Artificial lift surface equipment may seem different from decades ago. Not only have exteriors evolved, but many dynamic engineered changes abound in newly developed operational mechanics.

Within this ongoing story of innovation, National Oil-well Varco (NOV) Monoflo delivers solutions to production sites where operators want better results in terms of production efficiency, reliability, and low life-cycle cost.

Innovations in the Monoflo system

Many new innovations at NOV involve progressing cavity pumps (PCPs) simply because of their ability to typically generate high volumes and cope with wellbore solids better (handling 50% more) than other artificial lift alternatives. Recent innovations include the NOV No-Go System, which reduces intake blockages and systematically improves PCP inflow when production entails high solids content.

The insertable PCP system, in both single-run and double-run design, allows pump changing without pulling production tubing. It also can use any pump with no modification required. On a practical basis a service rig no longer has to be brought to the site to pull tubing and change a downhole pump, which reduces manpower, cost, and downtime.

The leak-free stuffing box was designed to save operators time and money. As an insertable cartridge, the box does not have to be removed from the field for rebuild, which reduces downtime and other potential problems. Additionally, opening a valve to test for leakage is not necessary since operators only need to check the leak detection gauge.

Hydrodynamic brake

The hydrodynamic brake, engineered to produce operational and safety benefits for operators, is a key component of the surface drivehead for PCP technology.

Essentially, the brake consists of a stationary half (stator) and the rotary half (rotor), with the rotor connected rigidly to the shaft and spinning in a clockwise motion during normal operation (Figure 1). When the drive is stopped for general maintenance or failure, a process that forces working fluid outside the rotor, a circular flow path is created within the brake cavity (Figure 2). When the rotor’s energized fluid contacts the stationary stator’s fins, energy is both transferred to the stator and back to the working fluid as heat. During these actions and reactions, new fluid is continually circulated through the system to prevent overheating and potential safety burn risks.

The end result is that working fluid within the reservoir functions as the braking medium. This allows energy stored in both the fluid column and rod string to safely dissipate without the drivehead reaching excessive speeds, which can cause system failure and significant safety risks. In field performance these operational steps deliver several innovative features and benefits including this nonfriction brake, eliminating wear on brake components. This contrasts with the typical brake pad, shoe, or drum that has to be changed. Rather, without a wearing component, the kinetic energy is put into a fluid, which is itself put into a larger reservoir and dissipated as indicated above. Therefore, the brake will last virtually as long as the drive or well will.

The brake is capable of 2,000 ft-lb resisting torque at 250 hp. Through its unique design only the brake’s action force is required. By putting out only the necessary torque, the brake does no extra work and does not generate any extra heat if it is not needed. The more torque the rod string emits, the more the brake resists, up to 2,000 ft-lb (Figure 3). It also should be noted that due to its angled blades, this brake has only one braking direction. In the other direction, by contrast, the brake has almost zero braking force.

Once the brake is attached to the affixing mechanism, there are no clutches engaging or disengaging, no needle valve, or even any kind of modifier adjustments. Its fixed components, so to speak, are always there. And therein is part of the brake’s reliability: It has nothing to modify or adjust, and it cannot be tampered with. The other part of reliability is that it brakes at exactly the same capacity over its entire life cycle. Therefore, as long as the same fluid medium is used, the result is exceptional reliability with no wearing components.

Backspin energy is absorbed by the working fluid. Since there is no wearing medium such as brake pad material, the energy is transferred directly from the brake into the fluid.

Heat generated by the braking is dissipated by the fluid reservoir. Designed for a braking capacity relative to the amount of heat it is going to generate, the strategy is to have enough surface area next to the metal to dissipate the heat as fast as the brake itself can generate the heat. On some of the larger drives there are proportional reservoirs with substantial fluid to cope with the heat.

There is consistent braking with minimal maintenance throughout the drivehead’s life. The brake never has to be rebuilt. As long as an actual seal exists, the brake will work.

Designed for optimal performance

The hydrodynamic brake is focused around requiring minimal maintenance, no adjustment, and no rebuilds. Its driven rotor accelerates oil retarded in the stator, and turbulence of that oil decelerates the rotor and therefore the polish rod. To ensure a defined braking torque, it is critical to maintain the retarder completely filled with oil.

With a system inlet in the center and a discharge channel with pipe and nozzle, the pipe makes it a certainty that both flows do not get short-circuited between inlet and outlet. An overarching benefit is that the brake does not store any potential energy. It does not begin braking until approximately 100 rpm, at which point no more torque is emitted. In disk braking systems some energy still remains on the brake, which can cause complications during servicing.

Built to ISO and ATEX (explosive environments) standards, the hydrodynamic brake is awaiting ISO certification (ISO 15136-2) with compliance factors all being met.