RU2254400C1 - Device for a cathode protection of the run down-well equipment - Google Patents

Abstract

FIELD: oil-producing and other industries; cathode protection of lowered into the well equipment.

SUBSTANCE: the invention is pertaining to the devices for cathode protection of the downhole equipment against corrosion and may be used by various industries. The device for the cathode protection of lowered into the well equipment includes a station of the cathode protection connected by a cable on a daylight surface to the casing string and to the oil-well tubing string and also to the anodic earth lead and to the equipment lowered into the well. Additionally the device includes an electric contact of the lowered into the well equipment to the casing string. The invention ensures an increased efficiency of the device for the cathode protection of the lowered into the well equipment in the all classes of the boreholes, due to complete exclusion of a capability of the casing string electrochemical corrosion.

EFFECT: the invention ensures an increased efficiency of the device for the cathode protection of the lowered into the well equipment in the all classes of the boreholes.

3 cl, 1 dwg

Description

The invention relates to devices for protecting downhole equipment, including deep-well, for example, electric centrifugal pumps (ESP), deep-well sucker-rod (SHG), diaphragm, screw and other pumps; deep batchers, valves and structures for gas lift and fountain oil production; electric heaters and other equipment - from corrosion with the imposition of a controlled potential difference (cathodic protection) and can be used in various industries, including oil.

A device is known for cathodic protection of downhole equipment, including an ESP installation [1], which includes a cathodic protection station (SCZ) equipped with a reference electrode and an ampervoltmeter and connected by a cable on the surface to the casing and to the anode earthing.

As a result of applying a potential difference between the cable connection point on the day surface to the casing and the anode ground electrode using an RMS equipped with a reference electrode and an ampervoltmeter, the potential of the protected downhole equipment is shifted and passivated.

A disadvantage of the known device is that it does not provide effective protection of downhole equipment, including the ESP launched in the well in areas remote from the day surface due to a decrease in the protective potential difference in them.

Closest to the proposed device is the cathodic protection of the ESP launched into the well [2], including the cathodic protection station (SCZ), connected by a cable on the surface to the casing string, to the tubing string (tubing) and to the anode earthing switch, with the SKZ additionally connected to the ESP of an additional residential power cable of the ESP installation. SKZ is additionally connected to the ESP of an additional residential power cable of the ESP installation through the cable connection point on the surface to the casing.

The disadvantage of the prototype is that, for example, in a perfectly vertical well with a large diameter of the production string and / or when using deep equipment, on the contrary, of a small diameter, when the contact of the latter with the casing is excluded, gradual corrosion (electrochemical corrosion) of the casing is possible due to her anode function in protecting the downhole equipment of a known device. Also, electrochemical corrosion of the casing is possible when using, for example, an ESP coated with an insulating material (varnish, paint, bitumen or epoxy material, sulfide growth).

The problem and the expected technical result solved by the proposed technical solution are to increase the efficiency of the device for the cathodic protection of the equipment lowered into the well for all categories of wells (including vertical, deviated, different diameters) by completely eliminating the possibility of electrochemical corrosion of the casing string.

The problem is solved in that the device for cathodic protection of the equipment lowered into the well, including a cathodic protection station (SCZ), connected by a cable on the surface to the casing and to the tubing string, as well as to the anode ground electrode and the equipment lowered into the well further includes electrical contact of the casing equipment lowered into the well. The electrical contact of the equipment launched into the well with the casing is made using a shock absorber installed on the equipment launched into the well. For cathodic protection of the equipment launched into the well with the installation of an electric centrifugal pump (ESP), the SCZ is connected to the ESP of an additional residential power cable of the ESP.

In addition to the indicated shock spring, other designs can be used as the electrical contact of the equipment being lowered into the well with the casing (depending on the size of the equipment being lowered into the well, the diameter of the casing, the depth and inclination of the well), which provide reliable electrical contact between the components of the equipment being lowered into the well with casing.

The proposed device with the option when a shock absorber spring is used as a design for electrical contact of the equipment lowered into the well (ESP) with the casing is shown in the drawing. Here:

1 - casing

2 - ESP installation

3 - tubing

4 - anode grounding

5 - cathodic protection station, equipped with a copper-sulfate reference electrode, reference electrode and ampervoltmeter

6 - cable (connecting)

7 - power cable installation ESP

8 - supply cores of the power cable of the ESP installation

9 - additional core of the power cable of the ESP installation

10 - shock absorbing spring as an electrical contact of the ESP with the casing.

The device operates as follows. The cathodic protection station is turned on and the necessary protection current is set, which is selected by the copper-sulfate reference electrode installed in the ground. The metal is uniformly polarized over the entire surface of the equipment to be protected by summing the protection currents through the upper and lower points of the downhole equipment, and the casing is also included in the process of uniform polarization due to the electrical contact of the ESP being lowered into the well with the casing. Thus, it is protected from electrochemical corrosion.

The procedure for working with the device.

1. Connecting the three cores of the four-core power cable to the power contacts of the electric centrifugal pump, and the fourth cores of the four-core power cable to the casing of the electric centrifugal pump, equipped with a shock absorber for electrical contact with the casing.

2. The descent and installation of the ESP equipped with a shock absorber for electrical contact with the casing.

3. Connecting the connecting cable to the anode ground electrode located in the zone of stable electrolytic contact and acting as a soluble anode.

4. Connecting the cable of the soluble anode to the positive terminal of the cathodic protection station.

5. Connecting VHF to apply negative protective potential with a cable on the surface to the casing of the well with subsequent electrical contact of VHF with tubing through wellhead fittings.

6. Connecting the fourth core of the four-core cable connected to the casing of the electric centrifugal pump to the negative terminal of the cathodic protection station (mainly through the cable connection point on the surface to the casing).

7. Application of the necessary protection current to the system “casing string - tubing string - ESP body, equipped with a shock absorber for electrical contact with the casing string - casing string - anode ground electrode”.

8. Monitoring the necessary protective potential difference using a measuring circuit of a copper-sulfate reference electrode installed in the soil in the zone of stable electrolytic contact with the casing string - tubing string system - ESP body equipped with a shock absorber for electrical contact with the casing string - casing string - anode ground electrode. ”

The scheme of electrochemical protection described in items 7-8 eliminates the possibility of gradual erosion of the casing, which loses the function of the anode, in a well of any design and with any downhole equipment.

The inventive device is effective and industrially applicable, because for its implementation use available equipment and materials.

SOURCES OF INFORMATION

1. Dautov F.I. et al. Cathodic protection of casing of wells against corrosion in oil fields, M., VNIIOENG, 1981, 55 pp.

2. RF patent №2215062, С 23 F 13/06, 10.27.2003.

Claims (3)

1. A device for cathodic protection of downhole equipment, including a cathodic protection station (SCZ), connected by a cable on the day surface to the casing and to the tubing string, as well as to the anode ground electrode and to the downhole equipment, characterized in which additionally includes the electrical contact of the equipment being lowered into the well with the casing. 2. The device according to claim 1, characterized in that the electrical contact of the equipment launched into the well with the casing is made using a shock absorber installed on the equipment launched into the well. 3. The device according to claim 1 or 2, characterized in that for the cathodic protection of the equipment launched into the well with the installation of an electric centrifugal pump (ESP), the SCZ is connected to the ESP of an additional residential power cable of the ESP unit.