Geophysical study of the structure and processes of the continental convergence zones: Alpine-Himalayan belt

Studies of the structure of the continental collision zones using seismic and body waves, theoretical modelling of the thermal regime of the convergence processes, and studies of earthquake mechanisms and deformation aspects of the model are covered

Geophysical study of the structure and processes of the continental convergence zones: Alpine-Himalayan Belt

Intracontinental deformation occurrence and the processes and physical parameters that control the rates and styles of deformation were examined. Studies addressing specific mechanical aspects of deformation were reviewed and the studies of deformation and of the structure of specific areas were studied considering the strength of the material and the gravitational effect

The interpretation of crustal dynamics data in terms of plate interactions and active tectonics of the Anatolian plate and surrounding regions in the Middle East

A detailed study was made of the consequences of the Arabian plate convergence against Eurasia and its effects on the tectonics of Anatolia and surrounding regions of the eastern Mediterranean. A primary source of information is time rates of change of baseline lengths and relative heights determined by repeated SLR measurements. These SLR observations are augmented by a network of GPS stations in Anatolia, Aegea, and Greece, established and twice surveyed since 1988. The existing SLR and GPS networks provide the spatial resolution necessary to reveal the details of ongoing tectonic processes in this area of continental collision. The effort has involved examining the state of stress in the lithosphere and relative plate motions as revealed by these space based geodetic measurements, seismicity, and earthquake mechanisms as well as the aseismic deformations of the plates from conventional geodetic data and geological evidence. These observations are used to constrain theoretical calculations of the relative effects of: (1) the push of the Arabian plate; (2) high topography of Eastern Anatolia; (3) the geometry and properties of African-Eurasian plate boundary; (4) subduction under the Hellenic Arc and southwestern Turkey; and (5) internal deformation and rotation of the Anatolian plate

The Interpretation of Crustal Dynamics Data in Terms of Plate Interactions and Active Tectonics of the Anatolian Plate and Surrounding Regions in the Middle East

During the past 6 months, efforts were concentrated on the following areas: (1) Continued development of realistic, finite element modeling of plate interactions and associated deformation in the Eastern Mediterranean; (2) Neotectonic field investigations of seismic faulting along the active fault systems in Turkey with emphasis on identifying seismic gaps along the North Anatolian fault; and (3) Establishment of a GPS regional monitoring network in the zone of ongoing continental collision in eastern Turkey (supported in part by NSF)

The interpretation of crustal dynamics data in terms of plate interactions and active tectonics of the Anatolian Plate and surrounding regions in the Middle East

The long term objective of this project is to interpret NASA's Crustal Dynamics measurements (SLR) in the Eastern Mediterranean region in terms of relative plate motions and intraplate deformation. The approach is to combine realistic modeling studies with an analysis of available geophysical and geological observations to provide a framework for interpreting NASA's measurements. This semi-annual report concentrates on recent results regarding the tectonics of Anatolia and surrounding regions from ground based observations. Also briefly reported on is progress made in using GPS measurements to densify SLR observations in the Eastern Mediterranean

Scattering Characteristics In Heterogeneous Fractured Reservoirs From Waveform Estimation

Offset-dependent characteristics of seismic scattering are useful in the interpretation of fractured reservoirs. Synthetic seismograms generated by a 3-D finite difference modeling are used to study elastic wave propagation and scattering in heterogeneous fractured reservoirs. We use two models having different background medium properties and different azimuthal AVO responses and build heterogeneous fracture density realizations through stochastic modeling. Gas-saturated fractured reservoirs and waveforms ill fracture normal and strike directions are considered in this paper. The multiple signal classification (MUSIC) frequency estimator is used in waveform estimation to provide frequency domain attributes related to seismic wave scattering by fractures. Our results indicate that the strength of the scattered field increases with increasing fracture scatter density and decreasing correlation length of spatial variations of fracture density. It is also a function of the background medium. The strength of the scattering field is stronger in model 1 which has smaller property contrasts in the background medium than model 2. The scattering characteristics for both models are different at the top and the base of the fractured reservoir. Our results show that the scattered field is weak at the top of a fractured reservoir. The first order results are dominated by velocity anisotropy of a mean crack density field. However, the base of the fractured reservoir corresponds to a strong scattered field on which fracture heterogeneity has a larger effect.Massachusetts Institute of Technology. Borehole Acoustics and Logging ConsortiumMassachusetts Institute of Technology. Earth Resources Laboratory. Reservoir Delineation ConsortiumUnited States. Dept. of Energy (Grant DE-82066-223II-1

Full-waveform Based Complete Moment Tensor Inversion and Stress Estimation from Downhole Microseismic Data for Hydrofracture Monitoring

Downhole microseismics has gained increasing popularity in recent years as a way to characterize hydraulic fracturing and to estimate in-situ stress state. Conventional approaches only utilize part of the information contained in the microseismic waveforms such as the P/S far-field amplitudes to determine the focal mechanisms and infer stress state. The situation becomes more serious for downhole monitoring where only limited azimuthal coverage is available. In this study, we developed a full-waveform based approach to invert for complete moment tensor. We use the discrete wavenumber integration method as the fast forward modeling tool to calculate the full wavefield in the layered medium. By matching the waveforms across the array, a stable moment tensor solution can be obtained without imposing additional constraints. We show that by using full waveforms, the resolution of the full seismic moment tensor is improved even with data from a single monitoring well. We also determine the stress drop from the S-wave displacement spectrum. We test our method using a downhole microseismic dataset from hydraulic fracturing treatments in East Texas. The results indicate the existence of non-double-couple components in the moment tensor. The derived fracture plane direction also agrees with that derived from multiple event location.Halliburton Compan

Characterizing Surface Roughness From Pressure-Joint Closure Measurements Using Inversion Procedure

An inversion procedure has been formulated to estimate the surface roughness of a joint (fracture) from the measured pressure-closure data. A gamma distribution for the local minima (or maxima) on a topography profile was used to account for the skewness in the measured distribution of the asperities. By using the distribution, the average height [bar over z] and the standard deviation a of the profile can also be characterized. An inversion procedure was formulated based on the modification of the theory proposed by Brown and Scholz (1985) and has been successfully tested with synthetic data. The inversion finds average height [bar over z][subscript 1], standard deviation σ, and average aperture. These three parameters characterize the surface roughness and aperture of a fracture and are the topography parameters governing permeability, electric conductivity and other transport properties of the fracture. Pressure-closure data from laboratory measurement of a rough and a smooth joint were also inverted to find the joint properties. The results agree with the profile measurement quite well. The variations of transport properties of a fracture with pressure are also studied.Massachusetts Institute of Technology. Full Waveform Acoustic Logging ConsortiumUnited States. Dept. of Energy (Grant DE-FG02-86ER13636

A Short Note On Permeability Anisotropy In Heterogeneous Porous Media

This paper presents some new results of theoretical modeling on permeability anisotropy in heterogeneous porous media. It is shown that the lineation of heterogeneities results ·in permeability anisotropy. However, to produce strong anisotropy, the permeability contrast between the lineated high permeability region and the background must be very high. We demonstrate this using two examples. The first is the fracture model in which the background has negligible permeability compared to the fractures. In the second example the fractures are replaced by impermeable stripes and the background has high permeability. In both cases permeability anisotropy with an order of magnitude difference is produced. These results compare well with the results of laboratory experiments performed to evaluate permeability anisotropy.Massachusetts Institute of Technology. Borehole Acoustics and Logging ConsortiumUnited States. Dept. of Energy (Grant DE-FG02-86ER13636

Estimate the Effective Elastic Properties of Digitized Porous Rocks by Inverting the Cracks Unresolved

Current imaging technique such as micro X-ray CT can provide us detailed 3D micro-structures of porous rocks that can be used in numerical simulation so as to predict elastic properties of rocks saturated with different fluids. However, limited by the resolution the imaging process can provide, we usually lose the small features of rocks such as cracks and micro-pores, consequences of which can cause over-predicted effective elastic properties of porous rocks. In this paper, we present an inversion scheme to estimate the lost cracks during imaging process with Monte-Carlo algorithm. This method combines numerical simulation with theoretical models – the differential effective media model and Kuster-Toksöz model. Compared to the traditional inversion algorithms solely based on theoretical models, the algorithm presented in this paper utilizes the micro-structures of porous rocks resolved and takes the advantages of computational results from the digitized rocks, which in fact provides us much information of rocks and limits our inversion space for cracks. At end, we demonstrate the capability of this method on predicting the elastic properties of Berea sandstones measured in laboratory.Schlumberger Doll ResearchMassachusetts Institute of Technology. Earth Resources Laborator