Interaction between a compliant guide and a coiled tubing during sub-sea well intervention in deep water

Abstract

Sub-sea well intervention in deep water is generally being conducted from mobile offshore drilling units using conventional drilling risers. To reduce cost, light well intervention (LWI) solutions using mono-hull vessels are being investigated. One of these is the spoolable compliant guide (SCG), which consists of steel pipe hung in an elongated S-shape between the vessel and wellhead. The S-shape is maintained by offsetting the vessel horizontally from the wellhead, while the guide pipe is supported by buoyancy modules.After deployment and connection of the SCG to the wellhead, coiled tubing is run through the guide pipe and inserted into the well for conducting well intervention operations. During operations the coiled tubing (inner pipe) is tensioned, which compresses the guide (outer pipe) due to geometric interaction.This paper investigates the load transfer within pipe-in-pipe interaction by physical model tests combined with numerical validation. The influence of the diameter ratio between the inner and outer pipes on the degree of force transfer has been examined by conducting four test phases each with a different inter-radial gap. The effect of guide shape on the magnitude of its load-response has been investigated by bending the system to inclination angles of 30°, 45°and 60°with respect to the pipe's axis.Results have shown that the magnitude of the transferred load does not change with inclination angles between 30°and 60°. In addition, the outer pipe's axial compression is independent of the inter-radial gap, whereas the differential moment increase could be determined as a function of load and gap. The numerical results match the test results within an acceptable order of magnitude. © 2010 Elsevier Ltd.