When something goes wrong with your drilling polymer fluid mid-shift, you need to know what to check, in what order, and what to do about it. That is what this is.
What are the four parameters I must check every day on site?
Marsh funnel viscosity, density, sand content, and pH. Check all four, every shift, without skipping.
Let me explain what each one tells you.
Marsh funnel viscosity tells you how thick your fluid is. You fill a Marsh funnel, let the fluid run out, and time how many seconds it takes. That number is your viscosity reading. During drilling, you want 40 seconds. Before concreting, bring it down to 35 seconds or below. Why? Because if the fluid is too thick when the concrete goes in, it will not displace cleanly. You end up with fluid trapped inside the pile. That creates problems you will not see until an integrity test fails weeks later.
Density tells you how much solid material has built up in your fluid. You measure it with a mud balance, a simple device that looks like a scale. During drilling, keep density below 1.01 g/ml. Before concreting, keep it below 1.05 g/ml. When density starts rising, it almost always means sand content is rising too.
Sand content tells you how much sand is suspended in your fluid. You measure it with a sand content kit, a small tube with a screen and a scale on the side. Keep it below 5% before you concrete. Research from DFI India 2023 confirms sand content above 6% can interfere with pile integrity testing after construction. The problem is you will not know something went wrong until the test comes back.
pH tells you how acidic or alkaline your fluid is. You check it with pH paper or a meter. Keep it between 9 and 10 during site operations. Below 9, the polymer starts losing performance. The fluid thins out in ways that are hard to predict. Add soda ash to bring it back up to around 10 to 11 whenever it drops.
Why does viscosity drop mid-shift and how do I fix it fast?
Viscosity drops for three reasons. Know which one you are dealing with before you do anything.
First, pH has dropped below 9. This is the most common reason. Check pH immediately. If it is below 9, add soda ash, agitate, and recheck after 10 minutes. Most of the time this fixes the viscosity problem on its own.
Second, you are drilling through a high-permeability formation. That means the ground is absorbing your fluid faster than you are replacing it. Coarse sand, gravel, and fractured zones do this. When this is the reason, add WG Visco Booster directly to the active fluid. It is a liquid additive, meaning you pour it straight in without stopping drilling. It restores viscosity quickly and adds stability in loose or sandy formations where the bore walls need extra support.
Third, the fluid has been recirculated too many times and the polymer chains have broken down. This happens on long running jobs. The fluid looks thin and does not respond well to soda ash or Visco Booster. At this point you need to partially refresh the mix with new polymer.
If viscosity is dropping and you are also losing fluid into the formation, add WG Bond. It is a plugging and sealing agent that controls mud loss by filling the pores in the formation. Use it before continuing drilling in that zone.
Do not keep drilling with thin fluid. In sandy or loose ground, thin fluid means the walls are not supported. A bore collapse at 22 meters costs you far more time and money than the five minutes it takes to fix the fluid.
What is the most common mistake made before concreting?
Not checking sand content.
When the shift is running late and the concrete truck is waiting, the sand content check gets skipped. The fluid looks fine. Viscosity is acceptable. The decision gets made to go ahead.
But sand settles during the waiting period between finishing drilling and starting concreting. What was 3% two hours ago could be 6% or higher now. You will not know unless you check.
Use a sand content kit within one hour of starting concreting. If the result is above 5%, recirculate the fluid and let the desanding equipment run before proceeding. The time this takes is nothing compared to the integrity questions that follow if you skip it.
The answer to the question at the top is this. The most common mistake before concreting is skipping the sand content check because the shift is behind schedule. Do not skip it.
For a complete guide on what drilling polymer is, how it works, and how it differs from bentonite, read:
What is Drilling Polymer and Why Do Piling Contractors Use It?