Borehole Geophysics - Resistivity

The objective of this Activity is to provide a basic framework and criteria for the use of resistivity tools. An exercise will be used to as a teaching tool for this Activity.
Formation resistivity is a key parameter in determining both water saturation and contaminant concentration. Resistivity measurements, in conjunction with other data from borehole geophysics can provide a qualitative and quantitative description of both the formation and formation fluids. The resistivity of a formation depends on:
• Resistivity of the formation water (salt concentration)
• Amount of formation water present (water saturation)
• Resistivity of invading fluids
• Rock type, rock texture and structure (porosity and lithology)
• Aquifer temperature.
Comparison of log responses and ratios of various resistivity parameters represent the heart of resistivity interpretation. Resistivity measurements, individually and in combination, are used to estimate true formation resistivity (Rt). Therefore, the characteristics and responses of various resistivity tools are extremely important to log interpretation.