Delving Deeper into Foundation Slurry Rheology-PPT Presentation

PPT Presentation

Pdf Summary

The presentation examines aging and viscosity behavior in foundation-drilling slurries made with ultra-long-chain, partially hydrolyzed polyacrylamide (PHPA). These linear polymers help limit fluid loss and support borehole stability, but their interaction with cement-derived calcium can cause flocculation and high skin friction.<br /><br />Laboratory and field observations showed that Marsh funnel viscosity can fall substantially overnight, even with little or no added shear, while Fann rheology remains comparatively stable. This difference suggests the decline is not simply polymer-chain breakage. The proposed explanation is that hydration gradually untangles the very long, initially entangled chains. Untangling lets them pass through the funnel opening more easily, reducing Marsh readings. Higher initial polymer concentrations showed larger declines, and transportation-related agitation may further reduce readings. The mechanism is not fully established; soda ash lowers viscosity, but does not eliminate the aging-related drop.<br /><br />In the reported tests, Marsh viscosity declined about 39% over 48 hours at one dosage. The presentation recommends anticipating typical decreases of 20–25% in 24 hours and 25–45% in 48 hours, and adding polymer regularly to restore target viscosity. For slurry used on successive days, it suggests roughly 20% extra polymer for the next day and 40% for two days.<br /><br />Maintaining high viscosity and slurry head pressure helps reduce fluid loss, balance downhole pressures, and prevent hole collapse. Soda ash should be used mainly with hard mix water (about 120 ppm hardness or greater); in softer water, excess salt may inhibit hydration and reduce viscosity. Dosage and viscosity predictions remain difficult because water chemistry, polymer concentration, aging, and handling all affect performance.

Keywords

foundation drilling

PHPA

viscosity aging

Marsh funnel

Fann rheology

polymer hydration

fluid loss control

borehole stability

soda ash

polymer flocculation