Beachpull Installation of Long Pipelines and Cables

Abstract

Conventional pipelay (i.e. S-lay) is not feasible in shallow water locations owing to the draft of pipelay barges. Pipelay using beachpull method provides an alternative to such restrictions. A typical long beachpull operation in shallow water environment presents a substantial challenge, which calls for a thorough engineering analysis along with a detailed installation procedure. This paper highlights the methods and techniques of pipelay using beachpull method that were employed on the John Brookes joint venture (Apache and Santos) and the Aramco Karan project. The John Brookes project (Varanus Island, Australia) included the installation of a landfall section comprising an 18” FBE coated pipeline featuring a beachpull length of 7.0 km, one of the longest of its kind. The Karan project (Saudi Arabia) comprised the installation of a 38” trunkline, requiring a beachpull length of 3.0 km and also the installation of a 15kV cable having a beachpull length of 4.0 km. Beachpull engineering comprised checking the pipeline’s lateral stability under the influence of near-shore current-induced hydrodynamic forces. For the Apache Project, the 7.0 km long beachpull coupled with the proximity to the existing pipeline and near-shore currents offered a unique challenge. Supplementary buoyancy was utilized to limit the required beachpull tension within allowable limits. The drifting of the pipeline from the installation corridor was restricted by installing sand-filled bulker bags at designed intervals. The beachpull installation on the Karan project offered a different challenge owing to a larger pipe size and a piggybacked cable in a shallow water depth. Special consideration was given to the attachment of supplementary buoyancy bags and dynamic loadings that were acting throughout the beachpull length, especially during cable installation. This paper describes the technical challenges faced during the estimation of the pull-in loads and weather-induced lateral displacements encountered during the beachpull. This paper also elaborates the assessment of proposed winch, design of supplementary buoyancy, design of bulker bags, etc. Data collected on-site during installation of the pipelines are in good agreement with computed / designed values, ensuring the correctness of the beachpull simulations. Detailed engineering studies along with well developed installation procedures resulted in successful completion of the installation.