Edwin F. Laine

Cross-borehole electromagnetic probing to locate high-contrast anomalies

Electromagnetic (EM) probing between boreholes is useful for locating high‐contrast geophysical anomalies such as a tunnel. Theoretical and experimental studies of EM field interaction with a tunnel show that minima in the received signal can be used for locating the tunnel. The theoretical studies show that as a transmitter and receiver are lowered in separate boreholes, the minima can be interpreted easily to yield both the lateral and vertical positions of the tunnel. The main mechanism of EM field interaction with the tunnel appears to be diffraction, and the spatial variation of the field strength is affected by the tunnel shape. Frequencies from 10 to 70 MHz were studied to assess the usable frequencies. The field in the receiver borehole was an effective diagnostic when a half‐wavelength in the surrounding medium was less than or equal to the diameter of the tunnel. EM probing at two test sites gave the locations of tunnels within 1 ft of the surveyed locations.

Design of a Miniature Directional Antenna for Geophysical Probing from Boreholes

In this report we describe a design for a miniaturized directional antenna for use in geophysical exploration from boreholes. Mathematical results are given which indicate the antenna characteristics. The concept we use involves an antenna eccentrically located within a high dielectric constant or high permeability sheath.

Remote monitoring of the steam-flood enhanced oil recovery process

Cross‐borehole seismic velocity and high‐frequency electromagnetic (EM) attenuation data were obtained to construct tomographic images of heavy oil sands in a steam‐flood environment. First‐arrival seismic data were used to construct a tomographic color image of a 10 m by 8 m vertical plane between the two boreholes. Two high‐frequency (17 and 15 MHz) EM transmission tomographs were constructed of a 20 m by 8 m vertical plane. The velocity tomograph clearly shows a shale layer with oil sands above it and below it. The EM tomographs show a more complex geology of oil sands with shale inclusions. The deepest EM tomograph shows the upper part of an active steam zone and suggests steam chanelling just below the shale layer. These results show the detailed structure of the entire plane between boreholes and may provide a better means to understand the process for in situ heavy oil recovery in a steam‐flood environment.

Subsurface Probing by High-Frequency Measurements of the Wave Tilt of Electromagnetic Surface Waves

An overview of the tilt of an electromagnetic surface wave propagating along the surface of the earth is given. High-frequency wave-tilt measurements can have important applications in low conductivity regions such as desert and permafrost areas. A specific application includes determining the depth of permafrost. Past applications of wave-tilt measurements were primarily with lower frequencies in regions with high ground conductivities. Thus low frequencies (<1 MHz) were needed to probe to significant depths. Wave-tilt calculations show that for low surface conductivities, it may be feasible to probe to significant depths using high frequencies (>1 MHz). This enables resolution of thicknesses of layers, a result that has not been possible at low frequencies in the higher conductivity media. It is noted that differences in wave tilt occur for vertically and horizontally polarized surface waves. These wave-tilt differences are useful because they indicate profile characteristics that are sensitive in different ways to the two polarizations.

A Computer Program for Four Probe Resistivity Measurements in a Horizontally Layered Earth

A computer code to plot the response of a dipole-dipole resistivity array over a many-layered earth is described.