CHALLENGE:
A previous erosion study had established the limits through the 10” production riser as it enters topsides at 36,000 BLPD (@ 150 psi boarding pressure). The constraints were based on erosion rate but not mixture velocity and wells had to be choked back once the fluid rates approached 36,000 BLPD. This prompted a review of how the limits were established and their accuracy.
SOLUTION:
With the aid of OLGA, our engineer established a new safe operating envelope for the subsea system and identified critical points for erosion. The new operating envelope covered the full range of possible operating conditions, while meeting the design life criteria of the equipment. It was found that the mixture velocity limit was more restrictive than the erosion rate limit. A different safe operating envelope was developed as a function of the Gas Liquid Ratio (GLR) and pressure. This included riser base gas lift conditions and considered the total GLR of the system. The new operating envelope resulted in flow limits being increased by up to ~25% of their previous limits.
TECHNOLOGIES IMPLEMENTED:
• OLGA
• PipeSIM
• ProcessNET
• ISIS / SIAM
• Prosper / GAP
