# Method for marine geoelectrical exploration with electrical current focusing

FIELD: physics.

SUBSTANCE: invention relates to marine geoelectrical exploration using controlled artificial sources of electromagnetic field. Using a dipole source, an electromagnetic field is generated inside the analysed medium by sending rectangular electric pulses with intervals in between into the medium. Geometrical probing is done along the profile during the current pulse, and probing on transient processes is done during the interval. Measurements are taken using measuring apparatus mounted on the seafloor, consisting of five electrodes: a central electrode with four others around it on corners of a square, two opposite sides of which are parallel to the axis of the profile. 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 differences between three pairs of external electrodes is measured. When the dipole source passes through different points, there is provision for equipotentiality of a closed line passing through four external electrodes of the measuring apparatus thereby eliminating the horizontal component of current density in each probing point inside this line. Values of the measured electric potential differences are used to calculate three sets of standard interpreted electrical parametres which are not subject to lateral effect of three-dimensional geological non-uniformities located outside the probing point. Using the derived parametres, the model of the medium is found and time sections of this model is constructed on electroconductivity of elements of the medium, induced polarisation coefficient and decay time constant of induced polarisation potential differences.

EFFECT: elimination of distorting lateral effect on probing results, which allows for deep sea delineation of hydrocarbon accumulation with high contrast.

4 cl, 6 dwg

The invention relates to the field of geophysical exploration and more specifically to methods of marine Geoelectromagnetic with controlled artificial sources of electromagnetic fields, and is intended for exploration and delineation of the hydrocarbon (HC) on the continental shelf on the basis of the focus electric current and a separate definition and mapping characteristic of each of the elements (horizons) the thickness of sedimentary deposits of rocks with anomalous values in the accumulation areas of the HC following three needed to solve the problem, electrophysical parameters: conductivity, induced polarization and time constant of decay of the potential difference induced polarization. Together, these three electrophysical parameters allow to distinguish the hydrocarbon from the surrounding rocks.

Methods geoelectricity, including marine, with controlled excitation of the investigated medium electric current known methods of resistance on both AC or DC, including transients, on the basis of dipole-axial installation ABMN). But they are intended to determine only one electrical parameter of the above three, namely, the apparent electrical resistance, and not a specific wish is the second portion of the study space, and the whole space, which penetrates propagating according to the law of diffusion of the electric current source. This is far from enough for exploration and delineation now offered for exploration of hydrocarbon accumulations, lying at a depth of more than 1000 m below the seabed.

Note that, according to theory and practice of Geoelectromagnetic on the basis of dipole-axial installation ABMN, we can distinguish at depths in the range of about 1000 m (but not contour) high contrast HC deposits (thickness not less than 50-100 m and with an electric resistance greater than the resistance of the surrounding rocks 50 or more times). But such deposits are rare, and to date, the majority already discovered.

Attempts sensing based on dipole-axial installation ABMN with controlled excitation current for the purpose of prospecting for hydrocarbon accumulations in the last 90 years has been repeatedly made in different ways, but because of their low efficiency for searches accumulations are not widely used. Electric dipole sensing has a high resolution at depths up to 500 m and in practice has been successfully used to search for buried water and ores, as well as in engineering surveys and archaeology.

The results of soundings on the basis of dipole-axial installation ABMN with controlled excitation current is calculated Caius is the existing electrical resistance ρ using a universal formula

where

I measured the surge current in the electric dipole source;

ΔU is the measured potential difference at the ends of the receiving electrodes MN;

K is the geometric factor of the probe installation. (Survey, Handbook of Geophysics. Ed. Achterhof. M., Nedra, 1980, s and s-406)[1].

With this approach, which is usually used when all traditional methods for determining the electrical resistance of Geoelectromagnetic controlled current source, due to the distribution of current on the law of diffusion, receive only summary information about all elements of the structure of the investigated medium, which is developing electric field, because the distribution in space of the measured current / source does not controlled. And information about this distribution in real three-dimensional inhomogeneous media no.

Among these methods of resistance in the marine Geoelectromagnetic bottom is used geometric sensing low-frequency alternating current on the basis of dipole-osvay installation ABMN named Norwegian company EMGS "(SBL - sea bed logging)" (S.E.Johansen, H.E.F.Amundsen, T.Rosten, S.Ellingsrud, T.Eidesmo and A.H.Bhuyian. Subsurface hydrocarbons detected by electromagnetic sounding. First Break, 23, March 2005, 31-36)[2]. It is also called "controlled soutce electromagnetic sounding (CSEM)" or "offshore hydrocarbons mapping (OHM)".

However, from the description of [2] and applied it figures it follows that the curve profiling method SBL is distorted by the influence of this geometrically large and high contrast in electrical resistance of the field already on the sixth kilometer at the approach of the measurement setup. And to the right of it four patterns between 17.5 km and 24 km crushed his side impact, and the task of determining the presence or absence of these hydrocarbons is not solved. On the edge detection circuit of deposits is not necessary to speak, as the transition from Samanthurai zone to the main reservoir on the resistance curve (actually measured and theoretical) continues for more than 3 km For tacos is bright HC deposits on its geometrical and electrical parameters is very little information.

In addition, at small depths of the sea a way CSEM (OHM, SBL) does not give even this meager information about HC deposits.

Thus, the methods of resistance, including geometric sensing without focusing electric current, which is unsuitable for exploration and delineation of the majority occurring in the geological subsurface hydrocarbon deposits at depths exceeding 1000 m relative to the level of the seabed, at least for three reasons: the first is logged only one necessary for this purpose three electrophysical parameters of the investigated medium (apparent resistivity), which is not always sufficient to detect accumulations of hydrocarbons in the thickness of the geological layers; the second - registered parameter (apparent resistivity) for the same purpose too rough because of them for lack of a vertical focusing of the electric current is logged resistance of the volume of all geological objects of the investigated medium, which is developing electric field power source, that is, the measurement results are significantly distorted by the side effects of geological heterogeneities; the third is not logged parameter induced polarization η with along with anomalous electrical resistance value in the area of hydrocarbon accumulations.

In Geoelectromagnetic influence of lateral geological neodnorodnosti the called side effects, which when looking hydrocarbon accumulations at depths of their occurrence over one kilometer affects the measurement results are laterally for several kilometers from the point of sensing, and these clusters become, in effect, invisible.

Distorting the side effect caused by the fact that the electric current in space does not apply, for example, in the form of an acoustic beam as in seismic exploration, and spreads on the law of diffusion in the direction of least electrical resistance. And if the dipole electric sounding shallow research has a high resolution, with increasing depth research, due to scattering of the current source, it loses this permission.

Marine DEATH due to the low electrical resistance of the sea water can be compared with the logging gradient sensing probes AMN in terms of filling wells salty mud. In filled with salt solution borehole Geophysics refused such a sensing more than fifty years ago, and the electrical resistivity of rock formations determine when assistance is based on the principle of radial focusing current side logging (Laterolog. Doll H.G.).

The task of the marine electrical exploration is to determine the presence of hydrocarbons in cent is Onno occurring seismic structures, when the presence of hydrocarbons have different electrical resistance from surrounding rocks not more than 20-30 times. Such structures hundreds of times more than structures of type TWGP. For example, all hydrocarbon fields in Western Siberia, the Gulf of Ob and on the shelf of the Kara sea, including the largest in its geometrical sizes, have different electrical resistance from the surrounding rocks by log data only in the range from three to thirty times. And if after conducting seismic surveys such structures as TWGP in the Norwegian sea, do not need further testing for the presence of hydrocarbons, due to the high cost of offshore drilling most of the structures without checking for the presence of hydrocarbons to drill risky. So, for example, Established UK oil and gas consultancy Hannon Westwood (see "Upstream boom likely to frustrate North Sea investment opportunities". First Break, 25. Januar 2007, p.22-24) does not recommend to invest in drilling the remaining undeveloped small and medium seismic structures in the North sea, as the drilling success rate at present in these structures is only about 20% (one good well out of five drilled).

Adverse seismic situation and on the Sakhalin shelf. There on the identified exploration of large Western-Shmidt unit ("Sakh the Lin-4") by British Petroleum drilled two exploration wells according to press reports, valued at $ 103 million, in which hydrocarbons were not detected (see the newspaper "Vedomosti" on 06.03.2008). Also turned out to be a dry hole drilled in one of the largest on the geometric dimensions of the Admiralty structure in the Barents sea (see Obmetko CENTURIES and other oil and gas prospects of the Admiralty Bank. International conference "Oil and gas of Arctic shelf - 2008". Murmansk. 12-14 November 2008) This is because the hydrocarbon accumulations are not always controlled only structural factor.

Known way marine Geoelectromagnetic with the focus electric current, which, thanks to the maintenance of equality to zero of the first axis or orthogonal to the electric potential difference in being in the marine layer measurement point sensing and determination of several electrophysical parameters of elements of the geological environment is less affected by lateral inhomogeneities and with a sufficient degree of probability allows to determine the presence of hydrocarbons in the detected seismic studies of the structures and delineate (Rachlinski NI, Davydycheva S.N., Lisin A.S. Way marine Geoelectromagnetic with the focus electric current. RF patent №2384555 from June 01, 2005, BI№27, 2006) [3].

The disadvantage of this method is that they Khujand is realized incomplete vertical focusing power: in its first embodiment is eliminated at the point of sensing only the orthogonal horizontal component of the current density, in the second, only the horizontal component of the axial current density.

In the proposed method solves the problem of the detection and delineation, with a clear boundary contour of oil and gas deposits on the continental shelf as in large and small depths of the sea, and the great depth of these deposits.

The technical result that allows to solve this problem is the possibility of complete elimination at the point of sensing the horizontal component of the current density j_{xy}as orthogonal j_{y}and axial j_{x}that completely eliminates the side effects and for this reason allows for great depths of the sea, at least up to four kilometers, find and with high contrast to delineate hydrocarbon accumulations in the thickness of the geological environment.

This technical result is achieved in that in the method of the marine geoelectricity, in which the axis of rectilinear profile sensing excite an electromagnetic field in the thickness of the investigated medium, passing through it a periodic rectangular current pulses with pauses after each of them with the help of passing along a horizontal electric dipole source; and at each point sensing during each current pulse and each time after it is turned off is measured with the settlement of oanim time interval Δt sequence of instantaneous values of the first and second differences of electric potentials, at the same time provide the condition of equality to zero of the result of the first difference of electric potentials;

form interpretable parameters and using them and differential equations of mathematical physics the strength of the electric field of a dipole source in the electrochemically polarized conductive medium

where

∇^{2}- Laplace operator,

- the electric field of a dipole source, expressed in the equation for the case of harmonic changes in the magnitude of the electric field in time,

σ(iωσ_{0}ητ) - frequency-dependent conductivity of the elements of the environment,

σ_{0}the electrical conductivity of the elements of the environment without the influence of induced polarization,

η is the coefficient of induced polarization,

τ is the time constant of decay of the potential difference induced polarization;

solve mathematical inverse problem, identifying inherent in each element of the environment three electrophysical parameters: conductivity σ_{0}induced polarization η and the time constant of decay of the potential difference induced polarization τ;

and build three temporary cut on these parameters;

according to the invention are laid on the seabed measuring a profile that passes through zafy is lirovannye on the seabed measuring device; each of which consists of five electrodes: Central and located equidistant around him on four vertices of a square, which two opposite sides are parallel to the axis of the profile.

within each period of the pulse-pause" spend geometric sensing when the current sensing on transients during a pause after turning off the current, measuring a second electric potential difference between all four external electrodes of the measuring system and the Central and the first electric potential difference between any of the three pairs of the four external electrodes of this installation;

when this measurement in each fixed on the measuring profile measuring system is carried out at the passing of a horizontal dipole source by the current profile runs parallel to the measuring and sdvinuta about it in terms in the orthogonal direction of y-axis length (y=-b) and height to the thickness h of the aqueous layer, sending current pulses in the test environment at all positions of the dipole source from a point with coordinates [(x=-L), (y=-b), (z=+h)] to the point [(x=-+L), (y=-b), (z=+h)], then the dipole source, deploy and transfer to another parallel current profile, padded and shifted in the plan will measure inogo in the opposite direction along the y-axis at a distance (y=+b) and the height to the thickness h, and continue the measurement when it is driven in the reverse direction from the point with coordinates [(x=+L), (y=+b), (z=+h)] to the point [(x=-L), (y=+b), (z=+h)];

using the measured values of the first and second differences of electric potentials, define two independent current source and horizontal components of the current density (j_{x}=0 and j_{y}=0) at the point of sensing interpretable parameter is one of R_{z}(t_{o}on the basis of geometrical sounding at all positions of the dipole source, calculated by the formula

R_{z}(t_{o})=[Δ(U_{M1M3}(I_{B1A1},t_{o})]:

:{[Δ^{2}U_{M1M2M3M4N}(I_{B1A1},t_{o})]+k_{1}(t_{o})·[Δ^{2}U_{M1M2M3M4N}(I_{A2B2},t_{o})]+

+k_{2}(t_{o})·[Δ^{2}U_{M1M2M3M4N}(I_{A3B3},t_{o})]+k_{3}t_{o})·[Δ^{2}U_{M1M2M3M4N}(I_{B4A4},t_{o})]},

and the other R_{z}(t_{i}on the basis of sensing of transient processes at four selected by the method of iterations, the most informative separations with coordinates of the dipole source [(x=-a), (y=-b), (z+h)], [(x=+a) (y=-b), (z=+h)], [(x=+a), (y=+b), (z=+h)] and [(x=-a), (y=+b), (z=+h)] of all explored calculated by the formula

Rz(t_{i})=[ΔU_{M1M3}(I_{B1A1}, t_{i})]:

:{[Δ^{2}U_{M1M2M3M4N}(I_{B1A1},t_{i})]+k_{1}(t_{i})·[Δ^{2}U_{M1M2M3M4N}(I_{A2B2},t_{i})]+

+k_{2}(t_{i})·[Δ^{2}U_{A3B3},t_{i})]+k_{3}(t_{i})·[Δ_{2}U_{M1M2M3M4N}(I_{B4A4}, t_{i})]},

where

k_{1}(t_{o}), k_{2}(t_{o}), k_{3}(t_{o}), the coefficients at the geometrical focus sensing, providing equipotentiality closed line passing through the four external electrodes of the measuring system and, thus, the exception in this line of the horizontal component of the current density j_{xy}at each point sensing on all geometric spacings during the current pulse, which is determined from the system of three equations:

1) {[ΔU_{M1M2}(I_{B1A1}, t_{o})]+k_{1}(t_{o})·[ΔU_{M1M2}(I_{B2A2}, t_{o})]

+k_{2}(t_{o})·[ΔU_{M1M2}(I_{A3B3}, t_{o})]+k_{3}(t_{o})·[ΔU_{M1M2}(I_{B4A4}, t_{about})]=0},

2) {[ΔU_{M1M2M3M4N}(I_{B1A1}, t_{about})]+k_{1}(t_{o})·[ΔU_{M1M3}(I_{A2B2}, t_{o})]+

+k_{2}(t_{0})·[ΔU_{M1M3}(I_{A3B3}, t_{o})]+k_{3}(t_{o})·[ΔU_{M1M3}(I_{B4A4}, t_{o})]=0},

3){[ΔU_{M1M4}(I_{B1A1}, t_{o})]+k_{1}(t_{o})·[ΔU_{M1M4}(I_{A2B2},t_{o})]+

+k_{2}(t_{o})·[ΔU_{M1M4}(I_{A3B3}, t_{o})]+k_{3}(t_{o})·[ΔU_{M1M4}(I_{B4A4}, t_{o})]=0},

k_{1}(t_{i}), k_{2}(t_{i}), k_{3}(t_{i}), the coefficients of focus when probing for transients in each of the th point sensing in the pause current at all times transient,
determined from the system of three equations

1) {[ΔU_{M1M2}(I_{B1A1}, t_{i})]+k_{1}(t_{i})·[ΔU_{M1M2}(I_{B2A2}, t_{i})]

+k_{2}(t_{i})·[ΔU_{M1M2}(I_{A3B3}, t_{i})]+k_{3}(t_{i})·[ΔU_{M1M2}(I_{B4A4}, t_{i})]=0},

2) {[ΔU_{M1M2M3M4N}(I_{B1A1}, t_{i})]+k_{1}(t_{i})·[ΔU_{M1M3}(I_{A2B2}, t_{i})]+

+k_{2}(t_{i})·[ΔU_{M1M3}(I_{A3B3}, t_{i})]+k_{3}(t_{i})·[ΔU_{M1M3}(I_{B4A4}, t_{i})]=0},

3){[ΔU_{M1M4}(I_{B1A1}, t_{i})]+k_{1}(t_{i})·[ΔU_{M1M4}(I_{A2B2}, t_{i})]+

+k_{2}(t_{i})·[ΔU_{M1M4}(I_{A3B3}, t_{i})]+k_{3}(t_{i})·[ΔU_{M1M4}(I_{B4A4}, t_{i})]=0},

t_{0}- time by passing a current pulse when the electric field transients is not different from its steady-state value corresponding to DC;

t_{i}the points in time at which the measured signals of transient processes at regular intervals of time Δt throughout pause after turning off the current.

[Δ^{2}U_{M1M2M3M4N}(I_{B1A1}, t_{o})], [Δ^{2}U_{M1M2M3MN}(I_{A2B2}, t_{o})],

[Δ^{2}U_{M1M2M3M4NA}(I_{A3B3}, t_{o})], [Δ^{2}U_{M1M2M3M4N}(I_{B4A4}, t_{o})] is the instantaneous value of the second difference of electric potentials between the four external electrodes M_{1}M_{2}M_{
3}M_{4}the measuring setup and the Central N, measured at time t_{0}the bandwidth of the current in the dipole source passing through both current profiles through equidistant from the Central electrode N of the measurement setup four points, respectively, with coordinates [x, (y=-b), (z=+h)], [+x, (y=-b), (z=+h)], [+x(y=+b), (z=+h)] and [x, (y=+b), (z=+h)];

[ΔU_{M1M2}(I_{B1A1}, t_{o})], [ΔU_{M1M2}(I_{A2B2}, t_{o})],[ΔU_{M1M2}(I_{A3B3}, t_{o})],

[ΔU_{M1M2}(I_{B4A4}, t_{about})]=0},[ΔU_{M1M3}(I_{B1A1}, t_{o})],[ΔU_{M1M3}(I_{A2B2}, t_{o})],

[ΔU_{M1M3}(I_{A3B3}, t_{o})],[ΔU_{M1M3}(I_{B4A4}, t_{o}),[ΔU_{M1M4}(I_{B1A1}, t_{o})],

[ΔU_{M1M4}(I_{A2B2},t_{o})],[ΔU_{M1M4}(I_{A3B3}, t_{o})],[ΔU_{M1M4}(I_{B4A4}, t_{o})] is the instantaneous values of the first three differences of electrical potentials between the three pairs of external electrodes M_{1}M_{2}M_{1}M_{3}M_{1}M_{4}measured at time t_{0}the bandwidth of the current in the dipole source passing through both current profiles through equidistant from the Central electrode N of the measurement setup four points, respectively, with coordinates [x (y=-b), (z=+h)], [+x (y=-b), (z=+h)], [+x (y=+b), (z=+h)] and [x, (y=+b), (z=+h)];

[Δ^{2}U_{M1M2M3M4N}(I_{B1A1}, t_{i})], [Δ^{2}U_{M1M2M3M4N}(I_{A2B2}, t_{i})],

[Δ^{2}U_{A3B3}, ti)], [Δ^{2}U_{M1M2M3M4N}(I_{B4A4}, ti)] is the instantaneous value of the second difference of electric potentials between the four external electrodes M_{1}M_{2}M_{3}M_{4}the measuring setup and the Central N, measured at time t_{i}transients in the pause current dipole source passing through both current profiles through equidistant from the Central electrode N of the measurement setup four points, respectively, with coordinates [(x=-a, (y=-b), (z=+h)], [(x=+a) (y=-b) (z=+h)], [(x=+a), (y=+b) (z=+h)] and [(x=-a), (y=+b), (z=+h)];

[ΔU_{M1M2}(I_{B1A1}, t_{i}),[ΔU_{M1M2}(I_{A2B2}, t_{i})],[ΔU_{M1M2}(I_{A3B3}, t_{i})],

[ΔU_{M1M2}(I_{B4A4}, t_{i})],[ΔU_{M1M3}(I_{B1A1}, t_{i})],[ΔU_{M1M3}(I_{A2B2}, t_{i}),

[ΔU_{M1M3}(I_{A3B3}, t_{i})],[ΔU_{M1M3}(I_{B4A4}, t_{i})],[ΔU_{M1M4}(I_{B1A1}, t_{i})],

[ΔU_{M1M4}(I_{A2B2}, t_{i})],[ΔU_{M1M4}(I_{A3B3}, t_{i})],[ΔU_{M1M4}(I_{B4A4}, t_{i})] is the instantaneous values of the first three differences of electrical potentials between the three pairs of external electrodes M_{1}M_{2}M_{1}M_{3}M_{1}M_{4}measured at time t_{i}transients in the pause current dipole source passing through both current profiles through equidistant from the Central electrode N ISM is satisfactory, install four points, respectively, with coordinates [(x=-a),
(y=-b), (z=+h)], [(x=+a) (y=-b), (z=+h)], [(x=+a), (y=+a), (z=+h)] and [(x=-a), (y=+b), (z=+h)].

Also the technical result is achieved in that in the method of the marine Geoelectromagnetic according to the invention, the current profiles for the passage of a horizontal dipole source lay at a given depth or on the surface of the sea.

Also the technical result is achieved in that in the method of the marine Geoelectromagnetic according to the invention, the distance L is six kilometres or more, the distances a and b is equal to one kilometer or more, the depth h of the dipole source is set in the range of twenty meters above the seabed to the surface.

Also the technical result is achieved in that in the method of the marine Geoelectromagnetic according to the invention the measuring system is placed on the measuring profile with equal step in 200-1000 meters.

The invention is illustrated by drawings.

Figure 1 is given the block diagram of the device for implementing the proposed method.

Figure 2 gives the layout plan on the seabed of the group of measurement units for measuring the profile sensing and two profiles parallel to the measurement, along which the moving dipole source in the thickness of the water layer of the sea above the sea bottom at a distance h or on the surface of the sea.

Figure 3 on the outline of the motion of a dipole source by the first of the two parallel sections on measuring.

Figure 4 gives the flow pattern of the dipole source on the second parallel profile on measuring.

Figure 5 shows the form of the electric field to focus the electric current in the direction of the vertical coordinate z by maintaining equality to zero of the first difference of electric potentials between each pair of outer measuring electrodes resulting from steps four equidistant from the Central electrode N of the measurement setup of the dipole sources. To maintain the equality to zero of the first difference of electric potentials between each pair of outer measuring electrodes resulting from the actions of four dipole sources is sufficient to measure the three first electric potential difference between any of the three pairs of the four external electrodes of this installation. In case of equality to zero of the difference of electric potentials between the four electrodes M currents from the four current sources AB penetrated inside formed by these electrodes square, focused and in the future may only be distributed in the vertical direction along the z coordinates in Addition, the vertical direction of the electrical current provided his focus is based on isoperimetric variations according to the Lagrange function (principle namenstag the action) (Landau L.V.,
Lifshitz E.M. field Theory. 2 ed. M. - L., 1948). In the plane of M_{1}M_{2}M_{3}M_{4}N the potential of the electric field takes the form of an ellipsoid of rotation with a minimum at the point N.

Figure 6 shows the form of a single pulse as a function of time t: (a) to form a single rectangular pulse of current I in the circuit of the dipole source AB; b) the shape of the pulses of the first and second differences of electric potentials.

The device for implementing the method (figure 1) contains a measuring unit for measuring the first and second differences of electric potentials. This setting is located on the measuring profile 1, laid on the seabed.

Here 2 - N 3 - M_{1}a 4 - M_{2}a 5 - M_{3}a 6 - M_{4}the electrodes of the second electric potential difference measuring units between all four external M_{1}M_{2}M_{3}M_{4}and the Central N; 3 and 4 - electrodes M_{1}M_{2}the first sensor of the first electrical potential difference; 3 and 5 - electrodes M_{1}M_{3}a second sensor of the first electrical potential difference; 3 and 6 electrodes M_{1}M_{4}the third sensor, the first electric potential difference (such measuring patellectomy sensors for measuring the profile 1 can be placed any number (figure 2), in addition, such sensors can be placed is and other measuring profiles,
parallel profile 1); 7 - meter for measuring a second potential difference electric field Δ^{2}U_{M1M2M3M4N}between all four external electrodes M_{1}M_{2}M_{3}M_{4}the measuring setup and the Central N; 8 - scaling resistance of the feedback input of the amplifier meter 7; 9, 10, 11, 12 - equal summing resistance to sum the potentials U_{M1}U_{M2}U_{M3}U_{M4}external measuring electrodes M_{1}M_{2}M_{3}M_{4}; 13 - meter first potential difference electric field ΔU_{M1M2}between the electrodes M_{1}M_{2}; 14 - meter first potential difference electric field ΔU_{M1M3}between the electrodes M_{1}M_{3}; 15 - meter first potential difference electric field ΔU_{M1M4}between the electrodes M_{1}M_{4}.

To ensure the focusing of the electric field at the point of sensing N parallel to the measuring profile 1 to the right and to the left of it is placed in the thickness of the water layer of the sea above the sea bottom at a distance h or on the surface of the sea two profiles: the first 16 and second 17, along which move the horizontal current dipole source, consisting of two electrodes 18-A and 19-B, fed by generator 20 of rectangular current pulses with pauses between each of impulso is.

Figure 3 shows the progress of the dipole source AB on the first profile - 16, located in the thickness of the water layer of the sea above the sea bottom at a distance h or on the sea surface parallel to the measuring - 1 and sdvinuta from him in terms of distance (y=-b). Promotion of the dipole source AB profile 16 exercise from the beginning [x, (y=-b), (z=+h)] until the end [+x, (y=-b), (z=+h)]. Then the dipole source AB (figure 4) transferred to a second profile 17 that is parallel to the measuring and shifted with respect to it in terms of distance (y=+b) and the height to the thickness h. Promotion of the dipole source AB profile 17 carried by the point with coordinates [+x, (y=+b), (z=+h)] to the point with coordinates [x, (y=+b), (z=+h)].

This complex profiling is required for measurement of any three of the first difference of electric potentials between the four external electrodes of the measuring system for achieving equality of potentials between the electrodes of the total action of the dipole source as it passes through the four points with coordinates [x, (y=-b), (z=+h)], [+x (y=-b), (z+h)], [+x (y=+b (z=+h)] and [x, (y=+b), (z=+h)]. This is evident, for example, from the measured first three differences of electric potentials: ΔU_{M1M2}=U_{M1}- U_{M2}=0, ΔU_{M1M3}=U_{M1}- U_{M3}=0, ΔU_{M1M4}=U_{M1}-U_{M4}=0. Whence it follows that U_{M1}=U_{M2}=U_{M3}=U_{M4}. The combination is equal to zero for any three differences of electrical potentials between the four external electrodes of the measuring system will always lead to equality of potentials between the four electrodes.

Equality of potentials between four external electrodes of the measuring system provides equipotentiality closed line through these four external electrode and, thus, the exception in this line horizontal components of the current density j_{xy}at each point sensing that provides focusing power along the vertical coordinate z within the closed equipotential lines.

Figure 6 (a) shows the form of a single rectangular pulse of current I in the circuit of the dipole source AB as a function of time t. Here T is the period (the current pulse - pause).

Figure 6 (b) shows the form of one of the pulses Δ^{n}U, where n=1 and 2. It also shows one of the values Δ^{n}(t_{0}in the period of the pulses in the dipole source AB and one of the values Δ^{n}U(t_{i}in the pause current.

Discuss the basics of the proposed method, its implementation and new features of the marine Geoelectromagnetic.

The proposed method marine Geoelectromagnetic allows using three profiles (figure 1) to eliminate the side effect by focusing current. This gives great depth sensing and high resolution laterally.

It is known that the electromagnetic field in lohaprasadaya environment is distributed in time t according deriving from the first and second of Maxwell's equations differential is territorial satuhelmia wave equation of mathematical physics the strength of the electric field, including in case of pulse changes

where

∇^{2}- Laplace operator;

E - electric field intensity, V/m;

µ - magnetic permeability is a constant value for nonmagnetic media, which include sedimentary geological formations, it is equal to 4π·10^{-7}GN/m;

σ_{o}conductivity polarizadas environment, Cm/m;

ε is the dielectric permittivity, f/m (VA ghirenko Fyedor. Electric and magnetic fields. M, Gosenergoizdat, 1960, s.257-263) [5].

In the case of highly conductive environment, which includes sedimentary rocks, due to the fact that σ_{o}numerically much larger ε, the second term in the right-hand side of equation (2) is small compared with the first, and his cast (LVN. Fundamentals of electromagnetic soundings. M., Nedra, 1965, p.28-30) [6]. Physically this means that the bias currents in conductive environments are neglected because they are small compared to conduction currents. Then the equation (2) takes the form

This equation in Geoelectromagnetic has an analytical solution only for one-dimensional axisymmetric environments, particularly for environments with unlimited horizontal stretching the boundaries. Moreover, we note that in reality the geological environment is always three-dimensional heterogeneous, so it is to it, first, there are local surface heterogeneity, secondly, in General the geological environment along the profile of research is constantly changing its electrophysical parameters. However, equation (3), as mentioned above, analytically solved only for one-dimensional axisymmetric environments, including environments with a horizontal plane-parallel boundaries.

Therefore, the solution of equation (3) in the inverse problems of Geoelectromagnetic for exploration and delineation of oil and gas deposits are permissible only in the case when field measurements are focusing electric current dipole source of the electromagnetic field, as in this case, at the point N (Figure 5) the shape of the field distribution resulting from the actions of four dipole sources B_{1}A_{1}, A_{2}B_{2}, A_{3}B_{3}B_{4}A_{4}while maintaining the zero result of the first difference of electric potentials between each pair of outer measuring electrodes are almost always the same as in three-dimensional heterogeneous environment, and in a one-dimensional plane-parallel horizontal boundaries.

From formulas(4), (5), (6) and (7) it follows that according to Ohm's law, the total horizontal component of the current density j_{xy}at the point of sensing N according to the principle of super is osili equal to zero.

Thus, at the point of measurement is the focus of current, leading to the exclusion of the horizontal component of the current density j_{xy}to preserve only the vertical components of the current density j_{z}that allows to avoid distorting the side effect on the results of sensing and the ability to correctly solve the inverse problem in three-dimensional inhomogeneous media, using the known analytical solution of the one-dimensional equation (14) for layered media with plane-parallel boundaries.

To ensure the exception of the horizontal components of the density j_{xy}at the point of sensing N with coordinates [(x=0), (y=0), (z=0)], in the proposed method is built corresponding formulas of the measured electrical parameters: one R_{z}(t_{o}on the basis of geometrical sounding at all positions of the dipole source, calculated by the formula

R_{z}(t_{o})=[Δ(U_{M1M3}(I_{B1A1},t_{o})]:

:{[Δ^{2}U_{M1M2M3M4N}(I_{B1A1},t_{o})]+k_{1}(t_{o})·[Δ^{2}U_{M1M2M3M4N}(I_{A2B2},t_{o})]+

+k_{2}(t_{o})·[Δ^{2}U_{M1M2M3M4N}(I^{A3B3},t_{o})]+k_{3}t_{o})·[Δ^{2}U_{M1M2M3M4N}(I_{B4A4},t_{o})]}, (4)

and the other R_{z}(ti) - based sensing on transient at four selected by the method of iterations, the most informative separations with POS is natami dipole source [(x=-α),
(y=-b), (z=+h)], [(x=+α), (y=-b), (z=+h)], [(x=+α), (y=+b), (z=+h)] and [(x=-α),(y=+b), (z=+h)] of all explored calculated by the formula

R_{z}(t_{i})=[Δ(U_{M1M3}(I_{B1A1},t_{i})]:

:{[Δ^{2}U_{M1M2M3M4N}(I_{B1A1}, t_{i})]+k_{1}(t_{o})·[Δ^{2}U_{M1M2M3M4N}(I_{A2B2}, t_{i})]+

+k_{2}(t_{o})·[Δ^{2}U_{M1M2M3M4N}(I_{A3B3},t_{i})]+k_{3}t_{o})·[Δ^{2}U_{M1M2M3M4N}(I_{B4A4},t_{i})]}, (5)

where

k_{1}(t_{o}), k_{2}(t_{about}), k_{3}(t_{o}), the coefficients at the geometrical focus sensing, providing equipotentiality closed line passing through the four external electrodes of the measuring system and, thus, the exception in this line of the horizontal component of the current density j_{xy}at each point sensing on all geometric spacings during the current pulse, which is determined from the system of three equations:

1) {[ΔU_{M1M2}(I_{B1A1}, t_{o})]+k_{1}(t_{o})·[ΔU_{M1M2}(I_{A2B2}, t_{o})]

+k_{2}(t_{o})·[ΔU_{M1M2}(I_{A3B3}, t_{o})]+k_{3}(t_{o})·[ΔU_{M1M2}(I_{B4A4}, t_{o})]=0},

2) {[ΔU_{M1M3}(I_{B1A1}, t_{o})]+k_{1}(t_{o})·[ΔU_{M1M3}(I_{A2B2}, t_{o})]+

+k_{2}(t_{about})·[ΔU_{M1M3}(I_{A3B3}, t_{o})]+k_{3}(t_{o})·[ΔU_{M1M3}(I_{B4A4}, t_{o})]=0},

3){[ΔU_{M1M4}(I_{B1A1}, tsub>
o)]+k_{1}(t_{o})·[ΔU_{M1M4}(I_{A2B2},t_{o})]+

+k_{2}(t_{o})·[ΔU_{M1M4}(I_{A3B3}, t_{o})]+k_{3}(t_{o})·[ΔU_{M1M4}(I_{B4A4}, t_{o})]=0}, (6)

k_{1}(ti), k_{2}(ti), k_{3}(ti), the coefficients of focus when probing on transients, providing equipotentiality closed line passing through the four external electrodes of the measuring system and, thus, the exception in this line of the horizontal component of the current density j_{xy}at each point sensing at all times of the transients in the pause current, which is determined from the system of three equations

1) {[ΔU_{M1M2}(I_{B1A1}, t_{i})]+k_{1}(t_{i})·[ΔU_{M1M2}(I_{B2A2}, t_{i})]

+k_{2}(t_{i})·[ΔU_{M1M2}(I_{A3B3}, t_{i})]+k_{3}(t_{i})·[ΔU_{M1M2}(I_{B4A4}, t_{i})]=0},

2) {[ΔU_{M1M3}(I_{B1A1}, t_{i})]+k_{1}(t_{i})·[ΔU_{M1M3}(I_{A2B2}, t_{i})]+

+k_{2}(t_{i})·[ΔU_{M1M3}(I_{A3B3}, t_{i})]+k_{3}(t_{i})·[ΔU_{M1M3}(I_{B4A4}, t_{i})]=0},

3){[ΔU_{M1M4}(I_{B1A1}, t_{i})]+k_{1}(t_{i})·[ΔU_{M1M4}(I_{A2B2}, t_{i})]+

+k_{2}(t_{i})·[ΔU_{M1M4}(I_{A3B3}, t_{i})]+k_{3}(t_{i})·[ΔU_{M1M4}(I_{B4A4}, t_{i})]=0}, (7)

t_{o}- time by passing a current pulse when the electric the field of transient processes is not different from its steady-state value,
the corresponding DC;

t_{i}the points in time at which the measured signals of transient processes at regular intervals of time Δt throughout pause after turning off the current.

[Δ^{2}U_{M1M2M3M4N}(I_{B1A1}, t_{o})], [Δ^{2}U_{M1M2M3MN}(I_{A2B2}, t_{o})],

[Δ^{2}U_{M1M2M3M4N}(I_{A3B3}, t_{o})], [Δ^{2}U_{M1M2M3M4N}(I_{B4A4}, t_{o})] is the instantaneous value of the second difference of electric potentials between the four external electrodes M_{1}M_{2}M_{3}M_{4}the measuring setup and the Central N, measured at time t_{0}the bandwidth of the current in the dipole source passing through both current profiles through equidistant from the Central electrode N of the measurement setup four points, respectively, with coordinates [x, (y=-b), (z=+h)], [+x, y=-b), (z=+h)], [+x (y=+b), (z=+h)] and [x, (y=+b), (z=+h)];

[ΔU_{M1M2}(I_{B1A1}, t_{o})],[ΔU_{M1M2}(I_{A2B2}, t_{o})],[ΔU_{M1M2}(I_{A3B3}, t_{o}),

[ΔU_{M1M2}(I_{B4A4}, t_{o})],[ΔU_{M1M3}(I_{B1A1}, t_{o})],[ΔU_{M1M3}(I_{A2B2}, t_{o})],

[ΔU_{M1M3}(I_{A3B3}, t_{o})],[ΔU_{M1M3}(I_{B4A4}, t_{o})],[ΔU_{M1M4}(I_{B1A1}, t_{o})],

[ΔU_{M1M4}(I_{A2B2}, t_{o})],[ΔU_{M1M4}(I_{A3B3}, t_{o})],[ΔU_{M1M4}(I_{B4A4}, t_{o})] is the instantaneous values of the first three differences electricity the definition of potentials between the three pairs of external electrodes M_{
1}M_{2}M_{1}M_{3}M_{1}M_{4}measured at time t_{0}the bandwidth of the current in the dipole source passing through both current profiles through equidistant from the Central electrode N of the measurement setup four points, respectively, with coordinates [x, (y=-b), (z=+h)],[+x, (y=-b (z=+h)],[+x, (y=+b), (z=+h)] and [x, (y=+b), (z=+h)];

[Δ^{2}U_{M1M2M3M4N}(I_{B1A1}, t_{i})],[Δ^{2}U_{M1M2M3M4N}(I_{A2B2},t_{i})],

[Δ^{2}U_{M1M2M3M4N}(I_{A3B3}, t_{i})],[Δ^{2}U_{M1M2M3M4N}(I_{B4A4}, t_{i})] is the instantaneous value of the second difference of electric potentials between the four external electrodes M_{1}M_{2}M_{3}M_{4}the measuring setup and the Central N, measured at time t_{i}transients in the pause current dipole source passing through both current profiles through equidistant from the Central electrode N of the measurement setup four points, respectively, with coordinates [(x=-a), (y=-b) (z=+h)],[x=+a) (y=-b), (z=+h),[(x=+a), (y=+b), (z=+h)] and [(x-=-a), (y=+b), (z=+h)];

[ΔU_{M1M2}(I_{B1A1}, t_{i})],[ΔU_{M1M2}(I_{A2B2}, t_{i})],[ΔU_{M1M2}(I_{A3B3}, t_{i})],

[ΔU_{M1M2}(I_{B4A4}, t_{i})],[ΔU_{M1M3}(I_{B1A1}, t_{i})],[ΔU_{M1M3}(I_{A2B2}, t_{i})],

[ΔU_{M1M3}(I_{A3B3}, t_{i})],[ΔU_{M1M3}(I_{B4A4}, ti)][ΔU_{M1M4}(I_{B1A1}, t_{i})],

[The U_{
M1M4}(I_{A2B2}, t_{i})],[ΔU_{M1M4}(I_{A3B3}, t_{i})],[ΔU_{M1M4}(I_{B4A4}, t_{i})] is the instantaneous values of the first three differences of electrical potentials between the three pairs of external electrodes M_{1}M_{2}M_{1}M_{3}M_{1}M_{4}measured at time t_{i}transients in the pause current dipole source passing through both current profiles through equidistant from the Central electrode N of the measurement setup four points, respectively, with coordinates [(x=-a), (y=-b), (z=+h)],[(x=+a, (y=-b), (z=+h)], [(x=+a), (y=+b), (z=+h)] and [(x=-a), (y=+b), (z=+h)].

Formulas (4) and (5) regardless of the magnitude of the current in the dipole AB any three-dimensional inhomogeneous medium at each point in space in the direction of the vertical coordinate z at the point of sensing N in the plane passing through the measuring electrodes at any distance x between the dipole source AB and point sensing N geometric sensing and throughout time t_{i}when sounding for transients, ensure equality to zero of the horizontal components of the current density j. It always happens regardless of what is in the process of changing the distance x between the dipole source AB and measurement point N or in the process of changing time t transients multipliers k_{1}(t_{o}), k_{2}(t_{o}), k_{3}(_{
about}and k_{1}(t_{i}), k_{2}(t_{i}), k_{3}(t_{i}that is changing. Due to this, when solving the inverse problem excludes the effect of a side impact, i.e. the electric field in three-dimensional inhomogeneous medium at the point of sensing N, described by formulas (4) and (5)almost always coincide with a field in one-dimensional horizontally layered medium with unlimited boundaries.

This allows to solve the inverse problem in the measurement point N for three-dimensional inhomogeneous medium using known analytical solution for one-dimensional environment with a horizontally-layered interfaces.

Note also that equation (3) is the equation of the propagation time of the electromagnetic field in a conductive polarizadas environment, which coincides with the well-known in mathematical physics the heat equation or diffusion and which in Geophysics in the way of resistance is usually used to study the distribution of the alternating electromagnetic field in the depths of the strata studied geological formations.

In this case it is considered that the conductivity σ_{o}particular geological horizon is the main and practically the only determining its electrical properties parameter has its own constant value for each horizon and does not depend on the frequency of excitation electromagn the private field.
However, geological sedimentary rocks under excitation applied Geophysics alternating low-frequency electric current characteristic of the resulting polarization η. Induced polarization is a dimensionless quantity that depends on the electrochemical activity of the sedimentary rocks. It is defined as the ratio of the differences of potentials measured on the sample of the breed after turning off the current pulses through 0.5 sec (ΔU_{RR}and until shutdown (ΔU). This ratio is usually expressed in percent

Induced polarization sedimentary Geology rocks is unique among physical parameters of stability and practically does not depend on the composition of rocks and their temperature. It is for an ion-conductive (sedimentary) rocks depends on many factors: humidity and porosity, composition and concentration of the solution in the pores of the rock structure and pore size, content of clay minerals, etc. (Whakamaru. The electrical method of polarization. Leningrad, Nauka, 1980, s) [7]. And, most importantly, induced polarization contains basic information about the presence in the geological environment with a high degree of polarization of oil and gas deposits.

Set (W.H.Pelton, S.H.Ward, P.O.Hallof, W.R.Sill and P.H.Nelson. Mineral discrimination and removal of inductive coupling with multi-frequency JP, Geophysics 43, 1978, c.588-603) [8]that the conductivity esadocs the x rocks is not constant, but it depends on the induced polarization and frequency of the excitation electric field is proposed, in particular, K.S.Cole and R.H.Cole in the form of harmonic changes over time of the empirical formula

in which the conductivity depends on ω, σ_{o}and τ;

where

η - induced polarization of rocks, a dimensionless quantity, usually expressed in percent;

τ is the time constant that determines the rate of decrease in the potential difference associated with the induced polarization, sec;

ω is the harmonic frequency of the electrical excitation, Hz;

with the dimensionless exponent, which, although not a physical parameter of rocks, but it depends on σ(iωσ_{o}ητ).

Induced polarization η at low frequency electrical excitation, in contrast to the dielectric constant ε, numerically not so small compared to the electrical conductivity σ_{o}for sedimentary Geology rocks, measured, for example, when currents of high frequencies (ω→∞), when, as seen from the formula (9), induced polarization is not shown. Consequently, the induced polarization in the study the purpose of exploration and delineation of oil and gas deposits of geoelectric parameters of the sedimentary geological rocks at low frequency alternating current already cannot be neglected.

Known Electromagnetics.
Handbook of Geophysics. Ed. Achmelvich and other M., Nedra, 1989, the second Book, s-102) [9]that for certain sedimentary Geology rocks within 0.5 sec after turning off the pulse of the exciting current value caused by the polarization potential difference, despite its rapid decline, yet retains the levels, the numerical values of which range from 0.2% to 10% of the numerical values of the differences of potentials direct fields associated with electrical conductivity σ_{o}measured, as described above, when the currents of high frequencies, caused when the polarization is not shown. To save in the form of a formula (9), the heat equation (3) we write for the case of harmonic changes in the magnitude of the electromagnetic field at a time, keeping in mind that

and considering the fact that

and

Then the equation (3) for conducting polarizadas environment, taking into account the transformation (10) takes the form

But since the conductivity of sedimentary rocks is not constant, but depends on the induced polarization and on the excitation frequency by the formula (9), equation (12) given this formula becomes four defining properties of polarizable environment parameter σ_{o}, η, τ and instead of one σ_{o}and for the case of harmonic is modify the magnitude of the electromagnetic field in time takes the form

and in General, taking into account (9) -

Replacement frequency-independent conductivity σ_{o}that is present in equation (12), frequency-dependent σ(iω), present in equation (14), mathematically correct and theoretically proved (Akkulka, Basemaker. The prospecting phase by the method of induced polarization. M., Nedra, 1978, p.24-26) [10]; (Grrat. Geoelectromagnetic. M., Nedra, 1987, p.61-62)[11].

For the proposed method the problem of detecting oil and gas deposits in the investigated rock mass as a mathematical inverse problem is solved according to equation (14) as a function of the distance x between the dipole source AB and measurement point N and as a function of time t transients and, as a consequence, functions, depending on the distance x and time t the depth of penetration of electromagnetic fields in three independent from each other, the environment parameters: conductivity σ_{o}; induced polarization η; time constant τ of the decay of the electric potential difference induced polarization; and the fourth, which is not the environment parameter, the exponent, derived from empirical formula (9).

This task, as the inverse mathematical problem is solved for the proposed method by using the whole array defined by the x in this way, at least two independent current sources normalized electrical parameters described by the formula(4) (5), (6) and (7).

It should be noted that at the sounding of the proposed method in each measurement point of the profile along its entire length to receive the digital information on the first and second differences of the electric potential with a step discontinuity at regular intervals of time Δt as each time switching the current in the dipole source in the sensing process (geometric probing), and in the pause the current sensing on transients).

If for geometric sensing obtaining information about the response of the medium from each defines the spacing of the probe installation current pulse necessary for sensing transient enough information from one sounding setup, but with such a spacing, which is the greatest information about the sensed geological environment (note that at large separations the transient signals are weak and difficult to distinguish against the background noise, and at small separations and sensing on transient has low propagation distance). Therefore, the solution of the inverse problem, in particular, is also tasked to find the iteration method is the most informative spacing probing setup among all explored.

ultimately,
the solution of the inverse problem given iteration find the model of the environment that is closest to the geometric structure and electrical parameters to study, build geoelectric cross sections of the obtained parameters σ_{o}, η and τ and allocate them to the areas with anomalous values corresponding to the plan's regulation of oil and gas deposits.

Specific example

Figure 1 shows the block diagram of the device for implementation of the proposed method. On the flowcharts shown placed in a column of sea water to a height h relative to the sea bottom or on the surface of the dipole source AB (18 and 19), powered by a generator 20 of rectangular current pulses. Note that when the location of the dipole source on the surface simplifies the design of the cable braid of the dipole source and creates the opportunity to increase the value of the electric current in the circuit of the dipole source. The location of the dipole source on the surface allows to study the proposed method at small depths (up to 300 m). At great depths (over 300 m) due to the absorption signals of transient processes in the thickness of the highly conductive seawater horizontal dipole source is immersed to a predetermined depth and its passage along the two current profiles do at this depth.

The device f is 1) contains a measuring system for measuring the difference of electric potentials. This setting is located on the measuring profile -1, laid on the seabed.

Here 2 - N 3 - M_{1}a 4 - M_{2}a 5 - M_{3}a 6 - M_{4}the electrodes of the measuring unit; 7 - meter for measuring a second potential difference electric field Δ^{2}UM_{1}M_{2}M_{3}M_{4}N between the four external electrodes M_{1}M_{2}M_{3}M_{4}the measuring setup and the Central N; 8 - scaling resistance of the feedback input of the decision making power meter 7; 9, 10, 11, 12 - equal summing resistance to sum the potentials U_{M1}U_{M2}U_{M3}U_{M4}external measuring electrodes M_{1}M_{2}M_{3}M_{4}.

The summation of the potentials U_{M1}U_{M2}U_{M3}U_{M4}external measuring electrodes M_{1}M_{2}M_{3}M_{4}using linear final amplifier that performs the algebraic summation of the four input signals U_{M1}U_{M2}U_{M3}U_{M4}with multiplication by a given constant R_{8}/R_{9}provided that R_{9}=R_{10}=R_{11}=R_{12}(see Byakugan. Electronic simulations and their application to the study of automatic control systems. Phys.-Mat. Ed. M 1963, p.60-64).

The second difference between the electric pot is Lalov from formulas (4) and (5) is determined by the ratio Δ^{
2}U_{M1M2M3M4N}=[Δ^{2}U_{M1 NM3}+Δ^{2}U_{M2NM4}=(ΔU_{M1N}-ΔU_{NM3})+(ΔU_{M2N}-ΔN_{M4})=(U_{M1}-U_{N})-(U_{N}-U_{M3})+(U_{M2}-U_{N})-(U_{N}-U_{M4})=U_{M1}+U_{M2}+U_{M3}+U_{M4}-4U_{N}. Thus, in the final amplifier of the measuring device 7 of the scaling ratio of the resistance R_{8}/R_{9}should be equal to 1/4.

The unit also provides a measurement of the first three differences of electric potentials: ΔU_{M1M2}between the electrodes M_{1}M_{2}, ΔU_{M1M3}between the electrodes M_{1}M_{3}and ΔU_{M1M4}between the electrodes M_{1}M_{4}.

The measured differential amplifiers amplify 7, 13, 14 and 15 and processed by computer to obtain numerical values according to the formulas(4), (5), (6) and (7).

Note that according to the mathematical modeling of the distance L is six kilometres or more, the distances a and b is equal to one kilometer or more, the depth h of the dipole source is set in the range of twenty meters above the seabed to the surface.

1. The way the marine geoelectricity, in which the axis of the profile sensing excite an electromagnetic field in the thickness of the investigated medium, passing through it a periodic rectangular current pulses with pauses after each of them with the help of passing along professorintie electric dipole source;
at each point sensing during each pause after turning off the current is measured with a constant time interval Δt sequence of instantaneous values of the first and second differences of electric potentials of transient processes, while delivering the condition of equality to zero of the result of the first difference of electric potentials;

form interpretable parameters and using them and differential equations of mathematical physics the strength of the electric field of a dipole source in the electrochemically polarized conductive medium

where ∇^{2}- Laplace operator,

- the electric field of a dipole source, expressed in the equation for the case of harmonic changes in the magnitude of the electric field in time

σ(iωσ_{0}ητ) - frequency-dependent conductivity of the elements of the environment,

σ_{0}the electrical conductivity of the elements of the environment without the influence of induced polarization,

η is the coefficient of induced polarization,

τ is the time constant of decay of the potential difference induced polarization;

solve mathematical inverse problem, identifying inherent in each element of the environment three electrophysical parameters: conductivity σ_{0}induced polarization η and constant directivity the time of decay of the potential difference induced polarization τ;

and build three temporary cut in these settings;

characterized in that lay on the sea bottom measuring a profile that passes through fixed on the seabed measuring units, each of which consists of five electrodes:

Central and located equidistant around him on four vertices of a square, which two opposite sides are parallel to the axis of the profile.

within each period of the pulse-pause" spend geometric sensing when the current sensing on transients during a pause after turning off the current, measuring a second electric potential difference between all four external electrodes of the measuring system and the Central and the first electric potential difference between any of the three pairs of the four external electrodes of this installation;

when this measurement in each fixed on the measuring profile measuring system is carried out at the passing of a horizontal dipole source by the current profile runs parallel to the measuring and sdvinuta about it in terms in the orthogonal direction on the y-axis at a distance (y=-b) and height to the thickness h of the aqueous layer, sending current pulses in the test environment at all positions of the dipole source from a point with coordinate what inatomi [(x=-L),
{y=-b) (z=+h)] to the point [(x=+L), (y=-b), (z=+h)], then the dipole source, deploy and transfer to another parallel current profile, padded and shifted in the plan for measuring in the opposite direction on the y-axis at a distance (y=+b) and the height to the thickness h, and continue the measurement when it is driven in the reverse direction from the point with coordinates [(x=+L), (y=+b), (z=+h)] to the point [(x=-L), (y=+b), (z=+h)]; using the measured values of the first and second difference of electric potentials is determined by two independent current source and horizontal components of the current density (j_{x}=0 and j_{y}=0) at the point of sensing interpretable parameter is one of R_{z}(t_{o}on the basis of geometrical sounding at all positions of the dipole source, calculated by the formula

R_{z}(t_{o})=[ΔU_{M1M3}(I_{B1A1}, t_{o})]:

:{[Δ^{2}U_{M1M2M3M4N}(I_{B1A1}, t_{o})]+k1(t_{o})·[Δ^{2}U_{M1M2M3M4N}(I_{A2B2}, t_{o})]+

+k2(t_{o})·[Δ^{2}U_{M1M2M3M4N}(I_{A3B3}, t_{o})]+k3(t_{o})·[Δ^{2}U_{M1M2M3M4N}(I_{B4A4}, t_{o})]}, and the other R_{z}(t_{i}on the basis of sensing of transient processes at four selected by the method of iterations, the most informative separations with coordinates of the dipole source [(x=-a), (y=-b), (z=+h)], [(x+a) (y=-b), (z=+h)], [(x=+a), (y=+b), (z=+h)] and [(x=-a), (y=+b) (z=h)] of all explored,
calculated by the formula

Rz(t_{i})=[Δ^{2}U_{M1M3}(I_{B1A1},t_{i}):

:{[Δ^{2}U_{M1M2M3M4N}(I_{B1A1}, t_{i})]+k1(t_{i})·[Δ^{2}U_{M1M2M3M4N}(I_{A2B2}, t_{i})]+

+k2(t_{i})·[Δ^{2}U_{M1M2M3M4N}(I_{A3B3}, t_{i})]+k3(t_{i})·[Δ^{2}U_{M1M2M3M4N}(I_{B4A4}, t_{i})]},

where k1(t_{o}), k2(t_{o}), k3(t_{o}- the coefficients of focus when geometric probing, providing equipotentiality closed line passing through the four external electrodes of the measuring system and, thus, the exception in this line of the horizontal component of the current density j_{xy}at each point sensing on all geometric spacings during the current pulse, which is determined from the system of three equations

1) {[ΔU_{M1M2}(I_{B1A1}, t_{o})]+k1(t_{i})·[ΔU_{M1M2}(I_{A2B2}, t_{o})]+

+k2(t_{o})·[ΔU_{M1M2}(I_{A3B3}, t_{o})]+k3(t_{o})·[ΔU_{M1M2}(I_{B4A4}, t_{o})]}=0,

2) {[ΔU_{M1M3}(I_{B1A1}, t_{o})]+k1(t_{i})·[ΔU_{M1M3}(I_{A2B2}, t_{o})]+

+k2(t_{o})·[ΔU_{M1M3}(I_{A3B3}, t_{o})]+k3(t_{i})·[ΔU_{M1M3}(I_{B4A4}, t_{o})]}=0,

3) {[ΔU_{M1M4}(I_{B1A1}, t_{o})]+k1(t_{o})·[ΔU_{M1M4}(I_{A2B2}, t_{o})]+

+k2(t_{o})·[ΔU_{M1M4}(I_{A3B3}, t_{o})]+k3(t_{o})·[ΔU_{M1M4}(I_{B4A4}, t_{o})]}=0,

k1(t_{i}), k2(t_{i}), k3(t_{i}) - the factors focus when probing on transient at each point sensing in the pause current at all times transient,
determined from the system of three equations

1) {[ΔU_{M1M2}(I_{B1A1}, t_{i})]+k1(t_{i})·[ΔU_{M1M2}(I_{A2B2}, t_{i})]+

+k2(t_{i})·[ΔU_{M1M2}(I_{A3B3}, t_{i})]+k3(t_{i})·[ΔU_{M1M2}(I_{B4A4}, t_{i})]}=0,

2) {[ΔU_{M1M3}(I_{B1A1}, t_{i})]+k1(t_{i})·[ΔU_{M1M3}(I_{A2B2}, t_{i})]+

+k2(t_{i})·[ΔU_{M1M3}(I_{A3B3}, t_{i})]+k3(t_{i})·[ΔU_{M1M3}(I_{B4A4}, t_{i})]}=0,

3) {[ΔU_{M1M4}(I_{B1A1}, t_{i})]+k1(t_{i})·[ΔU_{M1M4}(I_{A2B2}, t_{i})]+

+k2(t_{i})·[ΔU_{M1M4}(I_{A3B3}, t_{i})]+k3(t_{i})·[ΔU_{M1M4}(I_{B4A4}, t_{i})]}=0,

t_{0}- time by passing a current pulse when the electric field transients is not different from its steady-state value corresponding to DC;

t_{i}the points in time at which the measured signals of transient processes at regular intervals of time Δt throughout pause after turning off the current.

[Δ^{2}U_{M1M2M3M4N}(I_{B1A1}, t_{o})],[Δ^{2}U_{M1M2M3M4N}(I_{A2B2}, t_{o})],

[Δ^{2}U_{M1M2M3M4N}(I_{A3B3}, t_{o})],[Δ^{2}U_{M1M2M3M4N}(I_{B4A4}, t_{o})] is the instantaneous value of the second difference of electric potentials between all four external electrodes M_{1}M_{2}M_{3}M_{4}the measuring setup and the Central N measured at at the time t_{
0}the bandwidth of the current in the dipole source passing through both current profiles through equidistant from the Central electrode N of the measurement setup four points, respectively, with coordinates [x, (y=-b), (z=+h)], [+x, (y=-b), (z=+h)], [+x (y=+b), (z=+h)] and [x (y=+b), (z=+h)];

[ΔU_{M1M2}(I_{B1A1}, t_{o})],[ΔU_{M1M2}(I_{A2B2}, t_{o})],[ΔU_{M1M4}(I_{A3B3}, t_{o})],

[ΔU_{M1M2}(I_{B4A4}, t_{o})],[ΔU_{M1M3}(I_{B1A1}, t_{o})],[ΔU_{M1M3}(I_{A2B2}, t_{o})],

[ΔU_{M1M3}(I_{A3B3}, t_{o})],[ΔU_{M1M3}(I_{B4A4}, t_{o})][ΔU_{M1M4}(I_{B1A1}, t_{o})],

[ΔU_{M1M4}(I_{A2B2}, t_{o})],[ΔU_{M1M4}(I_{A3B3}, t_{o})],[ΔU_{M1M4}(I_{B4A4}, t_{o})] is the instantaneous values of the first three differences of electrical potentials between the three pairs of external electrodes M_{1}M_{2}M_{1}M_{3}M_{1}M_{4}measured at time t_{0}the bandwidth of the current in the dipole source passing through both current profiles through equidistant from the Central electrode N of the measurement setup four points, respectively, with coordinates [x, (y=-b), (x=+h)], [+x, (y=-b), (z=+h)], [+x, (y=+b), (z=+h)] and [x, (y+b), (z=+h)];

[Δ^{2}U_{M1M2M3M4N}(I_{B1A1}, t_{i})],[Δ^{2}U_{M1M2M3M4N}(I_{A2B2}, t_{i})],

[Δ^{2}U_{M1M2M3M4N}(I_{A3B3}, t_{i}),],[Δ^{2}U_{M1M2M3M4N}(I_{B4A4}, t_{i})] is the instantaneous values of the Oia second difference of electric potentials between all four external electrodes M_{
1}M_{2}M_{3}M_{4}the measuring setup and the Central N, measured at time t_{i}transients in the pause current dipole source passing through both current profiles through equidistant from the Central electrode N of the measurement setup four points, respectively, with coordinates [(x=-a), (y=-b), (z=+h)], [(x=+h), (y=-b), (z=+h)], [x=+a), (y=+b), (z=+h)] and [(x=-h), (y=+b), (z=+h)];

[{[ΔU_{M1M2}(I_{B1A1}, t_{i})],[ΔU_{M1M2}(I_{A2B2}, t_{i})],[ΔU_{M1M2}(I_{A3B3}, t_{i})],

[ΔU_{M1M42}(I_{B4A4}, t_{i})],[ΔU_{M1M3}(I_{B1A1}, t_{i})],[ΔU_{M1M3}(I_{A2B2}, t_{i})],

[U_{M1M3}(I_{A3B3}, t_{i})],[ΔU_{M1M3}(I_{B4A4}, t_{i})],[ΔU_{M1M4}(I_{B1A1}, t_{i})],

[ΔU_{M1M4}(I_{A2B2}, t_{i})],[ΔU_{M1M4}(I_{A3B3}, t_{i})],[Δ^{2}U_{M1M4}(I_{B4A4}, t_{i})] is the instantaneous values of the first three differences of electrical potentials between the three pairs of external electrodes M_{1}M_{2}M_{1}M_{3}M_{1}M_{4}measured at time t_{i}transients in the pause current dipole source passing through both current profiles through equidistant from the Central electrode N of the measurement setup four points, respectively, with coordinates [(x=-a), (y=-b), (z=+h)], [(x=+a) (y=-b), (z=+h)], [(x=+a), (y=+b), (z=+h)] and [(x=-a), (y=+b), (z=+h)].

2. The way the marine geoelectrical the key according to claim 1, characterized in that the current profiles for the passage of a horizontal dipole source lay at a given depth or on the surface of the sea.

3. The way the marine Geoelectromagnetic according to claim 1, characterized in that the distance L is six kilometres or more, the distances a and b is equal to one kilometer or more, the depth h of the dipole source is set in the range of twenty meters above the seabed to the surface.

4. The way the marine Geoelectromagnetic according to claim 1, characterized in that the measuring system is placed on the measuring profile with equal step 200÷1000 m

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