METHOD AND APPARATUS FOR SUPPRESSION OF THE AIRWAVE IN SUBSEA EXPLORATION

摘要

The far zone “airwave” that arises when surveying subsea formations is greatly diminished by deployment of the transmitter combining mutually orthogonal horizontal electric and magnetic dipoles with the electric and magnetic dipole moments being locked in a special relationship. At each of the operating frequencies, the amplitude and phase characteristics of the transmitter electric and magnetic dipole moments are determined either from a supplementary measurement earned out using natural and/or controlled field sources, or by minimization of the vertical magnetic field at a remote receiver. Similar results can be obtained when data acquired in two independent surveys—one with the horizontal electric dipole transmitter pointing in one direction and another with a horizontal magnetic dipole transmitter pointing in the orthogonal direction and towed over the same or close positions—are linearly combined to minimize the vertical component of the combined magnetic field at remote receivers.

主权项

1. A “Low-Bz” transmitter for marine electromagnetic, surveying or monitoring comprising:
an electric dipole combined with a magnetic dipole, which has the horizontal component of its magnetic dipole moment orthogonal to the direction of the horizontal component of the current dipole moment of the electric dipole, and which varies in time in accordance with the law assuring suppression of the vertical magnetic field at large horizontal separations from the transmitter either within the operational time window or at each operating frequency chosen for surveying.