Abstract
ABSTRACT Conventional casing design is based on single-string analysis which ignores annulus fluid heat-up loads and composite cemented string effects. This paper presents the design of a 7" production casing and 10-3/4" × 9-5/8" protective casing under high burst/collapse conditions. Uniaxial and triaxial safety factors are computed and compared for single-string versus multi-string analysis with and without temperature loads. In the multi-string analysis, casing stresses are calculated for the radially composite structure assuming the elastic properties of casing, cement, and formation. Results demonstrate a significant increase in burst safety factor for cemented casing and show that burst/collapse tendency for HPHT wells is strongly dependent on multi-string top-of-cement locations. For this HPHT application, reliable triaxial design is achieved with multi-string analysis using standard weights and grades of casing, which otherwise is not possible with single-string uniaxial analysis.
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