Method for marine geoelectrical exploration with electrical current focusing

摘要

Methods and apparatus for marine geoelectrical exploration use a dipole source, to send electric pulses into the medium. Geometrical probing is performed during current pulses, and probing on transient processes is performed in the intervals. Measurements are taken using measuring apparatus mounted on the seafloor. The apparatus includes, five electrodes: a central electrode with four others around it. During the current flow period and intervals between current pulses, the second electric potential difference between external electrodes and the central electrode, as well as the first electric potential difference between three pairs of external electrodes is measured. Measured values are used to calculate three sets of standard electrical parameters. A model of the medium is produced from the parameters. Techniques disclosed provide for elimination of lateral effect on probing results, and delineation of hydrocarbon accumulation with high contrast.

主权项

1. A method for estimating at least one geophysical property, the method comprising:
using a plurality of transmitter electrodes distributed in a conductive medium, periodically passing rectangular current impulses through the media; collecting a sequence of sounding data between each of the impulses with a receiver electrode disposed between the plurality; determining a first difference and a second difference of the electric potential between points of the collected data; when each of the transmitters is excited, acquiring a focused measurement by simultaneously calculating a combination of at least one orthogonally weighted measurement and at least one axially weighted measurement obtained by the receiver, wherein the weighting is obtained from a condition of equipotentiality in four outer electrodes of the receiver; using the focused measurement to estimate at least one of the following geophysical properties of the geological formation: σ(iωσ0ητ)—frequency-dependent electrical conductivity of elements of the medium, σ0—electric conductivity of elements of the medium, η—a coefficient of induced polarization, and τ—a time decay constant of the induced polarization; according to the relationship
∇×∇×E(iω)=iωμ·σ(iωσ0ητ)·E(iω)where
∇× represents operator curl (or rotor); E (iω) represents the electric field of a dipole source, expressed in the equation in frequency domain, μ represents magnetic permeability,