Flow Assurance

Transport and production systems are all different, and it is our experience that wax deposition and gelling can occur in spite of the best-laid plans. The approach to the problem has to be designed on a case-by-case basis. ROSEN has the capability and experience to act as troubleshooter to meet these various challenges:

• Pipelines with severe wax accumulations
• Oil fluid thermodynamic modelling for wax
• Prediction of potential wax deposits and their location
• Measuring and monitoring wax deposition and growth
• Designing pig runs for efficient wax removal and establishing criteria for the frequency of operations
• Pigging for wax in gas-dominated multiphase flow lines
• Dealing with waxy, high pour-point oils or with low temperature reservoirs
• Managing and maintaining tie-back lines to satellite facilities

Ordinary pigs face some limitations in a wax-heavy environment. Where wax thickness is more than a few millimeters, or where there are cubic meters of wax already formed, normal pigging of a pipeline runs the risk of a pig getting stuck. The Flow Assurance team works closely with our cleaning pig specialists to deploy the optimum package to get the problem fixed safely and expediently.

Many gas pipelines operate in multi-phase flow conditions. Liquid accumulation depends on the liquid loading of the gas, pipeline topography and the velocity of gas travelling through it. These pipelines must be operated carefully to avoid liquid management issues that occur during transient operations – start-up, ramp-up and pigging.

By utilizing sound flow assurance principles with rigorous flow modelling and simulation expertise, ROSEN helps clients understand flow stability in their pipeline network and can propose these various solutions for liquid management:

• Controlled start-up and ramp-up to eliminate or minimize liquid surge
• Sequencing production from high liquid-producing wells
• Minimize liquid build-up by sweeping using dry gas where available
• Deploy optimized pigging to maintain a low liquid inventory

When using cleaning pigs to remove liquids, there is a risk of a shutdown due to an excess liquid surge. Bypass pigging maintains high production flowrates while slowing down the pig and controlling liquid surge volumes.

ROSEN combines decades of expertise and innovation in bypass pig design and operation with extensive flow assurance analysis to estimate the ideal bypass opening and operating limits for a successful pigging campaign.

Modelling the “why” and “where” of the formation of hydrate clusters and how to deal with them has exercised the oil and gas industry for decades. We naturally recommend suppressants and methanol injections – but only as components of a programmed approach to dealing with hydrates. Profiling where and when there is susceptibility to hydrate build-up enables operators to design and implement lines deliberately to mitigate their effects.

Internal conditions in multiphase pipelines vary depending on fluid compositions, their properties, flow rates and pipe inclination. Accordingly, a variety of flow regimes may exist, including slug flow. In most cases, slugging is easily handled by a well-designed receiving vessel and control system. However, instabilities at the topsides receiving facility can develop when the magnitude of the slugs increases. If unchecked, severe slugging can, for example, cause problems such as poor separation, unplanned flaring and even emergency shutdowns of platforms. Slug-induced vibration is also a potential threat to offshore oil and gas facilities and subsea pipelines.

ROSEN can devise strategies to eliminate or minimize slugging, improve topsides stability and ensure maximum production during Life of Field operation. Typical studies include:

• Extensive multiphase transient simulations to determine the type and tendency of slugging
• Development of a flow regime envelope for Life of Field operation
• Detailed calculations to estimate the worst-case slug length, volume, velocity and frequency based on statistical analysis
• Benchmarking simulated results against available field data in order to validate the slugging mechanism
• Identification of the root cause of slugging and recommendation of mitigation strategies

Degradation in long-distance slurry transporting pipelines can result in substantial economic losses. The most common degradation mechanisms in such pipelines are often attributed to erosional wear, corrosion or a synergistic combination of these mechanisms. Understanding the root cause or the main degradation mechanism helps operators determine the optimum transport conditions to maintain integrity and long life of the pipeline.

Slurry pipe wear is occasioned by many factors, including physical and chemical properties of the slurry, the make-up of particles, and the design of the pipeline and its operating conditions. For these reasons, ROSEN employs detailed data-driven Root Cause Analysis (RCA) studies to determine the causal factors contributing to erosional wear. An important component of the analysis is a flow modelling study.

Different slurry flow regimes can occur in a pipeline. The damaging effect of the “sliding/moving bed” is well known, for example. The study’s holistic approach encompasses analysis of slurry chemistry and rheology, particle properties and flow modelling to determine a pipeline’s internal conditions. In order to determine the location of susceptibility, a range of studies is performed:

• Review of the slurry and particle physical properties and chemistry data
• Characterization of the solid particles and rheology
• Detailed hydraulic calculations to determine the laminar/turbulent transition
• Field data benchmarking of the hydraulic models
• Modelling and simulation of the solid deposition behavior in a non-Newtonian slurry system using mechanistic slurry transport models
• Rigorous multiphase pipeline flow modelling integrates with a specialized particle tracking module to assess the solid flow regimes with respect to pipeline elevation profile

Performing solid deposition calculations holistically with detailed hydraulic flow modelling, allied to in-house inspection data, provides ROSEN with unparalleled insights into the causal factors affecting pipeline degradation. Additionally, such hydraulic and solid deposition models can be further employed to optimize current and future flow conditions to reduce pipeline wear to a minimum.