Pump-stroke optimization (PSO) was developed to address problems encountered when rod pumping in rapidly changing flow regimes was observed with oil production from horizontal wellbores. Current Rod-Pump Controller (RPC) technology was developed for vertical wells. RPCs integrated with a variable-frequency drive (VFD) (hereafter, referred to as RPC-VFD) are often applied to horizontal wells. However, the results are often frequent full-spectrum speed changes and excessive low-pump-fillage events; both are undesirable.
A method that operators use to mitigate this problem is to manually reduce the maximum-working-speed setpoint to a value slightly above that required to handle all the daily production. This intervention must be performed routinely, and is counterproductive should the well see increased deliverability caused by events such as downtime or offset fracturing. PSO replaces human intervention by regularly adjusting the maximum working speed on the basis of analysis of several hours of observed pumping speeds and low-pump-fillage events.
Some RPC-VFDs allow for the downstroke to operate at a slower speed than the upstroke. For RPC-VFDs with this feature, the PSO device decreases the downstroke pumping speed preferentially, leaving the upstroke pumping speed unchanged until an operator set differential is reached. This practice results in less pump slippage, as well as additional time for evolving gas to exit the rod pump's gas anchor. This results in fewer strokes per day for the same production, which results in less downhole wear and less power consumption.
Field trials began in two Eagle Ford wells in March of 2015, with initial very successful results presented at an industry workshop in September 2015. An expanded twenty-well Eagle Ford pilot test was begun on 3 December 2015. Rather than handpicking wells that were similar to the initial two-well pilot, a wide range of production rates was chosen. After 45 days of operation, the following indicators were reviewed by the operator to determine overall success or failure:
Algorithm convergence (indicating successful PSO-device-supplied pumping speeds)
Greater average pump fillage (earlier load transfer being better for downhole equipment)
Fewer strokes per day without production loss (provided by greater fillage and less slippage)
Higher bottom minimum stress in final rod taper (indicating reduced buckling tendency)
Less electrical-power consumption
The data were obtained with standard industry supervisory control and data-acquisition (SCADA) software, as well as by manually reading power meters. In summary, the operator deemed ten wells highly successful, five marginally successful, and five not successful. The reasons contributing to success and failure will be explored to obtain higher success rates in future applications.