Apparatus and method

Abstract

An apparatus and method to measure the position of a portion of a pump assembly within a well particularly for use in an oil or gas well and for downhole pumps driven by a drive shaft running from a surface motor. The apparatus comprises at least one measurement device which senses the position of a portion of a pump assembly downhole. The information can be used to position a rotor of the pump assembly at a position relative to a pump housing of the pump assembly to produce fluids from the well at an increased rate. Where two measurement devices are provided, they can count the number of revolutions of the drive shaft of the pump assembly at two spaced apart points. The strain or torsion within the drive shaft can then be calculated.

Description

BACKGROUND OF THE INVENTION [0001] The present invention relates to an apparatus and method for determining the position of an elongate member particularly but not exclusively within a well. [0002] Progressive cavity pumps (PCPs) pump fluids from a well to the surface and their deployment in a well is common practice. Typically such a pump would be driven by a mechanism comprising an electric motor equipped with a speed reduction gearbox situated at the top of the well bore. The power is transmitted to the rotor of the PCP via an elongate member, known as a drive shaft, located within the production tubing conduit of the well. The speed of rotation of the drive shaft is selected to achieve optimum production rates from the well. The faster the rotation, the higher the rate of fluids produced but the greater the torsion and strain put on the drive shaft. [0003] The drive shaft is typically assembled from a number of rods screwed together to give the overall drive shaft length require...

AI Technical Summary

Benefits of technology

"The present invention provides an apparatus for determining the position and torsion of a pump assembly in a borehole. The apparatus includes a detection device that can measure the position of the pump assembly within the borehole and a communication device that can relay the information on the position to a controller. The detection device can measure the rotation of the drive shaft or the longitudinal displacement of the pump assembly within the borehole. The apparatus can also include a movement mechanism that can vary the longitudinal displacement of the pump assembly in response to the detected position. The invention also provides an apparatus for measuring the torsion in an elongate member, such as a pump assembly, in a well. The apparatus can help improve the accuracy and efficiency of drilling and pumping operations in wells."

Problems solved by technology

Equally, abrupt reductions in the speed of the pump can be caused by slugs of high viscosity fluids or solids.

These abrupt changes to the freedom of the rotor to turn in the pump cause drastic changes in the torque applied to the drive shaft, and it has been found that this can result in failure of the shaft.

Indeed, breaking of PCP drive shafts accounts for a high percentage of failures in such production systems, leading to large repair costs and associated loss of production revenue.

If the rotor is too close to the bottom of the pump housing, the in-use temperature can increase past the operational design limits of the pump, causing damage to and failure of the pump.

In practise it is difficult to accurately determine the distance to raise the drive shaft at the surface to correspond with the longitudinal displacement of the rotor in the housing, due to the uncertain amount of give provided in the individual rods of the drive shafts and their interconnections.

For wells which are at a non-vertical angle, this is even more difficult.

Thus the positioning of the rotor is approximate and can result in failure of the pump or a reduced production rate from the well.

Moreover, during use of the pump and rotation of the drive shaft, the give in the drive shaft may increase under continued stress and the drive shaft may also slip in the clamps, causing a change in the longitudinal displacement of the rotor, which can also result in failure of the pump or a reduced production rate.

Images