What Does Flat Gel Strength Mean?
Flat gel strength refers to the point at which the gel strength remains flat meaning there is little to no development in the gel strength with time. In this situation, the 10-second and 10-minute gel strength has similar values and will remain pumpable when left undisturbed in the hole.
Drilling mud with flat gel strength will not require excessive pressure to start the flow of the fluid.
Trenchlesspedia Explains Flat Gel Strength
Gel strength indicates the gelling that will take place once the circulation of drilling fluid is stopped. It measures the inter-particle forces that will prevent the cuttings from settling in the borehole.
To break circulation in a high gel mud, high pump pressure is required. The 10-minute and 10-second gel strength indicates the initial gel as per API, and is the shear stress measured at low shear rate after the mud is allowed to set for 10 minutes and 10 seconds respectively.
The 10-minute gel and 10-second gel strength are measured by slowly rotating the handwheel at the slow and steady motion of 3 rpm till the gel breaks. Before testing, the mud slurry is rotated at 600 rounds per minute (rpm) and allowed to rest for 10 minutes and 10-seconds respectively.