Sisi Nubi Area of Interest (SNB AOI) is an ongoing project to develop the marginal resources located in Sisi Nubi offshore field operated by Pertamina Hulu Mahakam (PHM). As the resources being developed are small and scattered, low cost solution platform design is required to develop these marginal resources. Therefore, design optimization is a must.

Fit-for-purpose design concept is used as the basis to develop process and safety facilities in new SNB AOI platforms while maintaining the compliance with government regulations and international codes and standards. Various exercises were performed in order to ensure optimized process, safety and operating philosophy requirement. Lesson learnt and benchmarking from various established platforms design including PHM's minimalist offshore/swamp platform were performed. The previous designs are reviewed, adopted and SNB AOI platform design is adjusted as per operating philosophy requirement.

Based on the available basis of design and operating parameters, fully rated topside facilities design is considered feasible to be applied for new SNB AOI platforms. With this design, relief system size (i.e. vent stack and vent knock-out drum) can be further optimized. In addition, closed drain drum and LP (low pressure) vent knock-out drum is also combined in one single vessel after careful safety verification. Other optimization is externalizing equipment that could be managed with Operating Expenditure (e.g. well offloading activity by using external facility).

As for process safety design, preliminary reviews based on international codes and standards showed that the following designs are considered feasible: portable Gas Detector by operator during platform visit (in lieu of permanent Gas Detection system), Fusible Plug loop installation only (instead of redundant protection using Flame Detector system), non-provision of dry fire water mains, application of Passive Fire Protection (PFP) only after confirmation from fire risk study (risk-based approach), and considering not permanently manned installation, 1 (one) stair & 1 (one) ladder combination on each platform deck (instead of dual stairs). Overall, the proposed design maintains the safety of installation with minimum impacts to future platform operation.

This optimization has contributed to reduction of dimension and weight of topside installation (i.e. 32% less compared to PHM's latest Offshore Minimalist Platform design) and also weight of the structure.

Design of SNB AOI project could become a good reference for other Pertamina affiliate and other companies and could open a further way forward to economically develop the "marginal resources", especially in offshore area, by implementing the "fit for purpose" design concept.

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