3.SP LOGs1

8/3/2019 3.SP LOGs1

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Presented By:

Ali Hameed and Muhammad Zubair Idrees

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` Introduction

` History

` Spontaneous Potential (SP) Log

` Operation

` Principle

` Log Presentation

` Tools

` Applications

` Reference

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Spontaneous potential(SP),

or self potential, is a naturally

occurring electric potential

difference in the earth,

measured by an electrode

relative to a fixed reference

electrode.

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` The first electric log was recorded in 1927 in a well in the small oil field of

France.

` In 1929, electric resistivity logging was introduced on a commercial basis

in Venezuela, the United States, and Russia.

` In 1931 the spontaneous potential measurement was included with the

resistivity curve on the electric log.

` In 1931 the Schlumberger brothers, Marcel and Conrad perfected a

method of continuous recording.Its usefulness has been realized for over 50 years

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The spontaneous potential log

measures the natural or

spontaneous potential differences

that exists between the borehole

and the surface in the absence of

any artificially applied current.

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` An electrode (usually lead) is

lowered down the well and an

electrical potential is registered at

different points in the hole with

respect to surface electrode.

` In order to record a potential the

hole must contain conductive mud,

as it cannot be recorded in air or oil-

base mud.

` Logging rate is approximately

1500m per hour and recordings are

continuous.

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` Mudcake Potential

Movement of charged ion through mudcake into permeable formation

` Shale wall Potential

Flow of fluids from borehole into shale formation.

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Electro chemical potential is

sum of Liquid junction and

membrane potential.

Fig1: Electrochemical Potential:

Liquid junction & membrane

potential

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Liquid Junction:The greater the contrast in salinitybetween mud filtrate and formationwater, the larger is the potential

E J = K1 log10(aw /amf )

Membrane Potential:Na+ ions penetrates through theshale from the saline formationwater to the less saline mudcolumn, a potential is set up.

EM = K2 log10(aw /amf )

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SP is presented in :

Track 1

mnemonic of SP.

No absolute scale.

Small bar represents a change of

10 mV.

Linear Scale

Recorded in the leftmost track of

the log suite, together with the GR

log.

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` In sand A, Rw is less than Rmf;i.e., formation water is saltier than

the mud filtrate.

` In sand B, the SP deflection is

less than in sand A, indicating a

fresher formation water.

` In sand C, the SP is reversed,indicating formation water that is

fresher than the mud filtrate (Rw >

Rmf).

` We may guess that, at about 7000

ft, Rmf and Rw are equal.

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` Electrodes

` A galvanometer

` Small 1.5 V battery

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Calibration:

` A small battery and a potentiometer is placed in series between the two

electrodes.

` The logging engineer can adjust the potentiometer so that the SP

appears in track 1.

` Remove all extraneous potentials to the membrane potential, the SP

needs to be normalised in a computing centre so that there is no

potential (SP=0.0MV) opposite shale beds.

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` Lithological Indicator

` Detection of Permeable beds

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The relationship between the SP and the

resistivities of the mud filtrate and the

formation water are determined

SP = -K log (Rmfe/Rwe)

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` When mud filtrate salinities are

lower than connate water

salinities (i.e., Rmf is > Rw), the

SP deflects to the left (the SP

potential is negative). This is

called a normal SP.

` When the salinities are reversed

(i.e., salty mud and fresh

formation water, Rmf < Rw), the

SP deflects to the right. This is

called a reverse SP.

` Other things being equal, there is

no SP at all when Rmf = Rw.

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V shale = (SPclean ± SPlog)/(SPclean-SPshale)

Vshale: shale volume

SPclean: maximum Sp deflection from clean wet zone

SPlog: Sp in the zone of interest (read from the log)

Spshale: SP value at the shale baseline (often considered to be zero)

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The Sp is used primarily as a lithology indicator and as a correlation tool.It

has other uses as well:

` Detecting permeable beds

` Rw determination

` Correlation from well to well

` Shale Volume Indicator

` Geological Information

` Detecting bed boundaries

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`GEOLOGICAL INFORMATION

`SHALE VOLUME CALCULATION

` Correlation and Facies

` Permeable Beds

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` Geological interpretation of Well Logs by Malcolm Rider

` http://en.wikipedia.org/wiki/Spontaneous_potential

` http://en.wikipedia.org/wiki/Spontaneous_potential_logging

` http://www.kaskus.us/showthread.php?t=899212&page=165

` http://www.petrolog.net/webhelp/Logging_Tools/sp/sp.html

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THANK YOU!

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3.SP LOGs1