Jeff Saponja, Oilify
Trey Kubacak, Ovintiv
Sucker rods are an essential component for rod pumping or rod lifting of oil and gas wells, but they have been limited by the use of metals and thermoset based non-metal composites (i.e., existing fiberglass sucker rods). Steel (metal) sucker rods have been limited by a low corrosion resistance, a low strength to weight ratio (i.e., too heavy), a low fatigue endurance limit and a relatively poor environmental, social and governance (ESG) rating during its lifecycle. Composite thermoset glass fiber (fiberglass) sucker rods have been limited by a low tensile modulus of elasticity (i.e., too stretchy relative to steel), a high cost (i.e., higher cost relative to steel), and a low toughness (i.e., low tolerance to compressional loads or high impact forces). Metal end fittings have also been a costly challenge for thermoset composite rods. Composite thermoset sucker rods using carbon fibers have offered a tensile modulus of elasticity comparable to steel but have been limited primarily by a very high relative cost to steel sucker rods.
Rod lifting has been further challenged by unconventional reservoirs and associated well designs comprised of vertically deep and long horizontal wellbores, where production is commonly comprised of high gas to liquid ratios and high initial liquid rates but with associated high decline rates. Electrical submersible pumps and gas lifting artificial lifting system are commonly used during the initial high production rate phase but eventually the well is transitioned to lower operating expense (OPEX) sucker rod pumping. Being able to transition to rod pumping as early as possible and at the highest production rate possible often provides the most attractive well economics. Unfortunately, high rate deep rod pumping has been challenged by excessive failure frequencies, mostly related to sucker rod failures. It is apparent that a cost effective and high reliability solution for deep high rate rod pumping is needed.
An ideal sucker rod for resolving its current limitations and application challenges has been defined and characterized as follows:
1. High strength to weight ratio,
2. High tensile modulus,
3. High toughness and fatigue/endurance limit,
4. High corrosion tolerance,
5. Cost comparable to low carbon steel alloys (i.e., KD rod), and
6. High ESG sustainability rating being recyclable and manufactured with a relatively low carbon footprint.
A composite material was identified, and it was hypothesized that it had the potential to satisfy development of an ideal sucker rod. Unidirectional fiber reinforced thermoplastic (FRTP) composite materials have gained significant attention in recent years due to their high strength/toughness, lightweight, excellent corrosion resistance, being partially recyclable with a relatively good lifecycle ESG rating and having comparable costs to steel sucker rods. This paper focuses on the development of fiber reinforced thermoplastic (FRTP) sucker rods, highlighting their potential advantages and challenges, for rod pumping (in general) and for offering an earlier transition from ESP pumping or gas lifting to reliable deep high rate rod pumping.
The development of fiber reinforced thermoplastic (FRTP) sucker rods involves the integration of unidirectional high-performance fibers, such as carbon or glass, into a semi-ductile thermoplastic matrix. This is vastly different from thermoset composites, which use a hard and relatively brittle epoxy matrix around the fibers. A major and unique feature of an FRTP composite rod is its remarkably high shear failure resistance as compared to a thermoset composite rod. A high shear failure resistance means the rods have compressional loading tolerance and that an entire sucker rod string could be comprised of FRTP sucker rods. The design process, prototyping/testing and recent well trials/results show promise for FRTP sucker rods. This paper explores the development of fiber-reinforced thermoplastic sucker rods as a promising alternative for overcoming the limitations of steel sucker rods and thermoset fiberglass sucker rods. Field trials will be shared and reviewed.