Offshore Pipeline Trenching In Arctic Regions: A Unique Concept 'The Arctic Subsea Bucket Ladder Trencher'

摘要

Pipelay in Arctic offshore regions comes with a number of challenges. The pipelay process includes safe burial of pipelines, while minimizing the disturbance to the natural environment is key priority. Deep trenching will be necessary, resulting from deep keeled ice features that can gouge the soil and present a threat to the pipelines. In addition, a fast trenching solution should be obtained to enable the pipelay operation to be carried out in the short open water season. So far, this can hardly be carried out by conventional equipment. This paper describes a deep and fast trenching method suitable for Arctic conditions. The concept is approached from a dredging industry perspective since the huge soil volumes to be excavated relate to practices common in the dredging industry. The views of operating and dredging companies are integrated, leading to a promising conceptual solution for Arctic trenching. The purpose of the design case was created to discuss several Arctic trenching challenges to find a conceptual solution for deep and fast trenching (6m) in the Arctic. The case was about trenching through stiff clay in which backpack size boulders are present, while keeping in mind a high required trenching speed (75m/hr) and the desire to keep the spoil to remain as insitu as possible to minimize the impact on the environment. For this base case The Arctic Subsea Bucket Ladder Trencher that is presented in the paper is a promising method. This Arctic Trencher (AT) has the following characteristics: 1. Precise excavation possible; 2. Highly capable of operating in stiff clay; 3. Relatively low cutting power required; 4. Capable of excavating without compromising the in-situ soil; 5. Boulder handling possible up to the size of the buckets; 6. Trenching possible in one operating season; 7. Proven method in dredging industry: expertise readily available. Based on the initial base case design conditions it was concluded that the presented design case has an excellent potential for successful trenching in the Arctic. Although some uncertainties remain, the authors are continuing development of the concept to further assure its feasibility. This paper shows that it is worthwhile to include the joint effort of field operator, pipelay/trenching operator and manufacturer of trenching equipment, to tackle the challenges when the difficulties of trenching operations increase.