Applications and Performance of Trenching Technologies in Asia-Pacific

Abstract

Description ofproposed paper: Burial ofsubmarine pipelines and cables is standard practice in offshore oil and gas regionswhere potentially damaging threats such as interaction with fishing gear anddragged anchors are high. The requirement to bury pipelines in Asia-Pacific hasnot had the same imperative as the North Sea for example but this region is nowseeing a growing demand for pipeline burial to increase mechanical protectionand stability. Performance benchmarks for most trenching systems are based onthe seabed soils typically found in the North Sea and consequently do notinclude the unusual carbonate rich seabed sediments that are prevalent in theAsia-Pacific region which are often cemented and pose a significant challenge to trenching. Application: Trenching isconsidered an activity with significant risk so it is particularly important toselect the correct tool for the field conditions and to establish realisticperformance criteria based on regional experience in the prevailing seabedsoils, including carbonate rich sediments. This paper addressesthe primary differences that exist in seabed sediments and trenching conditionsbetween Asia-Pacific and other regions and show how these dissimilaritiesimpact on the choice of burial equipmentand tool performance. Results, Observations, and Conclusions:A state of theart review of trenching methods and technologies is presented. Trenching casestudies from Australia and Asia are presented which highlight the challenges ofdesigning an appropriate protection and burial strategy for this region and providesindications of actual performance that can be expected across the range ofseabed conditions typically found in the Asia-Pacific region. This includesdata for trenching in harder cemented soils to help fill the gaps associatedwith performance predictions in carbonate sediments. Significance of Subject Matter: The significanceof this proposal paper can be summarised as follows:It provide a reference point onwhich to plan trenching work in Asia-Pacific region,It addresses the knowledge gapsassociated with the relative inexperience of trenching in Asia-Pacific regionPerformance benchmarking is extendedto include the carbonate rich and cemented sediments.

Perspective Review on Subsea Jet Trenching Technology and Modeling

“…In such circumstances, different burial technologies are adopted according to their different ranges of applications. Figure 2 gives a synoptic of the capabilities of different trenching methods [17]…”

“…Investigating the properties of the West Africa carbonate rich seabed sediments, the authors of reference [86] have stressed an urgent need to integrate the determination of the carbonate content into the traditional seabed characterization routine. Similarly, Brunning and Machinremarked that carbonate materials are quite prevalent in the Asia Pacific [17], but due to the lack of relevant expertise, associated trenching operations are still challenging. Indeed, in some cases, these materials can be very stiff and require the intervention of mechanical trenchers [87,88].…”

“…Although different burial techniques have been devoted to risk reduction for seabed installations [2,5,16], the selection of the appropriate trencher equipment depends on a number of factors. Among them, the properties of the soil from which the trench is to be excavated is the most critical for all the trenching tools [17]. The mechanical systems generally represent the best option for stiff to hard clays and coarse-grained materials.…”

“…They still have some difficulties to be implemented under certain conditions [11,18]. Jet trenching tools represent the "go-to" tools, which have advantages for sands and very soft clays [17]. For instance, the remotely operated vehicle equipped with jets can operate in deep water, steep topography, and soft sediments, which are unfavorable for the other methods.…”

“…The origin of the aforementioned trenching machines can be traced back to several decades ago [22]. Specifically, their developments were initiated in the 1970s with the construction of the first jet sled prototype, which was successfully applied to numerous trenching operations in the Gulf of Mexico [17]. In spite of its large popularity (it was the only system operated in deep water until the early 1980s) [4,23], the practice of the jetting technique became infrequent in favor of ploughs and mechanical systems in the late 1990s.…”