovered, additional work to characterize the fractures in the formation was undertaken. A petrophysical model based on the borehole data of the Woodford Shale was created, combining various techniques to simulate the rock properties and behavior. With a more complete rock physics model, a full stiffness tensor for the rock was obtained. From this model, synthetic seismic data were generated to compare to the field data. Furthermore, analytic equations were developed to relate crack density to AVAZ response. Currently, the application of this AVAZ method shows fracture orientation and relative variations in fracture density over the survey area. This work shows a direction for a quantified fracture density because the synthetic seismic data has a quantified fracture density at its basis. This allowed for a relationship to be established between explicit fracture parameters (such as fracture density) and AVAZ results and subsequently may be used to create regional descriptions of fracture and/or stress orientation and density.
A significantly expanded new edition of this practical guide to rock physics and geophysical interpretation for reservoir geophysicists and engineers.
This book is intended as a reference book for advanced graduate students and research engineers in shale gas development or rock mechanical engineering. Globally, there is widespread interest in exploiting shale gas resources to meet rising energy demands, maintain energy security and stability in supply and reduce dependence on higher carbon sources of energy, namely coal and oil. However, extracting shale gas is a resource intensive process and is dependent on the geological and geomechanical characteristics of the source rocks, making the development of certain formations uneconomic using current technologies. Therefore, evaluation of the physical and mechanical properties of shale, together with technological advancements, is critical in verifying the economic viability of such formation. Accurate geomechanical information about the rock and its variation through the shale is important since stresses along the wellbore can control fracture initiation and frac development. In addition, hydraulic fracturing has been widely employed to enhance the production of oil and gas from underground reservoirs. Hydraulic fracturing is a complex operation in which the fluid is pumped at a high pressure into a selected section of the wellbore. The interaction between the hydraulic fractures and natural fractures is the key to fracturing effectiveness prediction and high gas development. The development and growth of a hydraulic fracture through the natural fracture systems of shale is probably more complex than can be described here, but may be somewhat predictable if the fracture system and the development of stresses can be explained. As a result, comprehensive shale geomechanical experiments, physical modeling experiment and numerical investigations should be conducted to reveal the fracturing mechanical behaviors of shale.