Hybrid Well Completions

Flush joint connections between PVC casing and stainless steel screens.

By Edd Schofield

Hybrid water well designs intentionally combine stainless steel well screens with PVC casing to balance hydraulic performance, water quality protection, longevity, and overall cost.

The approach has gained momentum as groundwater chemistry, corrosion potential, and biological fouling increasingly influence modern well design decisions.

For as long as most in the groundwater industry can recall, achieving a uniform and easily assembled connection between PVC casing and stainless steel well screens has been a persistent challenge. The notable exception has been small-diameter environmental wells, which typically utilize standardized flush-thread fittings suited for shallow low-load applications.

Numerous crossover options exist today to connect stainless steel well screens to PVC well casing. However, most of these systems rely on bell ends, upsets, or external couplings whether glued, threaded, splined, or collar based.

While functional, these connection styles inevitably increase the outside diameter at the joint, complicating field assembly and introducing risks during installation, gravel packing, and grout placement.

New System Addresses Challenges

Two recent advancements now directly address these long-standing challenges by enabling truly flush connections between PVC casing and stainless steel well screens without bell ends or upsets.

These systems use modified flush-thread pipe machined onto heavy-wall SDR-17 PVC paired with identically machined, stainless steel wire-wrap screens connections. The connections may be achieved through either a flush spline connection or flush-threaded male-to-female joints.

They are rapidly becoming a mainstay for both new wells and re-completions, ranging from 6-inch to 16-inch production wells and suitable for depths exceeding 1000 feet.

The advantages of flush, heavy-wall PVC-to-stainless connections, both internally and externally, are significant. These include reduced initial drilled borehole diameters, faster and simpler field assembly, and the elimination of hang-ups during tremie pipe placement, gravel packing, and grout installation. The absence of external upsets improves construction efficiency and reduces installation risk.

Eliminating a Bacteria Nutrient Source

Beyond construction benefits, the use of heavy-wall PVC casing presents a compelling alternative to low-carbon steel casing by eliminating the iron as a nutrient source for iron-related bacteria (IRB).

Hybrid well completions fundamentally can offer significant benefits in addressing well rehabilitation challenges that ultimately come to bear with steel well completion. Unlike steel casing, heavy-wall PVC does not function as a continual iron source that fuels bacterial activity, biofouling, and subsequent declines in well performance.

Water quality and chemistry are playing an increasingly significant role in well design decisions in today’s market. For the past three decades, PVC products have taken a leading role in water well construction. Its usage is driven by water quality considerations, cost advantages, and reduced construction time when compared to low-carbon steel threaded or welded completions.

But growing concerns over long-term longevity, corrosion, and biological fouling—particularly iron bacteria such as Gallionella—are prompting renewed evaluation of traditional construction materials. As a result, the industry is once again focusing on open area, well efficiency, corrosion control, and effective fouling abatement as integrated well design objectives.

Ready for Hybrid Well Construction

With recent advancements in manufacturing, supply availability, and threaded connection technology, the industry is now better positioned to deliver hybrid well constructions.

These designs combine the hydraulic efficiency and corrosion resistance of stainless steel wire-wrapped screens with straightforward, reliable connections to PVC casing. They do so all through flush-thread fittings and flush spline couplings, both of which offer a high strength low-profile transition connection.

This evolution provides a practical and efficient solution that balances performance, durability, and constructability without the complexity or drawbacks historically associated with mixed-material well completions.

With the use of PVC, the amount of iron is significantly reduced in the well, reducing the attraction of naturally occurring iron bacteria. By reducing the nutrient source, the fouling rate and impact is drastically reduced.

By mitigating iron bacterial proliferation, impacts on fouling rates and water quality are reduced. As a result, hybrid completions extend both the structural and operational life of a well while improving water quality outcomes.

The performance, strength, and reliability of flush connected stainless steel wire-wrap screens paired with SDR-17 PVC casing are now well documented. As a result, hybrid well designs are increasingly viewed as a best practice for modern well construction, offering higher hydraulic efficiency through increased open area, simplified gravel packing, improved well development, and significantly longer service life.

Among the advantages are:

Recognizing Water Chemistry Realities

Aggressive groundwater conditions such as elevated dissolved oxygen, low pH, and the presence of microbiological influenced corrosion (MIC) organisms (e.g., Gallionella) continue to challenge traditional construction materials and are driving more careful material selection at the aquifer intake zone.

Stainless steel wire-wrap well screens offer a high open area, resulting in lower entrance velocities and improved well efficiency. They also provide greater resistance to biofouling and mineral encrustation compared to carbon steel or PVC screens, along with excellent corrosion resistance and compatibility with both native groundwater and aggressive rehabilitation chemistries.

Performance vs. Cost

PVC casing remains economical, lightweight, and easy to install while stainless steel screens deliver superior hydraulic efficiency, structural integrity, and durability where performance is most critical. Heavy-wall PVC casing or riser pipe is not only cost-effective and lightweight but also chemically inert in many groundwater environments.

Advancements in Connection Technology

Modern flush-thread and low-profile crossover connections now provide faster installation compared to welded or threaded steel casing. These connection systems have eliminated many historical drawbacks associated with mixed-material well completions, enabling straightforward and reliable hybrid construction. The minimized upsets help preserve annular seal integrity while allowing for simple field assembly without welding or specialized fabrication.

Typical Applications

Hybrid well designs are well suited for:

• Municipal and community water supply wells
• Industrial and agricultural production wells
• High-value groundwater sources with challenging chemistry
• Retrofit or replacement wells requiring performance upgrades without introducing full steel construction.

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The application of hybrid designs in retrofitting and replacement wells is a topic I will explore further in a future installment of Quick Hits.

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Edd Schofield is the technical sales manager–chemicals for Johnson Screens and has been with the company since 1988. He served as the Groundwater Foundation’s McEllhiney Distinguished Lecturer in Water Well Technology in 2007. He can be reached at edd.schofield@johnsonscreens.com.