As an electric supporting product for the electric submersible pump unit, the submersible oil cable is required to have good temperature resistance, water resistance, strong corrosion resistance and excellent electrical insulation properties due to the special nature of its working environment. In order to improve product quality, meet the needs of oil well production under complex well conditions such as offshore and land, and enhance the ability of enterprises to participate in international market competition, it is important to understand in detail the structure of submerged oil cables and related process elements.
1 The structure of submerged oil cables
1. 1 Conductor
Conductor material for oxygen-free copper rod drawn from the conductor, due to direct contact between copper and polypropylene will accelerate the aging of polypropylene, so polypropylene or modified polypropylene for the insulation of the cable conductor must be tinned, if the use of EPDM rubber for insulation, in order to prevent the infiltration of gas under the oil well to the conductor and insulation layer between the gap, the conductor should be coated with a special adhesive, through the continuous vulcanization of the conductor and insulation layer can be The conductor should be coated with a special bonding agent.
1. 2 Insulation layers
(1) Polypropylene insulation: Polypropylene (PP) insulation is a thermoplastic, suitable for use in environments from -20 to 100°C. It is brittle at low temperatures and easily deformed by ageing at high temperatures. The extrusion temperature from the extruder inlet to the head is generally 140-220°C. The insulation is extruded using an extrusion die.
(2) EPDM rubber insulation: EPDM rubber insulation is a widely used thermosetting resin material, it has good insulation properties, can work for a long time in the -40-180 ℃ environment, but the poor oil resistance of ethylene propylene rubber, can be coated by the conductor surface adhesive and insulation layer outside a layer of binding layer (such as polytetrafluoroethylene film and nylon silk wrapping) to effectively prevent its heat in the oil well Melt and swell. The extrusion temperature of the extruder is generally 60-95°C from the inlet to the head of the machine.
(3) Polyimide/F46 composite film + EPDM combination insulation. The outer layer of the conductor is covered with polyimide F46 composite film and then sintered, and a special structure is designed to coat the sintered layer of the film with a special adhesive, followed by the extrusion of EPDM rubber. After continuous vulcanisation the laminate film is bonded to the EPDM rubber.
1. 3 Barrier layer
PTFE (F40) film tape has good resistance to oil and high temperatures. The F40 film tape is wrapped around the insulation layer to block the intrusion of oil and gas into the EPDM rubber and prolong the service life of the cable.
1. 4 Sheathing layer
The sheath is made of nitrile rubber with good mechanical properties and strong oil and chemical resistance, and the surface is required to have a spline type outer flute to prevent damage to the sheath during armouring, and also to increase the friction with the interlocking steel belt armouring, so that the interlocking armouring can be balanced in longitudinal force.
(1) Lead sheath: The lead sheath is made of pure lead or lead alloy, and the lead sheath should be free from defects such as sand holes, cracks and impurities. The lead sheathing should be free from frit, cracks and impurities. A continuous extrusion machine is generally used, with a continuous extrusion temperature of 290-390°C.
(2) Nitrile sheathing: Nitrile rubber sheathing is produced by extruding rubber machines, and the continuous vulcanisation tube is filled with saturated steam, and the vulcanisation temperature is generally 170-190°C. Because of the small viscoelastic stretching properties of NBR, it is advisable to use extrusion moulds. The extrusion temperature of the extruder is typically 50-75°C from the feed port to the head.
1. 5 Armouring layer
The interlocking steel belt armour plays a longitudinal role in stressing and at the same time plays a key role in protecting the sheathing layer, without which the sheathing will break if the cable is lifted out or if there is a sudden change in pressure. The steel belt armour is overlapped and wrapped.
The overlap rate is >35%, it is difficult to control the roundness of the cable after armoring, especially the lead sheath cable is easy to deform the lead layer after armoring.
2 The current situation of submerged oil cables
The working conditions in oil wells are harsh, often at high temperatures, high pressures, and in corrosive environments such as oil and gas. Submersible oil pump power cables can be divided into two types: round and flat. Due to the constraints of the small space in the oil well casing, submersible pump power cables are usually
are mainly flat. Due to the asymmetric structure of the flat cable, when the power is transmitted
Hysteresis losses are caused by electromagnetic induction due to unbalanced magnetic fields, causing the cable to heat up. Round cables are preferred where the size of the well casing permits. Round cables with a symmetrical structure produce an evenly distributed electromagnetic field, with little mutual interference and good electrical and magnetic compatibility.
They are also easy to receive and discharge when laid in a well. At present, there are four aspects of submerged oil cable consumption: one is the annual oilfield new electric pump wells; two is the annual pumping cycle in the oilfield need to update the submerged oil electric pump; three is the various oilfields due to various reasons cable electrical breakdown damage, the need to update and repair the cable; four is the old oilfield is still the main oil-producing areas, these fields continue to exploit, the self-jet ability is weakened, the oil content in the well is greater reduction, in order to increase oil recovery, in order to increase the amount of oil recovery. In order to increase oil recovery, various methods of oil extraction have been used, one of the most used being the pumping unit (commonly known as a knapper), which has a low pumping efficiency, and the other being the electric submersible pumping unit, which has a high pumping efficiency. As these cables do not allow for joints, depending on the depth of the well
Each section of cable is purchased in lengths of over 2800m and has a short service life of 1 to 1.5 years.
They need to be replaced in 1 to 1.5 years.
3 Key points in the process control of submersible oil cables
The manufacturing process of submersible oil pump cables is different from that of ordinary cables. It is used downhole in high temperature, high pressure and highly corrosive environments, and is sealed when installed downhole and through the wellhead packer. Therefore, the requirements for each performance index and the control of the outer diameter of each manufacturing process are very high, and the following are the key process innovations in the production process, as follows.
3. 1 Conductor
The conductor is the first dimension to be controlled in the submersible oil pump power cable. In order to ensure that its performance indicators are stable and uniform, in addition to the use of equipment and the selection of good copper rod materials, the most important is the drawing process, the determination of the angle of each zone to ensure the minimum friction, to ensure that the product diameter is uniform and stable, thus ensuring that the three-phase DC resistance unbalance rate is not greater than 2%.
3. 2 Conductor winding
The winding of polyimide-F46 film around the conductor as the inner insulation of the cable has caused wrinkling in the actual production of the winding, which affects the outer diameter of the later process.
The problem was solved by the use and continuous improvement of this device.
3. 3 Insulation formulation design
The thickness and performance of the insulation is dependent on the temperature control range of the extruder, the stability of the haul-off speed, the stability of the draping position of the core in the curing tube and the stability of the pressure of the rubber in the extruder.