b.In preparing the log, the 0.25 foot reading, normal, arrangement should be plotted at the depth as readfrom the marked cable and the 2.5 ft readings about one foot above this point. This is because the cablemarkings have been measured from the current electrode. For the lateral arrangement, the values areplotted just as is the case for the normal arrangement. If the 10 ft normal is used, its reading should beplotted about 5 ft above the marked cable reading.2-6.2 Significanceof0.25ftSpacing. The reading obtained with the 0.25 ft spacing is heavily influenced by the fluid inthe well bore and hence it reads only some fraction of the formation resistively. However, the short spacing enables youto see changes in resistively with greater detail. With this electrode spacing, formations having a thickness of about 6inches or greater can be detected. Because of this ability to see small detail, the 0.25 ft curve should be used to "pick"formation boundaries.2-6.3 Significanceof2.5ftSpacing. The 2.5 ft electrode spacing provides you with very nearly the true formationresistively for wells having diameters up to about 16 inches and for formations thicker than about 5 ft. For largerdiameter wells or thinner formations, the measured resistively will depart somewhat from the true. For qualitativeinterpretation this departure is not significant. Because the 2.5 ft curve provides you with the formation resistively, it isused to identify the type of material penetrated.2-6.4 SignificanceoftheLateralLog. The lateral log obtained with the equipment is made by a combination of either the0.25 or 2.5 ft electrode with the 10 ft. electrode. Because the 10 ft electrode is at a distance fairly large compared witheither of the other two, the interpretation is essentially the same as for the normal log after using the appropriatecorrection factors.a.For the 0.25 lateral log, the meter factor is 1.025.b.For the 2.50 lateral log, the meter factor is 13.33.2-6.5 InterpretationofResistivelyValues.a.In interpreting the resistively values obtained, clays and shales will be low resistive and sands, gravels,sandstones and limestones will be high resistive. Igneous and metamorphic rocks (such as granites andgneisses) will most generally be extremely high resistive.b.The exact range of numerical values will depend upon the:1.Type of earth material making up the formation.2.Degree of cementation of the formation.3.Water quality of the formation water.4.Porosity of the formation.5.Diameter of the well bore.6.Resistively of the fluid in the well bore.2-10
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