Schlumberger

UniStar Downhole Protection VSD System

Overview Library

A new level of rod lift performance

The UniStar downhole protection variable speed drive (VSD) system maximizes production and equipment performance through sophisticated modeling that makes use of all available parameters, with particular focus on protecting downhole equipment.

At any instant during well operations, in particular within a pump cycle, there is a single constraint that limits production. Production can be maximized by “automating” the system to operate at the particular limiting constraint at each instant of time. Determining the applicable limits and operating smoothly across them in real time is the key differentiator of the UniStar system.

Downhole equipment protection

Polished rod and downhole pump loads, velocities, and positions are continuously measured and displayed. Downstroke speed is automatically adjusted to eliminate rod float, a potential source of equipment problems. Rod load limits can be preset to reduce stress, while load damping can be used to suppress oscillations and improve pumping system efficiency without the need for specific limits.

Improved energy management

Cumulative energy consumption and the effectiveness of input energy in delivering useful lift work are continuously monitored and considered within optimization routines. Power limiters allow the maximum and regenerative power supplied by the drive to be conserved. The UniStar system instructs power flow control to smooth power flow, reduce gearbox stress, increase pumping efficiency, and maximize production for highly variable inflows.

Pump fill optimization

Managing pump fill is important to protect downhole equipment. The UniStar system accurately determines and regulates the percentage of pump fill. Rather than stop a pump completely during a pumpoff condition, the system adjusts upstroke and downstroke speeds to maintain a target fill value and maximize production. This allows the pump to automatically adapt to changing well inflows, eliminating fluid pound, reducing peak rod load, preventing standstill sand infiltration, eliminating stresses associated with start/stop cycling, and improving pumping efficiency.

Sensor-free operation

A number of unique methods precisely determine polished rod and downhole pump position, velocity, and load without requiring external sensors. A range of system variables can be observed through monitor displays or recorded as time-based graphical plots. For operators who prefer to minimize sensors, the UniStar system is able to optimize performance across a range of operating conditions.

Gearbox protection

Gearbox torque is monitored and can be limited by the UniStar system to protect against damaging overload conditions. Excessive drive belt slippage or breakage is quickly detected, while a starting-torque manager eliminates inrush currents and extends the life of the system by reducing the violence associated with starting the pump. A counterbalance monitor and associated counterbalance assistant make it easy to adjust the counterweights to minimize gearbox stress and energy consumption.

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Control Capabilities

The UniStar system is able to monitor and control all key parameters necessary to protect downhole equipment and maximize production, using
  • pump speed control
  • pump fill optimization
  • rod load control
  • bridle separation control
  • Dynacard generator
  • power monitoring and control
  • production monitors
  • fluid-level monitors
  • gearbox monitors and limiters
  • counterbalance monitor
  • automatic restart
  • data capture and communications
  • system simulation.

Education and Training for Superior Performance

Rod lift training
Reduce risk, extend equipment life, increase production, and maximize the potential of your team through a range of training programs tailored to your specific requirements.
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