Applications of the Array Induction Tool in Saudi Arabia

Abstract

SPE Members Abstract Since its introduction in Saudi Arabia in 1993, the Array Induction Tool (AIT) has been run extensively in a wide variety of petrophysical environments. These include fresh mud, salty mud, high and low resistivity formations, hydrocarbon-bearing or water-bearing reservoirs in carbonates and clastics sequences. In some examples, the AIT was also run in conjunction with the Phasor Induction (PI) or Dual-Laterolog for comparison purpose. As with any resistivity device, the AIT's primary product, an accurate Rt measurement, should not be overlooked. However, owing to the AIT's multiple vertical resolutions and depths of investigation, we found that the tool yields additional information about the reservoirs that is not possible with older induction tools. The AIT improves the estimation of Rt in cases of thin laminations, complex invasion profiles or when the borehole correction is critical (wash-out, salty mud, high resistivity). In many instances, permeable beds that are invaded are much easier to identify with the AIT than with dual depths of investigation induction or laterolog tools. A typical case is the interpretation of annul us. Finally, we show the AIT characteristic response in a thin magnetic marker. Introduction Induction logging has long been the primary resistivity log for decades. In a drastic departure from past induction tools which rely on hardware focusing to provide two induction measurements at two depths of investigation, the Array Induction tool (AIT) utilizes the raw data from a simple array of eight receivers to derive by software means a set of logs with matched vertical resolution and with five median depths of investigation. The increase in data permits for the first time, more detailed investigations in the radial direction, which can be of value in complicated invasion profiles or oil-based mud systems. Another departure concerns environmental corrections. Conventional induction logs are usually presented uncorrected for environmental effects. It is well known that borehole effect is significantly different for the deep and medium induction, especially in large boreholes. Another challenge to interpreting deep induction, medium induction and spherically-focused logs is shoulder bed and invasion effects. Because of the different physics underlying previous resistivity measurements, certain combinations of bed thickness and resistivity contrast in invaded beds can mask or cause false curve separation, and thus obscure the resistivity interpretation. The AIT logs are always presented fully borehole corrected, and optimized such that the responses are a good compromise between radial and vertical focusing. Numerous papers have been written about the AIT tool design, physics and processing algorithm, so we invite the interested reader to refer to these documents. P. 581