presentation-sami ullah 01-161091-082.pptx

7/29/2019 Presentation-Sami ullah 01-161091-082.pptx

http://slidepdf.com/reader/full/presentation-sami-ullah-01-161091-082pptx 1/12

SPONTANOUS

POTENTIAL

LOGS



TYPES OF ELECTRIC LOGS

2

ElectricLogs

ResistivityLogs

InductionLogs

S.P. LogsPorosity

Logs



INTRODUCTION OF S.P

Natural currents flowing within the earth causea voltage to be produced.

The spontaneous potential log,

commonly called the SELF POTENTIAL log or SP

log, is a passive measurement taken by oil industry

well loggers to characterise rock formation

properties.

The log works by measuring small electricpotentials (in millivolts) between depths in the

borehole and a grounded voltage at the surface.

3



BASIC PRINCIPLE

Usually while drilling, drilling fluid invade the formation,changes in the resistivity are measured by the tool in the

invaded zone.

If water based mud is used and oil is displaced,

"deeper" resistivity logs (or those of the "virgin zone")

will show lower conductivity than the invaded zone. If oil based mud is used and water is displaced, deeper

logs will show higher conductivity than the invaded

zone.

This provides not only an indication of the fluids

present, but also, at least quantitatively, whether theformation is permeable or not.

4



5



METHODOLOGY Spontaneous potential is a DC voltage.

Voltage is measured between a ground electrode atthe surface and an electrode lowered down the well.

When formation water is saltier than the drilling mud,shale has a positive SP response and sand a negativeSP response.

Specialized probes are used to connect theinstrumentation

Probes must be non-polarizing

6



The SP device measures naturally occurring(spontaneous) potential in the well bore.

This tool utilizes a single moving electrode in the

borehole and a reference electrode at the surface,

usually located in the mud pit.

The SP curve therefore is a record of the potential

difference which exists between the surface electrode

and the moving electrode in the borehole.

7

SP TOOLS



1. The spontaneous potential tool measures

natural electrical potentials that occur in boreholes and generally distinguishes

porous, permeable sandstones from intervening shales.

2. The "natural battery" is formed when the use of drilling

mud with a different salinity from the formation waters, causes two solutions to be in contact that have different ion

concentrations.

3. Ions diffuse from the more concentrated solution

(typically formation water) to the more dilute. The ion flow constitutes electrical current, which generates a

small natural potential measured by the SP tool in millivolts.

S.P TOOL



Measurement of self-potentials

• Voltage is measured b/w ground electrode andan electrode lowered down the well.

• When formation water is saltier than the drillingmud, shale has a positive SP response andsand a negative SP response.

S.P LOG



USES OF S.P LOGS

The SP tool is one of the simplest tools and is

generally run as standard when logging a hole,

along with the gamma ray. SP data can be used to

find:

1. Where the permeable formations are

2. The boundaries of these formations

3. Correlation of formations when compared with data from

other analogue wells4. Values for the formation-water resistivity

10



Applications:-

SP logs are used to distinguish shale from sand

and to estimate percent sand.

In addition, it can be used to estimate pore water salinity inclean sands.

The SP log is also used in correlation work especially inconjunction with resistivity logs.



SPONTANEOUS POTENTIAL LOG

S.P logs comes out

like in this form.

presentation-sami ullah 01-161091-082.pptx

Documents