This paper discusses and summarizes the typical development engineering options about production relief and blowdown system, which based on the cases study of some large-scale offshore oil & gas fields in production worldwide and their features, functions and applications. The evaluation of flare system is based on safety, environment, constructability and cost effectiveness that safely minimize the flaring load. Total blowdown load could be further reduced by installation of Passive Fire Protection as fire proofing insulation but with higher CAPEX and OPEX cost. Generally, cold venting is not recommended especially for large scale offshore production due to safety concern and environment issues.
The Liwan3-1 gas field is located in the South China Sea, in approximately 1480 m of water depth, and 350 km far from the onshore. Total maximum yearly gas production gas project reaches 120×108 Sm3, and two flare systems are provided on the central platform. Various scenarios of relieving and depressuring cases are analyzed to determine the peak rate of each option. Depressuring or blowdown systems work in conjunction with the shutdown system is functioned to isolate and depressurize process systems in the event of a fire or incident where the process inventory is required to be removed. The high pressure and low pressure flare knock out drums are provided for both the HP and LP flare systems prior to gas disposal by combustion at the LP and HP flare tips. Both LP and HP flare system share a common flare boom, and high-integrity pressure protection system is applied to reduce the design capacity for the flare system. The flare radiation limit of 6.31kW/m2 is recommended and the mean wind speed is used as the criteria to be adhered to. The flare stack is designed for various orientations. The 45° inclined stack form horizontal is recommended based on safety concern as primary and cost.
According to the environmental conditions and the features of potential oil and gas structures in the South China Sea, the deepwater development engineering options of about production relief and blowdown system which will be suited for the area are proposed.
