1. n. [Drilling Fluids]

An instrument used together with a set of weights to conduct a shear-strength measurement test. This test procedure published by the API measures the shear strength of a mud (lbf/100 ft² or kPa). The typical use for this test is for evaluation of a static-aged mud sample left at high temperature for several hours. The shearometer tube is placed on the surface of the gelled mud and weights are applied until the tube sinks to a marked depth. The applied weight indicates shear strength of the mud sample.

Reference: Watkins TE and Nelson ME: "High Temperature Gellation of Drilling Fluids," Transactions of the AIME 193 (1953): 213-218.

See: gel strength,  gelation,  gelled-up mud,  gels,  lost circulation,  mud-aging cell,  pilot test,  progressive gels,  static aging test