1 Basic of Log Interp

7/30/2019 1 Basic of Log Interp

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Open Hole Well Logging: Tools,

Utility and

How to Interpret the Chart

Miftahul Firdaus

Petroleum Engineering UPNVeteran Yogyakarta

Yogyakarta, 19 July 2008


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The Short Course

What you should know

Basic hydrocarbon geology

Basic reservoir engineering

Basics of drilling a well

Basic Logging tools?

What you should learn..?

What logging means

Understanding of log analysis

Simple log analysis (Quick Look)Comparison to core

Introduction to computer (S/W) based interpretation


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The Logging Environment & Evaluation of HCPermeable Zone Logs.

Spontaneous Potential Log (SP)

Gamma Ray Logs (GR)

Resistivity Logs.

Induction Logs

Lateral Logs

Porosity Logs.

Neutron Logs

Densitas Logs

Sonic Logs

Clean Formation Interpretation

Shaly Formation Interpretation

Contents :


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Logging Environment &

Evaluation of Hydrocarbon


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Definitions

Log

Sampling rate / logging speed

Vertical resolution

Depth of investigation

Invasion

Logging truck/unit

Logging tools


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THE LOGGING ENVIRONMENT


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Maxis acquisition system

Winch man

Wireline /field Engineer Acquisition Equipment

Wireline cable to

downhole toolsCable drum

UnitEngineClient (Witness)


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Logging Truck


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Type of Logging

Open hole

logging

Perforation &

Productionlogging

Cased hole

logging


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What does logging mean?

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Tool string is moving at a certain logging

speed, and data are recorded at certain

intervals called sampling rate.


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And we get a group ofwiggly lines called a log


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First well logs recorded in 1927


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Modern logs have

more measurements

but the principle is the

same

Gamma Ray (GR)

0 (GAPI) 150

SP (SP)

0 (MV) 200

FXND

50 (PU) 0

1:220 Ft Pad

-180 180

Rt from HALS

RX18

1 1000

1 1000

Rt from AITH

1 (OHMM) 1000

Mud Resistivity from HALS

1 1000

Mud Resistivity from AITH

1 (OHMM) 1000

AHTPR

5.00

7.75

12.01

18.62

28.85

44.72

69.81

107.43166.51

258.08

400.00

90 0 90

1700

1600

Gamma Ray (GR)

0 (GAPI) 150

SP (SP)

0 (MV) 200

FXND

50 (PU) 0

1:220 Ft Pad

-180 180

Rt from HALS

RX18

1 1000

1 1000

Rt from AITH

1 (OHMM) 1000


1 1000


1 (OHMM) 1000

AHTPR

5.00

7.75

12.01

18.62

28.85

44.72

69.81

107.43166.51

258.08

400.00

90 0 90

1700

Gamma Ray (GR)

0 (GAPI) 150

SP (SP)

0 (MV) 200

FXND

50 (PU) 0

1:220 Ft Pad

-180 180

Rt from HALS

RX18

1 1000

1 1000

Rt from AITH

1 (OHMM) 1000


1 1000


1 (OHMM) 1000

AHTPR

5.00

7.75

12.01

18.62

28.85

44.72

69.81

107.43166.51

258.08

400.00

90 0 90

1700

1600

Some times a large group of

log curves are grouped andcolor coded into an Image.

More on this later

Shading is often added to

make the log curves easierto read.


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Vertical Resolution + Sampling Rate

Coarse sampling rate Fine sampling rate


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Volume of measurementdepth of investigation

Depth of investigation of different measurements J-curves


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Invasion Process


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The Process of Invasion

Mud pressure in the annulus (Pm)

Hydrostatic pressure of fluid in the formation pores (Pr)

Pm must be kept greater than Pr

Prevent a well blowout

Forces drilling mud into the formation

Invasion happens solid particles on the formation wall & form a mud cake

Liquid that passes into the formation and pushes back some of reservoir

fluids , mud fi l t rate


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Invasion


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Invasion Profile
http://c/petro95/help/sp/spchart.html


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Nomenclature:

Borehole:Rm = Resistivity of mud.

Rmc = Resistivity of mud cake.

Flushed Zone:Rmf= Resistivity of mud filtrate.

RXO = Resistivity of flushed zone.SXO = Water Saturation of flushed zone.

Uninvaded or Virgin Zone:RT = True resistivity of formation.

RW = Resistivity of formation water.

SW = Formation Water Saturation.

RS = Resistivity of adjacent bed or shoulder bed resistivity.di = Diameter of invasion.

dh = Borehole diameter.

h = Bed thickness.


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Impact of Invasion on Resistivity Measurement

1. Flushed zone diameter (df.)Containing only Mud Filtrate (Rmf)Residual HydrocarbonResistivity of Flushed Zone (Rxo).Water Saturation of Flushed Zone (Sxo).Thickness ~ 6 inches.

2. Transition zone diameter (dj.)

May extend several feet.

3. Undisturbed zone:

Resistivity of Formation Water (Rw)

True Resistivity of Formation (Rt)

Water Saturation (Sw) .


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Fundamental Interpretation Relations

Definition of Resistivities


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A. Resistivity of Formation Water (Rw).

First, the tank is filled with water containing 10 % NaClto simulate an formation water.

The ratio V / I1 (volts/amperes) is Rw

VRw = ----- [ ohmm]

I1

B. Resistivity of Formation (Ro).Sand is poured into the water filled tank.The voltage is applied and a current I2 is measured.

VRo = ----- [ ohmm] Ro > Rw

I2


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Formation Factor, F

The Resistivity, Ro must be proportional to Rw since only the water conducts.

Ro1 = F Rw1Ro2 = F Rw2Ro3 = F Rw3

Thus,Ro = F Rw (1)

The proportionality constant F is termed the Formation Factor

Dimana F = Formation Resistivity Factor.

On general principles, F must be related to porosity by relation of the form :

1F = ----------- (2)

m

m = Cementation exponent, m = 1.3 - 2.2


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Archies Plot, Formation Factor (F) Vs Porosity () & Permeability (K)


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C. True Resistivity (Rt).Fraction of the pore water is replaced by oil (Sw < 1)

The same voltage, V, and current I3VRt = ----- [ ohmm] Rt > Ro

I3Rt = I Ro

(3)

where, I = Resistivity Index

1I = ----------- (4)

Sw nwhere, n = Saturation exponent ( 2)

Knowing Ro and Rt (from eq. 1,2,3&4), Water saturation (Sw) can be calculated :

Ro F. RwRt = ----------- , Sw n = ------------

Sw n Rt

This is the basic equation of log interpretation


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Logging Tools


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Standard Logging String (Triple Combo)

Formation Gamma Ray

Neutron Porosity

Density (Porosity)

Caliper (hole size)

Pad Resistivity (good v.resolution)Resistivity (good depth investigation)

Spontaneous Potential

Mud Resistivity


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Conveyance

Open Hole Measurements :

Wireline Logging.

LWD (Logging While Drilling)

Logging on Drill Pipe (TLC)

Tractor


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Why we log ?


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Why we log ?

Lithology (reservoir rock?) Resistivity (HC,water,both?)

Porosity (how much HC?)

What type of HC

Multiwell Plots


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Multiwell Plots

Documents

1 Basic of Log Interp