INDUCTIVE SOURCE DESIGN FOR INDUCTIVE FRACTURE DETECTION

Abstract

Traditional inductive logging uses sources whose focussing input waveform does not change with borehole position. While this arrangement facilitates hardware design, the resolution which it provides varies from formation to formation, and is only accidentally optimal for any given sound position. Optimization theory provides a method for designing a distributed inductive borehole source array , which adaptively maximizes the response from an unknown inclusion in a known formation. The adaptive source waveform shaping can be hardwired or can be simulated using simpler source data. The independent information used for the adaptive focussing can be geometric in nature, such as FMS logs, or can be physical property estimates.

Source optimization is particularly important when attempting to detect a subtle feature, such as a fracture in a geothermal field, using triaxial source and triaxial receiver measurements, such as has been suggested in recent literature. A few simple numerical simulations demonstrate why this is so.