Differential drive

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Company Profile:

  • ROSTAROILGAS is a member of ROSTAR group.
  • ROSTAR deals with oil and gas industry equipment since 2004.
  • All company production areas are equipped with modern equipment.
  • There are such production technologies as molding, pressing and machining in the company.
  • Thought-out process chains involve high-precision part production.
  • There is our own design-engineering department, which together with trial facility helps to engineer, test and bring to batch production products of various complexities in the shortest period of time.
  • In 2004 the Company started to work on a new type of differential driving gear for oil well pump. It is used for high viscosity oil wells with emulsion generation, marginal wells and oil wells with periodic operating mode.

Problems of marginal wells working with periodic operating mode

1. Oil loss level for sour oil wells – 65 tons per year and about 160 tons per year for Devonian oil wells;
2. The rise of underground repair works (for about 10-20%) in order to prevent paraffin deposition;
3. The risk of wellhead equipment and gathering line freezing in winter time;
4. Additional “bad” starting loads on reduction gear and motor, which reduce their work resource;

Field of use and the results

Differential driving gear is used for oil well pump actuation.

Oil well pump application is most effective on high-viscosity oil wells with emulsion generation, marginal wells and wells with periodic operating mode.

Technical results:

1. Pump motions decrease and pumping unit is put on twenty-for-hour mode of operation;
2. Flow rates increase;
3. Power intensity decrease;
4. Drop of well maintenance level;
5. Pump efficiency increase;
6. Pump rod loads decrease;
7.Even generation of oil stratum;
8. Possibility to use pump rods with lesser diameter.

Basic driving gear can be substituted with differential driving gear without pump-unit design alteration.

Technical Description:

Drawing of a pump unit with a new driving gear

There are following parts in a bottom-hole pump rod unit:

  • 1 stand
  • 2 balance wheel
  • 3 pump rods
  • 4 driving gear, consisting of:
    • 5 electric motor
    • 6 reducer
    • 7 differential machine, which generates reciprocal motions at different opposite moves rate

The basis for differential machine is:

  • 8 outer central wheel
  • 9 inner central wheel
  • 10 satellite

There are several ways to fulfill the differential mechanism and also a number of variants how to make central wheels or place them.

Two connecting rods 11 and 12 are adjusted to outer central wheel 8 and to satellite 10. With their other ends they are connected to balance wheel 2.

With a new drive gear of a bottom-hole pump rod unit, pump rod goes up slowly than down due to differential machine. Drive gear of a bottom-hole pump rod unit works in a following way:

Electric motor 5 (pic.1), rotates inner central wheel 9 (pic.2) through reduction gear 6. In its turn, the inner central wheel will rotate about itself a satellite 10.

Satellite, by going down will pull connecting rods11 and 12 which are situated on both sides of inner central wheel.

Connecting rod 11 will put into rotation the outer central wheel 8. When satellite reaches the lowest rotation point and starts to go up, connecting rods move upwards too. At this time connecting rod 11 makes the outer central wheel 8 rotate in the opposite to the previous direction.

Satellite rotates about inner central wheel 9 due to its contact with outer central wheel 8, so, satellite rotation speed lowers when satellite moves downwards and increases when it moves upwards because of oscillating rotation of central wheel 8.

Thus the speed at which satellite rotates about inner central wheel is lower when it goes down than when it goes up. Connecting rods are adjusted to the balance wheel 2, that’s why the balance wheel oscillating movements to opposite sides will also be produced at different speed.

Unproductive preparatory pump rods 3 downward movements will be faster than upward ones.

The new driving gear can be used for both: pump units that are already in exploitation as well as for newly produced ones.

Tatneft testing report

Equipment specifications:

Standard drive gear of well 1333 8-3,5-4000 was substituted for differential drive gear and enabled constant mode of operation.

Standard drive gear: Differential drive gear:
Stroke length – 1,8 Stroke length – 1,8
Pump quantity – 3,3 min-1 Pump quantity – 1,4 min-1
Mode of operation: periodic Mode of operation: constant

Due to the speed difference between up and down movements ROSTAROILGAS driving gear decreases the reduced loads, thus increasing the run time.

Liquid flow

  Standard drive gear: ROSTAROILGAS drive gear:
Pump quantity, min-1 3,3 2,1 1,6 1,4
Average daily flow, t/day 1,1 1,22 1,15 1,3

Average daily flow of a standard pumping unit is 1, 1 t/day, when working 15- 16 days per month. Constant mode of operation involves flow growth.

Saved extractions

Pumping unit with a ROSTAROILGAS driving gear accumulates twice as much extraction in a certain period of time than a unit without it. Transfer to the constant operating mode explains this fact.

Operating time

Before ROSTAROILGAS driving gear was mounted, oil well was used 1536 hours in a 5 month period, after the mounting this time made up to 3364 hours, which is 2.2 times more.


1. Pumping movements number is reduced to the required minimum value;
2. Pumping unit is used in a 24-hour operating mode;
3. Oil flow rate increased twice;
4. Power consumption is lowered;
5. Pump rods loads are reduced;
6. Pump filling coefficient is increased;
7. Oil wells are used at the highest level of their potential.

Economic effects:

ROSTAROILGAS differential driving gear price - 750 thous.  rub.
Differential driving gear mounting/dismounting cost - 15 thous.  rub.
NPV for the exploitation period - (5 years)-  1021,85 thous.  rub.
Payback time – 2 years


Differential drive photo