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Penilaian Formasi Lanjutan

V 1 - 2006

Per m eab le Zon e Log s

Spontaneous Potential (SP) Log

R. Widijanto

September 29, 2006

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Agenda

Permeable Zone Logs

Basic Principle of Spontaneous Potential (SP)

Log1. Spontaneous Potential (SP) Log

2. SP Curve

Interpretation of Spontaneous Potential (SP)Log

1. Computation Rw From SP

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Permeable Zone Logs

1. Permeable Zones

Sands

Carbonate

2. Log used:

Spontaneous Potential (SP) Log (electrical measurement)

Gamma ray (GR) Logs (nuclear measurement)

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Basic Principle of Spontaneous Potential (SP) Log

1. Spontaneous Potential (SP) Log

SP Log is recording of the different in electrical potential between afixed electrode at the surface and a movable electrode in theborehole

Hole must be filled with conductive mud

No SP can be measured in

Oil-based mud

Empty holes

Cased holes

Scale in millivolts

2. SP curve is used to:1. Select permeable zones

2. Provide Rw values

3. Estimate the degree of shalines of reservoir rock

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Spontaneous Potential Curve

Limited to water-basedmud systems.

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SP Measurement

N

The SP is

measurementagainst depthof the potentialdifference

between thevoltage in thewellbore and anelectrode at thesurface

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SP Current Flow

The strength and direction ofthe current loop is dependenton the relative resistivities ofthe formation and the filtrate

SP

millvolts

Ek = Electrokinetic

Ej = Liquid JunctionEm= Membrane

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Salinity effects on the SP

The primary SP responseis due to the relativesalinities between themud filtrate and theformation fluids

Reverse SP Rw > RmfReverse SP Rw > Rmf

Normal SP Rw < RmfNormal SP Rw < Rmf

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Effect of bed thickness and resistivity on curve shape

R

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Shape of SP

Shape and amplitude controlled by:

relative resistivity of fluids

resistivity of the formation(hydrocarbons, porosity)

permeability

bed thickness

clay type and content

hydrocarbon suppression

tight streak

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Interpretation of Spontaneous Potential (SP) Log

1. Total Potential, SSP

2. Calculate Rw

1. Equations

2. Charts

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Resources

The Society of Petrophysicists and Well LogAnalysts: www.spwla.org

Society of Petroleum Engineers: www.spe.orgFormation Evaluation:http://www.spe.org/spe/jsp/basic/0,,1104_1714_1

003934,00.html

Schlumberger Interpretation Chart: www.slb.com

orhttp://content.slb.com/Hub/Docs/connect/reference/Chartbook/

http://www.spe.org/spe/jsp/basic/0,,1104_1714_1003934,00.htmlhttp://www.spe.org/spe/jsp/basic/0,,1104_1714_1003934,00.htmlhttp://www.slb.com/http://content.slb.com/Hub/Docs/connect/reference/Chartbook/http://content.slb.com/Hub/Docs/connect/reference/Chartbook/http://content.slb.com/Hub/Docs/connect/reference/Chartbook/http://content.slb.com/Hub/Docs/connect/reference/Chartbook/http://www.slb.com/http://www.spe.org/spe/jsp/basic/0,,1104_1714_1003934,00.htmlhttp://www.spe.org/spe/jsp/basic/0,,1104_1714_1003934,00.html

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Question?

http://content.slb.com/Hub/Docs/connect/reference/Chartbook/http://content.slb.com/Hub/Docs/connect/reference/Chartbook/http://content.slb.com/Hub/Docs/connect/reference/Chartbook/