Other Electrode and Toroid Devices
Electrode devices have been put to many other uses than those described in Chapter 5, the earliest of these being the measurement of the resistivity of the invaded or flushed zone Rxo. Historically, the first use of the invaded-zone resistivity was, in the absence of any other measurement, to make an estimate of the formation porosity. Since then Rxo has found many applications. In earlier chapters we saw that Rxo, when compared with Rt, gives a visual indication of permeable zones and evidence ofmoved hydrocarbons. In Chapter 5 we saw the need for Rxo in obtaining a better estimate of the deep-resistivity Rt. Rxo can be combined with other information to determine the water saturation of the invaded zone, Sxo, and thereby estimate the efficiency of hydrocarbon recovery. Sxo can also be a useful indicator of hydrocarbons on its own.
KeywordsDrill String Borehole Wall Guard Electrode Toroid Device Core Photograph
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