Schlumberger

Technical Paper: Wireline Dielectric Measurements Makes a Comeback: Applications in Oman for a New Generation Dielectric Log Measurement

Society: SPWLA
Paper Number: 2010fe
Presentation Date: 2010
 

Abstract

The contribution a dielectric measurement could make to petrophysics has been known but unfulfilled for 50 years. 27 years ago a fixed pad logging tool was developed to acquire a single frequency dielectric measurement. It was limited by hole rugosity, high salinity, and a simple response algorithm.

The new tool measures formation dielectric at 1-4 inches depth of investigation with 4 frequencies, 2 polarizations, 4 transmitter receiver spacing’s, and 2 shallow probes to determine the mudcake and mud properties. The antennas are on an articulated pad to improve contact inn rugose boreholes. The different frequencies provide a measurement of dielectric dispersion to quantify textural information . Low frequency electro-magnetic (EM) measurements from laterolog and induction tools are affected by this texture represented in their response equations by the Archie parameters m and n. The dielectric processing outputs when combined with the density--neutron porosity and lithology are water filled porosity, water salinity, mud cake thickness, and a textural index. From this texture a single Archie parameter of m=n is derived. These outputs are used to extrapolate the low frequency EM formation response which is compared with the measured shallow resistivity. This comparison provides verification of the dielectric log and interpretation model. The primary dielectric product is an almost parammeter-independeent measurement of the water volume within 1-4-in of the borehole. To obtain the equivalent shallow water saturation from conventional EM requires knowledge of fluid mixture salinities and Archie exponents.

Four logs in Oman show the robustness of this new measurement of shallow water saturation. The first was in laminated sand-shale to verify the presence of oil in an exploration well. The second was in a carbonate to quantify the amount of residual heavy oil. The third was in a clastic reservoir with low contrast pay to evaluate the residual oil saturation independent of resistivity. The fourth well was in an ultra-high salinity intra-salt carbonate reservoir. Objective was to evaluate Sxo and textural parameters in this challenging environment.

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