Modelling Of A Highly Integrated And Complex Offshore Network To Mitigate The Uncertainties And Minimize Risk For Offshore Hydrocarbon Evacuation
Authors: Kulkarni Sukrut , Supu Masnizah 
Published: October 2019

This paper demonstrates the efforts in mitigating uncertainties and minimizing risks while monetizing hydrocarbon and evaluating its evacuation in a highly integrated and complex offshore network environment by means of integrated network modelling approach. In oil and gas industry, it is always a challenge to determine the best evacuation path for a new offshore development tying-in to an existing infrastructure complex that has a network of more than 80 gas fields, 100s of export pipelines, multiple hubs, highways and receiving terminals. These network also has varying degree of ullages and bottlenecks as well as dissimilarities in accepted level of gas specification and blended fluid quality. Having a standalone development with its own dedicated evacuation infrastructure to shore would be a safer option but it may not be cost prudent in a highly competitive market.

Tie back options to an existing complex network would entails uncertainties and risks in the evacuation path such as ullage unavailability, pressure imbalance, ambiguous performance of critical elements, the potential violation of the facility constraints, uneven flow distribution (reverse flow, cross flow) as well as infringement to the end product specifications commitment. These may result in (a) concerns for system operability (b) vague results of end product specifications which may pose a threat in designing a production plant and facilities improvement requirements as well as firming up investment decisions for offshore development.

It is essential to evaluate these uncertainties and risks in a complex network by performing circumstantial analysis to cater for technical requisite prior to determining the evacuation route for a new development tie-in. It was apprehending that the availability of relevant simulation model for an integrated system in the market is limited hence a different approach was considered. A steady state network model that caters for an end to end value chain for a complex offshore network was developed using available tools from the industry. These integrated network model was validated against actual data and then deployed to optimize the evacuation options for new development tie-in to the existing network. Multi-faceted scenarios were evaluated in coming up with evacuation options considering system ullage, pipeline hydraulics (adhering to first principles), honoring the end product specifications commitments and network constraints. Sectionalization of sweet and sour gas corridor was performed and analyzed for these multiple tie-in options using the integrated network model and derived its effects on the overall network. It was assured that system parameters such as operating pressure, velocity limits and required specifications for the selected scenarios honors operating envelope and product specification commitments.

It was demonstrated that the integrated network model could optimize the best evacuation route in terms of technical and business requirements, has resulted into monetization of new offshore development. Impediments (uncertainties and risks) across network in terms of ullages, pressure imbalance, system constraints, cross flow, reverse flow, violations in the Gross Heating Values (GHV), CO2 levels etc. at terminal were forecasted as outcome from the model and its mitigations such as change in operating strategies, alternations in the evacuation path, modifications in the offshore network, was planned much in advance and was implemented accordingly.

Uniqueness of this concept is the ability to attain an optimized hydrocarbon evacuation route within the existing network with minimal changes to operating philosophy. A holistic solution was achieved by eliminating the dependancies on the multiple applications for optimization at various levels of integration. Output from the simulation suggested on the alleviations that lead to CAPEX optimization by letting new development evacuation within existing system boundaries.