This document discusses concepts related to well logging. It covers topics like borehole environment, fluid distribution around wells, invasion ratios for different porosity rocks, flushed and uninvaded zones, depth of investigation, formation resistivity, invasion and resistivity profiles, and provides examples of dual laterolog and induction logs through water-bearing and hydrocarbon-bearing zones. The document contains definitions of important parameters and concepts used in well logging and provides explanations for calculating invasion diameters and interpreting well log curves.

1. PETE-303: Well Logging
Spring 2016
Khaled Abdelgawad
Department of Petroleum Engineering
KFUPM ENGINEERING
Well Logging

2. Borehole Environment

3. Well QATIF-46
Borehole Environment 3

4. Well QATIF-46
Fluid Distribution around a Well 4

5. Well QATIF-46
Borehole Environment 5
h : Bed Thickness
hmc : Mudcake Thickness
dh : Borehole Diameter
di : Diameter of flushed zone.
dj : Diameter of Transition zone
Shy: Hydrocarbon saturation
Sw : Water Saturation
Sxo : Flushed zone water saturation
Sro : Residual HC. saturation
Rm : Mud resistivity
Rmc : Mudcake resistivity
Rmf : Mudfiltrate resistivity
Rs : Adjacent bed resistivity
Rt : True formation resistivity
Rxo : Flushed zone resistivity
Rw : Formation water resistivity

6. Well QATIF-46
Question
General for the same drilling fluid and layer
permeability, invasion diameters are:
dj/dh = 2 for ？ porosity rocks
dj/dh = 5 for intermediate porosity rocks
dj/dh = 10 for ？ porosity rocks
High or Low porosity? And why?
6

7. Well QATIF-46
Invaded zone (Cont.)
For the same drilling fluid:
The amount of invasion which takes place is dependent upon the
permeability of the mudcake and not upon the porosity of the rock.
An equal volume of mud filtrate can invade low porosity and high
porosity rocks.
The solid particle in the drilling muds bridge and form an impermeable
mudcake.
7

8. Well QATIF-46
Invaded zone (Cont.)
The mudcake then acts as a barrier
to further invasion.
Because an equal volume of fluid
can be invaded before an
impermeable mudcake barrier
forms, the diameter of invasion
will be greatest in low porosity
rocks.
Low porosity rocks have less
storage capacity or pore volume to
fill with the invading fluid, and, as
a result, pores throughout a
greater volume of rock will be
affected.
8

9. Well QATIF-46
Invaded zone (Cont.) 9
General invasion diameters are:
dj/dh = 2 for high porosity
dj/dh = 5 for intermediate porosity
dj/dh = 10 for low porosity

10. Well QATIF-46
Flushed zone
The flushed zone extends only a few
inches from the well bore and is part
of the invaded zone
Completely cleared of its formation
water (Rw) by mud filtrate (Rmf)
The remaining oil is called Residual oil
Sro: Residual oil saturation (ROS)
Sxo: Flushed zone water saturation
10
Sro = 1 – Sxo
Sro
Sxo
Uninvaded zone
Flushed zone

11. Well QATIF-46
Uninvaded zone
Located beyond the invaded zone.
Pores are uncontaminated by mud
filtrate and saturated with formation
water (Rw), oil, or gas.
Water saturation (Sw) of the uninvaded
zone is an important factor in reservoir
evaluation.
Recoverable oil.
11
Shc = 1 – Sw
SoR=Shc – Sro =(1-Sw)-(1 - Sxo)=Sxo– Sw
Sro
Sxo
Shc
Sw
Uninvaded zone
Flushed zone

12. Well QATIF-46
Depth of investigation 12
A distance that characterizes how
far a logging tool measures into
the formation from the face of the
tool or the borehole wall.
The depth of investigation
summarizes the radial response of
the measurement in one or more
directions.

13. Well QATIF-46
Formation Resistivity 13

14. Well QATIF-46
Formation Resistivity
Which of these “Archie Blocks” has the largest resistivity?
14
Rt=100 Rw Rt=25.5 Rw Rt=25 Rw
@ a=1
n=2
m=2
> >
> =
BVW= 0.1 BVW= 0.198 BVW= 0.2
Bulk Volume Water =𝝓 × 𝑺 𝒘

15. Well QATIF-46
Formation Resistivity 15

16. Well QATIF-46
Invasion and Resistivity Profiles 16
Step Profile
Transition Profile

17. Well QATIF-46
Invasion and Resistivity Profiles
Annulus Profile
• The annulus profile represents a
fluid distribution that occurs
between the invaded
• zone and the uninvaded zone and
only exists in the presence of
hydrocarbons.
• In the annulus zone, pores are
filled with formation water (RW )
and residual hydrocarbons.
17

18. 18

19. Well QATIF-46
Example 19
Dual laterolog curves
through a water-
bearing zone.
Rmf ~ Rw

20. Well QATIF-46
Example
Dual induction log
curves through a
water-bearing zone.
Rmf> 3Rw
20

21. Well QATIF-46
Dual induction log curves through a hydrocarbon-bearing zone 21
Rmf> 3Rw