This paper describes the design and implementation of a rules-based expert system for casing string design. The expert system functions as a front end to a sophisticated, technically-robust tubular design and analysis model which is capable of generating a minimum cost-safe casing string design considering both API load capacity and von Mises equivalent stress-intensity criteria. Consequently, the extensive input parameters required for such a computer model are greatly reduced.

Based on a limited number of input parameters, the expert system generates service conditions which depend on the function of the casing string – conductor, surface, protective, production, etc., design criteria including material grades and connectors, and hole diameters for buckling considerations.

General well information provided by the designer to the expert system consists of the well type – Exploratory or Development, to set the gas kick tolerance, the geology type – hard rock or recent sediments, to set the fracture gradient parameters, and the drilling environment – onshore or offshore, to adjust the fracture gradients and set the design criteria.

After execution of the expert system, the designer can either transparently let the casing model design the string or review the data created by the expert system. Of course if desired, the user can modify, delete, and/or add additional parameters to the casing model created with the expert system.

The benefit to the user of the expert input system for casing string design is a rapid and consistent generation of the standard input parameters for the sophisticated structural design and analysis program, allowing the well designer more time for actual well planning and review functions.

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