Value added by Xodus

Xodus are specialists in ‘Dynamic Process Simulation’ combining flow assurance and topside process software to provide a complete simulation of the whole system. This unique capability, in combination with our proven track record, enabled our client to make informed decisions on safety, performance and detailed design in confidence that the results truly represent the real world. 

Description

With a combined total of over 100 man-years of simulation experience, Xodus are considered dynamic process simulation specialists, linking process models such as HYSYS to external applications, e.g. OLGA, PROSPER and GAP.  

As part of a project detailed design, there was a requirement to test the cascade control philosophy for the separator, to ensure that the slugging fluids did not cause a knock on effect for the controls systems of the downstream plant, e.g. compressor operation.  

We developed a linked transient-dynamic model using OLGA and HYSYS Dynamics to assess the topsides trip settings and optimise the process design. The flow assurance covered the whole subsea system for a 27km, 14-inch NB bundled pipeline to the Platform.  

The scope included: 

• Normal operation and turndown to assess slug management options for a range of field life scenarios (early, mid and late life with different water cuts and gas to liquid ratios) 

• Start-up optimisation analysis and pipeline shut down with depressurisation to the flare system. 
• Safety related cases such as separator over-pressure and gas blowby were also completed.  

The simulations were used to assess the viability of the general cascade control system as well as the effectiveness of the inlet slug control valve. For this assessment it was vital to have a good integrated model of the topside control (HYSYS) and the pipeline operation (OLGA).     

Benefit: 

• Cost effective selection of the control scheme. A range of schemes easily tested for robustness and compared so that the best option could be taken into detailed design. 

• Safety related issues could be addressed and quantified to close out HAZOP actions and also feed into the overall flare and relief design. 
• The project was able to implement the optimum control scheme at the design stage without waiting to the commissioning phase when changes would be very costly and difficult to implement on live plant. 
• Plant response and provisional controller settings established well before actual plant commissioning took place, optimising production and minimising operational flaring.