Pyramid field personnel performing seismic testing
The geophysical technologies we use for our typical projects are part of a vast spectrum of physical wave energy technologies used in a wide swath of applications. Our techniques and expertise are concentrated on the types of technologies that work best in the dirty, wet, dense and occasionally organic environments in which we obtain our data. We are frequently trying to image those dirty, wet objects or the characteristics of the ground itself.
“I had experience with a variety of geophysical methods, but my research focused on using electrical geophysical methods (resistivity, induced polarization and self-potential) to monitor changes in the subsurface caused by oil degrading in the subsurface.
Using electrical resistivity, we monitored the long-term degradation of oil on a beach following the Deepwater Horizon oil spill. In terms of electrical resistivity, oil will in most scenarios present as a resistive anomaly. Over the course of eighteen months, we conducted daily measurements of the resistivity within this oil plume. The results showed a decrease in the resistivity within the plume, consistent with what others had observed in laboratory experiments. The decrease in resistivity is a result of the physical and chemical changes within the oil as it breaks down.
In a laboratory experiment, we used induced polarization to monitor the progress of Enhanced Oil Recovery process where bacteria known to breakdown the long carbon chains in oil were introduced to a very viscous oil for the purpose of lowering the viscosity and, in economic terms, increasing the amount of oil recovered from the reservoir. Using broad terms, induced polarization differs from electrical resistivity in that induced polarization in more sensitive to the properties of sediment grains and the grain surface interface. As an example, as oil degrades, acids are produced that etch the grain surface. This etching roughens the grain surfaces, increasing the surface area of the grains which generates a measurable response in the induced polarization data collected.
While these may seem like a very specific cases, the properties observed in this study are universal. The only thing that changes is the application and interpretation. These same methods can be applied to a number of scenarios, such as identifying caves and void spaces, mapping the horizontal and vertical extents of the contaminant plumes, mineral exploration, and characterizing hydrogeological properties, such as the water table, aquifer characteristics, subsurface flow channels, etc. Furthermore, these methods are sensitive to macro- and micro-scale changes, and since resistivity and induced polarization can be measured with the same instrument and field set-up these methods are very cost-effective and versatile.”
