Oil exploration via subsurface electromagnetic techniques

Each year thousands of boreholes are drilled into the Earth. Electromagnetic, Acoustic, Radiation, and other devices are suspended in these holes to record data pertaining to the physical composition of the subsurface formations. These data will, hopefully, help us to locate oil, gas, coal, minerals, and water. In the search for oil and gas, wells have been drilled to depths of nearly six miles. Temperatures in excess of F and pressures above 20,000 psi, although not experienced every day, are becoming more common. In addition to these subsurface methods, several surface methods are employed in geophysical applications. This paper concentrates on describing the Electromagnetic techniques that have been found useful in the quest for new energy sources, the location of mineral deposits and even potable water. Techniques for measuring naturally occuring electromagnetic phenomena such as Spontaneous Potential and Telluric currents are described. Measurements using man-generated electromagnetic fields are also discussed. These include descriptions of the Schlumberger and Wenner electrode arrays, laterologs, normals, focussed electrode arrays, induction devices, nuclear magnetic resonance methods, and electromagnetic propagation techniques. Examples of results from several of the techniques are presented. Methods of interpretation of the data, in conjunction with data from the aforementioned acoustic and radiation devices are also described.