Advanced Casing Wear Model

Abstract

Casing wear prediction is an important part of a well integrity assessment. Reduction in the thickness of the casing wall as a result of various wellbore operations can cause significant reduction in burst and collapse resistance. In addition to improving the safety of the operations by solidifying well integrity, there is a potential to decrease costs by reducing excessive safety factors.

Based on the current theoretical foundation for casing wear, a mathematical model has been developed. The model is complete with the ability to model torque and drag and the subsequent casing wear for a diverse set of operations and conditions. Several different modes are available where each mode includes additional effects and considerations. The different modes are compatible and includes a precise torque and drag correction procedure, inclusion of bending stiffness and buckling considerations.

To examine the validity of the model, analyses of two real wells on the Norwegian continental shelf has been performed. The wells have been simulated in detail using accurate survey, operational and wellbore data utilizing the developed model, DrillNet; an industry grade casing wear program and WellPlan; an industry leading torque and drag modelling software. Additionally, the results are evaluated in comparison to casing wear logs from one of the wells. A sensitivity analysis is performed to evaluate the validity of the results when input variables are subjected to controlled variation. The model was found to correspond well with the expected behaviour based on the theoretical foundation and identical simulations in DrillNet.

The torque and drag module predicts axial and normal forces in the string accurately in relation to the other modelling softwares. The consecutive casing wear is precisely modelled in terms of proportionality, but shows a slight underestimation in magnitude. The cause of the discrepancy has been found, evaluated and a solution has been proposed.