This article explores various aspects of flow assurance in subsea developments. Flow assurance is an understanding of multiphase flow fluid dynamics and analyses, an ability to identify flow-related problems using state-of-the-art prediction tools, and the knowledge to develop solutions that eliminate, mitigate or remediate flow-related issues encountered in subsea systems. Flow assurance is reliable, safe and cost-efficient management of hydrocarbons from reservoir to export without any flow-related issues over the life cycle of the oil field. Subsea developments continue to escalate in quantity and complexity as the exploration and production companies ramp up exploration of deep-water and ultra-deep-water reservoirs with complex formations in harsh environments with increased challenges. Some of the technologies under thermal solutions are thermal insulation, direct electric heating and electrically-heated pipe-in-pipe. Oil and gas companies generate revenue from the oil produced. If the oil flow stops, their revenue stops. The more it stops the more they lose cash. Hence it can be termed as cash flow assurance. With fluctuating oil prices and unpredictable production issues, engaging flow assurance at every stage starting with the early phase ensures uninterrupted transportation of reservoir fluid from pore to process facilities in a safe manner and insures cash flow.

Article

Flow assurance is an understanding of multiphase flow fluid dynamics and analyses, an ability to identify flow-related problems using state-of-the- art prediction tools, and the knowledge to develop solutions that eliminate, mitigate or remediate flow-related issues encountered in subsea systems. Flow assurance is reliable, safe and cost efficient management of hydrocarbons from reservoir to export without any flow-related issues over the life cycle of the oil field.

Subsea developments continue to escalate in quantity and complexity as the exploration and production companies ramp up exploration of deepwater and ultra-deepwater reservoirs with complex formations in harsh environments with increased challenges [1]. Typical challenges involve ultra-deepwater, longer offsets and tiebacks, arctic environments, high pressure and high temperature fields, heavy oil, and low-energy reservoirs. Subsea field development involves multi-discipline activity to generate an optimized solution and typically parallel activities are performed. There is a significant level of interaction between these activities and flow assurance is a key enabler and integral part of the field development activity. A complicating factor is that the field characteristics change over time and the flow assurance approach must adapt with the evolving field.

Flow assurance issues can be grouped into three different categories. They are

1 Production Chemistry Issues

2 Operational Issues

3 Integrity Issues

Typical production chemistry issues are hydrates, wax/paraffins, scales and asphaltenes. Operational issues are slugging, sand production, foam and emulsions. Corrosion and erosion fall under integrity issues. Figure 1 shows typical flow assurance issues like hydrates, wax and corrosion encountered in subsea oil fields.

graphic

The key concerns in any subsea field are upsets in fluid behaviour and excessive solids deposition which can cause operating problems, including production shutdown and expensive interventions. Addressing flow assurance and incorporating flow management strategies early in the conceptual design phase can minimize costly occurrences. It is applied during all phases of system selection, detailed design, surveillance, troubleshooting operation problems, increased recovery in late life etc., through the production flow path from well tubing, subsea equipment, flowlines, initial processing and all the way to export lines. Flow assurance facilitates operability by the development and implementation of strategies to analyze line sizing and insulation requirements and manage solids including hydrate, wax, asphaltenes, scale, etc. Typical flow assurance analysis addresses establishing design basis with general information on fluid properties, reservoir properties, bathymetry, production profile/targets, etc. and assess system hydraulic and thermal design. Analysis also includes modification of design for transient effects like start-up, shutdown, cool-down, rate changes, well testing, pigging, slugging, pressure surges, leaks, etc. and to develop operating strategies to assess system economics. Other key areas addressed are topside separator sizing, inhibitor requirements, cool-down time calculations, flowline warm-up time calculations and pigging time calculations.

The industry is using existing and mod­ified technologies combined with new approaches to maintain an uninterrupted flow of hydrocarbons from the reservoir to the topsides. Each field is different and there is not one simple solution for flow assurance. A tailored approach is needed to combat these issues for each field. Various state-of-the art flow assurance technologies [2] are available to mitigate these issues and these technologies are major enhancers and have great impact on cost effectiveness and production. These technologies are categorized into five different solution types such as

  • Thermal

  • Chemical

  • Hardware

  • Operating and

  • Software technologies.

Some of the technologies under thermal solutions are thermal insulation, di­rect electric heating and electrically-heat­ed pipe-in-pipe. Thermodynamic hydrate inhibitors, low-dosage hydrate inhibitors (LDHI), defoamers, asphaltene inhibi­tors, paraffin inhibitors, scale inhibitors, H2S scavengers, chemical demulsifiers and drag-reducing agents fall under chemical solutions. Subsea separation, subsea boosting, subsea compression, subsea coolers and pipe-in-pipe, bundles, coiled tubing tractors, desanders, ero­sion probes, acoustic sand detectors and acoustic leak detectors are some of the hardware solutions. Dead oil and hot oil flushing, pigging, depressurization and gas sweep­ing are operating solutions. Real-time flow assurance advisory systems and remote performance monitoring systems come under software solutions. Figures 2 and 3 show examples of thermal insulation and subsea separator.

graphic

graphic

But the success of flow assurance depends on the development of technologies that can enable cost-efficient and environ- mentally-friendly applications while contributing to increased earnings, production and improved recovery, enhancing and prolonging the use of existing infrastructure. These developments are based on the technology readiness and qualification stage, cur­rent industry application and growth potential, opportunities to go through improvements and advances to meet the new environ­mental regulations.

Oil and gas companies generate revenue from the oil produced. If the oil flow stops, their revenue stops. The more it stops the more they lose cash. Hence it can be termed as cash flow assurance. With fluctuating oil prices and unpredictable production issues, engaging flow assurance at every stage starting with the early phase ensures uninterrupted transpor­tation of reservoir fluid from pore to process facilities in a safe manner and insures cash flow. Déjá vu?

References

References
1.
Phaneendra
Kondapi
, Need for Industry Ready Education: Flow Assurance Course-A Case Study, Offshore Technology Conference, Houston, TX, May 5 – 8,
2014
2.
Phaneendra
Kondapi
and
Randi
Moe
, Today’s Top 30 Flow Assurance Technologies: Where do they stand?, Offshore Technology Conference, Houston, TX, May 6 – 9,
2013