Subsea tieback of a new field to an existing offshore production facility is one option to minimize development costs. Alternative flowline or equipment specification is another option in addressing development costs. The three papers here discuss slightly different approaches to subsea flowlines and to offshore heating systems. All three have progressed to at least a full-scale demonstration stage, if not to actual field installation.
Although carbon-steel flowlines have been the primary choice for most subsea flowlines, increasingly corrosive reservoir fluids lead to other material choices. In addition to corrosion-resistant-alloy cladding or pipe, thermoplastic composite pipe (TCP) is recognized as an alternative. As a result of a large joint-industry project, DNV recently issued a recommended practice for specification, design, and qualification of TCP. The use of a TCP recommended practice is expected to reduce project-specific implementation costs but maintain a consistent qualification approach. OTC 26512 discusses TCP properties, applications, installation, and operation.
Hydrate and wax flow-assurance risks are typically mitigated by continuous chemical injection, heat, insulation, pigging, or a combination of strategies. Heat conservation (insulation) may be effective in short- to moderate-length flowlines but is insufficient in longer flowlines; active heating is needed there. Direct electric heating is proposed for flexible pipe. OTC 26939 describes using the carcass and tensile armor of flexible pipe to pass electric current so that only one end of the pipe is required to have electrical connections. The qualification testing on a 12-in.-diameter, 125-m-long flexible pipe is discussed, including low-voltage and high-voltage scenarios.
Offshore-facility electric heating elements and power cables typically are low-voltage systems. Medium-voltage (up to 7,200 V) systems are suggested alternatives for facilities with megawatt-level electric heating requirements. Advances in metal-sheathed electric process heating and power controls suggest that significant savings are possible in footprint, efficiency, and reliability compared with conventional low-voltage systems. OTC 26389 discusses the case study used to select a medium-voltage, 2.6-MW heating system for a Gulf of Mexico location. Although the higher-voltage equipment capital cost is higher than the low-voltage equipment cost, installation, operating, and maintenance costs are less.
Offshore opportunities continue to drive new technology applications and approaches. The three papers highlighted here focus on minimizing costs while providing safe, reliable operations. I hope you find them interesting. They reminded me to keep my mind open to new options.
OTC 26832 Application of Flexible Composite Pipe as a Cost-Effective Alternative to Carbon Steel—Design Experience by Syafiah Adam, Brunei Shell Petroleum, et al.
OTC 24022 Buoyant Tower: Construction Challenges and Lessons Learned by Clyde Crochet, HortonGMC, et al.
OTC 27176 Use of Advanced Composites in Offshore Pipeline Design by Naveen Ravirala, Wood Group Kenny, et al.
Sally A. Thomas, SPE, recently retired as a principal engineer in production technology at ConocoPhillips. She holds BS and MChE degrees from Oklahoma State University in chemical engineering. Although mostly stationed in the US, Thomas has had international assignments in the UAE, the UK, and Venezuela. She has served in SPE local-section offices; on regional-meetings organizing committees; as a technical-paper reviewer; as chairperson of the SPE Books Committee; and as a member of the SPE Projects, Facilities, and Construction Advisory Committee and the JPT Editorial Committee.
Offshore Production and Flow Assurance
Sally A. Thomas, Retired, Principal Engineer in Production Technology, ConocoPhillips
10 October 2016