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Line 20: + + − The first step in the interpretation of the SP log is the establishment of “sand” and “shale” lines, as shown in Figure 1. These are arbitrary limits, with the sand lines normally representing the maximum deflection to the left and shale lines representing the maximum deflection to the right (in shales). Deflections to the left of the shale line are regarded as normal or negative, and correspond to porous and permeable zones containing a more saline interstitial water than the drilling mud (''R''<sub>w</sub> R<sub>mf</sub>).+ − − − If the mud is more saline than the formation water, the SP currents flow in the opposite direction and the corresponding deflection will be to the right of the shale line. Such a deflection is considered to be reversed or positive (Figure 2). If there is no salinity contrast between the mud and the formation water, no SP currents are generated and no deflection will be observed (SP = 0).+ − +
Water resistivity determination (view source)
Revision as of 22:06, 20 January 2014
, 22:06, 20 January 2014→SP method
==SP method==
==SP method==
[[file:determination-of-water-resistivity_fig1.png|left|thumb|{{figure number|1}}Example of a normal SP deflection. Copyright: Schlumberger Educational Services, 1987.]]
===Principle===
===Principle===
[[file:determination-of-water-resistivity_fig2.png|thumb|{{figure number|2}}Example of a reverse SP deflection. (From <ref name=pt04r3>Dewan, J. T., 1983, Essentials of modern open-hole log interpretation: Tulsa, OK, Penn Well Books.</ref>.)]]
[[file:determination-of-water-resistivity_fig1.png|thumb|{{figure number|1}}Example of a normal SP deflection. Copyright: Schlumberger Educational Services, 1987.]]
The first step in the interpretation of the SP log is the establishment of “sand” and “shale” lines, as shown in [[:file:determination-of-water-resistivity_fig1.png|Figure 1]]. These are arbitrary limits, with the sand lines normally representing the maximum deflection to the left and shale lines representing the maximum deflection to the right (in shales). Deflections to the left of the shale line are regarded as normal or negative, and correspond to porous and permeable zones containing a more saline interstitial water than the drilling mud (''R''<sub>w</sub> R<sub>mf</sub>).
[[file:determination-of-water-resistivity_fig2.png|thumb|{{figure number|2}}Example of a reverse SP deflection. (From <ref name=pt04r3>Dewan, J. T., 1983, Essentials of modern open-hole log interpretation: Tulsa, OK, Penn Well Books.</ref>.)]]
If the mud is more saline than the formation water, the SP currents flow in the opposite direction and the corresponding deflection will be to the right of the shale line. Such a deflection is considered to be reversed or positive ([[:file:determination-of-water-resistivity_fig2.png|Figure 2]]). If there is no salinity contrast between the mud and the formation water, no SP currents are generated and no deflection will be observed (SP = 0).
The magnitude of deflection from the shale base line to the maximum deflection developed in a thick, clean, waterbearing sand is referred to as the ''static SP'', or SSP.
The magnitude of deflection from the shale base line to the maximum deflection developed in a thick, clean, waterbearing sand is referred to as the ''static SP'', or SSP.