The apparent formation water resistivity (Rwa), the Ro overlay, and the Resistivity (Rt) Porosity (0) crossplot are among several methods used in picking out hydrocarbon-bearing zones. One condition essential to the use of these techniques is that the formation water resistivity (Rw) remains constant or varies in a narrow range over the interval analyzed. If this condition is not met, a zone with water resistivity abnormally higher than that of other zones within the interval of interest can be mistaken for a hydrocarbon-bearing zone. Also, a hydrocarbon-bearing zone with abnormally low water resistivity can be over looked. The use of Resistivity (Rt) Spontaneous Potential (SP) crossplot together with the Rt 0 crossplot can prevent such gross misinterpretations. This paper reviews the concepts of the Rt SP crossplot, its advantages and limitations. Field examples illustrating the proposed interpretation techniques are discussed.

Keywords:
well logging, field example 3, water trend line, SP crossplot, log analysis, hydrocarbon-bearing zone, field example 2, Crossplot, field example 1, porosity
Subjects:
Formation Evaluation & Management, Open hole/cased hole log analysis
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1984. Society of Petrophysicists & Well Log Analysts
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