Patent ID: 8524638

Claim:
A method for determining a Plug-Normal Stress Difference (ΔN 1(p) , the method comprising: providing a test base drilling fluid that is characterized by having a first normal stress difference N 1(TB) when measured in a rheological procedure that includes a rheometer, testing temperature, testing pressure, testing shear ramp rate, and testing gap setting; adding a first concentration of a test particulate to the test base drilling fluid; adjusting the concentration of the test particulate in the test base drilling fluid to achieve a minimum concentration of the test particulate in the test base drilling fluid that will substantially plug a tapered slot, testing the test base drilling fluid with the minimum concentration of the test particulate using the same rheological procedure to determine its first normal stress difference, N 1(TA) ; and calculating ΔN 1(p) =|N 1(TA) |−|N 1(TB) |.