Method and device for marine electrical exploration of oil and gas fields

FIELD: instrumentation.

SUBSTANCE: group of inventions refers to geophysics, in particular to equipment systems for geoelctric exploration by induced polarisation method and is intended for predicting hydrocarbon accumulations in transit shelf zone at depths up to 10 m. Essence: the system includes a set of sea-bed stations and vessel with generator and exciting field formation unit connected with submerged horizontal towed dipole with energising electrodes; non-radiative ballast device; equipment for reading and writing data from sea-bed stations, recording position and time of current pulses generation and sea-bed stations initialisation. Sea-bed stations are equipped with "braids" positioned along and across exiting line. Each of the "braids" contains at least 3 measuring electrodes located at distance of 50-500 metres from each other. Time series of the first and the second electric potential differences of electric field between electrodes are recorded both during passage of current and during pause between pulses. When interpreting, data on field both during current passage and during pause between pulses is used in wide space-time domain. Resistance of medium and its polarisation characteristics are determined.

EFFECT: providing higher-grade prediction of possible hydrocarbon material sources within studied zone at shallow depths.

3 cl, 6 dwg, 1 tbl

 

The technical field

The claimed group of inventions relates to the field of exploration Geophysics, in particular to methods implementation Geoelectromagnetic by the method of induced polarization, and is intended for forecasting of hydrocarbon deposits in the transit zone of the continental shelf at depths up to 10 meters

Prior art

Now for Maritime exploration of hydrocarbon deposits are widely used various methods associated with the impact on the seabed of the pulses of electromagnetic fields, registration of changes of electromagnetic parameters of benthic species and the analysis of the received data to detect existing anomalies and determine their nature (EN 2236028, 2004; SU 1122998, 1984; SU 1798666, 1996; SU 1434385, 1988; US 4298840, 1981; US 4617518, 1986), which are using different research complexes instruments and equipment (IR).

Thus, the known system for marine em on drifting ice, consisting of the exciting and receiving units, a source of alternating periodic current pulses and installation data. When using complex exciting and reception setup placed vertically beneath the ice in a stationary layer of water (EN 2069375, 1993). The applying pulses spend source of alternating periodic current pulses the power of several tens of amperes using ER is 72 or other installation, data processing using a digital electrical station type CCE. Profiling incision is performed with a fixed distance between the points of excitation and reception of signals after exposure to alternating pulse. Measure only the vertical component of the electric field. However, this technology cannot be used to measure the motion of the ship, because it is based on working with stationary relative to the layer of water ice, as well as inefficient when operating at shallow depths, where the loose drift ice is difficult.

A device for measuring the resistance of the seabed (GB 2390904) using a vertical electric and magnetic dipoles placed on a towed underwater apparatus, and a set of bottom stations. However, this device is fundamentally inapplicable in shallow water because of the cumbersome installation. In addition, based on its work method lacks precision, because not take full advantage of opportunities to investigate the polarization characteristics of the rocks of the seabed.

More versatile and promising for exploration using ships is the method of induced polarization (IP) (EN 2236028; EN 2253881, SU 1798666; SU 1434385; US 4298840; US 4617518)that allows you to build a profile to take into account both the conductivity and polarizability of the rocks of the seabed.

Known for the methods and devices (EN 2236028; EN 2253881), in which the medium is excited towed behind the vessel horizontal generating line, and the measurement of the primary and secondary signals are towed by the selection line length from 500 to 1000 meters This device practically unusable in conditions of shallow water, when the ship on which is based the installation must be at a sufficient distance from the shore zone of the great depths. In addition, when using the similar way of access to information is limited, because envisage only two options: either the excitation of the medium at a fixed symmetric relative to the point of sensing distance, either directly at the point of sensing when two measurement setups. Thus, in the patent RU 2236028 use unipolar current pulses and generating the dipole is located on the axis line measurements.

In particular, it is known (SU 1434385, 1988) complex, consisting of a spread on the bottom of the supply line, the length of which is 5 to 10 times greater than the specified depth research, it is connected to the generator and sensor measurements, connected to the measuring equipment. After setting up the equipment and compensation signals of the natural field and own the polarization of the electrodes of the sensors in line excite an electric field by passing current pulses, and at the end of each pulse after a specified shall interval time measure corresponding signals induced polarization and on the basis of the obtained results make the modeling section. The disadvantage is the poor performance of the method associated with a relatively small measurement area defined by the length of the power line

The closest in technical essence to the claimed technical solution was to research complex (RU 0048645, 2005), consisting of a vessel that hosts generator and block the formation of the exciting field (FFT)to generate the pulses in discrete mode, measuring equipment and auxiliary devices. FFT is associated with submerged vertical dipole with the feed electrode, the lower end of which is at a distance of not more than 100 m from the seabed. For reception of signals using the set of bottom stations (DS), which uses standard electric or magnetic bottom station with flexible rods serving to accommodate receiving electrodes. Station feature so that at least three stations were located in areas of potential fields, and some stations were outside. As an auxiliary device in IR includes, in particular, the power system snowsprite bottom stations, ballast device providing power dissipation generator in the intervals between pulses and representing a pair of multi-directional electric dipoles with Rav is diversified moments apparatus for determining the location of the vessel, the depth of the sea, etc.

The method of measurement is that at the exit of the vessel to the point of beginning of the profile before staging bottom stations is clock synchronization FFT and bottom stations. Bottom stations are installed along the profile measurements at predetermined points so that at least three stations were located in areas of potential fields, and some stations were outside. After establishing stations the ship comes to a point at a distance not less than the depths of the sea from the beginning of the profile, the generator line is lowered vertically to the bottom of the supply electrode was at a distance of not more than 100 m from the bottom, then run FFT, which generates bipolar pulses with pauses, providing a polarizing effect on the rocks of the seabed. In the pauses to the ship's generator is connected non-emitting ballast device that reduces current surges load. The BROKER carries out the measurement of the current in the dipole with a given software by discreteness both during the pulse and the pause between pulses with a timestamp at the beginning and end of each pulse. Bottom station registration of signals with the same resolution as in FFT, both during the pulse and the pause between pulses. On the basis of the obtained data characterizing ka is the conductivity, and the polarizability of the rocks of the seabed, built a profile cut on the basis of which it is concluded that the presence or absence of oil and gas fields.

The disadvantage of this solution was the practical impossibility of its application in the transit zone of the continental shelf in connection with the necessity of using vertical generating lines in length from several tens to several hundreds of meters, which is virtually impossible with depths up to 10 meters

The technical problem solved by the authors, was the creation of IR and method of measurement for work in the transit zone of the shelf, allowing more accurate and reliable information about the nature of the rocks of the seabed on the basis of the conductivity of rocks and their polarization characteristics.

The technical result in relation to the proposed method lies in the fact that as a source of information about the status of the species used information on the conductivity of rocks and their polarization characteristics, in particular computed as a continuous measurement of the first and second differences of the potentials of the electric field during the pulses and the interval between them in a wide spatio-temporal region. For this purpose, the generator line is towed behind the vessel on the sea surface, the excitation of the field exercise alternating rectangular pulses, R is gastronaut scan signals in time using a multichannel bottom stations equipped with a receiver lines (spits), having at least three electrodes located at a distance of 50-500 m from each other, record the time series of first and second differences of the potentials of the electric field between the electrodes while passing current in the interval between pulses, and during the interpretation of the information use the information on the field during passing current in the interval between pulses in a wide spatio-temporal region and determine not only the resistance of the medium, but also its polarization characteristics.

The technical result in relation to the claimed device is to create a system that allows you to record time series of first and second differences of the potentials of the electric field between the electrodes while passing current in the interval between pulses, which allows you to get an idea of the parameters of the electric resistance of the material of the seabed, and their polarization characteristics. This is achieved by the fact that in IR, consisting of vehicle (vessel), which is the instrument of formation of discrete bipolar pulse generator, non-emitting ballast device, apparatus for reading and recording information from the bottom stations, reception location and time of generation of pulses of current and initial the bottom emission stations; towed horizontal generating line; multi-bottom stations, equipped with a receiver lines (spits), having at least three electrodes located at a distance of 50-500 m from each other, allowing to register and signals the formation of the field ΔU and their spatial derivative Δ2U and record the measurement of the first and second differences of the potentials of the electric field during the pulses and the interval between them in a wide spatio-temporal region.

Analysis of ΔU and Δ2U allows you to more fully explore the spatial-temporal structure of the field, increases the reliability of the determination of all parameters. This allows the simultaneous formation of multiple profiles of observation.

Braids are placed parallel or perpendicular to the excitation, which is towed generator dipole (figure 1 and 2). The specific location of KOs is determined by the specific features of the site measurements. The combination generator of discrete pulses, towed horizontal dipole and KOs with recording electrodes provides the data, containing information not only on the resistance of the deep layers of rocks, but also their polarization characteristics, which yields better predictions about possible resources at glevodorodnogo raw materials in the study area.

The use of this group of inventions first appears the ability to forecast on the basis of measurements of parameters of electromagnetic fields both in time and in spatial areas simultaneously, which greatly increases the reliability of determining the analyzed parameters of the environment. In addition, the use of a fixed line registration reduces interference and improves the accuracy of measurement compared with receiving electrodes in motion.

The invention is illustrated by the following drawings.

Figure 1 shows the General scheme of the research complex, during which the vessel is moving parallel to the braids.

Figure 2 shows the General scheme of work the research complex, during which the vessel is moving perpendicular to the braids.

Figure 3 shows the dependence of the signal ΔU between the electrodes M and N from the measurement time for different spacings for axial location of the generating electrode and line location of KOs.

Figure 4 shows the dependence relation Δ2U/ΔU, where Δ2U - the difference between the signals measured on pairs of electrodes MO and ON, from the time measurements for different spacings for axial location of the generating electrode and line location of KOs.

Figure 5 shows the dependence of the signal ΔU between what electrode M and N from the measurement time for different spacings for the orthogonal arrangement of the generating electrode and line location of KOs.

Figure 6 shows the dependence relation Δ2U/ΔU, where Δ2U - the difference between the signals measured on pairs of electrodes MO and ON, from the time measurements for different spacings for the orthogonal arrangement of the generating electrode and line location of KOs.

In figure 1 the following symbols are used:

1 - small vessel, on Board of which ship is the generator 2, the shaping unit of the exciting field (FFT) 3 and unit registration and data processing (SOA) 4;

5 - towed generator line (dipole);

6 - ballast device;

7 is a bottom station;

8 - selection line (braid) with receiving electrodes 9.

Figure 3-6 use a solid line for the model calculation with the accumulation and altered rocks, dashed line shows the background.

Measurements at depths from 0 to 10 m along the profile system, which may be located along the coastline, and perpendicular to it.

Research complex works as follows.

Before starting work with the help of auxiliary boats along the observation profile (MO) are arranged receiving lines 8 so that the receiving electrodes 9 were placed in predefined points of the profile. The position of the electrode 9 is controlled according to the receiver-indicators (PI) of the GPS system. Indigenous all foster Lin is th 8 are connected to a bottom stations 7, which before putting on the bottom are initialized and synchronized with the clock FFT 3 on reference signals (for example, PPS signal of the GPS system). Bottom stations 7 with receiving lines 8 can be equipped with one or multiple profiles. Some stations with receiving lines can be placed at zero depth (Bank).

After placement of bottom stations small vessel 1 lies in the starting point of the excitation profile (PV), the direction of which may coincide with the direction of MO or be orthogonal.

The excitation generator is line 5, towed small carrier 1. Before towing on the basis of the generator 2 starts FFT 3, which generates bipolar pulses of rectangular shape with a specified duration and duty cycle, providing a polarizing effect on the rock shelf. The duration of the pulses and pauses depending on the challenges and characteristics of the equipment used is from 0.5 to 16 sec. In the pauses to ship generator 2, as a rule, connected, non-emitting ballast device 6, which reduces throws load the ship's generator.

BRO 4 carries out the measurement of the current in the dipole 5 with a given software by discreteness both during the pulse and the pause between pulses with a timestamp at the beginning and end of each pulse. When the volume of the bottom station 7 record time series data as the difference of potentials between the electrodes, and the second difference, which is analogous to the spatial derivative of the field. Upon completion of the PV is the rise of receiver lines and ground stations on Board the vessel, bottom stations is overwritten in BROUGH 4 for further processing and the whole cycle repeats.

The obtained results are processed, and used when interpreting the data on the field during the pulses and the interval between pulses. From the measured ground stations 7 signals through simulation retrieves information about changing parameters like resistance, and parameters of the induced polarization with depth of the rocks.

To assess the potential of the method was carried out mathematical modeling. In particular, there was a problem with the following initial data: the water depth is 5 m, the length of a horizontal electric dipole (GAD) with centre O', towed on the surface of 500 m, the current is 100 A. Measuring spit consists of three electrodes M 400 m 400 m, N, O - center installation. The model of the environment that simulates a marine Deposit of hydrocarbons, used for theoretical calculations, consists of 5 layers. Each layer in the model was set according to the formula Cole-Cole:

,

where ρω- electrical resistivity at the frequency ω, η polarizability, τ is the time constant and with - the exponent, j is the number of layers. The parameters of the layers in the table.

The number of layerOptions
ρ, Mmeη, %τ, sh (power m)
10.30--5
210.50.10.5100
31510.51900
4500--100
51 0.50.10.5100

Theoretical calculations are carried out for two variants of the measure - in the first case, the generator line and the profile bottom stations pines, the distance OO'=500, 1000 and 1500 m In the second case, the GAD moves along a profile perpendicular to the line MON, crossing it at a distance of 1000 m, the distance between the intersection point and the center O' is equal to 250, 500, 1000 meters

Were calculated for the following parameters: signal ΔU between the electrodes M and N, and the ratio Δ2U/ΔU, where Δ2U - the difference between the signals measured on pairs of electrodes MO and ON. The results are shown in figure 3 and 4 for the axial location of GAD and the measuring line and figure 5 and 6 for orthogonal installation. Solid line - model with accumulation and altered rocks, dashed line is the background. As can be seen from the data in the change of distance anomalous zone is evident in the signals differently. The use of a wide spatio-temporal region allows recovery of incision as impedance and polarization parameters.

The above results show the possibility of obtaining complex characteristics of rocks when using the inventive IR and its prospect for exploration of hydrocarbons in terms of Tr is nitnoy zone with the aim of realizing a higher quality Outlook on their presence beneath the seabed in the area of the search

The use of the inventive technology, in conjunction with data from other geophysical methods, can increase the reliability of determining the presence in the context of hydrocarbons and thereby increase the success rate of exploration drilling.

1. Way marine electrical exploration of oil and gas fields, including the placement of bottom stations in the area of research, the excitation of the electromagnetic field using a generator line that is placed in the zone of location of stations, the registration signal receiving electrodes benthic stations, removing from the stations received information about the electrical resistivity of the rocks of the seabed, modeling profile of these rocks and making predictions about the presence of hydrocarbons, characterized in that before diving synchronize the clock mounted on the block formation of the exciting field in the dipole and the ground stations, the dipole is towed behind the vessel on the sea surface along the profile, the excitation of the field carry out different periodic pulses with pauses between them, information is obtained using the set of multi-channel benthic stations, equipped with a receiver lines with at least three electrodes located at a distance of 50-500 m from each other with a uniform pitch along the entire profile of observations and recorded the comfort of the time series of first and second differences of the potentials of the electric field between the electrodes during the pulses, and in the pause between pulses, and used when interpreting the data on the field during the pulses and the interval between pulses in a wide spatio-temporal region and is defined as the resistance of the medium, and its polarization characteristics.

2. Research complex for marine electrical exploration of oil and gas fields, including the vehicle on which the apparatus forming discrete bipolar pulses, non-emitting ballast device, apparatus for reading and recording information from the bottom stations, reception location and time of generation of the current pulses and initialization of bottom stations, as well as a towed horizontal generating line, characterized in that the registration of the electric field is multi-channel ground stations using the receiver lines (KOs), having at least three electrodes located at a distance of 50-500 m from each other, and a base station keeps a record of the time series of the first and second difference of potentials of the electric field between the electrodes during the pulses and the interval between pulses in a wide spatio-temporal region.

3. Research complex according to claim 2, characterized in that the length of KOs is from 100 to 3000 m



 

Same patents:

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SUBSTANCE: measurement of magnetic field components is done from a point located at a certain distance from the central structure of the electromagnetic measuring system. The point is chosen in such a way that the magnetic field, arising from electrical current in the central structure substantially does not have effect on measurements of the magnetometer. The device, which allows for the given method, consists of central structure, several beams which have a first and second end. The second end is hinged to the central structure, while the first end is free. At least one of the electrodes and magnetometer is joined to each beam.

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SUBSTANCE: in three suggested versions of method electromagnetic field is exited in thickness of surveyed medium by sending into it rectangular pulses of current with intervals. Geometric probing is performed within the current pulse, and probing in transitive processes is performed within a pause. Also instantaneous values of the first and the second differences of electric potentials on the sea bottom are measured. Under the first version of the method three parallel profiles are laid. The medium profile is a measuring one; it passes through the probing point fixed on the sea bottom. Two other profiles are designed for transit of horizontal dipole source in a near bottom zone. The second axial and orthogonal differences of electric potentials are measured as well as differences of an axial, orthogonal and one any of four possible segmented between the two nearest exterior measuring electrodes differences of electric potentials are measured. There is provided the condition of equality to zero of resulting difference of electric potentials: axial, orthogonal and one of any segmented for exclusion of a horizontal component of current density in the point of probing. Two sets of normalisable interpretive electric parameters are calculated from values of the above said differences, considering these two sets are not influenced by side effect of three dimensions geologic non-uniformities located beyond the point of probing. Using obtained parameters an inverse problem is solved on the base of differential equation of mathematical physics for electrical field intensity of dipole source in electrochemical polarising conductive medium. Time-base sections are graphed on electro-conductivity of the medium, on coefficient of caused polarisation and on the constant of the period of fall of caused polarisation potential difference.

EFFECT: complete excluding horizontal constituent of current density in point of probing, excluding effects of side non-uniformities.

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The invention relates to the field of geophysical exploration and more specifically to methods of marine Geoelectromagnetic using adjustable artificial sources of electromagnetic fields

The invention relates to the field of geophysical research, and is intended for exploration and delineation of oil and gas deposits

The invention relates to the field of geophysical research, and is intended for exploration and delineation of oil and gas deposits

The invention relates to the field of geophysical research, and is intended for exploration and delineation of oil and gas deposits

FIELD: geophysical research, possible use for finding and contouring oil-gas deposits.

SUBSTANCE: method includes excitation of electromagnetic field within thick portion of researched environment, by letting through it a periodical series of rectangular current pulses with pauses between each one of them serially from two dipole sources. Between current pulses in pauses along whole length of these, momentary values of first and second axial and second orthogonal potentials differences are measured when resulting first difference of potentials between extreme measuring grounding parts is equal to zero. Along whole duration of each pause two momentary values positioned adjacently in time of first and second differences of potentials are selected, determining differences between their values. From values of differences, three normalized electrical parameters are calculated. Reverse problem is solved on basis of differential fading wave equation of mathematical physics for strength of dipole source in electrochemically self-polarizing conductive environment. Model of environment, most close to geometrical structure and electrical parameters of researched environment, is determined, and temporal cuts are constructed by electric conductivity, coefficient of caused polarization and time of fading of difference of potentials of aforementioned caused polarization.

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EFFECT: possibility to obtain data about specific resistance and polarisability of strata during exploration of deep water areas, and provision of more accurate predictions.

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EFFECT: enhanced measurement accuracy.

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SUBSTANCE: in three suggested versions of method electromagnetic field is exited in thickness of surveyed medium by sending into it rectangular pulses of current with intervals. Geometric probing is performed within the current pulse, and probing in transitive processes is performed within a pause. Also instantaneous values of the first and the second differences of electric potentials on the sea bottom are measured. Under the first version of the method three parallel profiles are laid. The medium profile is a measuring one; it passes through the probing point fixed on the sea bottom. Two other profiles are designed for transit of horizontal dipole source in a near bottom zone. The second axial and orthogonal differences of electric potentials are measured as well as differences of an axial, orthogonal and one any of four possible segmented between the two nearest exterior measuring electrodes differences of electric potentials are measured. There is provided the condition of equality to zero of resulting difference of electric potentials: axial, orthogonal and one of any segmented for exclusion of a horizontal component of current density in the point of probing. Two sets of normalisable interpretive electric parameters are calculated from values of the above said differences, considering these two sets are not influenced by side effect of three dimensions geologic non-uniformities located beyond the point of probing. Using obtained parameters an inverse problem is solved on the base of differential equation of mathematical physics for electrical field intensity of dipole source in electrochemical polarising conductive medium. Time-base sections are graphed on electro-conductivity of the medium, on coefficient of caused polarisation and on the constant of the period of fall of caused polarisation potential difference.

EFFECT: complete excluding horizontal constituent of current density in point of probing, excluding effects of side non-uniformities.

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FIELD: instrumentation.

SUBSTANCE: group of inventions refers to geophysics, in particular to equipment systems for geoelctric exploration by induced polarisation method and is intended for predicting hydrocarbon accumulations in transit shelf zone at depths up to 10 m. Essence: the system includes a set of sea-bed stations and vessel with generator and exciting field formation unit connected with submerged horizontal towed dipole with energising electrodes; non-radiative ballast device; equipment for reading and writing data from sea-bed stations, recording position and time of current pulses generation and sea-bed stations initialisation. Sea-bed stations are equipped with "braids" positioned along and across exiting line. Each of the "braids" contains at least 3 measuring electrodes located at distance of 50-500 metres from each other. Time series of the first and the second electric potential differences of electric field between electrodes are recorded both during passage of current and during pause between pulses. When interpreting, data on field both during current passage and during pause between pulses is used in wide space-time domain. Resistance of medium and its polarisation characteristics are determined.

EFFECT: providing higher-grade prediction of possible hydrocarbon material sources within studied zone at shallow depths.

3 cl, 6 dwg, 1 tbl

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

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