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Steady State / Transient modelling of multi-phase pipeline systems

Hydraulic performance and thermal characterisation are key Flow Assurance issues when designing a subsea pipeline system.

Hydraulic performance includes the assessment of either single phase or multi-phase systems with regard to evaluation of pressure loss and the impact of flow regime.

Thermal characterisation requires that system insulation performance be specified to meet both steady state and transient (shutdown / cooldown) requirements. Some fields cannot be developed solely through use of passive insulation and require the use of an active heating system in the form of either hot water bundles or electrical heating. Insulation performance also needs to be balanced against the simultaneous use of chemical injection. Optimal thermal management balances CAPEX, OPEX and risk.

Cooshie Doo understand the inherent uncertainty associated with production forecasts and the requirement to balance the hydraulic / thermal performance of the system against its operability. All analyses consider the expected range of flow and fluid compositions forecast over field life.

Through clever application / interpretation of industry standard software (including LEDAFLOW, OLGA, MAXIMUS, PIPESIM and MULTIFLASH) and bespoke tools we can ensure accurate determination of hydraulic and thermal performance.

Well Operations Modelling

The detailed thermo-hydraulic modelling of well bores is required to define the variation in FWHP and FWHT over field life. For simulations to generate representative data it is important to model geothermal profiles through the well and a detailed breakdown of the well completion including rock layers. In addition to providing flowing data for steady state operation the modelling of wells is also often required as part of transient thermo-hydraulic analysis in order to define start-up temperatures during well restart.

Cooshie Doo understand it is critical to accurately determine flowing well head pressures and temperatures during normal steady state and transient operations to be able to confidently specify the most appropriate design of the system.

Slugging Characterisation and Mitigation

Definition of the predominant flow regime in any multi-phase pipeline forms an inherent part of any Flow Assurance analysis. Associated flow characteristics impact many areas of Flow Assurance including corrosion, chemical injection and erosion. System hydraulic stability and the presence of unstable flow or slugging in the pipeline can have a major effect both on system operability and productivity.

Cooshie Doo therefore consider it important to identify the likelihood of slugging at an early date and define its characteristics. It can therefore be mitigated for within the system design and operating procedures, ensuring the process plant can remain operable.

Wax Deposition Modelling

Wax deposition in pipelines and risers can have a significant effect on production efficiency. Wax build-up can cause increased pressure drops and in more extreme cases, pipelines/processing facilities can block causing production to stop. Accurate fluid characterisation and an understanding of production chemistry is therefore critical for developments involving waxy fluids. Understanding wax behaviour can help avoid high costs resulting from output reductions or stoppages, or conversely from over specifying the required system thermal performance.

Cooshie Doo are able to perform detailed modelling of wax deposition and/or gelling of hydrocarbon production systems. Wax handling and wax intervention strategies can then be developed as part of the system operating philosophy.

Erosion and Corrosion Analysis

Output from steady state and transient thermo-hydraulic analysis is applied to assess the risk of erosion and corrosion through various system components.

Erosion analysis can comprise either a high level assessment of allowable operating velocities or a more detailed analysis of actual erosion rates, including erosion from suspended solids over field life.

Assessment of system operating conditions and fluid compositions is used to determine the risk of corrosion. For example, flow regimes and water condensation rates can be used to determine if a system will be susceptible to top of line corrosion, a problem particularly important in gas condensate systems and in systems which employ a wellhead cooling spool.

Cooshie Doo can apply a range of methods to assess erosion and corrosion risk over a range of conditions indicative of those expected over field life, providing key input to the pipeline mechanical design.

Solids Transport Analysis

Cooshie Doo can apply methods for investigating the transport of solids to ensure the flowline design can transport the predicted reservoir fluids and associated solids without risk of solids deposition or blockage. The analysis needs to consider detailed system geometry and flow in both horizontal and vertical pipeline sections. The impact of predominant flow regime and subsequent solids behaviour can be defined.

Production Chemistry Review

Definition and understanding of fluid behaviour is critical in mitigating the uncertainties and risks associated with Flow Assurance and defining system design and operating strategies.

Cooshie Doo have industry leading expertise in fluid behaviour and have worked with a wide variety of fluid types (e.g. complex heavy oils, gas-condensates) and understand the emphasis which must be put on definition of the fluid properties. Production Chemistry issues which can have a major impact on all Flow Assurance areas include PVT characterisation, Hydrate Formation, Wax Deposition, Scale / Salt deposition and Asphaltene deposition.

Operating Philosophies

Development of robust operating philosophies and strategies is imperative to ensuring a low risk production environment. The uncertainties associated with subsea developments must be recognised and addressed if systems are to be operated safely and economically. Operating philosophies must be developed taking account of these uncertainties and should be readily adaptable for changes to key parameters.

Cooshie Doo develop operating philosophies which address all likely steady state and transient operations. Typically the key issues addressed will include shutdown, start-up, turndown, blowdown and chemical injection. It is also critical that subsea production philosophies consider the interface with topsides equipment. Input from plant operators is central to ensuring the development of practical operating philosophies.

Production Optimisation

Production optimisation through integrated asset modelling allows rapid comparison between different production concepts. Total reserves produced over the life of field from various options may be assessed and an optimal production concept can be selected. An integrated asset model consisting of wells, pipeline networks, reservoir and topsides allows all relevant production constraints to be included.

Cooshie Doo personnel have experience developing integrated system models through application of the MBAL/Prosper/GAP suite of software. Global optimisation performed using RESOLVE software, and inclusion of the facilities constraints in the model, allows identification of the true system operating point at different stages of field life. The inclusion of facilities constraints in the simulation allows the interaction between the reservoir, sub-sea and facilities systems to be accurately modelled. This approach provides a more realistic assessment of life of field production potential.

Chemical Injection Philosophies

Production chemistry has a major impact on the chemical injection facilities required and analysis is therefore required in order to define chemical injection necessary for a specific development. Analysis addresses chemical type, dosage concentrations and rates and highlights the operational scenarios/periods when specific chemicals are required.

Cooshie Doo recognise that it is important to consider a range of operating conditions representative of full field life operation to allow development of a robust chemical injection program. Definition of chemical injection requirements needs input from both steady state and transient thermo hydraulic analyses.

Pigging Operations and Pipeline Integrity / Inspection Support

Pigging can be required to manage liquids in pipelines as well as to provide general maintenance tasks including wax management, corrosion control, hydrate control and cleaning / inspection.

In order to define an optimum cleaning / inspection pig train configuration it is often preferred to first assess the internal conditions in the pipeline through analysis. This analysis requires the benchmarking of pipeline models against historical operating data and subsequent application of the models to assess likely solids deposition, liquid hold-up and erosion / corrosion.

Cooshie Doo can model the actual pigging operations to define displaced liquid volumes and highlight equipment required for fluids / solids receipt. Analysis of operational pigging can also be performed to define displaced liquid volumes and a recommended frequency of pigging. Pigging philosophies can subsequently be developed.

Decommissioning Support

Prior to decommissioning it is often necessary to determine the residual condition of pipelines that have been taken out of service. Typically it is important to understand the likely volume of liquids and/or solids left in the line and the locations of these accumulations. Similarly for operational pipelines an understanding of historical corrosion and erosion mechanisms which may have taken place can be critical in determining the residual pressure containment limits of the pipeline and whether it is still fit for purpose.

Through clever application of software Cooshie Doo can model the historical operation of a system to predict its present condition. This data can then be applied as input to corrosion analysis and / or utilised to develop procedures for cleaning / flushing activities.

Environmental / Safety Support

The impact of a potential or actual pipeline leak can be a critical input to either environmental or operational safety performance assessments.

Cooshie Doo can provide support and technical modelling of pipeline leaks for these analyses. Typically both the impact of displaced fluids on the environment and also the impact of various mitigation measures on displaced volumes and risk to operations can be assessed.

Peer Assist and Third Party Review

The Cooshie Doo team is used to working both independently or as part of an integrated team. They provide Flow Assurance support when and where it matters in the form of objective, knowledgeable and experienced advice. The team is highly experienced and includes seasoned Flow Assurance experts with operator / contractor background and solid hands-on practical experience. This experience means that they understand and can quantify the risks and uncertainties that influence key decisions.

The level of experience Cooshie Doo personnel have and their understanding of how Flow Assurance fits into the bigger picture makes Cooshie Doo ideally placed to perform an independent review of third party work, peer assist and support to mergers and acquisitions.

Training Courses

Cooshie Doo offer a range of bespoke training courses covering the key issues commonly covered under the collective title Flow Assurance. Whilst covering specific Flow Assurance issues in depth, the courses provide an insight into the importance of the Flow Assurance interface with other project disciplines.