A Result of SP Log Interpretation
- Paulo Varjao De Andrade (Conselho Nacional Do Petroleo)
- Document ID
- Society of Petroleum Engineers
- Journal of Petroleum Technology
- Publication Date
- November 1955
- Document Type
- Journal Paper
- 59 - 60
- 1955. Original copyright American Institute of Mining, Metallurgical, and Petroleum Engineers, Inc. Copyright has expired.
- 5.8.5 Oil Sand, Oil Shale, Bitumen, 1.2.3 Rock properties, 5.6.1 Open hole/cased hole log analysis, 1.6 Drilling Operations
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Since 1949, attention has been directed in this laboratory to the interpretation of SP logs. It has been the aim of the work to get connate water resistivities to use in quantitative interpretation of the resistivity curves. Wyllie's theory was taken as the fundamental working hypothesis as it would provide a correct theoretical background to support the results. In order to have an idea of the precision of the method, it was decided to make a series of interpretations in wells which produced only water and to compare the calculated results with resistivities obtained from chemical analysis of water samples.
Several water analyses and electrical logs were available from wells in the Sergi sands in several fields of the Bahian Reconcavo. The Sergi sands are the highest member of the Brotas formation, presumably of Lower Cretaceous age, and were deposited all over the basin. They constitute a homogeneous body and can be correlated over distances of tens of miles with only minor changes in lithology. The upper part of the Sergi known as "C zone," is a medium to fine grained sandstone, medium consolidated to friable, with finely disseminated clay, 15 to 30 ft thick, good porosity and permeability. Fig. 1 shows a log of part of the upper Sergi with the shale section overlying it.
Water samples came from formation tests, being collected in the lower part of the column. In case of mud contamination, they were discarded. Analysis comprised routine determinations of chloride, sulfate, bicarbonate and carbonate, calcium and magnesium. Sodium was calculated by difference. Resistivities of water and mud were obtained using either the Schlumberger salinity-resistivity chart or a combination of the said chart with Dunlap's method (the low sulfate content of the brines made this method very simple and accurate). Bottom-hole temperatures were available either from log headings or from direct measurements made with a maximum thermometer. In order to avoid the influence of resistivity on the amplitude of the SP "peak," only water wells were used in this study. Corrections for bed thickness were unnecessary in the wells studied. All wells were rotary drilled.
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