Pressure Required to Break Circulation in Annular Formula |
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| \( P_{gs} \;=\; \dfrac{ y }{ 300 \cdot ( D_h - D_p ) } \cdot L \) | ||
| Symbol | English | Metric |
| \( P_{gs} \) = Pressure to Overcome Mud's Gel Strength Inside Annulus (psi) | \(lbf\;/\;ft^2\) | - |
| \( y \) = Gel Strength of Drilling Fluid | \(lbf\;/\;100\;ft^2\) | - |
| \( D_h \) = Diameter of Hole | \(in\) | - |
| \( D_p \) = Drill Pipe OD | \(in\) | - |
| \( L \) = Drillstring Length | \(ft\) | - |
The pressure required to break circulation in the annular space of a wellbore is the pressure needed to overcome the gel strength of the drilling fluid that has developed while the fluid was static. This gel strength is a measure of the drilling fluid's ability to suspend solids (like drill cuttings and weighting agents) when circulation is stopped.
Drilling fluids are typically non-Newtonian fluids, meaning their viscosity changes with the shear rate applied to them. Gel strength is a time-dependent property that reflects the fluid's behavior at very low or zero shear rates (static conditions). Different rheological models (like Bingham Plastic, Power Law, and Herschel-Bulkley) can be used to describe the fluid's behavior under various flow conditions. The gel strength is a specific parameter measured after a period of static condition, usually 10 minute.
The total pressure required to break circulation in the entire well includes the pressure needed to break the gel strength inside the drillstring as well as in the annulus.
The actual pressure required to break circulation can be used to estimate an "effective" gel strength, which might differ from laboratory measurements due to downhole condition.
