RU48645U1 - RESEARCH COMPLEX "VESOTEM" FOR MARINE ELECTRIC EXPLORATION OF OIL AND GAS DEPOSITS - Google Patents

Abstract

The utility model relates to the field of exploration geophysics, in particular to equipment complexes for the implementation of geoelectrical exploration, and is designed to predict hydrocarbon deposits during sounding of the seabed in the deepwater part of the shelf zone. The proposed set of instruments and equipment for offshore electrical exploration of oil and gas fields includes a vessel with a generator and an exciting field formation unit, connected by a cable with a vertical dipole immersed in water with supply electrodes, a data recording and processing unit on board the vessel, a set of bottom stations and auxiliary equipment, moreover, the dipole is located in such a way that its lower electrode is located at a distance of not more than 100 m from the bottom of the sea. The use of the claimed research complex “VeSoTEM” opens up the possibility of registering the polarization characteristics of rocks when exposed to an electromagnetic field, which allows a better forecast for the presence of hydrocarbons under the seabed in the search area.

Description

The utility model relates to the field of exploration geophysics, in particular to equipment complexes for the implementation of geoelectrical exploration, and is designed to predict hydrocarbon deposits during sounding of the seabed in the deepwater part of the shelf zone.

At present, various methods are widely used for offshore exploration of hydrocarbon deposits related to the impact of electromagnetic field pulses on the seabed, subsequent registration of changes in the electromagnetic parameters of benthic rocks and analysis of the data obtained to detect existing anomalies and determine their nature. Exploration is carried out using various research systems of apparatus and equipment (IR) (US Pat. RF No. 2236028, 2004; auth. St. USSR No. 1122998, 1984; auth. St. USSR No. 1798666, 1996; auth. St. USSR No. 1434385, 1988; US Pat. No. 4,298,840, 1981; US Pat. No. 4617518, 1986).

Thus, a complex for marine electrical exploration on a drifting ice floe is known, consisting of exciting and receiving installations, a source of alternating periodic current pulses and a data processing installation. When using the complex, exciting and receiving installations

placed vertically under the ice in a fixed layer of water (RU 2069375, 1993). The impulses are supplied by a source of alternating periodic current pulses with a power of several tens of amperes using an EDS 72 or other installation, data processing using a digital electric prospecting station of the CES type. Profile profiling is carried out. with a fixed distance between the points of excitation and reception of signals after exposure to an alternating pulse. Only the vertical component of the electric field is measured. However, this method cannot be used for measurements in the movement of the vessel, because It is based on work with a motionless layer of water relatively ice. In addition, the method is inoperable when working at a depth of more than 200 m.

More universal and promising when reconnaissance using ships are methods associated with the use for analysis of data on the polarization of rocks under the influence of an electromagnetic field (the method of induced polarization, field formation, etc.). (Pat. RF No. 2236028, 2004; aut. St. USSR No. 1122998, 1984; aut. St. USSR No. 1798666, 1996; aut. St. USSR No. 1434385, 1988; US Pat. No. 4,298,840, 1981; US Pat. No. 4617518, 1986)

In particular, in the author. St. USSR No. 1434385, 1988, an IR is proposed consisting of a feed line laid out at the bottom, the length of which is 5-10 times greater than the specified depth of research, a generator connected to it, and measurement sensors connected to measuring equipment. After installing the equipment and compensating for the signals of the natural field and the intrinsic polarization of the sensor electrodes in the line, passing current pulses excite the electric field and, at the end of the pulse, the corresponding signals of the induced polarization are measured after a predetermined time interval.

The disadvantage of this IR is the relatively low measurement accuracy and the impossibility of its use at great depths.

A known method of exploration of deposits using the method of induced polarization (US Pat. RF No. 2094829, 1993), in which register the intensity of the electromagnetic field of the induction induced

polarization, which is the difference between the total field strength and the field strength due to the process of induced polarization. Based on the results of the analysis, changes in this parameter over time are judged on the presence of geoelectric heterogeneities and their nature.

A typical IR used for marine electrical exploration includes a carrier vessel equipped with an echo sounder, a towed horizontal dipole with supply electrodes, and receiving electrodes. The set of equipment located on the vessel includes impulse generation blocks, registration and analysis of the received data, and auxiliary devices providing the vessel to the research point, fixing the depth of the sea, etc. (Pat. RF №1819354, 1990).

The closest in technical essence to the claimed solution is IR (US Pat. RF No. 2236028, 2003), which includes a vessel (watercraft), on which is located a rectangular current pulse generator, submerged electrodes of a horizontal current dipole, receiving electrodes installed on the axis of the profile through certain predetermined distances, computer recording and processing units, as well as auxiliary devices used to synchronize measurements and fix the sounding point (radio uk, satellite, etc.). In the course of studies, at the end of each current pulse and in the pauses between pulses, the instantaneous values of the first and second axial potential differences are measured and, using further calculations, a model of the medium is analyzed.

The disadvantage of this IR is the inability to work with it when exploring large depths due to the lack of a polarizing effect in this case.

The challenge facing the authors was the creation of an IC capable of reconnaissance of the seabed at depths of up to 5000 m.

The technical result is achieved due to the fact that in the IR, consisting of a vessel with a generator and a unit for the formation of the exciting field, connected

with a dipole immersed in water with feeding electrodes, recording devices, a data recording and processing unit, and auxiliary equipment, a vertical dipole is used instead of a horizontal supply dipole, the lower end of which is not more than 100 m from the sea bottom, and a set of bottom stations.

As it turned out during the study, the use of such a vertical dipole, in contrast to the horizontal one, can also cause polarization of rocks in the study of large depths of the sea.

The need to register changes in the electromagnetic field at great depths requires a transition from registration devices on board the vessel to the bottom stations, because otherwise, it is technologically difficult to record changes in the electromagnetic field at great depths. As bottom stations (DS), typical electric or magnetic bottom stations or a combination thereof are used. Such bottom stations, in particular, are described in US Pat. US No. 5770945, 1998 or in the English. Pat No. 2402745, 2003. Stations are arranged according to the traditional scheme, so that at least three stations are in the area of a possible deposit, and some stations are located outside it.

As auxiliary devices, the IR includes, in particular, the self-priming unit of the bottom stations, a ballast device that provides power dissipation of the generator between the pulses and consists of pairs of multidirectional electric dipoles with equal moments, equipment for determining the position of the vessel, the depth of the sea, etc. P.

Achievable technical result is the ability to carry out reconnaissance at significantly greater depths of the sea (from 200-300 to 5000 m) while maintaining the advantages of the VP method, which allows conducting studies with an increased degree of accuracy and reliability of measurement results.

The general IR scheme is shown in figure 1, where the following notation is used.

1 - a vessel, on board of which there is a ship generator 2, an exciting field generation unit (BFP) 3, and a data recording and processing unit (BRO) 4;

5 - generator line (dipole);

6 - upper feed electrode;

7 - lower feed electrode;

8 - first line (coaxial section of the cable of the generator set, supplying voltage to the supply electrode 6);

9 - second line (cable section of the generator set connected to the supply electrode 7);

10 - pressure measurement module and mini-sounder;

11 - ballast device;

12 - on-board acoustic unit of the self-flooding system of bottom stations;

13 - bottom stations;

14 - receiving electrodes;

15 - flexible mutually perpendicular rods, used to accommodate the receiving electrodes 14;

16 - induction sensors of the magnetic field;

17 - circuit breakers self-priming system of bottom stations;

18 - cargo, providing immersion station.

The research complex works as follows. When vessel 1 exits to the profile start point before setting the bottom stations, the FFT clock 3 and bottom stations 13 are synchronized by reference signals (for example, GPS PPS signal). Bottom stations 13 are installed along the measurement profile at predetermined points in such a way that at least three stations are in the field of a possible deposit, and some stations are located outside it.

After setting stations 13, the vessel leaves at a point located at a distance not less than the depth of the sea from the beginning of the profile, the generator line 5 is lowered vertically so that the lower supply electrode 7 is at a distance of not more than 100 m from the bottom, which is controlled by the readout of the mini-echo sounder of module 10 Next, BFP 3 starts, which forms bipolar pulses with pauses that have a polarizing effect on the rocks of the seabed. The duration of pulses and pauses is from 0.5 to 16 seconds. Depending on the challenges and features of the equipment used. In pauses, a non-emitting ballast device 11 is connected to the ship generator 2, which reduces the inrush current of the load. BRO 4 measures the current in dipole 5 with a programmatically specified discreteness, both during the pulse and in the pause between pulses with fixing the start and end times of each pulse. In the process of formation of the exciting field, the vessel 1 is positioned at a given point by GPS signals for at least 10 minutes. In this case, the bottom stations 13 carry out the registration of the signal with the same discreteness as in the BFP 3, both during the pulse and in the pause between pulses.

Then the vessel moves to the next predetermined point, where the process repeats. After completing the entire profile, the BFP 3 is turned off, the generator line (dipole) 5 is lifted aboard and a command is given to the self-priming unit of the bottom stations 12 for the subsequent ascent of the bottom stations 13. After raising the bottom stations, the mutual mismatch of the clocks of the bottom stations and the generator line 5 is measured The resulting residual is evenly distributed over the entire measurement period. The signals measured from the moments of current pulses and pauses from the bottom stations 13 are transferred to the BRO 4 for further processing and interpretation.

Figure 2 and 3 shows the results of calculating the electric fields recorded by the bottom stations for the offshore hydrocarbon field

with parameters of resistivity ρ and with parameters η, τ and c characterizing the frequency dispersion (VP) according to the Cole-Cole formula:

where j is the layer number;

when using the traditional scheme of excitation by a horizontal electric dipole (HED) at a depth of 500 m and when using a vertical electric dipole (FEA) at a depth of 1000 m (solid lines are a model with a deposit and altered rocks, the dotted line is the background).

As can be seen from the above data, when using HED already at a depth of 500 m, the difference between the fields in the presence of hydrocarbons and their absence is practically absent, while when using FEA, the differences in the late stage of the formation process (t> 0.5 s) are very significant and can be detected by bottom stations.

Figure 4 illustrates the change in signals in the event that the lower electrode of the dipole moves away from the bottom (t> 1.0 s). From the above graph it follows that when the electrode is removed from the bottom more than 100 m, the difference in the fields in the presence and absence of a hydrocarbon field becomes uninformative.

The above results showed the possibility of obtaining the polarization characteristics of the rocks when using the inventive research complex and its prospects for the exploration of hydrocarbon deposits in the deep shelf in order to make a better forecast for the presence of hydrocarbons under the seabed in the search area.

Claims (3)

1. The research complex for offshore electrical exploration of oil and gas fields, including a vessel with a generator and an excitation field generating unit, connected to a dipole immersed in water with supply electrodes, recording devices, a data recording and processing unit on board the vessel and auxiliary equipment, characterized in that the dipole with the supply electrodes is located vertically so that its lower end is at a distance of not more than 100 m from the bottom of the sea, and for recording signals form a set of bottom stations. 2. The research complex according to claim 1, characterized in that as auxiliary devices it includes a self-priming unit of the bottom stations and equipment for determining the position of the vessel and the depth of the sea. 3. The research complex according to claim 1, characterized in that as an auxiliary device it includes a ballast device.