ABSTRACT:

Recently, Baker Atlas introduced a new wireline openhole Multi-component Induction service, the 3D ExplorerSM, for measuring transverse electrical anisotropy. The measurement enables operators to detect and accurately quantify hydrocarbon reserves in certain depositional environments, for example, in thinly bedded reservoirs. The service employs new sensors and data processing principles. The 3DEX logging tool contains a number of coils, parallel and transverse to the borehole trajectory. In deviated wells, electrical charges accumulated in the formation and currents across layer boundaries produce very complex responses. Mud, borehole shape, invasion, and other environmental complications affect logs. To develop a real time processing, we use measurements at multiple frequencies and combine them in such a way that most of the environmental effects vanish. We call the technique Multi-Frequency Focusing (MFF). In traditional processing of induction measurements, we correct for the skin effect to achieve linearity with respect to formation conductivity. On the contrary, in MFF we correct for the linear component and utilize the skin effect. An important part of MFF in deviated wells is the principle of mode separation. From the multitude of measurements we extract the so-called ‘TE mode’, or, the magnetic field produced by currents flowing in the plane of thin beds. Similar to a vertical well, the magnetic field of the TE mode depends exclusively on the conductivity in the horizontal direction. Mode separation allows us to accelerate the data processing and increase its stability. The sensitivity of MFF processed data to remote formation volumes does not depend on the distance between transmitter and receiver. As a result, we achieve a large depth of investigation with a relatively short spacing between transmitters and receivers. We illustrate the capabilities of this new approach with benchmark models and a case study.

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