RU2497156C2 - Method for offshore inductive aeroelectrosurvey based on geomagnetic field variations - Google Patents

Abstract

FIELD: physics.

SUBSTANCE: method involves performing aeromagnetic survey on a network of row (RM) and crossing (SM) routes and direct measurement of variations on a base magnetic variation station (MVS). Geomagnetic field variations are estimated separately based on discrepancies of the observed field at intersection points of RM and SM - indirect adjustments and on MVS - direct adjustments. Variation anomalies are calculated from the difference between direct and indirect adjustments. These anomalies are indicated on RM and SM and a map of variation anomalies is plotted. Sections of the rock with anomalous electrical conductivity are determined from the variation anomalies.

EFFECT: mapping an offshore sedimentary section based on eletroconductivity along with aeromagnetic survey in order to increase reliability of estimating geological inhomogeneities.

Description

The invention relates to inductive methods of electrical exploration and can be used in regional searches of mineral deposits and geological mapping.

A known method of aero-electrical exploration by the method of inductive dipole profiling [1], in which the source of the magnetic field (MP) is a magnetic dipole (for example, a frame) rigidly mounted on an airplane, and a measuring dipole placed in a towed nacelle represents a generator frame. During the survey, the amplitude and phase of the vertical component of the magnetic field are recorded, associated with the secondary field of currents flowing in the ground.

However, the method is sensitive to the mutual movement of the aircraft and the nacelle, the MP source can effectively irradiate the lower half-space only at low altitudes and at shallow depths, and a high-intensity MP source is required for profiling along the electromagnetic fields of the sedimentary cover covered with salt water.

The well-known "System of aeroelectromagnetic shooting in the time domain, method and software for obtaining data" No. 2005119284, consisting of:

a) a towed device attached to the aircraft, while the towed device includes a flexible supporting frame, including:

- section of the transmitter containing the transmitting device;

- section of the receiver containing the sensor device;

b) a transmitter shaper connected to the transmitter section and located at a distance from the transmitter section, and this arrangement at a distance from each other is used to reduce the noise level, in which the transmitter shaper and the transmitter section in combination allow the system to generate magnetic field pulses in the direction of the earth that are effective for geological surveys;

c) a non-linear amplitude amplifier connected to a sensor device, providing non-compensating high-linear amplitude amplification of the response signal from the earth to a magnetic field pulse.

However, the system cannot effectively irradiate sedimentary rocks of the seabed located below sea water.

When shooting in water, when a layer of water removes the lithosphere from the radiation source and receiver, it is required to use a very powerful source, which is almost impossible. Another thing, if you use a heavy-duty source of magnetic field. For example, variations of the geomagnetic field. Magnetic variations induce electric currents in the lower half-space, which in turn become sources of a magnetic field [2].

For geophysical exploration, magnetotelluric fields of a regional nature, capturing large volumes of land and surface space, are of greatest interest [1].

An electromagnetic wave excited by a source located in the ionosphere reaches the earth's surface in the form of a plane wave [2]. If the geological environment is homogeneous, then instantaneous homogeneous currents and, accordingly, homogeneous (instantaneous) magnetic field sources will be induced in a large space.

Secondary magnetic fields will depend mainly on the geological structure. If these secondary fields are learned to measure, then it will be possible to increase the reliability of the mapping of geological heterogeneities.

If we establish a stationary (at the time of the survey) base terrestrial magnetovariational station (MVS) within a locally homogeneous rock block, then it will detect a change in the background variational field. An abnormal field of variations is recorded in flight during filming in the water, within which the electrical properties of the rocks change. The variations in the measured magnetic field of the Earth can be estimated by linking the observed field with PM and SM [3]. Then the anomalies of the variations are calculated by the difference between the distinguished variations in flight and the observed variations on the MVS.

The method of inductive electroelectric prospecting for variations of the geomagnetic field on the shelf can be used when performing an aeromagnetic survey over a network of ordinary (RM) and secant (SM) routes. In this case, direct measurements of variations at the base magnetovariation station (MVS) are also used. Variations of the geomagnetic field are estimated separately by the residuals of the observed field at the intersection points of the PM and SM [1] - the so-called indirect corrections and for the MVS - direct corrections. Anomalies of variations are calculated by the difference between direct and indirect corrections and link them according to RM and SM [1]. A map of difference variations is constructed and sections of rocks with anomalous electrical conductivity are identified by its anomalies, and the magnitude of the variation anomalies is used to judge the magnitude of the longitudinal electrical conductivity anomalies of the supporting thickness of the sedimentary cover. These are usually relatively conductive rocks lying on a high-yoy deep-lying reference horizon - the foundation.

Effect: mapping of geological heterogeneities at great depths and in the waters along the way with the implementation of aeromagnetic surveys.

Literature

1. Yakubovsky Yu.V., Lyakhov L.L., Electrical Exploration, M, Nedra Publishing House, 1964.

2. Yanovsky BM, Earth magnetism I: Morphology and theory of the Earth’s magnetic field and its variations, L., Publishing House of Leningrad State University (Leningrad University), 1964.

3. Palamarchuk V.K., f. Geology and Geophysics No. 10, Novosibirsk: SCIENCE, 1983.

4. Application 2005119284/28.

Claims (1)

The method of inductive aero-electric prospecting on the shelf according to variations of the geomagnetic field, including performing an aeromagnetic survey over a network of ordinary (RM) and secant (SM) routes and direct measurement of variations at a basic magnetovariational station (MVS), characterized in that the variations of the geomagnetic field are estimated separately from the residuals of the observed fields at the intersection points of RM and SM (indirect corrections) and MVS (direct corrections), calculate the anomalies of variations in the difference between direct and indirect corrections, link the anomalies of variations in RM and SM, with they create a map of anomalous variations and, according to its anomalies, select sections of rocks with anomalous electrical conductivity.