Flow assurance means different things to different people. To some it can resemble the oilfield version of Roto-Rooter, unclogging wells, tieback lines and jumpers, gathering stations and risers of production-robbing deposits of paraffin, scale or hydrates. Others value a more proactive approach, whereby data monitors are used to feed into dynamic production models that, among other things, enable prediction of flow problems in sufficient time to take mitigating action.

Because the conditions that impede flow are so diverse and pervasive, there is no "one-size-fits-all" solution. Sometimes, the answer is a chemical treatment, other times there is a mechanical solution. Insulating flow lines to preserve flow stream temperature can solve the problem, or perhaps it will be necessary to boost flow line temperature using heating elements. Sometimes a combination of these remedies fills the bill.

Traditional approach is flawed

The traditional approach of flow assurance systems selection for prevention and remediation that combines sampling, laboratory techniques and predictive modeling, is a one-way process. Often this takes place during front-end engineering and design of the well or the production systems. However, without a closed-loop process that provides continuous feedback and analysis results will be suboptimal. Fortunately, the very techniques that support continuous flow assurance also benefit effective reservoir management and production optimization.

Toward a more permanent solution

Unfortunately, many flow assurance techniques are prescriptive in nature, seeking to solve an immediate problem. While effective technology is quite advanced in this area, it is postulated that to transition from a reactive mode to a proactive one requires appropriate and timely information. Only through systematic data gathering can trends affecting flow efficiency be identified and mitigating prognoses be developed.

Happily, much of the data gathered for dynamic flow assurance is also used in reservoir and production management, leading to ultimate production optimization. Accordingly, the data acquisition required for flow assurance fits into a continuum or loop that benefits the overall asset management team.

The heart of effective flow assurance management is consistent fluid property data. The validity of these data is ensured by sample integrity and traceability throughout the entire data collection and analysis process. Instrumentation installed throughout the flow stream feeds a comprehensive suite of robust predictive models for organized solids deposition, corrosion, waxy crude rheology and thermodynamic modeling. Measurements, such as distributed temperature and multiphase flow parameters, improve and refine the accuracy of these models in real time.

The result is an effective closed-loop process, using fluids data, predictive flow models and real-time measurements. This loop drives the optimization of remedial strategies and must be included as early as possible into the design of a flow assurance system. Importantly, using a data-centric approach together with robust models, enables large area scaling of related solutions for maximum economy. Using this process, the over-treatment that often occurs when applications are designed to address worst-case scenarios can be eliminated. In general, the frequency of remedial techniques using thermal, chemical or mechanical methods can be reduced, and catastrophic problems such as plugging, avoided (Figure 1).

Focusing on the problem

While it is true that flow assurance challenges can exist virtually anywhere, the deepwater offshore arena has brought increased industry focus to the problem. Everything in deepwater from drilling and completion to production costs more, so it follows that to be viable development targets assets must have sufficient value to justify the added risk. With high upfront investments and asset valuations, the last thing an operator needs is flow problems. Transitioning a flowpath that could start at temperatures and pressures as high as 400°F (200°C) and 15,000 psi, exiting the wellhead into the near-freezing environment of the seabed, and then finally making its way to the relative ambiance of the surface can do strange things to crude oil.

In a dynamic situation, each potential problem exhibits different behavior, usually as a function of temperature and pressure, and to a certain extent, flow rate. Waxes, hydrates and scales exhibit a sort of "phase behavior" as they appear and agglomerate in the flow stream. And trouble nodes are created at different spots in the flow path depending on whether it's in the riser or the flow lines. The best solutions, too, are dependent on the environment to which they will be applied (Figure 2). Accordingly, without sufficient data, flow assurance prevention and remediation systems are often over-designed to cover extreme conditions. It can be seen that the best chemical solution may actually be counteractive to the best mechanical or thermal solutions, or vice versa. Inappropriate solutions may create additional concerns such as slugging and associated problems related to multiphase flow. It follows that a holistic analysis and solution set that takes into account all potential environments and conditions is most likely to succeed.

Schlumberger has developed subsea Production Assurance services for optimizing subsea field productivity. These services combine the company's experience in project management, systems engineering, data acquisition and analysis in a modular solution set that benefits both production management and flow assurance. Tying the reservoir, well bore, subsea and surface processing facilities into a complete network leverages the value of real-time data monitoring and system control. A key node is the wellhead interface. There is no doubt that new designs can incorporate the additional features needed to enable required data gathering. However, such a design could be excessively complex and not easily retrofitted to existing assets.

A new modular open architecture "plug n' play" module has been developed that can link all well monitors and controls with surface and flow line sensors. Called the Subsea Monitoring and Control (SMC) system, it incorporates the intelligent well interface standard (IWIS) so instrumentation and control modules from any supplier can interface seamlessly. The module fits on a subsea tree and can be deployed and retrieved when necessary using a remotely operated vehicle (ROV) without interrupting production. The system accommodates real-time production monitoring and control systems including those with fiber optic communication or distributed temperature sensors. It also supports data streams from monitors in downstream nodes including subsea flow boosters or flow line heaters. With real-time system surveillance, the entire production network can be optimized.

In addition to production optimization, flow assurance can be supported using the data to predict potential bottlenecks and schedule remedial actions, from changing the rate of methanol injection to planning a comprehensive workover. Optimization of production equipment such as gas-lift or electrical submersible pumps (whether installed downhole or as subsea boosters) can be facilitated using the SMC. Not only can these systems be kept running at maximum efficiency, but scheduled maintenance and refurbishing can be conducted when it creates the least disruption. Thus production and flow assurance are effectively linked by the SMC module, which is both part of the data gathering function and the solution implementation.

When monitoring and control data exist in a closed-loop dynamic production management decisions and analysis are enabled, providing an optimization path that leads from pore to process.