RU2309474C1 - Electric cable - Google Patents

Abstract

FIELD: cable engineering; feeding submersible power systems, primarily electric motors of submersible oil pumps.

SUBSTANCE: proposed oil-pump motor feeding cable designed for long-time service in boreholes at depths up to 3 000 m and stratal liquid temperatures of 80 to 210 °C has insulated current-carrying conductors and thermoelastolayer sheath disposed on each conductor and/or on all conductors; conductor insulation is made of acid-free radiation-modified high-density polyethylene and sheath, of thermoelastolayer. Such mechanical design of cable whose conductors are covered with air-tight insulation provides for radiation modification of high-density polyethylene dispensing with specific mechanical devices and attachments.

EFFECT: improved electrophysical and mechanical characteristics of insulation maintained even at high-speed cable lifting upon long-time service in boreholes; extended cable service life.

1 cl, 2 dwg, 1 tbl

Description

Electric cable refers to cable technology and can be used to power submersible electrical systems, mainly electric motors of submersible oil pumps.

The downhole and other factors affect the performance of the cables of the electric motors of submersible oil pumps:

- penetration of gas under pressure into the internal volume of insulation, a decrease in the insulation density leads to an increase in leakage currents - a decrease in the dielectric properties of the insulation;

- ESP rise in the presence of gas in the insulation, decrease in insulation density, radial micro-fractures (microcracks) of insulation at inappropriate ESP rise rates lead to an increase in leakage currents - to a decrease in the dielectric properties of the insulation;

- the presence of hot water above 80 ° C and its introduction into the insulation leads to the connection of the hydroxyl group (OH) with the molecular structure of the insulation, leads to a decrease in the dielectric properties of the insulation - an increase in leakage currents;

- leaching of ingredients from insulation (special additives that increase the life of the cable) leads to a decrease in the dielectric properties of insulation - an increase in leakage currents;

- the introduction of oily liquids of a non-dielectric nature under pressure into the insulation leads to a decrease in the density of the insulating material, an increase in leakage currents;

- the introduction of oily liquids under pressure into the insulation, in a closed volume under the armor cover, leads to compression of the middle core and thinning of its side walls, the result of this effect is the appearance of longitudinal cracks on the sides of the middle core and an increase in leakage currents;

- the introduction of chemicals in the volume of insulation, such as NaCl, H ₂ S hydrocarbon compounds and others, leads to a chemical compound with a molecular structure of isolation and an increase in leakage currents;

- high pressure negatively affects the operation of the insulation.

(Y.Z. Mesenzhnik “Cables for the oil and gas industry”, Tashkent, Fan Publishing House, 1972, p. 28, 29).

The famous "Electric cable" according to patent RU No. 2109359 C1, 6 НВВ 7/18, from 1997.01.22, publ. 1998.04.20. The electric cable contains three conductive wires located in parallel in the same plane, each of which has two-layer insulation from a composition based on high density polyethylene, a pillow under the armor in the form of a rubberized unvulcanized fabric laid over the wires, a common armor made of steel profiled tape, and an additional insulation element made of at least two fluoroplastic tapes superimposed with an overlap of 30-50% on the inner insulation layer.

Due to the fact that fluoroplastic tapes are located on top of the second insulation layer, air inclusions remain between them, which contribute to the electrical breakdown of the insulation. This design is designed to operate in a temperature range of 90-110 ° C, well fluid and no more, since polyethylene insulation, at temperatures above these, will lose dielectric properties.

The closest in technical essence is the design of a cable with insulation from radiation-modified high-density polyethylene (PM HDPE) manufactured by the Podolsky cable factory (GP Makienko “Cables and wires used in the oil and gas industry”, Perm-2004, p. 128 129, Fig. 3.6, Appendix 1), where the core insulation is treated with electron accelerators in the presence of air to increase the temperature resistance.

During R&D, the behavior of the insulation resistance from PM HDPE in a liquid medium with a change in temperature was studied. The studies showed that irradiation of high-density PE in the presence of air leads to deep oxidative degradation, which, in turn, is accompanied by an increase in the hydrophilicity of the insulation and, therefore, an intensification of the process of liquid diffusion into the insulation. This contributes to a sharp increase in insulation conductivity (decrease in insulation resistance) with increasing temperature. This factor limits the use of radiation-modified HDPE (high density polyethylene) as a two-layer insulation.

The dependence of the insulation resistance of different materials and temperature on samples with double-layer irradiated insulation of high density polyethylene (G. P. Makienko “Cables and wires used in the oil and gas industry”, Perm-2004, p. 129, Fig. 3.6, adj. one).

For a cable with two-layer insulation made of radiation-modified polyethylene, the insulation resistance begins to drop sharply with increasing temperature and at 102 ° C is less than 50 MΩ / km, instead of more than 2500 MΩ / km, the requirement is GOST R 51777-2001 (Novikov D.V. Development and research of heat-resistant cables for submersible oil pumps. Abstract of dissertation for the degree of candidate of technical sciences, M., 1999).

In the case of electron irradiation in the presence of oxygen, part of the radiation energy is spent on oxidation. The rate of destruction of the polymer under the influence of oxygen increases, and the rate of crosslinking decreases.

Radiation oxidation of the surface and volume of polyethylene, which significantly deteriorates the electrophysical and mechanical characteristics of insulation, significantly affects not only such a structurally sensitive characteristic as tanδ (leads to its increase), but also other electrophysical characteristics, which is especially manifested with increasing temperature. The temperature coefficients of the dielectric constant TKξ and the specific insulation resistance TKρv when irradiated in air are higher than when irradiated in an inert medium. In these cases, the absolute values of ξ and ρv also significantly differ (see Fig. 29 b, Table 21) (p. 211, Appendix 2) (“Cables for the gas industry” Y.Z. Mesenzhnik, publishing house FAN-Uzbek SSR, Tashkent, 1972). A sharp decrease in the insulation resistance of samples with radiation-oxidized insulation is also observed during prolonged (approximately 420 h) operation in water at atmospheric pressure at a voltage of 250 and 500 V AC of industrial frequency. The main decrease in insulation resistance occurs during the first 80 hours of exposure (“Cables for the gas industry” by Y. Z. Mesenzhnik, publishing house of the FAN-Uzbek SSR, Tashkent, 1972, p. 213, adj. 2).

In rooms where insulation is processed by electronic irradiation, creating an oxygen-free environment in a volume of more than 18 m ³ with a large number of technological openings requires serious technical solutions and investments (GP Makienko “Cables and wires used in the oil and gas industry”, p. 127 , adj. 1).

The objective of the proposed technical solution is to significantly improve the electrophysical and mechanical characteristics of insulation, including during high-speed cable rises after a long stay in the well, to increase the service life of the cable at depths of up to 3000 meters with a temperature of formation fluid from 80 to 210 ° C.

The problem is solved due to the fact that the electric cable for powering the electric motors of submersible electric pumps contains insulated conductive cores and a sheath made of thermoplastic elastomer, located on each core and / or all together, while the insulation of the wires is made of oxygen-free, high-density modified polyethylene through sheath of thermoplastic elastomer.

The location of the thermoplastic elastomeric sheath on each core and / or all together makes it possible to carry out oxygen-free radiation modification of high-density polyethylene, since after the thermoplastic elastomeric coating of the insulation of the conductive wires, air access to the insulation is excluded.

This design of a cable with protected and treated core insulation creates a condition for obtaining a product with a higher quality of dielectric properties of insulation, including leakage currents, since it does not worsen its dielectric properties over time, processed through a sheath of other materials continues to reduce its dielectric properties with time.

The set of features is new and, in addition to increasing the heat resistance of the cable, known from the prior art, leads to a new technical result identified during operation, a significant improvement in the electrical characteristics of the insulation (see table).

During the operation of the proposed cable design, a new, previously unknown technical result was revealed. The leakage currents of an oxygen-free cable modified through a sheath of thermoplastic elastomer are ten times less than that of a cable treated in air, and several times less than that of an oxygen-free radiation-modified cable through a sheath made of other materials, which is confirmed by the protocol.

Figure 1 shows a cable with an additional sheath located on each core, and in figure 2 - a common sheath located on all wires at once.

Figures 1 and 2 show conductive conductors 1, insulation conductors 2, sheaths for each core or sheaths 3, general sheath made of thermoplastic elastomer 4, pillow made of thermally bonded non-woven or needle-conducting technical fabric 5, armor 6.

The cable is made as follows: on the conductive core 1 there is an insulation of the core 2 made of at least two layers of high-density polyethylene, on top of which, either on each core or on all, the sheath 4 is made of chemically resistant thermoplastic elastomer, for example, elastollan.

Such a cable design with core insulation protected from air access creates a condition for oxygen-free radiation modification of high density polyethylene without creating special mechanical devices and devices.

Claims (1)

An electric cable for powering electric motors of submersible electric pumps, containing insulated conductive cores and a sheath of thermoplastic elastomer, located on each core and / or all together, characterized in that the insulation of the cores is made of oxygen-free radiation-modified high-density polyethylene through a sheath of thermoplastic elastoplastic.

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