PVC Casing and Screen Pipe Use in a Nebraska Irrigation Well

A farm in Nebraska, USA drilled an irrigation well. Depth: 75 meters. The water-bearing layer was medium-fine sand with an average grain size of 0.55 mm.

The contractor used 4-inch (OD 114 mm) PVC casing and screen pipe. Wall thickness: 5.0 mm. Ring stiffness: 250 kPa. Screen slot size: 1.2 mm.

Initial result:

After completion, the well produced 45 m³/hour. Sand content was below 0.05‰.

Six months later:

Flow rate dropped to 18 m³/hour. The pump impeller showed wear. A downhole camera showed that the screen pipe had several flattened areas. The slots were blocked by sand. The pipe joints had cracks.

Review of the setup:

The slot size (1.2 mm) was larger than the sand grain size (0.55 mm). Sand moved into the well over time. Sand also accumulated around the slots and blocked them. The ring stiffness (250 kPa) was lower than the typical value for 75 meter depth (above 400 kPa). The pipe was subjected to external pressure from the surrounding sand and deformed.

Change made:

The well was re-drilled with 6-inch (OD 168 mm) PVC-U pipe. Wall thickness: 8.3 mm. Ring stiffness: 550 kPa. Slot size: 0.60 mm. After re-completion, the well produced 42 m³/hour with very low sand content. The well operated for two years without change.