SITUATION
An offshore oil well operator operates an FPSO that processes crude. As part of that process, seawater is treated and pumped into the well at high pressure to increase reservoir pressure. This injected seawater is pumped at a pressure of 205 bar / 2,973 psig. To provide overpressure protection, the operator is using a forward acting, cross-scored rupture disc with an operating ratio of 90% and a burst tolerance of +/-10%.
However, this disc is prone to cycle failure due to the forward acting (tensile loaded) design. The disc’s operating ratio of 90% limits the pump’s operating pressure, which impacts the reservoir pressure. There have also been reports that the rupture disc is difficult to install and prone to damage during installation. This affects the disc’s product life and reliability. In addition, every rupture disc failure is reported to result in eight hours of non-productive time for the FPSO vessel.
The oil well operator wants to increase the reservoir pressure while also reducing down time caused by disc failure and lengthy installation processes. Specifically, they are looking for a new pressure relief device that will:
- Allow the seawater line to increase the operating pressure by 5%
- Be resistant to fatigue and withstand very high pressure/thermal cycles
- Be easy to install and maintain
ACTION
Our engineers recommended our welded HPSR solution for this situation. This is a single-piece, welded rupture disc assembly designed for use in ANSI RTJ connections. It is easy to install and offers the most robust rupture disc assembly on the market, being specifically designed for high burst pressures, high pressure/thermal cycle rates and high operating ratios. The HPSR supported the operator's goals in three ways:
- The HPSR has a 95% operating ratio rather than 90% and so allows for higher operating pressures.
> The HPSR supports the desired 5% increase in operating pressure for seawater injection.
- The reverse buckling design provides extended service life and limited occurrences of fatigue when compared to competitive disc types. Tests have shown that the HPSR has proven reliable after three years of service and 48,000,000 pressure cycles.
> The HPSR's reliability eliminates unwanted and unplanned disc activation.
- The HPSR features a single-piece design an duses thicker material for the disc.
> The HPSR is simple to install, with less opportunity for damage to occur during installation. The HPSR is a reliable solution even with minimal training and experience in the use of rupture disc assemblies.
RESULT
The 5% increase in operating pressure leads to an additional 200 barrels produced daily, equivalent to a $5.6MM annual increase (~ assumed 350 product days annually with an average price of $80/barrel).
The proposed HPSR investment volume over three years amounts to $120,000 (~ assumed annual PM of equipment).
Estimated gain over a three-year period: $8.91MM
