RU53460U1 - RESEARCH COMPLEX 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 performing geoelectrical exploration using the method of induced polarization, and is designed to predict hydrocarbon deposits in the transit zone of the shelf at depths of up to 10 m. A research complex for marine electrical exploration is proposed, which includes a set of bottom stations and vessel with a generator and a block for the formation of an exciting field that provides the generation of discrete bipolar pulses associated with immersed in water horizontal dipole towed with feeding electrodes recording devices and auxiliary equipment. Bottom stations are equipped with “braids” located along or across the excitation line, located along or across the excitation line, each of which contains at least 3 measuring electrodes located at a distance of 50-400 meters from each other. The use of the complex provides obtaining data containing information both about the resistance of the deep strata of rocks and about their polarization characteristics, which allows us to obtain a better forecast of possible hydrocarbon resources in the studied area.

Description

The utility model relates to the field of exploration geophysics, in particular to equipment complexes for geoelectrical exploration using the method of induced polarization, and is designed to predict hydrocarbon deposits in the transit zone of the shelf at depths of up to 10 m.

Currently, various methods are widely used for offshore exploration of hydrocarbon deposits, related to exposure to the seabed of pulses of an electromagnetic field, registration of changes in the electromagnetic parameters of benthic rocks and analysis of the obtained data to detect existing anomalies and determine their nature (RU 2236028, 2004; SU 1122998, 1984; SU 1798666,1996; SU 1434385, 1988; US 4298840, 1981; US 4617518, 1986), which are carried out using various research equipment and instruments (IR).

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, the exciting and receiving installations are placed vertically under the ice in a fixed layer of water (RU 2069375, 1993). The pulses 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 electrical prospecting station of the type TSES. Section profiling is carried out with a fixed distance between

points of excitation and reception of signals after exposure to alternating impulse. Only the vertical component of the electric field is measured. However, this technology cannot be used for measurements in the movement of the vessel, because It is based on working with a layer of water that is motionless relative to the ice, and is also inoperative when working at shallow depths, where free ice drift is difficult.

The more universal and promising method for reconnaissance using ships is the method of induced polarization (VP) (RU 2236028; SU 1122998; SU 1798666; SU 1434385; US 4298840; US 4617518).

In particular, in SU 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 research depth, a generator connected to it, and measurement sensors connected to measuring equipment. After adjusting the equipment and compensating for the signals of the natural field and the polarization of the sensor electrodes in the line, an electric field is excited by passing current pulses, and at the end of each pulse, the corresponding signals of the induced polarization are measured at a given time interval and a section is simulated based on the results obtained. The disadvantage of this method is the low productivity.

The closest in technical essence to the claimed technical solution was previously developed by the authors of IR (RU 0048645, 2005), consisting of a vessel on which a generator and a block for generating an exciting field (BPF) are placed, which allow generating pulses in a discrete mode, measuring equipment and auxiliary devices. The BFP is connected with a vertical dipole immersed in water with supply electrodes, the lower end of which is located at a distance of not more than 100 m from the bottom of the sea. To register the signals, a set of bottom stations (DS) is used, which are used as standard electric or magnetic bottom stations with flexible rods, which are used to place the receiving electrodes. Such bottom stations, in particular, are described in US 5770945, 1998 or in GB 2402745, 2003. The stations are arranged according to the traditional scheme, thus

so that at least three stations are in the area of a possible deposit, and some of the 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.

The disadvantage of this solution was the practical impossibility of its application in the transit zone of the shelf at depths of up to 10 m

The technical task was the creation of infrared for operation in the transit zone of the shelf, allowing to obtain data based on polarization characteristics.

The technical result was obtained by creating an IR based on a set of multi-channel bottom stations with measuring electrodes located on the “braids” at a distance of 50-400 meters from each other, a vehicle (vessel), on which non-radiating discrete bipolar generator pulse forming equipment is located ballast device, apparatus for reading and writing information from bottom stations, recording the place and time of generating current pulses and initializing bottom stations, as well as towed horiz on-line generator dipole. The braids are parallel or perpendicular to the excitation line along which the generator dipole is towed. Each “braid” contains at least 3 measuring electrodes and has a length of 100 to 3000 m.

The combination of a discrete pulse generator, a towed horizontal dipole and streamers with recording electrodes provides data containing information not only about the resistance of deep rock formations, but also about their polarization characteristics, which allows a better forecast about possible hydrocarbon resources in the studied area.

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

1 - a small 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 - towed generator line (dipole);

6 - ballast device;

7 - bottom stations;

8 - braid with receiving electrodes 9.

Measurements are carried out at depths from 0 to 10 m according to a system of profiles that can be located both along the coastline and perpendicular to it.

Bottom stations 7 are placed on each profile with a specified interval so that the braids 8 are located inside the profile along or across the proposed excitation line (dipole towing route) so that the electrodes 9 are evenly distributed as far as possible.

Excitation is carried out by the generator line 5, towed by a small carrier 1 along the same system of profiles, or to the side. Before towing on the basis of the generator 2, the BFP 3 is launched, which generates rectangular polarity different pulses with a given duration and duty cycle, which have a polarizing effect on the shelf rocks. The duration of pulses and pauses, depending on the tasks and features of the equipment used, is from 0.5 to 16 seconds. In pauses, as a rule, a non-emitting ballast device 6 is connected to the ship generator 2, which reduces the load surge of the ship generator.

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 this case, the bottom stations 7 record time series with data on both the potential differences between the electrodes and the second differences, which are analogous to the spatial derivative of the field. The results are processed, and the interpretation uses information about the field, both during the transmission of current and in the pause between pulses. From the signals measured by the bottom stations 7, through modeling, information is obtained on the change in parameters,

resistance, and the parameters of the induced polarization with the depth of the rocks.

To assess the prospects of the method, mathematical modeling was carried out. In particular, the problem was solved with the following initial data: the depth of the sea is 5 m, the length of the horizontal electric dipole (GEP) towed over the surface is 500 m.The model of the medium simulating the offshore hydrocarbon field used for theoretical calculations consists of 5 layers. The parameters of each model layer were set according to the Cole-Cole formula:

where ρ is the electrical resistivity at, frequency ω, η is the polarizability, τ is the time constant, and c is an exponent, j is the layer number. The parameters of the layers are given in the table.

Layer number Options ρ, Ohm η,% τ, sec from h (power, m) one 0.3 0 - - 5 2 one 0.5 0.1 D.5 one hundred 3 one 5 one 0.5 1900 four fifty 0 - - one hundred 5 one 0.5 0.1 0.5 one hundred

Theoretical calculations are carried out for the three positions GED-OO '= 500, 1000 and 1500 m, where O' is the center of the GED and for the measuring spit, consisting of three electrodes M 400 m O '400 m-N. The following values were calculated: the signals ΔU between the electrodes M and N and the ratio Δ ² U / ΔU, where Δ ² U is the difference between the signals measured on the pairs of electrodes MO 'and O'N. The results are shown in figure 2 and 3. Solid lines - model with a reservoir and altered rocks, dotted line - background. As can be seen from the data given when changing the distance, the anomalous zone appears in the signals in different ways. The use of a wide spatio-temporal region makes it possible to reconstruct the section both in terms of resistance and polarization parameters.

The above results show the possibility of obtaining the polarization characteristics of the rocks when using the inventive research complex and its prospects for exploration of hydrocarbon deposits in the transit zone.

Claims (2)

1. The research complex for offshore electrical exploration of oil and gas fields, which includes a set of bottom stations and a vessel with a generator and an excitation field generating unit that generates discrete bipolar pulses associated with a dipole immersed in water with supply electrodes, recording devices and auxiliary equipment, characterized in that the dipole with the supply electrodes is made with the possibility of towing it in a horizontal position, and the bottom stations are equipped with along or across the line of excitation by “braids”, each of which contains at least 3 measuring electrodes located at a distance of 50-400 meters from each other. 2. The research complex according to claim 1, characterized in that the length of the braids is from 100 to 3000 m