Alternate Path® technology (APT) is a field-proven gravel packing technique for multi-zone, long interval, or horizontal wells. This technique has enabled the successful completion of more than 70 deepwater wells in West Africa. Recent APT technology advancements continue to improve completion design options and significantly extend the gravel pack length.
In challenging well environments (e.g., deepwater, extended reach drilling), conventional gravel packing methods are often terminated prematurely due to sand bridging in the wellbore, resulting in incomplete gravel packing and decreased protection from sand ingress. APT provides alternate flow paths around a sand bridge by diverting the slurry (gravel + carrier fluid) through shunt tubes. The slurry is delivered to the annular voids through distributed nozzles in the shunt tubes until a complete pack is placed in the wellbore.
This paper reviews the fundamental Alternate Path design concept and discusses recent improvements resulting from detailed studies of fluid hydraulics, including flow through the shunts, nozzles, and gravel pack. Original designs used single- or multiple-ported shunt tubes, which limited the diverting distance of the slurry and thus the overall packing length. The modern shunt manifold design enables sustained self-diverting transport over much longer production intervals (~ 5000 ft) without the need of a downhole monitor or control loop. This unique self-diverting capability distinguishes APT from all other gravel packing methods in its simplicity and reliability, particularly in challenging well environments.
The ability to extend APT gravel packs to significantly longer lengths provides greater flexibility in reservoir depletion planning by creating more robust completion designs to meet demanding production requirements. As application opportunities continue to expand, and as APT is integrated with other emerging completion technologies, in-depth understanding of shunt design and fluid hydraulics is essential to successful field implementation.
Oil and gas production from weakly consolidated or unconsolidated reservoirs has been increasingly challenging. These challenges, which include deep-water, extended reach, high pressure/temperature, long intervals, high rate, and remote locations, raise both complexity and cost in drilling and completions, demanding fewer wells for an economical field development. While subsequent workovers may no longer be a viable option, the long-term reliability of sand control completions is becoming a major focus.
Drilling fewer development wells necessitates maximizing reservoir contact to capture various pay intervals and establish higher production rates from each well. One strategy is to penetrate reservoirs with extreme length wells. Combined with zonal isolation, extreme length wells provide greater flexibility for both reservoir and production management. When sand control is needed, an openhole gravel pack has been recognized to be a reliable and long-lasting completion for long interval, high rate wells.