Analysis of Tubular Failures in Riserless Environments

Abstract

Riserless drilling poses numerous operational challenges that manifests itself in a number of ways, that can adversely affecting the efficiency of the drilling process. The problems include increased torque and drag, increased vibration, poor hole cleaning, tubular failures by buckling above the mud line, poor cement jobs, and associated problems during tripping operations. Drilling in deepwater and ultra-deepwater as well as extending the reach to a greater along hole depth in the riserless environment requires both improved models and comprehensive analysis, especially when the larger diameter casing pipes are run and cemented. The present calculations without proper modeling will gravely underestimate the hook load values when the casing strings are run in deepwater situations. This paper proposes a modeling approach, which uses scenarios in which the drillstring/casing strings are in open water and in openhole reservoirs under different operating conditions to arrive at appropriate hook-load values in addition to torque and drag calculations. Both combinations of soft and stiff string models are used for the tension-force estimation as well as the wellhead-side loading calculations. The research results also present the hook-load calculations for scenarios when casing and inner string are run with drilling mud inside the inner string, sea water in the outer string, and pad mud in the hole below the mud line. The study concludes that various parameters influence the results, such as wellhead offset from the rig center, wellbore inclination, curvature, wellbore torsion, angle of entry into the wellhead besides the complexity from wind, wave forces, and ocean currents. This paper documents the comparison between the predicted mathematical simulation results with the actual well data from different wells to explain the rigor of implementation.

Study on dynamic characteristics of drill string in deep-water riserless drilling

“…Their result showed that the bending moment of the return pipeline was large at the suspension joint and the lower seabed pump. Samuel et al 11 established a predictive mechanical model of hook load and wellhead lateral force by using rigid and soft rope model. They provided a stress calculation method for drill string under the load of an internal drilling fluid and external wave and current.…”

Nonlinear Dynamic Characteristic Analysis of a Landing String in Deepwater Riserless Drilling

“…Everage et al [29] and Zheng et al [30] investigated methods for calculating the longitudinal vibration load on a landing string induced by platform heave motion during lowering of the casing. Samuel et al [31] presented a simulation approach for hook load, torque, and drag calculations and investigated various parameters' influence on these load, such as wellhead offset from the rig center, wellbore inclination, curvature, wellbore torsion, angle of entry into the wellhead, wave forces, and ocean loop currents. e dynamic problems involved in these studies are either for the longitudinal vibration of the string or for the transverse vibration.…”