Increase of efficiency and lifetime of Electric Cavity Pump units for the oil production with Starting Clutch.
The Electric Cavity Pump units (PCP) have been widely adopted at development of reserves of high-viscosity crude oil and oil with high contamination.
Long-term operating experience of PCP has shown that the cavity pumps are one of the most effective means of the oil production on such oilfields. Rather small length of PCP's allows applying them effectively in curved wells too.
The PCP's above mentioned advantages point out the urgency of researches and works on improvement of existing items and design of new kinds of equipment.
One of the reasons influencing the field reliability of PCP is its installation procedure.
It is known, that at starting up of PCP there are excess torque coursed by steel rotor friction about stator's elasomer on the submersible electric motor shaft, and coursed by dynamic efforts to acceleration of the rotor of submersible electric motor's weight and pump. It leads to starting currents increase up to 5 times and more and sequent usage of high-powered submersible electric motor and switchboards, allowing PCP operation in the given conditions.
It is known, that at temporary shut down of PCP in the wells with viscous oil, the oil can solidify in the production tubing's upper part and in discharge line of wellhead fittings especially in winter conditions, forming not fluid liquid. The direct start of PCP in these conditions leads to operating of the pump in "the closed latch" terms. So, considering the fact that a screw pump is the pump of displacement type, the pressure on its output and the specific loads on elastomer stator increase sharply, that, sometimes leads to its destruction.
Recently, the VSD Switchboards are used more often for the submersible electric pumps' output adjustment and optimum selection of formation liquids.
For the load reduction on stator's elastomer and thus for PCP's lifetime increasing in the well with high-viscosity oil at start up, the VSD switchboards for soft start of PCP with step-by-step (programmable) rated frequency rotation adjustment are used. However, the presence of starting currents in 4-5 times and more exceeding of the nominal demands using of VSD switchboards on currents 250A and above. The cost of such switchboards is essentially higher than direct start switchboards which are used now, that economically unfeasible for widely using them on oilfields.
Nowadays the centrifugal starting clutches are used for simplification of PCP start. But their application leads to occurrence of greater dynamic loadings on shaft of the pump, on ESP motor and on the clutch itself, what sometimes results in their destruction. It is necessary to note, that in some cases at pump's stating up at low angular speed or in drives of slow-speed units (up to 750 rpm), the designed of the starting clutch is unable to operate. The Stating Clutch MP-103 was designed and manufactured by CJSC ELEKTON. The main part of the starting clutch design is a wedge reducer, which allows reducing the torque on ESP motor's shaft up to 10 times during ESP unit starting up (Fig.1). Thus, on PCP's operating rotation frequency reaching, the torque on ESP motor shaft reaches the operating torque and rotation of ESP motor is transferred directly to a shaft of the pump.
The Starting Clutch MP-103 is installed between ESP motor and sealing. There are technical specifications represented in the table bellow.
|Rated shaft speed (max.), rpm
|Transmission ratio in start up moment
|Transmission capacity (max)
|Guarantee lifetime, hour/day
|Ambient temperature, , °С
|| Ø=103, L=1200|
The records of starting up currents are presented on Fig.2 at start up of PCP EVNM-5-16-1000 manufactured by Public Corporation "Livgidromash" with standard assembling and with use of Starting Clutch MT-103. Recording of currents was made by FLUKE device.
As evident from oscillograms, the using of starting clutch in drive of PCP, which reduces the torsion torque of PCP's shaft during start up of the pump and reduces the starting currents in 2 times that allows applying the VSD Switchboards of a smaller standard size. The cost of them is commensurable with cost of Switchboards with direct start operated now.
So, the starting clutches application jointly with VSD Switchboards will allow, at the pump unit's valuation changes, to reduce multiply starting currents, it is essential to lower loadings on stator's elastomer, to provide wide regulation of submission of the pump and, that, to raise efficiency and durability of the unit's operation.
The unit of PCP EVNM-5-16-1000 with electric motor EVNM-5-16-1000 manufactured by Public Corporation "Livgidromash", electric submersible motor PED22-117/4В5 and telemetry system Elekton-TMS with starting clutch MP-103 passed the tests and operated successfully on the well № 7038 in Public Corporation "Lukoil-Komi". The VSD Switchboard Elekton 05-250 with rated current up to 250 A was used for control and protection of submersible unit. The use of this switchboard has allowed to adjust the pump unit's rate from 10 up to 25 m/day and to start up PCP after a shut down during time set on the program. The unit was put into operating duty at supplying current frequency n=26 Hz, that corresponds to rotation frequency of electric motor n=780 rev/min. The starting currents have decreased from 220 A up to 95 A that in future will allow application of VSD switchboards on currents up to 100 A, which cost is comparable to the upgraded switchboards with direct start-up.
JSC ELEKTON designed and started production of the Starting Clutch for PCP units. The starting clutch application will essentially facilitate the start of PCP units in complicated conditions, such as unit's operating after hydraulic fracturing of formation, well capping operation etc. It is necessary to note, that the starting clutch using will allow completing the VSD units of a smaller standard size which will essentially lower cost of the maintained equipment.
Marketing Director, PhD