A generalized empirical expression for the collapse of worn tubulars with a crescent-shaped wear groove under combined loads
Andreas Teigland, Stein Inge Dale, Sigbjørn Sangesland, Bjørn Brechan
Abstract
As a large proportion of easily recoverable global hydrocarbon reserves is extracted and fields in operation are maturing, the oil and gas industry requires new methods of ensuring well integrity. Production of the remaining reserves may involve, for instance, extended-reach wells, multilateral wellbores, long horizontal sections and highly deviated trajectories. Moreover, wells in mature fields are being used to increase recovery through side-tracking. Casing wear has a significant influence on the well integrity in such operations and the ability to assess its effects is crucial, both in terms of its impact on health, safety and environment, and in terms of enabling cost-efficiency. This article utilizes the Finite Element Method (FEM) to analyze the stress distribution in worn tubulars with a crescent-shaped wear groove under external pressure. A model for tubular collapse is proposed using generalized empirical expressions for stress concentration factors in worn tubulars. The generalized expressions are based on 640 finite element analyses of different geometries designed to represent typical dimensions used in the oil and gas industry. Comparisons with experimental data and existing models demonstrate improvement in both accuracy and precision using the developed approach.