Halliburton Company

Shawn A Heath

Bryan K Waugh

Kris M Ravi

Rick L Covington

Improved apparatus and methods for determining the shear stress required for removing drilling fluid deposits formed on the walls of a well bore are provided. The methods basically comprise introducing a drilling fluid into a test apparatus which simulates a permeable section of a well bore. Drilling fluid deposits are caused to be formed on the walls of the permeable section, and the drilling fluid is circulated through the permeable section at progressively increasing flow rates for time periods whereby the pressure drop of the drilling fluid stabilizes. The stabilized pressure drop below which no appreciable erosion of the deposits takes place is determined by acoustically measuring and comparing the thicknesses of the drilling fluid deposits at each of the flow rates when the pressure drop stabilized. The minimum shear stress required to erode the deposits is determined from the pressure drop below which no appreciable erosion of the drilling fluid deposits takes place and the erodability of the drilling fluid which is inversely proportionate to the minimum shear stress can also be determined.

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Duncan, OK, United States of America

Shawn A Heath