SOCIETY
OF PETROLEUM ENGINEERS
Mid-Continent Section, Tulsa, Oklahoma
Abstracts courtesy of Ken Saveth, ksaveth@juno.com
Multilobe Progressing Cavity Pump: Operating Process Peculiarities, Geometrical Parameters Optimization & Fields of Operation - Dr. Fedor D. Balkenko: Russian State Oil & Gas Academy
In the last few years, Progressing Cavity (PC) hydraulic machines used as downhole hydraulic motors & pumps for oil recovery & transportation have gained wide distribution. According to the kinematic ratio i=Z2 : Z1, PC hydraulic machines operating organs are divided into single-lobe
(Z2=1) & multi-lobe (Z2>1) ones. In PC pump designs up to now, the operating organs with a single-lobe rotor has been used as it was proposed by R.Moineau in his first pump.
Therewith, the theoretical & experimental investigations as well as the many years of experience of using multi-lobe hydraulic motors for wells drilling, show that the potentialities of PC pumps have not yet been exhausted. One of the reserves for increasing the PC pumps efficiency in definite conditions is the conversion to the multi-lobe operating organs.
The detailed grounds of the multilobe PC pairs possible applications as the pump operating organs basic designs of such pump units were first given in 1979.
The use of a PC pump with multi-lobe operating organs compared to the standard pumps with all other conditions being similar (the same diameter & number of stages) gives a number of advantages among which are the following:
The increased operating volume; V; due to the multi-lobe mechanism many-fold action equal to the number of rotor lobes; Z2. So the conversion to the operating organs with the kinematic ratio I=5:6 (Z2=5) increases the pump operating volume by more than 3 times.
The decreased eccentricity; e; & this increases the life of the rotor connection with the driving shaft.
The decreased interlobe pressure drop; Pk; between operating chambers due to many-fold increase of contact lines separating high & low pressure areas in a multi-stage pump (kL=2 & kL=3) allows to increase pump pressure limited by leakages in pair without resorting to the undue increase of stages number (length) even with rotational speed equal to n=100 . . . 300 min-1.
The decreased necessary shaft rotational speed; n; providing for the given pump delivery. So the conversion from i=1:2 to I=5:6 decreases n by almost 3 times & this results in twofold decrease of slip speed; u; in the rotor-stator pair that is favorable for its life but therewith, the fluid flow velocity in the operating organs courses; w; being increased affecting the pump suction capacity.
The high power characteristics of multi-lobe pumps have been demonstrated in the course of its laboratory tests. The comparison of the PC pumps characteristics with multi-lobe (I=5:6) & standard operating organs of similar contour diameter (Dk = 46 mm) & stages number (kL = 5) with rotational speed being equal to n = 100 . . . 300 min-1, revealed the great influence of the kinematic ratio on the pump performance. The pump with multi-lobe operating organs produced in VNIIBT has an increased delivery; Q; as well as the higher volumetric; ho; & overall; h; efficiency. The pressure of a pump; p; with standard operating organs is most likely limited by leakages in the rotor-stator pair & because of this, with decreased rotational speed, its curve has the shape which is not typical for positive displacement hydraulic machines. This is explained by the fact that even with comparatively low pressures, the leakages in the rotor-stator pair are approached to the ideal pump delivery. Because of this, the companies producing high pressure pumps use rotor-stator pairs of more length & thereby go for the increase of stages number in order to form the adequate P-Q characteristic.
The PC pump with multi-lobe operating organs, thanks to the above factors, has a typical "fixed" P-Q characteristic because first, the ideal delivery; Qi; is many-fold increased, & second the interlobes pressure drop is many-fold decreased.
PC pump power factor; kN; equal to the product of non-dimensional operating volume
V = v/D3k
& number of chambers; k; separating pump inlet & outlet can be used as the generalized criterion of it’s efficiency:
kN = Vk
where k = (kL - 1)Z1 + 1
Power factor; kN; with given Dk, n, & Pk defines the pump effective horsepower PQ. As far as V & k are simultaneously increased with lobes number increase, kN is increasing more actively than V with the increase of Z2. The kN - Z2 relationships presented with different kL are the graphic illustration of the multi-lobe pump advantages; especially appreciable in the development of high pressure hydraulic machines.
In Russia, the works on designing & investigating the multi-lobe pumps are carried out in Moscow institutes: VNIIBT & GANG. Here again, there are the production & research facilities.
When designing multi-lobe PC pumps, the simple transfer of methods approved for the hydraulic motors is not correct so new approached to the optimization of their operating organs space & plane geometry are required. This is due to the fact that in PC mechanism driving conditions, the best geometry of operating organs is established from the conditions of self-braking elimination in the rotor-stator pair; while in pumping conditions, another criterion is required.
Based on this, the improved space & plane geometry of the pump operating organs providing both minimum contact line length & the minimum contact pressures in the pump, rotor-stator pair was proposed. The use of operating organs with the proposed geometry will allow to increase efficiency & life of multi-lobe PC pumps.
For carrying out the scientific investigations in the field of multi-lobe pumps, there is mounted test bench with necessary control & measurement equipment.
We have developed several designs of multi-lobe PC pumps:
High pressure pump of general use for pumping viscous & dirty fluids.
Oil-well sucker rod pump of decreased axial dimensions for oil recovery rigs.
Oil-well hydraulically driven pump unit (PDM-PC pump) having a number of advantages over hydraulic piston units.
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