Victoria Pons, Ph. D., Pons Energy Analytics
Anne Marie Weaver and L.J. Guillotte, Lightning Production Services
Justin Lundquist, P.E., Revolution Resources
Rod pumping unconventional wells can be challenging due to increased side loading conditions thru the curve section of the wellbore. Likewise, ‘S’ shaped wells and unintentional dog legs present a similar problem with increased failure rates. All of these conditions lead to higher side loading resulting in increased friction and wear and a corresponding decrease in Mean Time Between Failures (MTBF). This phenomenon can make lifting fluids with rod pumps problematic due to extreme deviations and the resulting forces.
As production and bottom hole pressures decline, many wells will be converted to rod pump at some point in their lives. Rod pumping is usually the preferred artificial lift method for lower gas to liquid ratio (GLR) wells with low or declining bottom hole pressure. When unconventional wells are converted to rod pump, they usually start out with the pump set above the kick-off point. However, as production declines, the operator may need to lower the pump to maintain economical production rates and maximize hydrocarbon recovery. To achieve these goals, operators have pumped the curve with varying levels of success. Historically, when lowering the pump into the curve, failure rates increase due to increased mechanical friction on the downhole equipment. Tubing leaks, rod parts and pump failures are the most common failure types for these applications.
When pumping through the curve, rod guides are often installed on sucker rods below kick off point as they provide a sacrificial wear devise that attempts to protect the tubing and rods. Unfortunately, rod guides increase the amount of friction in the system.
Thermoplastic liners, which are mechanically bonded to new or used tubing, significantly increase run time by preventing rod on tubing contact. Installing thermoplastic liners below kick off point can decrease failure rates by reducing the downhole mechanical friction.
The effects of different corrective measures to deviation and their respective coefficients of friction are detailed and discussed in this paper.
This paper presents results from a case study where thermoplastic liners were installed on high failure rate ESP wells that were converted to rod pump and provides evidence that pumping the curve can be an economical and feasible option for operators when designed properly.