Technical and Economical Comparison of Subsea Active Heating Technologies

Abstract

Active heating of subsea flowlines is an attractive solution for facing flow assurance issues related to always going deeper and longer, as well as more complex fluids and critical wellhead flowing conditions (pressure, temperature, flowrate) prone to pour point issues, hydrates and/or wax appearance risk. Over the last 15 years, several active heating technologies have been developed and operated in order to significantly help solve flow assurance issues from the subsea wellheads up to the surface support facilities. These technologies have demonstrated to be very different in their design and operability (use of hot water, direct or indirect electrical heating) but also in their efficiency and cost. In parallel with the development of heated flexible pipe designated IPB (Integrated Production Bundle) already used for field development in West Africa and Brazil as well as a rigid heated pipe-in-pipe technology, both using electrical heat trace cables, Technip has been involved in the design, construction and installation on several projects of all active heating technologies. Based on this extensive knowledge and track-record, this paper describes and compares the working principle as well as the advantages and drawbacks of the different active heating technologies. This paper also identifies their limitations with regards to field application, i.e. length and water depth based on their actual development status. On the basis of different generic case studies (shallow long tie-back, shallow in-field development, deep water tie-back and ultra-deep water in-field development), this paper finally reviews all the potential benefits the different active heating technologies can bring to a project and includes an economical comparison of these technologies.

An Overview of Flow Assurance Heat Management Systems in Subsea Flowlines

“…Oil and gas production is inherently a risky business and how this risk is managed will effectively determine its success. Flow assurance issues are part of these risks and with most of the conventional fields already being produced, operators are facing in the past 15 years increasing issues in developing fields that have changed from stand-alone host structures and largely concentrated resources to scattered ones with tie architectures to existing facilities or shores [160]. In the last 10 years [161], the numbers of long tie-backs doubled [162].…”

“…Truly, long tie-backs to existing infrastructures (higher than 10 miles for oil fields and 30 miles for gas fields) are planned, from a cost perspective, as they give entry to far reserves circumventing new topside installation [161]. By venturing further and into deeper subsea, together with growing flow assurance issues associated with fluid characteristics (hydrates, wax, high viscosity, pour point) as well as flowing conditions (temperature, pressure, flow rate), have expanded conventional flow assurance methods wax and hydrate prevention which included passive insulation to its limits, forcing the use of conventional or hybrid loop architecture (e.g., depressurization, dead oil circulations, and chemical injection to its limits) at elevated costs [160].…”

“…In this situation, active heating looks good enough as a cost-effective alternative for both subsea in-field and long tie-back developments [160]. From a technical viewpoint, the use of active heating permits transient and steady-state operations simplification of highly complex fluids by managing wax, hydrates, high viscosity and pour point issues with continuous or discontinuous heating [160].…”

“…In this situation, active heating looks good enough as a cost-effective alternative for both subsea in-field and long tie-back developments [160]. From a technical viewpoint, the use of active heating permits transient and steady-state operations simplification of highly complex fluids by managing wax, hydrates, high viscosity and pour point issues with continuous or discontinuous heating [160]. The conservation and line start over by active heating method permit the change to a single line framework that presents significant cost gains through a reduction in the number of flowlines from a conventional circuit system with chemical injection and dead oil circulation [160,[163][164][165].…”

“…From a technical viewpoint, the use of active heating permits transient and steady-state operations simplification of highly complex fluids by managing wax, hydrates, high viscosity and pour point issues with continuous or discontinuous heating [160]. The conservation and line start over by active heating method permit the change to a single line framework that presents significant cost gains through a reduction in the number of flowlines from a conventional circuit system with chemical injection and dead oil circulation [160,[163][164][165]. The active heating system involves the external addition of heat to the production flowline by an electrical heat source or circulated hot water [166,167].…”