GroundMetrics technologies are used for various types of Resistivity and Electromagnetic (EM) surveys from traditional Controlled Source EM (CSEM) and Induced Polarization (IP) surveys to reservoir imaging survey methods such as Borehole-to-Surface EM (BSEM) and GroundMetrics’ proprietary Full-Field Resistivity Surveys, Full-Field Resistivity Mapping and more scientifically Depth-to-Surface Resistivity (DSR). Electromagnetic (EM) surveys that acquire the electric-field component directly can be referred to as resistivity surveys synonymously.
These are different methods to conduct resistivity surveys, but what does it all really mean?
Resistivity, derived from electromagnetic geophysical surveys, is an electromagnetic property that quantifies the ability of a material to oppose the flow of an electrical current. Resistivity conveys information about the electrical properties of target materials and can be used to estimate saturation levels.
In this case the focus is on the high contrast of resistive materials (such as oil, gas & CO2) that exists when a highly resistive body is next to a body with low resistance (also known as conductive) like water.
- Natural Drive and Water, Steam, or Chemical Flood Oil Production – Water, steam and many chemicals are conductive and oil is resistive so resistivity maps or images can show locations of oil-water-contacts (OWC).
- Enhanced Oil Recovery – CO2 flood oil production is also known as Enhanced Oil Recovery (EOR). This method usually involves injecting CO2 after a long period of water injection (possibly after years of water flood) and then alternating water and CO2 thereafter (WAG). In this case the CO2 (resistive) is injected into water (conductive) so GroundMetrics images can show locations of CO2-water contacts.
- Geothermal Exploration – Hot rocks have a different resistivity compared to cool rocks or sediments. Identifying the location and properties of hot rocks can improve drill success rates for geothermal exploration and increase likelihood of hitting the most productive zones.
- Monitoring Underground CO2 Storage – CO2 Capture and Storage (CCS) programs usually involve injecting CO2 into deep salt water (saline) aquifers. These projects usually have Measurement, Monitoring and Verification (MMV) programs to help confirm the CO2 is not leaking out of the aquifer back to the surface, which would be counterproductive and possibly dangerous. Since the CO2 is resistive and the water is conductive resistivity measurements can show locations and movement of the CO2 in the water.
Borehole resistivity measurements, also known as well logs, have been used since the late 1920’s to identify lithologic and fluid boundaries within the borehole and to aid in borehole to borehole correlations, which estimate or extrapolate resistance or other properties between these well logs or point references. GroundMetrics can eliminate errors that inherently occur through such estimates or extrapolation by actually acquiring resistivity data between and far beyond well logs.
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