Geoexploration最新文献

This work describes and illustrates a method of reconciling time contours derived from different vintages of seismic data. The problem has been looked at from an areal viewpoint in contrast to the loop adjustments followed in conventional methods.

The algorithm involves contouring two individual sets of data points exhibiting misties separately and estimating the differences in the maps by back interpolation. Trend surfaces of progressively higher order are fitted on the differences to arrive at the magnitude of corrections for each of the control points. The final map that is produced after incorporating the corrections, retains the structural features depicted by either of the data sets, while resolving most of the mistie effects. The method is suitable for routine application with the aid of a contour mapping package on a personal computer or workstation.

Seismic data from a sedimentary basin have been interpreted and processed using this approach to illustrate the method.

To investigate radon migration in the ground a series of measurements have been made along a profile of 160 m length. The radon concentration was measured in the soil at different depths with the inverted cup technique. The emission of radon and the gamma emission were measured on soil samples from the profile and the exhalation of radon from two drill cores taken right below the profile was investigated. The radon profile agreed better with the drill core emission than with the measurements on the soil samples supporting the hypothesis that streaming transport from the bedrock exists and is important.

Migration with an erroneous velocity gives a curve along which the energy is smeared. In a single-shot experiment, this curve, or the apparent “reflector”, can be constructed as the envelope of ellipsoidal curves of equal traveltime, with the source and receiver at the foci of the ellipses. Associated with this reflector is another curve, the caustic, enveloped by the reflected rays. When data from a single-point diffractor in a constant velocity medium are considered, construction of the zero-distance phase front of reflection reveals that the position of the caustic is independent of the locations of the source and receivers. The caustic is cusped, and the position of the cusp suggests how to modify the imaging principle, or the velocity, so as to improve the quality of migration output.

This paper considers the influence of induced polarization (I.P.) on frequency and transient responses for three configurations used in the inductive methods of electroprospecting. Special attention is paid to the influence caused by the presence of relatively conductive inhomogeneities and to various approaches allowing one to separate the inductive effect from the induced polarization.

It is shown that the quadrature component is less sensitive to the I.P. effect than the inphase component. Also the transient field at the late stage is strongly affected by induced polarization. It is also shown that the dipole-dipole array is least sensitive to the I.P. effect.

A method is presented for calculating the resistivity and IP anomalies of a thin conductor. The conductor is represented by a two-dimensional conductive surface, and consequently the electric charge on its boundaries can be described as a two-dimensional surface charge.

The potential on the surface is solved from an integrodifferential equation. For moderate conductivity values of the surface, the same equation can also be used in calculating the potential outside the conductor. For high conductivity, however, the charge density on the conductor is first solved with the aid of Coulomb's law, where the potential acts as primary term. The potential outside the conductor is then calculated from the known charge density by again applying the Coulomb's law. This procedure is valid over the whole conductivity range from zero to practically infinite values. For a perfect conductor, the potential can also be calculated directly by applying the equipotential condition of the conductor.

As an application, the potential and charge distributions of the model are considered as a function of the longitudinal conductance of the conductor.