WELL LOG : Types of Logs, The Bore Hole Image, Interpreting Geophysical

1. &
Its
Response.
Bore Hole
Environment;
Resistivity Log

2. Introduction
 The Word Well Logging is derived from
Wireline Geophysical Log
 It is also called
 Geophysical Borehole Logging
 Downhole Geophysical Surveying
 Wireline Logging

3. Cont;
 First log measurement was made in 1927
 Equipment used was SONDE.

4. Objectives.
 Introduction.
 Conditions of Bore Hole.
 Invasion, Its Depth & Profile.

5. Introduction.
Bore Hole Environment:
• Mechanical alteration of rock by drilling.
• Alteration of fluid distribution within the rock pores.
• Mechanical alteration of bore hole geometry by the
circulation mud.

6. Conditions of Bore Hole.
 Hole Size.
 Drilling Mud.
 Mud Cake.
 Mud Filtrate.

7. Conditions of Bore Hole.
• Hole Size:
o Build up of mud cake which creates sloughing.
o Two types.
a. Over gauge hole: Larger dia than drill bit dia.
b. Under gauge: Hole narrower than drill bit.
• Drilling Mud:
It destabilizes the bore hole size by creating
following problems.
o Creates mud filter cake.
o Creates swelling problems.

8. Conditions of Bore Hole.
• Mud cake:
o Prevention is necessary for further invasion of liquid.
o Necessary determination of Mud cake thickness &
Volume by Filter Pressure.
• Mud Filtrate:
o Fluid of drilling Mud enters the permeable zone.
o Filtrate is usually water.

9. Invasion, Its Depth & Profile.
Invasion:
Penetration of Mud filtrate adjacent to the well bore in
to the invaded zone.
 Invaded Zone: Subsurface flushed portion of
permeable rocks with mud filtrate adjacent to the
well bore.

10. Invasion, Its Depth & Profile.
Invasion Depth:
Depth of invasion depends upon:
o Filtration characteristics of mud.
o Differential Pressure.

11. Invasion, Its Depth & Profile.
Invasion Profile:
• Invasion process creates invasion profile extending
from well bore into formation.
• Three zones are recognized.
1. Flushed zone.
2. Transition zone.
3. Undisturbed zone.

12. Invasion, Its Depth & Profile.
1. Flushed zone (Xo):
• Part of invaded zone.
• Area near well bore where mud filtrate completely
replaced the formation water and hydrocarbons.
• zone extend couple of inches back from well bore
and occurs between mud cake and transition of
annulus zone.

13. Invasion, Its Depth & Profile.
2. Transition zone:
• Part of invaded zone (annulus zone).
• Area between normal and abnormal high pressure
zone.
• Area in formation behind well bore in which mud
filtrate and formation filtrate are mixed.
• Located between flushed and un-invaded zones.

14. Invasion, Its Depth & Profile.
3. Undisturbed zone:
• Area of formation located back from the well bore.
• Formation fluids not diluted by mud filtrate.

15. Invasion Profile.
BED
THICKNESS
MUD
Rm
MUD CAKE
Rmc
THICKNESS
hmc
ADJACENT BED
Rs
ADJACENT BED
Rs
HOLE
DIAMETER
d
UNINVADED
ZONE
Rt
FLUSHED
ZONE
Rxo
TRANSITION
ZONE

16. Objectives.
 Law of Resistivity.
 Resistivity Logs.
 Uses.

17. Law of Resistivity.
Resistance (Ohms law):
 R = V/I.
R= Resistance (Ohms),
V = Voltage (volts),
I= Current (Amperes).
“R”; Resistance-Property of substance to resist flow of
current across it.

18. Resistivity Log.
 Resistivity & Conductivity:
 Resistivity (ohm meter): Resistance of one meter cube,
when current flows between opposite faces.
 Conductivity: Reciprocal of resistivity.

19. Resistivity Log.
Characteristics:
• Wireline well log.
• Measures resistivity & conductivity of rocks and
fluids in pore spaces adjacent to well bore.
Working Principle:
• Electrical current from generator on surface is
forced through formation.

20. Uses of Resistivity Logs.
These logs are used for:
a. Correlation.
b. Bit selection.
c. Permeability indication.
d. Formation fluid detection & water saturation.
e. Litho logy conformation & bed boundaries.

21. Objectives.
 Resistivity measurement tools.
 Types of Resistivity tools.

22. Resistivity measurement
tools.
Micro Resistivity tool:
• Made with electrodes on rubber fluid-filled pad pressed
to the well bore wall.
• Use to define narrow beds.
• Use to detect mud cake to indicate permeable rocks.
• Use to measure the resistivity of flushed zone.

23. Resistivity measurement
tools.
Medium/shallow Resistivity tool:
• Use to measure the resistivity of transition zone.
Deep resistivity tool:
• Used in undisturbed zone.
• Measures the true resistivity.

24. Types of Resistivity tools.
Lateral Log deep (LLD):
• Normal resistivity type.
• High resistivity formation.
• Saline mud.
• Deeper radius of investigation.
• Constant electric current from electrode passes on
sonde through formation in a well.
• Records the conductivity-resistivity of rocks and fluid on
smaller dia.

25. Types of Resistivity tools.
Lateral log Shallow (LLS):
• Normal resistivity type.
• shallow radius of investigation in transition zone.
• Constant electric current from electrode passes on
sonde through formation in a well.
• Records the conductivity-resistivity of rocks and fluid on
smaller dia.

26. Types of Resistivity tools.
Micro Spherically Focused Log (MSFL):
• Spherically focused micro resistivity log.
• Used in shallow investigating.
• Tool is mounted on pad against well wall.
• Measures flush Zone Resistivity.
• Records Gamma Ray ,SP and Calipar curves.

27. Types of Resistivity tools.
Induction Focused Log:
• Type of electric log, developed in 1970s for
nonconductive fluids like OBM.
• Now used with fresh WB & OB muds and air.
• Low to medium resistivity formations
• Saline Muds.
• Use to determine resistivity of transition & undisturbed
zone.
• It works by creating circular electric currents into the
formation adjacent to well bore.

28. Objectives.
 Measurement through Resistivity
logs.
 Measuring Logging Tools.
 Resistivity Profile.

29. Measurement through
Resistivity logs.
Resistivity logs are used for measurements in following
categories.
 Bore Hole.
 Drilling Fluid Types.
 Invasion.

30. Measurement through
Resistivity logs.
Bore Hole:
It includes the measurement of:
o Diameter of bore hole.
o Hole deviation.
o Mud cake.

31. Measurement through
Resistivity logs.
Drilling Fluid Types:
It includes the study of the indication of:
o Water base mud.
o Oil base Mud.
o Air drilled mud.

32. Measurement through
Resistivity logs.
Invasion:
It requires study through resistivity logs in following
field:
o Step resistivity profile.
o Transition profile.
o Annulus profile.

33. Measuring Logging Tools.

34. Measuring Logging Tools.

35. Resistivity Profile.