Well Logging Engineering Lecture 3

What is the reciprocal of resistivity?

Which of the following has low resistivity?

In what form is resistivity measured?

What factors influence resistivity measurements in a reservoir?

Which of the following is a characteristic of uninvaded formations?

Which fluid occupies the pore space of reservoir rocks affecting resistivity?

Which material is considered a high electrical insulator?

Why are resistivity measurements critical in geology?

What factors does the true resistivity of the formation (Rt) depend on?

What can hinder the accuracy of resistivity measurements in the invaded zone?

According to Archie’s experiments, how is the formation resistivity factor (F) calculated?

How does temperature affect the resistivity of formation fluids?

What is the formula to calculate the formation resistivity factor (F) related to porosity?

What does a higher value of tortuosity indicate about the cementation exponent (m)?

What is the relationship among oil saturation (So), gas saturation (Sg), and water saturation (Sw)?

What parameter does the invaded zone's resistivity depend on?

Well Logging Engineering - Lecture 3

Resistivity: A measurement of resistance. The reciprocal of resistivity is conductivity. Measured in ohm-meters.
Resistivity Formula: R = r * A / L (Where R = resistivity, r = resistance, A = cross-sectional area, L = length)
Resistivity of Rocks: Reservoir rocks contain constituents that affect resistivity:
- Matrix material: High resistivity
- Formation water: Low resistivity
- Oil: High resistivity
- Gas: High resistivity
- Water-based mud filtrate: Low resistivity
- Oil-based mud filtrate: High resistivity
Resistivity and Porosity: Resistivity is a function of porosity, fluid type (fresh/salt water, hydrocarbons), and rock type. Logging tools measure resistivity to determine hydrocarbon presence and reservoir porosity.
Uninvaded Formations: Resistivity in uninvaded formations depends on the amount of aqueous formation fluids, porosity, and water saturation. The goal is to calculate water saturation (Sw) using known formation resistivity (Rt) and water resistivity (Rw).
Invaded Zones: Drilling fluids can alter formation resistivity in invaded zones. Measuring and correcting for this effect requires knowing mud filtrate resistivity (Rmf), remaining formation water resistivity (Rw), mud filtrate saturation (Sxo), remaining formation water saturation (Sw), and porosity (Ø).
Effect of Temperature: Temperature significantly affects the resistivity of formation fluids and water-based drilling muds.
Archie's Experiments: Archie's work on formation resistivity factor (F) shows a relationship between formation resistivity (Ro) from a formation 100% water-saturated and the resistivity (Rw) of formation water (Ro=FxRw). F's values relate to the cementation exponent (m) and porosity (Ø) following the formula F = 1/Ø^m. Water saturation (Sw) is related to the formation resistivity (Rt) and formation resistivity factor (F) according to the equation Sw = (Ro/Rt)^1/n, where n is the saturation exponent
Effect of Salt Composition: Formation fluid resistivity depends on dissolved salt concentration (expressed as NaCl equivalent). A chart relating resistivity to temperature and salt concentration aids in accurate analysis.

Explore the essential concepts of resistivity and its implications in well logging engineering. This lecture covers resistivity measurement, the resistivity formula, and the factors that affect the resistivity of reservoir rocks. Understand the relationship between resistivity, porosity, and hydrocarbon presence.