Flow Assurance Analysis Tools

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Flow Assurance Analysis Tools

PIPESIM
PIPESIM is a workhorse for steady state thermal-hydraulic modeling of multiphase flow systems: both single-line and network systems. PIPESIM can model the entire system, from the reservoir to the production facilities. It competently models black oil and compositional systems. Industry-standard multiphase flow correlations and mechanistic models, including OLGA-S and TUFFP, are available. Each company uses its own experience to assure that appropriate correlations, equations of state, fluid variables, and other system options are used for the analysis being performed. Additionally, the PIPESIM Field Planning Tool is integrates reservoir models with the hydraulic model.

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[Mohamed]

OLGA
Many basic system design attributes can be determined using steady state analyses (i.e. with PIPESIM). However, transient simulation is needed to address more detailed design and operability considerations. OLGA can be used as a transient, multi-phase, thermal-hydraulic simulation software. Common uses for OLGA include determining system/component warmup and cooldown times, blowdown fluid rates and temperatures, and slugging behavior (rate change, hydrodynamic, and more severe terrain induced slugging). In addition, the three-phase version of OLGA is necessary for predicting liquid holdup in low rate gas/condensate systems. OLGA and transient simulation is used increasingly as more system detail is developed. The transient temperature and velocity behaviour of the transported fluids figure prominently in the operability design of the system.

[Mohamed]

Multiflash and PVTSim
Both Multiflash and PVTSim are used for physical property and phase behaviour prediction and characterization of reservoir fluids. They can both predict hydrate phase behaviour and inhibition prediction. PVTSim can model the thermodynamics of waxes and asphaltenes in produced fluids. The decision of which to use within the design process is based on their individual capabilities and experience. At the beginning of the process, it is particularly important to use these programmes and experience to evaluate available fluid data to assess its validity (a common problem with the limited fluid data obtained from exploration wells). During the rest of the process, the programmes will be used to develop fluid characterizations, to assess fluid thermodynamic behaviour, and to evaluate new fluid data as it becomes available. In particular, these programmes will be used to determine hydrate inhibitor performance and volume requirements. The understanding of inhibitor performance and volumes figures prominently in the operability design of the system. Multiflash is the thermodynamic and physical property package included in PIPESIM, giving PIPESIM full compositional capability and the ability to predict hydrates. PVTSim is the thermodynamic and physical property package included in OLGA.

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[Mohamed]

LedaFlow LedaFlow^® is a new dynamic multiphase flow simulator that meets significant market demand for a better dynamic multiphase flow simulator. It is the product of

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LedaFlow Capabilities
LedaFlow^® is used throughout field development in feasibility studies, conceptual studies, FEED and detailed designs and during operation of the field.
Some application examples:

• Transient analysis during normal conditions, startup, shutdown, depressurization, shut-in
• Line packing
• Terrain slugging
• Liquid surges in gas condensate systems
• Liquid inventory during pigging and rate changes
• Gas lift impact on flow conditions
• Thermal design of flowlines
• Optimal design for maximum operating envelope
• Process and control system design
• Slug mitigation and control
• Inhibitor tracking and hydrate risk assessment

Field Data Validations
ConocoPhillips and TOTAL have validated LedaFlow® against a large number of measured data from fields covering:
- both gas/condensate and oil dominated systems
- a large range of Gas-Oil-Ratio and Water Cut
- pipe diameters ranging from 2” to 38”
- a large variation in operational pressures
Some selected examples:

Field type Type Company
Gas/oil 42 km offshore pipeline Pipeline Total
Offshore gas field Pipeline ConocoPhillips
Gas/oil 2 km onshore pipeline Pipeline Total
Onshore gas field Pipeline ConocoPhillips
Gas/condensate 20 km offshore pipeline Pipeline Total
Gas 81 km offshore pipeline Pipeline Total
Oil well with gas lift Well ConocoPhillips
Gas/oil 4 km offshore pipeline Pipeline Total
Gas/oil 16 km pipeline Pipeline Total

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[Mohamed]

PIPESIM Flow Assurance
PIPESIM software offers the industry’s most comprehensive steady-state flow assurance workflows, both for front-end engineering design (FEED) and production operations. Specific flow assurance modelling capabilities include:

• Erosion prediction for sand-laden fluids
• CO2 induced corrosion prediction
• Emulsions handling
• Hydrate prediction including mitigation with inhibitors
• Slug characteristics and pigging operations
• Wax and Asphaltenes prediction
• Time-dependent wax deposition
• Liquid loading and slugging prediction
• Detailed heat transfer modelling

Corrosion and Erosion Understanding corrosion fundamentals is essential to design sound strategies that will effectively control corrosion. Corrosion occurs because an aqueous phase is almost always present in oil and gas fluids. Corrosivity depends on the concentration of CO2, temperature, pressure, flow regime, and flow rate. PIPESIM software identifies locations prone to corrosion and specifically predicts CO2 corrosion rates. The De-Waard corrosion model calculates a corrosion rate caused by the presence of CO2 dissolved in water. The concentration of CO2 is obtained from fluid property definitions (black-oil or compositional). Erosion is also potentially very damaging. It can occur in solids-free fluids but is exacerbated by entrained solids (sand). The rate of sand production is the main determinant of erosion rate. With PIPESIM software, engineers can model erosion to select proper equipment and materials. PIPESIM erosion-modeling methods include the API 14E and Salama models. The erosional velocity limit is calculated based on the prevailing flow conditions and presented as a ratio with the fluid mean velocity, in which values of one or greater indicate the degree of risk. Additionally, the Salama model predicts the rate of material loss due to erosion for fluids containing sand. Results along the flow profile, branch maximum erosion rates, and velocity ratios are reported in an output file and in plots. Emulsions
Emulsions resulting from oil and water mixtures can lead to processing problems and higher treatment costs. High liquid viscosities resulting from emulsion formation can cause high pressure losses in wells and flowlines. A number of emulsion correlations are available within PIPESIM software, including Woelfin, Brinkman, Vand, Richardson, and Leviton and Leighton. The inversion point that defines the continuous phase may be specified by the user or calculated using the Brauner-Ullman equation. Hydrates
Water and hydrocarbon fluids can form hydrates, which, if left untreated, can cause blockages. The physical properties of hydrates are similar to those of ice, but hydrates can form at relatively high temperatures in high-pressure systems. Once a plug is formed, intervention is required that may result in significant downtime. It is, therefore, very important to design and operate an offshore pipeline system to effectively manage hydrate risks. PIPESIM software includes the following hydrate migration strategies.

• Thermal insulation: The best way to mitigate the hydrate risk is to maintain the fluid temperature inside the pipeline above the hydrate formation temperature. By considering detailed heat transfer mechanisms, the effects of insulation and pipeline burial can be investigated with PIPESIM for front-end design.
• Chemical inhibition: If flowline insulation is not sufficient to maintain temperatures above the formation point, thermodynamic inhibitors such as methanol and MEG can be modeled to determine the necessary dosage rates to prevent hydrates.

Hydrate curves can be calculated by using the PIPESIM Multiflash-Hydrates module and superimposed on the phase envelope. These curves are useful for subsea pipeline design and operations, providing the pressure and temperature conditions the system should maintain to avoid hydrate formation. Additionally, the hydrate subcooling equipment is reported along the profile as well as maximum subcooling value for each branch. Liquid slugging
Slugging can cause major operational problems to downstream processing facilities. Slugging refers to varying or irregular flows and surges of gas and liquid in a pipeline. PIPESIM software models two types of slug flow.

• Severe slugging: This can occur in a multiphase transport system consisting of a log flowline followed by a riser. In PIPESIM software, the likelihood of severe riser slugging is determined by the Pots correlation, which computes the ratio between the pressure build-up rates of the gas phase and that of the liquid phase in a flowline followed by a vertical riser. Values less than one indicate that severe riser slugging is likely to occur.
• Hydrodynamic slugging: Slugs are formed by waves growing on the liquid surface of a height sufficient to completely fill a horizontal or near-horizontal pipe. The repeating impacts of hydrodynamic slugging can cause pipeline fatigue. PIPESIM software calculates the mean slug length as a function of distance travelled. A probabilistic model is then applied to determine a distribution of slug lengths and frequencies. The calculated size of slugs may be used to design liquid separators and slug catchers.

Wax and Asphaltenes
Wax and asphaltene deposition problems can become so severe that they can completely block a pipeline and may cost millions of dollars to remediate. When the temperature of crude oil is reduced, heavy solids like paraffin/wax (C18–C60) may precipitate and deposit on the pipe wall. The decreased ID results in a higher pressure drop.
In PIPESIM software, Multiflash is used to define the solids model, including Coutinho, which represents wax as a solid solution, and Multi-solid (RKSA), which approximates waxing behaviour by representing the wax as a mixture of separate phases. A proprietary wax deposition model developed by Schlumberger is available in PIPESIM software to predict wax deposition over time. This method is integrated with the dbrSOLIDS* fluid analysis software to accurately predict the thermodynamic properties of the wax based on laboratory experiments.

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