Well Logging Engineering Lecture 3
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Questions and Answers

What is the reciprocal of resistivity?

  • Permittivity
  • Admittance
  • Conductance (correct)
  • Inductance

Which of the following has low resistivity?

  • Formation water (correct)
  • Gas
  • Oil
  • Oil-based mud filtrate

In what form is resistivity measured?

  • Mho-meter
  • Ohm-meter (correct)
  • Siemens-millimeter
  • Ohm-cubic meter

What factors influence resistivity measurements in a reservoir?

<p>Type of fluid and porosity (A)</p> Signup and view all the answers

Which of the following is a characteristic of uninvaded formations?

<p>Measured bulk resistivity depends only on the aqueous formation fluids (A)</p> Signup and view all the answers

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

<p>Formation water (D)</p> Signup and view all the answers

Which material is considered a high electrical insulator?

<p>Matrix material (D)</p> Signup and view all the answers

Why are resistivity measurements critical in geology?

<p>To detect hydrocarbons and estimate porosity (A)</p> Signup and view all the answers

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

<p>Porosity, water saturation, and resistivity of the formation water (D)</p> Signup and view all the answers

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

<p>Presence of the mud filtrate (A)</p> Signup and view all the answers

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

<p>By dividing Ro by Rw (B)</p> Signup and view all the answers

How does temperature affect the resistivity of formation fluids?

<p>It varies greatly with changes in temperature (B)</p> Signup and view all the answers

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

<p>F = 1.0 / ∅m (D)</p> Signup and view all the answers

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

<p>It is higher (C)</p> Signup and view all the answers

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

<p>So + Sg + Sw = 1 (C)</p> Signup and view all the answers

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

<p>The resistivity of the mud filtrate and formation water (B)</p> Signup and view all the answers

Flashcards

Resistivity

A measure of a material's resistance to the flow of electric current.

Resistivity formula

R = (r * A) / L, where R is resistivity, r is resistance, A is cross-sectional area, and L is length.

Resistivity Units

Ohm-meter

High Resistivity Reservoir Constituents

Rock matrix, oil, and gas.

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Low Resistivity Reservoir Constituents

Formation water and water-based mud filtrate.

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Uninvaded Formation

A formation where the drilling fluid hasn't affected the rock's resistivity.

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Bulk resistivity

The effective resistivity of the rock considering all constituents in the formation.

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Conductivity

The reciprocal of resistivity and measures a material's ability to conduct current.

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Formation Resistivity (Rt)

The resistivity of a formation, dependent on porosity, water saturation, and formation water resistivity.

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True Resistivity

The resistivity of a formation in the uninvaded zone, containing oil, gas, and water.

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Invaded Zone

Area of the formation where drilling fluids have disturbed the natural formation fluids.

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Mud Filtrate Resistivity (Rmf)

Resistivity of the liquid portion of drilling mud that has penetrated into the formation.

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Formation Resistivity Factor (F)

Ratio of the resistivity of 100% water-saturated formation to formation water resistivity.

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Archie's Law

Formula linking formation resistivity factor to porosity (F = Ø^-m).

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Cementation Exponent (m)

Value representing how tightly the rock grains are packed, affects the formation resistivity factor.

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Water Saturation (Sw)

Proportion of water in the formation pores.

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Study Notes

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/Øm. 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.

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Description

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.

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