Landing String Slip System Numerical Analysis to Evaluate Pipe Crushing Problems

Abstract

As the technology of offshore drilling improves, the industry seeks oil in deeper waters, inhospitable environments, and challenging climatic conditions. The new harsher drilling conditions warrant modifications to existing downhole tools and development of new technology using numerical simulations. The landing-string slip system (LSS) is a tubular-holding tool in which slips act as a spider to grip landing strings or drill pipe during makeup or breakout of drill strings. This paper presents a detailed numerical methodology to evaluate the safe pull-load rating for pipe held in the LSS. The method uses advanced computational techniques and applies ASME section VIII Division 2, Part 5 design criteria to corroborate numerical findings.

First, laboratory tests were conducted on pipes with varying sizes to estimate the pipe load-carrying capacity without causing operational failure. Strain gauge measurements were taken at regular intervals during the laboratory tests. A detailed finite element analysis (FEA) using an explicit solver was conducted to computationally simulate the LSS operating mechanism. In particular, non-linear FEA was conducted on the 45° pipe section to simulate slip indentations followed by axial loading of the pipe. The maximum axial load applied on the pipe after slip indentation corresponds to 100% yielding load. ASME Section VIII Division 2, Part 5 design criteria involving ratcheting analyses was applied towards numerical studies at a 100% yield loading condition.

Extensive FEA studies were conducted to check the validity of the numerical results with laboratory testing and then to understand the LSS capabilities for field-based loading scenarios. FEA studies predicted stresses within 10% of the values obtained through laboratory measurements. Simultaneously, FEA plastic strain patterns revealed that the spread of plastic strains is highly localized to the penetrated surfaces of the pipe and is also generally absent through the thickness for load capacity up to 100% of the pipe yield strength. Based on ASME section VIII Division 2, Part 5, a ratcheting analysis was conducted that involved loading and unloading cycles on the pipe to monitor the plastic strain propagation. The ratcheting analysis determined that for a 90% yield load, the LSS safely held pipe for operational purposes.

The ratcheting evaluation was not possible using laboratory tests because of the cost and time required for a cyclic loading test. This paper introduces ASME section VIII Division 2, Part 5 design criteria to develop confidence in numerical results and justify the LSS design.