Ejectors offer an attractive solution for generating extra production from low pressure (LP) wells and thereby extending field life. Most commonly, shut-in or liquid loaded wells can be revived, as well as satellite or stranded wells deemed too expensive to recover with ‘traditional’ enhanced recovery techniques.
In many fields, it is common for gas from an HP well to be ‘choked’ to a lower export pressure which is a waste ‘usable’ energy. Instead of wasting available energy, the choke valve is bypassed and the HP gas is used to ‘drive’ an Ejector, which not only discharges gas at the export pressure, it lowers the pressure on LP (often marginal) wells thereby boosting production and sometimes bringing ‘dead’ wells back to life.
Transvac’s patented ‘Universal Design’ Ejectors allow new Internals (Nozzles and Diffusers) to be fitted as well pressures declined over time, thereby keeping the Ejector operating at its the optimal design point to maximise production.
As production rates decline over time, there are many existing gas compressors operating inefficiently in constant recycle conditions to maintain performance. When in recycle mode some high-pressure compressor discharge gas flow is diverted and lowered in pressure to the compressor inlet.
The energy wasted across the recycle (anti-surge) valve can be used to ‘drive’ an Ejector to lower the pressure on LP (often marginal) wells thereby boosting production and sometimes bringing ‘dead’ wells back to life.
This method of boosting LP well production is achieved ‘for free’ by making use of waste energy. In many instances where existing compressors cannot meet the required pressures of LP wells it a cost-effective way of maintaining and boosting gas production without the need to re-wheel or replace compressors.
Also, the performance of a compressor often benefits from the addition of extra gas flow.
There are many other opportunities in oil & gas installations to utilise waste energy to ‘drive’ an Ejector and generate extra production for ‘free’.
Transvac’s has made huge advances in the efficiency and capability of liquid motivated Ejectors. Offering very high compression ratios, these optimised Ejector designs open the door to a wealth of new applications throughout the Upstream and Downstream Oil & Gas Industry. The diagram shows just one simple but highly effective way in which operators can make use of this technology for enhanced recovery.
Typically, injection water or produced water is employed to motivate the Ejector, thus making use of existing facilities – perfect for brownfield developments. The Ejector can entrain and compress gas from a number of sources including a separator, manifold or individual well. The resultant reduction of backpressure on the upstream process delivers a boost to production and promotes steady flow where liquid loading is an issue, particularly in long tiebacks.
Multi-phase production can be enhanced using this simple technique to reduce separator pressure. The Ejector can be ‘driven’ using energy from compressor recycle gas, HP well gas, or even HP water (such as injection water, although introducing a liquid would require downstream separation). By lowering separator pressure, it is simply reducing the backpressure (resistance) on upstream production process, which increases production.
This technique has been sucessfully used to offer flow assurance in a 50km subsea tieback, which had been suffering from lumpy production due to liquid/condensate loading. The resulting pressure drop in the separator increased the specific volume of the gas in the tieback, resulting in steady, increased recovery for a number of years. As compressor recycle gas was used, no ‘new’ energy was required, making the project a win on many levels.