This paper describes a set of experiments, sponsored by Mobil North Sea Ltd (MNSL) and conducted at Heriot-Watt University, which were designed to investigate the carrying capacity of milling fluids. The objective of this work was to determine the fluid rheology which would most efficiently transport debris (swarf), generated during casing milling operations, out of the hole. The results of the experiments and subsequent analyses are presented in the paper.

The paper describes the equipment and procedures used in the experiments. It also presents the results of the experiments and subsequent analysis relating to the transport efficiency of a range of milling fluids used by MNSL. These experiments were conducted under static and dynamic conditions using a recently constructed settling column and the cuttings transport borehole simulator at Heriot-Watt University. The experiments demonstrate the impact of the rheological properties of the fluid, and the shape and surface area of swarf on transport efficiency. The paper concludes with recommendations on the formulation of fluids for milling operations of this type.

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