chapter 6 - new mexico institute of mining and...
TRANSCRIPT
Chapter 6
SP (Spontaneous Potential) Log
Lecture notes for PET 370
Spring 2012
Prepared by: Thomas W. Engler,
Ph.D., P.E.
SP (Spontaneous Potential) Log
• Identify permeable bed boundaries
• Stratigraphic correlations
• Estimation of shale content Vsh for shaly sand
formations.
• Determination of formation water resistivity, Rw
USES
+
-
+ -
Concentrated NaCl Sol’n
Dilute NaCl Sol’n
Cl -
Na +
Diffusion Potential
Porous medium
+
-
+ -
Concentrated NaCl Sol’n
Dilute NaCl Sol’n
Cl -
Na +
Membrane Potential
Shale membrane
SP Log Background
Schematic of diffusion-potential
generating cell Schematic of a membrane-potential
generating cell
Definition of Potential Cells
SP Log Background
Origin of SP Curve
Electrochemical
Membrane potential
Electrochemical
Diffusion potential
Electrokinetic
potentials
SP Log
Estimation of shale content Vsh
Schematic SP curve in sand/shale sequence
(Bassiouni, 1994)
Application
Estimated from linear relationship
of SP curve:
Vsh = 1 - EPSP/ESSP
where,
EPSP is the response in the shaly
zone of interest
ESSP is the response in the
adjacent, clean zone
Assumptions
zones of same salinity, shale
type....
Typically, overestimates volume of
shale
SP Log Application
Identification of boundaries (Helander, 1983)
SP Log Application
Stratigraphic Correlation
SP Log Application-Rw
Procedure to Obtain Rw
• Identify the shale baseline and clean sand lines on the SP log. The
difference is SP.
• Calculate the formation temperature
• Convert (Rmf)Tm => (Rmf)Tf
• If necessary, correct SP for bed thickness and invasion effects. Read bed
thickness, h and invaded resistivity, Ri. Obtain SSP.
• If necessary, Convert Rmf @ Tf to Rmfe @ Tf.
• Calculate Rwe by:
• Convert Rwe to Rw.
f0.133T61
SSP
10*mfe
Rwe
R
SP Log Application-Rw
Bed thickness/invasion correction
(Western Atlas, 1992)
SP Log Application-Rw
Procedure to Obtain Rw
• Identify the shale baseline and clean sand lines on the SP log. The
difference is SP.
• Calculate the formation temperature
• Convert (Rmf)Tm => (Rmf)Tf
• If necessary, correct SP for bed thickness and invasion effects. Read bed
thickness, h and invaded resistivity, Ri. Obtain SSP.
• If necessary, Convert Rmf @ Tf to Rmfe @ Tf.
• Calculate Rwe by:
• Convert Rwe to Rw.
f0.133T61
SSP
10*mfe
Rwe
R
SP Log Application-Rw
Procedures to Obtain Rw
Rmfe=0.03
Rw=0.20
SP Log Application-Rw
Example
SP = mV
Ri = ohmm
H = ft
SP Log References
Bassiouni, Z: Theory, Measurement, and Interpretation of Well Logs, SPE
Textbook Series, Vol. 4, (1994)
Chapter 6
Dewan, J.T.: Essentials of Modern Openhole Log Interpretation, Pennwell
Publishing, Ok (1983)
Helander, D.P.: Fundamentals of Formation Evaluation, OGCI
Publications,Tulsa, OK (1983)
Schlumberger, Log Interpretation Charts, Houston, TX (1995)
Western Atlas, Log Interpretation Charts, Houston, TX (1992)