A Group of manufacturers of surface drives for progressing cavity pumping (PCP) systems has supported the development of an industry standard for such equipment. The purpose of the standard is to provide guidelines for designing, specifying and using surface drives and to ensure acceptable levels of safety in the operation of this equipment. This paper describes the safety issues associated with this equipment that are addressed by the standard.
Progressing cavity (PC) pumping technology has grown dramatically from the first downhole pumps that produced less than 10 m 3/fluid per day to the newest pumps being used in Venezuela that are producing over 300 m 3/day. This growth in pumping capacity has also been accompanied by the technology being used in more diverse applications that range from primary heavy oil to dewatering in coalbed methane operations.
This proliferation of the technology prompted the development of a new ISO Standard (ISO 15136-1) to address the selection, manufacture, testing and use of progressing cavity pumps. This ISO Standard, however, does not address surface drive units that are required to drive these pumps. To close this gap, a group of manufacturers of surface drives for PCP systems took the initiative to support the development of a standard for PCP surface drives.
The purpose of the Standard is to provide guidelines for the design, specification and use of surface drive equipment, to ensure the safe operation of this equipment. The common format for drive specification defined in the Standard also provides end users with a simple means to compare operating limits for different models and manufacturers.
Surface Drive System Components
Currently, there are at least 10 manufacturers making more than 200 models of surface drive systems. These systems usually include the following components, arranged in different configurations:
- thrust bearing to support the rod string
- stuffing box to seal around the polished rod against tubing head pressure
- power train consisting of combinations of sheaves, belts, gears, hydraulic motors/pumps
- prime mover power source consisting of an electric motor or internal combustion engine
- braking system to manage the release of energy stored in the production system when the surface drive is shut down
Most of these components are typically incorporated into a single device that is mounted on the wellhead and is termed the surface drive, wellhead drive or drivehead. In this paper the term surface drive is used. The operating limits for surface drives are usually defined by maximum operating speed, torque and axial load. However, it must be recognized it is not possible to fully define the operational limits of the braking system by these parameters only.
Importance of the Braking System
During operation, energy is stored in the production system in two ways:
- torsional energy, in terms of elastic “winding ” of the rod string (similar to winding up a spring)
- fluid potential energy determined by the fluid level in the well annulus
Following a shut-down, this energy is released in different ways, depending on the conditions in the well at this time.
Author: Wagg, B. T.
Publisher: Canadian International Petroleum Conference, 11-13 June, Calgary, Alberta
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