Results

Summary

We present a new approach to generating 3D location maps for microseismic events from 3-component data. The method combines full-waveform vector migration with an imaging condition based on semblance-weighted deconvolution. The semblance-weighted deconvolution keys in on the signal-to-noise conditions of the data to give a high-resolution, low-noise estimate of the locations for the microseismic sources. As the method requires no explicit time picking or event association, it is well suited for an either fully-automated or a semi-automated process. Almost as a by-product, the method provides a natural measure of the uncertainty associated with the locations of the individual micro-earthquakes.

Summary

In the last four years there have been several attempts to execute full-waveform inversion (FWI) on 3D data sets. As field data or part of the data component is dominated with P waves, one feasible approach is to use acoustic approximation. This approach of FWI determines parameters related to the acoustic wave equation but mainly updates the velocities by minimizing the misfit between the observed data and the model data. The approach has shown tremendous potential especially in 3D wide-offset acquisitions using the pressure component of the collected data. This includes wide-azimuth streamer, ocean-bottom surveys and land types of geometries where the advantage of FWI has convinced the oil industry to pay close attention to the technology. The question still remains of how far can we properly describe the field data with the acoustic approximation, and at what point do we need to switch over to the much more expensive elastic wave equation implementation. If we acquire multi-component (4C) data, then we may be able to take advantage of the extra measured wavefields using elastic FWI. We previously demonstrated the application through synthetic data of which an example is an overthrust model and have also shown the uplift in a real data from the Gulf of Mexico (GoM).

Summary

A combination of the FDTD technique and Mittet's mapping method is a powerful and fast numerical tool for solution of marine controlled source electromagnetic problems. The efficiency of this technique can be further improved by using optimized, dispersion reducing finite difference coefficients for calculation of first derivatives in Maxwell's equations. We present a method for calculating such coefficients. It is demonstrated that by utilizing dispersion reducing coefficients, the discretization mesh size can be reduced up to two times in 3D diffusive problems.

Summary

We compare the effect of the smoothing of magnetic data on the estimation of the structural index by Euler deconvolution. We analyze physically-based as well as mathematical filters. In general, we found that low-pass filtering the data leads to an increase of the estimated structural index.

Summary

In recent years horizontal oil and gas well drilling has become an enhanced oil and gas recovery method. However, in the areas without 3D seismic data or only with a limited number of wells, reservoir characterization usually fails to meet the demand of the well trajectory design, possibly leading to a very low drilling success ratio. Based on the characteristics of multi-offset VSP technology (flexible shot point, accurate time-depth relationship, and multi-component seismic data), we present a method that successfully predicts reservoir, and adjusts the drilling path and direction in time. Our study shows that multi-offset VSP technology can acquire real-time results at a low cost, suggesting that multi-offset VSP is becoming one of the most feasible geophysical methods for guiding drilling on site.

Summary

As part of the 2011, 1^st International Archaeo-geophysical Student Field Camp, in Niš, Serbia, local archaeological targets were used as a basis for teaching geophysical data survey, processing, and interpretation techniques. The main geophysical goal of the project was to determine a subsurface existence of archeological objects on the site. This was achieved through several geophysical surveys: resistivity and geomagnetism profiling, and GPR. On the field, samples were taken for petrological and mineralogical studies of artifacts. Results of these studies will help to identify primary geological locations of material used for artifacts.

In 2013 the celebration of 1700 years of the Milan Edict will take place in Niš. The center of this celebration will be Mediana. Results of our investigations helped the archaeology team to better chose of locations for 2012 excavations, in order for Niš and Mediana celebrate this jubilee in all its glory.

SUMMARY

We present a solution to Maxwell’s equations using decoupled scalar and vector potentials in the frequency-domain. The decoupling is achieved using a Schur decomposition, and has numerous attractive attributes. A finite-difference numerical solution is presented, in which the symmetry of the underlying problem is retained and exploited to reduce memory requirements and problem size. The decoupled problems are well-posed, and excellent performance can be realized using reusable preconditioners that are independent of conductivity model or source frequency.

Summary

Unconventional gas reservoirs are characterized by low porosity and low permeability. Due to the low permeability in these types of plays, hydraulic fracture stimulation is required to achieve gas production. An effective stimulation connects the existing natural fractures and effectively links as much reservoir rock as possible with the wellbore.

Previous studies have shown that, if used under the right perspective, Lambda-rho/Mu-rho cross plots can be used to quantitatively grade reservoir rocks in conventional as well as in unconventional plays. The validity of this statement is corroborated with actual field data. Specifically, production logs recorded in four neighboring horizontal wells in the Lower Barnett after hydraulic fracturing was carried out, strongly agree with the hypotheses that:

1. Low values of Lambda-rho and Mu-rho are indicative of high porosity and therefore high reserves in place, in this case gas.

2. For any given porosity or original gas in place (OGIP), the recovery factor and therefore the gas rate increases with decreasing Poisson's ratio.

This study shows that production logs such as the temperature log and the differential gas production log when plotted in the Lambda-rho/Mu-rho background are in agreement with the two hypotheses. High temperatures correspond to high gas rates; therefore, high temperatures and high gas rates are clustered together towards the lower left hand side of the Lambda-rho/Mu-rho cross plot, while lower temperature and lower gas rates cluster towards the upper right hand side of the cross plot.

Summary

Permanent reservoir monitoring (PRM) using seabed arrays of seismic sensors is becoming a well recognised tool for optimizing production and increasing reserves at lower cost and risk through improved reservoir management. An approach based on fully fibre-optic sensors offers significant benefits in terms of long term reliability and reduced through-life costs. A successful PRM system will also require high stability of the output seismic data in terms of sensitivity, noise and other key performance attributes throughout its operating lifetime. We discuss issues which affect system stability, and describe how we have addressed these through a combination of careful system and mechanical design based on over 25 years experience of analogous systems and rigorous qualification, demonstrating over 30 years’ equivalent accelerated sensor lifetime without performance change. We present results from two field tests, 3 years apart, to show that highly stable sensor operation can be achieved in real field environments.

Summary

The present work aims at the representation (parameterization) of a two-dimensional compressional seismic velocity fields (functions) extracted from a geological model, through the use of orthogonal functions known as wavelets, specifically those so-called Haar Wavelets. Comparative experiments were made between the wavelet series with and without the use of scale function. The approximation of the velocity field, obtained by this technique, depends on the values of indexes used in the mentioned series, which influence the quality of the model representation. It was noted that the proposal parameterization offers a good accuracy to the field representation. In addition, the use of scale function in wavelet series is advantageous only in case that few low values for indexes are used.