Pump Stroke Optimizer
A Better Way to Operate a Rod Pumped Well
Bill Elmer
ENCLINE Artificial Lift Solutions LLC
Abstract
The Pump Stroke Optimizer (PSO) was invented to address problems encountered when rod pumping in the rapidly changing flow regimes observed with light oil production from horizontal wellbores. Current RPC (“Rod Pump Controller”) technology was developed to service vertical wells, where flow is able to separate at the perforations, with gas rising and liquids falling down to be lifted by a rod pump in a “sump” below the perforations. The RPC would quickly react to change speed when needed to keep pumpfillage within desired ranges, thus avoiding potentially damaging fluid pound and/or gas lock. The application of such RPCs to horizontal wells, with pumps positioned hundreds of feet above the lateral and thus exposed to intermittentslugsof gas and liquid, often results in frequent full spectrum speed changes and excessive low pump fillage events, both which are not desirable to well operators.
The common method operators employ tomitigate this problem is to manually reduce the RPC’s maximum working speed setpoint to a value just abovewhat is required to provide enough pump capacity to handle all the daily production. This intervention must be done regularly as the well declines, and is counterproductive should the well see increased deliverability due to events such as downtime in offset wells that are in reservoir communication. This intervention is also impacted by the available time and skill level of the personnel assigned this task.
The PSO replaces human interventionby regularly adjusting the maximum working speed based on several hours of observed pumping speeds. The result is significantly higher pump fillage, which results in significantly fewer strokes per day to lift the same production. This translates into less downhole wear and power consumption, and personnel are free to pursue other tasks.
Further, the PSO is able to enhance pumping efficiency by reducing pump slippage. Many RPC controllers allow for the downstroke to operate at a slower speed than the upstroke. For RPC’s with this feature, when calculating new maximum working speeds, the PSO is designed to decrease the downstroke pumping speed preferentially, leaving the upstroke pumping speed unchanged until an operator set differential is reached.
Field trials began in two horizontal wells in March of 2015. One well was a toe-up completion, and immediately experienced a decrease in strokes per day of 33%. The second well was toe-down, and experienced 24% fewer strokes per day. Both wells have since seen additional stroke reductions as additional algorithm testing progressed. Production did not change, and average pump fillageincreased in both wells.
A theory (with justification) that slower downstroke duration improves gas separator performance (hence pump fillage) for horizontal oil wells is presented. Other favorable pumping indicators and results, as well as more current data, will also be presented.