Making sure oil and gas flow freely through long, complex tiebacks is one of the critical challenges of production facilities. Many things can inhibit flow, including hydrates, paraffins, scales and asphaltenes, and these impediments can affect producing wells, flowlines and production facilities.
This problem impacts both onshore and offshore developments. Onshore, it is easier to deploy equipment and address flow issues, but offshore flow assurance challenges are somewhat more complicated because intervention costs increase with the distance from shore and the length and depth of flowlines. Temperature also can present a challenge because temperatures in deep water often are near or below 4.5 C (40 F).
Many companies have invested in R&D to develop ways to improve flow assurance, investigating such techniques as insulating pipelines or electrically heating lines to manage temperature and introducing chemicals to control wax and anti-agglomerators to prevent hydrates from forming plugs.
Flow assurance
There are multiple ways of remediating blockages. Flow can be modified so a specially designed pig can be deployed to cut through flow-restricting buildup and help improve throughput. The line can be heated, hot fluid can be circulated through the line, and coiled tubing (CT) can be inserted through a lubricator on the surface to deliver inhibitors like glycol or methanol into the face of the blockage.
A paper presented by FMC Technologies at the Offshore Technology Conference a few years ago identified and evaluated 30 flow assurance solutions, dividing them into five categories. Under “thermal solutions,” the authors included insulation, direct heating, electrically heated pipe-in-pipe, cold flow and phase-changing materials. Nine “chemical solutions,” ranging from thermodynamic hydrate inhibitors and low-dosage hydrate inhibitors to defoamers, H2S scavengers and drag reducing agents, were included, as were “operating solutions,” such as pigging, flushing, depressurization and gas sweeping. There were “evaluations” of nearly a dozen “hardware solutions,” including subsea separation, boosting, compression and cooling as well as acoustic sand and leak detectors, desanders and CT tractors. The final category identified software that can evaluate impediments to flow and provide treatment options.
Hardware in the line
Warrior Energy Services, a fully owned subsidiary of Superior Energy Services, offers a CT tool called CoilTac, a thruster designed for cleanout operations in pipelines with an inside diameter (ID) of 3 in. and larger. It has been used to distances in excess of 1,219 m (40,000 ft). The thruster removes paraffin, hydrate plugs, asphaltenes, scale and other blockages to the full ID of the pipeline. Operations can be performed from liftboats, deepwater vessels, platforms or on land. The system provides jetting ahead of the thruster while applying thrust force as it moves down the pipeline.
Simultaneously thrusting and jetting ahead of the tool with treatment chemicals applied directly to the pipeline obstruction allows the thruster system to clean farther than conventional CT applications. The tool sends data as it progresses through the line, providing a snapshot of current conditions. The company believes this technology also could impact future pipeline construction design by extending the reach of subsea tiebacks.
GATE Energy’s eelReel is another CT-deployed tool that has been used to resolve blockages, including hydrates, scale, paraffin and asphaltenes, as well as prejob stimulation, production enhancement, flowline abandonment and stuck pig retrieval. The tool is attached to CT and loaded into the flowline through an injector head positioned above the tree.
Power fluid (e.g., produced oil, diesel, chemical or water) enters the tool through the screen and pushes the tool through the line. High-pressure jets dispense the power fluid to remove debris, which enters through the tip and is extracted to the surface through the CT. The reverse screen subs on the front of the tip prevent debris from plugging the CT. According to GATE, eel- Reel jets clean the flowline to the original pipe ID.
Science and art
Because oil and gas is a data-driven industry, there has been a shift toward using modeling software that can evaluate a range of parameters that affect hydrocarbon flow. Instead of providing discrete solutions, oilfield service companies are developing systems that use data specific to the individual field to model hydrocarbon flow, determine where flow is likely to be inhibited and provide a range of solutions for restoring movement. Managing flow assurance has become both a science and an art that takes into account pressure and temperature profiles and uses a broad range of data to model hydrocarbon flow throughout the production system.
Production challenges are being simulated in laboratories, where hydrates, paraffin, asphaltene, emulsions, scale and corrosion can be studied in the context of a system. Using fluid flow software packages, engineers can evaluate the thermal hydraulic behavior for a wide range of systems and choose from an assortment of solutions.
Assured Flow Solutions LLC is one of the companies that offers a range of fluid flow testing capabilities to identify the multiphase flow challenges that are likely to occur during specific operating scenarios and provide a solid understanding of the transient behavior in a system. With this information in hand, engineers integrate reservoir, flowline/pipeline, riser, facilities, material and operational constraints to deliver a complete flow management system.
Having more data in hand to make decisions for improving system fluid flow is crucial to an appropriate life-of-field design; so it is not surprising that a number of companies are offering modeling as the foundation for understanding flow assurance issues and using the results to deliver solutions.
Schlumberger’s PIPESIM is one of these. It is a steadystate multiphase flow simulator that offers workflows for both front-end system design and production operations. The PIPESIM simulator often is used to identify situations that require more detailed transient simulation such as shut-in, startup, ramp-up, slugging, hydrate kinetics and wellbore cleanup. Advanced simulation is carried out using the OLGA multiphase flow simulator, which enables key flow simulation applications, including liquids handling, sizing separators and slug catchers, solids management, and pigging modeling for contingency planning. By identifying areas prone to slugging, corrosion and solids formation, engineers are able to pinpoint solutions appropriate to each particular flow challenge.
Halliburton’s SureStream flow assurance services, which the company refers to as “integrated flow optimization capability,” is another broad offering of flow assurance solutions. Through the SureStream suite of services, engineers provide analysis and assessment of an extensive range of parameters that impact the free flow of production and offer a range of chemical, mechanical and thermal cleaning programs as well as maintenance management support.
Baker Hughes, a GE company (BHGE), addresses flow assurance issues with FORSA flow assurance chemical solutions. BHGE uses what it calls a total systems approach process to analyze field conditions from the reservoir to the wellhead up to the surface storage tanks with the goal of identifying flow challenges and formulating the optimal mitigation option. After pinpointing potential threats, BHGE engineers can offer a solution from options that include scale mitigation treatments, paraffin control, asphaltene treatments and hydrate inhibition.
Tools for tomorrow
There is a lot at stake when hydrocarbon flow is curtailed. Not only does restricted production impact profitability, it can result in compromised or damaged equipment that can threaten the environmental integrity of operations.
As operators focus on improving safety and minimizing the footprint of offshore production, longer tiebacks and more subsea systems will be the norm. More real-time production data will be available, and creative engineers will mine that information to find even better ways to improve flow assurance.
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